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54 Cards in this Set
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Methicillin-Susceptible Staphylococcus aureus
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Description: Aerobic, Gram positive cocci in clusters, Coagulase positive
Location: Found on skin (primarily axilla and groin), mucus membranes; nasopharynx is the most common area colonized Diseases: Common cause of skin infections and both community and nosocomial Gram positive infections. Common cause of endocarditis, bacteremia, and catheter-related infections. Cause toxin-mediated diseases, including scalded skin syndrome, toxic-shock syndrome, and food poisoning. Resistance Issues: Produces B-lactamase active against penicillin, ampicillin, amoxicillin TX: oxacillin, nafcillin, and dicloxacillin, cefazolin Alternative: trimethoprim/sulfamethoxazole, doxycycline, clindamycin, and a multitude of other agents |
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Methicillin-Resistant Staphylococcus aureus
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Description: Aerobic, Gram positive cocci in clusters, Coagulase positive
Diseases: Common in nosocomial infections and in IV drug users; increasing prevalence in community-acquired skin infections Resistance Issues: Resistant to all penicillins, cephalosporins, most macrolides, clindamycin, quinolones; community-acquired strains are more susceptible to macrolides, clindamycin and quinolones but resistance is slowly increasing Methicillin resistance due to modified PBP-2a and is coded for by the mecA gene, also produces B-lactamase active against penicillin, ampicillin, amoxicillin TX: vancomycin Alternative: 1st line options: linezolid, daptomycin, quinupristin/dalfopristin, telavancin; 2nd line option: tigecycline; Step down oral therapy: TMP-SMX, doxycycline |
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Methicillin-Susceptible Staphylococcus epidermidis
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Description: Aerobic, Gram positive cocci in clusters, Coagulase negative
One of several coagulase negative staphylococci, often not speciated by micro labs; comprise ~ 10-20% of all S. epidermidis Location: Found on skin, mucus membranes. Colonizes and forms biofilm on artificial surfaces and devices, including indwelling catheter lines, joints, and valves. Diseases: Very common cause of prosthetic device infections, especially intravenous catheter-related infection; not a virulent organism Resistance issues: Produces B-lactamase active against penicillin, ampicillin, amoxicillin Bacteria have polysaccharide outer layer (glycocalyx AKA biofilm) that binds strongly to plastics. This helps prevent penetration of antibiotics, making treatment more difficult. TX: oxacillin, nafcillin, and dicloxacillin |
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Methicillin-Resistant Staphylococcus epidermidis
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Description: Aerobic, Gram positive cocci in clusters, Coagulase negative
Common form (80-90%) of all S. epidermidis Location: Found on skin, mucus membranes. Colonizes and forms biofilm on artificial surfaces and devices, including indwelling catheter lines, joints, and valves. Diseases: Very common cause of prosthetic device infections, especially intravenous catheter-related infection; not a virulent organism Resistance Issues: Resistant to all penicillins, cephalosporins, macrolides, clindamycin, quinolones Methicillin resistance due to modified PBP-2a and is coded for by the mecA gene, also Produces B-lactamase active against penicillin, ampicillin, amoxicillin TX: vancomycin Alternatives: Alternative: 1st line options: linezolid, daptomycin, quinupristin/dalfopristin, telavancin; 2nd line option: tigecycline; Step down oral therapy: TMP-SMX, doxycycline |
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Streptococci Group A (GAS)
(S. pyogenes) |
Description: Aerobic, Gram positive cocci in chains, B-hemolytic on blood agar
Location: Found on skin, mucus membranes Diseases: Common cause of “strep throat,” scarlet fever, pyoderma, erysipelas, cellulites, necrotizing (flesh-eating) fasciitis (aka streptococcal gangrene) Post streptococcal complications include arthritis, acute rheumatic fever, and glomerulonephritis. Toxin-producing organism responsible for toxic shock syndrome, scarlet rash, necrotizing fasciitis. Resistance issues: clinically, none; academically, some macrolide resistance observed TX: penicillin |
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Streptococci Group B
(S. agalactiae) |
Description: Aerobic, Gram positive cocci in chains, B-hemolytic on blood agar
Location: Normal flora of GI tract and female genital tract, periurethral area, perineal and perianal skin Diseases: Most common cause of neonatal sepsis, peripartum and postpartum infection; diabetics are predisposed to this organism Resistance issues: Does not produce -lactamase; bactrim often fails clinically TX: high dose penicillin, due to higher MICs and higher inoculum |
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Streptococcus pneumoniae
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Description: Lancet-shaped, aerobic, Gram-positive cocci in pairs or chains,
a-hemolysis on blood agar (green). All pathogenic bacteria surrounded by polysaccharide capsule allowing evasion from phagocytosis; >80 different capsular types Location: Normal flora of nasopharynx, ~ 25% of population are carriers Diseases: Most common cause of community-acquired pneumonia, otitis media, sinusitis, and other respiratory tract infections; high mortality rate (20%) with bacteremia Resistance issues; 30% + non-susceptible to penicillin/B-lactams (PI - penicillin intermediate, PR – penicillin resistant; 40% resistance to macrolides & TMP/SMX; cause mutations in bindings sites and produce efflux pumps TX: PSSP: penicillin, cefuroxime, ceftriaxone, cefotaxime, macrolide; PISP or PRSP: vancomycin, levofloxacin, moxifloxacin; Prevention: vaccine available, 23 valent for adults and children >5 yrs of age, 13 valent for children < 5 yrs of age |
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Viridans Streptococci
(S. mutans, sanguis, mitis, bovis) |
Description: Aerobic, group of several species, Gram-positive cocci in chains. Normal flora in the oral cavity. Low virulence
Diseases: infection associated with dental manipulation, common cause of native valve endocarditis and late-onset prosthetic valve endocarditis. Resistance issues: May be penicillin-resistant; requires susceptibility testing TX: penicillin Alternate: ceftriaxone or vancomycin |
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Pseudomonas aeruginosa
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Description: Aerobic, non-lactose fermenting, oxidase positive Gram-negative bacilli Location: lives in moist environments, water loving organism
Diseases: Opportunistic pathogen, rarely causing disease in healthy persons Common cause of nosocomial bacteremia, pneumonia, and UTIs in institution settings, diabetic foot wounds, surgical site infection, and pneumonia in cystic fibrosis patients Resistance Issues: Produces many B-lactamases and an efflux pump, as well as aminoglycoside-inactivating enzymes which promote multi-drug resistance TX: anti-pseudomonal B-lactam, anti-pseudomonal carbapenems, ciprofloxacin or levofloxacin, or combination therapy aminoglycoside + anti-pseudomonal B-lactam Traditionally active abx include aminoglycosides, ceftazidime, cefepime, aztreonam, imipenem, meropenem, doripenem, piperacillin or piperacillin/tazobactam, ticarcillin or ticarcillin/clavulanate, levofloxacin and ciprofloxacin |
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Acinetobacter spp
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Description: Aerobic gram-negative organisms; appear as diplococci or bacilli, oxidase-negative
Location: Ubiquitous soil and water saprophytes Disease: Opportunistic pathogen, associated mostly with nosocomial infections: UTI, meningitis, pneumonia, and bacteremia/sepsis – must distinguish between colonization and infection. Resistance issues: Resistance to many antimicrobials is common. TX: imipenem or meropenem; or amikacin or ampicillin/sulbactam (sulbactam is the active component not ampicillin), tigecycline, colistin |
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Enterobacter species
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Description: Aerobic, Gram-negative bacilli in the family Enterobacteriaceae; E. aerogenes, E. cloacae, and E. agglomerans
Diseases: Nosocomial pathogen, particularly in the ICU; common causes of pneumonia and bacteremia Resistance issues: B-lactamase producer, including Amp C and ESBLs; this makes third generation and lower cephalosporins unreliable Prior abx exposure increases abx resistance Aminoglycoside and quinolone resistance is increasing in conjunction with ESBL production TX: TMP-SMX, cefepime, carbapenems, aminoglycosides, and quinolones |
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Escherichia coli
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Description: Aerobic, lactose-fermenting Gram-negative bacilli, Oxidase negative, indole positive. Most common GNB associated with infection in humans.
Location: The major aerobic organism in the human intestine Diseases: Causes watery, inflammatory, and hemorrhagic (O157:H7 strain) diarrhea, neonatal meningitis, nosocomial bacteremia, surgical site infection, and the leading cause of UTIs Resistance issues: Resistance to ampicillin 40-60% (mean 50%); amp/sulbactam resistance often similar to ampicillin alone, also resistance increasing against 1st generation cephalosporins, fluoroquinolones, TMP/SMX. B-lactamase producer, including Amp C and ESBLs; rare incidence but slowly increasing is carbapenemase production TX: Neonatal meningitis: ceftriaxone/cefotaxime; UTI: TMP/SMX, quinolone, ceftriaxone |
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Klebsiella pneumoniae
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Description: Aerobic, facultative anaerobic Gram negative bacilli; Produces an outer capsule; K. oxytoca also a common pathogen
Diseases: Community-acquired infections include pneumonia (especially in alcoholics), UTI, and hepatobiliary infections Important cause of nosocomial infections: pneumonia, UTI, catheter-associated, bacteremia, and surgical wounds Mechanical ventilation and immunosuppression are risks Resistance issues: B-lactamase producer, including ESBLs Intrinsically resistant to pcn, ampicillin, Although all cephalosporins generally have activity, B-lactamase and ESBL production may render them ineffective (except cefepime); carbapenemase producing strains are increasing in prevalence (KPC) B-lactamase inhibitor combos have variable activity with sulbactam having the least activity TX: cefepime, aminoglycosides, quinolones, pip/tazo; if ESBL – carbapenems; if KPC - colistin |
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Proteus species
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Description: Aerobic, Gram negative bacilli known to swarm; P. mirabilis (90%) and P. vulgaris (8%) are the most common clinical species; possess flagella for motility and produce urease, which splits urea and raises urinary pH
Member of family Enterobacteriaceae Location: resides in GI tract and may colonize vaginal tract Diseases; Common cause of nosocomial UTI (catheterization is risk factor), and SSSI (post-op wound infections, infected decubiti) Resistance issues: Very susceptible to B-lactams due to no chromosomal B-lactamase production; Quinolone resistance ~50% in many regions of the country P. vulgaris is more resistant to abx than P. mirabilis due to cephalosporinase (resistance to ampicillin, 1st gen cephalosporins, cefuroxime, ceftriaxone, cefotaxime) TX: P. mirabilis: ampicillin; in ampicillin-resistance: 2nd or 3rd gen cephalosporins, extended spectrum penicillins, aminoglycosides, TMP/SMX TX: P. vulgaris: 3rd gen cephalosporins (ceftazidime) or aztreonam; alternatives cefoxitin or cefotetan, B |
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Chlamydophila pneumoniae (TWAR)
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Description: Obligate intracellular bacteria; require some host cell protein synthesis to replicate
Diseases: Important cause of community-acquired pneumonia (an atypical organism) and bronchitis Only one strain has been identified: TWAR (named after the two initial isolates [TW-183 and AR-39]) Only grows in cell (tissue) culture, serology used to diagnose TX: Macrolides and doxycycline (tetracyclines) and quinolones (ciprofloxacin not reliably active) |
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Haemophilus influenzae
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Description: Aerobic, small Gram-negative coccobacilli
Can be encapsulated (serotype a-f) or unencapsulated Location: Commensal in URT Diseases: Causes meningitis, epiglottitis, LRTI, otitis media, sinusitis Vaccine available against serotype b (major cause of URTI/meningitis in children) has decreased the incidence of disease from this particular strain Resistance Issues: B-lactamase production inactivating penicillin, ampicillin, and amoxicillin in ~ 30% of isolates TX: Meningitis:3rd gen cephalosporins + dexamethasone; rifampin for prophylaxis; LRTI: 2nd gen cephalosporin, amox/clav, azithro- or clarithromycin; OM: 2nd generation oral cephalosporin, amoxicillin/clavulanate |
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Legionella spp.
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Description: Fastidious, aerobic, gram-negative non-encapsulated bacillus. Behaves as a facultative, intracellular bacterium - 15 serotypes
Location: Ubiquitous in nature (aquatic) – becomes pathogen when aerosolized and the inoculum size is sufficient to overcome host’s immune defenses (large inoculum and/or immunosuppression) Disease: Causes Legionnaire’s disease, an atypical community-acquired pneumonia, and Pontiac fever. Primary route of transmission facilitated through human “amplifiers” (water heaters, hot tubs, etc.) and “disseminators” (showers, humidifiers, air conditioning, nebulizers, etc.) Diagnosis: Gram staining is very poor and unreliable; serologic testing is useful (e.g. DFA and IFA assays, urinary antigen assay); positive culture is diagnostic as there is no carrier state TX: Levofloxacin, moxifloxacin or azithromycin Alternative: erythromycin +/- rifampin |
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Moraxella catarrhalis
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Description: Aerobic Gram negative diplococci; Formerly Branhamella catarrhalis, formerly Neisseria catarrhalis
Location: normal flora of human respiratory tract Disease: Third most common cause of pediatric otitis media and maxillary sinusitis (behind pneumococcus & H. influenzae) In adults, responsible for ABECB (acute bacterial exacerbations of chronic bronchitis) and bronchopneumonia, especially in elderly and immunocompromised Resistance issues: Nearly 100% produce B-lactamase inactivating penicillin, ampicillin, and amoxicillin TX: Peds: 2nd/3rd gen cephalosporins or TMP/SMX or amoxicillin/clavulanate TX: Adults: 2nd/3rd gen c-sporin or TMP/SMX or doxycycline or Unasyn or amoxicillin/clavulanate |
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Mycoplasma pneumoniae
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Description: A mollicute, a class of bacteria that lacks a cell wall therefore does not Gram stain; Diagnosis made by clinical presentation and serology
Location: commensal and pathogen in humans; humans are the only known host Resistance issues: cell wall-active antibiotics are not active Disease: Causes community-acquired pneumonia (atypical pneumonia); antibiotic therapy may be beneficial but the need for it is disputed and debated TX: macrolides or tetracyclines (doxycycline); fluoroquinolones are also effective (except ciprofloxacin) |
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Enterococcus faecalis
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Description: Aerobic but facultative anaerobe, Gram positive cocci in pairs and chains
Location: Found in GI tract Diseases: Can cause UTI, soft tissue infection, endocarditis; often found in mixed infections (intra-abdominal infection) Resistance issues: Typically susceptible to ampicillin and glycopeptides; ampicillin/vancomycin resistance is increasing Low-level resistance to aminoglycosides allows combination use for synergy; can exhibit high-level aminoglycoside resistance Vancomycin resistance types: VanA (high level vancomycin resistance), VanB, VanC TX: ampicillin (if susceptible), vancomycin (if susceptible) plus or minus gentamicin or streptomycin (only combination therapy is bactericidal) or for VRE: linezolid, nitrofurantoin, doxycycline, daptomycin |
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Enterococcus faecium
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Description: Aerobic but facultative anaerobe, Gram positive cocci in pairs and chains
Location: Found in GI tract Diseases: Can cause UTI, soft tissue infection, endocarditis; often found in mixed infections (intra-abdominal infection); Less common than E. faecalis Resistance issues: Less common than E. faecalis but more likely to be ampicillin and/or vancomycin resistant Vancomycin resistance types: VanA (high level vancomycin resistance), VanB, VanC TX: ampicillin (if susceptible), vancomycin (if susceptible) plus or minus gentamicin or streptomycin (only combination therapy is bactericidal) or for VRE: linezolid, quinupristin/dalfopristin, nitrofurantoin, doxycycline, daptomycin |
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Mycobacterium tuberculosis
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Description: Acid-fast, slow-growing bacilli; divides every 15-20 hours, so culture may take 3 weeks to visualize the organism on an agar plate
Diseases: One-third of the world's population is infected with MTB; most common infectious cause of death in the world; in the last decade, HIV disease and multidrug-resistant MTB (MDRTB) have become important Infection precedes active disease; skin testing defines exposed/infected individuals; preventative therapy may reduce the risk of active disease Resistance: is either primary or acquired; acquired resistance occurs secondary to poor compliance (selective pressure) DOC/Treatment: Use at least three active agents initially, duration and effectiveness depend on the drugs used, intermittent therapy is as effective as daily therapy, although relapse can occur with short therapy, the organism is usually no MDRTB, a single drug should never be added to a failing regimen, non-compliance is the biggest cause of MDRTB TX: INH, rifampin, pyrazinamide, ethambutol, streptom |
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Giardia lamblia
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Description: flagellated enteric protozoan
Location: Acquisition of the parasite requires oral ingestion of Giardia cysts. This usually occurs through ingestion of contaminated water, but person-to-person and food borne transmission is also important. Diseases: Giardiasis (beaver fever); Waterborne outbreaks of diarrhea, particularly in children. Symptoms include bloating, cramps, weight loss, and inability to absorb fatty foods. The course of the disease is usually benign. TX: Metronidazole |
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Neisseria meningitidis
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Description: Aerobic Gram negative diplococci pathogenic only to humans
Only encapsulated strains cause invasive infection Location: Commensal of posterior nasopharynx; transmission via respiratory route only after prolonged close contact (not very infectious) Disease: Major cause of bacterial meningitis; breach of nasopharyngeal mucosa most common route of infection Bacteremia (meningiosepticemia) carries high mortality rate Endotoxin-mediated inflammation is major cause of tissue damage DOC/Treatment: Abx therapy must be highly active against the pathogen and penetrate well into the meninges to achieve high cidal levels Penicillin G or ampicillin; alternatives: ceftriaxone, or in true pcn allergy, chloramphenicol Close contacts should receive prophylaxis with rifampin (cipro is an alternative) Vaccine with short-term immunologic protection for adults only |
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Listeria monocytogenes
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Description: Aerobic, Gram positive bacillus
Location: human vagina canal Disease: Clinical infection common in neonates (sepsis and meningitis), pregnant women (3rd trimester), elderly (various focal infections), and immunosuppressed Resistance issues: Most abx active against Gm + bacteria are effective but some resistance has developed since late 1980s TX: ampicillin, add gentamicin in meningitis, encephalitis, endocarditis; TMP/SMX alternative in pcn allergy; Never use cephalosporins |
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Pasteurella multocida
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Description: Small gram-negative coccobacilli
Location: found in the naso-oropharynx and GI tract of animals and birds, typically cats and dogs. Disease: Commonly causes cellulitis around site of wound (animal bite especially dogs and cats), but may extend to other tissues, and develop into systemic disease. Resistance issues: Resistant to dicloxacillin, clindamycin, and cephalexin. Many strains resistant to erythromycin. TX: penicillins (PenG, ampicillin, amoxicillin or amoxicillin/ clavulanate) or doxycycline (tetracyclines). Fluoroquinolones, newer macrolides, and 2nd and 3rd generation cephalosporins may be effective. Do NOT treat with cephalexin or other 1st generation cephalosporins |
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Neisseria gonorrhoeae
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Description: Aerobic Gram-negative diplococcus
Disease: Transmissible through intimate contact of mucus membranes making it an ideal sexually transmitted bacteria Common cause of STD Resistance issues: Significant multi-drug resistance has developed, highly resistant to penicillin, increasing resistance to quinolones TX: Single dose therapy of STD is common Uncomplicated STD: ceftriaxone 125 mg IM x1 or cefixime 400 mg po x1 TX: Disseminated disease: ceftriaxone Chlamydia is common co-infectant; all treatment regimens should include anti-Chlamydial therapy too; screen for Syphilis |
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Chlamydia trachomatis
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Description: Obligate intracellular bacteria/parasite; require some host cell protein synthesis to replicate
Location: Exclusively a human pathogen. Disease: A major cause of sexually transmitted and perinatal infection. Common “co-infectant” in gonococcal infections. TX: Macrolides and doxycycline (tetracyclines); quinolones also active |
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Gardnerella vaginalis
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Description: Facultatively anaerobic, Gram-negative rod
Location: Found in human vagina Disease: associated with bacterial vaginosis Responsible for “fishy” odor with vaginal discharge TX: Metronidazole, either orally or vaginal gel, or intravaginal clindamycin cream |
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Trichomonas vaginalis
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Description: Motile, pear-shaped protozoan
Disease: Mostly venereal pathogen causing vaginitis, with foul-smelling vaginal discharge and painful urination. Common worldwide. TX: Metronidazole (single oral 2 gram dose). Topical gel is ineffective. |
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Treponema pallidum
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Description: Thin, tightly coiled spirochete; slow growing
Disease: Causes syphilis (STD); primary, secondary, latent and tertiary Primary: early after infection, characterized by an ulcer or chancre; TX: Benzathine PCN G 2.4 MU IM x1, doxycycline 100 mg po bid if patient is PCN allergic Secondary: spirochete dissemination, characterized by rash; TX: TX: Benzathine PCN G 2.4 MU IM x1, doxycycline 100 mg po bid if patient is PCN allergic Early latent: up to 1 year after infection when serology is only sign of infection; TX: Benzathine PCN G 2.4 MU IM x1, doxycycline 100 mg po bid if patient is PCN allergic Late (tertiary) syphilis: disease after 1 year of infection and tertiary-characterized by tissue destruction that appears 10-25 years after infection; TX: Benzathine PCN G 2.4 MU IM weekly x 3 weeks Neurosyphilis: 2-4 MU PCN G IV Q4H for 10-14 days Pregnancy: must use PCN G since it crosses the placenta and other antibiotics don’t |
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Influenza Virus
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Description: 2 types of virus, A and B. RNA virus with an envelope
Location: Not normal flora in humans, epidemics are fairly common and pandemics can occur and often have high mortality rates Diseases: Respiratory illnesses (predominantly pneumonia) accompanied by fever, myalgias and malaise, acute febrile illness in children. TX: Resolves untreated in many individuals; therapy includes amanitidine, rimantidine, oseltamivir, zanamivir. Prevention with annual vaccination is preferred. The vaccine consists of different serotypes every year. |
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Cytomegalovirus
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Description: Herpes DNA virus
Location: Infection is common in all human populations, reaching 60-70% in urban US cities, and nearly 100% in parts of Africa. Diseases: Many diseases: a) congenital infection of the liver, retina, and CNS with rash, b) mononucleosis similar to that of EBV, c) life-threatening disseminated infection in HIV and solid organ transplant patients TX: Ganciclovir or foscarnet, alternative cidofovir |
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Herpes simplex virus
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Description: Herpes DNA virus, with two predominant types (HSV-1, HSV-2)
Location: HSV has a worldwide distribution and are found in even the most remote human populations. There are no known animal vectors. Infection with HSV-1 is acquired more frequently and earlier than is infection with HSV-2. HSV-1 is transmitted via oral and genital secretion. HSV-2 is transmitted via genital secretions. Replication occurs in local epithelial cells until eruption occurs on surface as vesicles. Virus ascends the peripheral sensory nerves to become latent in the dorsal root ganglia of the jaw or groin. Virus can later descend the nerve to cause additional outbreaks. Diseases: Mucocutaneous vesicular and ulcerative lesions of the a) gums and lips (usually HSV-1) and b) genitals (usually HSV-2). Disseminated infectious complications include aseptic meningitis and encephalitis, eye infection, and pneumonia, among others. TX: Mucocutaneous-topical acyclovir, penciclovir, or docosanol; alternative oral acyclovir, famciclovir, |
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Respiratory Syncytial Virus
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Description: RSV is a paramyxovirus; two types are detected (A and B).
Location: Droplets or direct contact leads to infection of epithelial cells of respiratory tract. Viruses spread locally and symptoms are caused in part by antibody-dependent cell-mediated cytotoxicity Disease: Upper and lower respiratory tract infections in young children often less than 2 years of age (especially bronchiolitis) and the elderly TX: Aerosolized ribavirin may be helpful |
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Bacillus anthracis
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Description: Nonmotile, spore forming, Gram-positive rod that grows on blood agar
Location: Found in many domestic animals such as cows and sheep Diseases: Causes anthrax: cutaneous anthrax produces painless pruritic papules that enlarge in to vesicles and ulcerate to form eschar; pulmonary anthrax follows inhalation and mimics influenza initially, but patients develop dyspnea and hypoxemia-50% develop meningitis; majority of patients die of pulmonary anthrax (bioterrorism agent); GI disease is uncommon but fatal in 40% TX: penicillin for cutaneous anthrax; fluoroquinolones (ciprofloxacin) for pulmonary anthrax (expect poor outcomes) A vaccine is available |
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Clostridium perfingens
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Description: Anaerobic, spore-forming Gram-positive bacteria
Location: found in the human colon and vaginal tract Disease: Gas-producing organism, associated with abscess formation or deep tissue supparative infections, SSSI, or bacteremia TX: high-dose penicillin; alternatives are chloramphenicol or clindamycin or metronidazole |
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Clostridium difficile
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Description: Anaerobic, Gram-positive bacilli, spore-producing
Location: found in the human colon Disease: Produces non-specific watery diarrhea, to pseudomembranous colitis and toxic megacolon Produces toxin that are cellulytic Hospitalization and antibiotic therapy are risk factors for C. difficile infection; only observed following antibiotic therapy TX: mild-moderate diseases: oral metronidazole 1st line; oral vancomycin 2nd line; severe disease oral vancomycin 1st line |
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Candida albicans
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Description: Thin-walled yeast that reproduce by budding. May also produce pseudohyphae in tissues.
Disease: Most prevalent species of yeast in the human body. Candidiasis – disease may be local – cutaneous, mucocutaneous, vaginitis; or invasive/disseminated – esophagitis, cystitis, peritonitis, bacteremia, endocarditis. Susceptibility testing; not routinely done. Interpretation of MIC data is controversial. TX: Fluconazole is the drug of choice, however depending on patient, site, etc. any of the following may be used – amphotericin B, fluconazole, itraconazole, ketoconazole, voriconazole, caspofungin, micafungin, anidulafungin |
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Candida glabrata
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Description: Thin-walled yeast that reproduce by budding.
Disease: One of most common non-albicans species found in humans. Candidiasis – disease may be local – cutaneous, mucocutaneous, vaginitis; or invasive/disseminated – esophagitis, cystitis, peritonitis, bacteremia, endocarditis. Susceptibility testing; not routinely done. TX: Depending on patient, site, etc. any of the following may be considered a drug of choice – ampho B, itraconazole, ketoconazole, voriconazole, caspofungin, micafungin, anidulafungin. Dose dependent susceptibility to fluconazole, and decreased susceptibility to amphotericin B. |
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Cryptococcus neoformans
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Description/Disease: Currently is the second most common cause of fungal infections in the U.S. – disseminated disease is uniformly fatal if left untreated.
Approximately 50% of patients with cryptococcal infections are immunocompromised. Transmission most likely via inhalation, with respiratory tract serving as the primary infected site. May cause disseminated disease, or most commonly cryptococcal meningitis, particularly in HIV/AIDS patients. Diagnosis: cryptococcal polysaccharide capsular antigen detection (cryptococcal antigen titres); India ink stain (from CSF or culture) TX: ampho B or fluconazole; ampho B + flucytosine if meningitis; fluconazole and other azoles used for life long suppression in select patients |
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Dermatophytes (Trichophyton spp)
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Description/Disease: Organisms that commonly cause typical dermatophytoses.
Onychomycosis (tinea unguium, nail bed infection), tinea capitis (“ringworm”), tinea corporis, tinea pedis, and tinea cruris are usually caused by Trichophyton spp., TX: for skin infections topical therapy is preferred however, any of the following could be considered a drug of choice: miconazole, clotrimazole, terbinafine, tolnaftate, econazole, tioconazole, itraconazole, ketoconazole, fluconazole Topical therapy fails in treating onychomycosis, oral therapy is required. |
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Peptostreptococcus species
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Description: Anaerobic gram-positive cocci
Location: commensal flora of skin and mucosal surfaces (mouth, respiratory tract, intestines, vagina) Diseases: Involved in abscess formation (brain abscess), chronic otitis media, mastoiditis, chronic sinusitis, pleuropulmonary infections, diabetic foot infection, necrotizing cellulitis Many different species involved, seldom speciated by clinical labs TX: Often surgery /debridement is required along with antibiotics; generally a mixed infection is present so proper therapy is complicated; penicillin or clindamycin; metronidazole is also effective |
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Fusobacterium species
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Description: Long, thin anaerobic, Gram-negative bacilli
Location: normal flora of human mouth; F. nucleatum, F. necrophorum Diseases: Cause infections in oral cavity and upper respiratory tract (empyema, necrotizing pneumonia) Lemierre’s syndrome and Ludwig’s angina are caused by F. necrophorum Can cause severe clinical illness TX: Most Fusobacterium remains susceptible to penicillin, but some B-lactamase production can occur; also metronidazole, clindamycin, imipenem, all beta-lactam/B-lactamase inhibitor combos |
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Prevotella species
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Description: Anaerobic Gram negative bacilli
Location: normal flora of human mouth (P. melaninogenica, P. oralis, P. oris, P. buccae) and vaginal tract (P. melaninogenica) Diseases: Cause infections in oral cavity and upper respiratory tract (empyema, necrotizing pneumonia); periodontal infection; “clenched-fist” (and human bite) infection; often multiple anaerobic organisms are involved Lemierre’s syndrome also caused by Prevotella spp. Prevotella causes bacterial vaginosis following abx therapy (abx kill off lactobacilli) Resistance Issues: Produce B-lactamase making penicillin unreliable TX: Metronidazole, clindamycin, imipenem, all beta-lactam/B-lactamase inhibitor combos |
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Bacteroides fragilis
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Description: Anaerobic, Gram negative bacilli; normal flora of human colon; Bacteroides genus contains many species; speciation is not routinely performed by all clinical labs, and susceptibility testing is generally never performed. B. fragilis is the most pathogenic of the anaerobic GNB.
Location: Large bowel of humans Diseases: Nearly all infections involved abscess formation; frequently polymicrobial infections Common cause of abscess in abdomen, pelvis, perirectal area, SSSI Resistance Issues: Most produce B-lactamase TX: Active agents include clindamycin, chloramphenicol, metronidazole, cefoxitin, carbapenems, amp/sulbactam, ticar/clav, pip/tazo; follow local resistance patterns (if available); metronidazole and imipenem are uniformly active |
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Pneumocystis jirovecii (formerly carinii)
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Description: Organism that shares characteristics of both protozoa and fungus. Life cycle has 3 stages: trophozoite, cysts, and sporozoite.
Disease: Causes P. carinii pneumonia (PCP) in the immunocompromised host, e.g. HIV/AIDS, chemotherapy, etc. Diagnosis: cannot be grown on culture (therefore, no susceptibility testing either); requires demonstration of cysts or trophozoites within tissues or body fluids – e.g. BAL TX: treatment – TMP/SMX +/- dapsone; treatment alternatives include clindamycin + primaquine, pentamidine, atovaquone, and trimetrexate; prophylaxis |
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Rickettsia rickettsii
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Description: Obligate intracellular parasites about the size of bacteria.
Microscopically visualized as pleomorphic coccobacilli Location: Maintained in nature – life cycle involves an insect vector and an animal reservoir Disease: Causative pathogen in typhus and other rickettsial diseases such as (tick-borne) spotted fevers, Q-fever, and trench fever. Transmission/infection via skin (insect bite, insect feces) or respiratory route (infected dust in Q fever) Diagnosis usually through serologic testing TX: doxycycline (tetracyclines) – alternative agents include chloramphenicol and fluoroquinolones |
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Borrelia burgdorferi
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Description: Fastidius, microaerophilic spirochete; slow growing
Location: transmitted by Ixodid ticks (I. scapularis or deer tick) Disease: Causes Lyme disease; most Lyme disease occurs in New England, SE NY, NJ, PA, MD, DE, MN and WI Disseminates to the heart, CNS, and synovium after inoculation Causes characteristic rash (erythema migrans), cranial neuritis, carditis, and arthritis (late disease); diagnosis (via antibodies) is difficult TX: doxycycline, amoxicillin or cefuroxime; ceftriaxone may be alternative |
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Plasmodium falciparum
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Description: Parasite transmitted by the bite of infected Anopheles mosquitoes. The sporozoites then travel through the blood stream to the liver, where they invade hepatocytes and mature to tissue schizonts or become dormant hypnozoites. Merozoites released from the liver invade red blood cells, reproduce asexually, and release progeny after 48-72 hours.
Location: Climatic factors such as temperature, humidity, and rainfalls affect infestation with Anopheles mosquitoes. Malaria is transmitted in tropical and subtropical areas, where Anopheles mosquitoes can survive and multiply, and malaria parasites can complete their growth cycle in the mosquitoes ("extrinsic incubation period"). Temperature is particularly critical. At temperatures below 20°C (68°F), Plasmodium falciparum cannot complete its growth cycle in the Anopheles mosquito, and thus cannot be transmitted. Tropical regions of South America, sub-Sahara Africa, and the Asian subcontinent are areas at risk. Disease: Microvascular disease, ranging in |
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Salmonella enteritidis
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Description: Aerobic, facultative anaerobic, Gram negative bacilli of family Enterobacteriaceae
Diseases: Cause common food poisoning (gastroenteritis) Fecal-oral route of transmission; contaminated food or water N/V/D occurs 6-48 hours after ingestion; fever may also occur but stools are without blood. Usually self-limiting; resolves in 48-72 hours Carriage state may occur following recovery TX: No drug therapy necessary |
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Shigella species
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Description: Small, aerobic, non-lactose fermenting Gram-negative bacilli belonging to family Enterobacteriaceae
Location: S. sonnei seen in developed countries, S. flexneri and S. dysenteriae most common in developing countries Diseases: Cause acute diarrhea (with or without blood and mucus), high fever, and general toxicity Spread through oral-fecal route via food and water contamination, pools, and flies ABX are effective in shortening duration of diarrhea and fever and fecal spreading of organism Resistance Issues: Abx resistance is increasing; in vitro may not predict in vivo TX: fluoroquinolone (cipro, norflox, oflox), ceftriaxone in children; TMP/SMX no longer DOC due to resistance |
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Campylobacter jejuni
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Description: Motile, non-spore-forming Gram-negative rods; Microaerophilic (neither truly aerobic or anaerobic)
Location: found in GI tracts of many animals used for food production and in household pets. Usual route of transmission to humans is through ingestion of raw or undercooked food products or through direct contact with infected animals Disease: Usually causes diarrhea (Campylobacter enteritis). Other Campylobacter sp may cause diarrheal or non-diarrheal illnesses. Presence in human implies infection (not normal flora) Testing: stool Gram stain and culture; fastidious organism TX: ciprofloxacin (fluoroquinolone); alternative agents include erythromycin (macrolides) and doxycycline (tetracyclines); limited reports in Asia of strains resistant to both FQs and macrolides |
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Helicobacter pylori
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Description: Aerobic, Gram negative spiral bacteria
Location: found in the human stomach; high affinity for gastric acid epithelium; produces urease which allows for colonization and provides acid tolerance by ammonia generation Diseases: Universally responsible for gastritis and peptic ulcer disease (>95% except for NSAID induced disease) Diagnosis made by ELISA test for serum IgG antibodies to H. pylori or urea breath tests TX: Multidrug regimen necessary: usually H2 antagonist or proton pump inhibitor or bismuth + clarithromycin or metronidazole +/- ampicillin or tetracycline for 14 days |
