AmpC beta-lactamase producing bacterial isolates from Kolkata hospital.

BACKGROUND AND OBJECTIVE: The widespread use of beta-lactam antibiotics has lead to the development of resistance to this group of antibiotics in bacterial pathogens due to beta-lactamase production. Information on such pathogens is not available from eastern region of India. This study was undertaken to determine the AmpC beta-lactamase production in pathogens isolated from hospitalized patients in Kolkata. METHODS: Non-repeat clinical isolates (284) from pus, urine, sputum and other clinical specimens of hospitalized patients were taken. Disk agar diffusion (DAD) and minimum inhibitory concentration (MIC) with different beta-lactam antibiotics, and double disc synergy test (DDST) with clavulanic acid and sulbactam were done. Disk antagonism test (DAT) and three-dimensional extract test (TDET) were conducted for phenotypic confirmation of AmpC and inducible AmpC beta-lactamase production. Nitrocefin spot test and microiodometric assay of beta-lactamase were also performed. RESULTS: Twenty seven isolates were found to be resistant to cefoxitin, a alpha-methoxy-beta-lactam. Of these, 19 were observed to be AmpC beta-lactamase producers and 4 were inducible AmpC beta- lactamase producers by DDST, DAT and TDET. Remaining 4 were non AmpC beta-lactamase producers. Of the 23 AmpC beta-lactamase producers, the distribution of different species was as follows: Escherichia coli 11 (47.8%), Pseudomonas aeruginosa 4 (17.3%) Klebsiella pneumoniae 3 (13%), and Klebsiella aeruginosa 1 (4.3%). INTERPRETATION AND CONCLUSION: Our finding showed 6.7 per cent AmpC beta-lactamase and 1.4 per cent inducible AmpC beta-lactamase producing clinical isolates from Kolkata. AmpC beta-lactamase producing bacterial pathogens may cause a major therapeutic failure if not detected and reported in time.

Intraspecies transfer of a chloramphenicol-resistance plasmid of staphylococcal origin.

BACKGROUND & OBJECTIVES: The emergence of antibiotic-resistant bacteria is a phenomenon of concern to the clinician as well as to the pharmaceutical industry, because it is the major cause of failure in the treatment of infectious diseases. The genetic exchange of plasmids containing antibiotic resistant determinants (R-plasmids) between organisms of the same or different species is believed to play a crucial role in the evolution of antibiotic resistant bacteria. Staphylococcus aureus is well known for its multi-drug resistance (MDR). This work was undertaken to study the intraspecies transfer of a chloramphenicol (C) resistance staphylococcal R-plasmid among different clinical isolates of S. aureus. METHODS: From a MDR S. aureus MC524 strain, a small plasmid pMC524/MBM was isolated. Lysostaphin lysis and sucrose mediated detergent lysis were used for plasmid preparation. Agarose gel electrophoresis, transformation experiments, Southern blotting and hybridization were done. Restriction endonuclease (RE) digestions were performed. RESULTS: pMC524/MBM, which codes for C resistance could be transferred into some C sensitive clinical strains of S. aureus. The size and the RE digestion patterns of the plasmids isolated from the S. aureus transformants were identical to those of pMC524/MBM. INTERPRETATION & CONCLUSION: These results suggest that pMC524/MBM, without any modification is capable of transferring, maintaining, replicating and expressing itself in different clinical strains of S. aureus and hence may be responsible for the spread of C resistance.