ENTEROTOXIN-CODING VIRULENCE GENE SENB AND MULTIDRUG RESISTANCE GENES IN ESCHERICHIA COLI

Lateral gene transfer gives rise to new virulent and antimicrobial resistant Enterobacteriaceae around the world creating a concerning public health threat. Gene transfer can occur through conjugative plasmids that self-transfer through cell-to-cell contact, which can spread virulence and antibiotic resistance genes. The secreted enterotoxin TieB, encoded by the virulence gene senB, plays a role in the development of severe diarrhea in patients infected by Shigella and enteroinvasive Escherichia coli (EIEC). The senB gene has been found on a large conjugative plasmid which may facilitate its dissemination among bacteria. We hypothesize that mobile virulence and antibiotic resistance genes are found in environmental and clinical isolates. The objective of this study is to characterize virulence and antibiotic resistance genes present in environmental isolates and to show the spread of these genes throughout the world. As part of a survey, we collected water from Portage Bay in Washington, USA and isolated a multidrug resistant E. coli using selective media. An antimicrobial resistance profile was determined by a disk diffusion test. Plasmids were isolated, sequenced, and analyzed. The E. coli isolate contained five plasmids: a 119 kb IncF plasmid and four small plasmids of 6.6 kb, 4.0 kb, 3.2 kb, and 2.4 kb. The senB gene was found on the 119 kb IncF plasmid along with aminoglycoside (aadA5), macrolide (mph(A)), sulphonamide (sul1), and trimethoprim (dfrA17) resistance genes. senB was associated with the colicin Js receptor operon cjrABC on a transposon with insertion sequences similar to E. coli IS91 and IS1294. The genes aadA5 and dfrA17 were part of a class 1 integron next to a partial IS6100 transposon carrying mph(A) and sul1. Similar senB sequences (≥99% coverage, ≥99% identity) were identified in 27 plasmids from various clinical isolates (23 E. coli, two K. pneumoniae, and two S. boydii) around the world, and in two chromosomes from S. sonnei isolated from humans. The transposon containing senB, cjrABC, and rep (replicase) identified in our environmental E. coli is also present in 18 E. coli and two K. pneumoniae Inc F conjugative plasmids (≥ 99% coverage, ≥ 99% identity). The class 1 integron/transposon with aadA5, dfrA17, mph(A), and sul1 was also found in 14 E. coli, one K. pneumoniae, and one S. sonnei plasmids (≥ 99% coverage, ≥ 99% identity). Among them, only six E. coli IncF conjugative plasmids and one K. pneumoniae IncF conjugative plasmid contained both the senB transposon and the class 1 integron/partial transposon. This is the first record of a plasmid from an aquatic environmental E. coli with senB and the class 1 integron/transposon. The presence of senB and antibiotic resistance genes on mobile elements in aquatic E. coli and clinical isolates shows that virulence and antimicrobial genes are present in the environment and clinical settings, and can actively spread over time.