Abstract
Colistin is considered as a last resort agent for treatment of severe infections caused by carbapenem-resistant Enterobacterales (CRE). Recently, plasmid-mediated colistin resistance genes (mcr type) have been reported, mainly corresponding to mcr-1 producers. Those mcr-1-positive Enterobacterales have been identified not only from human isolates, but also from food samples, from animal specimens and from environmental samples in various parts of the world. Our study focused on the occurrence and characterization of mcr-1-positive Enterobacterales recovered from retail raw chicken in Egypt. From the 345 retail chicken carcasses collected, a total of 20 samples allowed to recover mcr-1-positive isolates (Escherichia coli, n = 19; Citrobacter freundii, n = 1). No mcr-2- to mcr-10-positive isolate was identified from those samples. The colistin resistance trait was confirmed for all those 20 isolates with a positivity of the Rapid Polymyxin NP (Nordmann-Poirel) test. Minimum inhibitory concentrations (MICs) of colistin for all MCR-1-producing isolates ranged between 4 and 16 μg/mL. Noticeably, 9 out of the 20 mcr-1-positive isolates produced an extended-spectrum β-lactamase (ESBL), respectively producing CTX-M-9 (n = 2), CTX-M-14 (n = 4), CTX-M-15 (n = 2), and SHV-12 (n = 1). Noteworthy, the fosA4 gene encoding resistance to fosfomycin was found in a single mcr-1-positive E. coli isolate, in which both genes were located on different conjugative plasmids. The pulsed-field gel electrophoresis (PFGE) patterns were identified, corresponding to 10 different sequence types (STs), highlighting the genetic diversity of those different E. coli. Whole-genome sequencing revealed three major types of mcr-1-bearing plasmids, corresponding to IncI2, IncX4, and IncHI2 scaffolds. The occurrence of MCR-1-producing multidrug-resistant Enterobacterales in retail raw chicken is of great concern, considering the possibility of transmission to humans through the food chain.
Highlights
The worldwide increase and spread of the plasmid-mediated colistin resistance (MCR), in particular in multidrug-resistant (MDR) bacteria of human and animal origin, is a major public health concern [1]
It is tempting to speculate that such selection of colistin-resistant E. coli isolates among Egyptian farms might be related to the overuse of colistin in the local farming industry [41]
Concerning strains isolated from food, a single mcr-1-positive E. coli strain was isolated from cheese [24] and beef sausage [23] in Egypt
Summary
The worldwide increase and spread of the plasmid-mediated colistin resistance (MCR), in particular in multidrug-resistant (MDR) bacteria of human and animal origin, is a major public health concern [1]. The mcr-1 transferable resistance gene was first identified on a conjugative IncI2 plasmid in China in 2015 [3]. MCR proteins are phosphoethanolamine transferases that modify the lipid A moiety of the lipopolysaccharide of Gram-negative bacteria, leading to decreased susceptibility or resistance to either polymyxin B or colistin [3]. The spread of the mcr-1 gene is associated with various plasmid backbones such as IncI2, IncX4, IncFI, IncFII, IncFIB, IncHI1, IncHI2, IncP, and IncY, the two first being the most prevalent [3,13,14,15,16,17,18]
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