Background: Group B streptococci (GBS; Streptococcus agalactiae) cause invasive infections and are typically susceptible to penicillin, although reports of non-susceptible isolates from Asia, North America and more recently, Germany have been described. Our study characterised phenotypically and genomically a presumptive Penicillin-resistant GBS (PRGBS) isolate recovered from a 47-year-old UK female patient with a chronic prosthetic joint infection and associated non-healing sinus.
Methods: Ampicillin, penicillin, erythromycin, clindamycin, tetracycline, teicoplanin, vancomycin and linezolid minimum inhibitory concentrations (MICs) were determined by gradient strip testing and interpreted using EUCAST guidelines. Illumina short read sequencing was carried out using a HiSeq 2500 platform, the core genome was compared with 35 type Ia contemporaneous GBS isolates circulating in England. Analysis determined sequence and capsular type and evaluated mutations in the penicillin binding protein (pbp) genes.
Results: The isolate was confirmed as GBS, capsular type Ia and MLST 144. We observed resistance to penicillin (MIC 1 mg/L), ampicillin (1 mg/L) and tetracycline (32 mg/L) but susceptibility to linezolid (1 mg/L), erythromycin (0.064 mg/L), clindamycin (0.064 mg/L), teicoplanin (0.064 mg/L) and vancomycin (0.25 mg/L). There were no closely related GBS isolates in the collection of 35 contemporaneous comparators (variation ranging from 153 - 6596 snps). Deduced amino acid sequences revealed substitutions and functional changes in pbp2x and pbp2b.
Conclusion: This work presents the identification of the first PRGBS isolate from a UK patient. With a seemingly increased frequency in isolation of PRGBS worldwide, it remains vital to have a programme of systematic GBS susceptibility testing and surveillance to identify and contain penicillin-resistant infection.