introduction to bacteria

Question 1

gram stain appearance

Answer 1

• Gram +ve = purple
  ○ Thick peptidoglycan layer
  
  • Gram -ve = red
    Thin peptidoglycan layer, thick lipopolysaccharide layer

Question 2

gram staining procedure

Answer 2

• Bacterial sample is spread on glass slide
• add crystal violet (purple dye) to slide, All bacteria in the sample take up the stain
• Add gram’s iodine fixative which forms crystal violet iodine complex in all the bacteria
• Add acetone alcohol which will decolourise gram -ve cells
• Add secondary dye basic fuchsine which is red, gram -ve cells take up this stain and appear red

Question 3

terminology for the shape of bacteria

Answer 3

• Cocci - spherical
  
  • Bacilli - rod shaped
    Coccobacillus (neither rod nor spherical, intermediate shape)
    two bacteria - diplococci
    chain - streptococcus
    cluster - staphylococcus

Question 4

cell surface features of bacterial cells (4)

Answer 4

• Plasma/cytoplasmic membrane
• Penicillin binding proteins (PBPs) cross links
• Peptidoglycan/murein
• lipopolysaccharide (LPS, endotoxin)

Question 5

capsule

Answer 5

• Not all bacteria have capsules
  
  • Helps prevent phagocytosis - macrophages cant engulf
    the bacteria
  • Strong rigid capsules prevent them getting eaten up
    Slimy capsules allow microfilm to be formed

Question 6

flagellum

Answer 6

• Various types of bacteria have various types of flagella
  
  • A-monotrichous Vibrio cholerae (1)
  • B-Lophotrichous Spirillum Spp. (one point)
  • C-Amphitrichous Rhodospirillum (both sides)
  • D- Peritrichous (all over)
  Escherichia coli and Salmonella enterica
  serovar Typhimurium
  Motility

Question 7

fimbrae

Answer 7

adherence to the bacteria, also have a role in biofilm formation - many bacteria growing for many days so they form a film which is enriched with bacteria, the film can affect various surfaces, they are increasingly difficult to get rid of

Question 8

spores

Answer 8

Spore formation mostly occurs in gram +ve bacteria

In gram +ve bacteria the spores help the bacteria survive long periods of desiccation or harsh environmental conditions

Question 9

plasmid exchange

Answer 9

Bridge formed between the pilli of the two bacteria, allows for exchange of genetic material via plasmids (not associated with chromosomes) in a process called conjugation, plasmid is exchanged from one bacterial cell to another

Question 10

bacterial replication

Answer 10

• Replicate by binary fission (divide and form identical progeny)
  
  • Genetic variation by:
    ○ Spontaneous mutation (can occur anywhere in the cell at any gene and at any time)
    DNA transfer via conjugation (this isn’t the only method, transduction is another method that occurs via bacteriophages, transformation refers to free flowing DNA in the environment and the bacteria takes up this DNA)

Question 11

bacteriophage

Answer 11

Viruses that eat up bacteria
End plate attaches to the bacteria
Injects genetic material inside the bacterial cell, this takes over the machinery of the bacterial cell and many phages are synthesised and burst out of the bacteria
DNA of the phage can also be integrated into the bacterial chromosome and can enter into the cell at any point and begin the lytic cycle
Bacteriophages aren’t harmful to humans and have been used to tackle drug resistance in bacteria

Question 12

classification and nomenclature of bacterial species

Answer 12

name is based on genus and species

strains of a species have similar characteristics

Question 13

penicillin binding proteins

Answer 13

Transpeptidases, carboxypeptidases, endopeptidases

○ These link various sugars in a particular cell membrane/wall

Question 14

Peptidoglycan/murein

Answer 14

○ Strength, shape to the bacterium

○ Carbohydrate polymers form it (NAM/NAG, β-(1,4)-glyosidic linkage) cross-linked with 3/5 amino acids.

Question 15

lipopolysaccharide

Answer 15

Component of gram -ve cell wall

elicit strong immune responses in animals and humans - over expression of LPS can lead to septic shock