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68 Cards in this Set

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How do Streptococci appear with a gram stain? Staphylococci?
Streptococci line up one after the other in a strip. Staphylococci appear as a cluster.
Which gram-positive bacteria is catalase positive?
Staphylococci possess the enzyme catalase, and are thus catalase positive.
What is the difference between beta-hemolytic and alpha-hemolytic strepptococci?
Beta-hemolytic streptococci completely lyse the RBCs on a blood agar plate. Alpha-hemolytic streptococci only partially lyse the RBCs, leaving a greenish discoloration of the culture medium surrounding the colony.
What Lancefield antigens are found on streptococci?
Lancefield group A, B, and D.
What are the streptococci that do not have Lancefield antigens?
Streptococcus pneumoniae
Streptococci viridans group
What is the group A Beta-hemolytic streptococci?
Streptococcus pyogenes
What are the diseases that Strep pyogenes can create?
Strep throat
Scarlet fever
Rheumatic fever
Post-streptococcal glomerulonephritis
What is the major virulence factor for group A streptococcus?
M protein. It inhibits the activation of complement and protects the organism from phagocytosis.
Plasma cells generate antibodies against the M protein, leading to opsonization and destruction by macrophages.
What are some enzymes that contribute to the pathogenicity of group A streptococcus?
Streptolysin O: oxygen labile (inactivated by oxygen), this enzyme destroys RBCs and WBCs. Antibodies develop against streptolysin O (ASO).

Streptolysin S: Oxygen stabile, also responsible for beta-hemolysis, but is not antigenic.

Pyrogenic exotoxin: Strains with this enzyme cause scarlet fever.

Streptokinase: Activates plasminogen to lyse fibrin clots
What are four types of disease caused by local invasion and/or exotoxin release from group A streptococcus?
1) Streptococcal pharyngitis
2) Streptococcal skin infections
3) Scarlet fever
4) Streptococcal toxic shock syndrome
What are two delayed antibody mediates diseases that can be caused by group A streptococci?
1) Rheumatic fever
2) Glomerulonephritis
What do you use to treat necrotizing fasciitis and streptococcal toxic shock syndrome caused by group A beta-hemolytic streptococcus?
Penicillin G with added clindamycin.
What are the 6 major manifestations of rheumatic fever?
1) Fever
2) Myocarditis (heart inflammation due to antibodies targeting heart antigens that are similar to strep antigens)
3) Arthritis (joint swelling)
4) Chorea which begins 2-3 weeks after
5) Subcutaneous nodules
6) Erythema marginatum (rash that has a red margin that spreads out from its center)
What is group B streptococcus?
Streptococcus agalactiae (also beta-hemolytic)

Think B for Baby
What can streptococcus agalactiae cause?
25% of women carry these bugs vaginally, and can transfer to babies during delivery. Can cause neonatal meningitis, pneumonia, and sepsis.
What are the three most common pathogens associated with meningitis in infants younger than 3 months of age?
Escherichia coli, Listeria monocytogenes, and group B streptococcus.
What are some of the viridans group streptococci?
Streptococcus salivarius, S. sanguis, S. mitis, S. intermedius, S. mutans
Are viridans streptococci alpha hemolytic or beta hemolytic?
Viridans streptococci are alpha-hemolytic (viridis is latin for green, since they leave a greenish discoloration on blood agar)
What are the 3 types of infections that viridans streptococci cause?
Dental infections (especially S. mutans)

Endocarditis (after dental manipulations): bacteria produce an extracellular dextran that allows them to cling to cardiac valves

Abscesses (caused by streptococcus intermedius group)
Streptococcus Intermedius = immediately asses for abscess
How is group D streptococci split up?
Group D streptococci is divided into two subgroups: the enterococci and non-enterococci
How are the enterococci significant clinically?
Enterococci are normal bowel flora. They are alpha hemolytic and are commonly the infecting agents in urinary tract infections, biliary tract infections, bacteremia, and subacute bacterial endocarditis (SBE)
What are some examples of non-enterococci group D streptococci?
What are some clinical implications of these bacteria?
Streptococcus bovis
Streptococcus equinus

Streptococcus bovis infection has a high association with colon cancer (50% of people with S. bovis infection have a colonic malignancy)
What is the clinical significance of Streptococcus pneumoniae?
AKA pneumococcus
Major cause of bacterial pneumonia and meningitis in adults, and otitis media in children.
What is the major virulence factor of Streptococcus pneumoniae?
The polysaccharide capsule
What are the two tests to identify the pneumococcus?
Quellung reaction: capsule will swell when mixed with antiserum (serum with antibodies to the capsular antigens)

Optochin sensitivity: an optochin disk is placed in agar dish. Streptococcus pneumoniae will be inhibited (viridans will continue to grow)
What does pneumococcus look like under the microscope?
Lancet-shaped diplococci
What are the three major pathogenic species of staphylococci?
Staphylococcus aureus
Staphylococcus epidermidis
Staphylococcus saprophyticus
What tests do you use to differentiate staphylococci from streptococci?
Gram stain: Staphylococci lie in grape-like clusters

Catalase test: Staphylococcus aureus is catalase-positive

Culture: Staphylococcus aureus can be differentiated from other beta-hemolytic cocci by their elaboration of a golden pigment on sheep blood agar.
What test do you use to differentiate between staphylococci?
Coagulase test: only Staphylococcus aureus is coagulase positive
What are some proteins that Staphylococcus aureus utilize to disable our immune defenses?
1) Protein A: binds the Fc portion of IgG, protects from opsonization and phagocytosis

2) Coagulase: leads to fibrin formation around the bacteria, protecting it from phagocytosis

3) Hemolysins: Alpha, beta, gamma, and delta. Destroy RBCs, neutrophils, macrophages, and platelets
4) Leukocidins: Destroy WBCs
5) Penicillinase: Secreted form of beta-lactamase inactivates beta-lactams
6) Novel penicillin binding protein: AKA transpeptidase, resistant to penicillins and cephalosporins
What are the proteins that allow Staphylococcus aureus to tunnel through tissue?
Hyaluronidase
Staphylokinase
Lipase
Protease
What are the exotoxins secreted by Staphylococcus aureus?
Exfoliatin: causes the skin to slough off (scalded skin syndrome)

Enterotoxins (heat stable): cause food poisoning, resulting in diarrhea and vomiting.

Toxic Shock Syndrome toxin (TSST-1): found in 20% of S. aureus isolates, causes toxic shock syndrome.
What are some diseases caused by S. aureus exotoxin release?
Disease caused by exotoxin release:
Gastroenteritis (food poisoning)
Toxic shock syndrome
Scalded skin syndrome
What are eight diseases resulting from direct organ invasion of S. aureus?
Pneumonia
Meningitis
Osteomyelitis
Acute bacterial endocarditis
Septic arthritis
Skin infections
Bacteremia/sepsis
Urinary tract infection
What is the pathogenesis of toxic shock syndrome?
Pyrogenic toxins, superantigens, bind to MHC class II molecules on APCs (macrophages). The toxin-MHC II complex causes a massive T cell response and outpouring of cytokines (TNF and IL1), resulting in toxic shock.
What are the symptoms of toxic shock syndrome?
Sudden onset high fever, nausea, vomiting, watery diarrhea
Followed in a few days by diffuse erythematous rash, desquamation of palms and soles.
Septic shock
Which bacteria is a frequent skin contaminant of blood culture, and infects via urine catheter and IV line placement?
Staphylococcus epidermidis
Staphylococcus epidermidis is the most frequent organism isolated from what?
Infected indwelling prosthetic devices, such as prosthetic joints, heart valves, and peritoneal dialysis catheters
What is the bacteria that is the second-most leading cause of urinary tract infections?
Staphylococcus saprophyticus
(second only to E. coli)
What are the two gram-positive spore-forming rods?
Bacillus and Clostridium
Which of the gram-positive spore-forming rods likes oxygen?
Bacillus is a facultative anaerobe (prefers an oxygen environment)
Clostridium lives in an anaerobic environment (obligate anaerobe)
What bacterium causes anthrax?
What is unique about this bacterium?
Bacillus anthracis
It is unique in that it is the only bacterium with a capsule composed of protein (poly-D-glutamic acid). This capsule prevents phagocytosis.
Where is Bacillus anthracis contracted from?
Bacillus anthracis spores are contracted from contaminated products made of hides and goat hair. Humans are also exposed to the spores during direct contact with infected animals or soil.
What are the symptoms of cutaneous anthrax infection?
Bacillus anthracis rapidly multiplies and releases a potent exotoxin. This exotoxin causes localized tissue necrosis, and leads to a painless round black lesion with a rim of edema.
This lesion is called a "malignant pustule" because without antibiotic therapy (penicillin), B. anthracis can continue to proliferate and disseminate through the bloodsteam. This will lead to death.
What is the pathogenesis of pulmonary anthrax? What are the symptoms?
Spores are taken up by macrophages in the lungs and transported to the hilar and mediastinal lymph nodes where they germinate. Mediastinal hemorrhage occurs resulting in mediastinal widening and pleural effusions.
Where to the anthrax toxins originate?
What are the three proteins that make up the toxin?
These toxins are encoded on a plasmid called pXO1.

Edema factor
Protective antigen
Lethal factor
What does the pXO2 plasmid encode?
It encodes three genes necessary for the synthesis of poly-glutamyl capsule, which prevents phagocytosis of the vegetative bacteria.
What does Bacillus cereus cause?
Food poisoning
What are the Clostridium bacteria?
Clostridium botulinum
Clostridium tetani
Clostridium perfringens
Clostridium difficile
What does the Clostridium botulinum toxin do?
It is a neurotoxin that blocks the release of ACh from presynaptic nerve terminals in the ANS and motor endplates, causing flaccid muscle paralysis.
What are the symptoms of adult botulism?
Bilateral cranial nerve palsies causing double visin and difficulty swallowing.
General muscle weakness, leading to sudden respiratory paralysis and death.
What are the symptoms of infant botulism?
Constipation for 2-3 days, followed by difficulty swallowing and muscle weakness.
Causes "floppy" babies
What does the Clostridium tetani toxin cause? How is it contracted?
Clostridium tetani causes tetanus.
It is classically cause by a puncture wound by a rusty nail, but can follow skin trauma by any contaminated object.
What is the pathogenesis of tetanus?
The Clostridium tetani toxin, tetanospasmin, is taken up at the neuromuscular junction (end plate) and is transported to the CNS. There the toxin acts on the inhibitory Renshaw cell interneurons, preventing the release of GABA and glycine.
What are the symptoms of tetanus?
Trismus (lockjaw)
Risus sardonicus, caused by spasm of the facial muscles (leads to a grinning expression)
What bacteria causes gas gangrene?
Clostridium perfringens
What are the two classes of infection with Clostridium perfringens?
1) Cellulitis/wound infection: Necrotic skin is exposed to C. perfringens, which grows and damages local tissue. Palpation reveals a moist, spongy, crackling consistency to the skin due to pockets of gas (crepitus).

2) Clostridial myonecrosis: C. perfringens secretes exotoxins that destroy adjacent muscle. These anaerobic bacteria release enzymes that ferment carbohydrates, resulting in gas formation. CT scan reveals pockets of gas within muscles and subcutaneous tissues.
What bacteria is responsible for antibiotic-associated pseudomembranous colitis?
Clostridium difficile (after the use of broad spectrum antibiotics)
What does C. difficile toxin A do? Toxin B?
Toxin A causes diarrhea
Toxin B is cytotoxic to the colonic cells (characterized by severe diarrhea, abdominal cramping, and fever).
If C. difficile infects the colon what can you use for treatment?
Treatment includes discontinuing the initial antibiotic and administering metronidazole or vancomycin.

The METRO train and VAN cruise down the GI tract, rather than being absorbed, and run over the hapless C. difficile bacteria.
What are the two gram-positive non-spore-forming rods?
Corynebacterium and Listeria
What is the pathogen responsible for diphtheria?
Corynebacterium diphtheriae
Where does Corynebacterium diphtheriae colonize?
What does it look like?
What does the toxin damage?
It colonizes the pharynx, forming a grayish pseudomembrane composed of fibrin, leukocytes, necrotic epithelial cells, and Corynebacterium diphtheriae cells.
The toxin targets the heart and neural cells.
Why is the Corynebacterium diphtheriae toxin considered a "human antibiotic"?
This exotoxin specifically inhibits protein synthesis in humans. The exotoxin contains two subunits, A and B. B subunit binds to target cells and allows the A subunit to enter the cell. Once inside the cells, the A subunit blocks protein synthesis by inactivating elongation factor (EF2), which is involved in translation of eukaryotic mRNA into proteins.
How do you diagnose Corynebacterium diphtheriae infection?
Throat and nasopharynx swabs are cultured on potassium tellurite agar and Loeffler's coagulated blood serum. On potassium-tellurite plate, colonies will become gray to black within 24 hours. Loeffler's blood serum will reveal rod-shaped pleomorphic bacteria.

TELL yoUR InTErn not to "LOAF around"
What do you use to treat diphtheria?
1) Antitoxin
2) Penicillin or erythromycin
3) DPT vaccine (Diphtheria, Pertussis, Tetanus)
What gram-positive organism has endotoxin?
Listeria monocytogenes
What populations does Listeria monocytogenes infect? What disease does it cause?
Listeria monocytogenes is a common cause of meningitis in neonates and immunosuppressed patients.