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Safety of probiotics
Starter LAB have a long record of safe use, as do bifidobacteria, and are generally regarded as safe.
Several Lactobacillus species, and also lactococci, have been identified as causal agents of infections in humans. However, these infections are rare and have tended to occur in patients with compromised immune systems e.g. individuals with HIV infections or on drug regimes to suppress the immune system.
Following the deaths of some 24 Dutch patients treated with probiotics who were suffering from pancreatitis the safety of probiotics has been questioned in the media. I will update this article as more information about what happened becomes available. In the meantime readers may wish to follow the discussions in the forum concerning the trial to determine the value of probiotics in treating pancreatitis.
There is an early review of the safety of these bacteria by Aguirre and Collins (1993) and a more recent study by Boyle, Robins-Browne and Tang (2006). While it would appear that some infections have arisen from patients' indigenous LAB, the possibility of infections arising from LAB consumed through fermented products can not be ignored.
LAB can produce two stereoisomers of lactic acid, D and L lactic acid. Since some LAB also have racemases, some strains will produce D/L lactate.
L-lactate is readily metabolised whereas the D-isomer is not. There have been concerns about infants, in particular, ingesting high levels of D-lactic acid and there is a maximum recommended intake level for D-lactate. Because Lb. acidophilus produces D-lactic acid there is some interest in using other probiotic lactobacilli or bifidobacteria in products for babies and young children.
Several cases of D-lactic acid acidosis have been described in patients that have had intestinal bypass surgery. This condition is associated with transient neurological symptoms including headaches, weakness and visual disturbances. The D-lactic acid acidosis has been shown to be due to the overgrowth of Lb. acidophilus in the small intestine, generally due to its selection by antibiotic therapy. As with babies and young children, people who have had jejunoileal bypass surgery should seek medical advice before taking probiotic products particularly those containing D-lactate producing bacteria.
Some LAB can produce biogenic amines such as putrescine, cadaverine, histamine, tyramine and 2-phenylethylamine. Some of these can cause unpleasant reactions (nausea, headaches, and respiratory disorders) including dangerously high blood pressure particularly in individuals with reduced monoamine oxidase (MAO) activity or those taking MAO inhibitors, an older class of antidepressant medication. Providing strains are screened properly biogenic amine formation should not be a problem.
Regardless of the safe record of using LAB and probiotics there is comparatively little data on their safe use in feeding babies and very young children. Hence it would seem sensible to exercise caution in using them with young children and if in any doubt to seek pediatric advice first. As stated earlier it might also be better to avoid using any probiotic that produces D-lactic acid e.g. Lb. acidophilus.
In the section on cheese starters mention was made of concerns about using enterococci as starters. One of the concerns is that enterococci resistant to vancomycin have been isolated. This resistance is due to their possession of a plasmid that contains vancomycin resistance genes. Vancomycin is an important antibiotic in that it one of the few treatments effective against a number of pathogens that are resistant to other antibiotics. Unfortunately the vancomycin resistance plasmid can be transferred to Staphylococcus aureus and probably other pathogens. This is another argument against using enterococci as starters.
Safety is an important area as far as probiotic use is concerned and one that will be kept under review. Readers requiring more information are recommended to download, 'Probiotic use in clinical practice: what are the risks?' by Boyle, Robins-Browne and Tang (2006). This article co-authored by pediatricians and immunologists and published in the American Journal of Clinical Nutrition provides a balanced, positive perspective on the use of probiotics. The documented cases of both fungal(yeasts) and bacterial sepsis arising from probiotic use are described. This paper should be helpful to anyone considering feeding neonates, babies, with probiotics.