Micro quiz entero and strep

Strep characteristics

Catalase negative, GPC in pairs or chains, aerotolerant, capnophiles

Where is strep usually found

mucous membranes

beta hemolysis

total hemolysis due to activity of streptolysin S and O

Lancefield classification

Used for beta hemolytic strep, based on C carbohydrates on cell wall

Strep pyogenes group and infections

Group A, pharyngitis, pyodermal, TSS like syndrome, necrotizing fasciitis

Not normal flora

Strep pyogenes virulence factors

Hyaluronidase (pyogenes), M protein, streptolysin O and S, pyrogenic exotoxin

M protein

Protein extends through cell wall to surface, resists phagocytosis

mmmm no thanks

Streptococcal pyrogenic exotoxin

Strep pyogenes, super antigen that causes scarlet fever

(pyro —> red —> scarlet)

What is the most common cause of bacterial pharyngitis

Strep pyogenes (GA)

Acute glomerular nephritis

Post streptococcal sequelae often after pharyngitis or skin infection

more common in children

Rheumatic fever

Post streptococcal sequelae most often after pharyngitis

Most serious complication is damage to heart valves

(rheumatic —> pneumatic valves)

Impetigo

Top layer of skin, localized, small vesicles that become large lesions

Cellulitis

Strep pyogenes getting deeper into tissue through skin

Streptococcal toxic shock syndrome

Entire organ systems collapse, leading to death

Pyrogenic exotoxin produced

Strep pyogenes rare neurological sequelae

Syndenhams chorea, PANDAS

Strep agalactiae

Small beta hemolytic zone, Group B, capsule, CAMP positive

Normal flora in genital tract

Group B screening protocol

Perform on pregnant women 35-37 weeks gestation

Culture vaginal/rectal sites for BHS Group B

Group C and G strep

Beta hemolytic, normal flora, infection with immunocompromised

Strep pneumoniae

Alpha hemolysis, most virulent member of alpha strep, normal flora

No Lancefield group

Autolysin

Produced by strep pneumo

Cell wall enzyme that causes lysis of bacteria

Donut colony appearance, tested for with bile solubility

Pneumolysin

Produced by strep pneumo

Inhibits phagocytosis, allows biofilms to form

What is the number one cause of bacterial pneumonia

Strep pneumoniae

Otitis media and sinusitis

Caused by strep pneumo, treated empirically

Can’t accept specimen from nasopharynx as strep pneumo can be normal flora there

Viridans strep

Alpha, normal flora, fastidious (need CO2)

Strep anginosus

Subset of viridans strep

Includes S. anginosus, constellatus, and intermedius

Butterscotch strep

Anginosus is inbetween stars

Strep bovis

Subset of viridans strep

Includes S equinas, infantarius, and gallolyticus (babies and animals)

Group D on lancefield, can cause bacteremia and endocarditis

Strep mutans group

Subset of viridans group

Includes S mutans and sorbinas

Can cause dental caries

Strep mitis

Subset of viridans group

Includes S mitis, sanguis, and oralis (might sanguinis in my mouth)

Normal flora of oral cavity but can cause endocarditis

Strep viridans transmission

Person to person contact, droplet

Pharyngitis rapid testing

Swab tests, high specificity but lower sensitivity

Follow up pharyngitis serology testing

Acute and convalescent serum to detect antibodies

Group A pharyngitis treatment

Penicillin or amoxicillin for 10 days

Strep pyogenes ID

Large beta colonies, group A, PYR positive, Bacitracin sensitive

Strep agalactiae ID

Small beta colonies, group B, CAMP positive, sodium Hippurate pos (hippos camp in space)

Strep pneumo ID

Mucoid alpha colonies, may be donut shaped, lancet cocci, bile soluble and optochin sensitive (P sensitive —>pneumo)

Strep viridans ID

Alpha colonies, elongated GPC, optochin resistant, bile insoluble, bile esculin neg

Listeria

Looks like group B (agalac) but gram positive bacilli

Enterococci

Catalase negative (can be pseudocatalase), GPC in pairs or small clusters, grey colonies, usually gamma but can be alpha. Normal flora in GI tract

Often found in urine cultures

Enterococci virulence factors

Survive in wide range of conditions and temperature, intrinsic resistance to beta lactam antibiotics, adhesions (endocarditis) and Cytolysin in E faecalis

Enterococci epidemiology

Usually nosocomial

Enterococcus ID

Gamma or alpha, GPC, catalase negative, growth in 6.5% NaCl, PYR pos, bile esculin pos

Rapid test for Enterococci

LAP hydrolysis pos, ESC pos, PYR pos

MGP rapid test for Enterococci

E faecalis and E faecium are negative

Pyruvate test

E faecalis is pos, E faecium is neg

Callouses are positively good

VISA and VRSA mechanism

vanA gene from Enterococci with vancomycin resistance likely transferred via plasmid

VISA and VRSA testing

MIC >16mm is resistant

Not reliable for intermediate isolates

Vancomycin screen agar

Plates contain BHI agar and 6 ug of vancomycin

0.5 McFarland suspension is spotted, growth of more than one colony is pos

VRE

Common

Some hospitals screen patients with rectal swabs

Treat with synercid or linezolid

VRE mechanism

Enterococci can become resistant via plasmid, most commonly E faecium or E faecalis

E gallinarum and E casseliflavus have intrinsic resistance, so not considered a VRE

VRE genes

VanA is acquired, common, and found in E faecium

VanB is acquired, rare, and found in E faecium and E faecalis

VanC is intrinsic so not considered VRE

How to detect VRE

Vancomycin screen agar, need to speciate enterococcus

Clindamycin resistance

Cross resistance to macrolides, lincosamides, and streptogrammins (MLS)

erm gene

D test

Indicated when org is resistant to erythromycin and sensitive to clindamycin

Penicillin resistance in S pneumoniae

Mutation altering penicillin binding protein

Resistance to MLS due to erm and mefA genes can occur as well