Molecular characteristics of antibiotic-resistant Escherichiacoli and Klebsiella pneumoniae strains isolated from hospitalizedpatients in Tehran, Iran

Background and Aim : We evaluated the distribution of carbapenem and colistin resistancemechanisms of clinical E. coli and K. pneumoniae isolates from Iran.Methods : ۱۶۵ non-duplicate non-consecutive isolates of K. pneumoniae and E. coli werecollected from hospitalized patients admitted to Iran’s tertiary care hospitals from September ۲۰۱۶to August ۲۰۱۸. The isolates were cultured from different clinical specimens, including wound,urine, blood, and tracheal aspirates. Antibiotic susceptibility testing was performed by discdiffusion and microdilution method according to the Clinical and Laboratory Standards Institute(CLSI) guideline. The presence of extended spectrum β-lactamases (ESBLs) genes,carbapenemase genes, as well as fosfomycin resistance genes, and colistin resistance genes wasalso examined by PCR-sequencing. The ability of biofilm formation was assessed with crystalviolet staining method. The expression of colistin resistance genes were measured by quantitativereverse transcription-PCR (RT-qPCR) analysis to evaluate the association between geneupregulation and colistin resistance. Genotyping was performed using the multi-locus sequencingtyping (MLST).Results : Colistin and tigecycline were the most effective antimicrobial agents with ۹۰.۳% and۸۲.۴% susceptibility. Notably, ۱۶ (۹.۷%) isolates showed resistance to colistin. Overall, ۳۳ (۲۰%),۳۱ (۱۸.۸%), and ۹۵ (۵۷.۶%) isolates were categorized as strong, moderate, and weak biofilmproducer,respectively. Additionally, blaTEM, blaSHV, blaCTX-M, blaNDM-۱, blaOXA-۴۸-likeand blaNDM-۶ resistance genes were detected in ۹۸ (۵۹.۴%), ۵۴ (۳۲.۷%), ۷۷ (۴۶.۷%), ۳ (۱.۸%),۱۷ (۱۰.۳۰%) and ۳ (۱.۸%) isolates, respectively. Inactivation of mgrB gene due to nonsensemutations and insertion of IS elements was observed in ۶ colistin resistant isolates. Colistinresistance was found to be linked to upregulation of pmrA-C, pmrK, phoP, and phoQ genes. Threeof blaNDM-۱ and ۳ of blaNDM-۶ variants were found to be carried by IncL/M and IncF plasmid,respectively. MLST revealed that blaNDM positive isolates were clonally related and belonged tothree distinct clonal complexes, including ST۱۴۷, ST۱۵ and ST۳۲۹۹.Conclusion : The large-scale surveillance and effective infection control measures are alsourgently needed to prevent the outbreak of diverse carbapenem- and colistin-resistant isolates inthe future.

کلیدواژه ها:

Klebsiella pneumoniae ، Escherichia coli ، Antibiotic resistance genes ، Carbapenem ، Colistin