QUALITY CONTROL IN MEDICAL MICROBIOLOGY

Quality control is divided into:

@ Internal quality control: performed locally inside lab.

@ External quality control: performed between district labs. in same country or worldwide.

Discussing quality control programs

Areas of Quality Control:

@ Specimen collection & transport.

@ Culture media.

@ Sensitivity techniques

@ Stains & reagents.

@ Equipment.

@ Reporting & recording results.

Culture media

Control of Sample Collection & Transport:

@ Define the correct specimen to collect.

@ The best time to collect.

@ Aseptic method for collection .

@ Best methods of storage and transport

@ How to handle specimens in lab., e.g.

blood cultures, CSF, urine, swabs, stool, wet slide preparations.

Sample Collection

Control of Culture media: @ Perform correct pH testing,

correct storage, and correct autoclaving. @ Standard control species are used for test performance of media@ No moisture to enter powder

media @ Caps are replaced quickly &

tightly.@ Store plates at 4 °C in plastic bag.@ Before use, dry surface of plates .

Correct autoclaving

@ Do not leave unused plates on bench overnight to avoid contamination.

@ Slope media & fluid media may be stored at room temp. if screw-capped

@ New batches of media are dated and

stored separate from old batches.

@ Shelf-life of each medium is noted.

@ Small batches of media are prepared to avoid waste.

Media ready for incubation

Trouble-Shooting for Media

@ Defective media:

* Use good quality media

@ Incorrect weighing:

* Check and correct the mistake.

@ Deteriorated media:

*Store media in airtight containers at the appropriate temperature

@ Bad water :

* Use distilled water for media preparation.

Use good quality media

@ Undissolved media:

* Dissolve powder by mixing & boiling.

@ Overheating of media after autoclaving:

* Open autoclave when pressure comes down & temperature is below 100°C * Cool media immediately after autoclaving.

@ Incorrect pH of medium:

* Measure pH when medium cools to room temp. * Pour a sample of medium in a beaker, let agar to solidify around the electrode, and read pH.

pH meter

Antimicrobial Susceptibility Tests

Control cultures :

• S. aureus ATCC 25923 (miscellaneous)• E. coli ATCC 25922 (urine)• P. aeruginosa ATCC 27853(Ps.)

@ Subcultured weekly & stored in Fridge.

@ To detect inhibitors in MH agar, inoculate E.faecalis (ATCC 29212),put co-trimoxazole disc and inhibition zone must be ≥ 20 mm

Antimicrobial Susceptibility Tests

Sources of Error in Sensitivity Testing

(1) Too small control zones: Due to:

@ Use of discs with low potency

@ Use of discs after expiry date.

@ Use of a too dense inoculum

@ Use of too thick medium layer

@ Presence of inhibitors MH agar medium

Too small zones

(2) Too large control zones: Due to: @ Use of discs with high potency.

@ Use of a too diluted inoculum

@ Use of a too thin medium layer

(3) Presence of colonies within inhibition zones: Due to:

@ Contamination of culture (large colonies)@ Presence of inhibitors in MH agar (small colonies) detected by co-trimoxazole

Too large zones

Control of stains & reagents :

@ A control smear is stained to check

quality of newly-made stains

@ Control smears of gram stain is made from a mixed culture of Staph & E.coli

@ Control smears are kept in lab. to check Z.N, Leishman, spore stains, etc

@ Control smears should be alcohol-fixed

Control smears of Gram stain

Control of equipment: @ Regular servicing & maintenance

@ Check glassware for good condition

@ Inspect tube caps and worn liners.

@ Regular check of working temp.

@ Check water of water-bath, etc

@ Use of indicators to check autoclaves, anaerobic jar, etc

@ Check distilled water.

Regular check of incubator working temp

Control of Results:

@ Printed forms or computer sheets must be used for reporting results.

@ Result must be typed clearly and checked by a senior lab. staff.

@ Copies of all results are kept in lab.

@ Dates, demographical data, type of specimen & technologist name must be included.

Typing laboratory results