Infection and Disease I

1. Infection and Disease I The Normal Microflora of the Human Body

2. Humans as Habitats • Bodies are great places to be! • Warm, stable, lots of nutrients available, constant pH and osmotic pressure, etc. • 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 (S. pyogenes, S. aureus, etc.) in low numbers in and on us

3. 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

4. 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.

5. 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 Clostridiumdifficile and some enterobacteria • One study demonstrated that bottle-fed infants were 4X as likely as breastfed ones to harbor C. difficile.

6. 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 specific regions

7. 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

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

9. 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.

10. 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.

11. Aromabacter malodorens is the bacterium that colonizes healthy human skin. This organism grows on sweat and produces butyrate and other organic acids which smell bad in high concentrations. • This past year, scientists affiliated with the International Society for Microbial Ecology created a genetically engineered strain of this microorganism that can help banish unpleasant underarm odor. • Scientists removed the butyrate synthase gene that causes one of the unpleasant odors. Scientists then inserted the DNA from an Asian Musk Deer that encodes muskolic acid. Muskolic acid is the compound that gives musk oil its characteristic smell. • In preliminary studies, this new strain of Aromabacter malodorens survives well on the human skin. Scientists are now working on ways for the genetically engineered bacteria to out compete native populations of foul-smelling bacteria. • The ISME plans to market an underarm deodorant containing these new bacteria and license this technology to other deodorant manufacturers. Because the deodorant is self-replicating, it requires only monthly application. • If this microorganism sells well, the ISME plans to genetically engineer a mint-flavored bacterium for the mouth. • If you would like more information or would like to participate in a deodorant trial, please email Dr. Gutensmell.Enjoy April Foolery.

12. 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.

13. Biofilm (plaque) formation • Begins as thin film of glycoproteins in saliva • This is colonized (quickly) by individual Streptococcus (S. mutans, etc.) cells, which grow to microcolonies • Extensive growth of these results in formation of a thick biofilm. Further colonization can include filamentous forms, spirochetes, and various anaerobes.

14. 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

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

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

17. 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

18. Normal flora of the GI tract (cont.)

19. 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

20. 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

21. Helicobacter pylori, cause of stomach ulcers

22. 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.)

23. 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.

25. 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

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

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