Sterilization &Disinfection By Prof. Dr. Zainalabideen A Abdulla, DTM&H., MRCPI, Ph.D., FRCPath. (U.K.)

LEARNING OBJECTIVES 1. Differentiate between sterilization, disinfection, and sanitization 2. Differentiate between bactericidal and bacteriostatic agents 3. Explain the process of pasteurization and lyophilization 4. List several methods used to inhibit the growth of microorganisms 5. Identify several factors that can influence the effectiveness of disinfectants

Sterilization Destruction or elimination of all microbes including cells, spores, and viruses - Sterile = Devoid of microbial life - Physical or chemical methods in healthcare Dry heat Autoclaving (steam under pressure) Ethylene oxide gas Formaldehyde Radiation (UV, gamma rays)

Disinfection The elimination of most or all pathogens (except bacterial spores) from nonliving objects; using: 1. Liquid chemicals (disinfectants) 2. Wet pasteurization Antiseptics: Disinfectants used on living tissues as the skin Sanitization: Reduction of the microbial population to safe levels, e.g. in resturants

Microbicidal agents - Suffix: cide or cidal = “killing” Examples: Bactericidal = Kill bacteria Sporicidal = Kill bacterial spores Viricidal = Kill viruses Fungicidal = Kill fungi Pseudomonicidal= Kill Pseudomonas Tuberculocidal = Kill M. tuberculosis

Pasteurization - A method to disinfect liquids (e.g. milk) - Is not sterilization - Not all microbes are killed - 63 Celsius 30 minutes 72 Celsius 15 seconds 140 Celsius 4 seconds

Microbistatic agents - Drugs or chemicals that inhibit reproduction and metabolism of microorganisms (NOT necessarily kill them) - Freeze drying & rapid freezing: Bacteriostatic - Freeze drying = Lyophilization; preserve m.o.

Sepsis: Presence of pathogens in blood or tissues Asepsis: Absence of pathogens - Medical or Surgical aseptic techniques, e.g., hand hygiene, sterile gloves, masks, and gowns Antisepsis: Prevention of infection Antiseptic technique: Use of antiseptics

Physical Methods Heat - The most common type of sterilization for inanimate objects able to with stand high temperatures - Effect depends on: 1. Temperature 2. Time - Pathogenic > susceptible than nonpathogenic

Thermal Death Point (TDP) Lowest temp. that kill all organism in a standardized pure culture within specified period Thermal Death Time (TDT) The length of time to sterilize a pure culture at a specified temperature

Dry heat – 165 Celsius 2 hours or – 180 Celsius 1 hour - In oven - Items: Metals, glassware, oils, waxes Incineration: Burning; contaminated disposable materials; must NOT overloaded with protein and moist materials as feces, vomitus or pus Flaming: Bunsen burner flame or electrical heat device for wires, loops or forceps

Moist heat 1. Boiling for 30 minutes, e.g. metal (needles), glass. Not effective against spores, viruses and Mycobacterium. 2. Autoclave (Moist heat + Pressure): - 15 psi Celsius for 20 minutes - Kills spores, viruses, and vegetative form - Rubber can be autoclaved - Indicators for completion: Autoclave tape or Solutions of bacterial spores - Keep cans open, bottles covered loosely

Cold - Refrigeration: Slows metabolism & growth rate - Slow freezing: Form crystals & rupture cells - Rapid freezing (liquid nitrogen): Keep/Preserve Freeze- Thawing of food: Unsafe (spores vegetative forms

Desiccation - Dried clinical specimens and dust may contain viable microorganisms. Radiation - UV: Sterilize vaccines, antisera, toxins May cause skin cancer, eye damage - X-ray, gamma and beta ray: Gamma ray sterilizes food as meat from Salmonella & Campylobacter

Ultrasonic Waves - For cleaning delicate equipment - Tank of water + short US waves then sterilize - In dental or medical clinics, e.g. glassware

Filtration - Different pore sizes; separate organisms (bacteria, viruses, others) from liquid or gases - Micro-pore filters - High-Efficiency Particulate Air (HEPA) used in operating rooms, patient room to filter air

Gaseous Atmosphere - Aerobs/ Microaerophiles: Remove O2 - Anaerobic: Provide O2 Hyperbaric Oxygen Chamber (increased pressure) to kill m.o.

Disinfectants (Chemical Agents) - Temporal or permanent - Factors affecting disinfectants: Prior cleaning/proteinaceous materials Organic matter load Bio-burden (microbial) Concentration Time Physical nature Temperature/ pH

cont./… Disinfectants - Susceptible: Vegetative state, fungi, protozoa, most viruses - Resistant: Mycobacteria, bacterial endospore, Pseudomonas spp., fungal spores, hepatitis viruses - Degree of resistance (see Table)

cont./… Disinfectants - Never use disinfectant if physical sterilization is possible - Do not destroy all bacteria & bacterial spores - Spore/ Mycobacteria/Viruses destruction: Formaldehyde / fumigation Ethylene oxide

Disinfectant characteristics Broad Fast-acting Not affected by organic materials Non-Toxic; Evaporation-Concentration Leave residual anti-microbial film Soluble in water Inexpensive Stable Odorless

Antiseptics - Chemicals used safely on human tissues such as skin - Reduce numbers of organisms on surfaces - Used at surgical incisions, at pores of folds of the skin - Antiseptic soup + Brushing