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. 2020 Dec 21;8(2):ofaa634.
doi: 10.1093/ofid/ofaa634. eCollection 2021 Feb.

Low but Increasing Prevalence of Reduced Beta-lactam Susceptibility Among Invasive Group B Streptococcal Isolates, US Population-Based Surveillance, 1998-2018

Miwako Kobayashi  1 , Lesley McGee  1 , Sopio Chochua  1 , Mirasol Apostol  2 , Nisha B Alden  3 , Monica M Farley  4 , Lee H Harrison  5 , Ruth Lynfield  6 , Paula Snippes Vagnone  6 , Chad Smelser  7 , Alison Muse  8 , Ann R Thomas  9 , Li Deng  1 , Benjamin J Metcalf  1 , Bernard W Beall  1 , Stephanie J Schrag  1
Affiliations

Low but Increasing Prevalence of Reduced Beta-lactam Susceptibility Among Invasive Group B Streptococcal Isolates, US Population-Based Surveillance, 1998-2018

Miwako Kobayashi et al. Open Forum Infect Dis. .

Abstract

Background: Invasive group B Streptococcus (iGBS) isolates with mutations in the pbp2x gene that encodes penicillin binding protein 2x can have reduced beta-lactam susceptibility (RBLS) when susceptible by Clinical and Laboratory Standards Institute (CLSI) criteria. We assessed the emergence and characteristics of RBLS strains in US iGBS isolates.

Methods: We analyzed iGBS isolates from 8 multistate population-based surveillance sites from 1998 to 2018. During 1998-2014, phenotypic antimicrobial susceptibility was determined by broth microdilution; criteria for 6 antibiotics were used to identify RBLS, followed by whole-genome sequencing (WGS). WGS for all isolates was added in 2015; we used phenotypic and genotypic results of >2000 isolates to validate phenotypic RBLS criteria and genotypic predictions. Since 2016, WGS has been used to screen for RBLS with broth microdilution confirmation of predicted RBLS isolates.

Results: Of 28 269 iGBS isolates, 28 (0.1%) were nonsusceptible by CLSI criteria; 137 (0.5%) met RBLS criteria. RBLS isolates were detected in all Active Bacterial Core surveillance sites. The RBLS proportion increased, especially since 2013 (odds ratio, 1.17; 95% CI, 1.03-1.32); the proportion that were nonsusceptible remained stable.

Conclusions: The RBSL proportion was low but increasing among US iGBS isolates. Ongoing monitoring is needed to detect emerging threats to prevention and treatment of GBS infections.

Keywords: group B Streptococcus; penicillin binding protein 2x; reduced beta-lactam susceptibility; whole-genome sequencing.

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Figures

Figure 1.
Figure 1.
Proportion of group B Streptococcus isolates with reduced beta-lactam susceptibilitya and beta-lactam nonsusceptibilityb by year, ABCs 1998–2018. A, GBS isolates with minimum inhibitory concentration values that exceeded the predefined breakpoints for at least 1 of the 6 beta-lactam antibiotics (ampicillin MIC ≥ 0.5 µg/mL, penicillin MIC ≥ 0.25 µg/mL, cefotaxime MIC ≥ 0.25 µg/mL, ceftizoxime MIC ≥ 1 µg/mL, cefazolin MIC ≥ 1 µg/mL, or cefoxitin MIC ≥ 16 µg/mL). B, Defined as ampicillin MIC > 0.25 µg/mL, penicillin MIC > 0.12 µg/mL, or cefotaxime MIC > 0.5 µg/mL. Abbreviations: ABCs, Active Bacterial Core surveillance; GBS, group B Streptococcus; MIC, minimum inhibitory concentration; NS, beta-lactam nonsusceptible; RBLS, reduced beta-lactam susceptibility.
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