Super bugs in local milk

The Daily Nation’s Horizon magazine of 1 November 2007 carried an article titled Super bugs in local milk. The article cited a study by researchers from Jomo Kenyatta University of Agriculture and Technology (JKUAT) which revealed that raw milk hawked in Nairobi’s Kahawa West area contained harmful bacteria with high levels of resistance to commonly used antibiotics.

I was drawn to this article largely because of my professional interest in microbial food safety in general and the safety of milk and dairy products in particular.

While the article is an eye-opener to potential milk-borne public health risks, I felt that there were a couple of issues that were not very clear.

First, one of the researchers argued that the high levels of drug-resistant pathogens in milk poses a major health risk because 90 per cent of milk sold in Kenya is raw. While it is true that the sale of raw milk is predominant in Kenya, almost all consumers who buy raw milk boil it first before they drink it, often together with tea leaves.

And boiling of milk effectively kills all pathogens, whether drug-resistant or not. Thus the question of consumption of contaminated milk being a likely cause of emerging multi-drug-resistant pathogens, as reported by the study, does not arise.

The same is true when milk is pasteurized (heated to 72 degrees centigrade for 15 seconds). Indeed, as would be expected, the JKUAT team did not find drug-resistant pathogens in the pasteurized milk samples.

Still, that is not to say that high levels of pathogens in raw milk are acceptable because the milk will be boiled anyway. On the contrary, good quality raw milk is necessary in order to prevent it from getting spoilt quickly. Training of milk handlers and traders on milk hygiene is therefore imperative in order to improve the quality of marketed milk in the country.

Another issue is that the article didn’t say whether the raw milk samples were tested to see if they actually contained antibiotic residues. This is a more likely cause of the emergence of drug-resistant bacteria, especially because neither pasteurization nor boiling will get rid of antibiotic residues in milk.

Drug residues can end up in raw milk if a dairy cow is on antibiotic treatment. After such treatment, there is a specified milk withdrawal period when the milk should not be sold in order to protect consumers from being exposed to the high levels of antibiotic residues.

It would be useful to know more about the prevalence of antibiotic residues in marketed milk (both raw and pasteurized) in Kenya, as this poses a worrying prospect of consumers unknowingly ingesting small amounts of drug residues as they drink their daily chai ya maziwa. Such a scenario can only worsen the existing problem of antibiotic-resistant super bugs.