Brief notes on selected enterics.

1. MICROBIOLOGY
Citrobacter, Edwardsiella, Arizonae
Palmos, Hanna C.
BSMT

3. Citrobacter

4. • Biochemically and serologically similar to
Salmonella, is an uncommon cause of
opportunistic infection. Like many other
Enterobacteriaceae, Citrobacter strains may
be present in the normal intestinal flora and
can cause opportunistic infections. Despite
reports of association with diarrheal
disease, present evidence does not indicate
that Citrobacter should be considered an
enteric pathogen. C. freundii has been
associated with neonatal meningitis and brain
abscess.

5. Clinically significant
species:
Citrobacter freundii
Citrobacter koseri/diversus

6.  Slow lactose fermenter
 Hydrolyzes urea (slow)
 Colonies resemble E. coli on MAC, colonies of C. freundii at
MAC are pink at 18-24 hrs.
 Colonies of other Citrobacter species are usually colorless
on MAC after 24hrs of incubation, but are light pink after
48hrs.
 Colorless colonies on Hektoenteric Agar
 Methyl red test +
 All species grow on Simmon Citrate Agar ( Citrate test + )
 motile
 Facultative anaerobe

7. Modes of transmission:
Endogenous, person to person
spread especially hospitalized
patients
Habitat: Human gastrointestinal
tract, soil, water

8.  Pathology: Citrobacter freundii can be isolated in diarrheal stool
cultures, and although it is a known extraintestinal
pathogen, its pathogenic role in intestinal disease is not
established. Citrobacter freundii has been associated with
infectious disease acquired in hospital settings.
UTIs, pneumonias, and intra-abdominal abscesses have been
reported. In addition, C. freundii has been associated with
endocarditis in IV drug abusers.

Citrobacter koseri is a pathogen documented as the cause
of nursery outbreaks of neonatal meningitis and brain
abscesses.

Nosocomial infections of respiratory tract, urinary
tract, and several other normally sterile sites, most frequently
infect hospitalized and seriously debilitated patients.

9.  Virulence factor/s: Endotoxins, capsules, adhesion
proteins, resistance to multiple antimicrobial agents
 Specimen: Diarrheal stool, extraintestinal blood and
wound
 Lab Diagnosis/Special Procedures:
 Isolate and differentiate from E.coli and other
Enterobacteriaceae members by their ABILITY TO USE
CITRATE as their SOLE CARBON SOURCE.
 Lysine decarboxylase test –
 Non acetyl methyl carbinol producer
 C. freundii produces A/AGH₂S+ reaction in Kligler Iron
Agar

10. C. freundii on gram stain

11. C. koseri ( C. diversus ) on CSF smear

12. Growth on MAC

14. Edwardsiellae

15. Clinically significant
species
Edwardsiella tarda

16.  Gram-negative, motile
 Facultative anaerobic rods that have
peritrichous flagella and measure 1 µm in
diameter and 2–3 µm in length
 lactose negative
 H2S-positive
 Oxidase-negative
 Catalase-positive
 Has a positive indole reaction
 produces hemolysin

17. Modes of transmission:
Uncertain, probably by ingestion of
contaminated water or close contact with
carrier animal
Habitat: Gastrointestinal tract of coldblooded animals such as reptiles

18. Pathology: Edwardsiella tarda is an
opportunist that can cause diarrhea, wound
infection, septicaemia, meningitis, and
enteric fever.
Virulence factor/s: Type III & Type VI
secretion enzymes, quorum sensing, 2
component systems exoenzymes

19.  Specimen: Stool; urine; cerebrospinal fluid; intrauterine
contents; pus; bile; peritoneal fluid; liver, tuboovarian, and intra-abdominal abscess; and blood
 Lab Diagnosis/Special Procedures: Isolation and
culture of the bacteria from clinical specimens on eosin
methylene blur agar (EMB agar), followed by
biochemical tests.
 MAC- colorless and NLF, Hektoenteric Agar- Red
colonies, XLD- yellow/colorless colonies with or without
balck centers
 TSI K/A or K/A H₂S+
 LIA K/K H₂S+

20. Edwardsiella tarda
Mixture of 3 biotypes of E. tarda on MAC based ET
Agar

21. View of E. tarda on Scanning electron microscopy

22. Arizonae
(Salmonella enterica serovar
Arizona )

23.  Salmonella enteric subspecies
 Gram negative bacillus and a member of
Enterobacteriaceae
 Slow lactose fermenter
 Utilizes malonate, liquefy gelatine
 KCN is its inhibitor
 Uncommon human pathogen
 As many as Enterica subspecies, Arizonae strains
ferment lactose within 48hrs.They may be routinely
discarded as non-pathogens if grown from feces. The
presence of H2S is an important diagnostic clue for
routine screening.

24. Modes of transmission: Ingestion of
contaminated dairy and egg products
Habitat: For serotypes causing non-typhoidal
salmonellosis, the primary hosts are domestic
and wild animals such as
cattle, swine, poultry, wild birds, and pets
(particularly reptiles) as well as flies.

25. Pathology: S. Arizonae causes serious
infection in individuals with connective tissue
diseases, immunodeficiency in infants and
usual interstitial pneumonia.
Virulence factor/s: serovars
typhi, paratyphus A, B und C
Specimen: Blood, urine, stool, pericardial
fluid

26. Lab Diagnosis/Special Procedures: Isolation
from blood, urine and stool then
biochemical tests; Gel liquefaction, Brilliant
Green Agar ph at 6.9 +- 0.2, Blood Agar
Plate

27. Growth on Blood Agar Plate

28. ~END~