Normal flora of the body medical bacteriology

Medical bacteriology, normal flora of the body

1. VIVEKANANDHA ARTS AND SCIENCE COLLEGE FOR WOMEN, VEERACHIPALAYAM, SANGAGIRI, SALAM. DEPARTMENT OF MICROBIOLOGY SUBJECT : MEDICAL BACTERIOLOGY TOPIC : NORMAL FLORA OF THE BODY SUBJECT INCHARGE SUBMITTED BY R. MYTHILI, K. KANMANI, HEAD OF THE DEPARTMENT, III- B.Sc. MICROBIOLOGY, DEPARTMENT OF MICROBIOLOGY, VIVEKANANDHA ARTS AND SCIENCE VIVEKANANDHA ARTS AND SCIENCE COLLEGE COLLEGE FOR WOMEN, FOR WOMEN, VEERACHIPALAYM VEERACHIPALAYAM, SANGAGIRI, SANGAGIRI, SALAM. SALAM.

2. Definition The term normal microbial flora denotes the population of Microorganisms, that inhabit the skin and mucous membranes of healthy normal persons from shortly after birth Until death. Introduction Human beings, like other animals, harbour a wide array of microorganisms both on and in their bodies. The normal microbial flora are more or less constant for each species and are broadly divided into residents and transients. Resident flora: constitute a constant population which cannot be completely removed permanently, while the latter very from time to time and are temporary. Transient flora: May be potentially pathogenic or non pathogenic organisms that are present at some point of time but not always.

3. Role of normal microbial flora : Normal flora play an important role in body economy. They can: Become pathogenic when host defences falter, Prevent or interfere with colonisation / invasion of the body by pathogens, Raise the overall immune status of the host against pathogens having related or shared antigen. The microflora of the intestinal tract synthesise Vitamin k and several B vitamins which supply on occasion the body's needs. The antibiotic substances produced some, for example, colicin, have a harmful effect on pathogens. On the contrary, the opportunistic pathogens among them cause disease when the body’s defence mechanisms fail. Their abnormal multiplication can cause disease such as enteritis and endotoxic shock. Penicillin's producing organisms can aggravate infection by interfering with therapy, certain streptococci of the mouth cause dental caries.

4. Normal flora of the skin The human skin is constantly and continuously bombarded by organisms present in the environment. It is also contaminated by one’s own secretion and excretions, the extent depending on the individuals personal hygiene. The flora depend on the area of the body, the clothing one wears, one’s occupation and environment. Transient microflora tend to occur more frequently on the skin. Cultures from the skin have frequently demonstrated diphtheroids, staphylococci( aerobic and anaerobic ) Gram positive, aerobic, spore bearing bacilli: S. Viridians: S. faecalis: Gram negative bacilli such as E. Coli, proteus and other intestinal organisms : mimieae: mycobacteria ( non pathogenic) : candida albicans: cryptococci pityrosporum ovale.

5. Often the skin of the face, neck, hands and buttocks carries pathogenic hemolytic Streptococci and staphylococci. Hair frequently harbours S.aureus forms a reservoir for cross infection. Normal flora of the conjunctiva The conjunctiva is relatively free from organisms due to the flushing action of tears. The predominant organisms of the eye are diphtherias( corynebacteria xerosis), Moraxella species, staphylococci and nonhemolytic streptococci. Normal flora of the nose, nasopharynx and sinuses The floor of the nose harbours corynebacteria, staphylococci and straptococci. Haemophilus species and Moraxella lacunata may be seen. The nasopharynx of the infant is sterile at birth but, within 2-3 days after birth, acquires the common flora and the pathogenic flora carried by the mother and the attendants. The nasopharynx can be considered the natural habital of the common pathogenic bacteria which cause infections of nose, throat, bronchi, and lungs. certain Gram negative organisms from tge intestinal tract such as pseudomonas aeruginosa, E. Coli, paracolons and proteus are also occationally found in normal persons.

6. After penicillin therapy, they may be the predominant flora. Normal flora of the mouth and upper respiratory tract The mouth contain a Plethora of organisms pigmented and nonpigmented micrococci, some which are aerobic, gram positive, aerobic spore bearing bacilli, coliform, lactobacilli. The gum pockets between the teeth , and the crypts of the tonsils have a wide spectrum of the anaerobic flora – anaerobic micrococci, microaerophilic and anaerobic streptococci, vibrio, fusiform bacilli, corynebacterium species, actinomyces,leptothrix are all found in varying extents. Among fungi, candida and geotrichum have been reported. The mouth of the infant is not sterile at birth. It generally contains the same types of organisms in about the same relative numbers as those present in the mother’s vagina, that is a mixture of micrococci, streptococci, coliform bacilli. The first 2-5 days after birth and replaced by the types of bacteria present in the mouth of the mother and nurse. With in 12 hours after birth alpha hemolytic streptococci are found in thevupper respiratory tract.

7. Normal flora of the gastrointestinal tract In 80-90 per cent newborn infants, the meconium is sterile but in 10-20 per cent a few organisms, probably acquired labour, may be present. In all cases, within 4-24 hours of birth intestinal flora is established partly from below and partly by invasion from above. In breastfed children the intestine contains lactobacilli, enterococci, colon bscilli and staphylococci. In artificially fed children L. Acidophilus and colon bacilli and in part enterococci, Gram positive aerobic and anaerobic bacilli are seen. In the normal adult, the microorganisms on the surface of the esophageal wall are those swallowed with saliva and food. The number of bacteria increases progressively beyond the duodenum to the colon, being comparatively low in the small intetine. In the adult normal colon, the resident bacterial flora are mostly anaerobes anaerobic streptococci, anaerobic lactobacilli, clostridia and bacteroidie.

8. Normal flora of the genitourinary tract Mycobacterium smegmatis, a harmless commensal, is found in the smegma of the genitalia of both men and women. This may, by it’s presence in the voided specimens of urine, cause confusion. From apparantly normal men, aerobic and anaerobic bacteria can be cultured frim a high proportion, including lactobacilli, G. Vaginalis, alphs hemolytic streptococci and Bacteroides species. C. Trachomatis and Urea plasma urealyticum may also be present. The female urethra is either sterile or contains a few Gram positive cocci. The vulva of the new born child is sterile but after 24 hours it aquires a varied flora of nonpathogenic organisms from the skin, vagina and intestines. The nature of the flora in the vagina depends on the pH of it’s secretions and it’s enzyme content. In the first 24 hours it is invalved by micrococci, enterococci and diphtheroids. In 2-3 days, the material estrin induces glycogen deposition in the vaginal epithelium. At puberty, the glycogen reappear and the pH changes to acid due to the metabolic activity of Doderleins bacilli, E. Coli and yeasts.

9. Normal flora of the genitourinary tract

10. This change probably helps prevent colonisation by possible harmful microorganisms. During pregnancy there is an increase in Staphylococcus epidermidis, Doderleins bacilli and yeasts. The normal vaginal flora often includes anaerobic cocci and bacilli, listeria, anaerobic streptococci, mimeae, mycoplasma, Gardnerella vaginalis, neisseriae and spirochetes. Bacteria in the blood and tissues The commensals from the normal flora of the mouth, nasopharynx and intestinal tract may get into the blood and tissues. They are usually quickly eliminated by the normal defence mechanisms of the body. Occasional isolation of diphtheroids or non hemolytic strptococvi from normal and abnormal lymph nodes may be those which escaped elimination. Unless the organisms of doubtful pathogenicity are isolated more than once in serial blood cultures, they have little significance.

11. Pseudomembranous colitis Indiscriminate administration of antibacterial agents may completely upset this function of the normal flora by eliminating the resident microorganisms, thus, permitting exogenous and endogenous pathogens to gain the upper hand and to cause disease. In particular, when patients are treated with broad- spectrum antibiotics administered orally, diarrhea may be a side effect due to overgrowth by yeast or staphylococci. When certain drug, especially clindamycin, are given, the anaerobic Gram- positive bacillus, clostridium difficile may be allowed to multiply due to suppression of other members of the flora : this may result in serious, life threating condition known as pseudomembranous colitis. Hence, wherever possible, narrow- spectrum antibiotics should be used at the correct dosage and for the correct duration of time, to prevent suppression of gut flora.

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