Background: Despite the widespread use and application of biocides knowledge about their exact mechanisms of action, especially at sub-inhibitory concentrations, and the bacterial response to such exposure, is relatively limited. Such knowledge may contribute with information on which compounds that are more likely to contribute to unwanted traits in bacteria such as antimicrobial resistance development.  This study aims to assess the effect of exposure of antibiotic-susceptible Gram-negative bacteria isolates to sub-minimum inhibitory concentrations (MIC).

Materials & Methods: This study involved Gram-negative bacteria strains isolated from various clinical specimens submitted to the microbiology laboratory at Aljala  hospital, Benghazi, Libya of July 2019. The antibiotic susceptibility patterns of the isolates were compared before and after exposure to sub-MIC of five common hospital disinfectants: hydrogen peroxide, Betadine,  chlorhexidine,  alcohol Rub and ethanol 96%.

Results: The results showed the mean MICs of the disinfectants  used in this study were not similar between the parent and mutant strains, also the results of  Gram-negative bacteria strains isolated  after exposure to sub-MIC  of  disinfectants showed a multiple resistance to antibiotics, a statistically significant increase was observed a resistance to Ceftriaxone  (P = .012), Aztreonam(P < .001), Cotrimoxazole(P < .001), Cefotaxime (P = .041), and ciprofloxacin (P = .008). of Klebsiellapneumoniae strains isolates after exposure to sub-MIC of Surfanios Premium.  In contrast, the results of Klebsiellapneumoniae strains isolates showed a resistance after exposure to sub-inhibitory concentrations of betadine showed a statistically significant increase  a resistance to amikacin (P < .001), Levofloxacin (P < .001), Cefotaxime (P = .041), and ciprofloxacin (P = .008).

Conclusion:  These results suggest that exposure to sub-MIC of biocides may lead to an increased selective pressure towards antibiotic resistance; Thus, the efficacy of biocides in eliminating bacterial contaminants within healthcare facilities has to be questioned with increasing use of products containing low concentrations of biocide.

Keywords: Sub-minimum inhibitory, Biocides, Antimicrobial, Resistant gram-negative bacteria strains, Disinfectants, Antiseptics