Microbiology Ch 7: Control of Microbial Growth

What is sterilization?

process that destroys or removes all viable microorganisms (including endospores)

What are disinfectants?

physical or chemical agents used to destroy/inhibit organisms, especially pathogenic ones, normally used on inanimate objects

Do disinfectants work on endospores?

no

What are antiseptics?

agents/chemicals that are used to reduce the number of microbes on skin surfaces and on wounds (living tissue)

Do antiseptics work on endospores?

no

What are bactericides?

agents that cause outright death of microbes

Do bactericides work on endospores?

no

What are bacteriostatics?

agents that inhibit growth and multiplication of bacteria; growth could resume

What are cellular targets of these control agents?

cellular membranes, proteins/nucleic acids

How do the agents target membranes?

damage to lipids or proteins, causing leaks

How do the agents target proteins and nucleic acids?

Protein denaturation

Damage to DNA

What happens with damage to DNA?

Inhibits DNA replication

Inhibits protein synthesis

Shape damaged, so can’t be copied or divide properly

How is heat used for microbial control?

sterilizes media, equipment, and glassware by incineration and denaturing enzymes

How is moist heat used for microbial control?

boiling (100C) kills vegetative cells but not endospores

How is an autoclave used for microbial control?

an autoclave is a pressurized chamber that kills organisms and endospores by increasing the temperature of the steam through increasing the pressure

Does autoclaving kill endospores?

yes

What can/can’t we sterilize with the autoclave?

glassware, liquids, medias, and any heat-resistant materials

not for oils, waxes, powders, anything that repels moisture

What is pasteurization?

a technique where heat is applied to liquids to reduce the number of microbes that cause infection and spoilage while retaining flavor

Does pasteurization kill endospores?

no

How do cold temperatures affect microbial growth?

slows the growth/activity of microbes, but cells are not adversely affected by long-term cooling or refrigeration

For sterilization or disinfection, would cold or hot temperatures be better?

hot temperatures

What is filtration?

passage of liquid through mesh with pores to sterilize heat-sensitive material

What kind of material is treated with filtration?

heat-sensitive material such as media, enzymes, and antibiotic solutions

How do we use salts/sugars for microbial control?

high concentrations can help preserve food due to the resulting hypertonic environment that causes water loss in cells (osmotic pressure)

What is ionizing radiation?

shorter wavelength and more energy, can penetrate solid barriers to dislodge electrons from an atom

What are examples of ionizing radiation?

x-rays and gamma rays

What is nonionizing radiation?

longer wavelengths and less energy, excites atoms

What is an example of nonionizing radiation?

UV radiation

What does ionizing radiation do?

Causes breakages in bonds in DNA

What does nonionizing radiation do?

Causes new formations of bonds so DNA cannot be copied properly

What do we use ionizing radiation for?

things that are heat/chemical sensitive, such as food, medical equipment (syringes, gloves, sutures, catheters), and even mail

What are the adverse effects of overexposure to UV radiation?

at 260nm, overexposure can result in DNA damage by causing thymine-thymine dimerization, which interferes with replication and transcription

What component does phenol and its derivatives target?

cell walls, membranes, and proteins

What does triclosan target?

targets enzymes needed for synthesis of fatty acids in bacterial cell membranes

What components do halogens target?

protein synthesis and cell membranes

What is the mode of action for chlorine and its compounds?

denatures proteins and halts metabolism

Which microorganisms is chlorine effective against?

bacteria, endospores, fungi, and viruses

What is an example of a hypochlorite?

household bleach (5% sodium hypochlorite)

What is the mode of action for alcohols?

denatures proteins and disrupts membranes

Which microorganisms is alcohol effective against?

bacteria and fungi (not endospores or nonenveloped viruses)

What is a surfactant?

surface acting agents that are weak microbicides

How do surfactants work?

Decrease surface tension of liquids to remove soil, grease, and debris that contain microbes

Which microorganisms is hydrogen peroxide effective against?

bacteria (especially anaerobic), fungi, viruses, and endospores

Is gram-negative or gram-positive bacteria more resistant to antimicrobials? Why?

gram-negative bacteria -- they possess the additional outer membrane that can filter out the antibiotic

What are the most resistant microorganisms to antimicrobials?

endospores and prions

What are prions?

infectious proteins resulting from abnormal folding