4 Gaps in Your Environmental Testing Program: #2 - Anaerobic and microaerophilic bacteria

In this series, product manager Stefan Widmann investigates four things you might miss when testing your food production environment.

#2: Anaerobic and microaerophilic bacteria

What are anaerobic and microaerophilic bacteria?

Anaerobic bacteria or, more generally, anaerobic microorganisms, can be divided into three groups: obligate, aero-tolerant and facultative. As their names indicate, they each have special requirements regarding the air, or more precisely, the oxygen, surrounding them. Obligate anaerobes such as Clostridioides difficile are harmed by oxygen and will die shortly after exposure. Aero-tolerant bacteria such as Clostridium botulinum cannot make use of oxygen and will neither die nor grow in its presence. Facultative anaerobes can use oxygen but do not need it for growth, as is the case with E. coli. There is also the group of microaerophilic bacteria such as Campylobacter that need oxygen to grow, albeit in much smaller amounts (1-2%) than in normal air.

Why should food producers care about anaerobic and microaerophilic bacteria?

Several pathogenic bacteria have these special growth requirements. Currently, thermotolerant Campylobacter species are cause for worry among public health professionals. On average, every other chicken is infected with Campylobacter, making poultry meat one of the most common causes of food poisoning. In the EU, illnesses caused by Campylobacter species occur twice as often as those caused by Salmonella. Of the anaerobic group, a Clostridia species such as C. botulinum is responsible for the foodborne illness known as botulism, often transmitted through canned (i.e. oxygen-poor) food, in which C. botulinum can thrive and produce the compound botulinum, which is toxic to humans. Another Clostridia species, C. perfringens, is the most common source of food poisoning in the US and Canada and causes symptoms such as abdominal cramping and diarrhoea. The risk of C. perfringens infection correlates especially strongly with food kept or stored in warm conditions for longer periods of time, which favours their growing to infectious numbers (10^4 cfu/g).

How can food producers detect anaerobic and microaerophilic bacteria?

While it is possible to detect all groups of anaerobic and microaerophilic bacteria with classic agar plates, they, with the notable exception of facultative anaerobes, can grow only under carefully controlled oxygen levels. For this reason, a common aerobic plate count (APC) will not detect these organisms. An additional concern is time: as with any other agar plating method, the incubation of anaerobic and microaerophilic bacteria takes at least two days before presumptive results are reached. By this time, a contaminated product may have already made its way to consumers.

This article originally appeared in International Food & Meat Topics 31 (2).