Culture results from tissues or swabs from northern or southern sea otters submitted to the Veterinary Medical Teaching Hospital at the University of California, Davis from 1997 to 2005 were reviewed for the isolation of anaerobes. One or more obligate anaerobic bacterial species were isolated from 19 of 68 animals (28%). Samples from three animals could not be evaluated for anaerobes due to overgrowth by swarming Proteus sp. Lesions or tissues yielding anaerobes, in descending order of frequency, included abscesses, abdominal fluid, lymph nodes, wounds, blood, and masses. Bacterial genera identified were Fusobacterium, Clostridium, Peptostreptococcus, Bacteroides, and Prevotella. Multiple anaerobic species were isolated from a single site from six samples; seven animals had more than one site where anaerobes were identified.
Anaerobic bacteria can be found as part of the normal flora of the mucous membranes and gastrointestinal tract of domestic mammals. Additionally, they are common in the environment. Entry of these organisms into sterile sites such as the pleural or peritoneal fluid, lung, or other internal organs requires a breach in host defenses such as ulceration, wound, or immunosuppression. Anaerobic organisms found in sterile sites can be acquired from endogenous (from the host) or exogenous (environmental) sources. Survival and growth of anaerobes requires an environment with reduced oxygen tension and/or no oxygen. Thus, conditions that favor their growth include loss of blood supply e.g., through trauma or other vascular compromise and in abscesses. The majority of sites where anaerobes were isolated in these cases also contained aerobic or facultative anaerobic bacteria. The presence of bacteria living aerobically can decrease tissue oxygen tension favoring anaerobic bacterial survival and multiplication.
Interpretation of Anaerobe Isolation
The bacterial genera isolated from sea otters are similar to those seen in domestic mammals. Similarly, the sites where anaerobic bacteria were isolated are also common in domestic animals with the exception of the lymph node. These findings suggest that anaerobic infections occur by comparable mechanisms in sea otters. One caveat of these findings is that some of these animals had been dead for a prolonged period of time; anaerobic organisms could have translocated from the gastrointestinal tract to other sites following death. This may account for the frequent isolation from peritoneal fluid and lymph nodes. Conversely, anaerobes were not always found in these tissues suggesting that isolation can reflect actual infection, at least in some cases. It is important to examine tissues pathologically for inflammation and tissue damage in order to interpret the significance of an anaerobic isolate. The failure to isolate anaerobes in some cases could reflect death of the organism during transportation to the laboratory as some anaerobes are sensitive to oxygen.
Sampling of tissues for anaerobic culture is worthwhile in live sea otters and those who have been dead for a short period of time. Sites or conditions to consider for sampling include abscesses, wounds, pleuritis, and peritonitis. Interpretation of a positive should be coupled with pathologic or clinicopathologic examination. Knowledge of the conditions or sites where anaerobic infections are likely can help to guide empirical antimicrobial therapy during rehabilitation.