Two Cases of Invasive Vancomycin-Resistant Group B Streptococcus Infection

Abstract

886 corrections ed on 500 mg of intravenous vancomycin after dialysis. His initial blood cultures grew S. agalac-tiae with a vancomycin MIC of 4 μg per millili-ter, which was noted 12 days after discharge. His infection was clinically resolved at that time, so vancomycin was stopped. Isolates were identified as vancomycin-non-susceptible group B streptococci by local and state health authorities and sent to the Strepto-coccus Laboratory at the Centers for Disease Control and Prevention, where both strains were confirmed as capsular serotype II, multilocus sequence type 22 S. agalactiae. The strains dif-fered in resistance pattern, with the New York strain showing resistance to erythromycin and clindamycin (Table 1). The two strains tested positive on polymerase-chain-reaction (PCR) as-say for a 941-bp vanG amplicon found in Enterococ-cus faecalis with the use of primers EG1 and EG2. 3 Subsequent unidirectional and conventional PCR and sequencing 4 of the vanG amplicon termini revealed putative vanW and vanXY counterparts in each strain, with each of the three gene pairs sharing sequence similarity (89.8%, 91.0%, and 95.7% identity between vanW, vanG, and vanXY, respectively). Furthermore, the New York strain shared complete sequence identity over the con-tiguous 2658-bp overlap with the corresponding E. faecalis vanG sequence (GenBank accession num-ber, DQ212986; GenBank accession numbers for the two sequences of group B streptococcus, KF722997 and KF722998). We report laboratory-confirmed clinical group B streptococcus isolates showing vancomycin resistance. The divergence in vanG sequences and lack of an epidemiologic link suggest inde-pendent resistance acquisitions. Further studies are necessary to identify the origin and mode of acquisition of the resistance mechanism, along with the clinical effect. These cases emphasize the importance of continued surveillance for re-sistant group B streptococcus. It may be impor-tant to establish vancomycin breakpoints for group B streptococcus and guidance for clinical laboratory testing. Clinicians and laboratories should be encouraged to report suspected vanco-mycin-resistant group B streptococcus to health authorities for confirmation, since this resistance profile may be emerging.