OVERVIEW: What every clinician needs to know

Pathogen name and classification

• Yersinia frederiksenii

• Yersinia intermedia

• Yersinia kristensenii

• Yersinia bercovieri

• Yersinia mollaretii

• Yersinia rohdei

All are Gram-negative coccobacilli, and are members of the family Enterobacteriaceae.

What is the best treatment?

• These species are generally associated with mild diarrhea, particularly in children. In such cases, the primary focus of therapy should be on appropriate rehydration.

• Because some strains are known to have an invasive phenotype, treatment with antibiotics is reasonable, particularly in more severely ill patients. Fluoroquinolones are the drugs of choice, based on in vitro antimicrobial resistance determinations. Trimethoprim-sulfamethoxazole and aminoglycosides may also have utility in therapy.

• Use of beta-lactam antibiotics is not recommended. Most strains/species show in vitro resistance to beta-lactam antibiotics (including third generation cephalosporins), and have been shown to carry beta-lactamases.

How do patients contract this infection, and how do I prevent spread to other patients?

• Epidemiology-

  • These species, many of which were initially categorized as "environmental" or "non-pathogenic" variants of Y. enterocolitica, before molecular genetic studies showed that they were separate species, are widely distributed in the environment, and in wild and domestic animals.

  • Isolation has been reported from a variety of foods, including raw meat (pork, in particular, but also chicken and beef), milk and fresh produce. Isolation rates from foods approach or surpass those reported for Y. enterocolitica.

  • Despite the fact that most of these isolates lack one or more of the "critical" virulence factors described for Y. enterocolitica, epidemiologic studies have shown a significant association between their isolation and occurrence of diarrheal disease, particularly in children.

  • Because these are newly-recognized species, and, in the past have been assumed to be non-pathogenic, incidence data are generally lacking. However, in reviewing older literature, it is possible that up to a third of reported Y. enterocolitica cases actually represent infection with one of these species.

  • Isolation has been reported globally, including several studies from South America, in addition to reports from Japan and Europe.

What are the clinical manifestations of infection with this organism?

• Patients infected with these species tend to present with diarrhea. Symptoms of mesenteric adenitis/pseudoappendicitis, prominent in the clinical presentation of other Yersinia species, do not appear to occur; as noted below, these species generally lack the genetic material for cell invasion found in Y. enterocolitica, Y. pseudotuberculosis, and Y pestis.

What common complications are associated with infection with this pathogen?

• The autoimmune complications linked with other Yersinia species do not appear to occur.

How should I identify the organism?

• Isolation from stool generally requires the use of specialized procedures. Recovery is facilitated by use of Cefsulodin-Irgasan-Novobiocin (CIN) selective agar; a cold enrichment step may also be helpful. When these (or any) Yersinia species are suspected in a patient with diarrhea, the microbiology laboratory should be notified so that appropriate isolation techniques can be used. Organisms will grow on blood and nutrient agar, and in standard blood culture media.

How does this organism cause disease?

• These strains/species do not carry the "standard" Yersinia virulence plasmid (pYV), which has been linked to cell invasion and resistance to phagocytosis. The chromosomal invertion gene is found in some species, but may be nonfunctional. Similarly, the attachment-invasion locus (AIL) is generally not found.

• Strains isolated from patients with diarrhea generally do produce enterotoxins, often within the heat-stable toxin family. Toxins may be novel, and unique to specific species.

WHAT’S THE EVIDENCE for specific management and treatment recommendations?