In sensitized individuals, exposure to S. cerevisiae may lead to respiratory symptoms, such as asthma, particularly baker's asthma, AR, and hypersensitivity pneumonitis (1). Additionally, skin symptoms such as AD and chronic urticaria are reported to be caused by S. cerevisiae (7). Anaphylaxis is rarely reported due to baker’s yeast hypersensitivity (12).
Allergic rhinitis
Inhalation of fungal allergens may trigger rhinitis in sensitized individuals (5). A study by Baldo et al. (1988) evaluated 47 fungal allergic (inhalant allergen) patients for allergic sensitivity to bakers' yeast. As per the result, 32 patients were radioallergosorbant test (RAST)-positive to bakers' yeast antigens. Enolase was the major allergen identified from S. cerevisiae. (16).
Asthma
Baker's asthma is a well-known occupational allergic condition that occurs due to hypersensitivity to different antigens, such as flour, bran, yeast, baking additives, storage mites, etc. Moreover, other ingredients found in baked goods and pastry have been reported to cause allergy (13). Baker’s yeast (S. cerevisae) is a bakery ingredient that has been reported to be associated with some isolated cases of baker’s asthma (14). However, sensitization to this baker’s yeast allergen is not common compared to the cereal flours or enzymes. Nonetheless, this needs to be considered in the clinical setting when no sensitization is observed for common bakery allergens (15).
Hernandez et al. (1996) presented a case of a 48-year-old bakery worker (nonsmoker) with recurrent episodes of hydrorrhea, sneezing, nasal obstruction, wheezing, spasmodic cough, and dyspnea within 1 or 2 hrs, following the start of his work. The symptoms at first were mild and worsened with time. However, his symptoms appeared to improve on holidays. The causative agent was found to be S. cerevisiae dry powder that created a dusty environment and possibly triggered occupational asthmatic condition in the baker (baker's asthma) (13).
Another case of baker's yeast true allergy in a boy with a history of mite-allergy and AD was reported by Pajno et al. (2005). The boy experienced generalized urticaria and asthma after eating pizza and bread (only fresh oven-baked). On investigation, he was found to be sensitized only to baker's yeast (S. cerevisiae), and the prick-by-prick procedure observed the severe systemic reaction. The severity of allergic reactions and urticaria subsided in 2 years. However, after the consumption of freshly baked and yeast-containing products, the patient still had a cough. The study suggested that continuous exposure to S. cerevisiae may result in immunotolerance and gradual reduction of allergic symptoms (11).
Atopic Dermatitis
S. cerevisiae exhibited a significant association between positive SPT and AD (6).
A study on 449 allergic patients reported that about 50% suffered from AD, 11% from AR and/or asthma, and 38.5% were nonatopic individuals. The study detected that AD patients with chronic dermatitis had considerably higher SPT reactions to S. cerevisiae than AR/ asthma or nonatopic controls. Skin-specific IgE was detected for brewer's yeast in 94% of patients with severe AD, 76% with moderate AD, and 25% with mild AD or no history of AD. This indicated that the brewer's yeast had caused sensitization. (8)
Other diseases
Invasive infection
Saccharomyces organisms are reported as a prime contributor to invasive infections, particularly in immunocompromised or severely ill patients (17). S. cerevisiae has been frequently isolated from the vaginal flora of 0.9% – 5.8% of women. Moreover, S. cerevisiae is thought to cause symptoms similar to Candida vaginitis in 0.4% of patients. S. cerevisiae was also isolated from the throat (16%), stool (23%), urine (10%), and perineum (20%) of patients with hematologic disease. Similarly, a comprehensive review of published reports on invasive Saccharomyces infection by Angoulvant et al. (2005) detected 92 confirmed Saccharomyces invasive infection cases, which was clinically similar to invasive candidiasis. In most patients, the causative organism of fungemias was S. boulardii (51.3%), a subtype of S. cerevisiae (17).
Irritable bowel disease (IBD) and S. cerevisiae autoantibodies
Anti- S. cerevisiae antibody (ASCA), an antiglycan antibody against the cell wall surface of baker’s yeast, is commonly detected in the sera of patients with Crohn’s disease (CD) and ulcerative colitis (UC), the subtypes of irritable bowel disease (IBD). The bakery workers commonly develop CD (also called baker’s disease), and a diet low in baker’s yeast has been found to lower CD. This indicates the involvement of ASCA in CD pathogenesis (18). Although the exact cause of ASCA generation is not clear, it has been postulated that higher permeability in the small bowel of CD patients may result in higher exposure of reactive immune cells towards yeast antigens (typically found in the intestinal microbiota), leading to CD (19). In CD patients, an increased level of IgG and IgA ASCA has been reported. In fact, IgG ASCA is considered as a biomarker for IBD (positive rate 60-70% in CD patients and 10-15% in UC patients) (18).
