Bacterial morphology and growth

Question 1

How many species of bacteria are there?

Answer 1

There are over 100 million species of bacteria.

But only <100 cause human disease.

Question 2

What are the methods of classifying bacteria? (6)

Answer 2

• Size
• Gross structure
• Cell wall structure
• Differential stains
• Morphology
• Growth requirements

Question 3

What is the size range for bacteria?

Answer 3

0.3μm - 3μm

Biggest
Thiomargarita namibiensis = 300,000 nm

Mycoplasma genitalium = 300 nm
Smallest

Question 4

What is the size range for virus?

Answer 4

0.02μm - 0.3μm

Question 5

What is the size range for WBC?

Answer 5

7μm - 25μm

Question 6

What are the structural components of bacteria?(9)

Answer 6

• Haploid (single chromosome) DNA (circular)
• DNA in nucleoid region : NOT bound in a nucleus,
• Ribosomes in cytoplasm
• Peptidoglycan membrane
• No mitochondria
• No membrane bound organelles
• +/- Capsule
• +/- Pilli / Flagella
• +/- Spore

Question 7

Describe the three cell walls in bacteria.

Answer 7

-Gram Negative ,eg. Escherichia.coli.
Extra outer membrane with
integral lipopolysaccharides
Periplasmic space.

-Gram Positive,e.g. Streptococcus pyogenes.
Thick peptidoglycan layer
integral with Lipo/teichoic acid.

-Acid Fast, e.g. Mycobacterium tuberculosis.
Thick outer layer of mycolic acids
linked by arabino-galactans
integral with lipoarabinomannan

Question 8

What is the Gram stain?

Answer 8

A differential cell wall stain
dividing bacteria into Gram positive and Gram negative.
It does not stain acid fast bacteria.

Question 9

What colour are gram positive bacteria?

Answer 9

Blue/Purple

Question 10

What colour are Gram negative bacteria?

Answer 10

Red/Pink

Question 11

Why are some bacteria gram negative?

Answer 11

Negative means the alcohol step damages the outer membrane and allows the BLUE/PURPLE Crystal Violet dye out. The second Safranin/Carbol fuschin dye then stains the cell wall RED/PINK.

Question 12

What stains acid fast bacteria?

Answer 12

Acid Fast
RED (Ziehl–Neelsen : ZN)
or
FLOURESCENT (Auramine)

Question 13

Why do some acid fast bacteria not stain?

Answer 13

Non Acid Fast = they do NOT retain (keep fast) the Carbol Fuschin/Auramine stain on cell surface when washed with acid

Question 14

What are the different bacterial shapes?(4)

Answer 14

Coccus, plural Cocci, in microbiology, a spherical-shaped bacterium. Pairs of cocci are called diplococci; rows or chains of such cells are called streptococci; grapelike clusters of cells, staphylococci; packets of eight or more cells, sarcinae; and groups of four cells in a square arrangement, tetrads

Bacillus- rod shaped bacteria

Bacterial spores

Spiral bacteria - helical shaped

Question 15

What happens if a bacteria does not have a cell wall?

Answer 15

No cell wall = no staining.

Have only lipoprotein outer coat..

Question 16

What are the factors affecting growth? (8)

Answer 16

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

Question 17

What are the different growth rates?

Answer 17

Rapid growers
Vibrio cholerae
Division every 20-40 minutes
= 1,073,741,824 bacteria from 1 starting cell overnight

Slow growers
Treponema pallidum (syphilis)
Division every 30 hours

Dormancy
Mycobacterium tuberculosis
Division every 18 hours (min) - 80 years?

Question 18

What are the growth (oxygen requirements)?

Answer 18

-Obligate Aerobes
Require SOME oxygen to make ATP (energy/growth)
Most tolerate O2 ( Air = 21% O2 : 0.04% CO2 )
eg Pseudomonas aeruginosa
Some (Microaerophiles) only tolerate 5% O2
eg Helicobacter pylori
Some (Capnophiles) require CO2 higher than in air (5-10%)
eg. Neisseria gonorrhoeae

-Facultative Anaerobes
Use oxygen or fermentation or anaerobic respiration
eg. E.coli

Aerotolerant Anaerobes

• Cannot use oxygen but can tolerate it
  eg. Clostridium botulinum (botulism)

-Obligate Anaerobes
Oxygen is toxic
eg. Clostridium tetani (tetanus)

Question 19

What are the growth (temperature requirements) ?

Answer 19

-Psychrophiles (-20ºC to 20ºC)
eg. Campylobacter jejuni
(food poisoning)

• Mesophiles (2ºC to 45ºC)
  eg. Most animal pathogens

-Thermophiles (42ºC to 80ºC)
eg. Bacillus stearothermophilus
(used for sterilisation strips)

• Extreme (hyper) thermophiles (60ºC to 250ºC)
  eg. Thermus aquaticus (source of Taq for PCR)

-Campylobacter jejuni (a common cause of food poisoning)
Grows between 0ºC to 45ºC.
This allows it to grow in cattle (humans 37ºC : cattle 42ºC)
AND
in badly prepared food IN YOUR FRIDGE!!!

Very few faecal organisms grow at 42ºC
We use this to differentially isolate
Campylobacter jejuni from stool samples

Question 20

What are the growth (pH requirements)?

Answer 20

(Helicobacter pylori (stomach ulcers) )Acidophile- pH 1-5.5
(Most human pathogens) Neutrophile - pH 5.5-8.5
(Bacillus cereus (food poisoning)) Alkaliphile- pH 7.5-11.5

Question 21

What is the growth (carbon usage)?

Answer 21

Bacteria with the Lac gene can ferment Lactose.

Pathogens are mostly non-lactose fermenting colonies.

Question 22

Why systemic classification?(4)

Answer 22

1. Shows how much is present ( + culture : shows viability)
   Important from normally sterile samples (blood, CSF)
   Quantification can give a measure of risk

2.Pathogen confirmation
Not all bacteria are pathogens (Commensals)
Commensals in one host can cause disease in another

3.Indicates treatment options
Clinico-pathological manifestations are often species specific
Antibiotic selectivity for bacterial targets

4. Speciation enables epidemiological study