Normal flora

1. Natural Human Flora
 What organisms are part of
normal flora
 Where do they colonize
- microbial ecosystems
 How are they able to cause
disease?
- exposure
- virulence factors

2. Normal flora
 All body surfaces possess a rich normal bacterial flora,
especially the mouth, nose, gingival crevice, large
bowel, skin
– This can be a nuisance in that
 it can contaminate specimens
 it can cause disease
– This is beneficial in that
 it can protect against infection by preventing
pathogens colonising epithelial surfaces
(colonisation resistance)
 removal of the normal flora with antibiotics can
cause superinfection, usually with resistant
microbes
 Endogenous viruses reside in the human genome
– worries about similar pig viruses in xenografts

3. Normal Flora Location:

4. STERILE BODY SITES
Central Nervous
system (CNS)
Internal Abdominal
Cavity & all
internal organs
Lungs
Bladder

5. NORMAL FLORA:
Streptococcus salivarius
Streptococcus mitis
Staphylococcus epidermidis
Haemophilus species
Moraxella sp.
Peptostreptococcus sp.
Fusobacterium sp.
Eikenella corrodens

6. NORMAL FLORA:
Enterobacteriaceae:
(E.coli, Proteus vulgaris, Klebsiella
pneumoniae, Enterobacter
cloacae, Serratia marcescens)
Bacteroides fragilis, etc
Clostridium perfringens, etc
Fusobacterium spp.
Peptostreptococcus spp.
Enterococcus spp.

7. Human Gastrointestinal Tract
 Stomach: pH 2.0,
~102-103 cfu/ml
 Small Intestine: pH 8.0,
~ 104-108 cfu/ml
 Colon: pH 6-7,
~ 1011 – 1012 cfu/ml
COLON:
- Anaerobes predominate
- > 500 bacterial species
- 75% of gut flora remain uncultured
- Firmicutes pylum:
(~60% of gut flora): Gram Positive with low G+C content
e.g. Clostridium bartlettii, Ruminococcus spp, Eubacterium spp,
- Cytophaga-Flavobacterium-Bacteroides (CFB) phylum:
(~ 25% of gut flora): Gram Negative
Firmicutes
60%
CFB
25%
Other
15%
CFB Firmicutes Other

8. Human Gut Microbiome
 Majority of bacteria in gut are uncharacterized
 Short Chain Fatty Acids (propionate, acetate,
butyrate) from microbial fermentation supply
~10% of host energy requirements)
 Imbalance in microbiome can lead to disease
(e.g. C.difficile, Crohn’s, etc)
 Microbiome sequencing expanding our
understanding
Duncan S, et al Cultivable bacterial diversity from the human colon.
Letters in Applied Microbiology 2007;44:343-350

9. NORMAL FLORA:
Lactobacillus spp
Prevotella spp
Enterococcus spp
Peptostreptococcus anaerobius
Porphyromonas melaninogenicus
Diphtheroids
Yeast
Bacterial vaginosus:
imbalance in vaginal microbiome

10. NORMAL FLORA:
S. epidermidis
Diphtheroids
Micrococcus sp.
Propionibacterium

11. Disease Burden in Humans
Infection: # Deaths % of all Deaths
Lower Resp 3,745,000 7.2
Tuberculosis 2,910,000 5.6
Diarrheal 2,455,000 4.7
HIV/AIDS 2,300,000 4.4
Malaria 2,700,000 2.9-5.2
Measles 960,000 1.8
Hepatitis B 605,000 1.2
Pertussis 410,000 0.8
Dengue fever 140,000 0.3
Principles & Practice of Infectious Diseases 5th Ed 2000, Mandell (ed)

12. Bacterial Pathogens:
Isolates/year; Diagnostic Lab
 Escherichia coli: 1637
 Staphylococcus aureus: 1643
 Pseudomonas aeruginosa: 716
 Staphylococcus epidermidis: 690
 Klebsiella pneumoniae: 414
 Enterococcus faecalis: 833
 Haemophilus influenzae: 156
 Bacteroides fragilis: 50
 Streptococcus pneumoniae: 57

13. Summary:
 Where do Normal Flora exist
 What organisms are considered
Normal Flora
(Gram stain and names)
 Gut Microbiome; role in health of host
 Normal Flora; role in infection
 Prevention/Treatment of infection due
to Normal Flora