Allies and Enemies: How the World Depends on Bacteria by Anne Maczulak Read Free Book Online Page B

self-inoculation, when touching their hands to the mouth,
    eyes, or nose. Adults touch their hands to their face hundreds of times a day, and children do it more frequently.
    A baby’s digestive tract has some oxygen in it so aerobic bacteria
    and facultative anaerobes prosper there first. E. coli colonizes the gut early on and uses up the oxygen. A population of anaerobes then begins to dominate: Bacteroides , Bifidobacterium , Enterococcus , and Streptococcus make up the common genera. The adult digestive tract distal to the mouth will eventually contain 500 to 1,000 different species of bacteria and a lesser number of protozoa.
    Pathogens make up a minority of all bacteria, but the word
    “germs” brings only bad connotations. A growing number of microbiologists have nonetheless begun to see the potential benefits of exposure to germs. In the 1980s German pediatrician Erika von Mutius investigated the apparent high incidences of asthma and allergies in industrialized nations compared with developing areas. She compared
    the health of children from households that received little housekeep—
    ing with counterparts in well-managed households with regular clean—
    ings. Children who had been exposed to a dirty environment had fewer
    respiratory problems than children from cleaner surroundings. Von Mutius therefore proposed that a steady exposure to germs might help
    youngsters develop strong immune systems.
    Von Mutius’s “hygiene hypothesis” drew criticism from microbiologists and, unsurprisingly, manufacturers of cleaning products. But
    pediatric allergist Marc McMorris supported the hypothesis, saying,
    “The natural immune system does not have as much to do as it did
    50 years ago because we’ve increased our efforts to protect our children from dirt and germs.”
     
    chapter 1 · why the world needs bacteria
    31
    Questions have not yet been answered on whether continued use
    of disinfectants and antimicrobial soaps change bacteria at the gene
    level. Medical microbiologist Stuart Levy has argued that antibiotic
    overuse combined with overzealous use of antimicrobials leads to bacteria resistant to the chemicals meant to kill them. These bacteria
    may develop subsequent resistance to antibiotics. Bacteria eject harmful chemicals and also antibiotics from inside the cell by using a
    pumplike mechanism. If bacteria use the very same pump for chemical disinfectants as for antibiotics, the vision of a new generation of super-resistant bacteria becomes probable. Imagine hospitals where no antibiotics can stop pathogens and few chemical disinfectants can
    kill them. Doctors and microbiologists have warned that medicine is
    inching closer to this very scenario.
    The body helps native flora defend against pathogens that
    attach to the skin. The enzyme lysozyme in tears and saliva kills bacteria, and skin oils contain fatty acids that inhibit gram-positive bacteria. If those defenses fail, the immune system sets in motion a hierarchy of defenses meant to find and destroy any foreign matter
     
    in the bloodstream.
    Dental caries can lead to more serious tooth decay and gum disease, or an infection of the blood if the oral lesions are severe. In plaque, Streptococcus mutans , S. sobrinus , and various lactobacilli (lactic acid-producing bacteria) initiate caries formation by producing acids. Lactic, acetic (also in vinegar), propionic, and formic acid diffuse into the tooth enamel and break it down by demineralization, meaning the removal of minerals such as calcium. Demineralization occurs several times a day in a cycle in which new dietary calcium and
    phosphate and fluoride from toothpaste replace the lost minerals.
    Dental caries offer an exception to the rule that native flora do not
    initiate infection.
    On the skin, some bacteria create a nuisance. Skin bacteria consume amino acids, salts, and water excreted by eccrine sweat glands.
    These glands located all over the body produce copious amounts of watery sweat