For lecture only

Sterilization, disinfection and antisepsis

Two very original methods for disinfection or BC Yang

For lecture only   

In 1866 J Lister suggested antiseptic surgery. His rational was: Putrefaction is caused by microbes Wound sepsis is a form of putrefaction Wound sepsis is caused by microbes Carbolic acid, phenol BC Yang

Carbolic acid, phenol: a toxic white soluble crystalline acidic derivative of benzene

 

various antiseptics various disinfectants



various germicides



adhesive dyes



perfumes



textiles



lubricating oils

  

Acute poisoning by ingestion, inhalation or skin contact may lead to death. Phenol is readily absorbed through the skin. Highly toxic by inhalation. Causes burns.



In the previous year Lister had heard that 'carbolic acid' was being used to treat sewage in Carlise, and that fields treated with the affluent were freed of a parasite causing disease in cattle.



Lister then began to clean wounds and dress them using a solution of carbolic acid. He was able to announce at a British Medical Association meeting, in 1867, that his wards at the Glasgow Royal Infirmary had remained clear of sepsis for nine months.



Opposition was great In England and the United States mainly against Lister's germ theory rather than against his "carbolic treatment."

Phenols and phenolics



Carbolic acid



Low level disinfectant



O-phenylphenol (Lysol)



Hexachlorophene (Phisohex)



High level for Staphylococcus sp. and

Streptococcus sp.



Surgical scrubs



Damage membrane, inactive enzymes, denature proteins

For lecture only

BC Yang

The day after SARS

蚊子少了

;

人離的遠了

;

官員被糾正

;

化學兵正當紅

• Ethylene oxide: denatures proteins • Highly penetrating • Most used in hospitals for plastic ware, textiles, etc…..

For lecture only

BC Yang

Mechanism of antimicrobial action



Damage to DNA: radiation, UV, DNA reactive agents



Protein denaturation: Heat, pH, metals



Disruption of cell membrane or cell wall: detergents, enzymes



Chemical antagonism: analogs



Removal of free sulfhydryl groups: oxidizing agents

For lecture only

BC Yang

To die or not to die, that is a question

For lecture only 

Sepsis: microbes contamination



Asepsis: absence of microbes contamination



Sterilization: 100% killing



Disinfection: loss the ability to cause disease



-cide or cidal: killing of microorganism



-static or stasis: inhibit growth or multiplication of microbes BC Yang

Types of antimicrobial agents

• Physical – Heat – radiation • Chemical – Vapors – selectivity

Scientific American284 (5):54-61

For lecture only

BC Yang

Killing is a probability

  

Die at a constant rate (logarithmically) Depend on exposure time and microbial load Rare will reach 100% (on purpose and money consuming)

For lecture only

BC Yang

Parameters of sterilization/disinfection



Action process



The rate/kinetics

: the death rate of a microbial population follows a logarithmic path.



Resistances

: pure empirical, varied from culture condition, nature of the environment 

Control/indicators

: 

Living:



heat : spores, themophilic bacteria



ethylene oxide and radiation: Bacillus subtilits var. nigar.



Chemical: succinic anhydride (120 o C), sulphur (115 o C); color change; etc..

For lecture only

BC Yang

Action index



A spoonful work already well?

 

Why not LD 50 ?

Phenol coefficient (PC)



American official analytical chemist’s use-dilution method



Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella choleraesuis



Filter paper method

For lecture only

BC Yang

The phenol coefficient (PC)



A water-soluble phenol-based disinfectant (amphyl, lysol) is tested for its bactericidal effectiveness as compared with phenol.



These disinfectants are serially diluted in a series of salmonella cultures and incubate for a while.



Chemicals with lower phenol coefficients have greater effectiveness



Restricted to phenolics PC= Greatest dilution of the phenolic that kills Test bacteria in 10 min, but not in 5 min Greatest dilution of phenol giving same result

For lecture only

BC Yang

As a matter of temperature

 

Heat

Boiling water  Moist heat (steam under pressure, autoclave)  Hot-air sterilization (Oven)  Pasteurization  Tyndallization  Incineration  

Low temperature

Refrigerator temp (4-7oC)  Deep-freeze (-20oC to -40oC); liquid nitrogen (-196oC)  Lyophilization (desiccation in low temperature) For lecture only

BC Yang

Pasteurization

   

Suggested by L. Pasteur It is used to render mild safe (tuberculoses) and extend its storage quality Keep the flavor of milk, wine 62 o C 30 min, 71 o C for 15 sec

For lecture only

BC Yang

Pasteurization

別呆了

,

不要喝尚青尚新鮮的牛奶

!

•

1909 John Ross Robertson finances the installation of Toronto's first milk pasteurization plant in the College Street hospital, 30 years before it becomes mandatory.

For lecture only

BC Yang

For lecture only

Tyndallization (Fractional sterilization)



John Tyndall was a man of science—draftsman, surveyor, physics professor, mathematician, geologist, atmospheric scientist, public lecturer, and mountaineer.



For killing both vegetative and spore forming bacteria at temperature of 100 o C or below for 30 min on the consecutive days BC Yang

Filtration

For lecture only

BC Yang

Filtration



Liquid



When subjects are heat-labile



0.22/0.45 mm membrane filter



Air



Large space Alternative: electrostatic precipitation



Particles passed through a high voltage electric field become charged, and attracted to and held by the plate of opposite potential (remove ~97% of bacteria)

For lecture only

BC Yang

Surfactants: breaks oily film on skin

Wash away: do you really clean your hands?

For lecture only

BC Yang

 

UV radiation

Ultraviolet is light with very high energy levels and a wavelength of 200-400 nm. One of the most effective wavelengths for disinfection is that of 254 nm.

For lecture only

BC Yang

Alcohols



High level disinfectant



Disrupt protein, disrupt membranes, dissolve lipids



70% ethanol



Used in tinctures

For lecture only

BC Yang

For lecture only 碘酒

Halogens (Iodine)



Iodine combines with tyrosine & oxidized SH groups on other amino acids



Tincture: 1-2% I2 + 2% Na2I in 70% ethanol (for surgical site disinfection).



Povidone-iodines: Betadine



Skin disinfection



Surgical scrub BC Yang

For lecture only

The choices?

It always depends!



The materials



The purpose



The nature of microbes

BC Yang