manure, feces, fecal material, turd, poop, caca, doody
Food ingredient risk classification: low. Material is naturally bacteriostatic, and a 1 log reduction of S. typhi every 3 days has been observed (Himathongkham Et. al, 1999). Growth is prevented by competitive flora, active LAB cultures, fermentation products, and will quickly dessicate to a final Aw <0.86.

Eventually, I realize that I’m correcting a fallacy so often that it necessitates its own blog post. See the following:

On the regular, I find myself talking with both food producers and lay folk who say “but why should I worry about contamination, this food has [low pH, high pH, low water activity (Aw ), high salt content, high sugar content, preservatives, alcohol content, active cultures, etc.], therefore bacteria can’t grow on it!

Okay…yes. If you have certain conditions in your product, bacteria won’t proliferate on it. That does make it lower risk than say, milk.

Salmonella growth in milk at 44ºf 7ºc

This does change our risk assessment when we imagine a contamination event. If you imagine a small amount of contamination in a product with one of these growth inhibiting conditions, then it’s nice to know it’s not going to proliferate into more organisms.

This is a barrier for foodborne illness caused by intoxication (e.g. Staph, and Clostridium Toxins), as the organisms won’t be able to proliferate and make those toxins. It’s also a contributing barrier to infection of organisms requiring a high infectious dose as small contamination events won’t always be able to build to larger numbers as the food moves towards the final customer.

In our chain of events leading to illness, having growth inhibition is certainly a link that could reduce our risk, BUT IT DOES NOT MEAN THE BACTERIA AREN’T THERE IN THE FIRST PLACE.

“No microbial growth” is the norm, not the exception

Here’s the funny thing, pathogens will not proliferate in MOST FOODS on their own. Hell, E. coli and Salmonella spp. won’t grow in fresh manure! Counts will slowly reduce to undetectable amounts!

Are you prepared to say that there’s no potential for illness in this product? All the justification is there to show pathogens won’t grow in it!

Certain growth inhibition conditions such as refrigeration/freezing or drying/desiccation will actually improve bacterial survival. A lot of  great research has been done on how Salmonella spp. will survive for long periods when subjected to dry conditions, and even become less susceptible to other lethality treatments in dry environments.

As we said on our end item testing rant, spontaneous generation was disproven in the late 1800’s. Bacteria don’t magically appear in your product, they’re transferred via contamination events or from expected contact with soil, water, or animals, and whether or not they can grow does not change the fact that they’re either present or not present in the first place.

The first requirement to cause illness is the presence or absence of a causative agent, regardless of whether it can continue to grow or not

If low Aw meant your products couldn’t make people sick, these outbreaks would have never happened.

If low pH meant your products couldn’t make people sick, these outbreaks would never have happened.

If Fermentation or adding cultures meant your products couldn’t make people sick, these outbreaks would never have happened.

If freezing meant your products couldn’t make people sick, these outbreaks would never have happened.

These are known outbreaks with hospitalizations. Ir we expand our known contamination events to include recalls, it’s difficult to find a food product that isn’t represented at some point as having been contaminated enough to present a risk.

There are no “low risk” foods, only “lower risk foods”. Certainly fresh mango is going to have the potential to both become contaminated and subsequently grow the number of pathogens in the food. But dried mango is going to preserve whatever bacteria were on there in the first place, and the initial exposure risk on the farm would have been identical.

When making risk management decisions, by all means use all of the information at your disposal to generate realistic models of pathogen exposure, growth, or survival in your product. Especially when designing detection programs where you want to find these contaminated materials before the bad guys die off. But do not use a slight advantage to trick yourself into thinking “never in my product”.

There are a dozen industries that thought they were immune to outbreaks until they weren’t. Don’t let your product be the next example.

References:

  • Nicholson, Fiona A., Simon J. Groves, and Brian J. Chambers. “Pathogen survival during livestock manure storage and following land application.” Bioresource technology 96.2 (2005): 135-143.
  • Himathongkham, Sakchai, Suphachai Nuanualsuwan, and Hans Riemann. “Survival of Salmonella enteritidis and Salmonella typhimurium in chicken manure at different levels of water activity.” FEMS microbiology letters 172.2 (1999): 159-163.
  • Himathongkham, Sakchai, et al. “Survival of Escherichia coli O157: H7 and Salmonella typhimurium in cow manure and cow manure slurry.” FEMS Microbiology Letters 178.2 (1999): 251-257.
  • Bovill (et al.), 2000: Predictions of growth for Listeria monocytogenes and Salmonella during fluctuating temperature. International Journal of Food Microbiology 59: 157-165.
  • Kothary, Mahendra H., and Uma S. Babu. “Infective dose of foodborne pathogens in volunteers: a review.” Journal of food safety 21.1 (2001): 49-68.
  • Maserati, Alice et al. “General response of Salmonella enterica serovar Typhimurium to desiccation: A new role for the virulence factors sopD and sseD in survival.” PloS one vol. 12,11 e0187692. 8 Nov. 2017, doi:10.1371/journal.pone.0187692
  • Finn, Sarah, et al. “Mechanisms of survival, responses and sources of Salmonella in low-moisture environments.” Frontiers in microbiology 4 (2013): 331.