Abstract
Staphylococcus aureus and S. epidermidis are the major teat skin bacteria and lead to severe bovine mastitis. Teat antiseptic is an important tool for controlling intramammary infection. The antibacterial activity of lactic acid (LA) against one reference strain of S. aureus ATCC 25923 and two field strains including S. aureus and S. epidermidis was investigated using the broth microdilution method. Its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were 0.5% for strains belonging to both species. An antiseptic preparation containing 5% LA with modified rice gel (LA-RG) was successfully prepared. Rheological behavior of LA-RG was found to be a pseudoplastic flow with thixotropy with viscosity of approximately 0.007 Pas. LA-RG exhibited a sufficient adhesive property in the rolling ball test with a length of 9.67 ± 0.04 cm. Killing kinetic studies of LA-RG showed that the killing rate of LA-RG was significantly faster than that of LA. After 32 min of exposure to LA-RG, approximately 86% and 60% of S. aureus and S. epidermidis were reduced, respectively. Abnormal bacterial cell surface after exposure to LA-RG was observed by scanning electron microscopy. It is concluded that LA-RG is a promising preparation as an alternative product for preventing mastitis in dairy cattle.
Highlights
The cutis is colonized by several types of epidermal flora including commensal and pathogenic bacteria
The antibacterial activity of lactic acid against Staphylococi was characterized by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using the broth microdilution method
The results showed that the MIC of lactic acid against all tested strains was 0.5% v/v
Summary
The cutis is colonized by several types of epidermal flora including commensal and pathogenic bacteria. Most of the active ingredients are chemical agents, which come with a risk of skin irritation and cause bacterial resistance [11]. The physicochemical characteristics of the modified rice powders can be feasibly made into good gelling agents in pharmaceutical gel preparation [17]. In developing antiseptic preparations, loading lactic acid into modified rice gel should have more advantage for biological and pharmaceutical aspects than synthetic chemical products. The main aim of the present study is an attempt to evaluate pharmaceutical gel preparation containing a biodegradable materials carrier (modified rice gel) and the natural antibacterial agent (lactic acid) on the epidermal surface. In order to achieve this aim, the antibacterial activity and the killing kinetic of lactic acid rice gel against bovine mastitis pathogenic staphylococci were investigated. Scanning electron microscopy (SEM) was used to identify cell morphology and membrane structure which could confirm the antibacterial property of the preparation
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