Antibiotic Susceptibility Patterns in Streptococcus Species
No, it is not common for a single Streptococcus bacterium to be sensitive to over 12 different antibiotic classes—this would be highly unusual and should prompt verification of laboratory results, as most clinical laboratories routinely test only 6-8 antibiotic classes for Streptococcus species. 1
Standard Antibiotic Classes Tested for Streptococcus
The typical susceptibility panel for Streptococcus species includes the following major antibiotic classes:
- Beta-lactams (penicillins, cephalosporins, carbapenems) 1
- Macrolides (erythromycin, azithromycin) 2, 3
- Fluoroquinolones (levofloxacin, moxifloxacin) 4, 2
- Tetracyclines (doxycycline) 2, 3
- Glycopeptides (vancomycin) 1
- Oxazolidinones (linezolid) 5
- Trimethoprim-sulfamethoxazole 2, 3
- Lincosamides (clindamycin) 1, 3
This represents approximately 8 major antibiotic classes routinely tested in clinical practice. 1
Why 12+ Classes Would Be Unusual
Most clinical microbiology laboratories do not routinely test more than 8-10 antibiotic classes for Streptococcus species because additional testing would include agents with limited clinical utility or overlapping mechanisms of action. 1
- The concept of "spectrum" characterizes the range of activity against bacterial species, and acquired resistance alters susceptibility patterns over time and place 1
- Cross-resistance occurs when bacteria develop insusceptibility to groups of antibiotics, particularly within the same chemical class (e.g., all beta-lactams, all macrolides) 1
- Streptococcus pneumoniae strains resistant to penicillin are frequently resistant to cephalosporins, macrolides, tetracyclines, and clindamycin simultaneously 1
Expected Resistance Patterns in Streptococcus
Multidrug-resistant Streptococcus pneumoniae (resistant to ≥3 antibiotic classes) accounts for 15-30% of isolates worldwide, making broad susceptibility to 12+ classes implausible in contemporary clinical practice. 6, 7
- Between 1995-1998, isolates resistant to three or more drug classes increased from 9% to 14% in the United States 7
- Penicillin-resistant isolates are significantly more likely to demonstrate high-level resistance to other antimicrobial classes 7
- Six international clones (serotypes 6A, 6B, 9V, 14, 19F, 23F) are responsible for most multidrug-resistant isolates globally 6
Specific Resistance Data for S. pneumoniae
Current resistance rates in the United States demonstrate limited susceptibility across multiple classes:
- Penicillin nonsusceptibility: approximately 40% of adult disease isolates 2
- Macrolide resistance: averaging 28% (range 23-30% geographically) 2
- Tetracycline resistance: approximately 20% 2
- Trimethoprim-sulfamethoxazole resistance: approximately 35% 2
- Fluoroquinolone resistance: low but increasing 3
Only vancomycin maintains 100% susceptibility, with no reported resistance in Streptococcus species 5, 2
Common Pitfalls to Avoid
- Do not assume that testing "sensitivity" to multiple agents within the same class (e.g., penicillin, ampicillin, amoxicillin) represents sensitivity to multiple classes—these are all beta-lactams and represent a single class 1
- Do not confuse the number of individual antibiotics tested with the number of antibiotic classes—laboratories may test 3-4 beta-lactams, but this still represents one class 1
- Verify laboratory methodology if results show susceptibility to >10 classes, as this may represent testing error, contamination, or misidentification of the organism 1
Practical Interpretation
If a laboratory report shows Streptococcus sensitive to >12 "different drugs," review whether these represent distinct antibiotic classes or multiple agents within the same class. 1 Most likely, the report includes multiple beta-lactams (penicillins, cephalosporins), multiple macrolides, or multiple fluoroquinolones, which should be counted as single classes for clinical decision-making. 1