Safety ofLactobacillusStrains Used as Probiotic Agents

SIR—We read with interest the excellent review of the role of probiotic agents in infectious diseases [1], as well as the accompanying editorial commentary [2]. Both reports suggest that lactobacilli used as probiotic agents are safe because, as Drs. Salminen and Arvilommi state in their editorial, “Lactic acid bacteria have a long history of safe use in foods….Therefore, the safety risk, if any, appears to be small” [2, p. 1578]. Drs. Alvarez-Olmos and Oberhelman, in their review [1], state that “some cases of sepsis or endocarditis caused by lactobacilli were reported in immunosuppressed patients…but none of these infections were related to lactobacilli used in probiotic food products” [1, p. 1571]. Here we present some concerns regarding the safety of lactobacilli used as probiotic agents. Lactobacillus species are generally considered to be nonpathogenic. However, several reports have shown that Lactobacillus strains isolated from patients with endocarditis, in comparison with laboratory or oral strains, had a greater ability to aggregate platelets, to bind collagen and fibrinogen, and to produce glycosidases and proteases [3]. These properties help them to survive and colonize vascular surfaces. The unusually high pathogenic potential of Lactobacillus strains that cause endocarditis raises the question of whether they are indigenous or ingested strains. Recently, we described an immunocompetent patient who had Lactobacillus rhamnosus endocarditis that complicated colonoscopy [4]. Interestingly, the patient reported large daily consumption of dairy products, especially yogurt. Our search of the literature revealed that, during the past decade (1992–2001), 16 cases of documented Lactobacillus endocarditis have been reported; in 4 of these cases [4–7], the patients reported daily consumption of yogurt, and, in another case [8], the patient reported use of a probiotic preparation containing L. rhamnosus. In 1 of these cases, standard methods could not distinguish the pathogenic isolate from the Lactobacillus strain isolated from the yogurt that the patient had been eating [7]. However, the 2 strains were finally proven to be different by use of more sophisticated methods, including PCR. In another case of Lactobacillus endocarditis, the strain isolated from blood cultures was indistinguishable from 1 of the organisms cultured from the probiotic capsules that the patient was using, with respect to appearance in culture (which was identical), reactions to the API 50CHL test, antimicrobial-susceptibility patterns, and pyrolysis mass spectrometry findings [8]. Lactobacillus species are also a rare cause of liver abscesses. In a recent report [9], a 74-year-old woman who reported a daily intake of dairy drinks containing L. rhamnosus strain GG for at least 4 months presented with a liver abscess due to L. rhamnosus. The isolate recovered from the patient and the strain of L. rhamnosus GG were identical and indistinguishable by use of pulsed-field gel electrophoresis. We are aware that both endocarditis and liver abscess due to Lactobacillus species are extremely rare conditions and that a recent study found no relation between Lactobacillus strains isolated from patients with bacteremia and strains used in the food industry [10]. Still, the increasing number of reports that suggest a pathogenic role for the lactobacilli used as probiotic agents raises some concerns and illustrates the need for more evidence regarding the safety of probiotics.