Normal Flora of the Human Body

• 1. Microbial Ecology


  is the study of the relationship between microorganisms and their environment
• resident flora


  organisms that are relatively of fixed types and are regularly found in a given area of the body at a given age
• transient flora


  those that inhabit the skin and mucous membrane temporarily for hours , days, or weeks and are derived from the environment
• skin


  the part of the human body that is in constant contact with the environment
• secretion of vit k
• production of mucin
• aids in digestion of foods by producing enzymes such as cellulose, galactosidase, and glucosidase
• helps in metabolism of steroids
• lysozyme breaks down the peptidoglycan layer of bacterial cell wall
• acidic pH due to sweat contains antimicrobial peptides such as dermcidin
• sebum production - oily substance which helps to lubricate the skin and maintain its hydration
• desquamation (skin shedding) - helps to remove microorganisms that may be present on the surface of the skin
• Staphylococcus epidermidis - major skin inhabitant, 90% resident aerobic flora
• Staphylococcus aureus - found in nose and perineum ; in the nose varies with age, greater in newborns than in adults
• Micrococci (Micrococcus luteus) - 20-80% of micrococci in the skin
• Diphtheroids (Coryneforms)
• lipophilic - axilla
• non-lipophilic - palms of hands
• Anaerobic diphtheroids - sebaceous glands
• Tongue and buccal mucosa - RF: Streptococcus viridans group (S. mutans, S. milleri, S. salivarus, S. sanguinis)
• Streptococcus viridans group - causative agent of dental caries
• Pharynx and Trachea - TF (potentially pathogenic); Haemophilus influenzae, Streptococcus pneumoniae, Neiseria meningitidis, and Mycoplasma pneumoniae
• Upper respiratory tract - Neisseria meningitidis, Corynebacterium diptheriae, and Bordetella pertussis
• Conjunctiva - Neisseria, Moraxella catarrhalis, Staphylococcus epidermidis, Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pneumoniae
• Esophagus - transient mouth flora
• Stomach - TF; Lactobacillus
• colonizer: Helicobacter pylori (urase that causes alkalinization of gastric acid)
• small intestine: TF; streptococci, lactobacilli, and bacteroids
• large intestine: RF; Bacteroides fragilis, Lactobacillus bifidum (breastfed infants), Lactobacillus acidophilus (bottle-fed infants), Eubacterium coli, and Enterobacteriaceae
• Anterior urethra: RF; Staphylococcus epidermidis, enterococci, and diphtheroids
• Male and female secretions: Mycobacterium smegmatis (normal commensals)
• Penile urethra: RF; Gardnerella vaginalis, Bacteroids, and alpha streptococci
• Female urethra: RF; Staphylococcus epidermidis
• Vagina: RF; Lactobacillus spp
• onset of puberty: Lactobacillus acidophilus, corynebacteria, peptostreptococci, streptococci, Bacteroids, and staphylococci
• 1 month until age of puberty: Staphylococcus epidermidis, streptococci, diphtheroids, and E. coli
• after menopause: fungi such as Torulopsis and Candida