Variable Efficacy of Clinically Important Biocides against Common Bacterial Pathogens Isolated from Tertiary Hospitals in Nigeria

Abstract

Aim: There has not been any critical assessment of the efficacy and choice of biocides/disinfectants used in various tertiary hospitals of Nigeria despite several reports of high-level bacterial resistance to the antibiotics. The aim of the study was to determine the activity of some commonly used biocides against bacterial isolates from tertiary hospitals of Nigeria. Study Design: This following study was a cross-sectional study. Methods: Fifty-three non-duplicate bacterial isolates were obtained from different tertiary hospitals. Susceptibility to the selected antibiotics was determined using the disc diffusion method, and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of a range of biocides been also determined using microtitre broth testing followed by inoculation onto agar. Results: A high prevalence of resistance to critical antibiotics were observed for Gram-negative bacteria (>85% of isolates were resistant to cephalosporins and >75% were resistant to fluoroquinolones). Imipenem remained active against >90% of Gram-negative isolates. Over half (52.2%) of the isolates of S. aureus were found to be resistant to cefoxitin, indicating methicillin resistance which is common. S. aureus showed the greatest tolerance to all the biocides that are used and compared to other species although all species exhibited tolerance to some agents. Whilst sodium hypochlorite remained effective against all the strains, (at 0.5 – 2%), like ethanol and triclosan which were less effective even at the popular70% formulation of ethanol. None of the S. aureus isolates was inhibited by any alcohol concentration tested and various other species had high levels of tolerance. Chloroxylenol was active against some strains but some were fully tolerant of the concentrations tested. All the test of biocides were bactericidal with MBC/MIC ratios of >4. There was no statistical difference between diffusion and dilution techniques in determining the susceptibility of the isolates to biocides except for P. aeruginosa. Conclusion: Sodium hypochlorite and chloroxylenol are the biocides of choice for hospital disinfection in Nigeria according to this study. Ethanol is unreliable at lower concentrations and should be used at high concentrations in order to achieve the requisite efficacy.