A decade of change in susceptibility patterns of Gram-negative blood culture isolates: a single center study.

BACKGROUND: Gram-negative bacteremia is one of the leading causes of mortality and morbidity in Indian hospitals. We hereby describe changing trends in Gram-negative isolates from blood cultures from a single center over a ten-year period.

METHODS: Antibiotic susceptibility patterns were collected for a total of 4128 non-repetitive blood culture isolates from 2003 to 2013. We analyzed clinically important Gram-negative isolates (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii) and their susceptibility pattern. A. baumannii was studied between 2009 and 2013 only.

RESULTS: There was a steady increase in extended-spectrum beta-lactamase (ESBL) production in E. coli (56% to 80%) and an even steeper increase in K. pneumoniae (50% to 81%). Susceptibility to carbapenems fell marginally for E. coli (p = .242) but significantly for K. pneumoniae (p = .000) and P. aeruginosa (.0005). All these changes were seen irrespective of the source of the isolate (outpatient, inpatient and critical care unit - CCU), with a statistically significant fall among CCU isolates of K. pneumoniae and P. aeruginosa. P. aeruginosa was more susceptible to carbapenems than beta-lactam /beta-lactamase inhibitors until 2009, but thereafter the pattern reversed. A. baumannii was isolated from the CCU only: 75% were resistant to carbapenems and susceptible only to polymyxin E and tigecycline.

CONCLUSION: There was a progressive increase in antimicrobial resistance in isolates of E. coli, K. pneumoniae, P. aeruginosa and A. baumannii isolated from blood cultures. ESBL production was seen in the majority of isolates of E. coli and K. pneumoniae. Carbapenem resistance in K. pneumoniae and E. coli is increasing rapidly. Resistance to even tigecycline and polymyxin E, antibiotics of last resort, has begun to emerge. There is an urgent need for antimicrobial stewardship and other measures to limit worsening of Gram-negative resistance in India.