Midterm 1 Flashcards
What is irregular about mycoplasma?
No cell wall
What is irregular about ureaplasma?
No cell wall
What is irregular about chlamydia?
Has cell wall but no peptidoglycan
Sub-classification of gram positive cocci based on microscope appearance
Pairs and chains: Enterococcus or streptococcus
Clusters: staphylococcus
Staphylococcus general properties
Facultative anaerobes
Catalase +
Common on skin and mucous membranes
Disease associated staphylococci
S aureus, S lugdunensis, S epidermidis, and S saprophyticus
S pseudintermedius is an animal pathogen increasingly seen in human infections
Catalase test
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)
Coagulase test
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)
S aureus virulence factors
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)
Coagulase negative staphylococci
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
S lugdunensis
Coagulase neg staphylococcus spp
Considered as virulent as S aureus
Produces clumping factor (slide coagulase)
PYR+, ornithine decarboxylase +
S saprophyticus
Coagulase negative staphylococcus spp
UTI pathogen primarily associated with young, sexually active women
S pseudintermedius
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
Shared characteristics of Enterococcus species
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
Sub-categorization of beta lactams
Penicillins, caphalosporins, monobactam, carbapenems
Common clinical isolates of enterococci
E faecalis (80-90%) E faecium (5-10%) Less common: E casseliflavus, E gallinarum
Common characteristics of streptococci
Gram positive cocci in pairs chains or tetrads
Catalase negative
Most facultative, a few are anaerobic
Haemolysis test
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
S pyogenes
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
Taxo A disk
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
PYR Test
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)
S agalacticae
Group b streptococci
CAMP test positive, weakly beta hemolytic
Associated with neonatal infections
Late pregnancy screening, treat prophylactically during delivery
CAMP Test
Synergistic haemolysis observed between s aureus and group B strep
Positive test: arrow head hemolysis pattern
Used to differentiate group b from other strep
Streptococcus anginosus group
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)
Streptococcus bovis group
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
