ANTIMICROBIAL PROPERTIES OF ESSENTIAL OILS AGAINGST BULK-TANK MILK ISOLATED BACTERIA

Abstract

Markets for and consumers of bulk-tank milk exist in many parts of the world; bulk-tank milk is consumed by a large number of people, especially in developing countries. Due to the nutritious nature of milk spoilage and pathogenic bacteria, can grow and multiply in it. Generally, microbial contamination of milk can occur through the development of a bacterial infection on a teat canal or an infected udder (clinical or subclinical mastitis) from the animal, milker (manual as well as automated), cow environment (bedding, housing) or unclean process water. Collectively, the presence of foodborne pathogens in bulk-tank milk either directly or indirectly increase the risk of ingestion and transmission of antibiotic resistant strains from animal origin, these transmitted strains that can persist in the human intestinal tract (Jamet et al., 2012). Antibiotic resistant bacterial strains have been increasingly recognized as a worldwide clinical and public health problem (Levy, 2002). The increased use of antibiotics, both in human or animal medicine, is considered a prime factor in spreading the antibiotic resistance (Hawkey and Jones 2009). However, the contribution of agricultural use of antibiotics on the emergence of antibiotic-resistant bacteria cannot be underestimated (Levy and Marshall, 2004). Silbergeld et al., (2008) asserted that the use of antimicrobial drugs in agriculture is the major driving force in spreading antimicrobial resistance worldwide citing four arguments as evidence: the agriculture sector is the largest consumer of antimicrobials worldwide, antimicrobial drugs in agriculture are used mostly at sub-therapeutic levels; every clinical class of drugs has been utilized in agriculture, and antimicrobial-resistant pathogens are exposed to humans through the ingestion of animal food products and passed on to the environment. Due to the growing concern of antibiotic resistance in food-related bacteria, many studies were undertaken previously to assess the antibiotic resistance of bacteria in agricultural products such as milk (Citak et al., 2005; Straley et al., 2006). These studies reported that a significant proportion of isolates recovered from the food products demonstrated extensive resistance to antibiotics. Antibiotic resistant bacteria in food products can transfer resistance genes to the intestinal and commensal flora of humans and these can be a reservoir of resistance genes for pathogenic bacteria (Aarestrup et al., 2008). Antibiotic resistance in bulk-tank milk bacteria is of significant importance as the milk is still consumed directly in many farm families, their employees and nearby families in many parts of the world (Oliver et al., 2009). The main aim of this study was to evaluate antimicrobial properties of essential oils against antibiotic resistant bacteria isolated from bulk-tank milk in a predetermined area of Mangaung. The objectives of the study were to: quantify and identify bacteria isolated from bulk-tank milk, evaluate antibiotic profiles of the isolated bacteria and assess antimicrobial properties of essential oils against isolated bacteria. The first part of the thesis; scientific literature on isolated bulk-tank milk bacteria and the antimicrobial resistance in food-associated bacteria is reviewed. The second part of the thesis, was the identification and quantification of isolated bulk-tank milk bacteria and in the final sections; antibiotic resistance profiles of isolated bacteria present are tested and alternative methods, particularly the use of essential oils are discussed.