Antibiotic-Resistant Bacteria in Milk - Term Paper Example

Antibiotic Resistant Bacteria in Milk Introduction: Food borne diseases are concern for society with regard to public health. Milk and milk products are common items of daily consumption. Bacteria present in milk and milk products pose a risk for public health. The issue becomes a matter of greater concern when the bacteria present in milk are resistant to antibiotics, as this resistance makes it difficult to control diseases that result from these bacteria. For a better understanding of the issue, this paper attempts a case study of antibiotic resistant bacteria in milk. Case Study: Contamination of milk with bacteria is usually occurs at the udder and from the teats. Mastitis within the udder and the presence of faeces, bedding material and soils are the factors that usually cause milk to be contaminated by bacteria that are present there. Advances in the field of analysis for the presence of bacteria in the milk of cows have permitted the identification of bacteria that do not have a detrimental effect on human beings and those that are human pathogens (Marco & Wells-Bennik, 2008). The list of bacteria present in milk is a long one as seen in the table below: Table -1 Milk- Associated Pathogens and Spoilage Bacteria Organism Detrimental effect Bacillus cereus human pathogen and milk spoilage agent Bacillus licheniformis milk spoilage agent Bacillus subtilis milk spoilage agent Campylobacter jejuni human pathogen Shiga toxin-producing Escherichia coli human pathogen and bovine mastitis Listeria monocytogenes human pathogen and bovine mastitis Mycobacterium avium bovine and human pathogen Pseudomonas flourescens milk spoilage agent Salmonella enterica human pathogen Salmonella typhimurium human pathogen Staphylococcus aureus human pathogen and bovine mastitis Streptococcus agalactiae human pathogen and bovine mastitis Streptococcus uberis bovine mastitis Streptococcus dysgalactiae bovine mastitis Yersinia enterocolitica human pathogen (Marco & Wells-Bennik, 2008) Consumption of raw milk is a continuing practice in many societies even in the developed world like the United States of America and the United Kingdom. The presence of disease causing micro organisms including bacteria in raw milk is well know, yet the belief that raw milk has better quality then pasteurized milk has led to the continuing consumption of raw milk and the sale of diary products made with raw milk including bottled raw whole milk, skim milk and cream. Several bacteria have been found to be present in the bulk raw milk tanks from which these products come raising the potential risk of the presence of these bacteria in the raw milk and raw milk products consumed. Greater awareness of the potential risk of raw milk consumption is required to curb the consumption of raw milk and raw milk products and the threat it poses to public health (Holt et al, 2003). Given that sale of raw milk continues to be legal, there is large use of raw milk still persisting in the developed world. Analysis of raw milk made available, which is bought and consumed shows the presence of several bacteria. Many of these bacteria may not be harmful pathogens capable of causing infection and harm to the humans consuming it, there are also present bacteria that can cause infection and harm to the humans that choose to consume raw milk instead of pasteurized milk (Baltic, 2007). An example of the possible harm due to infection arising out of raw milk consumption can be seen in the case of Enterohaemorrhagic Escherichia coli. Enterohaemorrhagic Escherichia coli are the usual causative factor for haemorrhagic colitis, thrombotic thrombocytopenic purpura and haemolytic uraemia in human beings. Enterohaemorrhagic Escherichia coli are known to inhabit the intestines of cows. From such cows Enterohaemorrhagic Escherichia coli can infect humans (Padola et al, 2002). In the last two decades there has been a dramatic shift away from small farming units to large scale intensive farming operations in the developed world. Such large scale intensive farming operations create a more suitable environment for the spread of zoonotic pathogens within the large number of animals in such intensive farms and the wider environment. This provides the means for such emerging organisms the means to access new host environments. The gradual increase in intensive farming practice has also brought with it widespread use of anti-microbial agents, which include antibiotics to prevent the spread of infection among the birds and animals in such intensive farming operations. The result of this practice of widespread use of antibiotics is the exponential increase in antibiotic resistance with the possibility of multi-antibiotic resistance in the milk and food products that come from such intensive farming operations. This has significance for public health, as it reduces the treatment option in clinical practice in the case of individuals exposed and infected by these bacteria that are present in the milk and other products of these farms. Even more worrying is the continued distribution and spread of such antibiotic resistant pathogens with naturally occurring bacteria in the food chain and within the animals and the human intestines (Duffy, Lynch & Cagney, 2007). The initial source of the presence of micro organisms like bacteria originates from the animals themselves. Current diary practices like the use of automated milking machines have been known to increase the possibility of bacterial contamination of milk. Reduced quality of milk in the form of total bacterial count and somatic cell count has been observed in the use of automated milking machines. Two reasons have been attributed to this. The first is that cleaning of the teats of the animal is insufficient when the milking of the animal is with the help of automated milking machines. The second factor is the possibility of slight injury to the teats during milking with automated milking machines, which increases the risk of contamination of milk with bacteria (Svennersten-Sjaunja & Pettersson, 2008). Studies of bacterial pathogens having similar biotypes from diary farms and from the incidence of human disease give credence to the model by which antibiotic resistant bacteria are transferred through contaminated milk. This model posits that the presence of antibiotic resistant bacteria come from the widespread use of antibiotics in dairy farms, which leads to amplification of resistant organisms in the bovine hosts and faecal dissemination in the dairy farm environment. The consequence of this is the permanent reservoir of antibiotic resistant pathogens that reach the human population through the consumption of contaminated raw milk or milk products made from raw contaminated milk (Oliver, Jayarao & Almeida, 2005). Lactic acid bacteria have the capability of producing antimicrobial substances that can prevent the growth of micro-organisms that are either pathogens or milk spoiling agents. This benefit comes with a catch in that lactic acid bacteria that contaminate milk from animals treated with antibiotics become populated with bacteria that have developed resistance to the antibiotics present in the milk from these animals. Most of these bacteria by themselves do not pose a threat to humans, but can do serious harm by constituting a reservoir of genes that are capable of conferring the same resistance to strains of bacteria that are pathogenic to human beings. The spread of resistance from the lactic acid bacteria to the human pathogens is a means by which infections from antibiotic resistant bacteria can occur in human beings, through the consumption of raw milk (Herreros, et al, 2005). The predominant manner in which the transmission of antibiotic resistance bacteria between animals and human population occur is through the food chain. More specifically diary products like raw milk and raw milk products that have not undergone any treatment that removes bacteria from them are a potential vehicle for antibiotic resistant bacteria to cross over from the indigenous flora of cows to the gastrointestinal tract of the human population. Though many of the food associated lactic acid bacteria are considered generally safe they pose a potential risk, because of their reservoir status for antibiotic resistant bacteria. This reservoir status danger lies in the possibility of the transfer of antibiotic genes from the lactic acid bacteria to the bacteria in the resident micro flora present in the gastrointestinal tract of the human population and through that to the pathogenic bacteria (Mathur & Singh, 2005). A clear example of this cross over of antibiotic resistance bacteria from animals to humans can be seen in Escherichia coli. Enteroccoci are a common resident in the intestines of animals and human beings. Raw milk is usually contaminated with enterococci. These enterococci pick up antibiotic resistance from the antibiotic reservoirs in the cows. Consumption of raw milk carries with it the potential risk of these antibiotic resistant enteroccoci entering the human body with the possibility of causing antibiotic resistant infections. The enterococci were for long not considered a serious threat to human beings. Over the last two decades there has been an increased focus on these micro organisms, because of they have been found to be medically important. It has been found that they have become severe pathogens, with particular emphasis on nosocomial infects and are responsible for a number of serious infections that include abdominal abscesses, urinary tract infections, endocarditis and bacteraemia. The very high levels of antibiotic resistance demonstrated by these pathogens have caused them to be regarded as severe infectious agents capable of causing life threatening infections (Teuber, Meile & Schwarz, 1999). Escherichia coli are among the resistant bacteria capable of being carriers of transmissible resistance genes. Resistance to antibiotics has become more frequent in bacteria that are found in animal, because of the rampant use of antibiotics in farms. This has resulted in not just pathogenic bacteria, but also commensal and conditionally pathogenic micro organisms developing resistance from food products like milk. Strains of Escherichia coli are a common contaminant of raw milk. Some of these strains are pose a risk to the health of the human population, because of the virulence they demonstrate, which becomes difficult to contain, when they develop resistance (Babak, Schlegelova & Vlkova, 2005). Transfer of antibiotic resistance from one pathogen found in milk to another is demonstrated by Salmonella typhimurium to Escherichia coli. Salmonella typhimurium has been known to be responsible for enteric infections. It has also demonstrated resistance to the several antibiotics, which include ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracycline. The strain Salmonella typhimurium DT104 has been found to be capable of transferring the antibiotic resistance that it has developed to Escherichia coli K12 at temperature ranges from 25 degrees centigrade to 37degrees centigrade. This has significance to the consumption of raw milk that is possibly contaminated with Salmonella typhimurium and the transference of resistance to Escherichia coli present in the milk or in the gastrointestinal tract (Walsh et al, 2008). The spread of antibiotic resistant bacteria happens easily as the practice of treating the cow with antibiotics is a common practice in farms. The dairy calves are fed with this milk that comes from cows treated with antibiotics. Faecal swabs taken from the calves and tested for beta-lactam antibiotic residues, as the penicillin group of antibiotics is one of the more frequently employed antibiotics in farms. Results from these swabs show that the incidence of antibiotic resistant bacteria was the least in calves that consumed raw milk from cows not treated with antibiotics, while the incidence of antibiotic resistant bacteria was much higher in the calves that consumed raw milk from cows that had been treated with antibiotics. An added feature was that resistance of the bacteria in the gut of the calves increased with the increasing concentrations of antibiotics in the milk that was consumed by the dairy calves (Langford, Weary & Fisher, 2003). The contamination of raw milk with antibiotic resistant bacteria is not restricted to the animals, the environment and the processes within the intensive farms in the developed countries, but continues down the cold chain involved in the transportation of raw milk in the form of the silos used to store the milk and the trucks involved in the transportation of the milk. Isolates from the trucks and silos were tested for the presence of bacteria resistant to the beta-lactam antibiotics and non-betalactam antibiotics. This testing demonstrated the presence of antibiotic resistant bacteria. What was even more remarkable was the fact that sixty percent of the bacteria showed multi-resistant traits (Munsch-Alatossava & Alatassova, 2007). Staphylococci bacteria are capable of causing life threatening infections in human beings and have shown the ability to develop resistance to commonly used antibiotics making them pose an even greater threat to humans. Over the last decade there has been an increase in the prevalence of coagulese-negative staphylococci in the milk of cows. In 1999 the presence of staphylococci in the milk of cows isolated from cows with sub-clinical mastitis was 16.2% among all the bacteria that were isolated. In 2004 the proportion between coagulese-negative staphylococci and other bacteria isolated from the milk of cows grew substantially to 42.2%. Eight species of coagulese negative staphylococci have been identified as the contributors to the high proportion of coagulese-negative staphylococci present in the milk of cows with sub-clinical mastitis. These are Staphylococcus chromogenes, Staphylococcus xylosus and Staphylococcus simulans have been found to be the predominant of these. These three coagulese-negative species are considered as resistant to all bet-lactam antibiotics consisting of penicillins, penicillins combined with beta-lactamase inhibitors and all the generations of cephalasporins (Sampimon, Vernooji, Mevius & Sol, 2007). Escherichia coli are bacteria found in the gastro-intestinal tract of human beings, are capable of severe infections with grave consequences when they reach other parts of the human body. The development of resistance in Escherichia coli increases the potential risk that these pathogens pose the human beings. Milk samples collected from nearly one thousand farms in Scotland showed that milk from these farms to be contaminated by Escherichia coli, with 10.6% of the samples showing incidence of both Escherichia coli and antibiotic resistant Escherichia coli. The incidence of both Escherichia coli and antibiotic resistant Escherichia coli was found to be higher when the animals were housed day and night, as is the practice in high intensity dairy practices than when they allowed grazing out in the open during the day. This shows that the practice of housing milk producing cows in close proximity to one another is a cause for the increased spread of antibiotic resistant bacteria among the animals, which leads to increased contamination of milk with antibiotic resistant bacteria. The percentage of antibiotic resistant Escherichia coli among the 1125 of Escherichia coli isolates found was 22.2%. Nearly half of these antibiotic resistant Escherichia coli were resistant to more than one antibiotic. The grave danger of infection from these antibiotic resistant Escherichia coli for those consuming raw milk remain high (Johnston, Bruce & Hill, 1983). Evaluation of the presence of antibiotic resistant Escherichia coli in dairy farms in Eastern Europe demonstrates a similar pattern of incidence in dairy farms in Czechoslovakia. The incidence rate of antibiotic resistant Escherichia coli and coli form bacteria were found to be 23%. Investigations into the causes for this incidence rate of antibiotic resistant Escherichia coli and coli form bacteria showed that the incidence rate was high, when antibiotics were widely used against mastitis in the animals and particularly so, when the antibiotic regime was used in a large manner during the dry periods (Cizek, et al, 2008). Mycobacterium avium ssp. Paratuberculosis is known to be responsible for Johne’s disease in cattle, sheep and goats. It is believed to have a role to play in Crohnes disease that afflicts human beings. Mycobacterium avium ssp. Paratuberculosis can be transmitted to human beings via the milk consumed, as Mycobacterium avium ssp. Paratuberculosis is known to contaminate milk, which can act as a vehicle for the transmission of Mycobacterium avium ssp. Paratuberculosis to humans. Consumption of milk contaminated with Mycobacterium avium ssp. Paratuberculosis is best avoided (Grantirene, 2006). Consumption of raw milk and raw milk products continue in spite of recurrent outbreaks of infections due to this practice. Raw milk has been considered by some and advocated by others to reduce the risks for several diseases that include atherosclerosis and arthritis. There is no scientific evidence to support such a position on the consumption of raw milk. However there is ample evidence to show that raw milk is a frequent source of infection from pathogens that include Escherichia coli O157:H7, Campylobacter, Listeria and Mycobacterium bovis. Creating awareness about the consequences of raw milk consumption could help reduce the consumption of raw milk with its ramifications on the human population (Tedrick, Nicholson & Bannerman, 2007). A probable solution to this issue of antibiotic resistant bacteria in may be looming on the horizon in the form of genetic engineering of dairy animals for milk production. Mastitis is a frequent disease that affects milk producing dairy animals by pathogens finding their way into the mammary gland through the canal in the teats present on the udder. This causes the need for frequent use of antibiotics that lead human pathogens like Staphylococcus aureus developing resistance and finding their way into human through the contaminated milk. Genetic engineering that makes the animal resistant to infection of the mammary gland without altering the nutritional and manufacturing values of milk reduces the need for use of antibiotics, while maintaining the quality and quantity of milk and reduces the development of a reservoir of antibiotic resistant bacteria in the animal (Donovan, Kerr & Wall, 2005). Literary References Babak, V., Schlegelova, J. & Vlkova, H. (2005). Interpretation of the results of antimicrobial susceptibility analysis of Escherichia coli isolates from bovine milk, meat and associated foodstuffs. Baltic, S. (2007). 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