Acinetobacter baumannii is a major cause of hospital acquired infections worldwide and is associated with resistance to routinely used antibiotics. Many clinical isolates of Acinetobacter baumannii  are found to be biofilm producers. Hence there is difficulty in treating patients with Multi Drug Resistant Acinetobacter baumannii  (MDRAB). This present study aimed to study antibiotic resistance of A. baumannii isolates  and to evaluate the biofilm formation of Acinetobacter baumannii  by Tube Method (TM) and Microtiter Plate Method(MTPM).In this study, 73 A. baumannii  isolates of various clinical specimens were evaluated. Confirmation was done through conventional methods. Testing for antimicrobial susceptibility was done by Kirby Bauer disc diffusion method. Biofilm formation was studied by TM and MTPM. Of the 73 isolates, 26(36%) were from urine, 19 (26%) from pus, 17 (23%) from sputum and 11 (15%) from other miscellaneous(body fluids excluding blood), out of which 81%(59/73) isolates were Multi Drug Resistant (MDR). 63% and 84% of isolates showed biofilm production in TM and MTPM, respectively. When comparing these two methods, MTPM assay was better than TM. Presence of a strong relationship between biofilm formation and MDRAB has been confirmed by the present study. Both methods used for detection of biofilm formation were found to be statistically significant. Sensitivity of MTPM was more than TM, which is supported by higher Positive Predictive Value of 87.5%. Therefore MTPM is a better method than TM and can be used as a screening method to detect biofilm production.

In view of the above perspective, the present study was carried out in a tertiary care hospital in Madurai to assess the prevalence of Glycopeptide resistant CoNS species in our region and also to assess the antibiotic of choice for them.

Introduction and Aim: The increasing resistance in colistin is a major concern. The aim of the study was to compare the methods to identify the prevalence of colistin resistance and antibiotic susceptibility patterns of colistin resistant strains isolates from blood, urine and sputum samples at all ICUs including NICU and PICU and wards.   Materials and Methods: A total of 1458 consecutive Gram-negative isolates were tested for colistin susceptibility by standard broth microdilution method, Mikrolatest method and VITEK 2 automation system. Intrinsically colistin resistant organisms including Proteus sps, Providencia sps, Serratia sps., and Morganella morganii were excluded. Enterobacteriaceae (e.g., Escherichia coli, Klebsiella), Pseudomonas   aeruginosa and Acinetobacter baumanii were included. The sensitivity, specificity, positive predictive value, negative predictive value of Vitek-2, BMD and Mikrolatest methods were compared.    Results: Sixteen (1.09%) colistin?resistant isolates were reported over 24 months. K. pneumoniae constituted 8(50%), E. coli 6 (37.5%) and Enterobacter cloacae 2 (12.5%) of the 16 resistant isolates. The sensitivity, specificity, positive predictive value, negative predictive value of Mikrolatest compared with that of VITEK2 were 87.5% vs 56.25%, 90.84% vs 82.65%, 9.58% vs 3.47%and 99.8% vs 99.3%, respectively for resistant isolates.  Mikrolatest shared good Category agreement of 1.24% with BMD Essential agreement was 1.5%. Comparing MICs of BMD with other tests, essential agreement was the lowest for the VITEK2, while the Mikrolatest MIC showed essential agreement greater than 1.5%. No errors and 100% categorical agreement (for E. coli, K. pneumoniae) were observed while comparing colistin susceptibility test results of the Mikrolatest MIC and BMD tests. The difference between the two methods in assessing colistin resistance were not statistically significant (P=0.89). Blood[37.5%] and pus[37.5%] samples recorded as the common sources of the isolate, followed by Urine [12.5%], and respiratory [12.5%) samples.   Conclusion: Automated VITEK, Mikrolatest MIC methods give variable susceptibility results and colistin should be prescribed only after Mikrolatest and BMD. K. pneumoniae and E. coli, the Mikrolatest showed better performance for isolates with ? 0.5 or ? 16 µg/mL MICs. For P. aeruginosa isolates, colistin resistant isolates must be confirmed Colistin resistance among Gram-negative bacteria, especially K. pneumoniae, is emerging in Indian hospitals. Re-evaluation is required of the methods available to address the numerous technical challenges associated with colistin susceptibility testing, and to determine which method yields the most meaningful results. These studies will provide critical information on the appropriate selection of colistin therapy, as well as evaluating novel and upcoming compounds with structure and properties similar to the Polymyxin.