13.3 Media, Cultures, and Procedure Matching

AMT III.8.B.3 asks you, within scope of practice, to recognize appropriateness of microbiological procedure ordered as it relates to: (a) test requested, (b) appropriate patient preparation and method of collection, (c) time of collection and processing, (d) specimen storage, and (e) specimen rejection criteria. Those five bullets are the same logic as urine suitability in Chapter 9, applied to cultures. You are not designing media. You are deciding whether this container may go on this bench—or must be rejected.

A CMLA processes microbiologic specimens using aseptic technique (competency checklist G). You plate only if SOP and lawful scope allow. You do not independently interpret high-complexity C&S or release AST. Inoculating a plate is not a license to report “heavy GNR, resistant to everything.”

Quick Answer: Match the test to the collection. Blood cultures: adequate volume, skin prep, bottles first in the draw, labeled at the bedside. Strep culture = throat. Influenza/RSV usually = nasopharyngeal (NP). Wound: aerobic versus anaerobic transport, label the site. Sputum ≠ saliva. Reject unlabeled, leaking, dry, delayed, or wrong-matrix specimens.

The five appropriateness checks

Work the list in order so you do not skip the reject.

If any row fails, do not “just plate it so the doctor has something.” Document the reason and recollect when possible.

Blood culture: volume and skin prep (without restaging Chapters 7–8)

Blood cultures are the first tube or bottle in the CLSI PRE02 order of draw (Chapter 7) because sterility and additive carryover both matter. Labeling still happens at the bedside with two identifiers (CLSI PRE01, Chapter 8). This section adds the microbiology reasons the set succeeds or fails: volume and skin antisepsis.

Volume. Manufacturers print a fill line. Adult bottles commonly target about 8–10 mL each; a set is often an aerobic plus an anaerobic bottle. Underfilling is a leading cause of false-negative bacteremia detection—too little blood, too few organisms. Overfilling can cause false positives on some continuous-monitoring systems. Pediatric volumes are weight-based and smaller; do not force an adult 10 mL into a neonate. Capillary microtainers are not blood-culture bottles (Chapter 8 already excluded capillary as a blood-culture method).

Skin prep. Resident skin flora are the usual contaminants. Follow the SOP: commonly alcoholic chlorhexidine with friction for adults, or 70% alcohol plus an iodophor, then air-dry. Do not wipe the dry site with a gauze that sat on the bed. Do not re-palpate the vein with a nonsterile finger after prep; if you must relocate, prep again. Draw from a peripheral stick, not a line, unless policy for line-draw paired cultures says otherwise. Collect two sets from two sites when the order and SOP say two sets—same-site double-fill is not two sets.

Invert bottles gently to mix. Keep them ambient and moving (Section 13.2). You already know not to ice them with ammonia tubes.

Throat versus nasopharyngeal

AMT already used throat versus NP as the official wrong-specimen example (I.2.B.2). Apply it to cultures and kits:

• Strep culture and most Strep A antigen kits: throat—tonsils and posterior pharynx, not teeth, not lips, not the nose.
• Influenza A/B, RSV, and many respiratory molecular panels: the IFU usually names NP swab or aspirate, not a leftover throat stick.
• Pertussis PCR, when ordered, is typically NP, not throat—follow the directory.

Do not run one swab through three methods unless every IFU validates that swab. Dual-collect when a negative Strep A needs backup culture or approved molecular testing.

Wound: aerobic versus anaerobic, and label the site

Aerobic wound culture assumes organisms that tolerate air. Superficial ulcers and many drainage swabs travel in Amies. Anaerobic culture is for deep abscesses, tissue, and fluid from normally sterile closed spaces. Those specimens need anaerobic transport (aspirate in a gassed vial is better than a swab). A dry aerobic swab of a surface scab is the wrong procedure for “anaerobic C&S.”

Label the site. “Wound” is not an anatomic site. Write left medial ankle ulcer, right post-op abdomen, decubitus sacrum, or whatever the SOP format is. Laterality, tissue versus drainage, and surgical versus chronic matter for interpretation and for public-health isolates. Unlabeled or “wound, unknown” is a reject or a recollect, not a memory exercise at the desk (Chapter 8 labeling rules still apply).

Clean the surface per protocol so you culture the lesion, not the crust flora, then collect exudate or tissue the provider obtained. Do not send a scab in a glove.

Sputum versus saliva

Sputum is material from the lower airways after a deep cough, often first morning, after rinsing the mouth with water (not mouthwash unless SOP says so). Saliva is spit from the mouth. Saliva-labeled-as-sputum overgrows oral flora and misses pneumonia pathogens. Laboratories may reject saliva when the Gram stain (read by qualified staff) shows abundant squamous epithelial cells and rare organisms. Your job is coaching and rejection before that wasted stain: if you see obvious spit, do not relabel it sputum.

Induced sputum and tracheal aspirates follow respiratory-therapy protocol. They are still not NP swabs and not throat swabs.

Storage, timing, and rejection—then who plates

Hold times from Section 13.2 apply here as appropriateness: a correct swab that sat dry for a weekend is now the wrong specimen. Reject when:

• Unlabeled or mismatched identifiers
• Leaking or contaminated exterior
• Dry swab for bacterial culture
• Wrong transport (aerobic swab for anaerobes; SST for blood culture; O&P vial for C. difficile)
• Obvious saliva for sputum culture
• Unpreserved urine beyond the time limit
• Blood-culture bottles grossly underfilled when policy sets a reject volume, or drawn from a site that policy forbids without documentation
• Specimen in formalin or other fixative that kills culture organisms

If SOP allows the assistant to inoculate media, you still streak as trained, incubate at the labeled atmosphere, and leave colony morphology, hemolysis interpretation, A&P-disk zones, identification, and AST to qualified personnel. Plating is processing. Reporting C&S is not.

Scenario

An adult “blood culture ×2, sputum culture, and wound aerobic/anaerobic C&S” arrives as: two bottles with 2 mL each drawn after the collector palpated the prepped site, a cup of spit, and one dry swab labeled “wound.” Reject or recollect. Fill bottles to the line after a complete dry skin prep without re-palpation, collect two labeled sets if two sets were ordered, coach a true sputum, and send site-labeled aerobic plus anaerobic transport—not one dry stick.

Exam traps

• Treating 1–2 mL in an adult bottle as “enough because it grew in the line.”
• Re-palpating after chlorhexidine.
• NP swab for Strep culture, or throat swab for an NP-only flu kit.
• Saliva as sputum.
• Unlabeled wound site.
• Independently releasing AST because you plated the media.

If the procedure ordered and the specimen collected are not the same story, stop.