What is the impact of climate change on microbial contaminations?

You’re feeling too warm under your microbiologist lab coats and dreaming of one thing: organizing the cold room?

No doubt about it, climate change is making its presence felt even in our labs!

But what about our (not always) friends—bacteria, molds, and other microorganisms?

Does climate change affect them? And what impact will that have on our labs?

To find out, we spoke with a SuperMicrobiologist Junior Expert on the topic: Louis Delaunay, who works in the SECALIM laboratories (INRAe team) at the Oniris site in Nantes (France).

He shared some fascinating—and at the same time, terrifying—examples with us!

Climate Change by the Numbers

To talk about climate change, you don’t need a crystal ball—or even a thermometer. Let’s rely on the experts from the IPCC (Intergovernmental Panel on Climate Change) instead.

According to them, the average global temperature could rise by 2.2 to 3.5°C by the end of the 21st century.

So far, we’ve already hit +1.1°C compared to pre-industrial times (1850), and the impacts are clear: droughts, floods, storms…

Oh, and here’s an important (and not so popular) fact: it’s proven that this warming is caused by human activity.

The good news is that we can change things. But that’s not the focus of this article… So, let’s get back to our little critters!

Direct Impact of Climate Change on Microorganisms

When we talk about climate change, the first thing that comes to mind is rising temperatures.

But that’s not all! There’s also increased humidity (due to higher rainfall and warmer temperatures), more frequent flooding, and decreased ocean salinity (caused by melting glaciers). All these changes affect the microorganisms around us.

Here are a few concrete examples:

Vibrio

Vibrio is a pathogenic bacterium that contaminates seafood (fish, shrimp, mollusk, etc.), producing toxins that cause food poisoning.

This bacterium thrives at 37°C in 3% salt (seawater).

See where this is heading? The hotter it gets, the more Vibrio multiplies. With heatwaves, sea temperatures along our coasts rise, creating perfect conditions for… Vibrio.

And since our seafood are caught near the coasts, it’s no surprise that contamination cases are increasing. QED.

Unfortunately, this trend isn’t expected to improve. The EFSA (European Food Safety Authority) even predicts a rise in Vibrio-related contaminations in the coming years.

So, it’s safe to say that testing for Vibrio will become more frequent in labs in the near future!

The most common species? Vibrio parahaemolyticus (in Europe), Vibrio vulnificus, and Vibrio cholerae, often linked to imported cases.

Campylobacter

Campylobacter is a pathogenic bacterium often found on poultry (as well as in livestock) and in water.

The WHO (World Health Organization) lists it as one of the leading causes of bacterial gastroenteritis. And since Campylobacter loves heat (optimal growth between 37°C and 42°C), it’s easy to see how climate change could make things worse.

An example? In Australia, the quintessential hot country, Campylobacter contamination rates are the highest among industrialized nations.

Studies also show that campylobacteriosis cases increase in summer (when it’s warmer) and that climate change could lead to a rise in contaminations in northern Europe.

In short, it seems likely that with climate change, we’ll be doing more and more Campylobacter testing in our labs… Unfortunately, it’s one of the bacteria that’s trickiest to grow there.

Unless, of course, we crank up global warming to 65°C, the temperature at which Campylobacter gets destroyed. Ready, set, fire up those engines!

Key species to watch out for are Campylobacter jejuni (the top offender) and Campylobacter coli (close behind).

Salmonella

It’s the same story as with Campylobacter.

When it’s hot and there’s heavy rainfall, the number of salmonellosis cases skyrockets. This trend has already been observed in some parts of the world, such as Australia and Canada¹.

With climate change, extreme weather events are likely to become more frequent, leading to an increase in salmonellosis cases…

Key serovars to watch: In 2023, Enteritidis takes the top spot!

Mycotoxins

Even though mycotoxins are classified as chemical hazards, they are produced by molds (microscopic fungi).

For example: DON is produced by Fusarium, while aflatoxin comes from Aspergillus.

With rising temperatures and increased humidity, conditions are becoming perfect for mold growth in cereals, legumes, and oilseeds, both in the field and during storage (if not properly maintained).

The result? A surge in mycotoxin contamination.

In the early 2000s, this issue primarily affected southern Europe. But since then, the affected area has been creeping northward… and it’s not showing any signs of stopping!

Indirect Impact of Climate Change on Contaminations

As we’ve seen, climate change can directly promote the growth of certain microorganisms. But it can also have indirect effects on some contaminations.

Here are three concrete examples to better understand:

Changes in Our Lifestyles

Climate change influences our daily routines and eating habits.

For example, we tend to have more barbecues in summer than in winter.

But with milder seasons and warmer temperatures, barbecue season lasts longer, and the cold chain is more easily disrupted.

And let’s face it—barbecues often lead to poor practices:

• Using the same knife and cutting board for chicken and tomato salad.
• Undercooked meat.
• Putting cooked meat back on the plate that held raw meat.

And then… BAM! Cross-contamination.

The solution? Educate the population about good food hygiene practices. Easier said than done!

STEC in Our Vegetables (Not Great News for Vegetarians!)

STEC (Shiga-toxin producing E. coli) are strains of E. coli that produce shigatoxins. Highly pathogenic, they mainly come from cattle farms and are typically found in meat and milk.

The problem? Recently, these bacteria have also been showing up in lettuce, onions, and other vegetables.

Remember the infamous 2011 Spanish cucumber scandal? Turns out it wasn’t cucumbers at all but Egyptian fenugreek sprouts in Germany, contaminated with E. coli O104:H4.

One theory suggests that these contaminations result from cross-contamination with unclean irrigation water.

After heavy rainfall, cattle manure spread on fields (and the bacteria it contains) could be washed into ditches and natural water reserves through soil runoff. If irrigation occurs during drought periods in the same geographic areas, fecal contamination could then spread to crops.

This might explain the contaminations… but the phenomenon is still relatively new and needs further study!

Noroviruses

Noroviruses are viruses that cause gastroenteritis.

Their main reservoir? Humans.

During outbreaks, large amounts of noroviruses end up in wastewater treatment plants.

The problem arises during heavy rainfall, which is becoming more frequent with climate change. When treatment plants overflow, their water spills into rivers, eventually reaching the coasts—right where our shellfish are farmed.

Noroviruses are also sometimes found in berries. Why? The same issue as with EHEC: the use of contaminated water for irrigation. Additionally, these products are very delicate, so they undergo only light cleaning.

The result? an increase in foodborne outbreaks, mostly linked to the consumption of raw shellfish.

Another indirect impact of climate change!

Emergence of New Microbial Contaminants?

It’s a fair question: will climate change lead to the emergence of new strains of microorganisms? And if so, which ones?

Given that microorganisms adapt much faster than we do, it’s highly likely that some strains will mutate and new ones will emerge.

However, it’s still difficult to predict exactly which strains, to what extent, and with what impacts.

What Can We Do in the Face of Uncertainty?

Now that we’ve laid out the facts (and maybe stirred up your worst fears… sorry about that!), what can we do to limit the impacts of climate change?

1. Preserve What We Have
   
   Reduce our carbon footprint as much as possible to limit global warming and its consequences. Water is, and will increasingly become, a precious resource!
   
   
2. Anticipate and Prepare
   
   • Conduct specific microbiological analyses, beyond routine tests, to better understand how contamination profiles evolve.
     
   • Adapt our microbiological practices:
     
     • Test different incubation temperatures and durations.
       
     • Use specialized culture media.
       
     • Adjust microbiological criteria, especially in summer.
       
       
3. Continue Research
   
   Why? Because understanding your enemy is the first step to defeating it! This is central to the work at SECALIM:
   
   • Study bacterial behavior in food (prevalence, primary contamination, growth potential, survival, virulence, adhesion, etc.).
     
   • Anticipate risks using modeling tools to predict and assess health risks, helping to design mitigation strategies.
     These strategies should reduce risks while having a positive environmental impact—thinking globally to avoid counterproductive effects on climate change.

Better anticipation is the key to protecting our health!

Have other examples or questions? Feel free to share them in the comments!

We would like to thank Louis Delaunay once again for sharing his expertise on the impacts of climate change on food safety.

1. Canada : Smith et al  2019
   Australie : Zhang et al. 2010 ↩︎