FORMULATION-DEPENDENT ANTIMICROBIAL PERFORMANCE OF FOUR ANTISEPTIC HAND HYGIENE PREPARATIONS AGAINST MDR NOSOCOMIAL PATHOGENS: IN VITRO MIC, MBC AND ZONE OF INHIBITION ANALYSIS

Background: Antiseptic hand hygiene products-isopropyl alcohol (IPA) 70%, chlorhexidine gluconate (CHG) 4%, and triclosan 0.5%-are commonly stocked in Indian hospitals and diagnostic laboratories. Selection is typically based on cost and availability rather than systematic efficacy data. With multidrug-resistant (MDR) infections rising across India, evidence-based comparison of these products against resistant bacteria is urgently needed. Objectives: To compare the in vitro antimicrobial activity of four hand hygiene formulations-assessed by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and zone of inhibition (ZOI)-against phenotypically confirmed MDR nosocomial isolates; and to determine whether formulation type influences outcomes against MDR organisms. Materials and Methods: Four antiseptic preparations were tested against 33 bacterial isolates (29 clinical + 4 ATCC quality control strains) from five nosocomial species with confirmed resistance profiles-methicillin-resistant Staphylococcus aureus (MRSA), ESBL-producing Klebsiella pneumoniae and Escherichia coli, and MDR Pseudomonas aeruginosa. Zones of inhibition (ZOI) were measured by agar disc diffusion; minimum inhibitory concentrations (MIC) by CLSI M07:2024 broth microdilution; and minimum bactericidal concentrations (MBC) by sub-culture from MIC plates. Bactericidal activity was defined as an MBC:MIC ratio of ≤ 4. Results: IPA 70% demonstrated superior performance- highest mean ZOI (22.1 ± 2.3 mm), lowest MIC (40–55% v/v), and bactericidal activity (MBC:MIC ≤ 2) against all 33 isolates including all MDR phenotypes. CHG 4% was bactericidal against susceptible organisms (MBC:MIC = 2) but only inhibitory against MRSA (MBC:MIC > 4; ZOI 11.1 ± 1.7 mm) and MDR P. aeruginosa (ZOI 6.2 ± 1.3 mm). Triclosan 0.5% inhibited but did not kill all MDR organisms. Plain soap showed no antimicrobial activity (ZOI = 0 mm). One-way ANOVA confirmed significant inter-formulation differences (F[3,128] = 187.4, p < 0.001); two-way ANOVA showed a significant formulation × resistance interaction (F[3,124] = 14.2, p < 0.001). Conclusion: IPA 70% is the only hand hygiene formulation that reliably kills bacteria regardless of resistance phenotype and should be the first-choice agent in institutional antiseptic formularies. CHG 4% retains a role in surgical antisepsis. Triclosan 0.5% should be phased out from all healthcare and laboratory formularies.