Structure, growth and taxonomy of bacteria

Question 1

Describe the structure of a typical bacterial cell

Answer 1

Inner/cytoplasmic membrane(phospholipid bilayer) > cell wall(peptidoglycan) > outer membrane (phospholipid bilayer) ; this is not always present

Single molecule of covalently closed circular DNA

Flagellum allows propulsion in aqueous environment ; anchored in cytoplasmic membrane

Pili allows adherence to epithelial cells

Question 2

Compare prokaryotes and eukaryotic protists (single celled)

Answer 2

Both contain nucleic acids
Eukaryotic protists have a membrane bound nucleus ; prokaryotes do not 
Mito found only in eukaryotic protists
Ribo in both 
Cell wall in prokaryotes only
ER/Golgi in eukaryotic protists only

Question 3

State the different ways bacteria can be classified

Answer 3

Phenotypic characteristics:
Macroscopic/microscopic morphology
Biochemical tests
Stereotyping - identifying antigen 
Antiobiogram patterns - how the bacteria responds to different drugs 

Genotypic characteristics :
%G+C ratios, 
DNA hybridisation via single stranded probes, 
Ribotyping,
MALTI-TOF mass spec

Question 4

What is a gram stain?

Answer 4

Test used to differentiate bacteria based on their cell wall structure
First line test in diagnosis of bacterial infections

Question 5

Compare the characteristics of gram positive/negative bacteria

Answer 5

Question 6

State and describe the steps in the gram test

Answer 6

Fix sample to slide
Add crystal violet stain (to stain all bacteria)
Add gram’s iodine (fixes violent stain)
Add decolouriser (removes violet stain from gram negative bacteria)
Add safranin red (gram negative stain red ; gram positive remain purple)

Question 7

Name 3 examples of gram -ve bacillus

Answer 7

E.coli
K.pneumoniae
H.influenza

Question 8

Name 2 examples of gram +ve coccus and describe the structure of their cell wall/ plasma membrane

Answer 8

Staphylococcus aureus

Streptococcus progenies

Question 9

Name 2 examples of gram negative diplococci

Answer 9

Neisseria meningitidis

Neisseria gonorrhea

Question 10

Functions of cell wall

Answer 10

Maintain rigidity and cell shape
Maintain osmolarity
Cell wall interacts with host membrane
Cell division - forms a wall in middle of cell separating into 2 daughter cells

Question 11

How does penicillin work

Answer 11

Preventing formation of cross linkages between peptide chain in the peptidoglycan cell wall

Question 12

Features of mycobacterium

Answer 12

E.g mycobacterium tuberculosis
Modified cell wall 
Mycolic acid waxy coat made of lipids 
Poor gram stain 
Acid fast stain is used instead using carbolfuschin

Question 13

Features of mycoplasma

Answer 13

No cell wall

Steroids in cell membrane

Question 14

What are spores and capsules

Answer 14

Spores allow survival in adverse conditions such as ; only gram +ve bacteria show this

Capsules provide protection against phagocytosis ; found in both +ve and -ve ; made from gelatinous polysaccharide/polypeptide

Question 15

Describe the morphological virulence factors of gram positive and negative bacteria

Answer 15

Gram negative:
Lipopolysaccharide/lipooligosaccharide can be shed - this triggers inflammatory response
Porins in outer membrane can inhibit penetration of toxic chemicals
Pili allow attachment

Gram positive:
Techoic/lipoteichoic acids/peptido fragments can trigger immune response
Surface proteins allow attachment

Question 16

What are the nutritional requirements of bacteria

Answer 16

Carbon/nitrogen source
Inorganic salts (Fe/Na/K/P/Ca/Mg)
Organic compounds such as amino acids

Question 17

How does the antibiotic polymyxin work?

Answer 17

Particularly effective against gram negative bacteria

Perforates outer membrane

Question 18

How do antibiotics gentamicin and tetracyclines work?

Answer 18

Bind to bacterial ribosomes and inhibit protein synthesis