Microbial Growth Control Chapter 7

Chapter 7: Control of Microbial Growth - 1

• Microbial control is necessary in many situations, including food systems needing sanitary conditions and hospitals requiring sterilization.
• Learning outcomes for this chapter include:
  • Using appropriate techniques (e.g., sterilization, decontamination, sanitization, pasteurization) for microbial control.
  • Comparing and contrasting methods used for microbial growth control in various settings (daily life, healthcare, microbiology labs, food production, water treatment facilities).
  • Explaining how factors like the type and number of microbes, environmental conditions, risk of infection, and composition of the item influence the choice of control methods.

Microbial Control

• Microbial control is essential in specific situations.
• Methods range from controlling sanitary conditions in food production to sterilization methods used in hospitals.

A Glimpse of History

• Joseph Lister's work revolutionized surgery, improving wound care through the application of carbolic acid to prevent infections, saving lives exceeding the mortality rates of wars.
• Before Lister's contributions, surgeries were high risk for infection due to a lack of understanding of microbes' spread and role in disease.
• Early surgical procedures didn't sterilize instruments or maintain clean environments.

CDC Biosafety Levels

• Biosafety levels range from BSL-1 (low risk), where microbes don't typically cause disease, to BSL-4 (high risk), encompassing deadly pathogens, where no vaccines or treatments are available.
• Each level of biosafety has specific criteria for handling and controlling microbes.

Approaches to Control - Food and Food Production Facilities

• Perishable foods remain fresh longer when contamination is eliminated.
• Heating (heat treatment) is the common method and considered reliable for fresh food.
• Irradiation is approved in some cases for preservation of foods, but it can affect their appearance and taste/flavor.
• Additives and chemical treatments are used to prevent food spoilage. Authorities (e.g., Abu Dhabi Food Control Authority) oversee the appropriate use.

Approaches to Control - Water Treatment Facilities

• Safe drinking water relies on methods to eliminate harmful pathogens.
• Chlorine is a traditional disinfectant and commonly used in water treatment.
• Regularly occurring chemical byproducts (DBPs) are linked to long-term health risks when present in drinking water.
• Some microbes resistant to chemical disinfectants exist.
• Regulations to minimize negative DBP impacts exist for water treatment facilities.

2-Selection Criteria

• Choosing suitable methods for microbial control is complicated, depending on numerous factors.

Selection Criteria - Factors

• Type of microbes, number of microbes, environmental conditions, risk of infection, and composition of item are key in determining the selection of an antimicrobial procedure.

Selection of an Antimicrobial Procedure - 1. Type of Microorganism

• Mycobacterium species (e.g., waxy cell walls) are resistant to many chemicals.
• Pseudomonas species can grow in various disinfection conditions.
• Non-enveloped viruses (lacking lipid envelopes) are highly resistant.
• Bacterial endospores exhibit extreme resistance.
• Protozoan cysts/oocysts exhibit resistance to disinfectants.

Selection of an Antimicrobial Procedure - 2. Number of Microorganisms

• Controlling microbes depends on population size, and larger populations take longer to eliminate.
• Decimal reduction time (D-value) refers to the time necessary to reduce the bacterial population by 90% using a disinfectant.

Selection of an Antimicrobial Procedure - 3. Environmental Conditions

• Environmental factors (e.g., dirt, grease, body fluids) reduce the effectiveness of treatments (e.g., heat).
• Organisms in biofilms (and their complex structures) exhibit increased resistance.
• pH and temperature are factors affecting treatment efficacy.

Selection of an Antimicrobial Procedure - 4. Risk

• Medical instruments are categorized by risk for infection:
  • Critical instruments come into contact with sterile tissues (e.g., needles).
  • Semi-critical instruments come into contact with mucous membranes (e.g., endoscopes).
  • Non-critical instruments only contact unbroken skin (e.g., stethoscopes)

Selection of an Antimicrobial Procedure - 5. Composition

• Certain items (e.g., plastics) are sensitive to heat-based, liquid disinfections.
• Irradiation can be an alternative, but it's sensitive to the composition of the item and risks damaging it, such as plastics.