Microbiology

Question 1

What is a pathogen?

Answer 1

An organism that causes or is capable of causing disease.

Question 2

What is a commensal bacteria?

Answer 2

Organism which colonises the host but causes no disease in normal circumstances.

Question 3

What is an opportunist pathogen?

Answer 3

Microbes that only cause disease if host defences are compromised.

Question 4

Define virulence/pathogenicity:

Answer 4

The degree to which a given organism is pathogenic.

Question 5

What is asymptomatic carriage?

Answer 5

When a pathogen is carried harmlessly at a tissue site where it causes no disease.

Question 6

The bacterial nomenclature includes:

Answer 6

Genus and species i.e. Staphylococcus aureus.

Question 7

What areas are open to bacterial colonisation?

Answer 7

Mucosal surfaces

Question 8

Bacterial classification is based on:

Answer 8

Morphology: coccus, bacillus (rod)

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Gram stain: positive (purple) and negative (pink)

Question 9

Cocci can be:

Answer 9

Diplococcus: in pairs
Chain of cocci
Cluster of cocci

Question 10

Rods can be:

Answer 10

Chain of rods
Curve rod (vibrio)
Spiral rod (spirochaete)

Question 11

What stains are used in the Gram stain?

Answer 11

Crystal violet
Iodine
Decolourisation
Counter stain with saffranin

Question 12

What temperature range do bacteria survive?

Answer 12

<-80 to +80 degrees (120 Celsius for spores)

Question 13

What pH range do bacteria live in?

Answer 13

<4-9

Question 14

How long can bacteria live without water?

Answer 14

2 hours - 3 months (>50 years for spores)

Question 15

Can bacteria survive UV light?

Answer 15

Yes - some species.

Question 16

Growth rate of viruses

Answer 16

Most viruses need cells and doubling time <1 hour.

Question 17

Growth rate of E. coli and S. aureus

Answer 17

Needs broth or solid media, doubling time takes 20-30 mins.

Question 18

Growth rate of Mycobacterium tuberculosis

Answer 18

Needs broth or media, doubling time takes 24 hours.

Question 19

Growth rate of fungi (Candida albicans)

Answer 19

Needs broth or media, doubling time takes 30 mins.

Question 20

Growth rate of Mycobacterium leprae.

Answer 20

Needs borth or media, doubling time 2 weeks.

Question 21

Endotoxin

Answer 21

Component of the outer membrane of bacteria, e.g. LPS in Gram negative bacteria.

It has a non-specific action, stable to heat, weak antigenicity and is not convertible to toxoid.

Question 22

Exotoxin

Answer 22

Secreted proteins of Gram positive and Gram negative bacteria. I.e. Tetanus toxin

It is a protein, with specific action, labile to heat, has strong antigenicity and can be converted to toxoid.

Question 23

Bacterial DNA

Answer 23

ds DNA

Question 24

Where does transcription and translation take place in bacteria?

Answer 24

In the cytosol (30S and 50S ribosomes)

Question 25

Bacterial genetic variation is due to mutation:

Answer 25

Base substitution, deletion or insertion.

Question 26

Gene transfer

Answer 26

Transformation via plasmid - Promotion genes - Antibiotic and virulence determinant genes - Maintenance genes Transduction via phage. Conjugation via sex pilus.

Question 27

Examples of obligate intracellular bacteria?

Answer 27

Rickettsia spp. Chlamydia spp. Coxiella

Question 28

MacConkey Agar is used for

Answer 28

Enteric bacteria

Question 29

Bacteria that can be cultured on artificial media can be grouped based on:

Answer 29

Cell wall. The one with no cell wall: mollicutes spp. (Mycoplasma pneumoniae)

Question 30

What are the groups of bacteria belonging to With a cell wall and growing as filaments?

Answer 30

Actinomyces Nocardia Streptomyces

Question 31

Bacteria with cell wall and growing as single cells:

Answer 31

Rods Cocci Spirochaetes

Question 32

What bacteria belong to spirochaetes?

Answer 32

Leptospira Treponema Borrelia

Question 33

Gram negative cocci is grouped as:

Answer 33

Anaerobic: Veillonella Aerobic: Neisseria (N. meningitidis; gonorrhoeae)

Question 34

Gram positive cocci is grouped as:

Answer 34

Aerobic: Staphylococcus and Streptococcus. Anaerobic: Peptostreptococcus

Question 35

Streptoccus can be:

Answer 35

Beta haemolytic: S. pyogenes Alpha haemolytic S. pneumoniae and oralis Non-haemolytic S. bovic. Enterococcus (E. faecalis)

Question 36

Lancefield group

Answer 36

Beta haemolytic streptococci are further differentiated / classified according to the properties of the antigens on their cell wall and given letters of the alphabet. This is known as the Lancefield grouping, hence ‘group A streptococci’ as an alternative name for S. pyogenes.

Question 37

Rods - Zielh-Neelsen stain positive

Answer 37

Mycobacteria

Question 38

Gram positive rods can be

Answer 38

Anaerobic: Clostridium spp and Propionibaterium spp. Aerobic: Corynebacterium spp, Listeria spp, Bacillus spp.

Question 39

Gram negative rods

Answer 39

Anaerobic: Bacteroides Aerobic: Vibrio, Campylobacter, Helicobacter, Haemophilus, Brucella, Bordetella, Pasteurella Facultative anaerobic: Coliforms (Escherichia, Klebsiella, Salmonella, Shigella, Citrobacter , Proteus, Yersinia, Pseudomonas