Antibiotic resistance threatens the effective prevention and treatment of disease in both humans and animals. When microbes are exposed to an antibiotic, those that are susceptible to that antibiotic die out. Those that are resistant to it survive, thrive, reproduce, pass on their resistance genes on to their descendants and become more common. If those surviving bacteria cause disease, then it’s bad news for health, because that antibiotic won’t be as effective for treating that disease anymore. But it turns out that even “bystander” bacteria may play a role in antibiotic resistance.
Both antibiotics and antibiotic resistance are completely natural. Microbes produce antibiotics as defensive and offensive weapons to help them compete for space and resources in their environment. In fact, most modern antibiotics were derived from drugs that were originally isolated from different species of soil bacteria. So, it’s not surprising that antibiotic resistance is also found in the environment – microbes naturally evolve resistance to defend themselves against the antibiotics that other microbes produce. Researchers find antibiotic resistant bacteria in glaciers and other locations that have never seen modern humans or modern antibiotics.
In a recent study, researchers collected water samples from a new dugout and new water bowls in eight empty pens at a new beef cattle feedlot in Western Canada. Nineteen different groups of bacteria from those water samples were tested for resistance to the different antibiotics used in the feedlot. More water samples were collected and tested weekly over eight weeks, as feeder cattle filled the pens.
On arrival, calves deemed to be at a higher risk for bovine respiratory disease (BRD) were given Draxxin, lower risk calves were given oxytetracycline, and the feed contained Tylan to control liver abscesses. Cattle that developed clinical signs of BRD were treated with Excede, Florkem or Forcyl according to the health protocol the feedlot and their veterinary consultant had developed. Antibiotic resistance genes from bacteria in the water samples were compared to antibiotic resistance genes in BRD bacteria collected in earlier studies.
Bacteria resistant to Florkem and Draxxin were found in the dugout and some of the water bowls, even before cattle began to enter the feedlot. The environment was a natural reservoir for these antibiotic resistant bacteria, albeit at low levels.
Resistance to each antibiotic was found in some water bowl samples as early as the first week cattle began arriving. Water bowls in all pens contained bacteria resistant to each antibiotic by the end of the eighth week, likely from contact with the cattle treated with antibiotics on arrival.
Even though water bowls and the bovine respiratory tract are very different environments, there was considerable overlap between the antibiotic resistance genes (and multidrug resistance patterns) found in water bowls and BRD bacteria.
Bottom line: BRD can spread among cattle when they congregate at the water bowl. But water bowls might also be a spot where antibiotic resistance spreads among bacteria and adjacent pens, and might present an opportunity to help manage antibiotic resistance.