Background: The emergence of the plasmid-mediated mcr colistin-resistance gene in bacteria poses a potential threat for treatment of patients, especially when hospitalized. The aims of this study were to search for the presence of mcr-1 and mcr-2 genes among colistin-resistant Escherichia coli ( E. coli ) and Klebsiella pneumoniae ( K. pneumoniae ) isolates from clinical specimens and to determine the fingerprint of strains by enterobacterial repetitive intergenic consensus sequences PCR (ERIC-PCR) method. Methods: In this study, 712 nonduplicate Enterobacteriaceae isolates from clinical specimens were examined. All of the isolates were subcultured on suitable media, and the isolated colonies were identified by standard biochemical tests. Antimicrobial susceptibility test on 7 antibiotics was performed by disk diffusion method, and minimal inhibitory concentration (MIC) of isolates to colistin was determined by the E-test method. These isolates were typed by ERIC-PCR method, and the presence of mcr-1 and mcr-2 genes was investigated by PCR method. Results: Out of 712 nonduplicate Enterobacteriaceae, 470 isolates, including 351 (74.7%) E. coli and 119 (25.3%) K. pneumoniae, were detected. The results of antibiogram tests showed that most of the isolates (81.3%) were resistant to ceftazidime; however, the most susceptibility among of E. coli and K. pneumoniae isolates was observed (81.5%) to colistin. The typing results by ERIC-PCR method showed 36 and 23 fingerprint patterns for colistin-resistant E. coli and K. pneumoniae strains, respectively. Among 64 (13.6%) colistin-phenotypically-resistant Enterobacteriaceae, 8 isolates (1.7%) had mcr-1 gene. These 8 isolates were attributed to E. coli and K. pneumoniae with 6 and 2 isolates, respectively. Whereas no isolates carrying the mcr-2 gene was found. These colistin-resistant isolates displayed colistin MIC values >2 μg/ml in the antibiotic concentration by E-test method. Conclusion: Spreading of Enterobacteriaceae strains harboring plasmid-mediated mcr could fail the colistin-included therapy regimen as the last line of treatment against multidrug-resistant bacterial infections.

The emergence of multidrug-resistant Escherichia coli has become a great challenge in treating nosocomial infections. The polymyxin antibiotic colistin is used as a 'last-line' therapy for such strains, but resistance to colistin is increasingly emerging all over the world. In this study, we investigated lipopolysaccharides (LPS) of colistin-resistant isolates and examined mutations in lpx genes in strains not harbouring mcr genes. We examined 351 clinical E. coli isolates with 38 showing reduced susceptibility to colistin. These isolates were collected from different clinical specimens including blood, urine, and wounds, but no stool. After confirmation of the isolates via a BD Phoenix-100 system (Becton Dickinson, USA), we performed antimicrobial susceptibility tests to characterize the resistance pattern of these isolates to different classes of antibiotics, using the disk diffusion test. The Minimum Inhibitory Concentration (MIC) of colistin was determined using E-test strips. The presence of mobile colistin resistance (mcr-1 and mcr-2) genes was tested for all isolates. LPS (including lipid A) were extracted from all isolates and associated lpx genes analyzed by PCR and sequencing. Among the 38 clinical E. coli isolates with reduced susceptibility to colistin, 52% were resistant to colistin. The MICs of colistin ranged from 0.5 μg/ml to >256 μg/ml. Within the 20 colistin-resistant strains, six isolates carried the mcr-1 gene, but not mcr-2. Heterologous expression of the mcr-1 gene in susceptible E. coli DH5α increased the MIC of colistin by eight-fold. The remaining 14 isolates, were negative for both mcr genes. Six isolates were further negative for LPS production and five showed rough LPS phenotypes. Here we present evidence that loss of LPS or lipid A-deficiency can lead to colistin-resistance in clinical E. coli isolates not harbouring mcr genes.

Currently, few studies have investigated the mechanisms of resistance to colistin in Iran. The aim of this study was to investigate mcr -harbouring Escherichia coli dissemination in livestock and sewage in Iran. A total of 115 samples from cows ( n = 38), chickens ( n = 47) and urban sewage samples ( n = 30) were collected. The presence of genes including mcr1–6 and ampC β-lactamase ( bla MOX , bla CIT , bla DHA , bla ACC , bla EBC , bla FOX ) for colistin-resistant isolates was investigated by multiplex PCR method. Genetic association of colistin-resistant strains was also evaluated by ERIC PCR. Sixty-five isolates were identified as E. coli . Meaningless were resistant to colistin. The highest (26.1%) and lowest (3.07%) resistance were shown to ampicillin and meropenem respectively. Among the three colistin-resistant isolates, 2 (66%) were multidrug resistant, with one of them being mcr-1 positive and the other one positive for DHA ampC β-lactamase gene. No mcr2–6 genes were found. Minimum inhibitory concentration of mcr -producing isolate was 4 mg/L by microbroth dilution. This study reports, first the detection of mcr-1 in E. coli from farm animals in Iran, a finding that is indicative of a global distribution of this plasmidic element and threatning the use of colistin as a last resort antibiotic. No clonal relationship was observed between the colistin-resistant E. coli isolates by ERIC-PCR. Monitoring the presence of these strains in animal sources help as to controlling the spread of resistance genes from animal to human is vital.

Background: The Cronobacter genus is a member family of the Enterobacteriaceae The isolates of C. sakazakii have been suggested to be responsible for fatal neonatal infections, which gives rise to sepsis, necrotizing enterocolitis, and meningitis, with a high mortality rates. The aim of the present study was to investigate the antimicrobial susceptibility and biofilm formation of C. sakazakii isolates from neonatal sepsis in Southwestern Iran.Results: During the period of study, 734/1045 bacterial positive growth samples were collected from patients. Overall, from 734 bacterial positive growth samples 120 isolates were C. sakazakii based on culture, biochemical tests and PCR amplification. seventy-four (61%) neonates had primary sepsis and (33%) had late sepsis. Regarding birth bodyweight, (22%) neonate weighted below 1000 gr, 61 (50%) between 1500 and 2500, and (26%) more than 2500 gr. In case of C. sakazakii isolates, the highest resistance rates belonged to Ampicillin (70%), followed Amoxicillin (%59) and Ampicillin/sulbactam (83%). However, C. sakazakii had low levels resistance to cefepime and tetracycline. In total, of the 120 isolated bacteria, (70%) were biofilm producers, of which, (37%) produced strong biofilms, (15%) produced moderate biofilms, (17%) were weak biofilm producers and (28%) were not biofilm producers.Conclusion: Taken together, the high rate of C. sakazakii in neonates was high in the NICU. Age, higher birthweight, and caesarian delivery were the most remarkable risk factors for C. sakazakii. The majority of C. sakazakii strains were hospital-associated, which is the indication of NICU admission patterns. Our findings suggest that the active surveillance of neonates for C. sakazakii is required to be considered as a part of strategies to detect importation and prevent transmission of C. sakazakii within the NICU.