The rates of resistant microorganisms are increasing worldwide and getting more serious in developing countries. This study was carried out in department of Microbiology, SVIMS a tertiary care teaching hospital, to determine the frequency of Gram-negative bacteria isolated in various departments like intensive care units (ICU), medical and surgical wards and to study their resistance rates to selected antibiotics. Aerobic Gram-negative bacteria isolated from various wards were included in our study. Antibiotic susceptibilities to various antimicrobial agents were determined by Kirby-bauer disc diffusion test as per CLSI guidelines. A total of 6900 isolates were obtained during our study out of which 2960 isolates were multidrug resistant organisms. Escherichia coli were the most frequently isolated Gram-negative species (36.99%), followed by Klebsiella spp. (13.44%). Pseuodomonas aerusinosa, Acinetobacter spp. and Enterobacter spp. were the other commonly isolated organisms. High resistance rates were observed for all antimicrobials studied except cefaperazone-sulbatam (62.64%), meropenem (70%), aminoglycosides (64%) and polymixin B (98.6%) appeared to be the most active agent against the majority of isolates. Although resistance rates exceeded 50%, for ciprofloxacin (80%), cephalosporins (74.35%) and cotrimaxazole (65.65%) the above mentioned antimicrobials were found to be relatively effective. Extended-spectrumβ-lactamase (ESBL) production appeared to be a major mechanism of resistance to β-lactam antibiotics (35.33%). This study has yielded high rates of resistance in aerobic Gram-negative isolates from various departments. High resistance rates in our study engendered carbapenems or cefaperazone-sulbatam as empirical choice of therapy for ICUs in our study. IntroductionHealth care facilities, despite their apparent impact on patient outcome, have become high-risk areas for nosocomial infections. The patients in various departments of health care facility has a high risk of nosocomial infection and 20–25% of all nosocomial infections develop in ICUs.1,2 Infections due to Gram-negative organisms continue to be one of the leading causes of morbidity and mortality. This is a consequence of a complex interaction between the patient’s underlying disease, the severity of illness, the type of department, the duration of stay, and the number, type and duration of invasive devices and procedures.1 Medical care of these patients involves closer and more frequent contact with nurses, physicians, or technicians. Hand washing and asepsis may be overlooked in urgent conditions, which may further promote horizontal transmission.3 Empirical and frequent use of broad- spectrum antibiotics results in the selection of resistant strains. Thus the patient frequently experiences colonization and infections by resistant pathogens, which pose major clinical problems despite the introduction of new and potent antibiotics.3, 4Limited data are available concerning infection and antibiotic susceptibility of pathogens from various departments within a healthcare facility, although studies have yielded higher infection and mortality rates with greater antimicrobial resistance in other parts of the world 1, 5.This study was undertaken to determine the frequency of Gram-negative bacteria isolated in various departments of healthcare facility and to study their rates of resistance rates to selected antimicrobial agents.Materials and methodsThis is a record based retrospective study, carried out at the office of HICC (Hospital Infection Control Committee) and at the Department of Microbiology, Sri Venkateswara institute of medical sciences(SVIMS), tirupati, a tertiary care teaching hospital. The study included aerobic Gram-negative bacteria isolated from various departments from January to june 2019. The culture and identification was carried out on the clinical specimens received from ICU patients in the Department of Microbiology as a routine procedure according to the Standard Operating Procedures (SOP) of the department. Culture media used for isolation of these organisms were blood agar, MacConkey agar and chocolate agar. Identification was done based on the colony morphology and biochemical tests. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk-diffusion method and was reported according to Clinical Laboratory Standards Institute (CLSI) guidelines . Ten different antimicrobials, including imipenem, ceftazidime, cefaperazone-sulbactam, cefotaxime, piperacillin/tazobactam, meropenem, gentamicin, amikacin, cotrimaxazole, polymixin B on Mueller–Hinton agar. For each isolate, the name of the department, a patient identifier and the source of material were recorded. For the data analysis, resistance rates were reported using the CLSI breakpoints for the susceptible category in which moderately susceptible isolates were classified as resistant.6ResultsOut of 2920 samples, 1779 were from male patients and 1141 were from female patients.Composition of isolate pool by patientsA total of 2960 MDR isolates were obtained from positive cultures. Of these 60.1% were isolated from male patients and 39.9% were isolated from female patients. More than 50% (61.11%) isolates were reported from age group of 41-70years.Composition of isolate pool by body siteThe great majority of organisms were isolated from the urinary tracts (44.35%) followed by respiratory tract (18%); 17.5% of isolates were cultured from blood, 15% from pus samples.Majority of MDR isolates were reported from ICUs (35.81%) followed by medical wards (29.18%), surgical wards (20.97%) and outpatient departments (14.02%).Antibiotic susceptibility rates of isolatesHigh resistance rates were observed for all antimicrobials studied except for polymixin B antimicrobials (98.6%) (Table I). Carbapenems and Aminoglycosides appeared to be the active agents against the majority of gram negative isolates. Majority of carbapenem resistant isolates were reported from emergency department ICU (28.61%) in our study. Although resistance rates exceeded 50%, cefaperazone-sulbactam, amikacin and meropenem were found to be relatively effective. Cefaperazone-sulbactam appeared quite effective against the Escherichia coli, Enterobacter sp and Acinetobacter sp (>50%).