MODULE 4A

• MICROBIAL ECOLOGY is the study of the relationship between microorgansims and their environment.
• NORMAL FLORA consists of a group of organisms that inhabit the body of a normal healthy individual in the community.
• NORMAL FLORA is these may be non-pathogenic or pathogenic and may at times behave as opportunities pathogens.
• Sterile body fluids contains: CEREBROSPINAL FLUID, SYNOVIAL FLUID and BLOOD
• SKIN is the part of the body that us in constant contact w/ the environment, making the most exposed to microorganisms.
• AXILLA, PERINUEM and TOE WEBS has higher moisture levels, higher body temperature and higher levels of surface lipids
• Staphylococcus epidermidis – major skin inhabitant
• Staphylococcus aureus – most commonly found in nose and perineum, in the nose it is greater in newborns than in adults
• Micrococci (micrococcus luteus ) – accounts for 20% to 80% of micrococci in the skin
• Diphtheroids (Coryneforms) have three classifications; LIPOPHILIC, NON-LIPOPHILIC and ANAEROBIC DIPHTEROIDS
• LIPOPHILIC is common in axilla
• LIPOPHILIC is attracted to fats/lipid
• LIPOPHILIC is the source of energy
• NON-LIPOPHILIC more common glabrous or hairless skin such as palms of hands
• NON-LIPOPHILIC is opposite of lipophilic, they are not attracted to fats/lipids
• ANAEROBIC DIPTHEROIDS thrive in areas which their is an absence of oxygen
• Gram-negative bacilli (Enterobacter, klebsiella, Escherichia coli, and proteus spp.) is seen in the toe webs and axilla
• Nail flora are fungi that may be present (aspergillus, penicillum, cladosporium, mucor)
• The normal flora of humans are exceedingly complex and consist of more than 200 species of bacteria
• Factors that influence the makeup of normal flora


  • Genetics
  • Age
  • Sex
  • Stress
  • Nutrition
  • Diet
• Three developmental changes in humans (weaning, eruption of teeth, onset and cessation of ovarian functions) invariably affect the composition of the normal flora in the intestinal tract, oral cavity, and vagina respectively
• Colonization of the body surfaces by normal flora

  1. Fetus is sterile in utero

  2. Colonization begins at birth when passing through birth canal

  3. Handling and feeding of infant leads to establishment of stable normal flora on skin, oral cavity and intestinal tract in about 48 hours
• A human adult houses about 10^14 bacteria on the skin, 10^9 in the mouth, and 10^14 in the gastrointestinal tract
• The number of bacteria in the gastrointestinal tract is far in excess of the number of eukaryotic cells in all the tissues and organs which comprise a human
• Microbial ecology


  The study of the relationship between microorganisms and their environment

  
• Normal flora


  A group of organisms that inhabit the body of a normal healthy individual in the community
• Normal flora


  • May be non-pathogenic or pathogenic and may at times behave as opportunistic pathogens
  • Protects the body's organs and systems that are in direct contact with the external environment
  • Synthesize important vitamins essential to humans
  • Secrete vitamin K needed for activity of some clotting factors
• Beneficial effects of normal flora


  • Prevent pathogenic organisms from attaching to and penetrating skin and other tissues
  • Aid in digestion of food by producing enzymes
  • Help in metabolism of steroid
• Sterile body tissues


  • Urinary bladder
  • Uterus
  • Fallopian tube
  • Middle ear
  • Paranasal sinuses
• Sterile body fluids


  • Cerebrospinal fluid (CSF)
  • Synovial fluid
  • Blood
• Skin


  • Most exposed to microorganisms
  • Factors that eliminate non-resident flora: lysozyme, acidic pH, free fatty acids, constant sloughing off
• Divisions of the skin

  • Axilla, perineum and toe webs
  • Hand, face and trunk
  • Upper arms and legs
• Normal flora on the skin


  • Staphylococcus epidermidis - major inhabitant
  • Staphylococcus aureus - most common in nose and perineum
  • Micrococci (Micrococcus luteus) - 20-80% of micrococci
  • Diphtheroids (Coryneforms) - lipophilic, non-lipophilic, anaerobic
  • Gram-negative bacilli (Enterobacter, Klebsiella, E. coli, Proteus) - in toe webs and axilla
  • Fungi (Aspergillus, Penicillium, Cladosporium, Mucor) - in nails
• Mouth and respiratory tract


  • Tongue and buccal mucosa - Streptococcus viridans group
  • Pharynx and trachea - similar to oral cavity, transient carriage of potentially pathogenic organisms
  • Upper respiratory tract - initial colonization by Neisseria, Corynebacterium, Bordetella
  • Lower respiratory tract - usually sterile, organisms destroyed by defense mechanisms
• Conjunctiva


  • Very scanty normal flora, held in check by flow of tears containing lysozyme
  • Transient bacteria include Neisseria, Moraxella, Corynebacterium, Staphylococci, Streptococci
• Digestive tract


  • Esophagus - transient mouth flora
  • Stomach - minimal bacteria due to acidity, Helicobacter pylori can colonize
  • Small intestines - scanty flora, transient bacteria
  • Large intestines - anaerobes (Bacteroides, Bifidobacterium, Eubacterium, Peptostreptococcus, Clostridium), facultative aerobes (E. coli, Enterobacteriaceae)
• Roles of intestinal flora


  • Synthesis of vitamin B complex and vitamin K
  • Conversion of bile into bile acids
  • Competition with transient flora for nutrients
  • Prevention of colonization by transient flora
  • Production of potentially pathogenic end-products toxic to transient flora
• Normal flora of the digestive tract

  • Enterococci
  • Lactobacilli
  • Enterobacteria
  • Enterococcus faecalis
  • Bacteroides
  • Bifidobacterium
  • Eubacterium
  • Peptococcus
  • Peptostreptococcus
  • Ruminococcus
  • Clostridia
  • Lactobacilli
  • Streptococcus
  • Staphylococcus
• Genitourinary tract


  • Urinary tract - sterile above distal 1cm of urethra
  • Anterior urethra - Staphylococcus epidermidis, enterococci, diphtheroids
  • Penile urethra - Gardnerella vaginalis, Bacteroides, alpha streptococci
  • Female urethra - sterile or Staphylococcus epidermidis
  • Vagina - flora varies by age, hormones, pH (lactobacilli in infants, cessation of glycogen secretion after 1 month to puberty)
• Bacteria


  • Lactobacilli
  • Peptostreptococcus
  • Enterobacteria
  • Ruminococcus
  • Enterococcus faecalis
  • Clostridia
  • Bacteroides
  • Bifidobacterium
  • Eubacterium
  • Streptococcus
  • Staphylococcus