Midterm 1

Question 1

What is irregular about mycoplasma?

Answer 1

No cell wall

Question 2

What is irregular about ureaplasma?

Answer 2

No cell wall

Question 3

What is irregular about chlamydia?

Answer 3

Has cell wall but no peptidoglycan

Question 4

Sub-classification of gram positive cocci based on microscope appearance

Answer 4

Pairs and chains: Enterococcus or streptococcus

Clusters: staphylococcus

Question 5

Staphylococcus general properties

Answer 5

Facultative anaerobes
Catalase +
Common on skin and mucous membranes

Question 6

Disease associated staphylococci

Answer 6

S aureus, S lugdunensis, S epidermidis, and S saprophyticus

S pseudintermedius is an animal pathogen increasingly seen in human infections

Question 7

Catalase test

Answer 7

Determines if organism produces catalase enzyme (enzyme that breaks down harmful metabolites of aerobic respiration, seen in aerobic and facultative anaerobic organisms)
Positive: able to breakdown hydrogen peroxide (eg Staphylococcus)
Negative: unable to breakdown hydrogen peroxide (eg Streptococcus, Enterococcus)

Question 8

Coagulase test

Answer 8

Used to test G+ catalase+ cocci in clusters to identify S aureus

Slide: clumping observed if organism expresses clumping factor and/or protein A (S aureus = pos, s lugdanensus, s pseudointermedius = neg)
Tube: clot forms if organism expresses free coagulase (S aureus, S pseudointermedius = pos, S lugdanensis = neg)

Question 9

S aureus virulence factors

Answer 9

Coagulase (leads to formation of fibrin coagulase, producing localized infection and protects organism from phagocytosis)
Protein A (inhibits opsonization and phagocytosis, anti-complement)
Enterotoxins (emetic)
Toxic shock toxin (super antigen leading to toxic shock syndrome)
Exfoliative toxin (disrupts cell adherence in the stratum granulosum layer of epidermis - superficial; less common in older children and adults due to natural neutralizing antibodies after first infection - not a big deal)

Question 10

Coagulase negative staphylococci

Answer 10

Everyone has on their skin
Affinity for synthetic materials - infection risk with devices inserted through the skin
Produce slime, a polysaccharide that allows it to stick to synthetic objects, anti-phagocytic, inhibits chemotaxis

Question 11

S lugdunensis

Answer 11

Coagulase neg staphylococcus spp
Considered as virulent as S aureus
Produces clumping factor (slide coagulase)
PYR+, ornithine decarboxylase +

Question 12

S saprophyticus

Answer 12

Coagulase negative staphylococcus spp

UTI pathogen primarily associated with young, sexually active women

Question 13

S pseudintermedius

Answer 13

Animal staphylococcus pathogen increasingly being reported in human disease
Slide coagulase neg, tube coagulase pos
Frequently methicillin resistant
Until mass spec, frequently misidentified as MRSA

Question 14

Shared characteristics of Enterococcus species

Answer 14

Growth at high salt conc, high pH (most bacteria cant)
Growth between 10-45degC
Growth in 40% bile
Catalase negative
Esculin hydrolysis - Esculin positive
LAP positive
PYR positive
Intrinsically resistant to cephalosporins, vancomycin reseistance a growing concern

Question 15

Sub-categorization of beta lactams

Answer 15

Penicillins, caphalosporins, monobactam, carbapenems

Question 16

Common clinical isolates of enterococci

Answer 16

E faecalis (80-90%)
E faecium (5-10%)
Less common: E casseliflavus, E gallinarum

Question 17

Common characteristics of streptococci

Answer 17

Gram positive cocci in pairs chains or tetrads
Catalase negative
Most facultative, a few are anaerobic

Question 18

Haemolysis test

Answer 18

Test that distinguishes organisms based on their abikity to break down blood cells (via haemolysis)
Culture on blood agar plate, see how colour changes
Beta hemolytic: complete haemolysis, media turns see through yellow
Alpha hemolytic: partial hemolysis, media turns translucent green
Gamma hemolytic: no haemolysis, media remains red
Test useful for human tissue organims like staph and strep

Question 19

S pyogenes

Answer 19

Group A strep
Beta hemolytic
Intrinsically susceptible to beta lactams (same for all beta hemolytic strep)
Distinguished from all other strep by taxo A disk

Question 20

Taxo A disk

Answer 20

Disk impregnated with bacitracin placed on streptococcus cluture plate
S pyogenes (group a strep) is sensitive, zone of inhibition will appear. All other strep resistant, no zone forms
Used to distinguish group a strep from other streptococci

Question 21

PYR Test

Answer 21

Tests for presence of pyrrolidonyl arylamidase
Enterococcus and group a strep are positive (red colour), s bovis and other streptococci are negative (yellow colour)
Used to identify s pyogenes, to differentiate enterococci from group d beta hemolytic strep, distinguish e coli from other indole positive, lactose positive, gram negative rods, and differentiate some staph (positive haemolytics from negative auricularis)

Question 22

S agalacticae

Answer 22

Group b streptococci
CAMP test positive, weakly beta hemolytic
Associated with neonatal infections
Late pregnancy screening, treat prophylactically during delivery

Question 23

CAMP Test

Answer 23

Synergistic haemolysis observed between s aureus and group B strep
Positive test: arrow head hemolysis pattern
Used to differentiate group b from other strep

Question 24

Streptococcus anginosus group

Answer 24

Milleri group (historically)
S anginosus, s intermedius, s constellatus
Mostly group F, but also C G and A
Smells like caramel on culture
Pinpoint colonies with beta hemolysis
associated with deep seated abscesses (liver/brain)

Question 25

Streptococcus bovis group

Answer 25

S equinus, S gallolyticus, S infantarius, S alactolyticus
Group D antigen
Differentiate from Enterococci: PYR test neg = bovis, pos = entero
Growth in bile, hydrolyzes esculin