Molecular characterization of quinolone resistance and antimicrobial resistance profiles of Klebsiella pneumoniae and Escherichia coli isolated from human and broiler chickens.

This study characterized quinolone (Q) resistance determinants in a series of Klebsiella pneumoniae (n = 26) and Escherichia coli (n = 19) isolates of human and animal origin. The presence of plasmid-mediated quinolone resistance (PMQR) and carabpenemase genes was examined by PCR. The quinolone resistance-determining regions (QRDRs) of gyrA and parC genes were sequenced. Thirty-three isolates had ciprofloxacin MIC≥8 mg/l. About 34.6% and 10.5% of K. pneumoniae and E. coli isolates were ESBL producers respectively. The PMQR genes were detected in 77% (n = 35) of isolates. The oqxAB was the most prevalent PMQR gene being identified in all K. pneumoniae isolates, followed by aac(6')-Ib-cr (34.6%), qnrS (23%) and qnrB (7.7%). The most frequently detected gene among E. coli isolates was qnrS (36.8%) followed by aac(6')-Ib-cr (10.5%) and qepA (5.2%). All Q resistant isolates harbored amino acid substitutions in both GyrA and ParC QRDRs. High prevalence of PMQR genes among food-producing animal isolates is an issue of great concern.

Prevalence and molecular determinants of colistin resistance among commensal Enterobacteriaceae isolated from poultry in northwest of Iran.

BACKGROUND: The emergence of colistin-resistant Enterobacteriaceae from human and animal sources is a public health concern as this antibiotic is considered to be the last line therapeutic option for infections caused by multidrug-resistant Gram-negative bacteria. Here we aimed to determine the prevalence of colistin resistance, among enterobacteria isolated from poultry and the possible underlying colistin resistance mechanisms. METHODS: A collection of 944 cloacal samples were obtained from poultry and screened for colistin resistance. To uncover the molecular mechanism behind colistin resistance, the presence of plasmid encoded colistin resistance genes mcr-1, mcr-2, mcr-3 and mcr-4 was examined by PCR. The nucleotide sequences of the mgrB, pmrA, pmrB, phoP, phoQ, crrA and crrB genes were determined. The genetic relatedness of the colistin resistant (ColR) isolates was evaluated by Multilocus sequence typing. Three ColR mutants were generated in vitro by repetitive drug exposure. RESULTS: Overall from 931 enteric bacteria isolated from poultry samples obtained from 131 farms, nine ColR bacteria (0.96%) with high level colistin resistance (MICs ≥ 64 mg/L) were detected all being identified as K. pneumoniae. The 9 ColR bacteria originated from different farms and belonged to 7 distinct Sequence types including ST11 (22.2%) and ST726 (22.2%) being the most prevalent STs followed by ST37, ST74, ST485, ST525 and novel sequence type 3380 (11.1% each). mcr-type genes were not detected in any isolate. In 88.8% of the isolates (n = 8), MgrB was inactivated by Insertion of IS elements (IS1-like, IS3-like, IS5-like families, positions + 75, + 113, + 117, + 135) and nonsense mutations at codons 8, 16, 30. All ColR isolates harboured wild type PmrA, PhoP, PhoQ or polymorphic variants of PmrB. Sequence analysis of the CrrB revealed a familiar S195N and 4 novel I27V, T150R, F303S and K325R substitutions. PmrB T93N substitution and mgrB locus deletion were identified in two laboratory induced ColR mutants and one mutant lacked alteration in the studied loci. In one ColR isolate with wild type MgrB an A83V substitution was detected in CrrA. CONCLUSION: It is concluded from our results that colistin resistance in the studied avian K. pneumoniae isolates was mostly linked to alterations identified within the mgrB gene.

Comparison of susceptibility testing methods for determining the activity of colistin against Gram-negative bacilli of clinical origin.

PURPOSE: Despite being in clinical use for decades, colistin susceptibility testing remains challenging because of its inherent cationic properties. We aimed to compare the performance characteristics of different methods for testing susceptibility to colistin in a series of clinical isolates of Gram-negative bacilli. METHODOLOGY: One hundred and nine clinical isolates of Klebsiella pneumoniae (n=34), Escherichia coli (n=20), Acinetobacter baumannii (n=17) and Pseudomonas aeruginosa (n=38) were studied for colistin susceptibility using broth microdilution (BMID), broth macrodilution (BMAD), agar dilution (AD) as well as disc-diffusion (DD) utilizing two different commercial disc sources. RESULTS: By using BMID as reference method, 88 and 21 isolates were found to be colistin susceptible and resistant, respectively. Overall, acceptable essential agreement (EA) and categorical agreement (CA) were observed between BMAD and reference method (100 %). Whereas the AD method revealed the lowest rate of EA (61.7, 11.7, 5.0 and 5.2 % for K. pneumoniae, A. baumannii, E. coli and P. aeruginosa, respectively), it showed acceptable or near acceptable CA for K. pneumoniae (100 %), E. coli (100 %) and A. baumannii (88.2 %) isolates but not for P. aeruginosa (13.1 %). DD failed to detect resistance in colistin-resistant (colR) P. aeruginosa (n=5, very major errors of 100 %) but successfully identified all high-level colistin-resistant A. baumannii and K. pneumoniae isolates. CONCLUSION: We found BMAD to be very reliable for colistin MIC determination. Methods AD and DD should not be used for colistin susceptibility testing in P. aeruginosa isolates as these are associated with false-resistant and -susceptible results, respectively.