Antibiotic resistance is an increasing health problem, but new research suggests it is not only caused by the overuse of antibiotics. It's also caused by pollution. Using a process known as genomic analysis, researchers from the University of Georgia found a strong correlation between antibiotic resistance and heavy metal contamination in an environment.
According to this study, published in the July issue of the journal Microbial Biotechnology, soils with heavy metals had a higher level of specific bacterial hosts that were accompanied by antibiotic-resistant genes. Hosts included Acidobacteriaoceae, Bradyrhizobium and Streptomyces. The bacteria had antibiotic-resistant genes, known as ARGs, for vancomycin, bacitracin and polymyxin. All three drugs are used to treat infections in humans. The bacteria also had an ARG for multidrug resistance, a strong defense gene that can resist heavy metals as well as antibiotics.
Overuse of antibiotics in the environment is one cause
When these ARGs were present in the soil, metal-resistant genes, or MRGs, were present for several metals including arsenic, copper, cadmium and zinc. The microorganisms develop new strategies and countermeasures over time to protect themselves. The overuse of antibiotics in the environment adds additional selection pressure on microorganisms that accelerates their ability to resist multiple classes of antibiotics. But antibiotics aren't the only source of selection pressure. Researchers say that many bacteria possess genes that simultaneously work on multiple compounds that would be toxic to the cell, and this includes metals.
Metal-resistant genes respond the same way as antibiotic resistant genes
However, researchers agree that more research needs to be done to determine if metal-resistant genes respond in the same way to bacteria as antibiotic-resistant genes. Unlike antibiotics, heavy metals don't degrade in the environment so "they can exert long-standing pressure". The study reports previous research identified antibiotic-resistance in heavy metal-contaminated streams on the site by examining water samples in the lab.
According to researchers, when you expose the sample to a drug on a petri dish or assay, it only represents a fraction. This doesn't give you a complete picture. Genomic analysis gives a better picture. Researchers are now hopeful that they can now start to characterize bacterial communities and specific ARG and MRG genes in the environment.
Experts underline need for understanding evolution of bacteria
It is clear that there are several human pathogens that develop antibiotic resistance -- overuse is not the only cause. Human activities like agriculture and the combustion of fossil fuels play a role. Having a better understanding of how bacteria are evolving over time will help scientists see how this has an impact on drinking water and food production and how this eventually affects health.