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Microbiology

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Sterilization and disinfection

Question
48 out of 97
 

All of the following are methods of phenotypic typing except; (AIIMS Nov 2011)



A Plasmid profile analysis
B Phage typing

C Bacteriocin typing
D Biotyping

Ans. A Plasmid profile analysis

a. Plasmid profile analysis is a genotypic method of typing.

b. Rest of the options are phenotypic methods of typing bacteria.

c. Biotyping relies on picking up differences in biochemical reactions. Strains are referred to as "biotypes". The particular biochemical reactions exploited are legion.

d. Examples of biotyping include C.diphtheriae (mitis, gravis and intermedius) and V.cholerae (classical and El Tor).

e. Bacteriocin Typing: Difference in production/susceptibility to bacteriocins eg Proteus spp., S. sonnei

f. Antibiogram: It can be used as typing method to verify whether the drug resistance pattern obtained is from the same strain or a different strain. Differences in susceptibility to a set of antibiotics

EXTRA EDGE

Sterilization: Process by which article, surface or medium is freed of all living microorganisms capable of giving rise to infections.

Disinfection means the destruction or removal of all pathogenic organisms. (bacteria, viruses and fungi not spores)

Antiseptics: Disinfectants which prevent infection by inhibiting growth of bacteria when applied to skin or any living tissue or surface

Cold sterilization:

Ionizing radiations such as X-rays, gamma rays and cosmic rays causes no appreciable increase in temp. in this method, it is referred as cold sterilization.

Savlon is combination of cetrimide and Hibitane

Bladder wash - 0.1 % KmnO4 (Condy's lotion), solution of acetic acid and silver nitrate.

Hand wash - Chloroxylenol, chloro Hibitane, savlon, spirit, iodophores, isopropyl alcohol.

For cleaning infected wound - Iodophors, acriflavine, savlon, H2O2.

Remove slough from wound - EUSOL, H2O2.

All disposable items like ETT, breathing circuits, face masks, reservoir bags, adaptors, airways (all are heat sensitive instrument) etc. are best sterilized by ethylene oxide gas sterilization.

(Second choice for these items is chemical sterilization by Glutaraldehyde 2% (Cidex solution).

For fiberoptic scopes/endoscopes 2% glutaraldehyde is preferred method of sterilization.

Laryngoscopic blades, Magill forceps & stylets and spinal/epidural sets for reuse can be autoclaved.

Efficacy of disinfection

a. In Riedel walker test phenol is taken as the standard and phenol coefficient of the disinfectant is measured. This test or the Chick Martin test are used for testing efficacy of chemical disinfectants

b. Moist heat efficacy is tested by Bacillus stearothermophilus

c. Spores of non-toxigenic strains of Clostridium tetani/ B.subtilis are used to test efficiency of dry heat (flaming, incineration, hot air oven etc.)

d. Clostridium botulinum spores are the most heat resistant organism and require 120oC for 4 min or 100oC for 330 minutes for their killing

e. Coxiella burnetii are relatively heat resistant and survives in the holder method of pasteurization of milk.

f. Bacillus stearothermophilus is used to test efficacy of plasma sterilization.

g. Bacillus pumilus spores are used to test efficacy of gamma radiation.

Hot air oven (160oC X 1 hour/150 C X 115 min)

Used for Glass wares / glass syringes, surgical instruments

Dusting powder, oils / greases, liquid paraffin

Vaseline, Petri dishes

It may destroy plastic, rubber, objects (mattresses)

Hot air has no penetrating power

Burning (incineration)

Infective material like soiled, dressings, beddings, animal carcasses.

Red hot in Bunsen flame

Metallic inoculating wires, loops, tips of forceps

Autoclaving-moist heat under pressure (attain temp of 121oC X 15 min. under 15 Ib/sq inch pressure)

Most effective for killing spores. Linen, dressings , gloves, metal syringes, metal instruments .

Suture material except catgut

Culture media – autoclaving 121o for 15 min .

Not suitable for plastics & sharp instrument ( sharpness destroyed )

Inspissator

Media containing egg or serum

80o-85oC for 1/2hr for 3 days. (solidification)

Tyndallization (Fractional/Intermittent sterilization)

Culture media containing sugar/gelatin, XLD, DCA, Selenite F, TCBS

100o C for 20 min in 3 successive day

kills spores and bacteria

* Seitz filters / Chamberland / Membrane filters

For vaccines, serum, toxins, sugars, culture media

Antibiotic solutions.

Vaccine bath at 60oC for 1 hr (water bath at 56oC for 1 hr)

Serum, body fluids, bacterial vaccines.

Coxiella burnetti is relatively heat resistant

Glutaraldeltyde

(2% solution = Cidex)

Lenses of cystoscope/ endoscope (immersed for 30 min. before use for disinfection). Kills M.tuberculosis bacterium in 10 minutes.

Rubber/ plastic tubes.

Sporicidal, active at alkaline ph

Ethylene oxide (GAS)

Heart lung machine, respirators, dental equipment Sutures, fabrics.

Effective against spores. Cycle takes about 24 hrs, temperature-37-63C

Iodine

Fumigation of OT / labs / rooms/ woolen blankets, wool and hides

Rubber Plastic disposable goods dispo syringes , catheters.

CATGUTS, bandages, adhesive dressing.

A drop of tincture iodine may be added to a litre of drinking water for disinfection in an emergency.

For Lippes loop, skin disinfection.

Bactericidal and moderate activity against spore.

Sodium Hypochlorite

Acts in way similar to bleaching powder but stronger (available Cl2 80,000 -180,000 ppm)

100-200ppm containing freshly prepared Hypo solution is recommended for sterilizing infant's feeding bottles.

Disinfectant in HIV+ pt.

Boiling­

­

Vegetative bacteria are killed at 90-100°C. but not recommended for sterilizing instruments of surgical procedures.

Boiling for 5-10min (rolling boil) will kill bacteria but not spores or viruses Spores destroy at l00oC (as in autoclaving).

Chlorination ­

Chlorine kills pathogenic bacteria, trophozoites of amoeba &

Giardia but it has no effect on spores & certain viruses (e.g.

Polio, HAV) except in high doses

Hepatitis A virus ,Cysts of amoeba and Giardia are not

killed by chlorine in amount used for water disinfection.[so,

water filtration ( Sand filters) & boiling are more effective than

chemical Tt]

Studies indicates that 1 mg/L of free residual chlorine can cause

destruction of HAV in 30 min. at pH 8.5

* HEPA (High Efficiency Particle Arrester) filters – Used in the laboratory to render safe the air withdrawn from an exhaust ventilated safety cabinet used for work with dangerous pathogens. Another use is to decontaminate the air input in to a laminar flow cabinet used for work, such as plate pouring, that needs to be protected from airborne contamination.

HEPA filters remove particles > 0.3 μm with an efficiency of 99.97% and are reserved for high risk surgeries like orthopedic implant surgeries.

Sterilization and disinfection Flashcard List

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