Establishment of tentative epidemiological cutoff values of faropenem against Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pneumoniae

Objective This study aimed to establish tentative epidemiological cutoff values (TECOFFs) for faropenem against Escherichia coli , Klebsiella pneumoniae , Staphylococcus aureus , Haemophilus influenzae , and Streptococcus pneumoniae based on minimum inhibitory concentration (MIC) distributions. Methods A total of 2,032 bacterial isolates were collected from Peking University First Hospital, Peking Union Medical College Hospital, Huashan Hospital affiliated with Fudan University, and Sir Run Run Shaw Hospital affiliated with Zhejiang University School of Medicine between 2019 and 2021. The susceptibility of these bacteria to faropenem was determined using the broth microdilution and disk diffusion methods in the clinical microbiology laboratories of these four hospitals. To establish wild-type TECOFFs for faropenem, isolates susceptible to ertapenem for E. coli and K. pneumoniae , those susceptible to oxacillin for S. aureus , and those with unscreened susceptibility for H. influenzae and S. pneumoniae were regarded as wild-type strains. Results The MIC TECOFF for faropenem against E. coli was determined to be 2 mg/L, with MIC ≤2 mg/L indicating wild-type strains and MIC ≥4 mg/L indicating non-wild-type strains. The corresponding inhibition zone diameter TECOFF for E. coli was 19 mm, where an inhibition zone diameter ≤18 mm indicates non-wild-type strains and ≥19 mm indicates wild-type strains. For K. pneumoniae , the MIC TECOFF was also 2 mg/L, with similar cutoffs established for the inhibition zones. The MIC TECOFF for faropenem against S. aureus was 0.25 mg/L, for H. influenzae was 1 mg/L, and for S. pneumoniae was 2 mg/L. The corresponding inhibition zone diameter ECOFF for faropenem against S. aureus was 31 mm, for H. influenzae was 14 mm, and for S. pneumoniae was 33 mm. Conclusion The TECOFFs for faropenem against the tested bacteria were established. These data are useful for clinical microbiologists and clinicians in the interpretation of the results of faropenem susceptibility testing.