General Microbiology — SCT I [Vol. 1]

Question 1

Describe the colour (in a Gram stained smear) of Gram positive and Gram negative bacteria, respectively!

Answer 1

Gram positive: dark blue (purple)
Gram negative: red (pink)

Question 2

Describe the 3 important parts of the bacterial lipopolysaccharide (LPS)!

Answer 2

1. Lipid A
2. Core polysaccharide
3. O-specific (polysaccharide) side chain

Question 3

Which 2 roles are attributed to bacterial pili (fimbriae)?

Answer 3

Adhesion; conjugation (sex fimbriae)

Question 4

Mention a bacterium and its virulence factor that is encoded by a lysogenic bacteriophage!

Answer 4

Streptococcus pyogens — erythrogenic toxin

Question 5

List the possible shapes of bacteria. Write one example for each cateogry!

Answer 5

Coccus (spherical): Staphylococcus, Streptococcus

Rod: E. Coli

Curved rod: Vibrio

Helical: Leptospira

Question 6

What are the essential components of bacterial cells? Specify at least 3!

Answer 6

1. Cytoplasm
2. Nucleoid (genome)
3. Cell membrane
4. Cell wall

Question 7

Which part of the bacterial cell carries the endotoxin?

Answer 7

Outer membrane of Gram negative bacteria

Question 8

What roles are attributed to the bacterial capsule in the infectious process?

Answer 8

Antiphagocytic effect, adhesion

Question 9

Describe the definition for obligate anaerobic bacteria

Answer 9

Able to replicate only in the absence of oxygen (under anaerobic conditions).

Some are quickly killed by oxygen, some are able to survive but do not grow with oxygen present

Question 10

Describe the definition for facultative anaerobic bacteria!

Answer 10

Are able to replicate both in presence or absence of oxygen.

Aerobic: respiration
Anaerobic: fermentation

Question 11

Mention 3 reliable methods of sterilization!

Answer 11

1. Hot air oven
2. Gamma-radiation
3. Gas sterilization

Question 12

Specify an exact set of parameters (temperature and time) necessary for effective sterilization by autoclaving!

Answer 12

121 °C for 20-30 min at 1 bar overpressure

Question 13

What does sterilization mean?

Answer 13

Is the killing or removal of all microorganisms (including bacterial spores)

Question 14

Specify an exact set of parameters (temperature and time) necessary for effective sterilization using a hot air oven (with circulation)!

Answer 14

160 °C for 60 min

Question 15

What does disinfection mean?

Answer 15

Killing of pathogenic microbes and to decrease the number of viable microbial cells.

Resistant microbes and spores may survive, so disinfection does not kill all microbes

Question 16

Mention 5 groups of disinfectants!

Answer 16

1. Alcohols
2. Detergents
3. Iodine
4. Chlorine
5. Aldehydes

Question 17

Mention 2 groups of disinfectants acting on the microbial membrane structures!

Answer 17

1. Alcohols (ethanol, isopropanol)
2. Phenol compounds (cresol, hexachlorophene, chlorohexidine)

Question 18

What does active immunization mean?

Answer 18

It’s the transfer of microbes or microbial products (vaccines) to the human body to induce long-lasting immunity against a specific infectious disease.

Question 19

What does passive immunization mean?

Answer 19

Administration of performed antibody (immune globulins produced in humans/animals) to the human body resulting in short-term protection against a specific infectious disease.

Question 20

Mention 2 bacterial infectious diseases that can be prevented or treated by passive immunization!

Answer 20

Prevention: tetanus
Treatment: Diphtheria