Non-fermenting gram negative bacilli (NFGNB) are known to account for nearly 12-16% all bacterial isolates from a clinical microbiology laboratory. The most common infections caused by these organisms were septicemia, pneumonia, urinary tract infections, surgical site infections, wound infections, osteomyelitis, etc. As multidrug resistances being very common and increasing among NFGNB and Pseudomonas and Acinetobacter being the most predominantly isolated NFGNB and its resistance towards colistin and imepenam type of antimicrobials is of major concern. To isolate, identify and characterize the prevalence of NFGNB along with their antimicrobial sensitivity pattern among the patients attending a tertiary care centre in Tamilnadu. A prospective study was conducted in our hospital for a period of two years from Jan2012 to Dec 2013. A total of 5052 clinical specimens were received during the above said period. Out of this 1699 were urine specimens, 315 were pus, 988 blood, 1470 respiratory samples which includes sputum and tracheal secretions, and 580 were other than the above mentioned samples (body fluids, stool, tissue biopsy, vaginal swabs etc). The isolates that showed non lactose fermenting (NLF) colonies on Mac conkey agar and failed to acidify the butts of triple sugar iron (TSI) agar were provisionally considered as NFGNB. Antimicrobial sensitivity was determined by Kirby Bauer disc diffusion method on Muller Hinton agar (MHA). Antibiotic discs were placed and plates were incubated at 37°C for 18‑24 hrs. Results were interpreted in accordance with central laboratory standards institute (CLSI) guidelines. In our study out of 5052 clinical samples 517 samples had shown positive for non-fermenting gram negative bacilli with a prevalence of 10.2%. Pseudomonas aeruginosa (53.9%) was found to be the most common organism isolated from the clinical samples followed by Acinetobacter baumanni (36.7%). The antibiotic sensitivity pattern varies for different clinical samples but colisitin and imipenam had shown the maximum sensitivity pattern for all the clinical samples. The sensitivity pattern for gentamicin, ceftazidime and ciprofloxacin was in the range of 30 - 70% which means highest resistance was seen with these antimicrobials. It is important to establish the clinical relevance of the isolated NFGB, before are considered as pathogens to avoid unnecessary usage of antibiotics and emergence of drug-resistant strains.

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