The Normal Microflora of the Human Body

Standard 11: Define the term normal flora and explain how its deviation can prevent or cause a disease or disorder At the conclusion of today I CAN: Identify normal flora in various body systems and its harm or usefulness by being engaged in class and taking good notes.

Important Vocabulary Colonization: the development of a bacterial infection on an individual, as demonstrated by a positive culture. The infected person may have no signs or symptoms of infection while still having the potential to infect others. Opportunistic infection: is an infection caused by bacterial, viral, fungal, or protozoan pathogens that take advantage of a host with a weakened immune system or an altered microbiota (such as a disrupted gut flora).

Humans as Habitats Bodies are great places to be! Warm, stable, lots of nutrients available, constant pH and osmotic pressure, etc. Normal pH: 7.35-7.45 Acidic: <7.35 Alkaline: >7.45 Our bodies are not uniform environments, though Each region or organ differs: skin, GI tract, respiratory tract, etc. provide different conditions Animals possess great defense mechanisms The successful colonizers (and the successful pathogens -- more on this next lecture) are those that can get around these defenses “Normal” doesn’t mean non-pathogenic; we sometimes have pathogens in low numbers in and on us

Humans as Habitats (cont.) Colonization (and infection) frequently begin at mucous membranes These are found throughout the body. Consist of single or multiple layers of epithelial cells, tightly packed cells in direct contact with the external environment. Bacteria may associate loosely or firmly Breaches in the mucosal barrier can result in infection (pathogenesis)by opportunistic pathogens

How we get our indigenous microflora? Normally, a human fetus has no resident microorganisms Initial colonization comes during breaking of fetal membranes and, especially, birth itself. Environment in general is colonization source: mother, father, doctor, etc. Can vary by wards. Initial microflora depends on whether infant is breastfed or not. Bifidobacterium vs. others.

Effects of breastfeeding vs. bottle-feeding on indigenous microflora Large effect seen -- breastfed infants develop primarily Bifidobacterium populations, bottle-fed get a mixture of various species of coliforms, Clostridium, Staphylococcus, Streptococcus, Lactobacillus, etc. Breastfed infants have lower pH and less buffering capacity in large intestine. This disfavors enterobacteria and favors Bifidobacteria. Bifidobacterium seem to compete with potential pathogens like Clostridium difficile and some enterobacteria One study demonstrated that bottle-fed infants were 4X as likely as breastfed ones to harbor C. difficile.

Normal flora of specific regions Skin Oral cavity Gastrointestinal tract Other areas Upper respiratory tract Lower respiratory tract Urogenital tract Microorganisms are normally not found in the organs, blood, or lymph. (if they are, you’re in trouble!)

Normal flora of the skin Skin surface is unfavorable habitat. Usually only populated by transient microbes Exceptions are moister areas: scalp, face, ears, underarms, genitourinary, palms, toes. Most resident skin microorganisms inhabit deeper layers of the epidermis, sweat glands, and follicles. Most of the residents are Gram-positives, especially Staphylococcus and Propionibacterium

Normal flora of the skin (cont.) The dermis and subcutaneous tissue are normally sterile

Normal flora of the skin (cont.) Microorganisms are primarily associated with glands: 1) Eccrine glands Widely distributed Main glands for perspiration; secrete a hypotonic saline solution with a variety of organic and inorganic substances Relatively devoid of microorganisms, probably due to salinity and low pH 2) Apocrine glands Restricted to underarms, genitals, etc. Don’t develop before puberty Apocrine sweat has higher pH than eccrine sweat Population numbers can be high 3) Sebacious glands -- associated with hair follicles Produce sebum, chief component of skin lipids These lipids have antibacterial activity, esp. against Gram-positive cocci.

Common Skin Bacterium May Be New Opportunistic Pathogen (A.H. Chagla, A.A. Borczyk, R.R. Facklam, and M. Lovgren. 1998. Breast abscess associated with Helocococcus kunzii. Journal of Clinical Microbiology. 36:2377-2379.) A usually harmless bacterium, commonly found on human skin, may be an emerging opportunistic pathogen, say researchers from the London Public Health Laboratory; the Central Public Health Laboratory of Toronto; the National Center for Streptococcus in Edmonton, Alberta, Canada; and the U.S. Centers for Disease Control and Prevention. They report a case of infection by this organism the August 1998 issue of the Journal of Clinical Microbiology. Helococcus kunzii is a recently identified bacterium that is thought to be a nonpathogenic member of normal human skin flora and is rarely associated with skin infections. In the study though, the researchers report the isolation of the organism from an infected cyst on the breast of a 57-year-old immunocompromised woman. "Our finding provides further support for the opportunistic role of H. kunzii in causing infection in both immunosuppressed and immunocompetent patients," say the researchers.

Normal flora of the mouth A great place to live! (in contrast to the skin) The only negatives: salivary enzymes (lysozyme and lactoperoxidase), and constant need to re-attach Initially (i.e. at birth), there are only a limited number of bacterial types (aerotolerant anaerobes like Lactobacillus and Streptococcus), then as teeth erupt there are more anaerobes and bacteria adapted to living in crevices and on smooth surfaces.

Scanning electron micrograph of dental plaque Scanning electron micrograph of dental plaque. The many different kinds of bacteria composing the plaque exhibit specific attachments to the tooth and to each other

Ca3(PO4) 2 scale (tartar) from human tooth Plaque accumulates calcium salts to form tartar http://www.buckman.com/eng/biofilm3.htm Ca3(PO4) 2 scale (tartar) from human tooth

Scale magnified 7,000x to show imbedded bacterial biofilm http://www.buckman.com/eng/biofilm3.htm

Normal flora of the GI tract The body is like a donut, with the alimentary canal the ‘inside’ of the donut. Things inside the alimentary canal are not truly ‘inside’ the body

Normal flora of the GI tract (cont.)

Stomach pH of stomach is low, around 2 Acts as a microbiological barrier Bacterial count of stomach contents is low, but walls can be heavily colonized. Primarily Lactobacillus and Streptococcus

Gram-stained preparation of the stomach wall of a 14-day old mouse, showing extensive development of lactic acid bacteria in association with the epithelial layer

Helicobacter pylori, cause of stomach ulcers

Journal of Clinical Microbiology. 37: 2456-2460.) Infection with Helicobacter pylori, the bacteria responsible for peptic ulcers, may be transmitted via the hands In the study, researchers analyzed H. pylori infections in a small, rural population in Guatemala, testing blood samples, oral samples and samples from underneath the fingernails. They found that over half of the subjects tested positive via blood test, nearly 90 percent tested positive for oral carriage of the infection and over half tested positive for fingernail carriage. "Helicobacter pylori infection remains one of the most common in humans, but the route of transmission of the bacterium is still uncertain," say the researchers. "The results of this study suggest that oral carriage of H. pylori may play a role in the transmission of infection and that the hand may be instrumental in transmission.” (S.A. Dowsett, L. Archila, V.A. Segreto, C.R. Gonzalez, A. Silva, K.A. Vastola, R.D. Bartizek and M.J. Kowolik. 1999. Journal of Clinical Microbiology. 37: 2456-2460.)

Normal flora of the GI tract (cont.) The upper portions of the small intestine are acidic and resemble the stomach. The lower portions have increasing numbers of bacteria, from 105 to 107 per gram. The large intestine has enormous numbers of bacteria, 1010 to 1011 cells/gram! Is essentially a fermentation vessel.

See http://www.sciencemag.org/cgi/content/full/289/5484/1483 Why don’t all these commensal bacteria produce a constant and massive inflammation of the GI tract epithelial cells? A recent study published in the journal Science indicates that the normal flora apparently shuts off the inflammation response in host epithelial cells See http://www.sciencemag.org/cgi/content/full/289/5484/1483

Normal flora of other places Urogenital tract -- bladder usually sterile but urethra epithelium colonized by Gram-neg. rods like E. coli. These can become opportunistic pathogens.

Upper respiratory tract -- Staphylococcus, Streptococcus, diphtheroid bacilli, Gram-neg. cocci. Also some pathogens Lower respiratory tract -- essentially sterile

Questions?