Campylobacteriosis is the prevailing foodborne infection in the EU, with a staggering 127,840 reported cases in 2021 alone. This infection manifests through distressing symptoms such as abdominal pain, diarrhea, and fever. The main culprit behind human infections is Campylobacter jejuni, which is often a result of cross-contamination from either raw meat or raw milk.
In 2020, the EU witnessed four outbreaks of C. jejuni linked to raw milk vending machines. Despite being equipped with coolers, the milk exceeded the recommended temperature threshold of less than 4°C, with a third of the milk reaching a temperature as high as 8°C and the maximum temperature recorded at an alarming 18.6°C. It is worth noting that C. jejuni thrives in high temperatures and low oxygen levels.
Under normal storage conditions, C. jejuni does not grow in raw milk. However, it possesses the ability to enter a dormant state known as the ‘viable but non-culturable’ (VBNC) state, making it undetectable through cultural detection methods while still maintaining its survival. It remains present in the milk, waiting for favorable conditions to reactivate.
A study published in the Journal of Food Safety emphasized the public health concern posed by the presence of C. jejuni in the VBNC state, as it remains more challenging to detect in raw milk.
To shed light on this matter, researchers conducted an experiment using a reference strain of C. jejuni and a field strain obtained from the feces of a dairy cow. Raw milk was spiked with these strains and monitored at temperatures of 5°C, 8°C, and 12°C. The colony-forming units (CFUs) were counted using culturally-dependent methods. Additionally, a culturally independent real-time v-qPCR method was employed to identify intact and potentially infectious units (IPIUs), which encompassed both CFUs and VBNC cells without overestimating the presence of C. jejuni by detecting dead cells.
The results revealed that solely measuring CFUs underestimates the prevalence of C. jejuni in raw milk. The CFU counts varied across temperatures and strains, with the field strain showing consistently higher levels. However, the presence of IPIUs, including VBNC cells, was consistently detected in all strains and temperatures using v-qPCR.
Although VBNC cells of C. jejuni are generally considered non-infectious, they possess the potential to transform into CFUs and gain infectivity under suitable conditions. Hence, it is imperative to move beyond solely checking for existing CFUs when examining raw milk.
Source: Journal of Food Safety, ‘Modeling the survival of Campylobacter jejuni in raw milk considering the viable but non-culturable cells (VBNC),’ published on June 30, 2023. DOI: https://doi.org/10.1111/jfs.13077. Authors: A. Knipper, C. Plaza-Rodríguez, M. Filter, I. F. Wulsten, K. Stingl, T. Crease.