Quality Control for Microbiological Culture Media

Dr maryam Sotoudeh Tehran heart Center

Categories of Microbiological Media

Media are divided into two main descriptive categories based on the purposes for which the media were designed :

Selective Non

selective (nutritive)

Categories of Microbiological Media

Nonselective media promote the growth of organisms

Selective media contain antimicrobial or chemical agents that inhibit the growth of certain microorganisms

Some nonselective and selective media also contain components that allow for organism differentiation.

An NCCLS national consensus standard (M22-A3)

Commercial media are divided into two additional categories, according to which are determined by quality control performance data collected by CAP (1984, 1988, 2001)

Exempt Nonexempt

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Reasons Given for Lot Failures

Exempt and Nonexempt Categories for Media Included in CAP Surveys (1984, 1988, 2001)

(From Jones RN, Krisher K, Bird DS, and the College of American Pathologists Microbiology Resource Committee. Results of the survey of the quality assurance for commercially prepared microbiology media.Arch Path Lab Med. 2003;127(6):661-665

CATEGORY EXEMPT NONEXEMPT

General bacteriologic media

Blood agarChocolate agarThioglycolate brothUrease agar

Nutrient broth

Blood culture media •Brain heart infusion (BHI) blood culture broth•Biphasic blood culture bottle medium•Thiol blood culture broth•Trypticase soy blood culture broth•Peptone broth

•brain heart infusion• trypticase soy broth•thiol-based media

User Quality Control Requirements for Nonexempt Media Only

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Visual Inspection

Satisfactory1. Intact petri dish2. Agar attached to bottom of dish3. Blood containing medium is opaque4. Medium is appropriate color5. Minimal moisture in package6. Not frozen or desiccated7. No visible contamination8. Agar has even depth of at least 3

mm9. Smooth agar surface10. No precipitates

UnSatisfactory1.Cracked/damaged petri dish2. Agar dislodged or loose3. Hemolysis of blood in medium4. Color differs from characteristic

appearance(possible pH problem)5. Excessive accumulation of moisture6. Evidence of freezing or medium

desiccated7. Gross contamination8. Uneven or under filled plates/agar

desiccation9. Excessive bubbles/rough surface10. Presence of precipitates

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Sterility Check

• For Sterility checking of a lot :• In batch of 100 or fewer units : 5% of any lot• In larger batch : a maximum of 10 units are

tested

Baily and scott’s

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Sterility Check

Record results

Satisfactory : No bacterial or fungal growth

Un Satisfactory : Bacterial or fungal growth detected

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Inoculum preparation for aerobic/anaerobic bacteria: Prepare a suspension of a 24-hour culture in sterile saline to match a 0.5 McFarland standard. (Primary Suspension) (PS). Acceptable performance should generally allow initiation of routine testing within 24-48 h for nonfastidious, more rapidly growing bacteria

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Preparation of Suspensions for Quality Control of Nonexempt Media

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• for Nonselective Media If the 1:100 dilution inoculum proves too dense,use a 1:1000 dilution to produce isolated colonies.

• for selective Media Use a 1:100 dilution if isolated colonies are not produced

Minimum requirements for media quality control include at least one organism to document support of growth. Testing additional organisms is recommended to confirm the performance of inhibitory or selective media

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