Openstax Microbiology Chapter 13: Control of Microbial Growth

Biological Safety Levels

Levels of safety determined by

agents infectivity

Ease of Transmission

Disease severity

Work being done with the agent

BSL1

no special precautions; basic teaching labs

e.g nonpathogenic E.coli

BSL2

lab coat, gloves, eye protection

e.g Staphylococcus aureus

BSL3

biosafety cabinets to prevent airborne transmission, self closing doors, directional air flow

e.g Mycobacterium Tuberculosis

BSL4

- Change clothing before entering lab.

- Shower upon exiting lab.

- Decontaminate all materials before exiting lab.

- All work with microorganisms must be performed in a ClassIII biosafety cabinet or by wearing a full body, positive pressure suit.

- Laboratory must have negative airflow, and exhaust air cannot be recirculated.

- The laboratory must be in a separate building or in an isolated and restricted zone of the building.

e.g Ebola and Marburg Viruses

How can we control microbial growth on formites

Disinfection, sanitization, sterilization

How can we control microbial growth on living tissue

Antisepsis and Degerming

Disinfection

reduce and destroy microbial loads with heat or chemicals.

Formite: Benches, clinical surfaces, and bathrooms

Method: Cl bleach and lysol

Sanitization

reduce microbial loads to public health levels with heat and chemicals

Formite: dishwashers, public restrooms

Method: detergents, industrial cleaners

Sterilizations

Eliminates all vegetative cells, endospores, and viruses.

Formite: surgical equipment, needles for injections

Method: Autoclave, chemicals, radiation

Antisepsis

reduces load on skin/ tissue with antimicrobial chemical

tissue: cleaning broken skin due to injury, before surgery

Method: Boric acid, IPA, H2O2, Iodine

Degerming

reduces loads through gentle scrubbing with mild chemicals

Tissue: hand-washing

Method: soap, alcohol swab

What is a vegetative cell?

An actively Metabolizing Cell

What type of chemicals kill?

The -cides

bactericides, viricides, fungicides

What type of chemicals inhibit growth?

The -statics

bacteriostatic and fungistatic

Microbial Death Curve

degree of control that can be evaluated. Progress and effectiveness described to evaluate a particular protocol

Heat

a fast, reliable, and inexpensive way to control microbial growth using temperature above the growth range.

At these temperatures proteins and nucleic acids are denatured and water is removed.

The effectiveness of heat sterilization

A function of time and temperature

Thermal Death point

the lowest temperature required to kill all microbes in a sample in 10 minutes

Thermal Death Time

shortest length of time required to kill all test microbes at a specified temperature

Dry heat sterilization

incineration destroys all microbes Direct flame or Hot air oven.

Moist Heat Sterilization

more effective, penetrates better, and takes less time. Boiling or autoclaving

Hot air oven

A hot air oven requires 2 hours at 170C to achieve sterilization.

Boiling

effective at kill vegetative cells only. Not considered very useful

Autoclaving

this method of pressurized steam is very dependable for killing bacteria. 15 psi, 121C, 15-20 minutes

Pasteurization

the process of treating a substance with heat to destroy or slow the growth of pathogens. Foods are not sterile and will eventually spoil

What are some times of pasteurization?

High tmeperature short time: exposes milk to 72C for 15 seconds

Ultra high temperature: expose milk to 138C for 2 seconds. can be almost sterile

Refrigerators

keep temperature between 0-7C. this inhibits microbial growth and helps preserve refrigerated products

Freezing

temperatures below - 2C. this may stop microbial growth and even kill some susceptible organisms. Bacteria growth may restart in thawed foods. If long term storage required the temperature may be -70C or lower

Pascalization

high pressure processing used to kill while maintaining quality and extending shelf life

Hyperbaric Oxygen Therapy

Used to treat infections be forcing in pure oxygen at a high pressure. This oxygen saturation kills anaerobe pathogens within hypoxic tissues.

Desiccation

removing water or moisture by drying out or dehydration. Life requires moisture for metabolic activity

what are some drying methods?

Sun drying, freeze drying, and lyophilization

Lyophilization

Exposure to cold temperature and desiccation.

Ionizing Radiation

X-rays, gamma rays, and high energy electron beams. They enter the cell, alter the molecular structure, and damage the cell. Introduces breaks in the DNA.

Use: For items that cannot be autoclaved

e.g. plastic, heat sensitive, drugs, or tissues

Non-ionizing radiation

Cells exposed to UV light directly. Doesn't penetrate cells, Surface Sterilants.

cause thymine dimers

Use; H2O purification, germicidal lamps

Sonication

Use of high frequency ultra sound waves to disrupt cell structure. the waves cause rapid changes in the pressure in the intracellular liquid, leading to bubbles within the cell causing lysis.

Use: in labs for research or for cleaning

Filtration

A process that separates materials based on the size of their particles. HEPA the high efficiency particulate air filter, which has a pore size of 0.3um. Small enough to catch bacteria, endospores, and viruses.

Membrane Filters

Only separate microbes from solutions. useful for removing bacteria from heat sensitive solutions, lie antibiotics. Autoclaving these materials could cause denaturation or some other damage

Phenolics

Denature Proteins and disrupt membranes

Triclosan, Cresols

Expensive, caustic, and have a pungent odor

e.g lysol, antibacterial soap

Biphenols

2 phenol molecules. great for disinfection and antisepsis

Heavy metals

binds to proteins and inhibit enzyme activity

mercury, silver, copper, etc

e.g. topical antiseptic, treat wounds and burns, mouthwash

Halogens

Oxidation and destabilization of cellular macromolecules. oxidize proteins, keep bacteria low, and disinfect

iodine, chlorine, fluorine

e.g topical antiseptic, bleach, water treatment

Alcohols

denatures proteins and disrupt membranes. Membrane disruption caused by LIPID DISSOLUTION. Effective against vegetative cells and not endospores.

IPA and ethanol

e.g. disinfectant, antiseptic

Surfactants

compounds that lower the surface tension of water

Soap and detergents remove microbes by emulsifying and solubilizing particles on the skin

Bisbiguanides

disruption of cell membranes

Chlorhexidine/alexidine

e.g. Oral rinse, hand scrub

Chlorhexidine

Disrupts membrane. Dependent on the concentration can be -static or -cidal. This works against enveloped virus. Alexidine can work faster

Alkylating Agents

inactivation of enzymes and nucleic acid by combination. sterilize materials at low temperatures

Formaldehyde, ethylene oxide

e.g disinfectant, storage, embalming

Peroxygen

oxidation and destabilization of cell macromolecules

H202, Benzoyl peroxide

e.g. Antiseptic, acne meds, toothpaste

Supercritical gases

penetrates cells, carbonic acid, and lowers ph

CO2

e.g. food preservation, medical devices, transplant tissues

Chemical food preservatives

lowers the ph, inhibit enzyme function

Sorbic acid, benzoic acid

e.g. preserve food products

Natural food preservatives

inhibitin of cell wall synthesis

nisin, natamycin

e.g. preserving dairy, meats, and beverages

High-level germicides

kill all pathogens, including endospores

Intermediate level germicides

cannot kill all viruses, less effective against endospores

Low-level germicides

kill vegetative spores, some enveloped viruses but ineffective against endospores

What is the effectiveness of a disinfectant dependent on?

length of exposure, concentration, temperature, and ph

Disk diffusion method

used to evaluate the efficacy of a chemical agent against a particular microbe