This document discusses the normal microbial flora of the skin, intestines, and vagina. It describes the most common bacteria that normally inhabit these areas, including Staphylococcus epidermidis and Streptococcus on the skin. In the intestines, it notes the high numbers of anaerobic bacteria and how the flora changes along the GI tract. It also explains how disruption of the normal flora through factors like antibiotics or medical procedures can allow pathogenic bacteria to colonize.

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).

36. Fungal vaginosis

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. Vaginal infections - summary

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