Bacterial Morphology and Growth

Question 1

Describe the structure of a bacterium?

Answer 1

Haploid DNA
DNA is nucleoid region: NOT bound in a nucleus
Ribosomes in cytoplasm 
Peptidoglycan membrane 
No mitochondria 
No membrane bound organelles
\+/- capsule- helps evade immune system
\+/- pilli/flagella- allows swimming & a sensing mechanism
\+/- spore- allows bacteria to sleep

Question 2

How can a cell wall differ in. bacteria?

Answer 2

Gram-negative:
E.g. E.coli
Extra outer membrane with integral lipopolysaccharides
Periplasmic space
Gram-positive:
E.g. S.pyogenes
Thick peptidoglycan layer integral with lipo/teichoic acid
Acid-fast:
E.g. M.tuberculosis
Thick outer layer of mycolic acids linked by arabinogalactans integral with lipoarabinomannan

Question 3

What is a gram stain?

Answer 3

A differential cell wall stain dividing bacteria into:
Gram-positive- blue/purple
Gram-negative- red/pink
Negative means the alcohol step damages the outer membrane and allows the blue/purple Crystal Violet dye out
The second is Safranin/Carbol Fuschia dye then stains the cell wall red/pink

Question 4

How does an acid fast stain?

Answer 4

Red (Ziehl-Neelsen: ZN) (with phenol to burn off the outer layer)or fluorescent (auramine)
Non-Acid Fast
No stain
Non-acid fast= they do not retain the Carbol Fuschin/Auramine stain on cell surface when washed with acid

Question 5

What are the factors affecting bacterial growth?

Answer 5

Division rate
Lag phase time
Oxygen availability
Carbon availability
Temperature
pH
Inhibitors
Growth Factors

Question 6

What are some bacterial growers?

Answer 6

Rapid growers
Vibrio cholerae
Division every 20-40mins
Slow growers:
Treponema pallidum (syphilis)
Division every 30 hours
Dormancy
Mycobacterium tuberculosis
Division every 18 hours (min)- 80 years?

Question 7

What are the different growth oxygen requirements?

Answer 7

Obligate Aerobes:
Require some oxygen to make ATP
Most tolerate O2 (Air= 21% O2:0.04% CO2) e.g. P.aeruginosa
Some (Microaerophiles) only tolerate 5% O2 e.g. H.pylori
Some (Capnophiles) require CO2 higher than in air (5-10%) e.g. N.gonorrhoeae
Facultative Anaerobes:
Cannot use oxygen or fermentation or anaerobic respiration e.g. E.coli
Aerotolerant Anaerobes:
Cannot use oxygen but can tolerate it e.g. C.botulinum
Obligate Anaerobes:
Oxygen is toxic e.g. C.tetani (tetanus)

Question 8

What are the different bacterial temperature requirements?

Answer 8

Psychrophiles (-20C to 20C)
E.g. Campylobacter jejuni (food poisoning)
Mesophiles (2C to 45C)
E.g. most animal pathogens
Thermophiles (42C to 80C)
E.g. Bacillus stearothermophilus (used for sterilisation strips)
Extreme thermophiles (60C to 250C)
E.g. Thermus aquaticus (sources of Taq for PCR)