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In this study, we have attempted to report the first clonal spread of colistin-resistant Klebsiella pneumoniae coproducing KPC and VIM carbapenemases in the neonatal unit of Rabta Teaching Hospital of Tunis (Tunisia). This retrospective study was performed from January 1, 2014 to December 31, 2014 in the Microbiology Laboratory at the Rabta University Hospital of Tunis. Twenty-one nonreplicate colistin-resistant K. pneumoniae were isolated from 19 patients hospitalized in the neonatal unit and 2 patients in the adult intensive care unit (ICU). Most of the strains were isolated from invasive specimens. Pulsed-field gel electrophoresis (PFGE) and PCR analysis and nucleotide sequencing of the blaKPC and blaVIM genes were performed. Mortality was reported in 92% of cases. All the strains were resistant to colistin (minimum inhibitory concentration [MICs] ranged from 8 to 12 mg/L). The MICs for imipenem of K. pneumoniae isolates ranged from 3 to 256 mg/L for 13 strains that were characterized as intermediate or resistant. The MICs for ertapenem were higher than 32 mg/L for the 19 resistant strains. All the isolates were sensitive to tigecycline and chloramphenicol. PFGE analysis revealed two clones (I and II). Twenty of the 21 colistin-resistant, carbapenem-resistant K. pneumoniae isolates belonged to clone I. Only one strain was related to clone II. PCR analysis and nucleotide sequencing revealed that the 20 isolates belonged to clone I, coproduced the blaKPC and blaVIM genes. A single strain (clone II), which was isolated in the ICU, did not produce KPC and VIM carbapenemases. All strains did not produce OXA-48.

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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.

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