Download Commensalism • Benefits both the host and the commensal

Commensalism
 Benefits both the host and the commensal.
 Commensal- gets ready supply of nutrients and sanctuary
 Host- commensal competes with other pathogens for nutrients
 Produces antimicrobial components
 Produces compound needed by host e.g. HCL
 Human body commensal is MICROFLORA
 Human microflora is mainly BACTERIA
Pathogen
 Disease causing organism e.g parasites cannot live without the host
Pathogenesis
 Ability for a pathogen to cause disease  Virulence factors
1. Overcoming or evading host defences
2. Structures that help attachment to surfaces so that pathogens can resist removal
3. Tissue degrading enzymes= tissue injury
4. Resistance to adverse condition s
5. Produce toxins
First Line of defences
Second line of defences
Third line of defences
1. Non-specific line of defence
2. Non-specific line of Defences
3. Adaptive line of defence
 Skin
 Natural killer cells
 Lymphocytes B & T Cells
 Mucous membrane
 Phagocytic WBC
 Antibodies
 Microbiota
 Inflammation
 Fever
 Antimicrobial substances
Barriers to Infection
SKIN
MUCOUS MEMBRANE
 Physical barrier, stratified
 Mucus prevents attachment
 Low moisture & increased salt
 In resp tract mucous and ciliated epithelium
helps removal of foreign materials
 Surface secretions of antimicrobial substances
e.g. lysozyme, sebum
 Secretes antimicrobials e.g. lysozyme, acid
Systemic line of defence
1. FEVER Rise in temp creates an undesirable environment for bacteria.
2. PLASMA PROTEINS  Immunoglobins, complement proteins and clotting factors
3. CELLS OF IMMUNE SYSTEM  neutrophils- phagocytosis
Opportunism
 Body’s own microflora causes disease by:
1. Displacement of organism to a new environment
2. Change in environment favours overgrowth of a particular commensal
3. Failure or weakness in host defences
Transmission of Infection
CONTACT
AIRBORNE
WARTERBORNE
 Transfer from one region to
 Particles in air > 1m
 Faecal-oral transmission
another e.g. person to
 E.g legionella pneumophillia
 E.g. diarrhoeal diseases
person or animals to fomites
Control of Microbial Growth
1. Sterilisation- total eradication of all living cells and spores and infective materials
2. Disinfection- killing/ inactivation of a large number of organisms
PHYSICAL
CHEMICAL
Antimicrobial therapies
1. Heat – incineration, dry heat sterilisation, boiling, -Reactions between the
1. Drugs with
wet heat (autoclaving)
2. Radiation- ionising radiation (disrupt DNA),
Ultraviolet (disinfect)
3. Filtration- physical barrier
agent and components of
infection agent e.g. alcohol
swabs, bleach
- Dosages basis
selective toxicity
2. Target
chemical/metaboli
c pathways specific
to the pathogen