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7/28/2019 Microbial Growth, Dissemination and Survival Within and Outside the Human Host
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4/11/2013
Microbial growth
&Dissemination and survival
within and outside the human host
Dr F Noordeen
Department of Microbiology
Faculty of Medicine
Peradeniya
April 2013
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1. Describe the dynamics of growth in
different types of micro organisms
2. List the different ways in which microorganisms survive for long periods
within and outside the human host
Learning outcomes
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Division by
binary fission
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BuddingBinary fission
Electron Microscopic view
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Nutrition – Need water, carbon,
nitrogen and inorganic salts• Phototrophs - Derive energy from sunlight
• Chemotrophs - Obtain energy from chemicals
• Autotrophs - Able to utilize atmospheric
carbon dioxide and nitrogen
• Heterotrophs - Depends on preformed organic
compounds
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• Oxygen requirement
– Aerobic – Anaerobic
– Some need carbon dioxide
• Temperature
– Usually 25-40oC, Normal incubation 35-
37oC
– Some can live in extreme temperatures
• Moisture• Light
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Static broth culture
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Bacterial growth curveLag phase - Prepare for
multiplication
Log phase – Multiplication
Doubling time - Constant
for a given strain. Eg; 13
min for V cholera, 24 h for M tuberculosis
Stationary phase -
Multiplication stops due to
depletion of nutrients and
accumulation of toxic
substances
Decline phase - Population
decreases due to cell death
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Bacterial growth curve
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Broth culture in which nutrients replaced
(simulates site of infection)
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Culture in artificial media
• Most can be cultured in artificial media
• M leprae, T pallidum can not be cultured
• Culture media depends on the species• Growth environment depends on the
species
• After 20- 30 divisions, form visiblecolonies
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Staphylococcus aureus Mycobacterium tuberculosis
Visible colonies
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Culture in artificial media
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Broth culture
Turbidity
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Anaerobic cultures
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subculture
Colony
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Plating a specimen
Sub culturing from a broth culture
Streaking Pour plate
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Laboratory process of isolating bacteria
in pure culture
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Factors Impacting Pathogens/
Microorganisms in the Environment• Temperature
• Freezing and thawing cycles
• Moisture• Sunlight
• Location (in solution vs surface)
• Competition• Predators
• pH
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Survival outside host
Why do we need to know?1. Transmission of infective agents
• Food
• Sewage / water sources• Air
• Soil
2. Sterile items used in treatment
3. Health care facilities
4. Survival in environment
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Prions and surgical
instrumentsDecontamination of surgical instruments from prions
In vivo findings with a model system for testing the
removal of scrapie infectivity from steel surfaces
Karin Lemmer, Martin Mielke, Christine Kratzel, Marion
Joncic, Muhsin Oezel, Georg Pauli and Michael Beekes
J Gen Virol 89 (2008), 348-358;
DOI 10.1099/vir.0.83396-0
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Survival of Bacteriaby forming a spore
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http://www.metapathogen.com/IMG/phagocytosis-diagram.png
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Survival within host
Ability to avoid or overcome phagocytes – Are in areas inaccessible to phagocytes
– Inhibit phagocyte chemotaxis (streptococcal streptolysin)
– Avoid provoking inflammatory response
– Hide antigenic surface with ‘self’ products
– Inhibit engulfment by phagocyte – (Surface components
of bacteria important for this)
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Survival within cells (intracellular bacteria) – Invade non phagocytic cells and survive within them
– Survive within phagocytic cells
• Inhibit fusion of phagocytic lysosome
• Survive within phagolysosome• Escape from phagosome
Survival within host…
Kill or damage phagocytes
Killing phagocytes before ingestionOrganism secretes substances which destroy the phagocyte
Killing phagocytes after ingestionMechanisms not fully understood
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Inhibit fusion of phagocytic lysosome Escape from phagosome
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Transmission of microbes
• Means of transfer
• Route of transfer
• Portal of entry
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Means of transfer
• HANDS
• AIR
• DUST
• INSECTS
• FOOD
• WATER
• SOIL
• BITE
- Skin infections
- Pneumonia
- Tuberculosis
- Dengue
- Food poisoning
- Cholera
- Tetanus
- Rabies
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Route of transfer
• INHALATION
• INGESTION
• DIRECT CONTACT• INOCULATION
• SEXUAL
TRANSMISSION
• PLACENTALTRANSFER
- Pneumonia
- Food poisoning
- Skin infections- Rabies
- Syphilis
- Syphilis
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Summary - Microbes
• Grow and survive within and outside the host
• Can be cultured in the lab for identification – Treatment
• Disseminate through various ways
