Safety Aspects of Lactic Acid Bacteria

Dear colleagues,

Lactic acid bacteria (LAB) are low G+C Gram-positive, non-spore forming microorganisms that produce lactic acid as the main end product of carbohydrate metabolism and include among others the genera Lactobacillus, Streptococcus, Enterococcus, Lactococcus and Leuconostoc. They are naturally associated to fermented food products, in which they carry out metabolic processes that improve their nutritional and sensory properties and ensure their safety and preservability. Moreover, LAB are a normal component of the oral, intestinal, and genito-urinary tract microflora and do activities that have been proven to be beneficial for human health, as demonstrated by numerous in vivo and in vitro studies. These include the treatment and prevention of infections, of antibiotic-associated diarrhea, and of many other medical conditions. Indeed, LAB comprise important probiotics commonly used to allow the instauration of a beneficial intestinal microbiota and for stimulation and modulation of the host's immune system.

However, LAB, though generally regarded as innocuous microorganisms, can occasionally pose health hazards that include the formation of toxic substances, such as biogenic amines in food, the production of host tissue-degrading enzymes, e.g., gelatinases, haemolysins, cytolysins, and infections, occurring mainly in individuals with underlying conditions, such as endocarditis, bacteremia, neonatal meningitis, and pleuro-pulmonary and urinary tract infections.

Another aspect regarding LAB safe use is the possibility that these bacteria participate to the spread of antibiotic resistance (AR) genes associated with mobile genetic elements or unstable chromosomal regions. Determinants for resistance to different antibiotic classes have been detected in nearly all LAB genera and the necessity to thoroughly check strains intentionally added to the diet or naturally present in food products for a comprehensive panel of AR genes is needed to avoid exposure to LAB strains carrying those genes and preventing their dissemination with the related risk for public health.

Given the high doses at which these bacteria are usually administered, it is essential to monitor their safety features, though this is not yet systematically done when selecting strains to be used as food cultures and probiotic preparations.

This Special Issue aims at collecting original research or review articles regarding the possible risks related to LAB use and strategies to avoid the detrimental effects that can be caused by strains carrying harmful genetic characters through safety assessment. The need for caution in the administration of LAB probiotics to individuals with particular sensitivity to infection or predisposing factors should be clearly presented through the description of ascertained LAB infection cases and studies on the possession and expression of hazardous traits.

Dr. Franca Rossi
Guest Editor

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