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60 Cards in this Set
- Front
- Back
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of the family Streptococcaceae, what genera are currently considered to be clinically significant to humans? |
Streptococcus, Enterococcus, and Aerococcus |
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relatively uncommon opportunistic organism from the environment that can cause infections in humans |
Aerococcus viridans |
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Streptococcus and Enterococcus: Gram: Catalase: produce _________ from carbohydrate fermentation |
Gram positive, tend to form chains in liquid media Catalase negative, a few strains of Enterococcus produces small bubbles in hydrogen peroxide produce lactic acid from carbohydrate fermentation |
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Describe Lancefield grouping |
many of the Streptococcus and Enterococcus have group specific polysaccharide antigens in the cell wall that form the basis of Lancefield grouping. now routinely identified by procedures other than Lancefield and referred to as group antigens instead of Lancefield group antigens |
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Describe clinically significant Group A Streptococci |
most Streptococci with cell wall antigen A are Streptococcus pyogenes, Beta hemolytic |
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Describe clinically significant Group B Streptococci |
one species, Streptococcus agalactiae, Beta hemolytic |
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Describe clinically significant Group C Streptococci |
Streptococcus equisimilis most common isolate from humans, Beta hemolytic |
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Describe clinically significant Group F and G Streptococci |
rarely of clinical significance to humans |
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Describe clinically significant Group D Streptococci |
two physiologically and genetically different groups that possess D antigens, Enterococcus and Nonenterococcus |
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Describe the Enterococcus Group |
Three non-hemolytic species commonly isolated from humans formerly designated as Streptococcus but now belong to the genus Enterococcus: Enterococcus faecalis (some strains are VRE) Enterococcus faecium (some strains are VRE) Enterococcus durans |
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Describe the Non enterococcus group |
Streptococcus equinus Streptococcus bovis |
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Describe the Streptococci not identified by Group Antigens |
Alpha hemolytic Streptococcus pneumoniae Streptococcus viridans |
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Describe the Streptococcus anginosus - milleri group |
tend to form small colonies enhanced by or require increased CO2 alpha, beta, or gamma hemolytic may or may not have group antigen may smell of buttersotch |
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Describe the cellular morphology of Streptococcus pyogenes |
Group A Streptococcus or GAS Gram positive cocci, 0.5-1 micrometer in diameter, tend to form chains in broth more spherical than typical Streptococci. capsules are not usually seen and S. pyogenes does not have spores or flagella |
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What are the Growth Requirements for Streptococcus pyogenes? |
Atmosphere -facultative with most strains growing as well or better in anaerobic conditions increased CO2 is not required Temperature -optimum temperature for growth is 35C Nutrients -medium enriched with blood or serum required for good growth BAP recommended for isolation |
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What are the Cultural Characteristics of Streptococcus pyogenes? |
typical cultres have a granular appearance that breaks up on shaking overnight colonies vary from 0.5-1mm gray to white opaque to translucent some colonies buttery, some matt beta hemolytic |
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What is Streptococcus pyogenes hemolysis due to? |
Streptolysin S - oxygen stable but acid labile Streptolysin O - oxygen labile and may be inactivated by exposure to oxygen |
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what is the genus ID for Streptococcus? |
G+ cocci that tend to chain and are catalase negative and nitrate negative are Streptococci |
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what tests provide presumptive ID for Streptococcus pyogenes? |
Bacitracin susceptibility (susceptible) PYR (positive)
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what is the definitive ID for Streptococcus pyogenes? |
detection of cell wall Group A antigen (latex and co-agglutination slide tests) GAS-D test, DNA probe for Group A Streptococcus |
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Group A-G antigens are _______________, while Group D antigen is ____________. |
carbohydrate residues composed of teichoic acid |
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Describe the general susceptibility of S. pyogenes to antimicrobial agents |
Penicillin: susceptible Erythromycin: Susceptible with rare resistance Tetracycine: usually susceptible but some resistant strains |
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what categories may clinical conditions resulting from S. pyogenes be separated into? |
upper respiratory infections (throat) cutaneous infections invasive infections post-strptococcal diseases |
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describe upper respiratory infections associated with Streptococcus pyogenes |
acute pharyngitis, Strep Throat sore throat, swollen lymph glands, fever, headache
when the strain of S. pyogenes produces a pyrogenic exotoxin, the patient will have scarlet fever rash on upper chest spreading to other parts of the body tongue is often symptomatic (strawberry tongue) |
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describe cutaneous infections associated with Streptococcus pyogenes |
pustular lesions, impetigo, infections following a trauma Erysipelas- when infection affects the underlying dermis |
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describe invasive infections due to Streptococcus pyogenes |
"flesh eating" disease or necrotizing fasciitis symptoms cellulitis with pain, fever, septic shock, respiratory distress, necrotizing fasciitis, renal dysfunction, liver dysfunction mortality rate may be as high as 30-50% |
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describe post streptococcal diseased |
Rheumatic fever: 1-5 weeks after pharyngitis. presence of M antigens in S. pyogenes cell wall are similar to myosin in heart muscle. Streptococcal antibodies attach to heart muscle causing inflammatory reaction and scarring of heart valves Acute glomerulonephritis: may follow pharyngitis or cutaneous infection. antigen-antibody complexes deposited on the glomerular membranes of the kidney, activating complement. results in damaged membrane, allows protein and blood to enter urine. |
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what is tested for patients suspected to have post streptococcal disease? |
Antistreptolysin O most frequently tested for |
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what is the cellular morphology for Streptococcus agalactiae? |
Group B Streptococcus Gram positive cocci, 0.5-1 micrometer in diameter, tend to form chains in broth capsules are not usually seen and S. agalactiae does not have spores or flagella |
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describe the growth requirments for Streptococcus agalactiae |
Atmosphere -facultative with most strains growing as well or better in anaerobic conditions increased CO2 is not required Temperature -optimum temperature for growth is 35C Nutrients -medium enriched with blood or serum required for good growth BAP recommended for isolation |
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Describe the cultural characteristics of Streptococcus agalactiae |
colonies on BAP approx. 1mm, semitransparent gray with a buttery or matt consistency. small zone of beta hemolysis. occasionally nonhemolytic and some strains have red pigment |
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what tests can be used for presumptive ID of Streptococcus agalactiae? |
CAMP (positive) Hippurate Hydrolysis (positive) |
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what tests can be used for definitive ID of Streptococcus agalactiae? |
latex or co-agglutination able to detect directly from body fluids: spinal fluid urine serum (unreliable) |
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describe the antimicrobial susceptibility of S. agalactiae |
susceptible to penicillin (use pen G or ampicillin) some strains penicillin tolerant, combination of ampicillin and gentamicin are recommended. Erythromycin and vancomycin alternates due to allergies |
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Describe the clinical significance of S. agalactiae |
tends to be an opportunistic infection may involve eye, ear, upper respiratory tract, surgical incisions or other parts of the body. post Streptococcal disease is not a concern. |
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what is the most serious infection caused by group B Streptococci? |
neonatal sepsis |
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where are Group B Streptococci sometimes normal flora/carried? |
normal fecal organisms, may be carried in the vagina |
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describe the cellular morphology of Group D Streptococci |
G+ cocci, form chains in liquid media. 0.5-1 micrometer in diameter. some cells may be elliptical or oval |
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describe the growth requirements for Group D Streptococci |
Atmosphere -facultative with most strains growing as well or better in anaerobic conditions increased CO2 is not required Temperature -optimum temperature for growth is 35C Nutrients -medium enriched with blood or serum required for good growth BAP recommended for isolation Growth on non-enriched media is better than for groups A & B |
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Describe the Cultural Characteristics of Group D Streptococci |
Overnight colonies on BAP are 1-2mm, gray, convex, and buttery. most strains are nonhemolytic or have a small zone of alpha hemolysis. Will grow on some types of MacConkey agar (usually selective for gram negatives) colonies on MacConkey will be small and have a deep pink colour due to lactose fermentation. |
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Describe 'psudocatalase' |
an enzyme produced by some strains of Group D Enterococci that gives a weak reaction in the catalase test. |
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Describe the tests used for Group D species identification |
may be identified by group D antigen or physiological tests. Group D antigen contains teichoic acid, may cause problems in detection of group antigen physiological (biochemical) testing is generally used. |
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what tests can be used for Group D ID? |
BEA (positive) PYR (Enterococci are positive while Nonenterococci are negative) NaCl Enterococci will grow in 6.5% NaCl, Nonenterococci will not |
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what does isolation of Streptococcus bovis from a blood culture indicate? |
neoplasm of the GI tract |
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describe the antimicrobial Susceptibility of Group D Streptococci |
Nonenterococci more susceptible to antimicrobials than Enterococci S. bovis usually susceptible to penicillin but combination treatments may be needed for eradication Enterococci resistant to low concentrations of penicillin and ampicillin serious enterococcal infections often treated with a combination of an aminoglycoside and penicillin. some strains of Enterococcus have developed resistance to this. VREs: E. faecium & E. faecalis
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Describe the clinical significance of Group D Streptococci |
normal fecal flora Enterococci more frequently found in infections than Nonenterococci Enterococcus faecalis most common isolate E. faecium is important nosocomial pathogen due to vancomycin resistance. S. bovis most common isolate of Nonenterococci. presence in blood culture associated with carcinoma of GI tract |
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describe the clinical significance of Beta hemolytic Streptococci not in Groups A, B, or D |
frequently isolated from clinical material. ID is usually made by cell wall group antigen Group C: animal pathogens, cause pharyngitis, pneumonia, septicemia and meningitis in humans Group F: infections in humans include oral infections, abscesses of the CNS, liver, and appendix, neonatal sepsis Group G: may infect animals, cause pharyngitis, middle ear infection, neonatal sepsis, endocarditis and meningitis reported in humans. |
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describe the screening procedure for VRE |
screening done using a solid agar plate containing vancomycin at a concentration of 6 mg/L Usually Enterococcus faecium May be tested for genetic markers: Van A, B, C |
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Describe the cellular morphology of Streptococcus pneumoniae |
G+ cocci, 1 micrometer in diameter. cells tend to be elongated. typically seen in pairs but singles and chains also seen. capsules usually present in exudate and fresh cultures. |
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Describe the growth requirements of Streptococcus pneumoniae |
atmosphere facultative with some strains requiring increased CO2. All S. pneumoniae should be incubated in 5-10% CO2 for primary cultures. Temperature 35C Nutrients Blood or serum required. BAP is suitible for growth |
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Describe the colonial morphology for S. pneumoniae |
typically wet, glistening, narrow zone f alpha hemolysis. 1-2mm but larger, mucoid colonies up to 5mm seen surface of the colony shows varying degrees of flattening depending on the age of the colony. flattening due to autolysis of cells due to the production of hydrogen peroxide produced as bacteria grow in air. this does not happen if colony has been incubated anaerobically. |
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What tests differentiate S. pneumoniae from S. viridans? |
Bile Solubility (S. pneumoniae is soluble, S. viridans is not) Optochin susceptibility (S. pneumoniae is susceptible, other Streptococci are not) |
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Describe the antimicrobial sensitivity of S. pneumoniae |
drug of choice is penicillin there are some resistant strains, tested for with 1 microgram oxacillin disc plated on Mueller Hinton agar enriched with 5% blood, incubated in CO2. zones greater than 20mm indicate susceptibility to penicillin |
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Describe the clinical significance of S. pneumoniae |
found in the upper respiratory tract of some healthy individuals most common cause of Adult lobar pneumonia -bacteria come from an endogenous source -sudden onset with accompanying septicemia -presence of diarrhea indicates a bad prognosis -middle ear infection, sinusitis, conjunctivitis and meningitis are complications of pneumococcal infections least common source of meningitis
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Describe the characteristics of Streptococcus viridans |
-alpha hemolytic Streptococci that are not S. pneumoniae or Group D (Bile esculin, Group D antigen, bile solubility, and optochin all negative) or -nonhemolytic Streptococci that do not have group D or B antigens (Bile esculin, Group B and D antigens all negative) |
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Describe the Cellular Morphology of Streptococcus viridans |
-G+ cocci, ~1mm in diameter -chains may be formed in broth -smears from solid media often show pleomorphic forms that may be club shaped resembling diphtheroids -direct smears from the upper respiratory tract often show chains of elongated cocci adhering to epithelial cells |
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describe the growth requirements of Streptococcus viridans |
grow best on enriched media such as blood agar optimum temp is 35C increased CO2 usually not required |
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describe the cultural characteristics of Streptococcus viridans |
pinpoint colonies with small zone of alpha hemolysis surface of the colonies may be flat or concave some strains are non-hemolytic |
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describe the antibiotic susceptibility of S. viridans |
majority of isolates susceptible to penicillin but some strains show resistance requiring high levels of antibiotic for treatment |
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describe the clinical significance of S. viridans |
S. viridans makes up a large portion of normal flora isolated from upper respiratory specimens S. viridans is the major cause of subacute bacterial endocarditis |
