Inhibiting Microbial Growth in Vitro: Matching Terms

Methods of Microbial Control in Vitro

• Microbial control involves methods of inhibiting microbial growth, inhibition, and destruction
• Methods of microbial control can be categorized into physical, chemical, and biological methods

Sterilization, Disinfection, and Antiseptics

• Sterilization: the complete destruction of all microbes, including cells, spores, and viruses
• Disinfection: the destruction or elimination of most pathogens from nonliving objects by physical or chemical methods
• Antiseptics: chemical substances used to disinfect skin and other living tissues
• Pasteurization: a method of reducing microbial populations to levels considered safe by public health standards

Heat Sterilization

• Heat is a practical, efficient, and inexpensive method of sterilization for inanimate objects
• Two factors determine the effectiveness of heat for sterilization: temperature and time
• Thermal death point (TDP) is the lowest temperature that will kill all organisms in a standardized pure culture within a specified time
• Dry heat: uses flame and incineration; moist heat: uses autoclave

Autoclave

• Autoclave is a common method of sterilization used in places where sterile items are required, such as tattoo parlors, microbiology labs, and medical facilities
• Autoclave uses pressure and steam to sterilize items, with typical specifications of 15 psi, 121°C, and 15-20 minutes
• Autoclaving destroys vegetative microorganisms, bacterial endospores, and viruses
• Quality control is essential to ensure that items are properly sterilized

Autoclave Quality Control

• Chemical indicators: temperature-sensitive tapes or bags
• Physical indicators: alloys that melt when exposed to correct temperature for at least 15 minutes
• Biological indicators: sealed ampules with heat-resistant bacteria

Common Faults in Autoclave Operation

• Inadequate precleaning of instruments
• Improper maintenance of equipment
• Cycle time too short or temperature too low
• Overloading or improper loading of sterilizer chamber
• Incompatible packaging material
• Interruption of sterilization cycle to add or remove an item
• Wrong cycle was selected
• Mechanical failure or insufficient water supply

Autoclave Safety

• Loosen screw caps on bottles and tubes of liquids before autoclaving
• Always check that chamber pressure has returned to zero before opening door
• Wear eye and face protection and heat-resistant gloves
• Stand behind door when opening it
• Slowly open door only a crack to allow residual steam to escape

Physical Methods of Inhibition

• Cold can have a static effect, halting growth
• Some methods preserve, such as penicillin produced by Penicillium mold

Antibiotics

• Ideal characteristics of antimicrobial agents:
  • Kills or inhibits growth of target pathogen
  • Causes no damage to host
  • No allergic reaction in the host
  • Stable when stored in solid or liquid form
  • Penetrates and remains in target tissue
  • No resistance
• Antibacterial agents can be organized by mode of action:
  • Cell wall: beta-lactams
  • Protein synthesis: glycopeptides
  • Genetic material: quinolones
  • Cell membrane: polymyxins
  • Metabolic process: sulfonamides and trimethoprim

Beta-Lactam Antibiotics

• Commonalities: beta-lactam ring, target cell wall, and are bactericidal
• Differences: side groups, specificity, and spectrum
• Examples: penicillin, cephalosporin, and carbapenems

Mechanisms of Drug Resistance

• Intrinsic resistance
• Mutations:
  • Chromosomal mutation that alters drug-binding site
  • Chromosomal mutation that causes a change in cell membrane permeability
• Acquisition:
  • Of resistance genes that destroy or inactivate drugs
  • Of genes that pump antimicrobials outside the cell

Strategies to Combat Drug Resistance

• Education