Molecular characteristics and antibiotic susceptibility of clinical strains of Streptococcus agalactiae

ObjectiveTo understand the serotypes, antibiotic susceptibility, virulence gene carriage and multi locus sequence typing (MLST) results of clinical isolates of Streptococcus agalactiae in a class Ⅲ (A) hospital in Beijing.

MethodsS. agalactiae strains were isolated from the hospitalized patients in 2018. The serotyping, MLST and virulence gene detection were conducted by using polymerase chain reaction (PCR). The susceptibility test of S. agalactiae strains to 7 antibiotics was conducted with VITEK 2 system.

ResultsA total of 31 strains of S. agalactiae were isolated in the hospital in 2018. In the sequence types (STs), ST10 (29.03%) was predominant, followed by ST17, ST19, ST1, ST12, ST24, ST485 and 2 new types. In the 4 identified serotypes, Ⅰb was predominant, accounting for 45.16%, followed by Ⅲ, Ⅴ and Ⅰa. The antibiotic susceptibility test showed that 31 strains were all sensitive to ampicillin, quinupristin, linezolid and vancomycin. The highest resistance rate was 64.52% for tetracycline, followed by 58.06% for levofloxacin and 38.71% for 1clindamycin. Clindamycin resistance was only found in the Ⅰb and Ⅴ serotype strains. PCR detection of virulence genes showed that all the strains were positive for hylB, cylE, cfb and lmb genes. The carriage of bac and fbsA genes varied in strains with different serotypes, and these virulence genes were carried in almost all the Ⅰb serotype strains.

ConclusionBased on MLST and serotyping, our study showed that different types of S. agalactiae had different antibiotic resistance and varied different virulence genes, suggesting that close attention should be paid to the antibiotic resistance of Ⅰb and Ⅴ serotypes and virulence genes of Ⅰb serotypes of S. agalactiae.