Maintaining a Healthy Microbiome
Introduction to Probiotics
Probiotics are living microorganisms that promote health when ingested in sufficient amounts (Shi 2016). Most probiotic supplements contain bacteria, and commonly include species from the Lactobacillus and Bifidobacterium genera (Ciorba 2012; Islam 2016; Saini 2010). Several species of fungal Saccharomyces are also used in probiotic supplements (Fakruddin 2017). Probiotic supplements are usually measured in colony forming units (CFUs), which represent the number of viable cells (Weese 2011; Wallace 2017).
Microorganisms are classified in a hierarchy of families, genera, species, and strains. The genus is indicated by an organism's first name; the species is its second name, and is followed in some cases by the strain designation (Khalighi 2016). For example, Lactobacillus acidophilus La-14 is a well-described probiotic (Stahl 2013) of the genus Lactobacillus, species acidophilus, and strain La-14 (Salvetti 2012).
A growing body of probiotic research is establishing the safety and therapeutic efficacy of many individual strains (Sanders 2010; Shi 2016).
Probiotics: Safety Considerations
Probiotics have a good safety record for human use for a variety of conditions. However, some potential areas of concern include the very young or very old, people with compromised immunity due to cancer, people who are taking potent immunosuppressive drugs after having received an organ transplant or those who are critically ill in intensive care (Happel 2018). A research study reported that most adverse effects were observed in frail elderly and terminally ill people, while in HIV-infected individuals the benefits of probiotics outweigh their risks (Happel 2018; Stadlbauer 2015).
One case report noted that fungemia with Saccharomyces boulardii developed in two newborns, of which only one was treated with the probiotic, and the second one contracted the infection from the first infant, who was located in the adjacent cot (Perapoch 2000). Fungemia with S. boulardii was also reported in an 8-month old infant with acute myeloid leukemia who was receiving probiotics to prevent chemotherapy-associated diarrhea (Cesaro 2000).
Fungemia with S. boulardii was reported in an elderly patient with Clostridium difficile colitis who was treated with vancomycin (Cherifi 2004), and in several patients in intensive care units treated with antibiotics who had central venous catheters (Lherm 2002). Bacteremia with L. acidophilus was seen in a patient with AIDS and Hodgkin disease (Ledoux 2006), and bacteremia with L. rhamnosus GG was reported in a 17-year-old boy with ulcerative colitis who was treated with systemic corticosteroids and infliximab (Remicade) (Vahabnezhad 2013).
Other populations potentially at risk from probiotic-related complications, according to the Food and Drug Administration, include people with artificial heart valves, and those with an active bowel leak or active intestinal disease such as colitis, due to the possibility that the probiotics would cross the gut wall (Doron 2015).
A systematic review and meta-analysis found that probiotics during pregnancy do not increase the risk of preterm birth and do not result in any adverse outcomes in the mother or the infant (Jarde 2018).
Consultation with a qualified healthcare provider is advised before probiotic use for people in the risk groups described here.