Abstract
Antibiotic resistance is an increasing global problem resulting from the pressure of antibiotic usage, greater mobility of the population, and industrialization. Many antibiotic resistance genes are believed to have originated in microorganisms in the environment, and to have been transferred to other bacteria through mobile genetic elements. Among others, β-lactam antibiotics show clinical efficacy and low toxicity, and they are thus widely used as antimicrobials. Resistance to β-lactam antibiotics is conferred by β-lactamase genes and penicillin-binding proteins, which are chromosomal- or plasmid-encoded, although there is little information available on the contribution of other mobile genetic elements, such as phages. This study is focused on three genes that confer resistance to β-lactam antibiotics, namely two β-lactamase genes (blaTEM and blaCTX-M9) and one encoding a penicillin-binding protein (mecA) in bacteriophage DNA isolated from environmental water samples. The three genes were quantified in the DNA isolated from bacteriophages collected from 30 urban sewage and river water samples, using quantitative PCR amplification. All three genes were detected in the DNA of phages from all the samples tested, in some cases reaching 104 gene copies (GC) of blaTEM or 102 GC of blaCTX-M and mecA. These values are consistent with the amount of fecal pollution in the sample, except for mecA, which showed a higher number of copies in river water samples than in urban sewage. The bla genes from phage DNA were transferred by electroporation to sensitive host bacteria, which became resistant to ampicillin. blaTEM and blaCTX were detected in the DNA of the resistant clones after transfection. This study indicates that phages are reservoirs of resistance genes in the environment.
Highlights
Recognized as a global problem [1], antibiotic resistance increases the morbidity and mortality caused by bacterial infections, as well as the cost of treating infectious diseases
Given that many genera found in diverse environments carry resistance determinants [6], it is feasible that antibiotic-resistance genes have originated in the environment and that they could have been transferred from the environment to pathogenic bacteria, which are currently found in clinical settings
We focused on two b-lactamases and a penicillin-binding protein. blaTEM belongs to class A serine b-lactamases, which have been described in epidemiological studies; blaCTX-M and blaTEM are the most prevalent broadspectrum b-lactamases and the most widely distributed enzymes worldwide [24,25,26]. mecA was included in this study because of the increasing incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA)
Summary
Recognized as a global problem [1], antibiotic resistance increases the morbidity and mortality caused by bacterial infections, as well as the cost of treating infectious diseases. Microorganisms produce many antimicrobials in nature [5,6] These antibiotic-producing organisms have become resistant to the antibiotics they produce, and the genes that confer such resistance can be transferred to other non-resistant bacteria. The presence of antibiotics in the environment may provide long-term selective pressure for the emergence and transmission of these resistance-conferring genes in non-producing organisms [5,7]. Given that many genera found in diverse environments carry resistance determinants [6], it is feasible that antibiotic-resistance genes have originated in the environment and that they could have been transferred from the environment to pathogenic bacteria, which are currently found in clinical settings. The mobile genetic elements (MGEs) for the horizontal transfer of such genes most commonly studied are plasmids, transposons or, as a few reports suggest, bacteriophages [9,10,11]
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