Microbiology Final Exam, Dr. Collins

What are the 4 microbial control mechanisms?

1) Disinfection

2) Sterilization

3) Antisepsis

4) Chemotherapy

Sterilization:

The complete destruction or removal of all viable organisms.

What is an example of a method of sterilization:

Bunsen burners

Disinfection:

The killing, inhibition, or removal of disease causing (pathogenic) organisms

What is an example of a disinfectant:

Ethanol

Characteristics of disinfectants:

• They are agents, usually chemical, used for disinfection.

• They are usually used on inanimate objects.

Antisepsis:

The prevention of infection of living tissue by microorganisms

Chemotherapy:

The use of chemicals to kill or inhibit growth of microorganisms within host tissue

Antiseptics:

Chemical agents that kill or inhibit growth of microorganisms when applied to tissue

Sanitization:

The reduction of microbial population to levels deemed safe (based on public health standards)

Cidal agents:

Kill microorganisms. The suffix -cide indicates that the agent kills.

Examples of cidal agents:

Bactericides, fungicides, algicides, and viricides

Germicide:

Kills pathogens and many nonpathogens but not necessarily endospores

Static agents:

Inhibit the growth of microorganisms. The suffix -static indicates that the agent inhibits growth.

Examples of static agents:

Bacteriostatic and fungistatic

What conditions influence the effectiveness of antimicrobial agent activity and why?

• Population size: because larger populations take longer to kill than smaller populations.

• Population composition: because microorganisms differ markedly in their sensitivity to antimicrobial agents. Some are harder to kill than others.

• Concentration or intensity of an antimicrobial agent: usually higher concentrations or intensities kill more rapidly.

• Duration of exposure: longer exposure = more organisms killed.

• Temperature: higher temperatures usually increase the amount of killing.

• Local environment: many factors (e.g., pH, viscosity, and concentration of organic matter) can profoundly impact the effectiveness of antimicrobial agents.

Rank the types of microbes from most resistant to antimicrobial agents to least resistant:

G+, G-, acid fast, endospores.

What are the physical microbial control methods?

• Heat

• Filtration

• Radiation

Moist heat:

Destroys viruses, fungi, and bacteria. Degrades nucleic acids, denatures proteins, and disrupts membranes.

Whats an example of moist heat?

An example of moist heat is boiling

What is not destroyed by boiling?

Boiling will not destroy endospores and does not sterilize.

Steam sterilization:

Effective against all types of microorganisms including endospores.

What is used to perform steam sterilization?

An autoclave is used for steam sterilization because it requires temperatures above 100^oC and saturated steam under pressure.

Pasteurization:

Controlled heating at temperatures well below boiling. The process does not sterilize but does kill pathogens present and slows spoilage by reducing the total load of organisms present.

What is pasteurization used on?

Milk, beer, and other beverages

Dry heat sterilization:

• Less effective than moist heat sterilization, requiring higher temperatures and longer exposure times. Heat oxidizes cell constituents and denatures proteins.

• Items subjected to 160–170^oC for 2 to 3 hours

What is dry heat sterilization used for?

This process is mostly used for sterilizing glassware.

What 2 devices are used for dry heat incineration?

• Bench top incinerators are used to sterilize inoculating loops used in microbiology laboratories.

• Bunsen burners are also examples of dry heat incineration.

Filtration:

Reduces microbial population or sterilizes solutions of heat-sensitive materials by removing microorganisms. Filtration does NOT kill microorganisms, it just removes them.

Membrane filters:

Porous membranes with defined pore sizes that remove microorganisms primarily by physical screening.

What are examples of heat-sensitive organisms?

Vitamins and antibiotics

What are ways to filter air?

• Surgical masks.

• Cotton plugs on culture vessels.

• High-efficiency particulate air (HEPA) filters: HEPA filters are used in laminar flow biological safety cabinets.

UV radiation:

Causes thymine dimers preventing replication and transcription. UV limited to surface sterilization because it does not penetrate glass, dirt films, water, and other substances.

What wavelength is the most bactericidal?

UV light has a wavelength of 260 and is the most bactericidal

Ionizing radiation:

Ionizing radiation is Gamma radiation that penetrates deep into objects. It destroys bacterial endospores but is not always effective against viruses.

What is ionizing radiation used for?

Is used for sterilization and pasteurization of antibiotics, hormones, sutures, plastic disposable supplies, and food (anything that is heat sensitive).

Non-ionizing radiation:

Less strong, UV light, limited to surface sterilization because it doesnt penetrate through liquid well.

What are the characteristics of a good disinfectant?

• A good disinfectant must be effective against wide variety of infectious agents at low concentrations.

• It must be effective in the presence of organic matter and should be stable in storage.

Phenolics:

Are commonly used as laboratory and hospital disinfectants. Phenolics act by denaturing proteins and disrupting cell membranes.

Phenolics are usually _______________, meaning they kill off the bacteria causing tuberculosis, they are effective in the presence of organic material, and are long-lasting.

tubercucidals

What is an example of a phenolic?

Triclosan, which is used in hand sanitizers

Alcohols:

• Alcohols are among the most widely used disinfectants and antiseptics, but are not very strong.

• They are bactericidal and fungicidal, but not sporicidal.

• They inactivate some viruses.

• Alcohols denature proteins and possibly dissolve membrane lipids.

What are the 2 most common alcohols used for disinfectants and antiseptics?

The two most common are ethanol and isopropanol

Iodine:

• Used as a skin antiseptic that oxidizes cell constituents and iodinates proteins.

• At high concentrations Iodine may kill spores.

• Skin damage, staining, and allergies can be a problem with Iodine use.

Iodophore:

Iodine complexed with an organic carrier. It is released slowly to minimize skin burns.

Chlorine:

• Chlorine oxidizes cell constituents.

• Destroys vegetative bacteria and fungi.

• Chlorine gas is sporicidal.

• Chlorine can react with organic matter to form carcinogenic compounds.

What happens if you drink too much chlorine?

It could cause diarrhea

What is chlorine useful for?

It is important in disinfection of water supplies and swimming pools, used in dairy and food industries, effective household disinfectant

Heavy metals:

Heavy metals like mercury, silver, arsenic, zinc, and copper have long been used for preservation and as disinfectants. They are effective but usually toxic.

How is copper used?

It is used to prevent algae

How is colloidal silver used?

It is used to treat burn victim’s wounds and as eye drops for infants. Colloidal silver can ONLY be used topically, if ingested it can cause Argyria.

Argyria:

Argyria is a rare condition where deposits of silver build up in your body at toxic levels. This causes your skin and nails to turn bluish-gray.

Aldehydes:

• Aldehydes are highly effective, broad-spectrum disinfectants, which sterilize by denaturing proteins and disrupting nucleic acids. They are highly reactive molecules.

• Aldehydes are sporicidal and can be used as chemical sterilants.

___________ interacts with other molecules of ______________

Glutaraldehyde

____________ interacts with the cell wall

Polyglutaraldehyde

What are examples of aldehydes commonly used for disinfection?

Commonly used agents are formaldehyde and glutaraldehyde.

What US federal agencies regulate the effectiveness of antimicrobial agents?

• Environmental protection agency: regulates disinfectants.

• Food and Drug Administration: regulates antiseptics used on humans.

Sterilizing gases:

• Sterilizing gases are used to sterilize moisture or heat-sensitive materials that cannot be sterilized by steam sterilization.

• The gas used is ethylene oxide, and this sterilization is carried out in an autoclave-type machine.

• This process is microbicidal and sporicidal.

Sterilizing gases are ________, so the process must be done inside a chamber

toxic

How do sterilizing gases work?

Sterility occurs when an Ethylene Oxide gas molecule reacts with and destroys the microbial DNA and proteins.

What are some examples of things sterilizing gases can sterilize?

• Plastics.

• Food.

• Hormones.

• Blood.

• Antibiotics.

What are some natural mechanisms that control microorganisms?

• Predation by Bdellovibrio.

• Viral-mediated lysis using pathogen specific bacteriophage lysins.

• Toxin-mediated killing using bacteriocins.

Chemotherapy:

Treatment of a disease by using a chemical substance

What is selective toxicity?

The ability of a treatment to selectively find and destroy a pathogen without harming the host

How did Alexander Fleming discover penicillin?

He had a plate of Staphylococcus aureus that was contaminated with Penicillium notatum. After noticing that there was inhibited growth of S. aureus on the plate, he determined that the penicillin bacteria was responsible.

Antibiotics:

Substances produced by microorganisms that in small amounts inhibit another microorganisms. Antibiotics should ONLY be used to fight bacterial infections, NOT viral.

Antimicrobial drug:

Drug that inhibits the growth of a microorganism. Not all antimicrobial drugs are antibiotics!

More than half of our antibiotics are produced from what species of bacteria?

Streptomyces.

We know that half of our antibiotics are produced from the Streptomyces bacteria, but what else can they be produced from?

A few are produced by species of Bacillus and by molds (genera Penicillium and Cephalosporium)

How are new antibiotics found?

By screening soil samples

Only a limited group of organisms make antibiotics. In _______ microbial cultures, only ______ of them yielded useful drugs.

400,000, 3

Broad spectrum antibiotics:

Antibiotics that affect a broad range of gram-positive and gram-negative bacteria

In what scenario are broad spectrum drugs usually used?

Broad spectrum drugs are typically used if the identity of the pathogen is NOT known

example of a Narrow spectrum antibiotic:

Penicillin G – affects gram-positive bacteria but few gram-negative bacteria

What antibiotic is used to target cell wall synthesis?

Penicillin

How does penicillin inhibit cell wall synthesis?

• Penicillin prevents the crosslinking of peptidoglycan during cell wall synthesis.

• Penicillin primarily targets gram positive bacteria because they lack an LPS layer.

• This weakens the cell walls of actively growing cells.

What classifies something as penicillin?

A common core structure of a beta-lactam ring and a side chain

Bacteriocins:

Substances produced that inhibit like/similar organisms.

Natural Penicillins:

Penicillin G and Penicillin V are two types of Penicillin that have been extracted from the culture of Penicillium and are considered natural penicillins.

Penicillin G:

• Is a narrow spectrum drug.

• Is the drug of choice against staphylococci, streptococci, and several species of spirochetes.

• The acidity of the stomach diminishes the concentration of penicillin G.

Penicillin V:

• Is stable inside the stomach.

• Narrow spectrum drug.

What are some disadvantages of natural penicillins?

They are narrow spectrum drugs and are susceptible to penicillinases (b-lactamases)

Semisynthetic penicillins:

Penicillins created to overcome the disadvantages of natural penicillins. Semisynthetic penicillins are effective against many gram-positive and gram-negative bacteria.

What are the 2 ways to create semisynthetic penicillins?

• By interrupting the synthesis of the molecule by Penicillium and only obtaining the nucleus.

• By removing the side chain from a natural molecule and adding a new side chain to make it more resistant.

Examples of semisynthetic penicillins:

Ampicillin, Amoxicillin, Carbenicillin and Ticarcillin

Which two semisynthetic penicillins specifically work better against gram-negative bacteria?

Carbenicillin and ticarcillin

Other antibiotics that inhibit cell wall synthesis:

• Carbapenems

• Cephalosporins

• Polypeptide antibiotics

Carbapenems:

• Are not made by penicillin but are still beta-lactam antibiotics.

• Is a broad spectrum drug.

Example of a carbapenem antibiotic:

An example of a carbapenem is Primaxin (active against 98% of all organisms isolated from hospitals)

Cephalosporins:

An antibiotic that also inhibits cell wall synthesis

Examples of Polypeptide antibiotics:

Bacitracin:

• Effective against many gram-positive bacteria.

• Topical use only.

Vancomycin:

• Used to treat MRSA.

• Antibiotic resistance can occur, resulting in Vancomycin-resistant enterococci (VRE).

What 3 antibiotics target protein synthesis?

Chloramphenicol, Streptomycin, and Tetracycline

How does Chloramphenicol inhibit protein synthesis in prokaryotes?

Binds to 50S region of the ribosome and inhibits formation of peptide bond

Hows does Streptomycin inhibit protein synthesis in prokaryotes?

It changes the shape of the 30S region of the prokaryotic ribosome, causing the code on the mRNA to be read incorrectly

How does Tetracyline inhibit protein synthesis in prokaryotes?

It interferes with the attachment of tRNA to mRNA-ribosome complex.

Where do antibiotics bind to in eukaryotic bacteria?

They bind to the 80S ribosome

Where do antibiotics bind to in prokaryotic bacteria?

They bind to the 70S ribosome

What is an antibiotic that injures the plasma membrane and what does it do?

Polymyxin B – is a bactericidal against gram-negative bacteria.

• Topical treatment only.

• Polymyxin B and bacitracin are usually combined with neomycin in non-prescription ointments such as neosporin.

How do antibiotics target nucleic acid synthesis?

They interfere with DNA replication and transcription. Drugs that inhibit DNA and RNA synthesis have limited usefulness though, and can only interfere with mammalian DNA and RNA.

What types of antibiotics target nucleic acid synthesis?

• Rifamycins

• Quinolones and fluoroquinolones