5.6. Microbial pathogenicity

In general microorganisms which are applied in biotechnology for production of fermented foods (e.g. lactic, propionic, acetic acid bacteria, yeasts (Saccharomyces, Kluyveromyces), some filamentous fungi like Penicillium, Aspergillus), are considered as safe for human use. They have a long story of common life with mankind and are considered generally as safe and nonpathogenic. There are some data about very rare cases of bacteriemia and endocarditis caused by some enteric lactic acid bacteria to patients with severe core disease. These cases by no means denote these microorganisms as food borne pathogens.

The food borne pathogens have invasive and/or toxigenic effect being in food or in the human gastrointestinal tract. Another group of microorganisms - opportunistic pathogens in general are not dangerous for a healthy person but in case of health-compromised people they represent some risk. Recently, using chance given by molecular techniques, the genomes of a lot of food-borne and opportunistic pathogens have been entirely sequenced and the genes responsible for their pathogenicity have been determined. These achievements give an opportunity for identification of similar genetic information in the genomes of different microorganisms used in food industry. Evaluation of data for several sequenced genomes of microorganisms used in food fermentation indicates two examples (Saccharomyces cerevisae, Lactococcus lactis) which do not possess known pathogenicity features.

In conclusion, the long term of safe use and the recently obtained genetic evidence show that the genetic background of the majority of microorganisms applied in food industry do not possess pathogenicity islands and other determinants for pathogenicity.

Besides these main considerations for pathogenicity there are some additional effects which should be taken into account.

Some undesired effects in genetically modified microorganisms resulted of genetic manipulation consequences such as metabolic discrepancy, expression of “silent” genes, change of cross-talk between microbe and intestinal immune system can be outlined. These effects concern increase of the amount of common metabolites with non basically toxic effect to non acceptable amount in lactic acid bacteria, yeasts (acetaldehyde, formic acid, biogenic amines); and the fungus Penicillium camamberti (roqueforti) (cyclopiazonic acid or roquefortin); expression of some genes coding for toxins; appearance of undesirable immune reactionp; undesirable reactions with other cells (e. g. enterocytes) of the GI tract.