406: Streptococcus pseudoporcinus: a unique organism that causes false positive gbs screens

Streptococcus agalactiae(GBS) is a common pathogen known to cause perinatal infectious morbidity. Streptococcus pseudoporcinus is a separate, recently identified beta-hemolytic gram-positive coccus that can cause false positive results on standard GBS agglutination assays. We compared the patient characteristics and antibiotic susceptibility patterns of S.pseudoporcinus and GBS in pregnant women. This is a 2-year retrospective cohort study comparing pregnant women colonized with S.pseudoporcinus to those with GBS. Culture techniques, MALDI-TOF MS, and gene sequencing identified women colonized with S.pseudoporcinus among those antenatally screened for GBS. Maternal age, race, BMI, medical comorbidities, and antibiotic susceptibility profiles were compared using t-tests, Pearson chi-squared, and Fisher’s exact tests. 3704 pregnant women were screened for GBS. 1102 (29.7%) tested positive for GBS. 60 “false positive” cases (1.6% of all screened, 5.4% of GBS positive patients) were identified and subsequently confirmed to be S.pseudoporcinus. Women colonized with S.pseudoporcinus were more likely to be African American (p<0.001), have a higher BMI (P<0.001), and to use tobacco (p=0.014). S.pseudoporcinus carriers were also more likely to have diabetes (p=0.008), a history of a sexually transmitted infection (p=0.013), or an HSV outbreak during the pregnancy (p=0.003). S.pseudoporcinus demonstrated less clindamycin resistance than GBS(p<0.001). Our study is among the first to characterize S.pseudoporcinus colonization in pregnant women. The prevalence of S.pseudoporcinus colonization in pregnancy is overall low. Yet, we demonstrate significant differences in the characteristics of S.pseudoporcinus carriers when compared to GBS carriers. S.pseudoporcinus is known to be beta-lactam susceptible and these data indicate a high susceptibility to clindamycin. The variation in clindamycin susceptibility between GBS and S.pseudoporcinus further supports their different biochemical properties. Because S.pseudoporcinus can cause false positive results on some standard GBS agglutination kits, it is important to further investigate the relationship between this Streptococcus subtype and perinatal infectious morbidities.