Development of a multiplex PCR for identification of β-hemolytic streptococci relevant to human infections and serotype distribution of invasive Streptococcus agalactiae in Thailand

Emergence of Multi-Drug Resistance and Its Association With Uncommon Serotypes of Streptococcus agalactiae Isolated From Non-neonatal Patients in Thailand

Group B streptococcus (GBS) or Streptococcus agalactiae is an opportunistic pathogen that causes serious illness in newborns, pregnant women, and adults. However, insufficient detection methods and disease prevention programs have contributed to an increase in the incidence and fatality rates associated with this pathogen in non-neonatal patients. This study aimed to investigate factors of the observed increased incidence by investigation of serotype distribution, virulence factors, and antimicrobial susceptibility patterns from invasive GBS disease among non-neonatal patients in Thailand. During 2017–2018, a total of 109 S. agalactiae isolates were collected from non-pregnant patients. There were 62 males and 47 females, with an average age of 63.5 years (range: 20 – 96). Serotypes were determined by latex agglutination assay and multiplex polymerase chain reaction (PCR)-based assay. Among those isolates, seven virulence genes (rib, bca, pavA, lmb, scpB, cylE, and cfb) were detected by PCR amplification, and were determined for their susceptibility to 20 antimicrobial agents using a Sensititre^TM Streptococcus species STP6F AST plate. Among the study isolates, serotype III was predominant (52.3%), followed by serotype V and serotype VI (13.8% for each), serotype Ib (11.9%), and other serotypes (8.2%). Of the seven virulence genes, pavA was found in 67.0%. Except for one, there were no significant differences in virulence genes between serotype III and non-serotype III. Study isolates showed an overall rate of non-susceptibility to penicillin, the first-line antibiotic, of only 0.9%, whereas the resistance rates measured in tetracycline, clindamycin, azithromycin, and erythromycin were 41.3, 22.0, 22.0, and 22.0%, respectively. Strains that were resistant to all four of those drugs were significantly associated with non-serotype III (p < 0.001). Using multi-locus sequence typing (MLST), 40.0% of the four-drug-resistant isolates belonged to serotype VI/ST1, followed by serotype Ib/ST1 (35.0%). Cluster analysis with global GBS isolates suggested that the multiple drug-resistant isolates to be strongly associated with the clonal complex (CC) 1 (p < 0.001). Compared to the 2014 study of 210 invasive GBS isolates conducted in 12 tertiary hospitals in Thailand, the proportion of serotype III has dramatically dropped from nearly 90% to about 50%. This suggests that resistances to the second-line antibiotics for GBS might be the selective pressure causing the high prevalence of non-serotype III isolates.

Zoonotic infection and clonal dissemination of Streptococcus equi subspecies zooepidemicus sequence type 194 isolated from humans in Thailand

Streptococcus equi subsp. zooepidemicus (SEZ) is a zoonotic pathogen associated with diseases in a wide range of animals as well as in humans. SEZ sequence type (ST) 194 strains have been associated with outbreaks in China, the USA, and Canada and have caused high mortality in pigs. Nevertheless, human infection by this ST has never been reported. This study conducted a retrospective analysis of 18 SEZ strains from human patients in Thailand during 2005-2020. The study revealed clonal dissemination of ST194 with the identical pulsotype in human patients throughout Thailand. Clinical manifestation was mainly septicemia (61.1%), while 72.2% had a history of eating raw pork products. There were six fatal cases (33.3%). Antimicrobial susceptibility testing revealed that all strains were susceptible to penicillin, ampicillin, cefotaxime, erythromycin, levofloxacin, clindamycin, chloramphenicol, tetracycline and vancomycin. Virulence-associated genes, including bifA, szM, szP, sdzD, spaZ, and fszF, were present in all tested strains. Some representative genes in four pathogenicity islands found in the swine outbreak SEZ-ATCC35246 (ST194) strain were detected in these SEZ strains. Whole-genome sequencing analysis of three representative SEZs in this study revealed no acquired antimicrobial-resistant genes and they contained the same virulence factors. The single-nucleotide polymorphism phylogenetic tree demonstrated that the current strains were clustered with swine ST194 strains. The results should be highlighted as a public health concern, especially to those who may directly or indirectly have contact with livestock or companion animals or have consumed raw meat products as risk factors for infections with SEZ.

Comparative genome analysis of three Group A Streptococcus dysgalactiae subsp. equisimilis strains isolated in Japan

Introduction . Streptococcus dysgalactiae subsp. equisimilis (SDSE) is a β-hemolytic streptococcus that causes severe invasive streptococcal infections, especially in the elderly and people with underlying diseases. SDSE strains are primarily characterized by Lancefield group G or C antigens.Hypothesis/Gap Statement. We have previously reported the prevalence of Lancefield group A SDSE (GA-SDSE) strains in Japan and have analysed the draft genome sequences of these strains. As GA-SDSE is a rare type of SDSE, only one complete genome has been sequenced to date.Aim. The present study is focused on genetic characteristics of GA-SDSE strains. In order to examine molecular characteristics, we also tested growth inhibition of other streptococci by GA-SDSE.Methodology. We determined the complete genome sequences of three GA-SDSE strains by two new generation sequencing systems (short-read and long-read sequencing data). Using the sequences, we also conducted a comparative analysis of GA-SDSE and group C/G SDSE strains. In addition, we tested multiplex and quantitative PCRs targeting the GA-SDSE, group G SDSE, and S. pyogenes.Results. We found a group-specific conserved region in GA-SDSE strains that is composed of genes encoding predicted anti-bacteriocin and streptococcal lantibiotic (Sal) proteins. Multiplex and quantitative PCRs targeting the GA-SDSE-specific region were able to distinguish between GA-SDSE, other SDSE, and S. pyogenes strains. The growth of GA-SDSE was suppressed in the presence of group G SDSE, indicating a possible explanation for the low frequency of isolation of GA-SDSE.Conclusion. The comparative genome analysis shows that the genome of GA-SDSE has a distinct arrangement, enabling the differentiation between S. pyogenes, GA-SDSE, and other SDSE strains using our PCR methods.