307 - Too Much Beta: When Group B Strep is Not Group B Strep

Poster Number: 307
Publication Number: 307.114

Kristin F. Butler, LSU Health Shreveport, Shreveport, LA, United States; Rhorer E. Legendre, Louisiana State University School of Medicine in Shreveport, Shreveport, LA, United States; Joseph A. Bocchini, Tulane University School of Medicine, Shreveport, LA, United States; John Vanchiere, LSUHSC-Shreveport, Shreveport, LA, United States

Background: The 2019 American Society of Microbiology (ASM) guidelines for detection of Group B Streptococcus (GBS) in vaginorectal specimens from pregnant women recommend that beta-hemolytic and non-hemolytic colonies be confirmed as GBS by Gram stain, catalase, and agglutination by antisera for the Lancefield group B antigen or by using proteomic methods. Importantly, the guidelines note that other beta-hemolytic streptococcal species, including Streptococcus pseudoporcinus and Streptococcus halichoeri, can be misidentified as GBS when clinical laboratories use latex agglutination methods.

Objective: To evaluate the clinical and microbiologic factors associated with vaginorectal colonization with beta-hemolytic streptococcal species other than S. agalactiae.  

Design/Methods: As part of an ongoing study at LSU Health Shreveport, all GBS isolates recovered from urine and rectovaginal swabs collected from pregnant women receiving care at Ochsner LSU Health are archived for molecular testing to identify antibiotic resistance genes after routine confirmation by latex agglutination (PathoDX Strep Grouping Kit, Remel) and antimicrobial susceptibility testing.

Results: In a subset of GBS isolates from 2016-2018 (n=355), we investigated 10 (2.9%) with atypical colony morphology and hemolysis patterns on Blood Agar (TSA w/5% Sheep Blood, Remel). Of the 10 aberrant isolates, 9 were available for further investigation. MALDI-TOF (Bruker MALDI Biotyper, BD) identified all 9 isolates as S. pseudoporcinus. Additionally, these isolates were included in a blinded and randomized set of 18 specimens (9 S. pseudoporcinus and 9 GBS) for nucleic acid amplification testing (NAAT) using the GeneXpert GBS LB assay (Xpert GBS LB, Cepheid).  All S. pseudoporcinus isolates were negative on the GeneXpert GBS LB analysis.Conclusion(s): Continued use of traditional methods such as latex agglutination will likely continue to misidentify S. pseudoporcinus as GBS. As such, identification of GBS colonization from maternal specimens using more sensitive and specific methods, such as MALDI-TOF and NAAT, should be implemented in order to reduce the unnecessary use of antibiotics during pregnancy, medical costs, and the potential contribution to emerging antibiotic resistance. Furthermore, additional studies are necessary to define the clinical significance of S. pseudoporcinus during pregnancy, including its potential relationship to adverse pregnancy outcomes.