MicroPara

• Definition of Terms:

  • Sterilization: process where all living cells, viable spores, viruses, and viroids are destroyed or removed from an object or habitat
  • Disinfectants: chemical agents used for disinfection on inanimate objects
  • Sanitization: reducing the microbial population to safe levels by public health standards
  • Antisepsis: prevention of infection or sepsis using antiseptics
  • Antiseptic: chemical agents applied to tissue to prevent infection by killing or inhibiting pathogen growth and reducing the total microbial population
  • Germicide: kills pathogens but not necessarily endospores
  • Bacteriostatic and Fungistatic agents: prevent growth but do not kill microorganisms
• Conditions Influencing the Effectiveness of Antimicrobial Agent Activity:

  • Population size and composition
  • Concentration or intensity of the antimicrobial agent
  • Duration of exposure
  • Temperature
  • Local environment
• Use of Physical Methods of Sterilization:

  • Heat (wet/dry)
  • Low Temperature
  • Filtration
  • Radiation
• Heat Sterilization Methods:

  • Wet Methods: coagulation of proteins (boiling, pasteurization, tyndallization, autoclaving)
  • Dry Methods: oxidation of cells (oven, incineration)
• Autoclaving:

  • Also known as steam under pressure
  • Conditions: 121°C, 15 psi, 15-20 minutes
  • Methods to verify completeness: special packaging tapes, probes (thermocouples), biological indicators like bacterial spores
• Approximate Conditions for Moist Heat Killing:

  • Different organisms have different killing conditions in terms of time and temperature
• Thermal Death Point (TDP) and Decimal Reduction Time (DRT) are important concepts in sterilization
• Low Temperature Methods:

  • Used for long-term storage of cultures
  • Examples include freezing, refrigeration, deep freezing, and lyophilization (freeze-drying)
• Filtration:

  • Physical separation of organisms from a solution
  • Membrane filters consist of porous membranes used to sterilize solutions
• Types of Filters:

  • Depth filters
  • Membrane filters
• Membrane Filters:

  • Circular filters made of porous membranes, used to sterilize pharmaceuticals
• Depth filters consist of fibrous or granular materials bonded into a thick layer filled with twisting channels of smaller diameter
• Membrane filters are circular, porous membranes, little over 0.1 mm thick, made of cellulose acetate, cellulose nitrate, polycarbonate, etc., used to sterilize pharmaceuticals, optical solutions, culture media, oils, antibiotics, and more
• Air can be sterilized by filtration, with examples like surgical masks and cotton plugs allowing air in but keeping microorganisms out
• HEPA filters remove 99.97% of 0.3 um particles, used in biological cabinets to protect workers from microbes and prevent contamination of the room
• Radiation can cause a lethal form of mutation, with ultraviolet (UV) radiation being non-ionizing and ionizing radiation being an excellent sterilizing agent that penetrates deep into objects
• Chemical agents used in control must be effective against a wide variety of infectious agents, stable upon storage, non-toxic to people, and relatively inexpensive
• Common disinfectants and antiseptics include phenolics, biguanides, alcohols, halogens, heavy metals, quaternary ammonium compounds, aldehydes, and sterilizing gas
• Phenolics are antiseptics and disinfectants that precipitate lipids-containing plasma membranes, with advantages like being tuberculocidal and effective in the presence of organic material
• Triclosan, a bisphenol present in various products, may increase antibiotic resistance in bacteria with extensive use
• Biguanides primarily affect bacterial cell membranes, being effective against gram (+) and gram (-) bacteria, with chlorhexidine being a well-known biguanide used for microbial control on skin and mucous membranes
• Alcohols are widely used disinfectants and antiseptics, bactericidal and fungicidal but not sporicidal, with ethanol recommended at 70% concentration for optimum effectiveness
• Halogen elements like iodine act as oxidizing agents, existing as diatomic molecules in the free state and forming salt-like compounds with metals
• Iodine, a halogen, is a skin antiseptic that kills by oxidizing cell constituents and iodinating cell proteins, with tincture of iodine being an example
• Iodine:

  • Acts as a skin antiseptic and kills by oxidizing cell constituents and iodinating cell proteins
  • At higher concentrations, it can kill some spores
  • Example: Tincture of Iodine (2% iodine in a water-ethanol solution of potassium Iodide)
• Disadvantages of using iodine:

  • Skin may be damaged
  • Stain is left
  • Allergies may occur
  • Iodophore is an alternative, which is iodine complexed with an organic carrier, water-soluble, stable, non-staining, and releases iodine slowly to minimize skin burns and irritation
  • Example: Betadine
• Chlorine:

  • Used as a disinfectant for water supplies and swimming pools
  • May be applied as chlorine gas, sodium hypochlorite, or calcium hypochlorite
  • Action: Causes oxidation of cellular materials and destruction of vegetative bacteria and fungi, although not spores
• Advantages of Chlorine:

  • Very effective
  • Inexpensive
  • Easy to employ
  • Disadvantage: Reacts with organic compounds to form carcinogenic trihalomethanes, which must be monitored in drinking water
• Heavy Metals as Germicides:

  • Include Mercury, Silver, Arsenic, Zinc, and Copper
  • Mechanism of Action: Binding to SH groups of bacterial enzymes
  • Property: Oligodynamic property where few concentrations are highly potent
• 1% Silver nitrate:

  • Often added to the eyes of infants to prevent ophthalmic gonorrhea
  • Erythromycin is used instead because it is effective against Chlamydia as well as Neisseria
  • Silver Sulfadiazine used on burns
  • Zinc undecylenate used as an antifungal
• Copper Sulfate:

  • An effective algaecide in lakes and swimming pools
• Surface-Active Agents:

  • Decrease surface tension among molecules of a liquid
  • Include soaps and detergents
  • Mechanism of Action: Soap breaks the oily film into tiny droplets, a process called emulsification, making them good degerming agents
• Quaternary Ammonium Compounds as Detergents:

  • Organic molecules that serve as wetting agents and emulsifiers
  • Due to their amphipathic nature, they solubilize otherwise insoluble residues
  • Very effective cleansing agents
  • Different from soaps, which are derived from fats
• Quaternary Ammonium Compounds:

  • Membrane and may also denature proteins
  • Anionic detergents have some antimicrobial properties
  • Examples: SLS, soaps, Benzalkonium chloride (Zephiran), cetylpyridinium chloride
  • Effective disinfectants that kill most bacteria but not M. tuberculosis or endospores
  • Mechanism of Action: Charged molecules that disrupt microbial
• Aldehydes:

  • Formaldehyde and Glutaraldehyde
  • Mechanism of Action: Combine with nucleic acid and proteins and inactivate them
  • Sporicidal and can be used as chemical sterilants
• Sterilizing Gases:

  • Ethylene oxide (EtO) is used to sterilize many heat-sensitive items like disposable plastic petri dishes, syringes, heart-lung machine components, sutures, and catheters
  • Mechanism of Action: Alkylation where EtO is both microbicidal and sporicidal, killing by combining with cell proteins
• Ethylene oxide (EtO):

  • Effective sterilizing agent because it penetrates packing materials, even plastic wraps
  • Sterilization is carried out in a special sterilizer, like an autoclave, that controls EtO concentration, temperature, and humidity
  • Explosive and supplied in 10%-20% concentration mixed with either CO2 or dichlorodifluoromethane
• Beta-Propiolactone (BPL):

  • Less extensively used than EtO
  • In liquid form, it is used to sterilize vaccines and sera
  • Mechanism of Action: Destroys microorganisms more readily than EtO but does not penetrate materials well and may be carcinogenic
• Dyes:

  • Gentian violet: Vaginal suppositories for yeast infections
  • Prontosil: Red dye
  • Phenazopyridine hydrochloride (Pyridium®): UTI treatment with a local analgesic effect when excreted in the urine
  • Basic Fuchsin: Ingredient of carbolfuchsin solution (Castellani’s paint) for the treatment of ringworm and athlete’s foot
  • Methylene blue: Fungal infection treatment for fishes and antidote for CN poisoning
• Bacteria can be classified based on their shape as cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped), or vibrio (comma-shaped).