Micro - Basic Bacteriology (Growth & Genetics)

Question 1

Draw the bacterial growth curve, labelling its axes and 4 key phases.

Answer 1

See p. 125 (image bottom right); Axes: x = Time, y = Number of viable bacteria; Phases: (1) Lag phase (2) Exponential growth phase (3) Stationary phase (4) Death phase

Question 2

What is the defining characteristic the lag phase of bacterial growth?

Answer 2

Metabolic activity without division

Question 3

What is the defining characteristic of the exponential/log phase of bacterial growth?

Answer 3

Rapid cell division

Question 4

In what phase of bacterial growth do penicillins and cephalosporins act, and why?

Answer 4

Exponential/log phase; Act here as peptidoglycan is being made

Question 5

What is the defining characteristic of the stationary phase of the bacterial growth curve?

Answer 5

Nutrient depletion slows growth

Question 6

In what phase of bacterial growth are spores formed, and why?

Answer 6

Stationary phase; Spore formation in some bacteria, due to nutrient depletion (which slows growth in this phase)

Question 7

What is the defining characteristic of the death phase of bacterial growth?

Answer 7

Prolonged nutrient depletion and buildup of waste products lead to death

Question 8

What is transformation? What is another term for this?

Answer 8

Ability to take up naked DNA (i.e., from cell lysis) from environment (also known as “competence”)

Question 9

What are examples of bacteria capable of transformation?

Answer 9

(1) S. pneumoniae (2) H. influenzae type B (3) Neisseria; Think: “SHiN in SHiNE SKiS” (from encapsulated bacteria mnemonic)

Question 10

What kind of DNA can be used in transformation?

Answer 10

Any DNA can be used

Question 11

What is a lab test/procedure relevant to transformation?

Answer 11

Adding deoxyribonuclease to environment will degrade naked DNA in medium –> no transformation seen

Question 12

What are the possible kinds of conjugation?

Answer 12

(1) F+ x F- (2) Hfr x F-

Question 13

What is the significance of the F+ plasmid? How is it transferred? What is the term for bacteria without this plasmid?

Answer 13

Contains genes required for sex pilus and conjugation; F+ plasmid (dsDNA) is replicated and transferred through pilus from F+ cell. No transfer of chromosomal genes; F-

Question 14

What is an Hfr cell? What may result from replication in this case?

Answer 14

F+ plasmid can become incorporated into bacterial chromosomal DNA, termed high-frequency recombination (Hfr) cell; Replication of incorporated plasmid DNA may include some flanking chromosomal DNA. Transfer of plasmid and chromosomal genes.

Question 15

What is transposition? What may result from it?

Answer 15

Segment of DNA that can “jump” (excision and reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice versa; When excision occurs, may include some flanking chromosomal DNA, which can be incorporated into a plasmid and then transferred to another bacterium

Question 16

What are the types of transduction? What kind of event is each type?

Answer 16

(1) Generalized - a “packaging” event (2) Specialized - an “excision” event

Question 17

What type of event is generalized transduction? What are the steps/results of generalized transduction?

Answer 17

A “packaging” event; Lytic phage infects bacterium, leading to cleavage of bacterial DNA. Parts of bacterial chromosome DNA may become packaged in viral capsid. Phage infects another bacterium, transferring these genes

Question 18

What type of event is specialized transduction? What are the steps/results of specialized transduction?

Answer 18

An “excision” event; Lysogenic phage infects bacterium; Viral DNA incorporates into bacterial chromosome. When phage DNA is excised, flanking bacterial genes may be excised with it. DNA is packaged into phage viral capsid and can infect another bacterium.

Question 19

What are 5 bacterial toxins for which genes are encoded in a lysogenic phage?

Answer 19

(1) ShigA-like toxin (2) Botulinum toxin (certain strains) (3) Cholera toxin (4) Diphtheriae toxin (5) Erythrogenic toxin of Streptococcus pyogenes; Think: “ABCDE”