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Normal flora, disturbance &
         infections
        Dr. B. K. Iyer
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
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 )
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.
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.
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.
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.
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.
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.
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.
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.
Normal Intestinal flora,
disturbance & infections
       Dr. B. K. Iyer
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.
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.
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.
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.
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
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
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)
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
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
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
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
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.
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.
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.
Normal Vaginal flora,
disturbance & infections
       Dr. B. K. Iyer
Normal physiology of vagina
• Normal physiology of vaginal discharge
  include:
  – Cervical & vaginal epithelial cells,
  – Normal bacteria flora ,
  – Water,
  – Electrolytes and
  – Other chemicals.
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.
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.
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
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.
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
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
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).
Fungal vaginosis
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
Vaginal infections - summary
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

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Normal flora

  • 1. Normal flora, disturbance & infections Dr. B. K. Iyer
  • 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Normal Intestinal flora, disturbance & infections Dr. B. K. Iyer
  • 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Normal Vaginal flora, disturbance & infections Dr. B. K. Iyer
  • 28. Normal physiology of vagina • Normal physiology of vaginal discharge include: – Cervical & vaginal epithelial cells, – Normal bacteria flora , – Water, – Electrolytes and – Other chemicals.
  • 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. 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. 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. 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. 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. 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. 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).
  • 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
  • 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