Staphylococcus and Micrococcus

clusters

Staphylococcus gram stain cocci appearance

tetrads

Micrococcus gram stain cocci appearance

SBA

tryptic soy agar base enriched with sheep blood

-not selective

-can be differential (hemolysis)

CHOC

-lysed sheep blood containing hematin (factor X) and nicotinamide adenine dinucleotide (NAD, factor V)

CNA Columbia agar (CNA)

-selective, enrichment agar

-sheep blood (enrichment)

-colistin and nalidixic acid (inhibit Gram neg bacilli)

Phenylethyl alcohol (PEA)

-selective, enrichment agar

-sheep blood (enrichment)

-phenylethyl alcohol (inhibits Gram neg bacilli and Proteus swarming)

MSA

-selective and differential

-high salt concentration (7.5%) (inhibit most gram pos and neg)

-mannitol (fermentation)

-phenol red (indicator)

-yellow = mannitol fermentation (lowers pH)

S. aureus, some S. saprophyticus

organisms that ferment mannitol

-yellow MSA

PMNs

cell type seen on direct smear

catalase

-identification test: staph/micro vs strep

-hydrogen peroxide → water + O2

-bubbles = pos → staph/micro

-no bubbles = neg → strep

slide coagulase

cell bound coagulase (clumping factor) allows bacteria clumping

bound

slide coagulase tests for free/bound coagulase

free

tube coagulase tests for free/bound coagulase

tube

detects free coagulase 

-causes protective fibrin clot to form around bacteria

Staphaurex

detects both clumping factor and protein A in S. aureus cell wall

-plasma coated latex particles with fibrinogen (reacts with clumping factor) and IgG (protein A)

pos

pos/neg agglutination test for Staph aureus

neg

pos/neg agglutination test for Staph epidermidis

Novobiocin

test for coagulase neg Staph

-S. sapro: R

-S. epi: S

R

Staph saprophyticus is Novobiocin R/S

S

Staph epidermidis is Novobiocin R/S

Bacitracin

-antibiotic disc test

-differentiates Micrococcus from Staph spp.

-Staph spp.: R

-Micrococcus: S

R

Staph spp. are Bacitracin R/S

S

Micrococcus are Bacitracin R/S

Furazolidone

-antibiotic disc

-differentiates Micrococcus from Staph

-Micrococcus: R

-Staph spp.: S

R

Micrococcus are furazolidone R/S

S

Staph spp. are furazolidone R/S

oxidase

-1% dimethyl-p-phenylene-diamine-dihydrochloride/tetramethyl-p-phenylene-diamine-dihydrochloride

-purple = pos → Micrococcus

-none = neg → Staph spp.

pos

Micrococcus are oxidase pos/neg

neg

Staph spp. are oxidase pos/neg

PYR

-detects L-pyrrolidonyl arylamidase

-pyrrolidonyl-a-naphthylamide hydrolysis

-S. lugdenensis: pos

-other staphs: neg

pos

Staph lugdenensis is PYR pos/neg

ODC

-ornithine decarboxylase detection

-carboxyl group removal from aa → amine or diamine and CO2

-purple = pos → Staph

-neg = yellow

coagulase

test that differentiates Staph aureus (+) from others (=)

PYR, ODC

test that differentiates Staph lugdenensis (+) from others (=)

Novobiocin

test that differentiates Staph saprophyticus (R) from others (S)

epidermidis, saprophyticus, lugdenensis

coagulase neg staphylococcus

Staph epidermidis

-normal skin flora

-infects: shunts, catheters, IV caths, prosthetic joints

Staph saprophyticus

-UTIs

-infects: young women of childbearing age

-Novobiocin R

Staph lugdenensis

-normal skin flora

-infects: sim to aureus

-slide pos, tube neg, staphaurex neg

-PYR and ODC pos

Rothia mucilaginosa

-oral and resp flora

-immunocomp inf: bacteremia, endocarditis, peritonitis

-large GPC

-sticky colonies

-weak catalase pos

HA-MRSA, CA-MRSA

primary staph aureus pathogens

hemolysins

-staph aureus virulence facators

-alpha: PLTs/WBCs/tissue

-beta: RBC memb (sphingomyelin)

-gamma: leukocidin (PMN exotoxin)

-delta: less toxic

alpha

hemolysin targets PLTs, WBCs, tissue

beta

hemolysin targets RBC sphingomyelin (cell memb)

-promotes colonization on skin

gamma

hemolysin targets PMNs by exotoxin: leukocidin

delta

less toxic hemolysin

enterotoxin A/D

-staph aureus virulence factor

-food poisoning

enterotoxin F

-staph aureus virulence factor

-TSST-1 (menstruating assoc toxic shock syndrome

enterotoxin B

-staph aureus virulence factor

-pseudomembranous enterocolitis (GI issues)

exfoliative toxin

-staph aureus virulence factor

-epidermolytic toxin

-epidermal skin layer slough off

-SSS/Ritter’s disease

-bullous impetigo, folliculitis, furuncles (boils)

protein A

-staph aureus virulence factor

-binds Fc portion of IgG to block phago

-tested in staphaurex (IgG agglut)

hyaluronidase

-staph aureus enzyme virulence factor

-targets connective tissue

lipase

-staph aureus enzyme virulence factor

-allows skin colonization

-lyses fats and oil sec by sebaceous glands

staphylokinase

-staph aureus enzyme virulence factor

-activates plasminogen to break fibrin mesh network made in immune response to localize infection

nosocomial infections

-hospital acquired

-inf caused by: S. aureus, coag neg staph (S. epidermidis)

-UTIs

-prosthetic valve endocarditis

oxacillin/cefoxitin screen, PCR

tests done on MRSA and MRSE

S

MSSA, MSSE are oxacillin R/S

R

MRSA is oxacillin R/S

high

MRSA OXA MIC is low/high

low

MSSA, MSSE OXA MIC is low/high

cefoxitin

indicator drug for MRSA

S

MSSA, MSSE are cefoxitin R/S

R

MRSA is cefoxitin R/S

low 

MSSA, MSSE FOX MIC is low/high

high

MRSA FOX MIC is low/high

neg

MSSA, MSSE are neg/pos for mecA PCR

pos

MRSA is neg/pos for mecA PCR

S

MSSA, MSSE are S/R to amoxicillin and clavulanic acid

R

MRSA is S/R to amoxicillin and clavulonic acid

neg

MSSA, MSSE are pos/neg in PBP2A

pos

MRSA is pos/neg PBP2A

macrolide

resistance to these antibiotics by erm gene mutation

erm

gene that confers macrolide resistance

-erythromycin induces resistance to clindamycin

-D zone: pos

msrA

gene for neg D-zone test

-erythromycin R, clindamycin S

-no erythromycin induced resistance to clindamycin