Genotypes and cephalosporin susceptibility in extended-spectrum beta-lactamase producing enterobacteriaceae in the community.

INTRODUCTION: Infections from extended spectrum beta lactamases (ESBLs) producing enterobacteriaceae are increasingly being reported in the community setting. These infections are often multidrug resistant, with clinical and epidemiological implications, and necessitate surveillance measures based on local data. In the present study ESBLs genotypes were correlated with susceptibility to cephalosporins among ESBL-producing Escherichia coli and Klebsiella pneumoniae isolates acquired in the community.

METHODOLOGY: We investigated 28 E. coli and 24 K. pneumoniae isolates by PCR for the presence of blaSHV, blaCTX-M, and blaTEM. Minimum inhibitory concentration (MIC) for cephalosporins was determined by use of E-tests.

RESULTS: blaCTX-M was detected in 46 (88.5%), blaSHV in 13 (25%) and blaTEM in18 (34.6%) of the isolates. Nineteen (36.5%) isolates had more than one genotype detected. Urine specimens provided most of the ESBL-producing isolates (71%) followed by respiratory specimens (11%). MIC50 for cefotaxime, ceftazidime, and ceftriaxone were at 60 µg/ml, 13 µg/ml, and 139 µg/ml, respectively. There was a statistically significant association (p-value = 0.017) between blaSHV and resistance to ceftazidime. Though other associations could be seen among the genotypes and susceptibility profiles of the three drugs, they were not statistically significant. Twenty-four (52.2%) of the blaCTX-M isolates were sensitive and nine (19.6%) resistant to ceftazidime. For cefotaxime, 29 (63%) of blaCTX-M isolates were resistant and two (4.3%) were sensitive.

CONCLUSION: The predominant ESBL genotype in the local community-acquired infections is blaCTX-M , most of which involved the urinary tract. ESBL genes elevated MICs for the cephalosporins, but only blaSHV could predict resistance to ceftazidime.