Carbapenem resistance and phenotypic detection of carbapenemases in clinical isolates of acinetobacter baumannii.

Background and Objectives: Multidrug-resistant Acinetobacter baumannii (MDR-Ab) reported worldwide has become one of the most difficult nosocomially acquired Gram-negative pathogens to control and treat. The clinical utility of carbapenems is under threat with the emergence of acquired carbapenemases, particularly Ambler class B metallo-lactamases (MBL). Because of the global increase in the occurrence and dissemination of MBLs, early detection is critical. This study was undertaken to detect resistance to carbapenems in clinical isolates of A. baumannii from hospitalized patients by both disk-diffusion and minimum inhibitory concentration (MIC) methods and to assess the rate of carbapenemase and MBL production among the isolates. Materials and Methods : A. baumannii were identified from various clinical samples and antibiotic susceptibility profile was determined by the standard disk-diffusion method. Meropenem-resistant strains were tested further by agar dilution MIC for meropenem. Resistant isolates were screened for carbapenemase production by the modified Hodge test and positive isolates were further checked for metallo-β-lacatmase production by the EDTA disk synergy test. Results : 42 isolates (31.81%) showed resistance to meropenem by the disk diffusion method. 47.6% were carbapenemase positive by the modified Hodge test and 19% were MBL producers phenotypically by the EDTA disc synergy test (EDS). These meropenem-resistant isolates were resistant to most of the other antibiotics tested. These 42 isolates were recovered mostly from patients admitted to intensive care units. Four isolates of the A. baumannii complex were pan drug resistant and showed resistance to even tigecycline and polymyxin B. Conclusion : Carbapenem resistance has been increasingly reported, necessitating their detection. This study reports simple, carbapenemase, and MBL detection method that can be easily incorporated into the daily routine of a clinical laboratory.

An increase in enteric fever cases due to Salmonella Paratyphi A in & around Chandigarh.

BACKGROUND & OBJECTIVE: Enteric fever is a major public health problem in India. It is classically caused by Salmonella enterica serotype Typhi. Salmonella enterica serotype Paratyphi A which had been reported less frequently from cases of enteric fever has shown an increasing trend since 1996 in India. There is also variation in the antimicrobial susceptibility of Salmonella Paratyphi A from different parts of the country. An attempt is therefore made to study the rate of isolation and antimicrobial susceptibility pattern of Salmonella Paratyphi A from cases of enteric fever coming to a tertiary care hospital at Chandigarh. METHODS: The blood samples of patients suspected of having enteric fever and admitted to Government Medical College and Hospital, Chandigarh, from January 2006 to April 2007 (11,240) were processed by conventional methods. Antimicrobial susceptibility was tested by Kirby-Bauer disc diffusion method. The minimum inhibitory concentration to two antibiotics- ciprofloxacin and chloramphenicol was determined by agar dilution technique. Simultaneously, retrospective analysis was done from January 2003-December 2005 to study any difference in the incidence and antimicrobial susceptibility pattern of Salmonella Paratyphi A among enteric fever patients. RESULTS: Of 305 total isolates, 231 were S. Typhi and 84 S. Paratyphi A rise. The number of Salmonella Paratyphi A cases rose from 27 in 2006 (34.18%) to 13 (40.63%) in four months of 2007. All were sensitive to ciprofloxacin and cefotaxime but MIC to ciprofloxacin was raised (0.125-0.5 microg/ml). Resistance to nalidixic acid was 92.5 per cent. Chloramphenicol sensitivity re-emerged with 90 per cent isolates sensitive to it while sensitivity to ampicillin dropped (72.5%) as compared to previous years. Only one isolate was multi-drug resistant. INTERPRETATION & CONCLUSION: The present study conferencing Salmonella Paratyphi A as the rapidly emerging pathogen of enteric fever. With increasing resistance to fluoroquinolones and possibility of re-emergence of sensitivity to chloramphenicol, the policy of empirical treatment of enteric fever needs to be rationalized.