L6: INHIBITON AND DESTRUCTION OF MICROORGANISM BY PHYSICAL AGENTS

What is the difference between sterilization and disinfection?

• Sterilization kills all forms of microbial life, including bacterial spores.

• Disinfection destroys pathogenic organisms but not necessarily all microorganisms or spores.

What is the primary goal of disinfection?

To destroy pathogenic agents or potential pathogens and reduce the total microbial population.T

What happens when an object is subjected to sterilization?

It becomes totally free of microorganisms, spores, and other infectious agents.

Why is sterilization of instruments essential?

To ensure that bacterial endospores are destroyed.

What is the most common and effective physical agent for sterilization?

Heat

What are the two types of heat sterilization?

Moist heat (steam or hot water) and dry heat (hot air oven).

What is the mechanism of action of moist heat?

Kills by coagulation of proteins (enzyme and structural proteins).

What instrument is used for moist heat sterilization?

Autoclave

What is the standard autoclave setting for sterilization of culture media?

121°C at 15 psi for 15-20 minutes.

What is the autoclave setting for sterilization of infectious medical waste?

132°C at 15 psi for 30-60 minutes.

What is the biological indicator or quality control organism for autoclave sterilization?

Bacillus stearothermophilus in vials or spore-strip-set tests.

What is the mechanism of action of dry heat?

Causes protein oxidation.

What instrument is used for dry heat sterilization?

Hot air oven.

Why is dry heat sterilization preferred for glassware and metal instruments?

It does not corrode them.

What is the standard setting for dry heat sterilization?

160-180°C for 1.5-3 hours.

What is the primary goal of disinfection?

To destroy pathogenic organisms and reduce microbial population but not necessarily kill spores.

What types of agents are used for disinfection?

Chemical agents applied to inanimate objects.

Give an example of an object disinfected in a lab setting.

Tables, chairs, and working tables in the lab.

What is the effect of boiling on bacteria?

Kills vegetative forms (e.g., Escherichia coli) but not spores.

What are the standard boiling times and temperatures for disinfection?

15-30 minutes at 100°C.

What is pasteurization used for?

Preventing food spoilage in milk and wine.

Who discovered pasteurization, and when?

Louis Pasteur in the 1860s.

What is the standard pasteurization setting?

63°C for 30 minutes.

What is antisepsis?

Prevention of infection or sepsis using antiseptics.

What is the difference between antiseptics and disinfectants?

Antiseptics are used on living tissue, while disinfectants are used on inanimate objects.

Give examples of antiseptics.

Alcohols and hand sanitizers.

What does the suffix “-cide” indicate?

The agent kills microorganisms (e.g., bactericide, fungicide, sporicide).

What does the suffix “-static” indicate?

The agent inhibits growth but does not kill microorganisms (e.g., bacteriostatic, fungistatic).

How does population size affect sterilization or disinfection?

A larger microbial load requires a longer exposure time.

Why is population composition important in sterilization?

Some organisms, like bacterial endospores, are more resistant.

How does concentration of an antimicrobial agent affect its effectiveness?

Higher concentration can kill faster, but some agents (e.g., 70% ethyl alcohol) are more effective at lower concentrations due to water enhancement.

Which is more effective: 70% ethyl alcohol or 95% ethyl alcohol? Why?

70% ethyl alcohol because its activity is enhanced by water, while 95% evaporates too quickly.

How does duration of exposure affect microbial destruction?

Longer exposure time results in greater microbial reduction.

How does temperature influence disinfectants and sterilants?

Extreme temperatures can enhance or inactivate them.

What environmental factors affect the efficiency of disinfection?

Acidic foods (easier to pasteurize) and biofilms (protect bacteria).

What organic materials can inactivate disinfectants?

Blood, pus, and mucus.

Why is compatibility of disinfectants important?

Some disinfectants are incompatible and should not be used together (e.g., bleach and quaternary ammonium compounds).

What culture medium was used to test microbial growth?

Nutrient broth.

What is the evidence of bacterial growth in the nutrient broth?.

Turbidity

What does it mean if the broth remains clear after incubation?

The bacteria were killed.

What bacteria were used in the experiment?

Escherichia coli and Bacillus subtilis.

Describe the procedure for testing microbial inhibition by physical agents.

Impregnated filter papers were exposed to different sterilization methods and incubated in nutrient broth at 37°C.

How is bacterial growth determined in this experiment?

By observing the turbidity of the nutrient broth.

What does a turbid nutrient broth indicate?

The bacteria were not killed.

What does a clear nutrient broth indicate?

The bacteria were killed.

What were the results of the control group?

Turbid, meaning bacteria were not killed.

What were the results for boiling and 80°C?

• Escherichia coli: Killed.

• Bacillus subtilis: Not killed.

What were the results for hot air oven and autoclave?

Both Escherichia coli and Bacillus subtilis were killed.

If asked for the interpretation of results, what should you answer?

Escherichia coli was not killed by boiling.

If the organism is not specified, how should you answer?

Bacteria were killed in boiling/80°C/hot air oven/autoclave

If asked for the result, what should you state?

Whether the broth was turbid or clear.