Third-generation cephalosporin and carbapenem resistance in Streptococcus mitis/oralis. Results from a nationwide registry in the Netherlands

Summary For Review We investigated the prevalence of beta-lactam resistance and the relationship between penicillin MIC and (1) amoxicillin/ampicillin, (2) third-generation cephalosporin and (3) carbapenem resistance in the Netherlands. From the database of the Dutch national surveillance system for antimicrobial resistance (ISIS-AR) the first S. mitis/ oralis isolate per patient that was tested for penicillin resistance between 2013 and 2017, was included. We observed third-generation cephalosporin resistance in less than 8% of isolates and meropenem resistance in less than 1.3% isolates. For amoxicillin/ampicillin susceptible isolates median penicillin MIC was 0.047mg/L (IQR 0.023-0.094; n=327), for intermediate isolates 0.75mg/L (IQR 0.38-1.0; n=34) and for resistant isolates 2.0mg/L (IQR 1.0-4.0; n=29). For cefotaxime/ceftriaxone susceptible isolates median penicillin MIC as determined by gradient test was 0.064 mg/L (IQR 0.032-0.19; n=463), whereas for cefotaxime/ceftriaxone resistant isolates it was 2.0 mg/L (IQR 1.0-4.0; n=57). Penicillin MICs of the meropenem-resistant isolates were 8 and 32 mg/L (gradient test, n=2) and >4 mg/L (automated MIC determination, n=1). We conclude that for mitis group streptococci in the Netherlands, broad-spectrum beta-lactam resistance should be taken into account. Not all laboratories routinely test viridans group streptococci for broad-spectrum beta-lactam agents. Elevated penicillin MICs should prompt additional cephalosporin and carbapenem susceptibility testing.