Normal flora


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Normal flora

  1. 1. Normal flora, disturbance & infections Dr. B. K. Iyer
  2. 2. Microorganisms of the skin and mucous membranes• Microbial flora of the skin and mucous membranes consist of: 1. Resident flora, usually commensal microorganisms 2. Pathogenic microorganisms
  3. 3. Normal flora of the skin• Staphylococcus epidermidis• Staphylococcus aureus (in small numbers)• Alpha-hemolytic and nonhemolytic Streptococcus• Micrococcus species• Peptostreptococcus species• Neisseriae species ( nonpathogenic )• Propionibacterium species• Diphtheroids• Candida species ( small numbers )• Acinetobacter species ( small numbers )
  4. 4. Normal flora of the skin• The skin is particularly apt to contain transient microorganisms, because of its constant exposure to and contact with the environment• There is a constant and well-defined resident flora, modified in different anatomic area by secretions, proximity to mucous membranes (mouth, nose, perineal areas) and habitual wearing of clothing.
  5. 5. Normal flora of the skin• Neither profuse sweating nor washing and bathing can eliminate or significantly modify the normal resident flora• The number of superficial microorganisms may be diminished by vigorous daily scrubbing with soap, but the flora is rapidly replenished from sebaceous and sweat glands even when contact with other skin area or with the environment is completely excluded.
  6. 6. Normal flora of the skin• Placement of an occlusive dressing on the skin tends to result in a large increase in the total microbial population and may also produce qualitative alterations in the flora.
  7. 7. Normal flora of the skin• Anaerobic and aerobic bacteria often join to form synergistic infections (gangrene, necrotizing fasciitis, cellulitis) of skin and soft tissues• The bacteria are frequently part of the normal microbial flora• It is usually difficult to pinpoint one specific organism as being responsible for the progressive lesion, since mixtures of organisms are usually involved.
  8. 8. Role of the resident flora• Role of resident flora of the skin and mucous membranes: – To prevent colonization by pathogens and possible disease through bacterial interference.• The mechanisms of bacterial interference : 1.Competition for receptors or binding site on host cells 2.Competition for nutrients 3.Mutual inhibition by metabolic or toxic products 4.Mutual inhibition by antibiotic materials or bacteriocins.
  9. 9. Role of the resident flora• The factors that may be important in eliminating nonresident microorganism from the skin are the low pH, the fatty acid in sebaceous secretions, and the presence of lyzozyme.• Suppression of the normal flora creates a partial local void that tend to be filled by microorganisms from the environment or from other part of the body.
  10. 10. Role of the resident flora• Members of the normal flora may themselves produce disease under certain circumstances.• Such organisms behaves as opportunists and may then become pathogens.• These organisms are adapted to the noninvasive mode of life defined by the limitations of the environment.
  11. 11. Role of the resident flora• If we forcefully remove the restrictions of that environment and they are introduced into the blood stream or tissues, these organisms may become pathogenic. – Eg. Large numbers of Streptococcus viridans (normal flora of the upper respiratory tract) introduced into bloodstream (following tooth extraction or tonsillectomy), they may settle on deformed heart valve and produce infective endocarditis.
  12. 12. Normal Intestinal flora,disturbance & infections Dr. B. K. Iyer
  13. 13. Normal flora of the intestinal tract• At birth the intestine is sterile, but organisms are soon introduced with food.• Bowels of newborns in intensive care nurseries tend to be colonized by Enterobacteriaceae, e.g. Klebsiella, Citrobacter, Enterobacter.• Diet has a marked influence on the relative composition of the intestinal fecal flora.
  14. 14. Normal flora of the intestinal tract• In breast-fed children, – the intestine contain large numbers of lactic acid streptococci and lactobacilli. These aerobic and anaerobic, gram positive, nonmotile organisms (e.g. Bifidobacterium species) produced acid from carbohydrates and tolerate pH 5.0• In bottle-fed children, – a more mixed flora exist in the bowel, and lactobacilli are less prominent. As food habits develop toward the adult pattern, the bowel flora changes.
  15. 15. Normal flora of the intestinal tract• In normal adults, the esophagus contains microorganisms arriving with saliva and food.• The stomach’s acidity keep the number of microorganisms at minimum (103 – 105 /gr content ) unless obstruction at pylorus favors the proliferation of gram +ve cocci & bacilli.• The normal acid pH of the stomach markedly protects against infection with some enteric pathogens, e.g. cholera.
  16. 16. Normal flora of the intestinal tract• Administration of H2 receptor blockers like cimetidine for peptic ulcer leads to great increase in microbial flora of the stomach, including many organisms usually prevalent in feces.
  17. 17. Normal flora of the intestinal tract• As the pH of intestinal content become alkaline, the resident flora gradually increases. – In the adult duodenum, there are 103 -106 bacteria per gram of content; – In the jejunum and ileum, 105-108 bacteria/gr; and – In the cecum and transverse colon, 108-1010 bacteria/gr
  18. 18. Normal flora of the intestinal tract• As the pH of intestinal content become alkaline, the resident flora gradually increases. – In the upper intestine, lactobacilli and enterococci predominate, but in the lower ileum and cecum, the flora is fecal – In the sigmoid colon and rectum, there are about 1011 bacteria/gr of content, constituting 10 – 30% of the fecal mass
  19. 19. Normal flora of the intestinal tract• Anaerobes outnumber facultative organisms by 1000-fold. In diarrhea the bacterial content may diminish greatly, whereas in intestinal stasis the count rises• In the normal adult colon, 96 – 99% of the resident bacterial flora consists of anaerobes – Bacteroides sp, especially B. fragilis – Fusobacterium sp – Anaerobic lactobacilli, e.g. bifidobacteria – Clostridia ( C.perfringens, 103 -105/gr) – Anaerobic gram positive cocci (Peptostreptococcus sp)
  20. 20. Normal flora of the intestinal tract• Only 1 – 4% are facultative aerobes: – Gram negative coliform bacteria – Enterococci – Small number of protei, pseudomonads, lactobacilli, candidae – More than 100 distinct types of organisms, which can be cultured routinely in the laboratory, occur regularly in the normal fecal flora
  21. 21. Normal flora of the intestinal tract• There probably are more than 500 sp of bacteria in the colon including many that are likely unidentified.• Minor trauma(e.g. sigmoidoscopy, barium enema) may induce transient bacteremia in about 10% of procedures
  22. 22. Normal flora of the intestinal tract• Intestinal bacteria are important in : – Synthesis of vitamin K – Conversion of bile pigments and bile acids – Absorption of nutrients and breakdown products – Antagonism to microbial pathogens• The intestinal flora produces ammonia and other breakdown products that are absorbed and can contribute to hepatic coma – Among aerobic coliform bacteria, only few serotypes persist in the colon for prolonged periods, and most serotypes of Escherichia coli are present only over period of a few days
  23. 23. Normal flora of the intestinal tract• Antimicrobial drugs taken orally can, in human, temporarily suppress the drug susceptible component of the fecal flora• This is commonly done by preoperative oral administration of insoluble drug. – For example, neomycin plus erythromycin can in 1 – 2 days suppress part of the bowel flora, especially aerobes
  24. 24. Normal flora of the intestinal tract• Metronidazole accomplishes that for anaerobes. – If lower bowel surgery is performed when the counts are at their lowest, some protection against infection by accidental spill can be achieved• However, soon thereafter the counts of fecal flora rise again to normal or higher than normal levels, principally of organisms selected out because to relative resistance to the drug employed.
  25. 25. Normal flora of the intestinal tract• Drug susceptible microorganisms are replaced by drug resistant ones, particularly staphylococci, enterobacters, enterococci, protei, pseudomonads, Clostridium difficile and yeast.• The anaerobic flora of the colon, including B. fragilis, clostridia and peptostreptococci play a main role in abscess formation originating in perforation of the bowel.
  26. 26. Normal flora of the intestinal tract• Prevotella bivia, P. disiens are important in the abscesses of the pelvis originating in the female genital organ. These species are penicillin-resistant• The feeding of large quantities of Lactobacillus acidophilus may result in the temporary establishment of these organisms in the gut and the concomitant partial suppression of other gut microflora.
  27. 27. Normal Vaginal flora,disturbance & infections Dr. B. K. Iyer
  28. 28. Normal physiology of vagina• Normal physiology of vaginal discharge include: – Cervical & vaginal epithelial cells, – Normal bacteria flora , – Water, – Electrolytes and – Other chemicals.
  29. 29. Normal flora of vagina• The normal vaginal vaginal flora often includes also alpha hemolytic streptococci, anaerobic streptococci( peptostreptococci), Prevotella sp , clostridia, Gardnerella vaginalis, Ureaplasma urealyticum, and sometimes listeria or Mobiluncus sp• Normal vaginal pH varies from 4 – 4.5.
  30. 30. Normal flora of the vagina• Soon after birth, aerobic lactobacilli appear in the vagina and persist as long as the pH remains acids (several weeks).• When pH become neutral (remaining so until puberty), a mixed flora of cocci and bacilli is present.• During birth, Vaginal organisms present at time of delivery may infect the newborn (e.g. group B streptococci) that subsequently leads to neonatal sepsis and meningitis.
  31. 31. Normal flora of the vagina• At puberty, aerobic and anaerobic lactobacilli reappear in large numbers and contribute to the maintenance of acid pH through the production of acid from carbohydrates, particularly glycogen.• This appears to be an important mechanisms in preventing the establishment of other, possibly harmful microorganism in the vagina
  32. 32. Normal vaginal response• Lacto bacillus produces lactic acid fatty acid and organic acid .• Glucose is the source of organism. After menopause as there is decrease in glucose availability in the vaginal secretions, there is a decreased substrate for acid production.• This lead to increase vaginal pH.• FSH has direction relation with vaginal pH while estradiol has inverse relation.
  33. 33. Normal flora of the vagina• If lactobacilli are suppressed by the administration of antimicrobial drugs, yeast or various bacteria increase in numbers and cause irritation and inflammation• After menopause, lactobacilli again diminish in number and mixed flora returns.• The normal vaginal flora includes group B streptococci in as many as 25% of women
  34. 34. Vaginal infections• The cervical mucus has antibacterial activity and contain lyzozyme that reduces chances of infection.• In some women, the vaginal introitus contain a heavy flora resembling that the perineum and perianal area• This may be a predisposing factor in recurrent urinary tract infections
  35. 35. Vaginal infections• Vaginal infection are often (varies between countries between 20 to 40% of vaginal infections) a mix of various etiologies, which present challenging cases for treatment.• Indeed, when only one cause is treated, the other pathogens can gain in resistance and induce relapses and recurrences.• The key factor is therefore to get a precise diagnosis and treat with broad spectrum anti- infective (often inducing adverse effects).
  36. 36. Fungal vaginosis
  37. 37. Bacterial vaginosis• Most common vaginal infection in women of reproductive age.• It reflects a shift in vaginal flora from lactobacilli dominant to mixed flora (genital microplasma ,g.vaginalis , anaerobes)• no causative agent has been identified.• Due absence of inflammation in biopsy, hence the term vaginosis rather than vaginitis
  38. 38. Vaginal infections - summary
  39. 39. Normal flora of the urethra• The anterior urethra of both sexes contains small numbers of the same types of organisms found on the skin and perineum• This organism regularly appear in normal voided urine in numbers of 102 – 104/mL