MOD11 Non Lactose Fermenters

Shigella on MAC

NLF

H2S neg

Shigella sonnei

LLF

ONPG pos

flat, spready colonies w jagged edges

Shigella spp

dysenteriae → A

flexneri → B

boydii → C

sonnei → D

Shigella key tests

non motile

glucose → anaerogenic (no gas)

lactose → neg (sonnei delayed pos)

TSI → K/A

orn → neg (sonnei pos)

Shigella vs E.coli lysine

Shigella neg E.coli pos

Shigella clinical significance

shigellosis aka bacillary dysentery

resistant to acidic environment of stomach

fecal-oral route of transmission

production of shigatoxin → dysenteriae

Salmonella on MAC

NLF

Salmonella on enteric media

produces H2S on XLD HEK SS

Salmonella key tests

glucose → aerogenic (gas)

lactose → NLF

TSI → K/A, G, H2S

lysine → pos → paratyphi A neg

orn → pos → typhi neg

PDA/TDA → neg

motile

citrate → pos → typhi neg

Salmonella non-typhi vs typhi

typhi: no gas, weak H2S, ORN-, CIT-

Salmonella antigens

O: heat stabile somatic

H: flagella

Vi: heat labile capsule

Salmonella serotyping OVi

agglutination = Salmonella spp

proceed to individual antisera

Salmonella clinical significance

enteric/typhoid fever

gastroenteritis

enteric/typhoid fever

caused by Salmonella typhi and S.paratyphi

ingestion of contaminated food/water or from typhoid carriers

8-14days post exposure → fever, headache, muscle pain, GI symptoms

2-3wks → fever, delirium, enlarged spleen, characteristic rose spots

gastroenteritis

often caused by Salmonella typhimurium

ingestion of contaminated foods → poultry, milk, eggs

nausea, vomiting, cramps, non-bloody diarrhea

self limiting

Citrobacter clinical significance

normal stool flora

UTI, septicemia, resp, wound, cutaneous infcs, endocarditis, meningitis, brain abscess

infc in neonates + immunocompromised pts

Citrobacter on media

MAC: LLF

enteric: LF w H2S

slow fermenting Citrobacter spp vs Salmonella spp

ONPG +

lysine -

arginine +