microbial flora of human body

Normal Miicrobial Flora:

Microorganisms that are usually found associated with healthy ody tissue are called noral microbial flora. Normal flora is almost found on the surface of body expose to the envirnoment. While internal organs such as central nervous system, kidney, heart, bolld etc. are sterile. Foetus first gains its normal flora while passing through the birth canal.

Normal flora are commensals i.e they get bebefits from the host but the host is not affected while others are mutastic i.e they get to benefit from the host and at the same time give benefit yo the host. Furthurmore some normal flora is oppourtinistic pathogen. i.e they cause diseases if ressistance capacity of the host is decreased.

Beneficial role of normal flora:

• It prevents attachment of the pathogenicity. Microorganisms to the host tissue by occupying their habitat.
• Much normal flora produces mucin that forms mucus blanket and prevents attachment of pathogenic bacteria.
• Some normal flora produces the antimicrobial substance that kills pathogens.
• Some intestinal bacteria produces the vitamin.
• Some antibody produce in response to normal flora kill pathogenic organism having common antigen.

Harmful effects of Normal flora:

• Some normal flora acts as the oppourtunistic pathogen and causes disease when disease resistance capacity of the host is decreased.
• Some normal flora causes diseases outside their normal habitat eg, E.coli normally lives in interesting if it enters the urinary bladder tract it cause urinary tract infection.

Normal flora of skin:

Skin consists of outer epidermis and inner dermis with hair follicle, sweet gland and sebaceous glands. Although large number oforganisms are found in skin, some factor responsible to affect their growth. They are:

1. Dryness of skin prevents growth of most bacteria. Skin of some area such as genital area nipples and toes are rich in sweat glands and sebaceous glands therefpre number of organisms are high in these relatively moist skin.
2. Normal p^H of skin is 3-5 which prevents the growth of most bacteria.
3. Skin also contains a large number of antimicrobial chemical such as lysozyme which kills many microorganisms.

Skin contains mainly two types of normal flora i.e. transient and resident. Transient normal flora come into skin from other sources. For eg, by contamination with other materials they cannot multiply in skin and usually die. However resident normal flora are natural inhabitants of skin. They do not only survive but also multiply in skin. Some commonly occurring resident normal flora multiply in skin is Staphylococcus aureus, Staphylococcus epidermis, Propionibacterium acne and some lipophilic yeast such as Pityrosporum.

Normal flora of gastro-intrestinal tract:

gastro-intrestinal tract consists of oesophagus, stomach, small intrestine and large intrestine. Since, different part Gastro-intrestinal tract differs in their envirnomental, chemical and physical properties the number and type of flora is different in different path;

1. Normal flora of intrestine:stomach receives many microorganisms from mouth along with food. However bacterial activity of HCL in stomach kills most of them. Only few organisms can tolerateacidic p^H can form resident flora of stomach. Common eg; Lactobacillus, Candida albicians and Helicobacter pylon. Immediately after ingestion of food, number of organism increases in stomach but the number decreases the gastric juice is secreated.
2. Normal flora of small intrestine: Duodenum lies adjacent to the stomach and here is slightly acidic. Therefore, microorganisms of duodenum are similar to that of stomach i.e lactobacillus and Enterococca. From duodenum, the p^H gradually increases from duodenum to ileum. In jujenum, Enterococci, Lactobacillus Diptheroids, and candida albicans are found. Microorganisms of ileum resemble that of large intrestine.
3. Normal flora of large intrestine: large intrestine contains the largest number of microorganisms mainly anaerobes and facutative anaerobes. facultative anaerobes utilize O₂ in large intrestine and make it anaerobic common orgaisms they are:

• Anaerobes: Bacteroid, Bifidobacterium, Clostridium perfringes, Peptococcus, Peptosterococcus.
• Facultative Anaerobes: E. coli, Streptococcus faecal, Candid Albicans
• Protozoa: Trichomonas hominids.

Normal flora of respiratory tract:

1. Upper respiratory tract: It includes nasopharynx, oropharynx and throat. Although many microorganisms enter into upper respiratory tract from air, most of them are removed by mucus lining of respiratory tract. first microorganisms are trapped in mucus than beating of cilia causesthe mucus to flow into oropharynx. From oropharynx these organisms are swalloed and destroyed in stomach by HCL. mucus also contains lysozyme that kills microorganisms.
2. Lower respiratory tract:It doesn;t contain normal flora. As the air enters into the lower respiratory tract,its velocity decreases. Then microorganisms settle on the wall of respiratory tract. In this wall ,mucous moves upward by movement of cilia so that microorganisms are removed and cannot reach to the lung are then removed by phagocytic cell of lung called alveolar macrophages.

Normal flora of Mouth:

Abundant moisture and sufficient food facilities rapid growth of microorganisms. However the continuous flow of saliva from mouth removes many microorganisms into the stomach. Desquamation is other mechanism which removes many microorganisms into the stomach. Desquamation is other mechanism is the other mechanism which removes microorganisms from mouth. It is a removal of epithelial cell inhibited by microorganisms. Predominant normal flora of mouth are Streptococcus, Neisseria, Veillonella, Actinomycetes and lactobacillus.

Normal Flora of teeth:

Bacteria commonly found in teeth are Streptococcus mutants, Bacteriol and Fusobacterium. Streptococcus mutants attached to the surface of the teeth by its capsule and causes dental carries.

Normal flora of genito-urinary tract:

In healthy person kidney, urinary bladder and ureter are free of normal flora. However, urethra of male and female contains Staphylococcus epidermis, Streptococcus faecal and Corynebacterium species, Neisseria and E. coli are occasionally found.

Normal flora of vagina:

it depends upon menstrual cycle. In general acid tolerant organisms such as Lactobacillus, Enterococcus, Candida, and Diptheroids are found in vagina. Lactobacillus breakdown glycogen into lactic acid and maintain the vaginal p^H about 4.4-4.6

References:

C.H.Collins. (1995). Microbiological Methods. Oxford Univ Press.

D.Greemwood, R. S. (2002). Medical Microbiology. London: Churchill Livingstone.

M.J.Pelezar. (1993). Microbiology. Tata McGraw hill.

M.T.Madigan, J. a. (1997). Biology of microorganisms. London: Prentice hall International Inc.

R.N.Atlas. (1984). Fundamentals and Applications. NewYork: MacMiHiam Publishing Co.