Lecture 2 - Bacterial Diseases

bacteria revision

Bacteria

• Prokaryotes

• 1-3 microns 

• commensal 

• primary pathogens

• opportunistic pathogens

What does commensal mean?

bacteria that form part of the natural microbiome of an organism, necessary for physiology

What are some examples of bacterial disease?

• tuberculosis

• mastitis

• strangles

• glanders

• salmonellosis

What are the routes of transmission for bacterial infection?

• airborne

• droplet

• contact

• vectors

• fomites

What are some examples of fomites?

surgical instruments, utensils, needles, examination equipment, doorknobs etc. 

Where do obligative bacteria replicate?

intracellular environments

Where do faculative bacteria replicate?

both extracellular and intracellular

What does the mgtC gene enable bacteria to do?

evasion of macrophage killing

for example in salmonella enterica and mycobacterium tuberculosis

How does the mgtC gene work?

• located in inner cell wall

• enables growth in Mg2+ depleted medium (one of the ways phagocytosis works is by depleting nutrients inside the phagosome which prevents growth)

• requires phagosome acidification for activation

What does ‘delta’/ Δ mean in a scientific context?

missing or without

what does the cell wall of gram positive bacteria consist of?

PGN

What does the cell wall of gram negative bacteria consist of?

Double layer cell wall, thin PGN layer, extra phospholipid membrane, outer layer contains lipopolysaccharides

What colour do gram positive bacteria stain?

purple (dark)

What colour do gram negative bacteria stain?

pink (lighter)

What does the host use to recognise bacteria?

PAMPs (pathogen associated molecular patterns)

What are some examples of PAMPs?

• PGN - peptidoglycan

• LP - lipoprotein

• LTA - lipoteichoic acid (only gram pos)

• LPS - lipopolysaccharide (only gram neg)

What disease does streptococcus equi cause?

strangles

True or false: streptococcus equi is gram positive

true

What are some symptoms of strangles?

• Abscesses in head and neck lymph nodes (capable of rapid proliferation in tonsils and draining lymph nodes)

• Persists in guttural pouches (which is how its transmitted to naive horses)

What do the pili present in the cell wall of streptococcus equi do?

play a role in the adhesion of the bacteria to the host

How does  streptococcus equi resist phagocytosis?

• hyaluronic acid capsule (obscures PAMPs on cell surface)

• SeM surface protein bind fibrinogen that masks C3b binding (disrupts complement pathway)

• Cell surface protease (SeCEP)x cleaves and inactivates IL-8 (IL-8 is pro-inflammatory cytokine and recruits neutrophils)

How do antibiotics target bacteria?

• target cell wall and membrane

• beta-lactams target PGN cross linking (e.g. penicillin, cephalosporins, carbapenems)

• Vancomycin prevents PGN synthesis

• Polymyxins target outer cell membrane of gram negative bacteria

What is the flagella used for?

• Bacterial motility

• assists invasion

• present in gram positive and negative bacteria

• virulence factor (proven by lower recovery of bacteria when flagella is removed)

What receptor is involved in recognition of flagella?

TLR5

recognition is species specific

Capsule

• made of polysaccharide chains

• recognised by C-type lectins

• involved in immune evasion

• prevents desiccation

• stained (negative) with india ink

How can DNA be used in epidemiology?

• enables tracking of bacterial evolution and transmission chains

• monitor spread of AMR