MICROBIO 310 Exam #3

• What are the six reasons that microorganisms are naturally resistant to certain antibiotics?

-1. Organism lacks structure the antibiotic inhibits 2. Organism is impermeable to antibiotic 3. Organism can inactivate the antibiotic 4. Organism may modify the target of the antibiotic 5. Organism may develop a resistant biochemical pathway 6. Organism may be able to pump out the antibiotic (efflux)

• What is a disc diffusion assay?

-A common assay for antimicrobial activity. -A Petri plate containing an agar medium is inoculated with a culture of the test organism. Known amounts of an antimicrobial agent are added to filter-paper discs, which are then placed on the surface of the agar. During incubation, the agent diffuses from the disc into the agar, establishing a gradient: the farther the chemical diffuses away from the filter paper, the lower is the concentration of the agent. -The zone of inhibition is an area of no growth around the disc.

• What is the therapeutic index?

-A comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxicity. -High therapeutic index = low host toxicity

• What are depth filters?

-A fibrous sheet or mat made from a random array of overlapping paper or borosilicate (glass) fibers. The depth filter traps particles in the network of fibers in the structure.

• What is a HEPA filter?

-A high-efficient particulate air (HEPA) filter is typically a single sheet of borosilicate glass fibers that has been treated with a water-repellent binder. -It is pleated, to increase overall surface area and mounted in a rigid, supportive frame.

What is an auto-clave?

-A sealed heating device that uses steam under pressure to kill microorganisms. -Allows temperature of water to get above 100°C (Above 100 is required to kill endospores).

• What are growth factor analogs?

-A synthetic compound that is structurally similar to a growth factor, but subtle structural differences between the analog and the authentic growth factor prevent the analog from functioning in the cell, disrupting cell metabolism.

• What are fusion inhibitors?

-Antiviral agents that prevent viruses from successfully fusing with the host cell. -Also used for treatment of HIV

• What are β-Lactam antibiotics?

-Antibiotics of the β-Lactam group are some of the most important of all time, both historically and medically. -Include penicillins, cephalosporins, and cephyamycins. -Over half of all antibiotics used worldwide.

• What is Chemical Growth Control?

-Antimicrobial agents can be classified as bacteriostatic, bacteriocidal, and bacteriolytic.

• Why are antiviral agents also dangerous to the host?

-Because viruses used their eukaryotic hosts to reproduce and perform metabolic functions, so most antiviral drugs also target host structures.

• What are protease inhibitors?

-Class of antiviral agents that are used as an effective treatment of HIV and work by binding to the active site of HIV protease; which inhibits the processing of large viral proteins into individual components.

• Describe Penicillins.

-Discovered by Alexander Fleming as the first antibiotic (penicillin-G was the first clinically useful antibiotic). -Primarily effective against gram-positive bacteria -Some synthetic forms are effective against some gram-negative bacteria. -Target (inhibit) cell wall synthesis.

What are the three methods of physical antimicrobial control?

-Heat sterilization, radiation sterilization, and filter sterilization.

• What is HAART?

-Highly active anti-retroviral therapy. -A revolutionary combination consisting of nucleoside analogs and a protease inhibitor that is used for treatment of HIV infections. -HAART is designed to target two independent viral functions; the nucleoside analogs target virus replication and the protease inhibitors target virus maturation.

• What are the 4 semisynthetic penicillins?

-Methicillin: acid-stable, β-Lactamase-resistant -Oxacillin: acid-stable, β-Lactamase-resistant -Ampicillin: broadened spectrum of activity (especially against gram-neg Bacteria), acid-stable, β-Lactamase-sensitive -Carbenicillin: broadened spectrum of activity (especially against Pseudomonas aeruginosa), acid-stable but ineffective orally, β-Lactamase-sensitive

• What is filter sterilization?

-Method of decontamination and sterilization of heat-sensitive liquids and gases. -Pores allow liquid or gas to pass through and are too small for organisms to pass through.

Describe radiation sterilization.

-Microwaves, UV, X-rays, gamma rays, and electrons reduce microbial growth. -Sources of radiation include cathode ray tubes, X-rays, and radioactive nuclides. -Radiation is used for sterilization in the medical field and food industry (approved in US and by WHO).

• What are membrane filters?

-Most common type of filters used for liquid sterilization in the microbio lab. -Functions more like a sieve. -Filtration can be accomplished by syringe, pump, or vacuum. -A type of membrane filter is the nucleation track (nucleopore) filter: very thin polycarbonate films treated with nuclear radiation and then etched with a chemical. Radiation causes film damage, etching chemical enlarges damaged locations into holes.

Explain Heat Sterilization.

-Most widely used method of controlling microbial growth. -Effectiveness of heat as a sterilant is measured by the time required for a 10-fold reduction in the viability of microbial population at a given temperature (also called the decimal reduction time or D).

• What is natural penicillin?

-Naturally occurring antibiotic. -Benzylpenicillin (penicillin G): Gram-positive activity, β-Lactamase-sensitive.

• Where are most drug resistant genes located in drug resistant bacteria?

-On the R plasmids. -This could be evidence that shows R plasmids predate the antibiotic era.

• What are Nonnucleoside reverse transcriptase inhibitors?

-Other antiviral agents that target and bind directly to reverse transcriptase and inhibit it.

What are endospores?

-Some bacteria produce highly resistant cells called endospores. These cells can survive heat that would rapidly kill vegetative cells. -Water content of the endospore coupled with the concentration of SASPs (small acidic-soluble spore proteins) determine its heat resistance.

• What are the different types of antibacterial growth factor analogs?

-Sulfa drugs: The first widely used growth factor analogs that specifically inhibited the growth of bacteria. Initially used to treat streptoccal infections. Resistant bacteria learn to absorb folate from their environment. -Isoniazid: a growth factor analog effective only against Myocobacterium. -Nucleic acid base analogs: have been formed by the addition of bromine or fluorine. -Quinolones: antibacterial compounds that interfere with DNA gyrase (ciprofloxin CIPRO).

• What is antimicrobial drug resistance?

-The acquired ability of a microorganism to resist the effects of a chemotherapeutic agent to which it is normally sensitive.

• What are antimicrobial drugs classified on?

-The molecular structure -The mechanism of action -The spectrum of antimicrobial activity

• What is the most successful and commonly used antiviral agents for chemotherapy?

-The nucleoside analogs. -They block reverse transcriptase and production of viral DNA. -Also called nucleoside reverse transcriptase inhibitors. -Azidothymidine (AZT) was the first compound to gain universal acceptance in this category.

What is pasteurization?

-The process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids. -Pasteurization does not kill all organisms, so it is different than sterilization.

• What is the minimum inhibitory concentration (MIC)?

-The smallest amount of an agent needed to inhibit growth of a microorganism. -MIC varies with the organism used, inoculum size, temp, pH, etc.

Compare and contrast UV and ionizing radiation.

-Ultraviolet radiation: •Has sufficient energy to cause modifications and breaks in DNA. •UV is useful for decontamination of surfaces. •UV cannot penetrate solid, opaque, or light-absorbing surfaces. -Ionizing radiation: •Electromagnetic radiation of sufficient energy to produce ions and other reactive molecular species from molecules with which the radiation particles collide •Generates electrons, hydroxyl radicals, and hydride radicals. •Irradiated means no contact and is not radioactive.