A beta-hemolytic Lancefield antigen A-, B-, C-, D-, F-, and G-positive Enterococcus durans strain was cultivated from the rectovaginal swab of a pregnant woman who underwent antenatal screening for Streptococcus agalactiae. The isolate raised concern as to what extent similar strains are misrecognized and lead to false diagnosis of group B streptococci.
Streptococcus agalactiae (group B Streptococcus [GBS]) inhabits the human gut, from where it can then colonize the genitourinary tract (1). Up to 30% of pregnant women are asymptomatic GBS carriers, and neonates can therefore acquire the organism vertically at the time of birth unless penicillin or ampicillin is given intravenously as intrapartum antibiotic prophylaxis (IAP). Newborn colonization may establish in 50% of the cases and involves different mucosal and skin sites. One percent to 2% of neonates develop early GBS infection, including bacteremia and/or pneumonia and/or meningitis (1, 2). For these reasons, the CDC (Centers for Disease Control and Prevention) has suggested that women between the 35th and 37th weeks of gestation be screened for GBS carriage through rectovaginal cultures. As IAP has been shown to reduce the risk of vertical S. agalactiae transmission, all GBS-positive women receive prophylaxis as soon as labor begins or when rupture of the amniotic membranes occurs (1).GBS screening is based on the recognition of Gram-positive catalase-negative cocci, mostly beta-hemolytic (on sheep blood agar), showing the Lancefield group B antigen. Nonhemolytic (gamma-hemolytic) variants have been described, however, and may be missed because they are not easily detected. Hence, the CDC recommends the use of chromogenic media that are designed to highlight GBS growth through species-specific coloration of colonies (that may vary depending on the manufacturer) (1).A pregnant woman attending the Spirito Santo Hospital in Pescara, Italy, was screened for rectovaginal GBS colonization according to the CDC guidelines. On Trypticase soy agar (Liofilchem, Italy), beta-hemolytic (Fig. 1) catalase-negative colonies were grown. The isolate formed pairs and chains and showed group B antigen agglutination (detected with the Liofilchem Strepto B latex kit). It was therefore believed to be GBS. Nevertheless, it grew in purple colonies (Fig. 1) on Chromatic StrepB (Liofilchem), whereas this chromogenic medium is designed to support GBS growth in light blue-green colonies (based on the manufacturer's indication, the purple color we observed instead placed the isolate within the Enterococcus genus). Accordingly, the strain was found to produce a negative CAMP reaction (10) (mild enhancing of hemolysis was observed, however).Identification as Enterococcus durans was provided by the Vitek 2 GP card (bioMérieux, France) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) using Bruker Biotyper software 2.0 (Bruker Daltonics, Germany) and the Vitek MS v2.0 system (bioMérieux). Sequencing of a 16S rRNA gene 1,458-bp amplicon, analyze...