 could help mitigate its prevalence and reduce the nearly 250,000 cases of food-borne illness it causes in the U.S. alone annually. The colonization is hypothesized to occur from older cows, and the presence of this bacteria is linked with a lower diversity of gut microflora in young calves; however, their diversity then increases as they age.
“We think that the younger calves tend to have a higher burden of these disease-causing pathogens compared to older cows simply because their immune systems and GI-tract microbiota are immature,” Jeong says. “We hypothesize that as the calves age and their immune systems mature, it learns to kick out the harmful bacteria, leading to a healthier microflora composition.”
KC Jeong, far right, and his laboratory research team: (from left to right) visiting scholar Haitao Yu, PhD student Peixin Fan, post-doctoral researcher Zhengxin Ma, and PhD students Lin Teng, Shinyoung Lee and Ting Lui.
Similar to the E. coli study, Jeong’s lab discovered that beef calves become colonized with cephalosporin-resistant bacteria in their GI tract even when they are raised without the use of antibiotics. Conventional dogma dictates that overuse of antibiotics in agricultural and large-animal veterinary contexts has driven the rapid increase in antibiotic resistant bacteria in farm animals through selective pressures. But Jeong’s research into animals free of antibiotic exposure acquiring resistant bacteria points to an important alternative pathway: they also get it from the environment.
Building on this study, his lab next sampled soil and agricultural water sources on the affected farms and found cefotaxime-resistant bacteria to be highly prevalent. By analyzing fecal samples from cattle, and environmental samples from 17 different farms, and combining the findings with a survey of husbandry practices, his team uncovered some fascinating trends. They found that 98.7 percent of the soil samples contained the resistant bacteria, as did 95.7 percent of the forage, and 88.6 percent of the water samples. Cefotaxime-resistant bacteria (CRB) in the cows’ feces ranged from a prevalence per farm of 21 to 87.5 percent.
Due to the wide range in occurrence of CRB from farm to farm, Jeong suspects that husbandry methods were influencing the presence of CRBs in these cattle. Further analysis revealed that when cows’ water troughs were cleaned regularly, they tended to have among the lowest CRB counts of any samples in the study, and farms with fewer than 500 cows had a far lower prevalence of CRB than farms with greater numbers of cattle.
“A lot of my research can seem very disparate at first glance,” Jeong says. “But it is all connected under the umbrella of the one health concept, the idea that animal health and people health is connected. It is my hope that we can learn how to reduce harmful bacteria in food animals, to not only increase the safety of our animal foods, but also to increase our own human public health.”
How did antibiotic-resistant bacteria get into our soil?
Consider that bacteria are the most abundant microorganisms in soil, and that a single gram of backyard dirt may contain billions of these "bugs." There are many different types of bacteria which have evolved over eons to survive against predators such as other bacteria or fungi. They produce all kinds of materials to kill the “other guys,” which is where our modern arsenal of antibiotics come from. One of the self-defense survival tools bacteria have evolved is production of the extended-spectrum beta-lactamase (ESBL) enzyme — which protects them from having their cell walls destroyed by naturally-occurring antibiotic substances produced by other bacteria. As a side effect, ESBL-producing bacteria just happen to be mucking up modern medicine, because microorganisms that can emit this substance are resistant to many different types of antibiotic drug therapies — including penicillins and cephalosporins.
Written by DeLene Beeland; All photos by Tyler Jones/IFAS. Special thanks to KC Jeong for his time.
Read KC Jeong’s EPI profile here.
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