Review on Metal Resistance and Its Association with Antibiotic Resistance in Microbes

Antibiotic resistance is recognized as a major global threat to public health by the World Health Organization. The major driver for the development of antibiotic resistance is considered to be the use, misuse and overuse of antibiotics in humans and animals. Non-antibiotic compounds, such as antibacterial biocides and metals, may also contribute to the promotion of antibiotic resistance through co-selection. This may occur when resistance genes to both antibiotics and metals/biocides are co-located together in the same cell (co-resistance), or a single resistance mechanism (e.g. an efflux pump) confers resistance to both antibiotics and biocides/metals (cross-resistance), leading to co-selection of bacterial strains, or mobile genetic elements that they carry. Micro-organisms have evolved mechanisms to detoxify heavy metals, and some even use them for respiration. To survive under metal stressed conditions, bacteria have evolved several types of mechanisms to tolerate the uptake of heavy metal ions. These mechanisms include the efflux of metal ions outside the cell, accumulation, complexation and reduction of the metal ions to a less toxic state. These microbial interactions with metals may have several implications for the environment. The microbes may play an important role in the biogeochemical cycling of toxic metals as well as remediating metal contaminated environments. Antibiotic resistance has become a major concern as a medical and an economic problem. The dissemination of resistance traits could reduce the efficacy of drugs to only a few antibiotics and this could increase health care costs. It is estimated that resistant bacterial infections increase health care costs. Microbes can resist antibiotics and metals by; drug tolerance (loss of affinity or alternation of metabolic pathway), enzymatic destruction of drug/metal, by lose of previous porin (drug impermeability), by modifying target site of the antibiotic.