Microbiology lec2

1. Medical MicrobiologyMedical Microbiology
Lecture 2Lecture 2
Dr. Saleh M Y OTHDr. Saleh M Y OTH
PhDPhD
Medical Molecular Biotechnology and Infectious DiseasesMedical Molecular Biotechnology and Infectious Diseases
02/10/201002/10/2010
IMS - MSUIMS - MSU

2. Infection: The growth of microorganisms in the host
without causing damages to the host.
Definaations
Bacteria may be divided into three types based on
their potential to cause diseases;
- pathogens,
- commensals, and
- nonpathogens.
Must to know: Morbidity, mortality, infections, parasite, host, vector, fomite,
contagious (infectious) disease, epidemic, endemic, pandemic, Zoonosis,
Epizootic, Attack rate.

3. Normal flora;Normal flora; (commensals, indigenous organisms): (commensals, indigenous organisms):
Bacteria which do not normally cause diseases and can Bacteria which do not normally cause diseases and can
be found commonly in healthy individuals. be found commonly in healthy individuals.
They may cause diseases They may cause diseases
(1) in an immunocompromised host, or (1) in an immunocompromised host, or
(2) after being introduced into different body sites, or (2) after being introduced into different body sites, or
(3) overgrow in favorable conditions. (3) overgrow in favorable conditions.
They are considered as They are considered as opportunistic pathogensopportunistic pathogens. .
Nonpathogens:Nonpathogens: Certain bacteria, such as Certain bacteria, such as
Lactobacillus acidophilusLactobacillus acidophilus, almost never cause disease., almost never cause disease.

4. Normal flora;Normal flora;
Frequently found on or within the body of
healthy persons, protect the host by protect the host by
competing with pathogens. competing with pathogens.
* * 1010
66
streptomycin-resistant streptomycin-resistant Salmonella Salmonella were were
needed to infect an experimental animal. needed to infect an experimental animal.
* * Fewer than 10 cells were needed to infect an Fewer than 10 cells were needed to infect an
animal pre-treated with streptomycin to suppress animal pre-treated with streptomycin to suppress
the normal flora in the GI tract. the normal flora in the GI tract.

5. The composition of the The composition of the normalnormal flora varies in flora varies in
different body sites. different body sites.
Ultimately, the flora composition is determined Ultimately, the flora composition is determined
by by ecological factorsecological factors including the presence including the presence
of receptors of host cell surface for bacterial of receptors of host cell surface for bacterial
adherence, pH, oxygen, availability of adherence, pH, oxygen, availability of
nutrients, water, host defense and personal nutrients, water, host defense and personal
hygiene. hygiene.

6. Some tissues, organs are dense with normal flora,
others are normally sterile
a. colonized sites
i. alimentary/intestinal tract
ii. upper respiratory tract
iii. distal genitourinary tract
iv. skin
b. normally sterile sites
i. blood
ii. CSF
iii. interstitial fluid and spaces
iv. lymph

7. Disease; damage caused by presence of
microorganisms or their products.
Colonization - presence of microorganisms without
disease at that point.
This term applies to surfaces only, i.e., the blood
cannot be colonized and host cells with intracellular
infection are not colonized.

8. Carrier state; colonization with a pathogen
Pathogen; any organism that has the potential to
cause disease

9. Pathogenicity:Pathogenicity: The ability of a bacterium to The ability of a bacterium to
inflict damages on the host. inflict damages on the host.
Virulence:Virulence: The degree of pathogenicity The degree of pathogenicity
associated with a bacterium. associated with a bacterium.
Virulence factorsVirulence factors: Bacterial products or : Bacterial products or
strategies that contribute to virulence. strategies that contribute to virulence.

10. Adherence and colonization:Adherence and colonization:
Bacteria need to avoid being washed away by Bacteria need to avoid being washed away by
non-specific host defense mechanisms (e.g., non-specific host defense mechanisms (e.g.,
saliva). saliva).
Most bacteria possess specific adherence factors which Most bacteria possess specific adherence factors which
bind receptors on the surface of the host cells or tissue.bind receptors on the surface of the host cells or tissue.
The specific interaction between bacterial The specific interaction between bacterial adhesinsadhesins and host and host
receptorsreceptors explains the observed tissue explains the observed tissue specificityspecificity of bacterial of bacterial
infections. infections.
For example, For example, N. gonorrhoeaeN. gonorrhoeae adheresadheres better to human urogenital better to human urogenital
epithelia than to other tissue. epithelia than to other tissue.

11. Pili and Afimbrial Adhesins
bacterium
host cell
receptors
pili with adhesins
at the tip
afimbrial adhesins
host cell
receptors
bacterium
Pili - fimbrial Adhesins
Afimbrial Adhesins
(No pili)
Adherence and colonization ……..Adherence and colonization ……..

12. Pili (fimbriae): Pili (fimbriae): E. coliE. coli as an example.. as an example..
Most the strains of Most the strains of E. coli E. coli do not adhere to the do not adhere to the
small intestine epithelia. small intestine epithelia.
They are normally found in large intestine. They are normally found in large intestine.
Pathogenic strains can colonize small intestine and Pathogenic strains can colonize small intestine and
cause diarrhea. cause diarrhea.
Adherence and colonization ……..Adherence and colonization ……..
Assignment (1): write in 6 pages about the pathogenic strains of E. coli.

13. The ability of the pathogenic strains of to cause The ability of the pathogenic strains of to cause
diseases is intimately associated with the expression diseases is intimately associated with the expression
of various pili. of various pili.
E. coliE. coli colonization factor antigen I (CFA) pili found in colonization factor antigen I (CFA) pili found in
enterotoxigenic enterotoxigenic E. coliE. coli ( (ETECETEC) strains. ) strains.
ETECETEC strains adhere to small intestinal mucosa and strains adhere to small intestinal mucosa and
produce symptoms by elaborating toxins that act on produce symptoms by elaborating toxins that act on
mucosal cells to cause diarrhea.mucosal cells to cause diarrhea.
Adherence and colonization ……..Adherence and colonization ……..
Assignment (1): write in 6 pages about the pathogenic strains of E. coli.

14. Nonfimbrial AdhesinsNonfimbrial Adhesins (Afimbrial Adhesins) (Afimbrial Adhesins)
- S. aureus- S. aureus: Lipoteichoid acid : Lipoteichoid acid
- Staphylococcus- Staphylococcus: Slime : Slime
- Group A streptococci- Group A streptococci: F protein (non-fibrillar, : F protein (non-fibrillar,
mediates attachment to fibronectin). mediates attachment to fibronectin).
- Streptococcus pneumonia- Streptococcus pneumonia: Capsule: Capsule
Adherence and colonization ……..Adherence and colonization ……..

15. Growth:Growth:
Bacteria Bacteria have have two distinct phasestwo distinct phases in their life in their life
cycle: cycle: activeactive or or vegetativevegetative stage and stage and inactive inactive
or spore-forming or spore-forming stage. stage.

Bacteria need nutrients to grow. Bacteria need nutrients to grow.
Iron is an essential growth factor for many Iron is an essential growth factor for many
bacteria. bacteria.
At neutral pH, iron usually exists in a highly At neutral pH, iron usually exists in a highly
insoluble ferric state (Fe3+). insoluble ferric state (Fe3+).

16. Within human body;Within human body;
transferrin, lactoferrin, ferritin and hemin bind transferrin, lactoferrin, ferritin and hemin bind
most of the available iron. most of the available iron.
Many bacteria produce iron-chelating Many bacteria produce iron-chelating
compounds call siderophores to help getting compounds call siderophores to help getting
iron. iron.
Growth …..Growth …..

17. Within human body;Within human body;
Siderophores are low molecular weight Siderophores are low molecular weight
compounds that chelate iron with very high compounds that chelate iron with very high
affinity. affinity.
The siderophores are excreted into the The siderophores are excreted into the
medium and then the iron-siderophore medium and then the iron-siderophore
complex is taken up by the cells through complex is taken up by the cells through
receptors. receptors.
Growth …..Growth …..

18. Within human body;Within human body;
Many bacteria also can Many bacteria also can useuse transferrin, transferrin,
lactoferrin, ferritin or lactoferrin, ferritin or heminhemin as a source of as a source of
iron. iron.
Growth …..Growth …..

19. Mechanisms of Bacterial Pathogenesis
EXPOSURE TO PATHOGENS
ADHERENCE (ADHESION),
COLONIZATION, GROWTH
INVASION
TISSUE DAMAGES,
DISEASE
ESCAPE HOST DEFENSES
TOXICITY
Virulence factors are
bacterial strategies or
products which
contribute to each of
these steps leading
ultimately

20. Functions and stages of pathogens and
disease
1.encounter
2.entry
3.spread (+/-)
4.multiplication
5.evasion of host defenses
6.damage
7.outcome
a. transmission to new host (+/-)
b. recovery or not

21. Growth and Toxins produced by pathogens Growth and Toxins produced by pathogens
Toxins: Toxins:
Toxicity Toxicity
Exotoxins:Exotoxins: Toxic proteins, many are excreted into the Toxic proteins, many are excreted into the
medium; may damage host tissue away from where medium; may damage host tissue away from where
bacteria infections occur. bacteria infections occur.
Endotoxins:Endotoxins: LPS, embedded in the G- organism outer LPS, embedded in the G- organism outer
membrane, released during bacterial lysis. membrane, released during bacterial lysis.

22. P
P