The common hippopotamus occurs in rivers, lakes and wetlands in sub-Saharan Africa and is known for its aggressive behaviour when defending its territory and its young. Massive and surprisingly agile on land, hippopotami lead an amphibious lifestyle. They are often misrepresented as comical river dwellers. Yet, its reputation among local communities tells a darker, more sobering tale.

Until recently, little was known about the bacteria that live in the mouths of these formidable creatures. But a groundbreaking, novel study led by Prof Anita Michel, research professor at the Faculty of Veterinary Science of the University of Pretoria (UP), with a research focus on bacterial zoonotic diseases transmitted at the wildlife-livestock-human interface, has illuminated a new layer of risk. “We knew the injuries were extraordinary especially with the exceptional biting force hippos possess,” she explains, “but we didn’t fully understand the link between the microbes and the severe complications from wound infections the clinicians had to deal with.”

Prof Michel and her team which included Dr Annelize Jonker, a veterinary specialist bacteriologist from the faculty and Mr Francois Roux, an ecologist from the Mpumalanga Tourism and Parks Agency (MTPA), examined the oral bacteria of 34 healthy hippopotami captured during routine wildlife operations in the Mpumalanga province. What they discovered was a complex bacterial community: 41 different species, many of them typically found in aquatic environments and capable of causing opportunistic infections in humans.

“This was the first time anyone systematically studied the bacterial flora of hippos’ mouths,” says Prof Michel. “And what we found was concerning—not just the types of bacteria, but their resistance to some of the most commonly used antibiotics.”

An antibiogram to determine the antibiotic resistance

The team tested the bacteria against a panel of antibiotic drugs and found moderate to high resistance to commonly prescribed treatments like amoxicillin/clavulanate and early-generation cephalosporins. These are staples in emergency medicine, especially for bite wounds from dogs and cats. But as Prof Michel points out, “Using these standard antibiotics for a hippo bite may delay effective treatment and allow infections to take hold.”

Hippo teeth can cause serious bite wounds

Conversely, the study revealed that antibiotics from the tetracycline, aminoglycoside, and quinolone families were more effective, offering a potential lifeline in future cases. Yet, even with these options, time remains a critical factor. The researchers strongly recommend that wound cultures be taken as early as possible to identify the exact pathogens involved to ensure the best outcome for the patient admitted to a hospital. “It is critically important that wound infections, whether in animals or humans, are treated early on with an effective antibiotic regimen aligned with the expected causative infectious agents,” Prof Michel says.

The implications of this study extend beyond individual injuries. It offers a stark reminder that antibiotic resistance is not just a clinical or hospital issue—it is a wildlife issue too, shaped by ecosystems, species interactions, and the limits of human preparedness.

“Our goal,” says Prof Michel, “is to work in a One Health approach with healthcare providers in regions where humans and wildlife intersect to ensure that they are not caught off guard. When you’re dealing with a hippo bite, minutes matter—and so does the right antibiotic.” 

Click here for the published article in One Health Outlook