5 Targets to Test for in Your Production Environment: #5 Total Count

#5 – Total Count (microorganisms)

What do we mean by total count?

Total count is a very general term that, in this context, requires a more specific definition. Total count normally refers to “total aerobic mesophilic count”. Sometimes the term “total viable count” (TVC) is used, but there is no way to count anaerobic and aerobic organisms on agar plates under the same conditions. Furthermore, the term APC (aerobic plate count) is not specific enough as there are different temperature ranges, meaning that a mesophilic plate count (MPC) does not include psychrophiles and thermophiles. Colony forming units (CFUs) and APC (aerobic plate count) refer only to counting methods using agar plates; these are the most common but not the sole methods of total count analysis.

Where do they come from?

As we are talking here about the global microorganism population, the contamination sources are nearly many and can include:

  • Soil and water: Many bacteria are carried in soil and water, which may contaminate food. 
  • Animal feed: A source of Salmonella contamination in poultry and other farm animals.
  • Animal hides: Studies have shown that they may be a primary source for E. coli O157:H7, Salmonella, and Listeria in cattle. 
  • Gastrointestinal tract: Members of the Enterobacteriaceae group may be found in feces of livestock and poultry. 
  • Food handlers: The microbiota on the hands and outer garments of handlers generally reflect the environment and hygienic habits of these individuals, and the organisms in question may come from hides, gastrointestinal tracts, soil, water, dust, and other environmental sources. 
  • Food Utensils: Saws, cutting boards, knives, grinders, mixers, etc. may become contaminated during slaughter and processing operations and are a primary source of cross-contamination.
  • Air and dust: A variety of bacteria may be found in air and dust in food processing operations at any one time. Listeria is an example of a Gram-positive organism that survives in the processing environment. 

Why should I test for total count?

The real value of a “total” microorganism count is derived from historical data trends. If counts are higher than known or accepted numbers, corrective actions may be taken. This very general parameter does not indicate the presence of any harmful organisms, but may help in measuring potential food spoilage. Keeping the total microorganism count low would result in a lower risk of pathogen contamination and an extended shelf life.

How can you test for total count?

There are many ways to gain information on the global population of microorganisms in a product sample. Direct counting techniques do not rely on cell growth; one example of these are microscopic analyses in which magnification is used to make individual cells visible. Other procedures for counting microorganisms have therefore relied on cultivation or metabolic activities. Direct methods are fast but are often labor intensive or expensive, while cultivation-based methods are slower but affordable. So-called “reporter assays” are a diverse group and, at moderate cost, can be positioned between those two methods. Here is a brief summary of methods:

  • Direct counting: microscopy, automated cytometry 
  • Culturing so that the biomass becomes visible: plate count, MPN 
  • Reporter assays by which metabolic components are measured: colorimetry, impedance, ATP, turbidometry

This article was originally published in International Food and Meat Topics, vol. 30, no. 1 (February 2019).