Description of the first identification of a penicillin resistant GBS isolate amongst referrals to England's national reference laboratory.

Objectives: In Europe, group B streptococci (GBS; Streptococcus agalactiae) are often considered universally susceptible to penicillin, although reports from Africa, Asia, North America, and few countries within Europe including Germany, Spain and Sweden have described GBS isolates with reduced susceptibility or resistance to penicillin. The aim of this work was to characterise a penicillin resistant GBS (PRGBS) isolate recovered from an UK patient, by determining the phenotypic antibiotic susceptibility profile, identifying potential genetic mechanism(s) of resistance and describing the isolates relatedness to other UK GBS isolates. 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 whole genome sequencing (WGS) was carried out, using a HiSeq 2500 platform, to compare the isolate with contemporaneous GBS isolates circulating in England, to determine ST (Sequence Type) and capsular type and evaluate mutations in the pbp genes. Results: The GBS isolate was confirmed 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). Single nucleotide polymorphism (SNP) variation ranged from 153 - 6596 SNPs when compared to other contemporaneous sporadic UK GBS sequences. Deduced amino acid sequences revealed substitutions and functional changes in pbp2x and pbp2b. Conclusion: This report describes the first identification of a penicillin resistant GBS isolate amongst referrals to England's national reference laboratory.