Assist Prof Microbiology
Syed Yousaf Kazmi
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Define and classify normal microbial flora of
human body
Explain the beneficial role of microbial flora
Explain the disease causing ability & clinical
importance of microbial flora
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Population of microorganisms that inhabit the skin and
mucous membranes of healthy normal persons (also
called commensals)
Commensals are organisms that derive benefit from
another host but do not damage that host
Internal organs/ cavities are sterile
Two groups:
◦ The relatively fixed type of org
◦ The transient flora –org that inhabit the skin or mucous
membranes for hours, days, or weeks
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IMPORTANT
◦ Staphylococcus epidermidis
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LESS IMPORTANT
◦ Staphylococcus aureus, Corynebacterium (diphtheroids), various
streptococci, Pseudomonas aeruginosa, anaerobes (e.g.,
Propionibacterium), yeasts (e.g., Candida albicans)
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low pH, the fatty acids in sebaceous secretions, and the
presence of lysozyme-eliminate nonresident microorganisms
CLINICAL SIGNIFICANCE
◦ Staph epidermidis imp cause of infective endocarditis
◦ Propionibacterium and Peptococcus-situated in the deeper follicles in
the dermis-cause of acne
◦ Candida albicans-can enter into blood through I/V lines, drips that can
result in systemic candidiasis
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NOSE
◦ Staph aureus -Imp cause of Staph aureus infections
◦ Other-S. epidermidis, Corynebacterium (diphtheroids), various
streptococci
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MOUTH
◦ Viridans streptococci-cause of sub-acute endocarditis
◦ Strep mutans- cause of dental plaques
◦ Gingival crevices-Various anaerobes, e.g., Bacteroides,
Fusobacterium, streptococci, Actinomyces israeli
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THROAT
◦ Viridans streptococci, Streptococcus pyogenes and
Streptococcus pneumoniae, Neisseria species
Muhammad Talha 58-years-old man, smoker presents with
shortness of breath, cough, expectoration of rusty colored
sputum. His Chest X-rays showed consolidation of right lower
lobe of lung. Sputum and blood culture isolated Strep
pneumoniae. The most likely source of this pathogen in this
patient is
a.
From another patient in community
b.
Patient’s own GIT flora
c.
Patient’s own throat flora
d.
Ingestion of contaminated water from community
e.
None of the above
Correct Answer: c
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SMALL INTESTINE
– Duodenum, jejunum and upper ileum- Enterococci and
lactobacilli
– Lower ileum, ceacum and large intestine- Fecal flora
LARGE INTESTINE
– Approx 96-99% fecal flora are Anaerobes
– Bacteroides fragilis, Fusobacterium spp, Clostridium spp
(C perferingens), Anaerobic lactobacilli, Anaerobic
streptococci (Peptostreptococci)
– 1-4% are Coliform (e.g. E. coli, Klebsiella ), Enterococci,
Pseudomonas
– Candida in 10% population
– Minor trauma e.g. sigmoidoscopy, enema etc-bacteremia
in 10%
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Lactobacillus-maintains acid pH of vagina and prevent
overgrowth of pathogens e.g. Candida albicans
Intake of antimicrobials supress Lactobacillus- Candida
vaginitis
B. fragilis, Clostridium perfringens, C. albicans
E. coli, group B streptococci-may colonize in certain ♀
CLINICAL IMPORTANCE
Group B streptococci-imp cause of neonatal sepsis in
newborn
Recurrent UTI in ladies colonized by E coli
A 25-years-young lady reported with upper respiratory tract
infection. General practitioner prescribed Tab Co-amoxiclav
for 3 days. On 4th day, lady experienced itching, thick curdy
discharge from vagina. Gram stain of the discharge reveal
numerous pus cells and gram positive budding
microorganism. The cause of this infection is most likely due
to:
a.
Fecal contamination of vagina
b.
Recto-vaginal fistula
c.
Antimicrobial intake
d.
Catheterization
e.
Per-vaginal exam
Correct Answer: c
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The nonpathogenic resident bacteria interfere
colonization by pathogenic bacteria by:
◦ Competition for receptors or binding sites on host cells,
◦ Competition for nutrients,
◦ Mutual inhibition by metabolic or toxic products
◦ Mutual inhibition by antibiotic materials or bacteriocins
◦ Other mechanisms
The intestinal bacteria produce several B vitamins and
vitamin K
Development & function of the mucosal immune system
Certain bacteria metabolize dietary carcinogens
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Microbial flora are low pathogenicity org
Outside these anatomical barrier-cause disease
Suppression of normal flora-allows pathogenic
organism to overgrow & cause disease e.g. Candida
vaginitis, Pseudomembranous colitis by Clostridium
difficile
Important cause of endogenous infections e.g. Strep
pneumoniae pneumonia, Cervicofacial Actinomycosis
etc.
• Muhammad 24-years-young met a RTA. He sustained multiple
injuries and was hospitalized. At laparotomy, it was found that
there was a laceration in ascending colon 50 cm from ceacum.
The laceration was stiched but three days later, he experienced
pain right side of abdomen and fever. USG revealed pus
collection near stitched laceration of ascending colon. The most
likely organisms to be isolated will be
1. Vibrio cholerae and Staph aureus
2. Strep pyogenes
3. Mycobacterium tuberculosis
4. Mixed normal gastrointestinal flora
5. Neisseria meningitidis
Correct Answer: 4