Antibiotic resistance profiles of oral flora in hippopotami (Hippopotamus amphibius) : implications for treatment of human bite wound infections

BACKGROUND : The common hippopotamus (Hippopotamus amphibius) is found in aquatic environments throughout sub-Saharan Africa and is known to cause attacks on humans living or working close to water bodies. Victims surviving an attack often suffer from the consequences of severe wound infections caused by the animal’s sharp canine teeth. OBJECTIVE : Isolation of normal flora bacteria from the oral cavity of common hippopotami (Hippopotamus amphibious) followed by antibiotic susceptibility testing to aid in the identification of a targeted antibiotic treatment regimen for hippopotamus attack victims. METHODS : Oral swabs were collected from 34 free-ranging hippopotami in three reserves within the Greater Kruger National Park Complex in South Africa and cultured for aerobic and anaerobic bacteria. Antibiotic susceptibility testing was conducted using the disc diffusion method (Kirby-Bauer method) and a panel of 16 antibiotic drugs representing 10 antibiotic categories. RESULTS : Culturing of 50 oral swab samples from 34 hippopotami yielded 188 aerobic isolates belonging to 30 bacterial genera and 41 bacterial species (Gram-negative: 70.7%; Gram-positive: 29.3%) and 16 obligate anaerobic isolates from two genera. Three bacterial species, namely Aeromonas hydrophila, Aeromonas sobria and Shewanella putrefaciens accounted for 52% of the aerobic isolates. The anaerobic isolates were identified as Prevotella melaninogenica and Clostridium spp. Antimicrobial susceptibility testing was performed for 112 aerobic isolates (Gram-negative: 93 (83%); Gram-positive: 19 (17%)) representing all isolated bacterial species. High levels of antibiotic resistance were observed among the Gram-negative species especially to most beta-lactam antibiotics (50.5% to 80.7%). Multidrug resistance was detected in 22.6% of Gram-negative isolates and in 24.1% of all isolates. CONCLUSIONS : This study provides the first investigation of the oral flora bacteria of the common hippopotamus. Among the 32 mostly aerobic bacterial genera the most abundant bacterial species were A. hydrophila, A. sobria and S. putrefaciens. They are typical inhabitants of the aquatic habitat of the hippopotamus and of zoonotic importance as opportunistic human pathogens. The antibiotic susceptibility profiles demonstrated that quinolones, aminoglycosides, and tetracyclines were highly efficacious against these bacterial species which otherwise showed moderate to high levels of resistance to the traditional bite wound treatment with amoxicillin/clavulanate and 1st and 2nd generation cephalosporins.