LFS103 Lecture Notes - Lecture 12: Biofilm, Zoonosis, Botulism
WEEK 12
12.1 Microbes and disease
Spontaneous generation: Life can spontaneously arise form non-living matter
Disproved by Louis
Pasteur: Microorganisms
present in air can
contaminate sterile
solutions
Koch’s Postulates
Robert Koch concluded
infection carried from
person to person on
hands of midwives and
doctors
Worked with anthrax in
cattle
Microbiological advances
60% of deaths were due
to infectious diseases
100 years ago
< 5% today in developed
world
Improvement due to:
Improved equipment for protection and detection (genomic advances)
Modern medicine including medicines, antibiotics and vaccinations
Identification of causative agent
Strategies for control - Agencies i.e. WHO, CDC
12.2 Host-microbe interactions
Normal (flora) microbiota: types of organisms
Most common = bacteria
Other = yeast (Candida), some protozoa & latent viruses
Resident microbes are permanent microbial residents for life
Some establish for long periods but not considered resident microbiota (colonise)
Some are carried briefly (e.g. on hands) = transient microbes
Usually considered contaminants - Cling to skin surfaces, but do not replicate there
Symbiosis: biological term used to describe two organisms living together. The 3 types of interactions
between host and microbe:
Mutualism: two organisms live together to mutual benefit
Commensalism: one organism benefits without harm to other
Parasitism: one organism benefits at expense of other (host) organism
Opportunistic microorganisms
Relationships can change under certain conditions!
Imbalances in the normal microbial communities, or damage to host and/or invade host tissues can
provide certain microorganisms the opportunity to cause infection
E.g. when normal gut microbe communities killed by AB
↓ microbes allows certain microbes to ‘take-over’
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In large numbers these microbes cause infection e.g. C. diff infections
Clostridium difficile, most common cause of AB associated infections
12.3 Spread of infection and disease transmission
Infection & disease
Infection: Microbes become established or colonise human body, penetrate host defences, invade
tissues & multiply
Disease
Results of infection à clinical symptoms
“Any harmful alteration to the physiological or
metabolic state of the host”
Symptoms: subjective - how sufferer feels e.g. pain
Signs: objective - measure/observe e.g. lesions, swelling, fever
Syndrome: specific group of signs or symptoms always associated with disease
Infectious disease: Disease caused by a microorganism or its products (e.g. toxin)
Pathogen: Any organism capable of causing disease
Pathogenesis: How microbe causes disease
Steps for pathogenesis
1. Transmission- to host
2. Adherence- attach to target cells/tissue
3. Invasion/colonisation- survive and multiply
4. Disease- damage to host, mechanisms that cause damage include;
Destroy host tissue (invading cells and/or hijacking cell machinery)
Produce toxins (cause damage to host)
Stimulate overwhelming host immune response (stimulate immune system to attack
own)
5. Exit from body (e.g. blood, sputum, seminal fluids, skin, aerosol etc.)
6. Survival outside host for transmission to another host
Transmission of disease: how passed from one host to next
Communicable infectious disease
Easily spread from one host to another
E.g. Chickenpox, measles
Non-communicable infectious disease
Not usually spread from one host to another
E.g. Normal flora, tetanus
Factors influencing disease transmission
Host: age, sex, genetic susceptibility, nutritional status, health status
Ability of host to resist invasion by a pathogen determines whether a disease will
occur
Factors contributing to patient/person susceptibility include:
Underlying diseases (e.g. Diabetes or anaemia)
Immunosuppression (includes elite athletes)
Chemotherapy & diseases of immune system
Poor nutritional status
Alcoholism & iv drug use
Age (elderly and neonates vulnerable)
Genetic makeup
Environment: weather, housing, geography, sanitation, access to healthcare, air quality, food
External factors
General environment & hygiene
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Spontaneous generation: life can spontaneously arise form non-living matter. Pasteur: microorganisms present in air can contaminate sterile solutions. Robert koch concluded infection carried from person to person on hands of midwives and doctors. 60% of deaths were due to infectious diseases. Improved equipment for protection and detection (genomic advances) Modern medicine including medicines, antibiotics and vaccinations. Strategies for control - agencies i. e. who, cdc. Other = yeast (candida), some protozoa & latent viruses. Resident microbes are permanent microbial residents for life. Some establish for long periods but not considered resident microbiota (colonise) Some are carried briefly (e. g. on hands) = transient microbes. Usually considered contaminants - cling to skin surfaces, but do not replicate there. Symbiosis: biological term used to describe two organisms living together. The 3 types of interactions between host and microbe: Mutualism: two organisms live together to mutual benefit. Commensalism: one organism benefits without harm to other. Parasitism: one organism benefits at expense of other (host) organism.
