ANTIMICROBIAL RESISTANCE GENES SUL2, STRA, STRB, AND BLATEM-1 IN ENVIRONMENTAL E. COLI

Conjugative plasmids are self-replicative extrachromosomal DNA molecules that can be transferred through cell-to-cell contact. Mobilizable plasmids are those that use the self-replicative machinery of another cellular element to transfer. Bacterial plasmids acquire genes through mobile genetic elements: transposons, integrons, and insertion sequences. These plasmids have been shown to be responsible for disseminating antimicrobial resistance genes among bacterial populations. This is a threat to public health because of the increasing accounts of infection by antimicrobial resistant bacteria. E. coli is a diverse bacterial species composed of commensal and pathogenic strains, which cause intestinal or extraintestinal infections (such as urinary tract infections). The purpose of this study is to identify mobile genetic elements containing antimicrobial resistance genes in an E. coli isolate from the environment. An E. coli isolate was collected from seawater at Doheny Beach, California and tested by disk diffusion test to assess its resistance profile. The isolate was conjugated to test plasmid mobility, and its plasmidic DNA was extracted and sequenced. Six plasmids (sizes: 43.5, 33.9, 10.1, 6.2, 3.3 and 3.0 Kb) were assembled. The 6.2Kb plasmid contains a sul2 (sulfonamide resistance), strA and strB (aminoglycoside resistance) combined with IS91 (insertion sequence). The 43.5Kb IncX1 conjugative plasmid carries the blaTEM-1 gene, coding for a beta-lactamase (beta-lactam resistance), in close proximity to Tn3 (transposon). No antimicrobial resistance genes were found in the 33.9, 10.1, 3.3 and 3.0Kb plasmids. Both the original isolate and its transconjugant selected on sulfisoxazole, displayed resistance to streptomycin (aminoglycoside), sulfisoxazole (sulfonamide), and ampicillin (beta-lactam). The original isolate was resistant to chloramphenicol (phenicol), tetracycline, and trimethoprim. The IS91 in the 6.2Kb plasmid is known to mobilize by rolling circle replication with an origin (oriIS) and a terminus (terIS). We only found the terIS upstream of the IS91 in silico. This plasmid has been well described in clinical cases throughout the world (E. coli and Shigella), including one E. coli isolate similarly extracted from seawater in Jiaozhou, China. The 43.5Kb conjugative plasmid has similar plasmids already reporting Tn3 with blaTEM-1 in clinical isolates (Salmonella, Shigella, E. coli); however, no 100% plasmid identity match was found depicting the plasmid type with the Tn3 and blaTEM-1. The same and or similar conjugative and mobilizable plasmids of the environmental E. coli were found to contain the same antimicrobial resistance genes present in clinical cases worldwide.