Microbiology

Question 1

G+ve vs G-ve bacteria

Answer 1

1. Outer membrane: G+ve does not have outer membrane, only a thick peptidoglycan cell wall. G-ve has a thin peptidoglycan wall, but with an outer membrane thus protecting it from penicillin
2. G+ve stains purple while G-ve stains pink.
3. G+ve has teichoic acid and lipoteichoic acid giving it flexibility. G-ve has lipoproteins, linking OM to peptidoglycan wall.

Question 2

Microbial succession

Answer 2

1. Early colonisation by pioneer bacteria
   Streptococci and Actinomyces (G+ve)
   Bacteria attach to pellicle via weak bonds: complementary adhesin-receptor bonding.
2. Biofilm matures w poor OH.
   Fusobacterium nucleatum - bridging mechanism as env shifts from high O2 to low O2, joining both aerobic early colonisers and anaerobic late colonisers.
3. Climax community - Matured biofilm
   High biodiversity, multiple species,
   Higher pH, low O2

Question 3

Oral bacterial species I have to know

Answer 3

Early colonisers - G+ve
Mostly aerobic bacteria, facultatively anaerobic
1) Actinomyces
2) Viridans Streptococcus (group of Strep species) - includes
S. mitis, S. mutans (caries), S. salivarius, S. vestibularis (increase pH)
3) Lactobacilli - from roughened surfaces of carious lesions - aciduric and acidogenic
4) Lactamase - breaks down antibiotics (B-lactam)
5) Catalase in Staphylococcus epidermis and S aureus - protects frm oxidative damage.

Late colonisers - G-ve
Anaerobic - found in deep perio pockets and deep papillae
Haemolytic and asaccharolytic –> breaks down RBCs to strip O2, creating low O2 env + absorb iron.

1) Prevotella - P denticola and P intermedia - Black pigment for O2 quenching.
2) Fusobacterium nucleatum - bridging mechanism
3) Porphyromonas gingivalis - Haemolytic & asaccharolytic,
Aggressive - produces gingipains which is a proteinase that causes periodontitis

Question 4

More components of bacteria

Capsule -
Fimbriae -
Endospores -

Answer 4

Capsule: protects bacterium from desiccation - antimicrobials cannot penetrate well. => Evades host response and aids attachment.

Fimbriae - aids attachment - high affinity to CHO on host cell membranes

Endospore - state where bacteria are alive but inactive, and is highly resistant to environmental challenges

Question 5

Role of GCF in inflammation

Answer 5

GCF flushes out bacteria and debris out of the gums
But worsens inflammation and fuels growth as it is rich in inflammatory proteins which asaccharolytic bacteria can break down to use as nutrients.