BAMS

Question 1

What is a habitat?

Answer 1

A site where organisms grow

Question 2

Define ‘Microbial Community’

Answer 2

Microorganisms growing in a particular habitat

Question 3

What is an ecosystem?

Answer 3

Microbial community in a specific habitat and their surroundings
Physical, chemical and biological properties dictate composition of community
Those which survive and dominate and those which die

Question 4

What is a niche in terms of ecology?

Answer 4

Function of an organism within its community
Organisms compete for a niche, in mixed communities it is only stable if there is a niche for all the different types of organisms

Question 5

What are resident microflora?

Answer 5

Organisms regularly isolated (found) in a site

Question 6

What are pathogens?

Answer 6

Microorganisms with the potential to cause disease

Question 7

What is dental plaque?

Answer 7

Consists of bacteria and degraded mammalian cells. Surrounded by matrix containing both protein and polysaccharide.

Question 8

What bacteria can the mouth harbour which can cause serious systemic disease?

Answer 8

H. pylori - causes gastritis, peptic ulcers etc. Can reside in periodontal pockets of patients with periodontitis

Question 9

How do the teeth act as a microbial habitat?

Answer 9

Teeth accumulate dental plaque as they are a non-shedding surface. The dental plaque usually accumulates on the smooth surfaces, gingival crevices, pits and fissures.
In disease plaque microflora shifts away from that in health.

Question 10

What are the features of the mucosal surfaces in the oral cavity and how can they contribute to the microbial habitat?

Answer 10

The tongue is a highly papillated surface and thus acts as a reservior for anaerobes

The palate is keratinised
The cheek and lips are non-keratinised
Biomass is restricted by desquamation of epithelium (shedding)

Question 11

What is the structure of the oral mucosa?

Answer 11

2 layers
Stratified squamous epithelium
Lamina propria

Question 12

What is the difference in the structure between keratinised and non-keratinised squamous epithelium in the oral mucosa?

Answer 12

Keratinised squamous epithelium consists of 4 layers (deepest first); stratum basale, stratum spinosum, stratum granulosum, stratum corneum

In non-keratinised epithelium the two deep layers (basale and spinosum) remain the same but the outer layers are termed the intermediate and superficial layers.

Question 13

What are the features of saliva?

Answer 13

Lubricates mouth

Acts as a buffer (bicarbonate - acid buffer)

Contains mucins and glycoproteins which do the following:

• Adsorb to tooth surface - create pellicle for microorganisms to attach
• Nutrient source for bacteria (carbohydrate, protein)
• Aggregate microorganisms and clear them from the mouth
• Inhibit growth of some bacteria

Question 14

What are the features of Gingival Crevicular Fluid (GCF)?

Answer 14

Serum-like fluid
Nutrient source
Flow can remove non-adherent organisms
IgG, IgA, IgM, complement system

Question 15

What are the factors affecting microbial growth in the mouth?

Answer 15

Temperature - affects bacterial metabolism, enzyme activity etc
Anaerobiosis - the mouth has a few if any truly aerobic species
Ph - 6.5 ideal for microbial growth, 5 after sugar intake - lactate produced by bacteria, saliva can’t penetrate plaque at the enamel surface - Ph gradient exists, in caries acid producers like strep and lactobacilli assume a larger niche = ph fall lower
Nutrients - exogenous (saliva/GCF), endogenous (fermentable carbohydrates produce acid
Adherence - EPS promotes adherence to surfaces
- Adhesins
- Receptors
Antimicrobials - e.g. antibiotics can either inhibit/promote microbial growth
Host defences - cellular immunity (GCF), antibodies (saliva and GCF)

Question 16

What are the 6 steps in bacterial colonisation?

Answer 16

Obtain nutrients from saliva and diet
Tolerate variables - pH, oxygen tension, ionic strength
Overcome host defences
Grow at rate either greater to or equal to other species
Resist other bacteria that may prey on them or that produce toxins
Adhere to surfaces

Question 17

What is gram positive?

Answer 17

A form of bacterial morpholgy
Cell wall is 
- Thick multi layered
- Cross linked peptidoglycan
- Teichoic and lipoteichoic acid
- Retains crystal violet stain

Question 18

What is gram negative?

Answer 18

Bacterial morphology
Cell wall
- Doesnt retain gram stain
Outer membrane:
- Unique to gram -ve
- Contains transmembrane proteins e.g. porins
- Allows diffusion of hydrophillic molecules
Periplasmic space:
- Between ouiter membrane and cytoplasmic membrane
- Contains sugar transport systems
- Hydrolytic enzymes (breakdown macromolecules for metabolism)

Question 19

What are the passive forms of membrane transport systems?

Answer 19

1. Simple diffusion - molecule moves directly through opening in membrane without interacting with another molecule
2. Facilitated diffusion - molecules transported across membrane by binding to one or more carrier protein in the membrane

Question 20

What are the transport molecules involved in facilitated diffusion?

Answer 20

Uniport - single solute carrier from one side
Symport - co-transport of two different substances in the same direction
Antiport - co-transport of two different substances in the opposite direction

Question 21

What is active transport and what are 3 examples of active transport across a membrane?

Answer 21

Energy required to move subtances against a concentration gradient
Energy provided by ATP and a specific ATPase

1. H+/Lactose symporter - H+ translocation creates electrochemical gradient that drives uptake of lactose
2. Phosphotranseferase system
3. Histidine periplasmic system