The role of bacteriophages -- viruses that infect bacteria -- could be crucial in the transfer of antibiotic resistance genes between bacteria, and this process could favour the emergence of resistant bacterial strains in the natural environment.
This is one of the main conclusions of an article published in the journal Antimicrobial Agents and Chemotherapy by the researchers Maite Muniesa, Joan Jofre, Marta Colomer-Lluch and Lejla Imamovic, from the Generalitat-supported Health-Related Water Microbiology (MARS) Research Group, part of the Department of Microbiology at the Faculty of Biology of the University of Barcelona.
Antibiotic resistance, a global problem
Antibiotic resistance, which is the focus of the World Health Organization's 2011 World Health Day, is caused by multiple factors, including antimicrobial abuse and acquisition of resistance genes. It is currently believed that the origin of some forms of resistance lies in the transfer of genes between microorganisms in the natural environment.
"Resistance to antibiotics is one of the main problems encountered in the treatment of infectious diseases across the world," explain the lecturer Maite Muniesa, from the UB's Department of Microbiology. "Traditionally, most scientific studies of multi-resistance genes have focused on plasmids, which are circular, covalently closed DNA molecules that act as the principal vehicle for inter-bacterial gene transmission."
The article focuses on samples of faecal waste from different animals (cattle, pigs and poultry) from farms in Catalonia, some of which have not been treated with antibiotics. Specifically, the experts behind the study analyse the horizontal transfer of pathogenicity genes between enteric bacteria by bacteriophages: the genes blaTEM and blaCTX-M,involved in resistance to betalactamic antibiotics, and mecA,associated withmethicillin resistance in staphylococci, which are responsible for a large proportion of hospital infections.
Bacteriophages as messengers
It is clearly described in scientific literature that bacteriophages are highly efficient vectors for the inter-cellular transfer of DNA fragments. But what role do phages play in the emergence of new bacterial resistances? As a step towards answering this question, the study shows for the first time that bacteriophages contain antibiotic resistance genes and are potentially excellent vehicles for the propagation of bacterial resistance genes in the environment.
As professor Joan Jofre notes, "bacteriophages facilitate the transfer of antibiotic resistance genes between different biomes, and the potential scope of this process in the natural environment has not yet been described." In their role as mobilizers of antimicrobial resistance genes, explains Maite Muniesa, "bacteriophages are more durable than plasmids and, surprisingly, can be found in high concentrations in the natural environment. What we need to do now is identify the types of viruses that are transferring the resistance genes between bacteria."
New resistances, new scientific challenges
Antibiotic resistances detected in the clinical setting are also genetically present in bacteria found in the natural environment. Despite the numerous measures taken to control the use of antibiotics in agriculture, new forms of antimicrobial resistance continue to emerge. According to experts, the evidence suggests that the appearance of new resistances is not simply the result of selective pressure from antibiotics but is also due to the mobilization of resistance genes in the environment, a natural process in which the biological role of phages cannot be ignored.
The new study brings an ecological perspective to the problem and defines the boundaries that restrict the emergence of new antimicrobial resistances in the natural environment. Moving forwards, this research area could contribute to the detection of resistances that have not been described in the clinical setting and, by extension, broaden research into new antimicrobial agents. "In the field of antimicrobial resistance, we must remember that there are many factors to consider which are not being taken into account. For example, certain antibiotic treatments targeting bacteria are also capable of activating the mobilization of different types of genes by bacteriophages. In this field of research, it is something that must be given particular consideration," warns professor Joan Jofre.
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