Multicenter comparison of Etest, Vitek2 and BD Phoenix to broth microdilution for beta-lactam susceptibility testing of Streptococcus pneumonia

• Published in: European journal of clinical microbiology & infectious diseases Vol. 43; no. 7; pp. 1375 - 1381
• Main Authors: Martens, Steven, Cuypers, Lize, Bélik, Florian, Briers, Pieter-Jan, Ceyssens, Pieter-Jan, Denis, Olivier, Huang, Te-Din, Magerman, Koen, Strypens, Thomas, Van den Abeele, Anne-Marie, Desmet, Stefanie
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2024; Springer Nature B.V
• Subjects: Amides; Amoxicillin; Ampicillin; Antibiotics; Bacteria; Benzylpenicillin; Biomedical and Life Sciences; Biomedicine; Breakpoints; Cefotaxime; Internal Medicine; Medical Microbiology; Meningitis; Minimum inhibitory concentration; Original; Original Article; Penicillin; Performance assessment; Pneumonia; Streptococcus infections; Streptococcus pneumoniae; β-Lactam antibiotics; Antimicrobial susceptibility testing; EUCAST breakpoints; Beta-lactam; Streptococcus pneumoniae
• ISSN: 0934-9723; 1435-4373; 1435-4373
• DOI: 10.1007/s10096-024-04847-2

Purpose To assess performance of Etest®, Vitek®2 and BD Phoenix™ to determine the susceptibility of Streptococcus pneumoniae strains to penicillin, ampicillin and cefotaxime. Methods Sixty unique S. pneumoniae challenge strains were selected to cover a wide range of penicillin, ampicillin and cefotaxime minimal inhibitory concentrations (MICs). Strains were analyzed in four different Belgian laboratories. Etest® benzylpenicillin (BEN), ampicillin/amoxicillin (AMP) and cefotaxime (CTA) (bioMérieux), Vitek®2 AST-ST03 (bioMérieux) and BD Phoenix™ SMIC/ID-11 testing were each performed in two different labs. Results were compared to Sensititre® broth microdilution (BMD) (Thermo Fisher Scientific) results. MIC results were interpreted using EUCAST non-meningitis breakpoints (v 13.0). Results Essential agreement (EA) was ≥ 90% for all methods compared to BMD, except for Etest® BEN on Oxoid plate (58.3%), Etest® AMP (both on Oxoid (65.8%) and BD BBL plate (84.2%)). Categorical agreement (CA) for penicillin was only ≥ 90% for Vitek®2, for other methods CA ranged between 74 and 84%. CA for AMP was for all methods < 90% (range 75.8–88.3%) and CA for CTA was between 87 and 90% for all methods except for Etest on Oxoid plate (79.2%). Conclusions Our study indicates that Vitek®2 and BD Phoenix™ are reliable for providing accurate pneumococcal susceptibility results for BEN, AMP and CTA. Using Etest BEN or AMP on Oxoid plate carries a risk of underestimating the MIC and should be interpreted with caution, especially when the obtained MIC is 1 or 2 doubling dilutions below the S or R clinical breakpoint.