Beta-Lactamase Genes in Soil Bacteria Isolated from the Banks of the Niangua River in Missouri

Abstract

Beta-lactam antibiotics are among the most widely prescribed antibiotics in clinical settings. As a result, it is not uncommon to encounter clinically isolated bacteria that produce beta-lactamase as a means of resistance to these antibiotics. Among the many beta-lactamases currently known, TEM-type beta-lactamase is the most widespread beta-lactamase observed in clinical settings. However, less is known regarding its prevalence among bacteria in natural settings. To determine how widespread the TEM-type beta-lactamase gene is in the environment, experiments were designed to detect this and other beta-lactamase genes from environmentally isolated bacteria. Briefly, soil was collected along the banks of the Niangua River located in west-central Missouri. Diluted soil preparations were plated onto tryptic soy agar plates containing ampicillin and allowed to incubate at room temperate for up to 14 days. Colonies (n = 58) growing on the plates were selected and total DNA isolated from each strain. Using 7 groups of beta-lactamase specific DNA primers, the polymerase chain reaction was employed to amplify beta-lactamase genes, if present. In total, 58 isolates were positive for an 800 base pair amplicon indicative of a TEM-type beta-lactamase. DNA sequencing of the amplified fragment from each strain was sequenced to identify the TEM variant present. The data indicated that TEM-116 beta-lactamases are widespread among natural populations of bacteria from this location. In total, 56 of the genes were TEM-116, 1 was TEM-1, and 1 was TEM-118. These genes were most predominate in the genera Bacillus and Pseudomonas. Attempts to transfer the resistance genes via transformation and conjugation were unsuccessful.