Genetics and pathology associated with Klebsiella pneumoniae and Klebsiella spp. isolates from North American Pacific coastal marine mammals.

Southern sea otters (SSO: Enhydra lutris nereis) are a federally-listed threatened subspecies found almost exclusively in California, USA. Despite their zoonotic potential and lack of host specificity, K. pneumoniae and Klebsiella spp. have largely unknown epizootiology in SSOs. Klebsiella pneumoniae is occasionally isolated at necropsy, but not from live SSOs. Hypermucoviscous (HMV) K. pneumoniae strains are confirmed pathogens of Pacific Basin pinnipeds, but have not been previously isolated from SSOs. We characterized the virulence profiles of K. pneumoniae isolates from necropsied SSOs, evaluated killing of marine mammal K. pneumoniae following in vitro exposure to California sea lion (CSL: Zalophanus californianus) whole blood and serum, and characterized lesion patterns associated with Klebsiella spp. infection in SSOs. Four of 15 SSO K. pneumoniae isolates were HMV and all were recovered from SSOs that stranded during 2005. Many K. pneumoniae infections were associated with moderate to severe pathology as a cause of death or sequela. All HMV infections were assessed as a primary cause of death or as a direct result of the primary cause of death. Klebsiella-infected SSOs exhibited bronchopneumonia, tracheobronchitis and/or pleuritis, enteritis, Profilicollis sp. acanthocephalan peritonitis, septic peritonitis, and septicemia. All SSO HMV isolates were capsular type K2, the serotype most associated with HMV infections in CSLs. Multiplex PCR revealed two distinct virulence gene profiles within HMV isolates and two within non-HMV isolates. In vitro experiments investigating CSL whole blood and serum killing of K. pneumoniae suggest that HMV isolates are more resistant to serum killing than non-HMV isolates.

Pathogenesis of Erysipelothrix piscisicarius infection in tiger barbs (Puntigrus tetrazona).

Erysipelothrix piscisicarius is an emerging bacterial pathogen and the aetiologic agent of piscine erysipelosis, a recently recognized disease of ornamental fish. However, little is known regarding the dynamics of infection in fish. The purpose of this study was to gain a better understanding of the pathogenesis of piscine erysipelosis in the tiger barb (Puntigrus tetrazona) by investigating tissue tropisms and responses to bacterial dissemination following immersion challenge with a virulent strain recovered from diseased fish. The challenge resulted in 83% mortality by day 16. Erysipelothrix piscisicarius DNA was first detected in the skin using quantitative PCR, and bacteria were visualized in association with microscopic lesions on day 4. By day 8, E. piscisicarius DNA was further detected in intestines, hearts, spleens, gills and skin; parenchymal organs were largely spared. The data suggest a primary cutaneous portal of entry and tropism for collagenous tissues, particularly those within vascular walls. Initial spread occurs directly from the dermis into interstitial areas of skeletal muscle, then centrally to the peritoneum and coelomic cavity following collagenous tissue pathways. Although histopathology revealed widespread bacterial dissemination over time, the severity of skin and muscle lesions with high levels of bacterial DNA identifies these tissues as primary targets of infection.