Controlling spore-forming bacteria in food processing

8 June 2016 – Heat-resistant spore-forming bacteria are a major difficulty for the food industry. Dr Erwin Berendsen has discovered new approaches to the problem; he defended his thesis on 3 June at the University of Groningen.

Spore-forming bacteria are an established cause of food spoilage. Manufacturers trying to prevent spoilage are heating food products to temperatures higher than 100 °C. This approach, however, is often ineffective as certain bacterial spores are strongly heat-resistant. Berendsen investigated the spore heat-resistance of 14 lab and industrial strains within the common B. subtilis group and was able to distinguish two specific responses. “The first group displayed very low heat-resistance, being inactivated after a one-hour heat treatment at 100 °C”, he illustrates. “The second group showed very high heat-resistance, with almost all spores surviving the same heat treatment.” This contrasted with what was expected: that the contrast between high and low-resistance would be less marked.

Jumping genes
Berendsen identified links between heat-resistance of spores and features of the bacterial genome. “We discovered that strains with high heat-resistant spores had specific genes in their DNA, the spoVA2mob operon”, he explains. Remarkably, this spoVA2mob operon was present on a transposon – a ‘jumping genetic element’ and thereby able to move from one strain to another.

The results underline the importance of detecting strains with spores of high heat-resistance and preventing genes from ‘jumping’. “Manufacturers can, for example, decide for extra pre-treatment before heating of ingredients that often contain high heat-resistant spores, such as herbs and spices, before adding them to the rest of the product recipe.”

Challenged to think differently
Berendsen is continuing his research career at TNO, focussing on detection and identification of micro-organisms. He really values his experience as a PhD fellow at TiFN: “For the first time, I found myself working hand-in-hand with research institutes and manufacturers – a unique position”, he says. “I was doing fundamental research, but I was regularly challenged to think about the applicability of my work; this is crucial in my new position at TNO.”