Antimicrobial Activity of Plain and Medicated Soaps on Sale in Nairobi on Selected Microorganisms

Abstract

Background: Soaps are made of fats and oils as the main ingredients and other components such as soda ash, salts and detergents. The main function of soap is cleaning, killing and removing microorganisms. Some soap additionally has antibiotics and are thus referred to as medicated soaps. Such soaps tend to be more expensive than the plain soaps. However, there is insufficient information on the enhanced efficacy of medicated soaps compared to plain soaps in Kenya. Objectives: This study aimed at comparing the antimicrobial effects between medicated and plain soaps against selected microorganisms. Materials and methods: This was an experimental laboratory-based study. Purposive sampling method was used to collect seven brands of medicated and seven brands of plain soaps present in the market. The samples were delivered to the Department of Medical Microbiology - University of Nairobi and were coded as either medicated (MS001 to MS007) or non-medicated (NMS001 to NMS007) before processing. Approximately, 2g of each soap sample was weighed into universal bottles, dissolved in sterile distilled water and tested for antimicrobial activities against selected pathogenic microorganisms of the species; Pseudomonas aeruginosa, E. coli, Staphylococcus epidermidis, Staphylococcus aureus, Staphylococcus capitis, Streptococcus pneumonia and Candida albicans. Diameter zones of inhibition, minimum inhibition concentration and bactericidal concentrations were compared. Analysis of variance and Fisher’s exact test were utilized to analyze the antimicrobial activities of the soap samples against the test microbes and the significance considered at 95% confidence interval (p<0.05). Results: All 14 (100%) of the soap brands were effective against P. aeruginosa with average inhibitory zone diameters of 9.1mm for non-medicated soaps and 9.0 mm for medicated soaps. Three medicated soaps (MS005, MS006 & MS007) and one non-medicated soap (NMS007)

were effective against S. pneumonia, S. aureus, S. epidermidis and P. aeruginosa. In terms of minimum bactericidal concentrations and minimum inhibitory concentrations, medicated soap 005 and 007 had low concentrations hence highly active against S. aureus with minimum bactericidal concentration of 62.5mg/ml and minimum inhibitory concentration of 31.25mg/ml, respectively. Non-medicated soap NMS007 was low hence active against S. aureus, E. coli, and C. albicans with MBC of 62.5mg/ml and MIC of 31.25mg/ml respectively. One non-medicated soap’s antimicrobial activity was comparable to that of medicated/antiseptic soaps. There was significant association between the MIC and MBC of medicated and non-medicated soaps tested in the present study (P≤005). Conclusions and recommendations: The findings of the present study suggest that medicated soaps are better antimicrobial agents compared to non-medicated soaps. However, some non-medicated soaps such as brand NMS007 have more antimicrobial activities as indicated by inhibition zone diameters, MBC and MIC compared to some medicated soaps. The choice of soap should be that which is effective against disease causing bacteria at low concentrations. The public should be encouraged to use effective non-medicated soaps such as NMS007 since it was widely effective in low concentrations against pathogenic microorganisms.