Study guide
3.2 Media Types, Components, and Selection
ASCP Microbiology Technologist M ASCP
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1 Introduction & Exam Overview
1.1 Current M(ASCP) Exam Facts 1.2 CAT, Scoring, Retakes, and CMP 1.3 Eligibility Routes and Clinical Experience
2 Preanalytic: Collection and Transport
2.1 Patient Identification and Specimen Labeling 2.2 Specimen Collection, Sterile Technique, and Blood Cultures 2.3 Transport Devices, Atmosphere, Time, and Temperature
3 Preanalytic: Processing, Media, and Incubation
3.1 Prioritization, Rejection, and Specimen Preparation 3.2 Media Types, Components, and Selection 3.3 Inoculation, Incubation Conditions, and Slide Preparation
4 Preanalytic: Stains
4.1 Gram Stain: Procedure, Principle, and Interpretation 4.2 Acid-Fast and Modified Acid-Fast Stains 4.3 KOH, Calcofluor-White, Trichrome, Giemsa, and Acridine Orange
5 Bacteriology: Blood and Bone Marrow
5.1 Blood Culture Systems and Rapid Identification 5.2 Bloodstream Pathogens and Skin Flora Significance 5.3 Endocarditis, Bone Marrow Pathogens, and Pathogenicity
6 Bacteriology: CSF and Sterile Body Fluids
6.1 CSF Sources and Acute Meningitis Pathogens 6.2 Shunt Infections, CSF Correlates, Antigen and Molecular Methods 6.3 Sterile Body Fluids: Pathogens, Flora, and Molecular Methods
7 Bacteriology: Respiratory Tract
7.1 Lower Respiratory Specimens, CAP, and HAP Pathogens 7.2 Cystic Fibrosis Pathogens and Quantitative Reporting 7.3 Upper Respiratory: Pharyngitis, Otitis, Sinusitis, Antigen/Molecular
8 Bacteriology: Gastrointestinal Tract
8.1 Enteric Pathogens: Culture and Colony Morphology 8.2 Clostridioides difficile, Shiga Toxin, and Serotyping 8.3 Helicobacter pylori Detection and GI Pathogenicity
9 Bacteriology: Skin, Soft Tissue, and Bone
9.1 Skin, Soft Tissue, and Bone Pathogens 9.2 Bite Wounds and Zoonotic Infections 9.3 SST Pathogenicity and Virulence Mechanisms
10 Bacteriology: Genital Tract and Urine
10.1 Genital Flora and Vaginitis Pathogens 10.2 Neisseria gonorrhoeae, Chlamydia trachomatis, GBS, and Mycoplasma 10.3 Urinary Pathogens, Colony Counts, and Urinalysis Correlation
11 Bacteriology: Identification Methods
11.1 Colony Morphology and Rapid Presumptive Tests 11.2 Conventional Biochemicals and Commercial Kits 11.3 Automated Methods, MALDI-TOF MS, Molecular, and 16S Sequencing
12 Bacteriology: Antimicrobial Susceptibility and Resistance
12.1 Microbroth Dilution, Disk Diffusion, and Gradient Diffusion 12.2 Phenotypic Detection of Resistance 12.3 Antibiotic Classes, Intrinsic Resistance, and Genetic Markers
13 Bacteriology: Resistance Screening and Select Agents
13.1 MRSA/MSSA, VRE, ESBL/CRE Screening 13.2 BSL-3 Pathogens and Select-Agent Presumptive Identification 13.3 Laboratory Response Network and Select-Agent Pathogenicity
14 Mycobacteriology and Nocardia
14.1 Specimens, Major Pathogens, and Disease States 14.2 Acid-Fast Reaction, Colony Morphology, and Growth Characteristics 14.3 Identification Methods, Direct Molecular Detection, and TB Therapy
15 Virology
15.1 Respiratory, Vesicle, Meningitis, and GI Viruses 15.2 Hepatitis, HIV, and Immunocompromised-Host Viruses 15.3 Direct Detection Methods and HPV Cervical Screening
16 Parasitology
16.1 Blood, Tissue, and Brain Protozoa 16.2 Intestinal/Urogenital Protozoa and Helminths 16.3 Microscopy, Antigen/Molecular Detection, Insects and Arthropods
17 Mycology
17.1 Yeasts: Candida, Cryptococcus, and Malassezia 17.2 Dimorphic Fungi and Dermatophytes 17.3 Mucorales, Hyaline Molds, Pneumocystis, and Identification Methods
18 Serology
18.1 Immunoglobulin Response and Antigen-Antibody Methods 18.2 Viral Serodiagnosis: Hepatitis, EBV, HIV, CMV, Rubella, Measles 18.3 Treponema, Borrelia, and TB Infection Serodiagnosis
19 Laboratory Operations: Postanalytic Procedures and Quality
19.1 Documentation, Critical Values, Corrected Reports, and Public Health 19.2 Quality Control, Root-Cause Analysis, and POCT 19.3 Proficiency Testing, Competency, and Accreditation
20 Laboratory Operations: Safety, Mathematics, and Instrumentation
20.1 Biosafety, PPE, Bloodborne Pathogens, and SDS 20.2 Emergencies and Packaging/Transportation of Specimens 20.3 Laboratory Mathematics and Instrumentation
3.2 Media Types, Components, and Selection
Key Takeaways Explain This Topic AI
Name media by function: nutrient, enriched (chocolate, BCYE, BHI-blood), selective, and differential; many plates are both selective and differential.
Chocolate agar supplies X factor (hemin) and V factor (NAD); BCYE supplies L-cysteine and iron for Legionella.
Map specimen to primary plates: sterile sites to blood/chocolate/broth; urine to a calibrated blood-MacConkey setup; stool to an enteric battery plus Campy-BAP.
Mycobacteria are inoculated to LJ, 7H11, and MGIT; fungi to Sabouraud, inhibitory mold agar, Mycosel/DTM, and BHI with blood.
Bordet-Gengou and Regan-Lowe recover Bordetella, but pertussis plating is SM-only on the current pharyngitis list; BCYE/Legionella remains M-tested.
Last updated: August 2026
Media selection is how the laboratory turns a mixed specimen into isolated, identifiable colonies. Outline I.B asks for types (nutrient, selective, differential, enriched), components (blood, X and V factors, bile salts, antibiotics, indicators), application, and selection by specimen and organism. Specialized media for fastidious bacteria, mycobacteria, and fungi are fair game on M(ASCP). Bordetella media appear on some older lists; on the current guideline, Bordetella is SM-only in the pharyngitis cluster—know that Bordet-Gengou and Regan-Lowe exist, but do not treat pertussis plating as an M-tested pharyngitis item. BCYE for Legionella is M-tested.
Media types
Nutrient or general-purpose media (tryptic soy agar, nutrient agar) supply carbon, nitrogen, and salts for nonfastidious organisms and are rarely used as the only primary plate in clinical work. Blood agar is nutrient plus enrichment. Enriched media add extra nutrients or growth factors so fastidious pathogens can grow: chocolate agar, buffered charcoal yeast extract (BCYE), and brain-heart infusion (BHI) with blood. Selective media contain dyes, bile salts, antibiotics, or low pH that suppress part of the flora so the target can appear: Columbia CNA and PEA for Gram-positive cocci, MacConkey for Gram-negative rods, Thayer-Martin for gonococci, Campy-BAP for Campylobacter . Differential media produce a visible reaction—hemolysis on blood agar, lactose fermentation on MacConkey, H2S on HE or XLD, black colonies of Salmonella , red centers on CIN for Yersinia . Many plates are both selective and differential; MacConkey is the prototype. Do not call chocolate differential just because it is brown; it is enriched, not a biochemical indicator plate.
How the exam phrases type questions
If a stem says “inhibits Gram-positive organisms so enteric Gram-negative rods can grow,” the type is selective (MacConkey, HE). If it says “distinguishes lactose fermenters as pink colonies,” the type is differential (still MacConkey). If it says “heated blood releases factors required by Haemophilus ,” the type is enriched (chocolate). You can, and should, assign more than one type to the same plate when both functions are present.
Components and what they do
Sheep blood (typically 5%) supplies nutrients and demonstrates alpha, beta, or gamma hemolysis; it is also the base for detecting CAMP reactions and pigment. Chocolate agar is blood agar heated until red cells lyse, releasing X factor (hemin) and V factor (NAD) required by Haemophilus influenzae and helping Neisseria spp. grow. Bile salts and crystal violet in MacConkey inhibit Gram-positive organisms. Antibiotics convert an enriched plate into a selective plate: vancomycin, colistin, nystatin, and trimethoprim on modified Thayer-Martin suppress flora around N. gonorrhoeae ; cefsulodin, irgasan, and novobiocin define CIN for Yersinia enterocolitica ; cycloheximide on Mycosel or mycobiotic agar suppresses saprophytic molds so dermatophytes can grow; chloramphenicol in inhibitory mold agar reduces bacterial overgrowth. Indicators include phenol red, neutral red, and bromothymol blue for fermentation; ferric salts for H2S; charcoal in BCYE to bind inhibitors; and the pH indicator in dermatophyte test medium (DTM) that turns red when dermatophytes grow.
Ingredient-to-organism pairs
X and V disks or a Staphylococcus streak on blood agar still demonstrate Haemophilus satellitism when chocolate is not the primary plate. TCBS uses a high pH, bile, and sucrose to select Vibrio and differentiate V. cholerae (yellow, sucrose positive) from many V. parahaemolyticus isolates (green). Malachite green in Lowenstein-Jensen is the selective dye against contaminating bacteria. L-cysteine and soluble iron in BCYE are growth factors, not antibiotics; a BCYE plate poured without cysteine is the negative control that fails to grow Legionella . Know the component that makes the plate work, not just the brand name.
Selection by specimen
Primary plating is protocol-driven. A CSF or other sterile fluid is inoculated to blood agar, chocolate agar, and usually a broth (thioglycollate or BHI); MacConkey is added if a Gram-negative rod is seen or if the laboratory’s sterile-fluid setup includes it. Sputum and other lower-respiratory specimens receive blood agar, chocolate, and MacConkey (or another enteric plate); add CNA or PEA when mixed oral flora is expected. Urine is plated to blood agar and MacConkey (or a biplate) with a calibrated loop. Stool for bacterial culture uses a battery: MacConkey or EMB, HE or XLD, Campy-BAP, and often CIN or SMAC depending on season and orders; TCBS is added for suspected Vibrio (seafood, cholera-endemic exposure, watery rice-water stool). Genital specimens for N. gonorrhoeae go to Thayer-Martin, NYC, or Martin-Lewis, incubated in CO2. Wound and tissue setups combine blood, MacConkey or EMB, CNA/PEA, and anaerobic media when the source is valid for anaerobes. Blood-culture broth is a liquid enrichment; positives are subcultured to blood and chocolate, with MacConkey and anaerobic plates as indicated by the Gram stain.
Specialized media the M exam names
Chocolate agar is the primary plate for Haemophilus , pathogenic Neisseria from sterile sites, and many fastidious respiratory organisms. BCYE with L-cysteine and iron is required for Legionella ; charcoal binds fatty acids that otherwise inhibit growth. Thayer-Martin and New York City (NYC) agar recover N. gonorrhoeae from genital and other contaminated sites. Campy-BAP (blood agar with cephalothin or cefoperazone, vancomycin, and an antifungal) is incubated at 42°C in a microaerophilic atmosphere for Campylobacter jejuni/coli . CIN yields bull’s-eye red colonies of Y. enterocolitica , often after cold enrichment. TCBS is the Vibrio plate.
Bordet-Gengou (potato-blood-glycerol) and Regan-Lowe (charcoal-cephalexin) recover Bordetella pertussis . Flag them as SM-only on the current pharyngitis list: M candidates should recognize the names so they are not confused with BCYE, but pertussis media are not an M-tested pharyngitis requirement. Legionella /BCYE remains in M scope.
Mycobacteria and fungi
Mycobacteria require egg-based Lowenstein-Jensen (LJ), agar-based Middlebrook 7H10/7H11, and liquid Middlebrook 7H9 in MGIT or similar automated bottles. Contaminated specimens reach those media only after NALC-NaOH digestion (Section 3.1). Fungi are plated to Sabouraud dextrose agar (SDA), inhibitory mold agar (IMA), Mycosel or DTM for dermatophytes, and BHI with blood for dimorphic fungi and Cryptococcus from sterile sites. Cycloheximide helps dermatophyte recovery but can inhibit Cryptococcus and some significant molds, so a pair of media—with and without cycloheximide—is the usual mycology setup. Do not send a CSF fungal request to DTM; DTM is a dermatophyte plate for skin, hair, and nails.
- Specimen Primary plating media (typical M-level setup)
- CSF / sterile fluid Blood, chocolate, broth; MacConkey as indicated
- Lower respiratory Blood, chocolate, MacConkey (± CNA/PEA)
- Urine Blood + MacConkey, calibrated loop
- Stool MacConkey/EMB, HE/XLD, Campy-BAP, ± CIN, SMAC, TCBS
- Genital (GC) Thayer-Martin, NYC, or Martin-Lewis in CO2
- Wound / tissue Blood, MacConkey, CNA/PEA, anaerobic media if source appropriate
- Legionella request BCYE with L-cysteine (± selective BCYE)
- Mycobacteria LJ, 7H11, MGIT (after NALC-NaOH if contaminated site)
- Fungi SDA, IMA, Mycosel/DTM, BHI with blood
If you can map those rows and name the key ingredient (X/V, L-cysteine, bile salts, malachite green, cycloheximide), you can answer the media cluster on M(ASCP).