Abstract
BackgroundOral beta-lactam antimicrobials are not routinely tested against Streptococcus pneumoniae due to presumed susceptibility based upon penicillin minimum inhibitory concentration (MIC) testing. Currently, Clinical and Laboratory Standards Institute provides comments to use penicillin MIC ≤0.06 to predict oral cephalosporin susceptibility. However, no guidance is provided when cefotaxime MIC is known, leading to uncertainty with interpretation. The purpose of this study was to evaluate cefotaxime and penicillin MICs and their respective correlation to oral beta-lactam categorical susceptibility patterns.Methods249 S. pneumoniae isolates were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-ToF) and then tested by broth microdilution method to penicillin, cefotaxime, amoxicillin, cefdinir, cefpodoxime, and cefuroxime.ResultsUsing Clinical and Laboratory Standards Institute (CLSI) non-meningitis breakpoints for cefotaxime, 240/249 isolates were classified as susceptible. Of the cefotaxime susceptible isolates, 23% of the isolates are misrepresented as cefdinir susceptible. Amoxicillin correlated well with penicillin MIC breakpoints with only 1 discordant isolate out of 249.ConclusionThe correlation between amoxicillin and penicillin creates a very reliable predictor to determine categorical susceptibility. However oral cephalosporins were not well predicted by either penicillin or cefotaxime leading to the possible risk of treatment failures. Caution should be used when transitioning to oral cephalosporins in cefotaxime susceptible isolates, especially with higher cefotaxime MICs.
Highlights
Oral beta-lactam antimicrobials are not routinely tested against Streptococcus pneumoniae due to presumed susceptibility based upon penicillin minimum inhibitory concentration (MIC) testing
The Infectious Diseases Society of America (IDSA) guidelines recommend empiric therapy for hospitalized patients for community-acquired pneumonia or Invasive Pneumococcal Disease (IPD) consisting of an intravenous beta-lactam (β-lactams) such as ampicillin or ceftriaxone depending on local antimicrobial resistance rates [1]
For Streptococcus pneumoniae, Clinical and Laboratory Standards Institute (CLSI) recommends susceptibility testing in different tier groupings, seen in Table 1, which includes a range of Murphy et al BMC Infectious Diseases (2021) 21:679
Summary
Oral beta-lactam antimicrobials are not routinely tested against Streptococcus pneumoniae due to presumed susceptibility based upon penicillin minimum inhibitory concentration (MIC) testing. In the US, the most commonly used oral beta-lactam agents for this transition, per guideline recommendations, are amoxicillin, amoxicillin-clavulanate, cefdinir, cefuroxime, and cefpodoxime [1, 6]. In spite of these guidelines, not all oral beta-lactams are tested in the laboratory because of the assumption of similar class beta-lactams correlate to other beta-lactams in the same class [7]. A noted comment, comment 5 of M100, references penicillin MIC of ≤0.06 μg/ml to predict susceptibility to oral beta-lactams including amoxicillin, cefdinir, cefpodoxime, and cefuroxime, and cefotaxime and meropenem [7]. There is no note or reference made about third generation cephalosporins predicting susceptibility of the oral cephalosporins
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