Module 12 Flashcards by Taylor Horlock

What are the B-hemolytic groups of Strep?

A- mostly S. pyogenes

B- S. agalactiae

C- S. equisimilis

F and G- rarely clinically significant

D- two different groups

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What are the group D Enterococci?

Nonhemolytic

E. faecalis

E. faecium

E. durans

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What are the group D non Enterococci?

S. equinis

S. bovis

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What are the Strep organisms that are alpha hemolytic?

Not identified by antigens.

S. pneumoniae

S. viridans

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What are the characteristics of the S. anginosus-milleri group?

May be in group A, C, F, G or none.

Pinpoint colonies that are require CO2

Alpha, beta or gamma hemolytic.

Butterscotch smell.

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What are the characteristics of nutritionally variant Strep?

May be grouped with S. viridans.

Require think compound or vitamin B.

Two distinct species.

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What are the growth conditions for group A Strep?

Facultative anaerobes, don’t require increased CO2.

Temp- 35°C

Enriched media with blood or serum.

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What are the cellular characteristics of group A Strep?

Smaller than Staph (0.5-1um).

Spherical

No capsules, spores or flagella.

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What are the colonial characteristics of group A Strep?

Grey-white

Opaque to translucent

Buttery or matte

Beta hemolysis

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What is group A hemolysis due to?

Streptolysin S (acid labile)

Streptolysin O (oxygen labile)

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What is the genus ID of group A?

Catalase negative

Nitrate negative

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What is the presumptive ID for group A?

Bacitracin- 99% susceptible (other beta hemolytic Streps are also susceptible)

PYR- nearly 100% positive

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What is the definitive ID for group A Streps?

Specific cell wall antigen detection (latex and coagglutination tests).

Direct detection- only 65-90% sensitivity.

GASD- DNA probe

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What antimicrobials are group A Strep sensitive to?

Universally sensitive to penicillin.

Erythromycin

Tetracycline

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What infections do group A Strep cause?

Upper respiratory- may produce pyrogenic exotoxin

Cutaneous- erysipelas if the underlying epidermis is affected, usually preceded by infection

Invasive- bacteria enters deeper tissue through an initial wound, nectrotizing fasciitis, treatment is penicillin with erythromycin inclusion

Post Strep diseases- rheumatic fever (ABs attach to heart muscle) and acute glomerulonephritis (antigen-AB complexes are deposited on the glomerulus)

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What is antistreptolysin O (ASO) and when is it found?

ABs that remain weeks after infection.

High level indicates recent infection and/or post Strep disease.

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How many people carry S. pyogenes in their respiratory tract without signs of infection?

5-15%

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What are the colonial characteristics of group B Strep?

1mm

Semitransparent

Grey

Buttery or matte

Small zone of beta hemolysis- occasional strain is nonhemolytic or has red pigment

What is the genus ID for group B Strep?

Catalase negative

Nitrate negative

What is the presumptive species ID for group B Strep?

cAMP- positive (also some group A)

Bacitracin- susceptible

Hippurate hydrolysis- positive (also some group D)

What is the definitive ID for group B Strep?

ID of specific group wall antigen.

Listeria monocytogenes may cross agglutinate but looks different in Gram stain.

Direct ID from spinal fluid, urine, serum (not reliable), vaginal swabs

What is the susceptibility of group B Strep?

Most respond to penicillin G or ampicillin.

If penicillin tolerant- combo of ampicillin and gentimycin or erythromycin or vancomycin.

What is the pathogenicity of group B Strep?

Opportunistic infection

Neonatal sepsis from bacteria in mother vagina.

Rapid onset- in utero or during birth, high mortality

Late onset- seen after first week, lower mortality rate

What increases the risk of rapid onset neonatal sepsis?

Complications during delivery

Prematurity

Heavy colonization of mother

When are mothers to be screened to determine if their vaginas are colonized by group B Strep?

34-36 weeks gestation Can be given antibiotics before delivery.

What are the colonial characteristics of group D Strep?

1-2mm Grey Convex Buttery Most are nonhemolytic or have a small alpha hemolytic zone Will grow on MAC agar without crystal violet

What is the genus ID for group D Strep?

Catalase negative Nitrate negative May give weak catalase due to pseudocatalase production

What is the species ID of group D Strep?

Tests for group D antigen (teichoic acid beneath cell wall), requires longer enzyme extraction. Other genera can react with group D antisera giving false positives. BEA- positive for bile tolerance and esculin hydrolysis (S. viridans occasionally gives positive) PYR- Enterococci is positive, Nonenterococci is negative (group A is also positive) 6.5% NaCl- Enterococci will grow but Nonenterococci will not

What are the members of the Streptococcaceae family and their characteristics?

Streptococcus, Enterococcus and Aerococcus Gram positive cocci, chains. Lactic acid from carbohydrate fermentation. Catalase negative. Group specific polysaccharide antigens in cell wall.

What is the susceptibility of group D Strep?

More resistant S. bovis- susceptible to penicillin Aminoglycoside and penicillin combo for serious infections Some Enterococci have acquired resistance to aminoglycosides by a transferable plasmid.

What is the pathogenicity of group D Strep?

Normal fecal flora Enterococci is more often found in infections. E. faecalis is the most common isolate. E. faecium is an important nosocomial pathogen. S. bovis is the most common Nonenterococcus isolate (GI tract carcinoma)

What is the clinical significance of group C, F and G Strep?

C and F- pharyngitis, pneumonia, septicaemia, meningitis G- pharyngitis, otitis media, neonatal sepsis, endocarditis and meningitis

What are the characteristics of VRE?

Normal intestinal flora. Screening- agar dilution test with vancomycin, any growth = Enterococci Most strains are E. faecium.

What are the colonial characteristics of alpha hemolytic Strep (S. pneumoniae)?

Capsules in exudate and fresh cultures. Narrow alpha hemolysis zone. Varying degrees of flatness due to H2O2 auto lysis (no catalase). Poor growth in chocolate agar (autolysis, no catalase). Temp- 35°C Facultative anaerobes, some require increased CO2 Normally see in pairs (I know this is cellular morphology but whatever)

What is the genus ID of S. pneumoniae?

Catalase negative Nitrate negative

What is the species ID for S. pneumoniae?

Bile soluble, but if older than 24hr may be insoluble. Susceptible to optochin (>/=14mm) Antigen ID- no Strep group antigens but others, rapid agglutination is positive, capsular swelling reactions Two out of the three tests must match, they don't always work great.

What is the susceptibility of S. pneumoniae?

Penicillin but there is some tolerance so testing is required. Oxacillin (1ug) disc diffusion, >/=20 is susceptible.

What is the pathogenicity of S. pneumoniae?

Upper respiratory infection- most common cause of adult lobar pneumonia. Third most common cause of purulent meningitis (usually in children).

What are the characteristics of S. viridans?

Alpha hemolytic Strep that's not S. pneumoniae, group D or Enterococci. Nonhemolytic Strep that don't have group D or B antigens.

What is the cellular and cultural morphology of S. viridans?

Pleomorphic forms. Small colonies (0.5mm) with a narrow alpha hemolysis zone. Flat or concave surface.

How is alpha hemolytic S. viridans differentiated from S. pneumoniae?

Bile insoluble Optochin resistance

How is nonhemolytic S. viridans differentiated from group D Strep?

Bile esculin negative PYR negative

What is the susceptibility of S. viridans?

Majority are susceptible to penicillin, some have moderate resistance requiring high levels.

What is the clinical significance of S. viridans?

Upper respiratory normal flora. Subacute endocarditis after dental work.