Detection of Carbapenem and Colistin Resistant Gram-negative Bacteria in a Tertiary Care Hospital, Visakhapatnam, India

Aims: Among the most clinically significant multidrug-resistant bacteria are the carbapenemase-producing Enterobacteriaceae (CPE) which are detected all over the globe, with a marked endemicity according to enzyme type. These bacteria usually remain susceptible to polymyxins like colistin; however increasing use of colistin causes acquired colistin resistance which may now be added to the carbapenem resistance trait in Enterobacteriaceae. The present study was aimed to isolate and identify Gram-negative Enterobacteriaceae organisms from various clinical samples of patients suffering with various infections and to study the antibiogram of Gram-negative Enterobacteriaceae organisms with reference to carbapenem and colistin antibiotics.

Methodology: Different clinical samples collected from both in-patients and out-patients constituted the material for the study. Demographic variables of the patient were recorded include age, sex, type of patient (in-patient or out-patient) and type of samples. Standard microbiological techniques were used for the identification of pathogenic bacteria which include Gram staining, cultural and biochemical methods. Antibiotic susceptibility testing was performed according to Clinical Laboratory Standards Institute (CLSI) guidelines using Mueller-Hinton agar plates. Extended-spectrum beta-lactamase (ESBL) production was tested with the CLSI confirmatory test using Ceftazidime (30 µg) disc alone and in combination with Clavulanic acid (10 µg). The bacterial isolates which were resistant to imipenem through disk-diffusion method were regarded to be screening positive and were further confirmed by EDTA combined disc test. Modified-Hodge test and E-test method were used to identify the carbapenem and colistin resistant strains. Frequency and percentages were calculated for categorical and ordinal variables. Chi-square test was carried out and p-value ≤0.05 were considered statistically significant.

Results: Male predominance (59%) is seen while compared to females (41%). The maximum cases were reported in the age group 51-60 years (31%). Majority of the isolates like Klebsiella species (30.6%) followed by E. coli (25.9%) and few isolates reported were Proteus species (5.8%). Extended spectrum beta-lactamase production was identified in test isolates at a range of 95.2% by using ceftazidime/clavulanic acid combination antibiotic susceptibility test. The prevalence rate of metallo-beta lactamase isolates was quite high i.e. 66.6% and carbapenemase producers was 77.3%. The major isolates were Klebsiella spp. and E. colishows Metallo-beta-lactamase production.

Conclusion: The study helps the clinicians in choosing the correct antimicrobial agent which contribute not only to better treatment but their judicious use will also help in preventing the emergence of drug resistant strains which are still sensitive.