Dissemination of mcr-1-carrying Escherichia coli in Seawater and Sewage Across Lebanon

Abstract

Antibiotic resistance has become one of the core public health concerns. Excess use and misuse of antibiotics, especially the last resort antibiotic, colistin, led to emergence and dissemination of colistin resistant Escherichia coli carrying the mcr-1 gene to different countries worldwide. Detection of mcr-1 in humans and animals has a significant risk of contamination to seawater and sewage water. Many studies done in Lebanon illustrated the prevalence of mcr-1 in the agricultural-environmental-human sectors; therefore, we first hypothesized the potential contamination of mcr-1 alongside other antimicrobial resistance genes in the Mediterranean Sea water; along the Lebanese coastline.

Samples were collected from 22 different locations from North to South of the Lebanese coast. Approximately, 45.5% of the samples were contaminated with colistin-resistant E. coli; out of which a total of 16 isolates were mcr-1 positive. The colistin minimum inhibitory (MIC) for these isolates ranged between 4 μg/mL and 32 μg/mL and antimicrobial susceptibility (AMR) testing showed that all the E. coli isolates were multidrug-resistant; showing resistance to at least 3 classes of antibiotics. The isolates were susceptible or exhibited intermediate resistance to carbapenems. Moreover, the extended-spectrum β-lactamase genes (ESBL), blaTEM, were detected in five isolates. A variety of plasmid types were detected in the isolates, especially the ones responsible for the global dissemination of the mcr-1, IncX4. BOX- PCR showed that 87.5 % of the isolates were genotypically diverse. The mcr-1-carrying isolates can persist in the water milieu for more than 35 days. Based on these outcomes, we further hypothesized that the mcr-1 positive isolates detected in seawater might be related to the direct discharge of sewage water. Samples were collected from 6 main sewage outfalls from North to South of Lebanon. The samples were 100% positive for colistin-resistant E. coli, yielding to 60 mcr-1 positive isolates which were confirmed by PCR analysis. The colistin MIC for these isolates ranged between 8 μg/mL and above 640 μg/mL, and AMR testing showed that 3.3% of the E. coli isolates were (PDR), 20% XDR, and 76.6% were MDR. 78% of the plasmids were IncX4 type.

It is the first study to highlight the dissemination and characterization of mcr-1-positive E. coli in seawater and sewage in Lebanon.