Bacteriology

1. Bacteriology I (MeLS-M3293) for MLS Students
By Temesgen W/medhin (MSc – Medical Microbiology)
Wolaita Sodo University CHSM
Oct. 2023
Normal Microbial Flora (Chapter Six)
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2. Normal Microbial Flora
 The term "normal microbial flora" denotes the population of mos that
inhabit the skin & mucous membranes of healthy normal persons
 The human body, which contains about 10¹³ cells, routinely harbors
about 10¹⁴ bacteria .
 This bacterial population constitutes the normal microbial flora .
 Normal flora - microbes that colonize the body and usually do not
cause disease.
 Opportunistic pathogens - microbes that normally do not cause-
disease, but may under certain circumstances. 2

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5. Normal Microbial Flora…
 The normal flora can be divided in to two groups:
1. The resident flora:
 The microorganisms that usually live on or in a particular
body site are called the resident flora (or microbiota).
 Relatively fixed types of microorganism regularly found
in a given area at a given age
 If disturbed, it promptly reestablishes itself.
 The resident flora at each site include several, or even
several hundred, different types of microorganisms.
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7. Normal Microbial Flora…
2. The transient flora:
 Mos that colonize people for hours to weeks but do not
establish themselves permanently are called transient flora.
 The transient flora consists of nonpathogenic or potentially
pathogenic mos that inhabit the skin or mucous membranes
for hours, days, or weeks ...
 It colonizes the superficial layers of the skin, is more
amenable to removal by routine hand hygiene.
 If the resident flora is disturbed, transient mos may colonize,
proliferate, and produce disease.
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10. Role of the Resident Flora
 Resident flora of certain areas plays a definite role in
maintaining health and normal function.
 Members of the resident flora in the intestinal tract synthesize
vitamin K and aid in the absorption of nutrients.
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11. Role of the Resident Flora…
 The resident flora may prevent colonization by pathogens
and possible disease through "bacterial interference."
 The mechanism of bacterial interference may involve:
o Competition for receptors or binding sites on host cells,
o competition for nutrients,
o inhibition by metabolic or toxic products,
o inhibition by antibiotic materials
 Help the development of mucosa immunity
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12.  Generally, these normal flora provide us with many benefits,
which include:
 They prevent colonization by pathogens by competing for
attachment & nutrients.
 Some synthesize vitamins that are absorbed as nutrients by
the host (e.g. Vit K & B12).
 Some produce substances that inhibit pathogenic species.
 They stimulate the development of certain tissues, e.g.
colon and lymphatic tissues in gastrointestinal tract.
 They stimulate production of cross-reactive antibodies.
Since the normal flora behave as antigens in an animal,
they induce low levels of antibodies that cross react with
similar antigens on pathogens, preventing infection or
invasion
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13. Harmful effects of the normal flora
 Competition with host for nutrients
 Transformation of food to carcinogens
 Bacterial synergism between normal flora and potential
pathogens (microbial synergism is defined as the microbial
interaction in which both or all the microbial population
involved gets benefitted, by supporting each other's growth
and proliferation).
 Causes diseases
o Transition to an abnormal region
o opportunistic infection (immunocompromised)
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14. Nosocomial infections
 Also called hospital acquired infections (HAI)
 Health care associated infections are infections that patients
acquire, while they are in contact with the healthcare system
 They also include infections acquired by patients in the
hospital or facility but appearing after discharge, and
occupational infections among staff.
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15. Types of Nosocomial infections
 Bloodstream infections (bacteraemia)
o Due to IV catheters and cannula
 Wound infections and abscesses
o Post-operative; surgical site infections
 Urinary tract infections
o Catheter associated
 Respiratory tract infections
o ventilator pneumonia
 Diarrhoeal infections
o Clostridium difficile (antibiotic associated)
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16. Nosocomial infections…
 Sources of infection
Patients own microbial flora (self infection)
Cross infection
oFrom other patients
oFrom hospital staff
oHospital environment
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17. Health care
associated infections
Microbial factors
- Drug resistance
- Virulence factors
Hospital procedure
- Surgery
- Catherterization
-Antibiotic chemotherapy
Host factors
- Immunological state
- Age
- Debilitating conditions
Hospital settings
- Space
- Ventilation
- Cleanliness
Factors determining health care associated infections
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18. Prevention of Nosocomial infections…
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19. Draft guidelines on prevention of Nosocomial infections
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