Clinical, phenotypic and genotypic profile of carbapenem resistant gram negative infections in intensive care units

Abstract

Carbapenems are currently the only active beta-lactams effective against the ESBL producing pathogens; this has led to an increase in their use not only for documented infections but also for empirical treatment of acquired infections in ICU patients. Thus, there is a selective pressure for carbapenem resistance in intensive care units of tertiary care hospitals. Carbapenem resistant infections are associated with high morbidity & mortality. 1. To screen for carbapenem resistance among gram negative infections in ICU patients by disc diffusion & confirmation by Vitek 2 system; 2: To detect the carbapenemase production by phenotypic methods; 3: To confirm the presence of resistant gene by PCR; 4: To find out the attributable risk factors from the clinical history of such patients; 5: To follow up & estimate mortality rate in such infections and its statistical correlation A total of 160 gram negative isolates [E.coli(71), Klebsiella(63), Acinetobacter(10), Pseudomonas(9) and Enterobacter(7)] from patients of various intensive care units were screened by disc diffusion out of which 53(33.12%) were carbapenem resistant. Resistant isolates were further tested by Vitek 2 system for determination of MICs, Modified Hodge test(MHT) and Combined Disc test(CDT) for carbapenemase production and subjected to multiplex PCR for detection of resiatant gene i.e., bla NDM-1, bla VIM, bla IMP and bla KPC. Follow up of all the cases till the end of hospital stay was done and mortality rate was calculated.Results: 53 isolates(33.12%) were carbapenem resistant, 17 isolates were MHT positive while 39 were CDT positive. 24 isolates [E.coli(12), Klebsiella(7), Acinetobacter(3), Pseudomonas(1) and Enterobacter(1)] showed the presence of NDM-1 gene on PCR. Gentamicin(35%), Amikacin (45%), Tigecycline(88%) & Colistin(100%) were sensitive for carbapenem resistant GNBs. Mortality in carbapenem sensitive infections in ICUs was 21% whereas resistant infections showed 37% (p value <0.05).Conclusion: 45% of carbapenem resistance is due to presence of NDM-1 gene, E.coli was the commonest isolate. Other mechanisms of resistance such as excessive ESBL production, porin loss may be responsible for resistance in remaining isolates. Effective infection control measures should be taken to prevent the spread of these super bugs in a ICU.