Yersinia spp

• Y. enterolitica
• Y. fredericksonii
• Y. intermedia
• Y. pestis
• Y. pseudotuberculosis

Gram Stain

• Gram negative bacilli - fermenter

Clinical Significance

Yersinia spp are found in water environments (lakes/reservoirs) and as commensal organisms in warm blooded animals.

Y. enterolitica – associated with terminal ileitis/lymphadenitis (may be difficult to differentiate from acute appendicitis) and acute enterocolitis, sometimes in outbreak settings. It is typically acquired by ingestion of contaminated food/water but can also be transmitted person to person especially in daycare settings.

Y. fredericksonii - associated with enterocolitis but generally considered to be non-pathogenic.

Y. intermedia - rarely associated with enterocolitis but generally considered to be non-pathogenic.

Y. pestis - causative agent of plague with transmission to humans by fleas. Two epidemic forms exist including urban plague (maintained in rat populations) and sylvatic plague (maintained in prairie dogs, mice, rabbits, and rats).

Y. pseudotuberculosis – associated with mesenteric adenitis which clinically manifests as acute appendicitis. It has also been associated with septicemia especially in debilitated/immunocompromised patients. 
 

Usual Susceptibility Pattern

Y. enterolitica produces an inducible chromosomal beta-lactamase as well as a broad spectrum penicillinase conferring resistance to ampicillin, amoxicillin/clavulanate, and 1st/2nd generation cephalosporins.

Y. pseudotuberculosis tends to be more susceptible to beta-lactam agents. 

Yersinia species are typically susceptible to quinolones, tetracyclines, TMP/SMX, and 3rd generation cephalosporins.

Ceftriaxone is preferred over cefotaxime as it achieves higher intraluminal concentrations.