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Interpretive breakpoints for Streptococcus pneumoniae for selected antibiotics

Interpretive breakpoints for Streptococcus pneumoniae for selected antibiotics

Antibiotic	Susceptible	Intermediate	Resistant
Penicillin G (parenteral)
Meningitis	≤0.06 mcg/mL	–	≥0.12 mcg/mL
Non-meningitis*	≤2 mcg/mL	4 mcg/mL	≥8 mcg/mL
Penicillin V (oral)*	≤0.06 mcg/mL	0.12 to 1 mcg/mL	≥2 mcg/mL
Amoxicillin (non-meningitis)	≤2 mcg/mL	4 mcg/mL	≥8 mcg/mL
Cefuroxime
Parenteral	≤0.5 mcg/mL	1 mcg/mL	≥2 mcg/mL
Oral	≤1 mcg/mL	2 mcg/mL	≥4 mcg/mL
Cefotaxime, Ceftriaxone
Meningitis	≤0.5 mcg/mL	1 mcg/mL	≥2 mcg/mL
Non-meningitis	≤1 mcg/mL	2 mcg/mL	≥4 mcg/mL
Cefpodoxime	≤0.5 mcg/mL	1 mcg/mL	≥2 mcg/mL
Cefdinir	≤0.5 mcg/mL	1 mcg/mL	≥2 mcg/mL
Ceftaroline	≤0.5 mcg/mL	–	–
Clindamycin	≤0.25 mcg/mL	0.5 mcg/mL	≥1 mcg/mL
Rifampin	≤1 mcg/mL	2 mcg/mL	≥4 mcg/mL
Azithromycin	≤0.5 mcg/mL	1 mcg/mL	≥2 mcg/mL
Clarithromycin	≤0.25 mcg/mL	0.5 mcg/mL	≥2 mcg/mL
Gemifloxacin	≤0.12 mcg/mL	0.25 mcg/mL	≥0.5 mcg/mL
Levofloxacin	≤2 mcg/mL	4 mcg/mL	≥8 mcg/mL
Moxifloxacin	≤1 mcg/mL	2 mcg/mL	≥4 mcg/mL

When the E-test is used to determine minimum inhibitory concentrations (MICs), exact results are reported rather than the twofold dilutions that were used when the cut-offs were defined. An MIC value that falls between standard twofold dilutions must therefore be rounded up to the next dilution in order to be categorized. As an example, an S. pneumoniae isolate from a patient with meningitis with a cefotaxime/ceftriaxone MIC of 1.5 mcg/mL would be rounded up to 2 mcg/mL and would be considered resistant.

* For nonmeningitis isolates, the penicillin MIC can predict susceptibility to other beta-lactams as follows:

Penicillin MICs ≤0.06 mcg/mL indicate susceptibility to ampicillin (oral or parenteral), ampicillin-sulbactam, cefaclor, cefdinir, cefditoren, cefpodoxime, cefprozil, ceftizoxime, cefuroxime, imipenem, loracarbef, and meropenem.
Penicillin MICs ≤2 mcg/mL indicate susceptibility to amoxicillin, amoxicillin-clavulanate, cefepime, cefotaxime, ceftriaxone, and ertapenem.

Data from:

Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Susceptibility Testing; Nineteenth Informational Supplement. CLSI document M100-S19. Clinical and Laboratory Standards Institute 2009.
Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Susceptibility Testing, 31^st ed. CLSI Supplement M100. Clinical and Laboratory Standards Institute 2021, p.95.

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