The Salmonella pathogen is typically transferred to humans through contaminated food. In the United States, some 42,000 cases of salmonellosis—the infection caused by the Salmonella pathogen—are reported annually, with about 400 people dying from the contamination, according to the U.S. Centers for Disease Control and Prevention (CDC).
The Salmonella bacteria has been found to develop a resistance to one group of antibiotics and to also be less susceptible to the effects of an unrelated antibiotic and a biocide that is used in common household products, according to research funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Medical Research Council.
University of Birmingham researchers, Professor Laura Piddock and Dr. Mark Webber, from the Antimicrobials Research Group, found that a common mutation in Salmonella makes the pathogen resistant to fluoroquinolones, a class of antibiotics. The mutation also allows Salmonella to survive in the presence of other antibiotics and triclosan, a biocide. Triclosan is an antibacterial and antifungal agent that is often an ingredient in toothpastes, deodorants, and soaps.
The Food and Drug Administration (FDA) previously announced it is reviewing triclosan, and several studies have indicated that the chemical may alter hormone regulation in laboratory animals or cause antibiotic resistance. The Environmental Protection Agency (EPA) has registered triclosan as a pesticide and has rated it high for human health and environmental risks.
The current research found that the mutation, which changes DNA gyrase (the target of fluoroquinolones) in Salmonella, also alters the structure of bacterial. These changes prompt stress responses, which protect the bacterium, allowing the germ to survive when in the presence of a number of unrelated antibiotics, such as triclosan, the University of Birmingham wrote. “This study shows that use of a common antibiotic confers fundamental changes allowing bacteria to survive exposure to several antibiotics plus an antimicrobial found in products commonly used in the home,” Professor Piddock said.
The study also looked at what would happen when two specific amino acids within DNA gyrase recreated common changes seen in resistant strains that were isolated from patients. Both mutants were resistant to quinolone antibiotics and one substitution led to a significant increase in survival when exposed to 25 other drugs. These data indicate that the nature of the mutation is critical in surviving antibiotic exposure, the research found. The change in gyrase also altered susceptibility to the range of antibiotics, according to the University of Birmingham.
The study revealed that a typical mechanism of resistance to one group of antibiotics also provides protection against other antibiotics, suggesting that these bacteria will survive better in the presence of many antimicrobials, including biocides. “Our work has helped understand how developing antibiotic resistance can change the biology of bacteria in a profound way. Identifying the conditions which select for resistant bacteria and promote their survival will help use current drugs in better ways,” said Dr. Webber.
We routinely discuss the dangers of antibiotic misuse and overuse, and how these practices are directly linked to antibiotic resistant diseases that can wreak havoc on the body and increase widespread drug resistance. Antibiotic overuse and misuse encourage bacteria to remain—while killing off good bacteria—growing more and more resistant. This has enabled, and continues to enable, bacteria to outsmart antibiotics and to survive, thrive, and strengthen so that existing drugs are powerless against their eradication.
