Emergence of In-Vitro Colistin and/or Tigecycline resistance among Carbapenemase producing Gram negative Bacteria in nosocomial set up

Resistance to Tigecycline and/or Colistin among nosocomial pathogens is an emerging problem. Objective of the study was to record the drug susceptibility pattern of carbapenemase producing gram negative bacteria causing various nosocomial infections. This study was performed over six months from January to June2013 with 167 nonrepeat culture isolates causing various nosocomial infections.Antimicrobial Susceptibility testing was performed as per CLSI guidelines (2013) in Modified Kirby-Bauer technique. Carbapenemase production was Phenotypically confirmed by Modified Hodge test. Out of total isolated 37 Carbapenemase producers, 6 were resistant to Tigecycline but sensitive to Colistin (16.21%) and 2 were sensitive to Tigecycline but resistant to Colistin (5.04%). Four isolates were resistant to both the drugs (10.81%). As a whole, 12 strains were resistant to Tigecycline whereas 6 were resistant to Colistin. Out of 17 Carbapenemase producing Klebsiella pneumoniae, 4 were resistant to Tigecycline (23.8%). All of them were susceptible to Colistin. Isolated Klebsiella oxytoca was resistant to Tigecycline but susceptible to Colistin. Isolated E.coli were susceptible to Tigecycline and resistant to Colistin All of the Carbapenemase producing Acinetobacter were sensitive to both Tigecycline and Colistin. Four Pseudomonal isolates were resistant to both Colistin and Tigecycline and one was resistant to Tigecycline but susceptible to Colistin. Out of total 12 Tigecycline resistant isolates, 4 (33.33%) were susceptible to aminoglycosides. All isolates were susceptible to Polymyxin-B, the only reliable therapeutic option.