Investigation of Escherichia coli isolates from pigs and humans for colistin resistance in Lao PDR- a cross-sectional study.
Phomsisavath V., Roberts T., Seupsanith A., Robinson MT., Nammanininh P., Chanthavong S., Chansamouth V., Vongsouvath M., Theppangna W., Christensen P., Blacksell SD., Mayxay M., Ashley EA.
BACKGROUND: In Laos, colistin is not currently registered for use in humans. This One Health study aimed to estimate the prevalence of meat-producing pigs carrying colistin-resistant Escherichia coli, and investigate if E. coli causing invasive human infections were colistin-resistant. METHODS: Between September 2022 and March 2023, rectal swabs were collected from 895 pigs from abattoirs in 9/17 Lao provinces. Pig rectal swabs and stored E. coli isolates from human blood cultures, submitted to Mahosot Hospital Microbiology laboratory between 2005 and 2022, were screened for colistin resistance on selective chromogenic agar with organism identification confirmed using MALDI-TOF MS. Suspected colistin-resistant isolates underwent colistin susceptibility testing by broth microdilution following European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. Isolates with MIC values of ≥2 μg/ml were tested for plasmid-mediated colistin resistance genes (mcr-1, mcr-2, and mcr-3) by multiplex SYBR Green PCR. RESULTS: A total of 15/620 (2.41%) invasive human E. coli isolates were phenotypically colistin-resistant by broth microdilution (MIC values 4 to 8 μg/ml). The earliest isolate was from 2015 in a patient from Phongsaly province in Northern Laos. A total of 582/895 (65.02%) pig rectal swab samples contained colistin-resistant E. coli. The detected colistin resistance genes were predominantly mcr-1 (57.8%, 346/598), followed by mcr-3 (20.23%,121/598), and 22.24% (133/598) were found to co-harbour mcr-1 and mcr-3. Among the 15 human isolates with colistin MIC values of ≥4 μg/ml, 12/15 were mcr-1. CONCLUSIONS: We found that colistin resistant E. coli is causing invasive infection in humans in Laos despite the fact it is not available for human use. Use in animals seems to be widespread, confirmed by high carriage rates of colistin-resistant E. coli in pigs. It is probable that food-producing animals are the source of colistin-resistant E. coli bloodstream infection in Laos, although these have been infrequent to date. This is a serious public health concern in the region that needs to be addressed by appropriate enforceable legislation.