Lactobacillus (Probiotic)

Synonyms: Lactobacillus acidophilus, Doderlein's bacillus

Lactobacillus acidophilus is a species of gram-positive, rod-shaped bacteria often found in the intestinal tract of humans and animals, the human mouth, and vagina. It is an anaerobic organism that produces lactic acid which reduces the pH. This may have an inhibitory effect on other organisms, especially candida.

• There are a number of species of lactobacillus that represent just one of many bacteria to be normal commensals of the human body, especially the gut and vagina.
• There are about 500 species of micro-organisms in the body of which 30 to 40 predominate. In a healthy body that has not recently taken antibiotics, the number of bacteria represent about about 10 to 50% of all cells in the body. The total weight of bacteria in a healthy adult is about 3.5kg.
• Gastric acid kills many bacteria in the stomach but the concentration in the colon is about a million times as high. Bacteria represent about half of the mass of faeces.
• Lactobacillus acidophilus is the best known of the “friendly bacteria” but others include Bifidobacterium bifidum and B. longum.

A "probiotic" is defined as a "live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance". Originally it applied to animal feeds but now it is applied to humans. The major source of probiotics for humans is dairy-based foods containing intestinal species of lactobacilli and bifidobacteria. The definition implies that consumption of the probiotic affects the composition of the intestinal flora. A number of potential benefits arising from changes to the intestinal milieu through the agency of probiotics have been proposed, some of which should be greeted with much scepticism. They include:

• Increased resistance to infectious diseases, particularly of the intestine
• Decreased duration of infectious diarrhoea and possibly benefit in preventing travellers' diarrhoea¹
• Beneficial effect on irritable bowel syndrome, inflammatory bowel disease and bowel cancer²
• Reduction in blood pressure³
• Reduction in serum cholesterol concentration⁴
• Reduction in allergy in infants but not in older children⁵
• Stimulation of phagocytosis by peripheral blood leucocytes
• Modulation of cytokine gene expression
• Regression of tumours
• Reduction in carcinogen or co-carcinogen production

Lactobacilli are amongst the most widely used of probiotics but they are not so much part of the physician's armamentarium as the province of “health foods” and “natural healing” where evidence is based on anecdotes rather than RCTs. That is not to suggest that there is no evidence to support the use but the situation is far more complex and incompletely developed than the industry would have the consumer believe.

Lactobacilli are usually ingested in the form of live yogurt. If the yogurt is pasteurised or heated at all the bacteria are killed. The efficacy of changing the gut flora is uncertain. A study in which the subjects were given yogurt containing the organisms Lactobacillus delbrueckii and Streptococcus thermophilus for 15 days failed to find these organism in the faeces of the subjects.⁶

The normal flora of the gut can be readily disrupted by the ingestion of antibiotics. Oral penicillin given to experimental animals reduces the total population of anaerobic bacteria by a factor of 1,000 including Lactobacilli. As the good bacteria are killed, the potentially harmful bacteria increase rapidly. Care must be taken in direct extrapolation to humans as laboratory animals are often vegetarian and far more dependent upon their intestinal flora. If rabbits take oral penicillin it can be fatal.

Candida overgrowth of the gut is a potential problem in humans, especially after antibiotic therapy. The normal flora helps prevent overgrowth of candida⁷ and this leads to potential for the use of probiotics. A study of children aged 6 months to 10 years who received outpatient courses of antibiotics showed that the addition of lactobacilli species reduced the incidence of diarrhoea.⁸ At the other end of the age spectrum, the elderly are susceptible to pseudomembranous colitis due to infection with Clostridium difficile after antibiotics but probiotic bacteria can reduce the toxicity considerably.⁹
A recent randomised double blind placebo controlled study of 135 hospital inpatients in London showed that a commercially available probiotic yogurt drink significantly reduced the incidence of C. difficile associated diarrhoea and antibiotic associated diarrhoea.¹⁰

Probiotics are effective in reducing the incidence and severity of necrotizing enterocolitis in very low birth weight infants.¹¹
Candida and other bacteria produce IgA proteases that may conceivably impair the gut's ability to resist invasion and even allow entry to the body of potential allergens that can sensitise.

The lactobacillus is very important in the vagina to keep the pH low to deter infection especially with candida. Hence natural yogurt may be thought to be beneficial either taken orally or inserted into the vagina. Clinical Evidence reviewed the matter and found 2 poor quality crossover RCTs identified by a systematic review.¹² They provided insufficient evidence about the effects of a diet containing oral lactobacillus yogurt in women with recurrent vulvovaginal candidiasis. The review identified no RCTs of vaginal lactobacillus yogurt. A more recent review found poor quality studies and conflicting results.¹³
In recurrent vaginal candida infection the bowel would seem to be an important source of infection but this has since been denied.¹⁴

Regular consumption of probiotics has been claimed to improve a number of risk factors for CHD. In a study, just 8 weeks of fermented milk products reduced systolic blood pressure, lowered LDL cholesterol and raised fibrinogen in an at-risk group.¹⁵

Most vaccines are given by injection and produce a short term IgM and long term IgG response. Most infections are acquired via the gut or respiratory tract where the first line of defence is IgA. The food-grade Lactococcus lactis is a potential vector to be used as a live vehicle for the delivery of heterologous proteins for vaccine and pharmaceutical purposes.¹⁶ This could be a useful way to induce the appropriate type of immune response. Orally ingested probiotic bacteria may modulate the immune response and increase antibody titres against enteric infections by bacteria or viruses. In a study in which 2 types of lactobacillus were given along with polio vaccine, probiotics increased poliovirus neutralizing antibody titres and affected the formation of poliovirus-specific IgA and IgG in serum.¹⁷

• Lactobacilli are amongst the most important of the “friendly” bacteria. There is good evidence that the flora of the gut is very important in health and disease.
• Probiotics, of which the Lactobacillus species are amongst the most important do have an important role in diarrhoea, especially where it is related to antibiotics.
• These bacteria may also have some benefit reducing susceptibility to allergies from food.
• The value of Lactobacilli whether taken orally or vaginally for vaginal thrush is not clear as studies appear to be of poor quality rather than negative.
• Probiotics may have some benefit in terms of reducing risk factors in CHD but should be just one of many interventions. A low fat diet and an ideal weight are much more important.
• These bacteria may be a very useful tool for the delivery of new vaccines with superior qualities.
• Other claims like tumour regression and treatment of autism should be greeted with due scepticism.
• Latobacilli are important and valuable and this is an area of important and exciting developments.