Yes, Bacteria Can Live in the Freezer
Research has confirmed that many species of bacteria can live in freezing temperatures. Some can even live in your freezer, and on your ice cream.
Many of us assume this that bacteria and other pathogenic microbes cannot survive in freezing environments. We assume that bacteria cannot survive in frozen food or freezers.
That, however, is an incorrect assumption.
Extremophiles and psychrophiles
Not only are there a whole host of bacteria that regularly dwell in unlikely places. Those that live in very hot or high pressure climes are called extremophiles. And those that live in freezing environments are called psychrophiles. But there are also many species of rigorous pathogenic bacteria living around us in normal climes that will also survive the freezer.
Yes, it appears rare that frozen food will be contaminated. Freezing temperatures certainly dissuade bacterial contamination because these temperatures freeze water, and hydrophilic (water loving) bacteria need water to be free-flowing to get their hydration needed to form strong biofilms.
And they need to eat too. Frozen environments often limit off available food sources.
But certainly, if there is food available in the form of sugar or other food source, many bacteria can not only survive the freezer, but may colonize within a frozen food.
Now if the food happens to be contaminated before freezing, and that food also supplies the food for bacteria to grow – especially sugar but also dairy or other animal product – that bacteria can live.
Five hospitalized and three die in ice cream contamination
This is in fact what is believed to have happened in the case of an ice cream that was recently the cause of five people being hospitalized in Topeka Kansas. The people were infected with the Listeria monocytogenes bacteria from ice cream products from the Blue Bell Creamery.
According to a News Release from the Kansas Department of Health and Environment, the frozen products that were possibly contaminated include:
All the products contain sugar and/or dairy, so they provided the Listeria bacteria with readily available food. After the unlikely contamination. Four of the five sickened people ate milkshakes that utilized the Scoops® product – containing both sugar and dairy.
In follow up testing, Blue Bell ice cream products contained at least three different strains of Listeria monocytogenes, and these were similar to those found among infected patients.
Eventually, three of the patients died from their Listeria infections.
The newest development in this contamination is that the Blue Bell company has now withdrawn all of their products from the market, as additional products – such as the chocolate chip cookie dough ice cream – have now been found to be contaminated with Listeria.
Other instances of ice cream contamination
This is not the only isolated case of ice cream contamination. There have been many reports of contamination of ice cream products.
For example, researchers from Al Azhar University tested 100 ice cream samples from ice creams sold in the Gaza region in 2013. They found that 42 tested positive for fecal coliform and 37 samples tested positive for Klebsiella species of bacteria. Klebsiella species can cause respiratory and digestive ailments.
In a 2000 study from the University of Zimbabwe found many ice creams contained bacteria. The researchers tested 95 samples of local ice cream and found that many contained bacteria. These included species such as Streptococcus, Bacillus and Staphlocuccus species.
The reality is, ice cream – with its high sugar and dairy content – is the perfect storm for potential contamination. Even though it is frozen.
Residual freezer contamination
In the recent US contamination, the CDC and the Kansas Health Dept. warned that while contaminated Blue Bell ice creams have been withdrawn from the market, contaminated product might still be out there. In other words, there might be freezers out there that either currently contain the contaminated ice cream, or the freezer itself is contaminated.
This is especially true if the ice cream was put back after using. The contaminated ice cream might have been spilled onto the outside of the ice cream container, releasing it into the freezer environment.
If the freezer is contaminated – from the Listeria species getting out of the package – then more of the food in the freezer may be contaminated. Yes, freezers do slow the biofilm growth of bacteria – but they do not prevent it.
The solution if one has had the Blue Bell in their freezer, is to make sure the freezer is cleared out and cleaned – using a vinegar and lemon solution or perhaps even some chlorine if there was spillage.
The other food in the freezer – if they not completely contained and airtight – could also possibly be contaminated as well. Tossing items not completely contained, and carefully cleaning those that are contained is also a good idea.
Regularly clean out the freezer
This should be done periodically anyway. The freezer should be cleaned with old foods removed is a good idea in any case – especially if a lot of fruits or ice creams are stored.
Is freezer burn contaminated?
Most will tell you no – because most foods that are dry and frozen will not be contaminated in the freezer unless there is another source of contamination. The lack of moisture will reduce its likelihood.
However, a moist food with freezer burn should be suspect. The original moisture could have been contaminated and as the moisture is drawn away during the freezer burn, some bacteria may colonize.
Such a contamination is often accompanied by a foul odor.
The morale of the story: While freezers can slow contamination and will lengthen the duration of food storage dramatically, they can still become a source of food contamination if not kept clean.
Kansas Department of Health and Environment. Five Kansans ill from Listeriosis outbreak linked to Blue Bell Creameries. Mar 13, 2015.
CDC. Outbreak of Listeriosis Linked to Blue Bell Creameries Ice Cream Products. Mar 13, 2015.
Eimanama AA. Antibiogram of Klebsiella spp. isolated from ice cream samples in Gaza Strip. Jnl Al Azhar Univ. 05/2013; 15:79:88.
Igumbor EO, Obi CL, Milingo T. Bacteriological examination of milk and milk products sold in Harare. Afr J Health Sci. 2000 Jul-Dec;7(3-4):126-31.