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Colistin-resistance detected via mcr-1
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The mcr-1 gene may be used as a marker of colistin-resistance in Enterobacteriaceae isolates, according to data presented at ECCMID 2016.
“Colistin (polymyxin E) has broad-spectrum activity against most species of the family Enterobacteriaceae and is considered as one of the last resort antibiotics for the treatment of gram-negative pathogens,” researchers wrote. “The emergence of colistin-resistant carbapenem-resistant Klebsiella pneumoniae has led to an international pandemonium. [WHO] has warned its member nations against the return to the pre-antibiotic era. Action plans are needed to respond to this emerging threat of antimicrobial resistance.”
Mcr-1 prevalent in colistin-resistant isolates
Findings previously published in The Lancet Infectious Diseases showed colistin resistance was traced to the mcr-1 gene. For the current study, researchers sought to determine the value of using mcr-1 for the rapid detection of resistance. They examined K. pneumoniae isolates, including two blood specimens, one tissue sample, one urine specimen, one sample of peritoneal fluid and one wound swab, collected at a tertiary teaching hospital in Malaysia between February 2015 and August 2015.
All isolates were screened for resistance to imipenem and meropenem with VITEK2 (bioMérieux), resistance to ertapenem with a disc diffusion technique, and resistance to colistin by Etest. According to the researchers, all isolates were resistant to imipenem and/or meropenem, or showed monoresistance to ertapenem. In addition, all isolates were resistant to amoxicillin-clavulanate, ampicillin-sulbactam, ceftriaxone, ciprofloxacin, piperacillin-tazobactam and amikacin. Five isolates also were resistant to trimethoprim-sulfamethoxazole.
The researchers reported that the mcr-1 gene was detected in five of the seven isolates. The mechanism of resistance for colistin in the other two isolates was not determined; however, the researchers wrote that other mechanisms may include inactivation of the mgrB gene, upregulation of the PhoP/PhoQ signaling system, activation of the PmrA-regulated pmrHFIJKLM operon, and the presence of ArnB. Researcher Kartini Abdul Jabar, MBChB, of the department of microbiology at the University Malaya, told Infectious Disease News that the data are not yet finalized, and sequencing results are pending.
“We support the evidence that the detection of the mcr-1 gene in colistin-resistant Enterobacteriaceae may be useful for rapid detection in clinical isolates,” the researchers wrote. “Rapid detection would assist in patient management and in enforcing strict infection control measures.”
Researchers develop assay for rapid detection of mcr-1
During another presentation, researchers discussed a new real-time PCR assay they developed to rapidly detect mcr-1. The assay’s performance was assessed with a mcr-1–containing Salmonella isolate, a panel of 26 mcr-1–containing isolates obtained from livestock fecal specimens, and surveillance isolates collected from 39 patients treated at a tertiary hospital in the Netherlands. The assay correctly identified all mcr-1–containing isolates, and also detected mcr-1 in Escherichia coli isolates obtained from a clinical culture of a typically sterile site and from two of 18 patients with colistin-resistant E. coli.
Mcr-1, however, was not detected in patients with colistin-resistant Klebsiella, Enterobacter, Pseudomonas, Vibrio, Salmonella, Aeromonas, and Acinetobacter isolates.
“The newly developed real-time PCR assay specifically detects the mcr-1 gene and was validated to accurately confirm the presence of this new gene in colistin-resistant clinical isolates,” the researchers concluded. “This molecular assay may facilitate rapid mcr-1 identification in stool specimens and can therefore be important to further improve clinical management and infection control.”
References:
Jabar KA, et al. Abstract 7485. Presented at: European Congress of Clinical Microbiology and Infectious Diseases; April 9-12, 2016; Amsterdam.
Liu Y-Y, et al. Lancet Infect Dis. 2015;doi:10.1016/S1473-3099(15)00424-7.
Nijhuis R, et al. Abstract 7471. Presented at: European Congress of Clinical Microbiology and Infectious Diseases; April 9-12, 2016; Amsterdam.
Disclosure: Infectious Disease News was unable to confirm relevant financial disclosures at the time of publication.