Non-fermenting Gram-negative bacilli: Phenotypic identification and a correlation between biofilm formation and antibiotic susceptibility testing

Abstract

Non-fermenting Gram-negative bacilli (NFGNB) are the primary cause of nosocomial infections worldwide. They produce biofilm, which is life-threatening if not monitored by proper surveillance and treatment. Thus, this study was conducted to identify the non-fermenters, to analyse their antimicrobial susceptibility and biofilm formation. The cross-sectional study was done in the department of microbiology at Saveetha Medical College and Hospital. Identification was made based on P.C. Schrekenberger matrix. Biofilm formation was done by microtitre plate method and the antimicrobial susceptibility testing was done by Kirby Bauer disc diffusion testing. In this study, 3500 samples were cultured, out of which 240 yielded NFGNB. Predominant (102) were Pseudomonas aeruginosa, followed by other non-fermenters. 99 multidrug resistant and 19 pan drug-resistant strains were isolated. 19 were weak, 19 were moderate and 97 were strong biofilm producers. Biofilm producers were highly sensitive to Amikacin. In this study, 13 species of non- fermenters were isolated. After performing different biochemical tests, the study could derive a simple flowchart for identification with reference to P.C. Schreckenberger matrix. Moreover, there is no significant correlation between the antibiotic susceptibility and biofilm formation. Hence, it can be stated that all biofilm producers will not show resistance to antibiotics. However, after the biofilm has been produced, because of certain factors like less penetration power etc., the antibiotic susceptibility will vary. Thus, the comprehensive surveillance and monitoring of these organisms are mandatory to control the hospital-acquired infections.