What is a primary bacterial infection?
Initiated by a single organism in a healthy host
What is a secondary bacterial infection?
Microbial invasion subsequent to primary infection
What does the term ‘pyogenic’ mean?
Pus-forming, typically staphylococcal infections
What are the key characteristics of the normal bodily flora?
Highly diverse
Adapted to local environment
Potentially pathogenic if they travel around the body
-Throat, bowel & vaginal flora
What areas of the body are microbe free?
Brain and CNS
Circulatory system
What does a pathogen need in order to survive?
Resevoir
Transport
Adherence to host
Invade host defence
Life cycle
Potential to damage
Movement between new/old hosts
What is horizontal transmission of infection?
Transmission of an infectious agent from an individual to a contemporary (human-human)
What is vertical transmission of infection?
Passed from mother to baby during pregnancy, childbirth or breastfeeding
Why is heat stability an important factor in transmission?
-Microorganisms that resist drying spread more rapidly in the environment
-Spores
-Remain infectious for longer
-Sensitive to drying
What is the impact of drying stability on transmission
Stable:
Spread in air or soil
Unstable:
Sexual contact, water/food, close respiratory contact
What is pathogenesis?
Characteristics of a bacteria that enable it to cause infection
Main entry sites are typically mucous membranes
How do microbes adhere to the hosts?
Typically adherence to epithelial cells
Bacteria have macromolecules (adhesins) that assist in colonisation
What is biofilm?
A complex, structured community of microorganisms that attach to surfaces and each other.
They form a slimy, protective layer called extracellular polymeric substance (EPS) to assist in survival
What is extracellular polymeric substance (EPS)?
A protective layer formed of sugars, proteins and DNA
It improves survival by trapping nutrients, improves gene transfer, concentrates extracellular enzymes
What are the key mechanisms of biofilm tolerance to antibiotics?
Slow penetration
Increased genetic transfer
Expression of resistance genes
Hypermutation
What are fimbriae?
Fine, hair-like protein appendages on some bacteria to assist in attachment to surfaces
Name THREE enzymatic virulence factors that assist in invasion
Streptokinase:
Fibrinolytic, dissolves fibrin clots
Coagulase:
Induces fibrin clotting
Collagenase:
Breaks down collagen
What is an exotoxin?
A toxic substance usually excreted by the organism
What is an endotoxin?
An antigenic structural component in gram negative cell walls
Name THREE key characteristics of gram negative bacterial cell walls
-Lipopolysaccharide
-Porins
-Phospholipids
What are THREE basic properties of endotoxins
Produced only in gram negative cells
Extremely heat-stable
Pyrogenic
Moderate toxicity
What are THREE basic properties of exotoxins
Gram positive and negative
Inactivated at 60-80C
Non-pyrogenic
Highly toxic, toxoid producing
What are membrane-disrupting toxins?
Cytotoxins that disrupt the integrity of the plasma membrane
E.g:
Haemolysins (lyses RBCs)
Phospholipases (attack phospholipids)
What is tetanus and what is its effect?
Clostridium tetani, it forms deep wounds to the body and produces toxin tetanospasmin
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Microbial pathogenicity32
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Aerbobes, anaerobes and spore-forming bacteria16
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Bacterial respiratory tract infections12
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Antimicrobial susceptibility testing11
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Beta-lactams & Aminoglycosides37
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Treatment of anaerobic infections13
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Glycopeptides22
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Flouroquinolones and quinolone antibiotics20
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Antimicrobial resistance0
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Extras from Teja content35
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Safoora combined4
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Resistance mechanisms7
