Coliform and E. coli

Coliform bacteria, which are tested for in cheese are actually several species from the Esherichia, Citrobacter, Klebsiella, Enterobacter, and Aeromonas genera.

The coliform bacteria level indicates a “good manufacturing practices” problem in processed foods such as cheese, especially pasteurized milk cheese. The coliform count seems to be useful in monitoring pasteurized milk cheeses but the data from our group is showing that there are frequently coliform bacteria in raw milk cheeses. These cheeses are mostly made from very low or no coliform count milk so I think that they are growing and more may be getting in during the process of cheesemaking. The coliform bacteria may be present on equipment and in the environment and, since they ferment lactose and produce carbon dioxide, it is easy to imagine how they might get in and grow during cheesemaking. They may also get into the cheese during brining (because some of the brine samples have had low coliform counts) and ripening (from cheese boards, plastic matting and racks). Coiform counts below 10,000 are not of a concern to me (personally) in raw milk cheese. Coliforms can be kept out of pasteurized milk cheeses by having good sanitation, clean brines, and packaging over the rinds. Most of the farmers in our group make fresh pasteurized cheeses that are packaged rather soon after they are made and their aged cheeses are made from raw milk.

Esherichia coli (E. coli) is one genus of bacteria in the coliform group who’s origin is in the gastrointestinal tract of warm-blooded animals and are shed in feces., therefore being known as fecal coliforms. The E. coli count is the real indicator of a potential problem in cheese because some of the E. coli strains are pathogenic (O157.H7) and any kind of count indicates fecal contamination, which farmers who make the cheese can probably figure out how these bacteria got into the milk or the cheese.

The results that I am getting from my raw milk cheeses have coliform levels of 200-2,000. These cheeses are all with humid natural rinds and I am finding that the boards, matting, and plastic racks that the cheeses are sitting on or near are a source of colifom bacteria. There is also a high level of non-coliform bacteria from these samples (environmental swabs and cheese), which must represent all of the various good microbes that inhabit the cheese rinds. None of the cheeses have had E. coli; all counts have been less than one.

My pasteurized milk cheeses have always tested with coliform less than one. This includes the bloomy rind cheeses that are two weeks old. The way we are having Agrimark test milk and cheese samples for the group is, to first of all, do a coliform count. If this is more than 100 they do an E. coli count. If E. coli is found then they test for the pathogen (O157.H7).

Just for your information the EU standards for maximum levels of E. coli in pasteurized soft cheeses (meaning soft-ripened) is 100/ gram and in raw milk cheeses it is 1,000/ gram. Of course there must also be the absence of pathogens: E. coli, Listeria, and Salmonella.

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