Tunisian Multicenter Study on the Prevalence of Colistin Resistance in Clinical Isolates of Gram Negative Bacilli: Emergence of Escherichia coli Harbouring the mcr-1 Gene

Abstract

Background: Actually, no data on the prevalence of plasmid colistin resistance in Tunisia are available among clinical bacteria. Objectives: This study aimed to investigate the current epidemiology of colistin resistance and the spread of the mcr gene in clinical Gram-negative bacteria (GNB) isolated from six Tunisian university hospitals. Methods: A total of 836 GNB strains were inoculated on COL-R agar plates with selective screening agar for the isolation of GNB resistant to colistin. For the selected isolates, mcr genes, beta-lactamases associated-resistance genes and molecular characterisation were screened by PCRs and sequencing. Results: Colistin-resistance was detected in 5.02% (42/836) of the isolates and colistin-resistant isolates harboured an ESBL (blaCTX-M-15) and/or a carbapenemase (blaOXA-48, blaVIM) encoding gene in 45.2% of the cases. The mcr-1 gene was detected in four E. coli isolates (0.59%) causing urinary tract infections and all these isolates also contained the blaTEM-1 gene. The blaCTX-M-15 gene was detected in three isolates that also carried the IncY and IncFIB replicons. The genetic environment surrounding the mcr-carrying plasmid indicated the presence of pap-2 gene upstream mcr-1 resistance marker with unusual missing of ISApl1 insertion sequence. The Conclusions: This study reports the first description of the mcr-1 gene among clinical E. coli isolates in Tunisia and provides an incentive to conduct routine colistin susceptibility testing in GNB clinical isolates.

Colistin Resistance Genes in Broiler Chickens in Tunisia

“…As far as North Africa is concerned, previous studies detected the highest prevalence of colistin resistance in Tunisia [ 7 ] where the presence of colistin-resistant Gram-negative bacteria has been well documented in clinical specimens [ 24 ], animals such as chickens [ 25 ], bovids [ 26 ], camels [ 27 ] and wild boars [ 28 ], retail meat [ 16 ], and wastewater [ 29 ]. Only the mcr -1 variant has been highlighted so far.…”