Food Microbiology Chapter II: Intestinal Bacteria and Probiotics

Intestinal Bacteria and Probiotics

• The human gastrointestinal (GI) tract contains over 10^14 microorganisms, which is more than the total number of human body cells, and they coexist as mutualists.
• These microorganisms are metabolically diverse and active, and have a significant influence on human well-being.

Dominant Phyla in the GI Tract

• The human GI tract harbors three dominant phyla: Bacteroidetes, Firmicutes, and Actinobacteria.
• Approximately 1000 microbial species are present in the GI tract, but only 30-40 species constitute 95% of the population.

Microbial Counts in the GI Tract

• Aerobic microbes are present in the upper part of the GI tract, while anaerobic bacteria are present in the lower part of the GI tract.
• The intestine of a fetus is sterile, but at birth, it is inoculated with vaginal and fecal flora from the mother.
• Subsequently, a large variety of microorganisms enter the digestive tract of infants from the environment.

Establishment of Normal Flora

• The normal flora of the GI tract is established from the environment, and age, food habits, and health conditions greatly influence the species and their levels.
• Lactobacillus acidophilus, Lactobacillus reuteri, and Bifidobacterium are considered the main indigenous species.

Characteristics of Beneficial Bacteria

• Lactobacillus acidophilus, Lactobacillus reuteri, and Bifidobacterium are Gram-positive rods that grow under anaerobic conditions.
• They are less sensitive to stomach acid and highly resistant to bile, lysozyme, and pancreatic enzymes present in the small intestine.
• These species help maintain the ecological balance of the GI tract microflora by controlling the growth rate of undesirable microflora.

Benefits of Probiotics

• Probiotics provide protection against enteric pathogens.
• They supply enzymes to help metabolize some food nutrients, such as lactase to hydrolyze lactose.
• They detoxify harmful food components and metabolites in the intestine.
• They stimulate the intestinal immune system.
• They improve intestinal peristaltic activity.
• They reduce tumorigenesis.
• They ameliorate chronic disorders.

Specific Benefits of Probiotics

• Lactose hydrolysis: Probiotics can help lactose-intolerant individuals by supplying lactase in the small intestine.
• Reducing serum cholesterol levels: Probiotics have been associated with low levels of serum cholesterol in humans.
• Reducing colon cancer: Probiotics can reduce the production of enzymes that activate pro-carcinogens and aid in the removal of fecal material.
• Preventing and controlling enteric infections: Probiotics can reduce the growth of undesirable bacteria and prevent enteric infections.
• Modulating immune response: Probiotics can regulate systemic and local immune responses, especially during the development of lymphoid tissues in the gut.
• Reducing allergic diseases: Probiotics can suppress inflammatory responses to food antigens and reduce allergic reactions.

Aspects to Consider

• The health benefit theory of fermented foods and beneficial intestinal bacteria is controversial.
• In selecting bacterial strains, considerations such as strain variation, sensitivity to stomach acids, biles, and pancreatin, viability and injury of cells, dose level, and duration are important.
• The use of antibacterial substances, such as bacteriocins, can also be beneficial.

Definition of Probiotics

• Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.