The strong selective pressure exerted by excessive use of antibiotics in the last decades has increased the acquisition of resistance genes by horizontal gene transfer. Horizontal gene transfer contributed to the diversification of microorganisms by influencing traits such as metabolic potential of a bacterial cell, antibiotic resistance, symbiosis, fitness, and adaptation. The study of biotic relationships helped to examine how they may contribute to virulence such as transfer of toxin genes, antibiotic resistance genes. The current study examines the pattern of distribution of Ambler (molecular) classes of β-lactamases (A, B, C, D) that provides a basic understanding and an initial assessment of resistance genes that may have a different role in the natural environment in free living and symbiotic nosocomial pathogens. The distribution of the four different Ambler (molecular) classes of β-lactamases (A, B, C, and D) differs among different bacterial species. The results from absolute abundance data showed prevalence of class B β-lactamases was highest in free living and lowest in symbiotic bacterial species. Interestingly, class D β-lactamases was absent in symbiotic bacterial species. However, relative abundance class D β-lactamases was lowest for free-living bacterial species. The prevalence of class B β-lactamases based upon the total number of sequences checked predominated in pathogens that are free living when compared to other Ambler classes of β-lactamases. The study of biotic relationships helps to understand what selective or stimulatory pressures are driving the spread of antibiotic resistance genes. In the future, this may help to design effective strategies for preventing further increases in the incidence of antibiotic-resistant bacteria.

β-lactamases, symbiotic bacteria, free living bacteria, antibiotic resistance genes