MICROBIOLOGY

Citrobacter, Edwardsiella, Arizonae

Palmos, Hanna C.BSMT

Citrobacter

• 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.

Clinically significant species:

Citrobacter freundii

Citrobacter koseri/diversus

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

Modes of transmission: Endogenous, person to person spread especially hospitalized patients

Habitat: Human gastrointestinal tract, soil, water

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.

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

C. freundii on gram stain

C. koseri ( C. diversus ) on CSF smear

Growth on MAC

Edwardsiellae

Clinically significant species

Edwardsiella tarda

Gram-negative, motileFacultative 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 reactionproduces hemolysin

Modes of transmission: Uncertain, probably by ingestion of contaminated water or close contact with carrier animal

Habitat: Gastrointestinal tract of cold-blooded animals such as reptiles

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

Specimen: Stool; urine; cerebrospinal fluid; intrauterine contents; pus; bile; peritoneal fluid; liver, tubo-ovarian, 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+

Edwardsiella tarda

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

View of E. tarda on Scanning electron microscopy

Arizonae

(Salmonella enterica serovar Arizona )

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.

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.

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

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

Growth on Blood Agar Plate

~END~