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Microbiology Lab Exam 3

Terms in this set (61)

What is the importance of studying bacteriophages?
Bacteriophages are a promising alternative to chemicals and antibiotics.
What is a bacteriophage?
Viruses that infect bacteria that typically manifest strain- or species-level specificity.
What are the 6 steps in the life cycle of viruses?
1. Attachment
2. Penetration
3. Uncoating
4. Biosynthesis
5. Assembly
6. Release or exit
What two cycles compose the bacteriophage life cycle?
1. Lytic cycle
2. Lysogenic cycle
What is the lytic cycle?
Lytic infection produces progeny virus via cell lysis; thus, the virus genome replication cannot persist
What is the lysogenic cycle?
The phage and bacteria can form a stable, long-term relationship. The viral genome gets incorporated into the host genome. Prophage can become active and initiate a lytic cycle for the release of the virus particles.
What are phage titers?
Expressed in PFU (plaque forming units)/mL. Lysates with a final concentration greater than 109 PFU/mL are "high titer" lysates.
How do you determine pFU/mL?
PFU/mL = # of plaques / dilution factor ^-x = # of plaques x dilution factor ^x.
Example: You see on your 1/1000 (10-3) plate 150 plaques. The PFU/mL = 150/10-3 = 150 x 103 = 150,000 PFU/mL
Bacteriophage T4 targets ___________.
E. coli
True or false: Bacteriophages can infect human cells
False
What is sterilization?
Destroys all living cells, including endospores and viruses
What is pasteurization?
Destroys most of the pathogenic microbes that can contaminate food. Invented by Louis Pasteur.
What determines a positive test result for a phenol red glucose broth?
Turbidity and orange color
What are the properties of a good disinfectant?
- Effective against gram positive and gram negative, mycobacteria, and endospores
- Nontoxic to human
- Noncorrosive
- No smell or pleasant smell
- Stable in storage
- Can get into cracks
- Cheap
How do phenolics affect microbes?
Denature proteins and disrupt cell membranes
How do alcohols affect microbes?
Denature proteins and dissolve lipid membranes
How do halogens affect microbes?
Oxidize cell components, can kill spores
How do heavy metals affect microbes?
Inactive proteins
What is Triclosan?
A widely used disinfectant that targets bacterial enzymes and stops lipid synthesis. Contains a phenol, alcohol, and halogen group.
What do efflux pumps do?
What is an example of a bacteria that utilize these pumps?
Help bacteria survive when toxic chemicals are present in the environment.
Pseudomonas aeruginosa
___________________ contains efflux pumps and other means of removing toxins from the cytoplasm.
Staphylococcus aureus
What is UV light?
A form of radiation with a wavelength shorter than visible light. It has more energy than visible light. Increased energy causes DNA damage, or pyrimidine dimers.
What two kinds of dimers can result from UV light damage?
Thymine and cytosine dimers
What are the shortcomings of UV light for sterilization?
Cannot penetrate far, so it can only sterilize a surface. Cannot pass through glass, plastic, or liquid.
What cell structures are common targets of antibiotics?
Cell wall and protein synthesis
What is the mode of action for penicillin?
Inhibit transpeptidation of peptidoglycan
What is the mode of action for vancomycin?
Inhibit transpeptidation of peptidoglycan
What is the mode of action for tetracycline?
Inhibit binding of aminoacyl tRNA to the 30s subunit of the ribosome
What is the mode of action for erythromycin?
Prevents peptide chain elongation by binding to the 50s ribosomal subunit
What is MIC?
Minimal inhibitory concentration, or the lowest concentration of antibiotic required to prevent the growth of an organism.
Why study nitrogen-fixing bacteria?
Nitrogen is an essential component that is part of several amino acids. Has important implications in agriculture.
What are the two types of nitrogen fixing bacteria?
1. Free-living (non-symbiotic) such as Cyanobacteria
2. Symbiotic (or mutualistic) such as Rhizobium
True or false: Mannitol is a source of carbon for bacteria, but NOT a source of nitrogen
True
It is estimated that one gram of soil contains __________ bacterial cells.
1 billion
How do bacteria impact soil?
Impact soil organic matter content, soil structure, and the soil microbial community through secreting antibiotics and exhibiting antagonistic activities
What is the importance of Koch's Postulates?
Developed the methodology to determine which microorganisms cause disease.
What microorganism is commonly used as an indicator of coliform presence in drinking water?
E. coli
What test is commonly used to determine whether water is safe to drink?
Traditional coliform-based bacteriological test
What are the steps involved in the traditional coliform-based bacteriological test?
1) Lactose tube test (yellow w/ gas is positive)
2) EMB plate (green sheen = E. coli)
3) Green bile tube (turbidity + gas is positive)
What is decontamination?
reduce pathogens to levels considered safe to handle
What are antiseptic techniques used for?
Sanitize and disinfect infections on skin.
How does iodine affect microbes?
oxidizes cell constituents and iodinates proteins
What is disinfection?
Killing, removing, or inhibiting pathogenic microorganisms.
__________ was first used by Joseph Lister to disinfect surgical instruments and its derivatives are a common ingredient in disinfectants such as Lysol.
Phenol
_____________ is used as a disinfectant in municipal water and is the active ingredient in bleach.
Chlorine
___________ is a chlorinated aromatic compound with antifungal and antibacterial activity.
Triclosan
Due to antibiotic resistance, the number of ___________ infections is increasing.
nosocomial
The method we used to assess antibiotic resistance is the _________________ method, also called the Kirby-Bauer method.
disk diffusion
Which bacteria are involved in yogurt production?
Lactic acid bacteria
How does the pH of milk change in the process of yogurt production?
pH drops from 6.5 to around 4.5 which inhibits the growth of spoilage microbes.
What are the two methods of bacteriological examination of milk?
1. Methylene blue reductase test
2. Standard plate count
What are the USDA categories of milk and how are they defined?
Class 4: Poor milk, loss of blue color in less than two hours
Class 3: Fair milk, loss of blue color in 2-6 hours
Class 2: Good milk, loss of blue color in 6-8 hours
Class 1: Excellent milk, loss of blue color after 8 hours
How do you calculate CFU/mL when performing a live cell/standard plate count on milk examination?
If a plate was obtained from 0.1mL of inoculant, the number of cells must be multiplied by 10 to get units in colony forming units/mL.
In which cycle of viral replication can viruses form a stable, long-term relationship with bacteria?
Lysogenic cycle
What is a prophage?
Bacteria genome with bacteriophage nucleic acids incorporated
What are Koch's Postulates?
1. The microorganism must be present in every case of the disease but absent in healthy organisms.
2. The suspected organism must be isolated and grown in pure culture.
3. The same disease must result when the isolated microorganism is introduced into a healthy host.
4. The same microorganism must be isolated again from the diseased host.
What is one limitation of Koch's Postulates?
Some viruses can be present in hosts without causing disease or can cause latent infections.
What two started cultures are most often used in commercial yogurt? Why?
Streptococcus thermophilus & Lactobacillus bulgaricus. Initially S. thermophilus ferments the lactose; as the level of acid accumulates it is suppressed. L. bulgaricus, which is more acid tolerant, continues to ferment the remaining lactose.
What causes the taste and texture of yogurt? Why?
Lactic acid - it changes the structure of milk protein.
True or false: Mammals are the only organisms that produce lactose.
True
Only organisms that are capable of producing the enzyme _____________ can use lactose as a carbon source and thus grow in milk.
beta-galactosidase
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