Medical Microbiology SBM 2044

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Medical MicrobiologySBM 2044

• Assoc Prof Dr Othman Abd Samah
• Tel [phone]
• Email oas_at_iiu.edu.my
• Sr. Intan Azura Shahdan
• Tel [phone] ext 2816
• Email intan_azura_at_iiu.edu.my

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SBM 2044 LECTURE 1 INTRODUCTION TO MODULE
Value 4 credit hours

• Methods of assessment
• Module Aims Objectives
• Course structure, Reading, etc.
• Introduction Recall some foundations from
  Principles of Microbiology SBM 2053

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SBM 2044 Aims
To foster knowledge and understanding of
certain microbial pathogens, selected to
illustrate

• various kinds of host-pathogen interactions
• experimental approaches used to study
  bacterial/viral pathogens
• molecular mechanisms in bacterial pathogenicity
• clinical diagnosis and treatment

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Course Content

• Microbes Man interactions Week 1-3
• Medical Bacteriology Week 4-6
• Medical Virology Biological Agents of Warfare
  Week 7-10
• Medical Mycology Week 11-12
• Emerging infectious diseases Week 13
• Introduction to the diagnosis and treatment of
  infection Week 14

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Microbes Man interactions
Lecture 1

• Why is this subject important?

• The normal human flora

• Factors influencing bacterial-host interactions

Lecture 2

• Introduction to bacterial pathogenesis

Lecture 3

• Weapons delivery and deployment

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Today

• How do we recognise pathogens?
• Only a tiny proportion of all known microbes
  cause disease
• How do we identify a particular microbe as the
  cause of a particular disease?
• Which microbes cause disease?
• How do they do it?
• How do we stop them?
• How do we identify a particular microbe as the
  cause of a patients illness?

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Deaths in children (0 4 years) in 1998
Data from WHO 1999
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Vineeth, 7 months old and identified as
HIV-positive, cries at the Community Health
Education Society orphanage in Madras, India.
The WHO estimates 800,000 children were infected
with HIV in 2001 alone, almost all through
mother-to-child transmission.
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(No Transcript)
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Premature deaths (0 44 years) in 1998
Nutritional
Maternal
Perinatal
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3
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INFECTIOUS DISEASE
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48
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Various non- communicable
Injuries
Data from WHO 1999
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Human priorities ?
Spending 1995 (in billions )
Deaths 1945 1993 (in millions)
AIDS Malaria TB
War
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150
864
AIDS Malaria TB
Military
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Malaysian Facts

• Population 24,821,286 (July 2007 est.)
• Death rate 5.05 deaths/1,000 population (2007
  est.)
• HIV/AIDS (2003 est.)
• adult prevalence rate 0.4
• people living with HIV/AIDS 52,000
• HIV/AIDS - deaths 2,000
• REFERENCE www.cia.gov/library

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How do we identify a particular microbe as the
cause of a particular disease?

• The Koch Henle postulates
• Isolate the organism from every case
• Propagate in pure culture in vitro
• Reproduce disease by injecting the organism into
  a suitable recipient
• Re-isolate the organism
• OK for major acute diseases like plaque,
  smallpox, typhoid..

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• Pathogens vs. non-pathogens the Normal Flora
• Only a minute fraction of the organisms in the
  environment cause disease.
• Isolation of an organism from a patient does not
  imply disease.
• many different forms of association between
  microbes and humans
• many yet unknown, non-culturable eg. In soil,
  water, extreme environments
• Others colonise other living organisms, virtually
  all multicellular organisms have their own normal
  flora, organisms with which they coexist.

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Factors controlling growth
1. Nutrient availability

• Essential elements

• Major C, O, H, N, S, P, K, Mg, Ca, Fe, Na, Cl

• Minor Zn, Mn, Co, Cu

• All present in vivo, but all not readily
  available
• to infecting bacteria e.g. Fe

• Concentration in plasma ca. 20µM

• Freely available 10-18M

• Pathogens

• All heterotrophic (need organic C source)

• Many fastidious

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Factors controlling growth
2. Physical environment

• Water activity (aw) - not limiting in vivo

• Osmotic pressure (p) - moderate/high

• Too high for some bacteria

• Oxygen availability depends on location in
  vivo

• Anaerobic

• Aerobic

• Microaerophilic

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Factors controlling growth
2. Physical environment contd.

• Temperature 37ºC little variation

• pH Mostly ca. pH 7.0 in vivo, but can vary

• Skin pH 5.5

• Stomach pH 2.0 5.0

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Factors controlling growth
3. Competition from normal flora

• Cells occupying your space

Approx. number
Total
10
1013
Human
90
1014
Bacteria
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NORMAL HUMAN FLORA

• Internal organs/tissues normally sterile

• External surfaces accessible internal
  niches
• colonised by certain bacterial species
  include

• Skin

• Conjunctiva (eye surface)

• Oral cavity

• Upper respiratory tract

• Nares (nostrils) nasopharynx

• Gastroinsteinal tract

• Urogenital tract

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NORMAL HUMAN FLORA

• Numbers composition varies depending on
  location

Mouth 1010
Skin 1012
Intestines 1014

• May also vary at different sites on same tissue

e.g. skin - approx 2 square meters -
moist areas more densely populated

• Complex flora gt 200 species

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NORMAL HUMAN FLORA

• Skin dominated by

• Staphylococcus epidermidis

• Micrococcus sp.

• Coryneforms (e.g. Propionibacterium acnes)

• 20 30 individuals Staphylococcus aureus

• Conjunctiva

• Numbers usually low

• Mostly S. epidermidis certain coryneforms

• Occasionally S. aureus, some streptococci,
• Neisseria sp.,
  Haemophilus sp

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NORMAL HUMAN FLORA

• Oral cavity multiple sp., including

• Oral streptococci (a haemolytic)

• S. salivarius, S. mutans, S. sanguis

• Lactobacillus sp, Staphylococcus sp.
• Corynebacterium sp.
• Many anaerobes esp. Bacteroides sp.

• Upper respiratory tract

• Nares S. epidermidis, Corynebacteria,
• S. aureus (20 30 individuals)

• Nasopharynx Mostly a-haemolytic streptococci
• other Streps., Neisseria sp.,

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NORMAL HUMAN FLORA

• GI Tract multiple sp., including for example

• Escherichia coli other Enterobactericeae

• Clostridium perfringens

• Enterococcus faecalis

• Bacteroides sp.

• Urogenital tract

• Antherior urethra S. epidermidis, enteric
  bacteria

• Vagina various sp., including
• Lactobacillus acidophilus

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Different types of symbiotic associations
Mutualism
Commensalism
reciprocal benefit
Harmless
Parasitism
unilateral benefit
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Factors controlling growth
4. Host defences Innate and specific

• Dynamic, interactions with bacteria outcome
• depends on the balance

Host defences
Bacterial virulence
Multiple factors
Multiple factors

• Pathogenicity usually a multifactorial process

• Normal flora - balance in a particular host
  niche,
• but not necessarily at other sites

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Virulence

• Quantitative extent of ability to cause
  disease

Completely avirulent
Extremely virulent
Overwhelm defenses rapidly kills host
No capacity to survive in/on host
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Opportunistic pathogens
Completely avirulent
Extremely virulent
B
H
H
B
Normal defences No disease
Compromised defences Disease
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• Other sites are normally sterile, and the
  presence of bacteria suggests an infection
• Blood (septicaemia)s
• Cerebrospinal fluid (meningitis)
• Deep tissues (abscesses)
• The digestive tract contains large numbers of
  organisms up to 1/3 of faeces can be bacteria
  some anaerobes are actually oxygen-sensitive

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• The vast majority of normal flora organism do not
  cause disease, but coexist with the host -
• commensals
• Much of the normal flora is actually beneficial
  to the host they can exclude pathogen, by
  producing antibiotics, or other bactericidal
  substances (bacteriocins)
• Removal of the normal flora by e.g. antibiotics
  can make the host much more susceptible to
  pathogenic organisms which would otherwise not
  cause disease because the normal flora will
  prevent them from colonising the host.

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Homework

• Read about the Roles of Normal Flora
• Brooks chapter 11
• OR
• Schaechter chapter 2