Background: The incidence of carbapenem-resistant enterobacterales (CRE), Escherichia coli and Klebsiella pneumoniae increased twofold and tenfold within the past 20 years, respectively. CRE is resistant to most antibiotics and monotherapy cannot provide greater than 90% coverage. Combination antimicrobial regimen is introduced to increase the susceptibility rate and to recommend clinicians to make more informed decision in the selection of empirical therapy.

Materials and Methods: Cross-sectional study on carbapenem-resistant E. coli and carbapenem-resistant K. pneumoniae isolated from blood, sputum, and urine of adult inpatients in Naresuan University Hospital were examined for 24 months, between January 1, 2018 and December 31, 2019. The susceptibility data were formulated in accordance with the Clinical and Laboratory Standards Institute M39 guidelines and the combination antibiogram was developed. Chi-square test and Fisher’s exact test were used to determine the differences in susceptibility rates.

Results: Forty-three isolates of the carbapenem-resistant E. coli and 208 isolates of the carbapenem-resistant K. pneumoniae were included for the analysis. More CRE organisms were found in the Internal Medicine than in the non-Internal Medicine wards. Monotherapy regimen with amikacin was shown to cover 97.67% of the E. coli CRE in vitro and when used as an additional agent as meropenem plus amikacin, imipenem plus amikacin, piperacillin-tazobactam plus amikacin, or levofloxacin plus amikacin, which all the percent susceptible increased to 97.67% (p<0.001). The K. pneumoniae CRE data showed that only 1.92% was susceptible to meropenem. Meropenem plus gentamicin, imipenem plus gentamicin, piperacillin-tazobactam plus gentamicin and levofloxacin plus gentamicin could increase the percent susceptibility but to less than 90% with p<0.001.

Conclusion: Aminoglycosides are the proposed addition for the empiric antimicrobial combination therapy to treat possible CRE infections. Meropenem plus amikacin, imipenem plus amikacin, piperacillin-tazobactam plus amikacin, or levofloxacin plus amikacin are proposed to use against E. coli CRE. No combination therapy is recommended for K. pneumoniae CRE.

Keywords: Enterobacteriaceae; Carbapenem-resistant Klebsiella pneumoniae; Carbapenem-resistant Escherichia coli; CRE; Antimicrobial susceptibility; Combination antibiogram

DOI: 10.35755/jmedassocthai.2022.05.13304

Received 13 December 2021 | Revised 14 February 2022 | Accepted 22 February 2022