1. Minor Enterobacteriaceae Pathogens
Yersinia enterocolitica and Yersinia pseudotuberculosis
@ Y. enterocolitica & Y. pseudotuberculosis
are gram-negative rods. Transmitted to
humans by contamination of food with
excreta of domestic animals, e.g. dogs,
cats, and cattle.
@ Y. enterocolitica causes enterocolitis
that is not distinguished clinically from
that caused by Salmo­nella or Shigella.

3. @ Y. enterocolitica & Y. pseudotuberculosis
cause mesenteric adenitis that resemble
acute appendicitis.
@ These organisms are involved in
bacteremia or liver abscess & spleen, in
persons with underlying diseases.
@ Y. enterocolitica is isolated from stool
and forms a lactose-negative colonies on
Mac Conkey agar.
@ It grows better at 25°C. Biochemical tests
are positive at 25°C & negative at 37°C

5. @ Incubation of stool at 4°C for 1 week
(cold enrichment) increases frequency of
recovery of the organism.
@ Y. enterocolitica & Y. pseudotuberculosis
are distinguished by biochemical tests.
@ Cultures are rarely made to diagnose
Y. pseudotuberculosis. Serology not done
@ Enterocolitis and mesenteric adenitis do
not require treatment.
@ For bacteremia or abscess, give co-
trimoxazole or ciprofloxacin.

7. Citrobacter
@ Citrobacter species are gram-negative,
motile rods, and related to Salmonella &
Arizona.
@ They occur in the environment and in
the human colon
@ They are opportunistic, and can cause
sepsis in immunocompromised patients
@ C. freundii is the most species isolated.

9. @ May be isolated from urine, blood and
pus specimens.
@ Because Citrobacter species can be late
or non-lactose fermenters, they require
differentiation from salmonellae.
@ Many strains of C. freundii ferment
sucrose whereas Salmonella species are
non-sucrose fermenters.

11. Arizona @ Arizona species are gram-negative rods,
ferment lactose slowly.
@ Arizona hinshawii is found in the feces
of chickens and other domestic animals
@ In Man it causes diseases similar to
those caused by Salmonella, such as
enterocolitis and enteric fevers.
@ The organism is usually transmitted by
contaminated food, eg, dried eggs.

13. Edwardsiella
@ Edwardsiella species are gram-negative
rods, resembling Salmonella.
@ Edwardsiella tarda causes enterocolitis,
sepsis, and wound infections.
Erwinia
@ Erwinia species are gram-negative rods,
found in soil and water.
@ Erwinia herbicola rarely involved in
human disease.

15. Hafnia
@ Hafnia species are gram-negative rods,
found in soil and water
@ Hafnia alvei is an opportunistic bacteria,
& may be cultured on Mac Conkey agar
Pectobacterium
@ Pectobacterium is gram negative rods.
@ Plant pathogens of potato and carrot.
@ They are opportunistic and may cause
human infections.