Macrolide Resistance Detection in *Streptococcus pneumoniae* (or *Streptococcus spp.*), by Culture and Susceptibility Testing
This test checks whether certain bacteria, like *Streptococcus pneumoniae*, may be resistant to macrolide antibiotics (e.g., azithromycin, clarithromycin) by examining their growth in culture and how they respond to these drugs.
["Helps determine if your doctor should choose a different antibiotic for bacterial infections."]
Key facts at a glance
- LOINC
- 105811-4
- Short code
- ERMC
- Synonyms
- Bac macrolide res ErmC Ct Bld +
- Category
- chemistry
- Sample
- whole-blood
- Container
- Positive blood culture bottle (aerobic, anaerobic, or pediatric) processed per laboratory protocol; aliquot transferred to sterile molecular-grade tube or PCR reaction vessel.
- Units
- N/A
- Ref low
- 15
- Ref high
- 40
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- probe-amp-tar
- CPT
- 87641
- SNOMED
- 122450004
- Specimen volume
- 1-2 mL aliquot from positive blood culture bottle sufficient for nucleic acid extraction and PCR testing
- Stability
- Stable for up to 24 hours at room temperature (15-25°C) or 48 hours refrigerated (2-8°C) from positive blood culture bottle. For prolonged delays, store at -70°C or below.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 1–8 hours
- Order
- routine
Understanding why this test matters can help you take an active role in your care, because the results give your doctor valuable information about how your body is functioning and help guide the decisions that shape your diagnosis, treatment options, and long-term health plan.
Macrolide antibiotics are commonly used to treat infections caused by bacteria like *Streptococcus pneumoniae* (pneumonia), *Streptococcus pyogenes* (strep throat), and other respiratory infections. This test helps ensure the right antibiotic is prescribed by checking if the bacteria are resistant to these drugs.
During the test, your care team follows a careful, step-by-step process to collect the information your doctor needs, and knowing what happens at each stage can help you feel more comfortable, prepared, and confident on the day of your appointment.
The test involves growing bacteria from a sample (often from blood, sputum, or other bodily fluids) in a lab. After growth, the bacteria are exposed to macrolide antibiotics. If they grow despite the antibiotic presence, it suggests resistance. This process is called **culture and susceptibility testing (C&S)**.
Before your test, your doctor's office will give you specific instructions, which may include fasting for a certain number of hours, adjusting your regular medications, or avoiding certain foods and drinks, so follow those directions closely and call the office if anything is unclear.
No special preparation is usually needed unless your doctor specifies. You may need to provide a sample (e.g., blood, sputum, or urine) depending on the suspected infection. Follow your doctor’s instructions carefully.
After the test is complete, most people can return to their normal activities right away, although your care team may give you a few simple instructions to follow at home, and your doctor will review the results with you, explain what they mean, and talk about any next steps.
Results may take several days to a week, as the bacteria must grow and be tested. Your doctor will discuss the findings and adjust your treatment plan if needed.
Reference range
Negative (ErmC gene not detected). Cycle threshold (Ct) value reported when positive; lower Ct values indicate higher bacterial load. Typical positive Ct range: 15-40 cycles depending on organism density.N/A
No special patient preparation required. Test is performed on specimens obtained from positive blood culture bottles flagged by continuous-monitoring blood culture systems.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Macrolide Resistance Screening (C&S)
Frequently asked questions
Macrolide resistance can lead to ineffective antibiotic treatment, increasing infection risk or requiring stronger (and potentially more toxic) antibiotics. Early detection helps prevent unnecessary antibiotic use and reduces antibiotic resistance in the community.
Yes, this test is typically covered by insurance if prescribed for diagnosing or managing a bacterial infection. However, check with your insurance provider for specifics, as coverage may depend on clinical necessity.
Results can take **5 to 7 days** or longer, depending on lab processing times. Your doctor will contact you once results are ready.
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy