Bacterial Growth Flashcards
What nutrients and environmental conditions are needed for bacterial growth?
Explain this curve.
What is the difference between facultative intracellular bacteria, obligate intracellular bacteria, and extracellular bacteria.
Which one requires the most growth factors? The least?
Facultative - can live inside or outside depending on conditions
Obligate - have to live inside cells
Extracellular - capable of sustaining life without host
Obligate requires most, extracellular requires least
Bacterial growth is determined by appropriate ______ and ______.
Nutrients and environment
Describe why oxygen is toxic to anaerobic bacteria.
During their metabolism, bacteria produce reactive oxygen species, particularly superoxide. Anaerobic bacteria lack enzymes that are able to detoxify these oxygen compounds, which ultimately results in cell death. Additionally, presence of oxygen in the environment will also inactivate some of their essential enzymes, also leading to cell death.
Describe how bacteria are classified using thioglycollate broth.
Thioglycollate broth is a reducing agent, so it scavenges oxygen that is dissolved in the broth. The broth thus forms an oxygen gradient, with low oxygen at the bottom and higher at the top. Bacteria can be introduced into this media and the location within the tube where they are able to grow informs you of the metabolic type of bacteria.
The oxidase test checks for the presence of cytochrome oxidase. All _______ are oxidase positive.
Aerobes
Why are facultative anaerobes oxidase negative?
They are able to utilize glycolysis, TCA and oxidative phosphorylation. However, they lack cytochrome oxidase and instead contain a quinone electron carrier so that have an ETC but no oxidase –> oxidase negative.
Facultative anaerobes
- _______ b/c grow in absence of O2
- _______ b/c do not require absence of O2
Anaerobes
Facultative
What are microaerophiles?
They require oxygen but only in limited amounts
What is a capnophile?
A bacteria that grows best in the presence of high CO2
Growth in the presence of oxygen requires what enzymes?
Detoxifying enzymes
Superoxide dismutase
Catalase
NADH dependent peroxidases
What is vertical gene transfer?
What is horizontal gene transfer?
Occurs between non-related cells
- Describe the griffith experiment
- What bacteria was used in the experiment?
- What is the name for this observation?
- Streptococcus pneumoniae
- Horizontal gene transfer or bacterial transformation
Describe the
Describe the Avery, Mcleod and McCarthy experiment.
Proved that the material that was transferred that caused change in the organism was DNA
In the genetic information that is transferred, what do the genes encode for that causes virulence?
The polysacharride capsule
Capsule genes are _____, which allows ease of transfer and regulation of expression.
Capsule genes are flanked by _______, which are mobile genetic elements.
Clustered
Transposons
Why do bacteria have so many clustered genes for their capsule?
B/c their hosts (humans) have developed good methods of recognizing their capsules so they need many genes to evade host immune system
What are the consequences of bacterial capsular diversity on human vaccination?
Vaccines must be polyvalent and recognize multiple sugars in the capsule
What is a pathogenicity island?
Genes associated with virulence are not randomly distributed but are clustered into these specific regions within bacterial genome. Examples of pathogenicity islands include those that encode for adherence factors (allow binding to epithelial cells), siderophores (iron scavenging compounds), protein secretion systems.
What evidence in pathogenicity islands suggests that bacteria evolved these mechanisms in response to the human immune system?
Due to the many methods that are present in the pathogenicity islands that are used to exchange and integrate DNA (Ex: Integrons - elements that collect transposable elements, which mediate excision and integration into new genome)
What is a plasmid?
A small circular DNA molecule that replicates autonomously of the genome
Do plasmids have origin of replication?
Are they single or multiple copies?
Examples of what types of genes they carry?
Yes
Either
Nutritional markers and antibiotic resistance
What is conjugation?
What is transduction?
The host cell chromosome is fragmented during phage infection, so some small amounts of bacterial DNA will be incorporated into the viral DNA so when the phage infects the next bacteria it could pass on some bacterial DNA.
What is the difference between temperate phage genetic trasduction and lytic phage genetic transduction?
Lytic phage - bacteriophage infects bacteria with viral genome, phage hijacks bacterial machinery to produce more phage, by random chance incorporates some of host DNA into some phages, host eventually lyses and phage are released to infect other cells. Those that contain bacterial DNA can tansfer that information to subsequent bacterial cells.
Temperate phage - bacteriophage infects bacteria, phage DNA incorporates into bacterial DNA and lies dormant, can be transferred vertically with further binary fission of bacterial cell. Environmental stress can cause the phage to activate and enter the lytic phase, will hijack host machinery to reproduce virual capsule + nucleic acid and then lyse host cell. When phage DNA is excised from host chromosome, a small amount of host DNA can sometimes be excised with phage DNA. The phage that is created from that DNA can then infect other bacteria and transfer some host bacterial DNA to the next bacteria it infects.
