Epidemiology of bacterial colonization at intensive care unit admission with emphasis on extended-spectrum β-lactamase- and metallo-β-lactamase-producing Gram-negative bacteria - an Indian experience

An important risk factor for nosocomial infection in an intensive care unit (ICU) is prior colonization. This study was undertaken to determine the spectrum of bacterial colonization and predisposing risk factors in patients being admitted to an ICU in India, with special emphasis on extended-spectrum beta-lactamase (ESBL)- and metallo-beta-lactamase (MBL)-producing Gram-negative bacteria. Nasal, oral and rectal swab samples were collected and processed for isolation of ESBL-producing Gram-negative bacteria and MBL-producing Pseudomonas aeruginosa and Acinetobacter species. Bacterial colonization (of one or more sites) on admission was detected in 51 out of 96 patients included in the study. Non-fermenters, i.e. P. aeruginosa and Acinetobacter baumannii, were the most common colonizers, present in 37 patients, with simultaneous colonization in 12 patients. A total of 16 patients were colonized with MBL-producing members of the family Enterobacteriaceae, out of which 11 isolates (from 5 patients) were also carrying ESBL-encoding genes. As for MBLs, most of our patients have shown colonization with ESBL-producing bacteria. On admission, 47 of 51 patients (92%) have been colonized by ESBL-producing members of the family Enterobacteriaceae, at one or more of the three anatomical sites. The most common MBL subtype was bla(IMP) (51.56%), whereas bla(CTX) was the most common gene (84.9%) identified among ESBL producers. Risk factors for colonization on admission to the ICU were hospitalization for more than 48 h, use of >= 3 groups of antibiotics, co-morbidities and mechanical ventilation for more than 48 h prior to ICU admission. There is an increasing incidence of MBLs and ESBLs in the Indian population. The identified risk factors can be used as a guide for empiric antibiotic therapy targeted to these resistant bacteria.