The aim of this study was to characterize the prevalence of fecal carriage of extended-spectrum beta-lactamases and carbapenemase-producing Gram-negative bacteria among healthy humans in Tunisia.Fifty-one rectal swabs of healthy volunteers were plated on MacConkey agar plates supplemented with cefotaxime or imipenem.The occurrences of resistance genes, integrons, 8 Piece Outdoor Sectional and phylogroup typing were investigated using PCR and sequencing.The genetic relatedness of isolates was determined by pulsed-field-gel-electrophoresis (PFGE) and multilocus-sequence-typing (MLST).
Whole-genome-sequencing (WGS) was performed for the carbapenem-resistant isolate.Sixteen ESBL-producing Escherichia coli isolates and one carbapenem-resistant Enterobacter bugandensis were detected out of the fifty-one fecal samples.The ESBL-producing E.coli strains contained genes encoding CTX-M-15 (n = 9), CTX-M-1 (n = 3), CTX-M-27 (n = 3), and CTX-M-55 (n = 1).
Three CTX-M-1-producers were of lineages ST131, ST7366, and ST1158; two CTX-M-15-producers belonged to lineage ST925 and ST5100; one CTX-M-27-producer belonged to ST2887, and one CTX-M-15-producer belonged to ST744.Six isolates contained class 1 integrons with the following four gene cassette arrangements: dfrA5 (two isolates), dfrA12-orf-aadA2 (two isolates), dfrA17-aadA5 (one isolate), and aadA1 (one isolate).E.bugandensis belonged to ST1095, produced IMI-2 Coffee Creamers carbapenemase, and contained qnrE1 and fosA genes.
A genome-sequence analysis of the E.bugandensis strain revealed new mutations in the blaACT and qnr genes.Our results reveal an alarming rate of ESBL-E.coli in healthy humans in Tunisia and the first description of IMI-2 in E.
bugandensis.