Prevalence of Colistin Resistance among Third Generation Cephalosporins- or Carbapenem-Resistant Enterobacteriaceae Isolated from Clinical Specimens in Ratchaburi Hospital, Thailand

Abstract

    Currently, carbapenem and colistin resistant Gram negative bacilli are increasingly reported worldwide. Moreover, mcr-1, a plasmid-mediated colistin resistant gene, has recently been reported. The finding has brought clinical concern because colistin is the last-resort antibiotic for the treatment of extensively drug-resistant Gram-negative infections. Therefore, the prevalence data of colistin-resistant bacteria in different areas of the country can be used to support the prevention and control measures of these organisms. The objectives of this research were to determine the prevalence of colistin resistance and investigate the mcr1 genes among third generation cephalosporin- or carbapenem-resistant Enterobacteriaceae isolated from patients in Ratchaburi Hospital during June 2016 to May 2017. A total of 243, non-duplicated and non-intrinsic resistance to colistin, clinical isolates of third generation cephalosporins- or carbapenem-resistant Enterobacteriaceae were used in this study. The bacterial isolates were screened for colistin resistance using Mueller-Hinton agar containing 2 µg/mL of colistin. The colistin resistant isolates were determined the MIC of colistin using broth microdilution and the mcr-1 gene was investigated using PCR assay. Forty (16.5 %) of 243 third generation cephalosporins- or carbapenem-resistant isolates were resistant to colistin. These strains were mostly detected in surgery, medicine and ICU wards at 45.0, 37.5 and 10.0 %, respectively. Urine, sputum and pus/swab were the top three sources where 42.5, 27.5 and 15.0 %, respectively, of colistin-resistant isolates were detected. The colistin MICs of these isolates ranged from 4 to > 64 µg/mL. The mcr-1 gene was detected in 6 isolates, 5 from surgery and 1 from a medicine ward, in 3 pus/swab, 2 sputum and a blood sample, all of which were identified as Escherichia coli. The colistin MICs of the mcr-1 positive isolates ranged from 4 to 16 µg/mL. In conclusion, the prevalence of colistin resistance and the existence of mcr-1 gene in third generation cephalosporins- or carbapenem-resistant Enterobacteriaceae among patients in Ratchaburi Hospital would raise the awareness and proper use of antibiotics. The information could also be used as an input for prevention and control of the hospital spreading of these resistant organisms.