Superbugs Lurk in Shared Waters of Kenya’s Maasai Mara, Yearlong Study Finds

In the water-scarce rangelands surrounding Kenya’s famed Maasai Mara National Reserve, the same rivers and open water pans that quench the thirst of people, cattle, and wildlife are also harboring an invisible and growing menace: bacteria that shrug off nearly every antibiotic thrown at them. A new yearlong study, published in PLOS Global Public Health, has documented widespread antimicrobial resistance (AMR) in the surface waters of Narok West subcounty, finding that every single Escherichia coli isolate recovered from shared waterpoints was resistant to at least one antibiotic, and that roughly three-quarters carried resistance to three or more drug classes. The findings offer one of the most detailed pictures yet of how resistance circulates in a landscape where humans, livestock, and wild animals drink from the same sources.

The research team, led by Brian Marvis Waswala-Olewe of Maasai Mara University together with collaborators at the University of Nairobi, Washington State University, and the World Health Organization, collected water samples from 28 randomly selected waterpoints—eight river sites and twenty open water pans—between April 2024 and May 2025. Sampling occurred once every three months, allowing the investigators to track resistance across both wet and dry seasons in a landscape where rainfall swings between roughly 500 and 1,800 millimeters per year. Water was drawn aseptically from 10 to 15 centimeters below the surface, taking care not to disturb sediments where microbes settle, and transported to the laboratory for analysis within 24 hours.

In the laboratory, the team filtered samples through 0.45-micrometer membranes and cultured bacteria on chromogenic coliform agar, confirming presumptive E. coli colonies through subculture on MacConkey agar. E. coli, a gram-negative bacterium that the World Health Organization treats as the key indicator of fecal contamination in water, turned up in 92.9 percent of the sampled sites—26 of 28 waterpoints. Over the study period the researchers accumulated 70 isolates, which they then subjected to Kirby-Bauer disc diffusion susceptibility testing against eight antibiotics, following Clinical and Laboratory Standards Institute protocols. The panel included penicillin, amoxicillin, ceftazidime, gentamicin, levofloxacin, nitrofurantoin, tetracycline, and kanamycin—drugs that Kenya’s Ministry of Health and the WHO rank from important to critically important, and that the World Organisation for Animal Health classifies as veterinary critically important agents.

The resistance patterns were stark. Every isolate was resistant to penicillin, 92.6 percent resisted amoxicillin, 78.6 percent resisted nitrofurantoin, and just over half—52.9 percent—resisted ceftazidime, a third-generation cephalosporin classified by WHO as a highest-priority critically important antibiotic. At the other end of the spectrum, the bacteria remained largely vulnerable to gentamicin and levofloxacin, each showing susceptibility rates near 98.6 percent, with kanamycin close behind at 91.4 percent. When the team grouped results by antibiotic class, beta-lactams topped the list at 33.8 percent resistance, followed by nitrofurans at 31.2 percent, tetracyclines at 24.7 percent, aminoglycosides at 9.1 percent, and fluoroquinolones at just 1.3 percent.

Perhaps most alarming was the prevalence of multidrug resistance, defined as resistance to three or more antibiotic categories. Across the five classes tested—aminoglycosides, fluoroquinolones, nitrofurans, tetracyclines, and beta-lactams—73.1 percent of all E. coli isolates qualified as MDR, and 80.8 percent of sampled sites harbored at least one such isolate. One site yielded an isolate resistant to all five classes, and the mean MDR score per site hovered around three antibiotic classes. Open water pans actually fared slightly worse than rivers in this respect, with MDR rates of 77.8 percent versus 62.5 percent, although the difference between the two source types was not statistically significant. Notably, 60 percent of the isolates—42 of 70—showed a resistance pattern suggestive of extended-spectrum beta-lactamase (ESBL) production, enzymes that hydrolyze third-generation cephalosporins and render beta-lactam therapy ineffective.

Seasonality mattered. Resistance peaked during the short-wet and short-dry seasons, at 51.3 percent and 51.5 percent respectively, and the seasonal variation was statistically significant (p = 0.04). Rivers carried a higher burden of resistant isolates than open water pans—51.4 percent versus 40.4 percent—a difference that also reached statistical significance. The researchers suggest that seasonal flooding may flush contamination from upstream wastewater treatment facilities and human settlements into rivers and pans, while drying pans concentrate both animals and pollutants in shrinking pools. In a landscape increasingly stressed by climate variability, these hydrological pulses may act as conduits for the transport of resistance genes to downstream communities.

To probe the geography of resistance, the team employed spatial scan statistics using SaTScan software, running a purely spatial multinomial model in which a circular scanning window moved across geocoded sampling sites, comparing observed versus expected resistance profiles with Monte Carlo significance testing. Two exploratory clusters emerged, though neither reached statistical significance. Cluster 1, adjacent to areas of dense human settlement, showed a relative risk of resistance of 0.78—meaning isolates there were slightly less likely to be resistant than elsewhere. Cluster 2, dominated by sites along the Maasai Mara National Reserve where dense human populations are wedged between protected wildlife conservancies, showed an elevated relative risk of 1.26. The authors caution that these clusters are hypothesis-generating rather than confirmatory, but the pattern hints that anthropogenic activity—poor sanitation, livestock transhumance, and antimicrobial misuse in pastoral herds—shapes the distribution of resistant bacteria across the ecosystem.

The study also quantified who is most exposed. Using cost-distance analysis built on Dijkstra’s algorithm, WorldPop population grids at roughly 100-meter resolution, and the Malaria Atlas Project’s walking-only friction surface, the researchers modeled travel time from every pixel in the landscape to the nearest waterpoint where resistant isolates had been detected. The result: at least one-third of the Maasai Mara Ecosystem population is at elevated risk of encountering AMR E. coli through surface water, simply because piped water is scarce. Nationally, about 60 percent of Kenyans lack access to potable water, and in Narok County fewer than 10 percent have piped connections, making shared rivers and pans the primary water source for most residents—and for the livestock and wildlife that converge on them daily.

The implications ripple outward through the One Health framework that now underpins global AMR strategy. Resistant bacteria and antibiotic residues in shared waters can exert selection pressure on natural microbial communities, kill susceptible strains, and propagate resistance genes through aquatic ecosystems, with documented harms ranging from genotoxicity and developmental disruption in fish to altered plankton dynamics and impaired photosynthesis. Because the Mara-Serengeti landscape is a major international tourist destination, the authors also flag the risk of travel-related transmission of resistant enteric bacteria, alongside the threat posed by using contaminated river water for horticultural irrigation of raw produce. The team calls for urgent expansion of water, sanitation, and hygiene infrastructure, stricter antibiotic stewardship in both human and veterinary medicine, seasonal surveillance of AMR in surface waters with microbial source tracking, and genomic characterization of resistant strains—reporting through WHO’s GLASS and WOAH’s ANIMUSE systems. In a water-stressed ecosystem where people, cattle, and wildlife share every drop, the study makes clear that protecting the Mara’s waters means protecting the global commons of antibiotic effectiveness itself.

Subject of Research: Antimicrobial resistance in shared human-animal surface water sources in the Maasai Mara Ecosystem, Kenya

Article Title: Spatiotemporal patterns of antimicrobial resistance in shared human-animal waterpoints in the Maasai Mara Ecosystem, Kenya

Article References: Waswala-Olewe, B. M., Omondi, G. P., Olewe, M. A., Njuguna, B., Nyararai, Y., Mutono, N., Thumbi, M., Webala, P. W., & Abila, R. (2026). Spatiotemporal patterns of antimicrobial resistance in shared human-animal waterpoints in the Maasai Mara Ecosystem, Kenya. PLOS Global Public Health, 6(10), e0007393. https://doi.org/10.1371/journal.pgph.0007393

Image Credits: AI Generated

DOI: 10.1371/journal.pgph.0007393

Keywords: antimicrobial resistance, Escherichia coli, Maasai Mara, water quality, One Health, multidrug resistance, surface water, Kenya, ESBL, spatial analysis, public health, water scarcity