A case of penicillin-resistant group B Streptococcus isolated from a patient in the UK

Objectives
In England, group B streptococci (GBS; Streptococcus agalactiae) are considered universally susceptible to penicillin. Reports from Africa, Asia, North America and a few European countries have described GBS isolates with penicillin MICs above the epidemiological cut-off (0.125 mg/L). Our aim was to characterize a penicillin-resistant GBS (PRGBS) isolate recovered in 2016 from a patient treated with long-term antimicrobials in the UK.

Methods
Antibiotic susceptibility of a referred isolate from a discharging sinus overlying a chronic prosthetic joint infection was determined using gradient strip testing for seven antibiotics. Illumina short read sequencing was carried out using a HiSeq 2500 platform to determine MLST, capsular type, to detect mutations in the pbp genes, and to compare the isolate with contemporaneous GBS isolates circulating in the UK.

Results
The GBS isolate belonged to capsular type Ia and MLST 144. We observed resistance to penicillin (MIC = 1 mg/L) and tetracycline (32 mg/L) with 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). Deduced amino acid sequences revealed substitutions and non-synonymous changes in PBP2x and PBP2b. Genomic analysis of contemporaneous cases (n = 34) from across the UK identified single nucleotide polymorphism (SNP) variation ranged from 153–6596 SNPs.

Conclusions
We confirm the first identification of a PRGBS isolate amongst referrals to the UK’s national reference laboratory. Substitutions in pbp1a, pbp2a, pbp2x and pbp2b were identified that likely developed in the face of long-term beta-lactam antibiotic use.