NORMAL MICROBIAL FLORA OF
GIT
Assistant Professor Microbiology
College of Medicine
Majmaah University
OBJECTIVES OF LECTURE
1. Identify Normal
Microbial Flora of GIT
2. Discuss Beneficial Role
& Disease causing
ability of Normal Flora
of GIT
3. Discuss use of
Antimicrobials & their
influence on normal
microbial flora of GIT
NORMAL MICROBIAL FLORA OF GIT
A 26-years-young man underwent tooth extraction of first molar tooth
right lower jaw from a dentist due to dental caries. Ten days later, he
noticed pain and swelling right lower jaw and two days later pus
discharge from lower jaw right side was noticed. Culture of the pus
yielded growth of Actinomycese israeli that was sensitive to Penicillin.
There is no risk of spread of this infection to other people because
1. The organism isolated is not very pathogenic
2. The infection arose as a result of implantation of endogenous mouth
flora into wound of tooth extraction
3. The transmission of this organism is difficult as nobody else has
tooth extraction
4. This organism is not a pathogen of systems outside oral cavity
NORMAL MICROBIAL FLORA OF GIT
• GIT, Digestive system
and Alimentary canal
• GIT consist of oral
cavity, esophagus,
stomach, small and
large intestine, rectum
and anal canal
NORMAL MICROBIAL FLORA OF GIT
• ORAL CAVITY
– Sterile at birth
– 4-12 hrs-Colonize by viridans
Streptococci (Main bacteria)
– Aerobic & Anaerobic
Staphylococci
– Gram Negative diplococci
(Neisseria, Moraxella)
– Diphtheriods, Lactobacilli
– Adult- Anaerobic Spirochaetes,
Prevotella spp,
– Actinomycese
– Yeast (Candida)
NORMAL MICROBIAL FLORA OF GIT
A 19-years-young man underwent dental treatment
at a clinic. Four weeks later, patient reported with
low grade fever, myalgias and fatigue. His temp is
100.2o C, spleen is palpable and systolic cardiac
murmur is heard in precordium. Suspecting infective
endocarditis, blood cultures were taken. Which
organism is most likely to be isolated?
1.
2.
3.
4.
5.
Salmonella typhi
Shigella dysentriae
Mycobacterium tuberculosis
Viridans streptococcus
Vibrio cholerae
NORMAL MICROBIAL FLORA OF GIT
• Esophagus
– Bacteria from food
– Transient and not
permanent
• Stomach
– Acidity keeps bacterial
growth low
– 103 to 105
– ↓ pH prevents
pathogens to cause
disease
– Antacids, PPI
(Omeprazole etc) ↓
resistance
NORMAL MICROBIAL FLORA OF GIT
• Muhammad is a known case of peptic ulcer and is
taking omeprazole. He went out for dinner with his five
friends. All of them drank unhygienic water from a local
shop. Next day, Muhammad developed profuse
diarrhea and vomiting and he was hospitalized. He was
diagnosed as a case of cholera. Apart from
Muhammad, none of his friend acquired the disease
because
–
–
–
–
Muhammad has some immune deficiency
All his friends were healthy
Muhammad has peptic ulcer disease
PPI(omeprazole) ↓ acid in stomach and so less pathogens
can cause disease
– Vibrio cholerae is normal intestinal flora
NORMAL MICROBIAL FLORA OF GIT
• Intestine
– Duodenum, jejunum and upper
ileum- Enterococci and lactobacilli
– Lower ileum, ceacum and large
intestine- Fecal flora
– 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%
Beneficial Role & Disease causing
ability of Normal Flora
• Beneficial Role
1. Protective function
•
•
Indirect :- Physically covering the receptors for
pathogens and competing for nutrition
Direct:- Production of antimicrobial factors e.g.
bacteriocins, lactic acid etc
2. Development of local immune system
•
Induce secretion of IgA, modulate local T cells
3. Metabolic function
•
•
•
Vit K, Biotin, folate
Metabolize dietary carcinogens
Assist fermentation of non digestible food residue
Beneficial Role & Disease causing
ability of Normal Flora
• Disease causing ability
– Microbes of normal flora are
harmless at site
– Outside these anatomical barriers,
cause disease
– These flora cause disease by
A. Breach in the anatomical barriers
(By procedures like
sigmoidoscopy, urinary
catherization, dental procedures
etc)
B. Suppression by antimicrobials
with selecting out of drug
resistant org
Antimicrobials effect on Normal Flora
 Broad spectrum
antimicrobials-suppress gut
flora
 Those microorgansism
resistant to the drug-select
out and proliferate
 Clostridium difficile
enterocolitis
 This org overgrows, release
toxin and causes ulceration
and necrosis
 Metronidazole or Vancomycin
for treatment
MCQ
• A 24-years-young man 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 caecum. The laceration was stitched
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.
2.
3.
4.
5.
Vibrio cholerae and Staph aureus
Strep pyogenes
Mycobacterium tuberculosis
Mixed normal gastrointestinal flora
Neisseria meningitidis
MCQ
• Ahmed was admitted to the hospital due to lobar
pneumonia affecting right lower lobe. He was prescribed
Co-amoxiclav (Augmentin) 1 gm BD. At 4th day post
admission, Ahmed experienced diarrhea with blood and
mucus and pain abdomen. There was distention of
abdomen. Which of the following organisms is likely to
overgrow and release toxin as a result of co-amoxiclav
induced suppression of gut micro-flora?
1. Enterococcus spp
2. Staphylococcus epidermitidis
3. Pseudomonas aeruginosa
4. Candida albican
5. Clostridium difficile