Infection and Disease I

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Infection and Disease I

• The Normal Microflora of the Human Body

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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 doesnt mean non-pathogenic we
  sometimes have pathogens (S. pyogenes, S. aureus,
  etc.) in low numbers in and on us

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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
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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.

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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.

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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, youre in
  trouble!)

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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

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Normal flora of the skin (cont.)

• The dermis and subcutaneous tissue are normally
  sterile

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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.
• Dont 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.

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• 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. 362377-2379.)
• 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.

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• 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.

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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.

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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.

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• 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

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• Plaque accumulates calcium salts to form tartar

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• Scale magnified 7,000x to show imbedded
• bacterial biofilm

http//www.buckman.com/eng/biofilm3.htm
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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

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Normal flora of the GI tract (cont.)
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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

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• 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

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Helicobacter pylori, cause of stomach ulcers
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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.)
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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.

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Why dont 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

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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.

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

• Lower respiratory tract -- essentially sterile