Background and Objectives: Bacterial isolates from Intra–abdominal infections, in particular, peritonitis and their unpredictable antimicrobial resistance patterns, continue to be a matter of concern not only globally but regionally too. An attempt in the present study was made to study the patterns of drug resistance in bacterial isolates, especially gram negative bacilli in intra–abdominal infections (IAI) in a tertiary care centre. Materials and Methods: From 100 cases of peritonitis, identification of isolates was done as per recommended methods. Antimicrobial susceptibility and extended–spectrum Beta–lactamase (ESBL) testing were performed following the CLSI guidelines. Results: In this study, the most common pathology was acute appendicitis which accounted for 49%.Peritonitis accounted to about 35% followed by  Intra abdominal abscess with 9 % and Pelvic abscess with 4%.Out of these 100 cases, 32 (32%) cases were culture positive and 68 (68%) cases were Culture negative. Of the 32 culture–positive cases, Escherichia coli was isolated from 7 (21.9%) cases followed by Proteus vulgaris 6 (18.8%), Proteus mirabilis  5 (15.6%),Klebsiella oxytoca 5 (15.6%)and Klebsiella pneumoniae 4(12.5%).The overall prevalence rate of ESBL was 31.25%.Of which 2(20%)isolateswereESBLpositiveandProteusspp.5(50%)wereESBLpositive.Among Klebsiella isolates, 30 % (n = 3) were ESBL positive.Tigecycline and Colistin appeared as the most active drugs against ESBL E.coli and Klebsiella spp.Conclusion:Knowing the prevalent pattern of antimicrobial resistance is an important issue especially when gram negative isolates continue to exhibit rampant resistance to various currently in use antimicrobial agents. Therefore, empirical selection of the right kind of anti–microbial therapy is significant in reducing morbidity and mortality.