ABSTRACT
Rapid distribution of antimicrobial resistance among bacterial populations currently poses a major therapeutic challenge worldwide. A lot of extensive research has been carried out to understand the potential factors attributing this resistance. Horizontal gene transfer (HGT), also called lateral gene transfer (LGT), via the process known as conjugation or mating has been established as the predominant reason for the dissemination of antibiotic resistance through bacterial species (OECD, 2010; Malik et al., 2008). This phenomenon refers to a unidirectional exchange (donor to recipient) of genetic material between closely related or phylogenetically distant organisms. Mobile genetic elements (MGEs) or mobilomes, such as plasmids or conjugative transposons of bacteria can be transferred from a donor to a recipient by conjugation, which has been described as intimate physical contact between bacterial populations due to the activity of specialized protein complex, mating pair formation (Mpf) system. Mpf serves as an apparatus for the formation of surface-exposed sex pili that establish the conjunction between mating cells, and functions along with coupling protein (CP) associated with processing of deoxyribo nucleic acid (DNA) for transport (OECD, 2010; Schroder and Lanka, 2005; Daugelavicius et al., 1997). Thus, horizontal transfer of plasmid-encoded antibiotic resistance genes from bacteria to bacteria is induced and more bacterial populations develop the same phenotype. Emergence and propagation of resistant bacterial mutants occur in the environment due to antibiotic selective pressure, which is very common in hospitals as a consequence of intensive use of antimicrobial agents to treat general and nosocomial infections (Rai et al., 2012; Dzidik and Bedekovic, 2003). These mutants may even carry multiple antibiotic resistance genes when patients are provided with prolonged treatment with various antimicrobials. Antibacterial drugs administered to treat infections are only partly metabolized by patients’ body while large amounts of these compounds are discharged directly into hospital effluents or the environment (Malik et al., 2008). Therefore, prolonged exposure of a large bacterial community in the environment to such antimicrobial agents results in the emergence of resistance genes, which are then transported to other closely or distantly related species by means of lateral transfer. A wide variety of gram-negative as well as gram-positive bacteria has been found to harbor small to large molecular-weight plasmids, which are potentially associated with high antimicrobial resistance (Hossain et al., 2011; Grohmann et al., 2003). Conjugative transfer of multiple antibiotic resistance genes by plasmid-containing bacteria may occur at high frequency and
efficiency (Carattoli, 2003). Increased antimicrobial resistance and subsequent evidence of horizontal transfer of resistance genes may pose more serious threat to global healthcare in years to come.
