Microbiology – Control of Microbial Growth

Chapter 13: Control of Microbial Growth

Chapter 14: Antimicrobial Drugs

I. Approaches to Control - The methods used to destroy or remove

microorganisms and viruses can be physical, such as heat treatment, irradiation

and filtration or chemical.

A. Principles of Control

1. _____________________________ removes or destroys all

microorganisms and viruses on or in a product.

2. _____________________________ eliminates most or all

disease-causing bacteria or viruses on or in a material.

3. Chemicals used for disinfecting inanimate objects are called

_____________________________; those formulated for use on

skin are called _____________________________.

4. _____________________________ utilizes a brief heat

treatment to reduce the number of spoilage organisms or kill

disease-causing microbes.

5. A decontaminated item has been treated to reduce the number

of disease-causing microbes to a level that is safe to handle.

6. A sanitized item has a substantially reduced microbial

population that meets accepted health standards

B. Situational Considerations

1. In daily life, washing and scrubbing with soaps and detergents

achieves routine control of undesirable microorganisms and

viruses.

2. Hospitals must be scrupulous in controlling microorganisms

because of the danger of _____________________________.

3. Microbiology laboratories must use _______________________

to avoid contaminating cultures with extraneous microbes and to

protect workers and the environment from contamination.

4. Foods and other perishable products retain their quality and

safety when the growth of contaminating microorganisms is

prevented.

II. Selections of an Antimicrobial Procedure

A. _____________________________

1. One of the most critical considerations in selecting a method of

destroying microorganisms and virus is the type of microbial

population present on or in the product.

2. The endospores of _____________________________ and

_____________________________ are by far the most resistant

forms of life.

3. The waxy cell wall of _____________________________

makes them resistant to many chemical treatments.

4. _____________________________ are common environmental

organisms that not only resistant to some chemical disinfectants,

but can actually grow in them.

5. Viruses that lack a lipid envelope are more resistant to

disinfectants than are enveloped viruses.

6. Chemical disinfectants are categorized according to their

germicidal activity against resistant microbes.

B. _____________________________

1. The amount of time it takes for heat or chemicals to kill a

population of microorganisms is dictated in part by the number of

organisms initially present.

2. Microbial death generally occurs at a _____________________,

thus only a fraction of the organisms die during a given time

interval.

3. In the commercial canning industry, the __________________,

or decimal reduction time, is defined as the time it takes to kill ____

of a population of bacteria under specific conditions.

C. _____________________________

1. Factors such as pH or presence of fats and other organic

materials strongly influence the microbial death rates.

2. The presence of dirt, grease and organic compounds such as

blood and other body fluids can interfere with heat penetration and

the action of chemical disinfectants.

D. _____________________________

1. To guide medical biosafety personnel in their selection of

germicidal procedures, items are categorized according to their

potential risk of transmitting infectious agents

2. _____________________________ items come into direct

contact with body tissues.

3. _____________________________ items come into contact

with mucous membrane, but do not penetrate body tissue.

4. _____________________________ instruments and surfaces

only come into contact with unbroken skin.

III. Using Heat to Destroy Microorganisms and Viruses - Heat can be used

to destroy vegetative microorganisms and viruses, but temperatures above

boiling are required to kill endospores.

A. Moist heat

1. Moist heat, such as boiling water and pressurized steam,

destroys microorganisms by causing the irreversible coagulation of

their _____________________________.

2. _____________________________ utilizes a brief heat

treatment to destroy spoilage and disease-causing organisms,

increasing the shelf-life of products and protecting consumers.

3. Pressure cookers and _____________________________ heat

water in an enclosed vessel that causes the pressure in the vessel

to increase beyond atmospheric pressure, which kills

_____________________________.

4. The most important aspect of the commercial canning process is

to ensure that endospores of _____________________________

are destroyed.

B. Dry heat

1. Direct flame and ovens generate dry heat which destroy

microorganisms by _____________________________ cells to

ashes or irreversibly denatures their proteins.

2. Dry heat takes much longer than wet heat to kill

microorganisms.

IV. Using Chemicals to Destroy Microorganisms and Viruses

A. Selecting a Chemical Germicide

1. _____________________________ can be used to disinfect

and, in some cases, sterilize, but they are less reliable than heat.

They are especially useful for destroying microbes on heat-

sensitive items and large surfaces.

2. Most chemical germicides react irreversibly with vital enzymes

and other proteins, the cytoplasmic membrane, or viral envelopes.

3. Germicides registered with either the FDA or EPA are grouped

according to their potency as _____________________________,

_____________________________ disinfectants,

_____________________________ disinfectants or

_____________________________ disinfectants.

4. Factors that must be included in the selection of an appropriate

germicidal chemical include the toxicity, residue, activity in the

presence of organic matter, compatibility with the material being

treated, cost and availability, storage and stability, and ease of

disposal.

B. Examples of Germicidal Chemicals

1. Solutions of _________________________________________

in water rapidly kill vegetative bacteria and fungi by coagulating

enzymes and other essential proteins, and by damaging lipid

membranes.

2. _____________________________ and

_____________________________ destroy microorganisms and

viruses by inactivating proteins and nucleic acids. A 2% solution of

alkaline gluteraldehyde is one of the most widely used chemical

sterilants.

3. Chlorhexidine is a biguanide extensively used in antiseptic

products.

4. _____________________________ is a gaseous sterilizing

agent that penetrates well and destroys microorganisms and

viruses by reacting with proteins.

5. _____________________________ (liquid bleach) is one of the

least expensive and most readily available forms of chlorine.

Chlorine dioxide is used as a sterilant and disinfectant.

Iodophores are iodine-releasing compounds used as antiseptics.

6. _____________________________ interfere with protein

function. Silver-containing compounds are used to prevent wound

infections.

7. _____________________________ is used as an alternative to

chlorine disinfection of drinking water and waste water.

8. _____________________________ and peracetic acid are both

strong oxidizing agents that can be used alone or in combination as

sterilants.

9. Phenolics destroy cytoplasmic membranes and denature

proteins. Triclosan is used in lotions and deodorant soaps.

Hexachlorophene has been associated with neurotoxicity

and antiseptic lotions containing it are only available with a

prescription.

10. Quaternary ammonium compounds are cationic detergents

that are non-toxic enough to be used to disinfect food preparation

surfaces.

V. Removal of Microorganisms by Filtration

A. Filtration of Fluids

1. _____________________________ filters have complex,

tortuous passages that retain microorganisms while letting the

suspending fluid pass through the small holes.

2. _____________________________ filters are produced with

graded pore sizes extending below the dimensions of the smallest

known viruses.

B. Filtration of Air

1. ___________________________________________________

(HEPA) filters remove nearly all microorganisms.

2. HEPA filters are used in specialized hospital rooms to protect

patients who are exquisitely susceptible to infection.

3. HEPA filters are used in biological safety cabinets,

____________________________________________________,

which protect laboratory personnel who work with airborne

pathogens.

VI. Radiation

A. Gamma irradiation

1. Gamma rays cause biological damage by producing

_____________________________ and

_____________________________.

2. Irradiation can be used to sterilize heat sensitive materials and

to decrease the numbers of microorganisms in foods.

3. Irradiation has been approved by the FDA to control insects in

fruits, vegetables and grains, to destroy the trichina parasite in

pork, and to control Salmonella and E. coli O157:H7 in meats.

B. Ultraviolet radiation

1. Ultraviolet light damages the structure and function of nucleic

acids by causing the formation of covalent bonds between adjacent

thymine molecules in DNA, creating

_____________________________.

2. UV light is used to disinfect surfaces.

C. Microwaves

1. Microwaves do not effect microorganisms directly but they can

kill microorganisms by the _________ they generate in a product.

VII. Preservation - Preservation techniques slow or halt the growth of

microorganisms to delay spoilage.

A. Chemical preservatives

1. ________________________, ________________________

and _____________________________ are organic acids that are

sometimes added to foods to prevent microbial growth.

2. _______________________ and _______________________

are added to some foods to inhibit the germination and subsequent

growth of Clostridium botulinum endospores. It also reacts with

myoglobin to form a stable pigment that gives a pink color

associated with fresh meat.

B. Low temperature storage

1. Low temperatures above freezing inhibit microbial growth

because many enzymatic reactions are slow or non-existent.

2. Freezing essentially stops all microbial growth.

C. Reducing the available water

1. Sugar and salt draws water out of cells, preventing the growth of

microorganisms.

2. _____________________________ is used for preserving food.

The food is first frozen and then dried in a vacuum.

VIII. Antimicrobial Drugs – any drug that has been used to treat microbial infections

A. History and Discovery of these drugs

1. For millennia, people have used microbes (and their fermentations) and plants that have been known to compete with infectious microbes and treat diseases.

2. Paul Ehrlich in the early 20^th century begins a systematic search for the “magic bullet” that will target infectious microbes

3. Alexander Fleming accidentally discovers a natural antibiotic, penicillin

4. Gerhard Domagk and colleagues use a breakdown product of a synthetic dye, prontosil, to make sulfanilamide, the first synthetic antimicrobial drug

B. Fundamentals of Antimicrobial Chemotherapy

1. Antimicrobial chemotherapy – the clinical application of antimicrobial agents to treat infectious diseases. They come in 5 classes: Antibacterial drugs, Antifungal drugs, Antihelminthic drugs (treat parasitic worms), Antiprotozoan drugs (treat nucleated cell infections), and Antiviral drugs .

2. Considerations when selecting an antimicrobial drug:

a. Does the drug need to be bacteriostatic or bactericidal?

1. Depends on the lethality of the infection and the immune status of the patient. Bacteriostatic drugs are typically gentler on the patient and the patient’s normal microbiota.

2. If the infection is life-threatening or the patient is immunocompromised, bacteriocidal drugs are required.

3. Bacteriostatic - Capable of inhibiting the growth or reproduction of bacteria.

4. Bacteriocidal - Capable of killing bacteria outright

b. The dosage and route of administration are important considerations when selecting an antimicrobial to treat and infection. Other considerations include the patient’s age, mass, ability to take oral medications, liver and kidney function, and possible interactions with other drugs the patient may be taking.

3. Narrow-spectrum drugs target specific subsets of microbes. If the infectious agent is known, this will minimize collateral damage to normal microbiota.

4. Broad spectrum drugs are used if the infectious agent is unknown or became resistant to previous drugs.

5. Superinfections are secondary infections that occur when drugs have killed protective microbiota, allowing opportunistic pathogens resistant to the drug therapy to proliferate.

C. How do antibacterial drugs target microbes?

1. Antibacterial compounds exhibit selective toxicity because of the differences between prokaryotic (bacterial) cells and the eukaryotic cells of people.

2. Cell wall synthesis inhibitors interfere with peptidoglycan synthesis, making bacterial cells more prone to osmotic lysis.

a. ex. β-lactams, the glycopeptides, and bacitracin

3. Broad spectrum bacterial protein synthesis inhibitors selectively target the prokaryotic 70S ribosome of bacteria (human ribosomes are 80S)

a. ex. aminoglycosides and tetracyclines

4. Lipophilic polypeptide antibiotics target the lipopolysaccharide component of gram-negative bacteria, disrupting the integrity of their membranes.

a. ex. polymyxins

5. nucleic acid synthesis inhibitors

a. rifamycins target bacterial RNA transcription

b. fluoroquinolones target bacterial DNA replication

6. Antimetabolites act as competitive inhibitors for bacterial metabolic enzymes.

a. Sulfonamides and trimethoprim interfere with bacterial folic acid synthesis.

b. Isoniazid interferes with mycolic acid synthesis in mycobacteria.

D. Drug Resistance

1. Antimicrobial resistance is on the rise. Causes include:

a. selection of drug-resistant strains in clinical environments

b. overuse and misuse of antibacterials

c. use of subtherapeutic doses of antibacterial drugs

d. poor patient compliance with antibacterial drug therapies

2. How do microbes acquire antimicrobial resistance?

a. Mutations, rare spontaneous changes of the bacteria's genetic material, are thought to occur in about one in one million to one in ten million cells. Different genetic mutations yield different types of resistance.

b. Bacteria can acquire antibiotic resistance genes from other bacteria in several ways. (Watch video of E. coli become resistant: https://youtu.be/plVk4NVIUh8 )

1. By undergoing a simple mating process called "conjugation," bacteria can transfer genetic material, including genes encoding resistance to antibiotics (found on plasmids and transposons) from one bacterium to another.

2. Viruses are another mechanism for passing resistance traits between bacteria. The resistance traits from one bacterium are packaged into the head portion of the virus. The virus then injects the resistance traits into any new bacteria it attacks.

3. Bacteria also have the ability to acquire naked, "free" DNA from their environment.

3. Problematic microbial strains showing extensive antimicrobial resistance are emerging; many of these strains can reside as members of the normal microbiota in individuals but also can cause opportunistic infection.

E. How do we test the effectiveness of antimicrobials?

1. The Kirby-Bauer disk diffusion test helps determine the susceptibility of a microorganism to various antimicrobial drugs. The drugs produce zones of inhibition that are measured.