Phenotypic Identification, Frequency Distribution and Antibiogram of Carbapenemase Producing Enterobacteriaceae in Clinical Isolates

Abstract

Objective: To differentiate between Ambler class A, B and D of carbapenemase-producing Enterobacteriaceae by using simple phenotypic methods that can be carried out in the laboratory without requiring any specialised techniques.

Study design: Cross-sectional study.

Place and duration of study: Microbiology Department, Army Medical College, NUST, Islamabad, from November 2015 to November 2016.

Methodology: Clinical specimens were subjected to identification of Enterobacteriaceae by colony morphology and API 20 E. Carbapenem resistance was detected by applying meropenem disc (10 µg) by disc diffusion method according to CLSI (Clinical Laboratory Standard Institute) criteria. Carbapenemase production among Enterobacteriaceae was detected by Modified Hodge test. Phenotypic methods, Phenylboronic acid (for Class A KPC producing Enterobacteriaceae) and EDTA inhibition tests (for Class B MBL producing Entrobacteriaceae) were applied. Presence of OXA 48 was detected by phenotypic method using imipenem 10 µg, EDTA and PBA discs. Antibiotic susceptibility was determined by Kirby-Bauer disc diffusion method.

Results: Forty-three out of 45 (95.45%) were carbapenemase producers. Thirty-eight out of 43 (88.3%) were KPC producers and 4 out of 43 (11.62%) were MBL producers. All KPC producers were Klebsiella pneumoniae. Among five MBL producers, one each (20%) was Enterobacter cloacae and Escherichia coli and 3 (60%) were Klebsiella pneumoniae. All MBL producers were resistant to aztreonam and amoxicillin/clavulanate. Two of the KPC producing Klebsiella pneumoniae were pan-drug resistant (resistant to colistin and tigecycline). Two were non-carbapenemase producers.

Conclusion: Enterobacteriaceae strains producing KPC-type carbapenemase were the most prevalent (88.3%) in the studied healthcare setup.