RESUMEN
Background & objectives: Plasmid mediated AmpC β-lactamase (PMABL) resistance in Escherichia coli and Klebsiella spp. is an emerging problem worldwide. Phenotypic methods are commonly used for detection of PMABL production in Gram-negative isolates, but molecular data about the prevalence of plasmid-mediated AmpC-type resistance at the national level are needed. Hence, a prospective study was undertaken to determine the occurrence of PMABL gene and its types among clinical isolates of E. coli and K. pneumoniae obtained from six different hospitals in India. Methods: A total of 241 nosocomial isolates of K. pneumoniae (n=109) and E.coli (n=132) from six geographically distant hospitals in India were included. These were screened for cefoxitin resistance. AmpC disk test and modified three dimensional extraction test were used for phenotypic detection of PMABL production. Molecular types were determined by a multiplex PCR. Results: Among the 241 isolates, 187 (77.5%) were found to be cefoxitin resistant (K. pneumoniae n=83, E. coli n=104). AmpC activity was detectable in 153 (63.4%) isolates, (K. pneumoniae n=69, E. coli n=84). By PCR, the plasmid encoded AmpC genes were found in 92 (38.1%) isolates and the molecular types of the genes detected predominantly were DHA, CIT followed by MOX and ACC types. Interpretation & conclusions: A high percentage of plasmid-encoded AmpC enzymes was noted in E. coli and K. pneumonia isolates obtained from different parts of the country. Phenotypic methods alone may not reflect the true number of PMABL producers. Genotypic methods need to be employed in national surveillance studies.
RESUMEN
AmpC â-lactamases are cephalosporinases that hydrolyze cephamycins as well as other extended-spectrum cephalosporins and are poorly inhibited by clavulanic acid. Although reported with increasing frequency, the true rate of occurrence of AmpC â-lactamases in different organisms, including members of Enterobacteriaceae, remains unknown. The present study was designed to determine the occurrence of AmpC enzyme-harbouring Gram-negative clinical isolates in a tertiary care hospital in Pondicherry state, South India. A total of 235 Gram negative clinical isolates were tested for resistance to cefoxitin, third generation cephalosporin (3GC) antibiotics, ampicillin, amikacin, co-trimoxazole, gentamicin, meropenem and tetracycline by disc diffusion method. Isolates found resistant to 3GC and cefoxitin were tested for the production of AmpC â -lactamases by three dimensional extraction method and AmpC disc method. Isolates found to sensitive to 3GC were subjected to disc antagonism test for inducible AmpC production. One hundred and thirty four (57 percent) strains were resistant to 3GC, among which 63(47 percent) were positive for plasmid-mediated AmpC beta lactamases production. Among the 101 strains sensitive to 3GC, 23 (22.7 percent) revealed the presence of inducible AmpC beta lactamases by disc approximation test. A total of 80.9 percent (51/63) of screen positive isolates were detected by Amp C disc test and 93.6 percent (59/63) by three dimensional extraction method. Out of the 86 AmpC producers, 67 (77.9 percent) were cefoxitin resistant .Inducible AmpC was not found in Esch.coli and Klebsiella spp. The AmpC producers also concurrently showed multidrug resistance pattern. AmpC producers were found to be prevalent in our hospital and though three dimensional extraction test detects AmpC better, the disk test is easier to perform routinely and is user- friendly.