Is there a link between exposure to pesticides and antibiotic resistance in Gram-negative bacteria isolated from Thai farmers?

BACKGROUND

The organophosphate pesticides have the potential to impact microbial diversity, but their influence on antibiotic resistance (AR) in bacteria remains understudied.

OBJECTIVES

The objective of our study was to evaluate the impact of exposure to acetylcholinesterase inhibitors on glyphosate tolerance and AR in Gram-negative bacteria isolated from the digestive tracts of Thai farmers.

METHODS

Human fecal samples from Thailand, grouped by pesticide exposure level measured by acetylcholinesterase blood concentration, were cultured on MacConkey (McK) agar with or without 7 g/L of a glyphosate-based formulation (GBF). Antibiotic susceptibility and glyphosate minimum inhibitory concentration (MIC) of isolated strains were assessed using the disk diffusion and broth microdilution methods, respectively.

RESULTS

A total of 547 GNB were isolated from 112 human fecal samples. GBF medium predominantly selected Escherichia coli, Klebsiella pneumoniae, and Citrobacter freundii. GBF MICs ranged from 2 g/L to 16 g/L with K. pneumoniae species harboring the highest median MIC (16 g/L). AR rates were not significantly different between exposed and not exposed groups to pesticides. In contrast, six mobile colistin resistance (MCR)- and/or extended spectrum beta lactamase (ESBL)-producing E. coli strains were isolated from pesticide-exposed group, while only one colistin-resistant K. pneumoniae strain was isolated from a sample which was not exposed to pesticides.

CONCLUSIONS

The results of our study underscore the need for further research, particularly on the impact of glyphosate exposure on colistin resistance and the prevalence of ESBL-producing strains. Additionally, we emphasize the importance of testing a broad range of pesticides to better understand their impact on AR.