2015 Epidemic of Severe Streptococcus agalactiae Sequence Type 283 Infections in Singapore Associated With the Consumption of Raw Freshwater Fish: A Detailed Analysis of Clinical, Epidemiological, and Bacterial Sequencing Data

Subspecies Typing of Streptococcus agalactiae Based on Ribosomal Subunit Protein Mass Variation by MALDI-TOF MS

Background: A ribosomal subunit protein (rsp)-based matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method was developed for fast subspecies-level typing of Streptococcus agalactiae (Group B Streptococcus, GBS), a major cause of neonatal sepsis and meningitis.

Methods: A total of 796 GBS whole genome sequences, covering the genetic diversity of the global GBS population, were used to in silico predict molecular mass variability of 28 rsp and to identify unique rsp mass combinations, termed “rsp-profiles”. The in silico established GBS typing scheme was validated by MALDI-TOF MS analysis of GBS isolates at two independent research sites in Europe and South East Asia.

Results: We identified in silico 62 rsp-profiles, with the majority (>80%) of the 796 GBS isolates displaying one of the six rsp-profiles 1–6. These dominant rsp-profiles classify GBS strains in high concordance with the core-genome based phylogenetic clustering. Validation of our approach by in-house MALDI-TOF MS analysis of 248 GBS isolates and external analysis of 8 GBS isolates showed that across different laboratories and MALDI-TOF MS platforms, the 28 rsp were detected reliably in the mass spectra, allowing assignment of clinical isolates to rsp-profiles at high sensitivity (99%) and specificity (97%). Our approach distinguishes the major phylogenetic GBS genotypes, identifies hyper-virulent strains, predicts the probable capsular serotype and surface protein variants and distinguishes between GBS genotypes of human and animal origin.

Conclusion: We combine the information depth of whole genome sequences with the highly cost efficient, rapid and robust MALDI-TOF MS approach facilitating high-throughput, inter-laboratory, large-scale GBS epidemiological and clinical studies based on pre-defined rsp-profiles.

The role of CNS macrophages in streptococcal meningoencephalitis

In the healthy brain, microglia and other CNS macrophages are the most abundant immune cell type. Thus, they form the natural immune cell interface with streptococci, which are the leading cause of bacterial meningitis and encephalitis in infants and young children. In homeostasis, the blood-brain barrier allows for very limited access of immune cells circulating in the periphery. During bacterial meningoencephalitis, however, origin and fate of CNS macrophages are massively altered. This review summarizes the emerging knowledge on the sequence of reciprocal events between streptococci and CNS macrophages leading to host resistance, acute inflammation, changes in resident innate immune cells of the brain, and long-term neuronal damage.

Role of Two-Component System Response Regulator bceR in the Antimicrobial Resistance, Virulence, Biofilm Formation, and Stress Response of Group B Streptococcus

Group B Streptococcus (GBS; Streptococcus agalactiae) is a leading cause of sepsis in neonates and pregnant mothers worldwide. Whereas the hyper-virulent serogroup III clonal cluster 17 has been associated with neonatal disease and meningitis, serogroup III ST283 was recently implicated in invasive disease among non-pregnant adults in Asia. Here, through comparative genome analyses of invasive and non-invasive ST283 strains, we identified a truncated DNA-binding regulator of a two-component system in a non-invasive strain that was homologous to Bacillus subtilis bceR, encoding the bceRSAB response regulator, which was conserved among GBS strains. Using isogenic knockout and complementation mutants of the ST283 strain, we demonstrated that resistance to bacitracin and the human antimicrobial peptide cathelicidin LL-37 was reduced in the ΔbceR strain with MICs changing from 64 and 256 μg/ml to 0.25 and 64 μg/ml, respectively. Further, the ATP-binding cassette transporter was upregulated by sub-inhibitory concentrations of bacitracin in the wild-type strain. Upregulation of dltA in the wild-type strain was also observed and thought to explain the increased resistance to antimicrobial peptides. DltA, an enzyme involved in D-alanylation during the synthesis of wall teichoic acids, which mediates reduced antimicrobial susceptibility, was previously shown to be regulated by the bceR-type regulator in Staphylococcus aureus. In a murine infection model, we found that the ΔbceR mutation significantly reduced the mortality rate compared to that with the wild-type strain (p < 0.01). Moreover, this mutant was more susceptible to oxidative stress compared to the wild-type strain (p < 0.001) and was associated with reduced biofilm formation (p < 0.0001). Based on 2-DGE and mass spectrometry, we showed that downregulation of alkyl hydroperoxide reductase (AhpC), a Gls24 family stress protein, and alcohol dehydrogenase (Adh) in the ΔbceR strain might explain the attenuated virulence and compromised stress response. Together, we showed for the first time that the bceR regulator in GBS plays an important role in bacitracin and antimicrobial peptide resistance, virulence, survival under oxidative stress, and biofilm formation.

Comparative genomics inferred two distinct populations of piscine pathogenic Streptococcus agalactiae, serotype Ia ST7 and serotype III ST283, in Thailand and Vietnam

The genomes of Streptococcus agalactiae (group B streptococcus; GBS) collected from diseased fish in Thailand and Vietnam over a nine-year period (2008-2016) were sequenced and compared (n = 21). Based on capsular serotype and multilocus sequence typing (MLST), GBS isolates are divided into 2 groups comprised of i) serotype Ia; sequence type (ST)7 and ii) serotype III; ST283. Population structure inferred by core genome (cg)MLST and Bayesian clustering analysis also strongly indicated distribution of two GBS populations in both Thailand and Vietnam. Deep phylogenetic analysis implied by CRISPR array's spacer diversity was able to cluster GBS isolates according to their temporal and geographic origins, though ST7 has varying CRISPR1-spacer profiles when compared to ST283 strains. Based on overall genotypic features, Thai ST283 strains were closely related to the Singaporean ST283 strain causing foodborne illness in humans in 2015, thus, signifying zoonotic potential of this GBS population in the country.

Group B Streptococcus Infections Caused by Improper Sourcing and Handling of Fish for Raw Consumption, Singapore, 2015-2016

Policies and guidelines regarding sale of ready-to-eat raw fish dishes have been updated.

We assessed microbial safety and quality of raw fish sold in Singapore during 2015–2016 to complement epidemiologic findings for an outbreak of infection with group B Streptococcus serotype III sequence type (ST) 283 associated with raw fish consumption. Fish-associated group B Streptococcus ST283 strains included strains nearly identical (0–2 single-nucleotide polymorphisms) with the human outbreak strain, as well as strains in another distinct ST283 clade (57–71 single-nucleotide polymorphisms). Our investigations highlight the risk for contamination of freshwater fish (which are handled and distributed separately from saltwater fish sold as sashimi) and the need for improved hygienic handling of all fish for raw consumption. These results have led to updated policy and guidelines regarding the sale of ready-to-eat raw fish dishes in Singapore.

Characterisation of bone and joint infections due to Group B Streptococcus serotype III sequence type 283

In 2015, an epidemic of Group B Streptococcus (GBS) serotype III sequence type 283 (ST283) disease was reported in Singapore, associated with consumption of raw freshwater fish. In this study, we further characterise the characteristics of bone and joint infections associated with ST283 GBS in adults and the differences between ST283 and non-ST283 manifestations. A retrospective study of 54 inpatients with invasive GBS disease involving bones and/or joints from 2010 to 2015 was performed. Archived isolates were identified as GBS serotype III and ST283 positive using PCR methods. Clinical data were collected from a review of clinical charts. Twenty-three cases were ST283 and 31 were non-ST283. ST283 GBS patients were more likely to be of Chinese ethnicity, have lower Charlson comorbidity scores, and have fewer overall comorbidities, including diabetes mellitus with end-organ damage, peripheral vascular disease, and previous stroke, compared to non-ST283 GBS patients. ST283 patients had more oligoarthritis, with greater involvement of the knee, shoulder, and vertebrae, compared to monoarticular joint involvement in non-ST283 patients. Six patients had a unique combination of knee and shoulder joint involvement. All ST283 cases were mono-microbial, compared to a significant proportion of polymicrobial cultures in non-ST283 patients. Non-ST283 patients had a significantly longer length of stay and were more likely to undergo amputation or wound debridement. This study adds to growing evidence of a distinct clinical presentation associated with ST283 GBS, involving predominantly healthier patients without significant comorbidities, and with distinct clinical manifestations with regard to bone and joint disease.

A Case Report: Organs From a Donor With Highly Virulent Zoonotic Outbreak Strain of Streptococcus agalactiae Serotype III, Multilocus Sequence Type 283 Infective Endocarditis Did Not Result in Transmission With Adequate Prophylactic Antibiotic Cover

In 2015, an outbreak involving a highly virulent zoonotic outbreak strain of Streptococcus agalactiae serotype III, multilocus sequence type 283 occurred in Singapore with increased neurologic complications, septic arthritis, and spinal infections in healthier patients. We report a case of a successful dual kidney transplant from a deceased donor with infective endocarditis and disseminated infection with the same strain of S agalactiae and we review the current literature.

Isolation and molecular characterization of group B Streptococcus from laboratory Long-Evans rats (Rattus norvegicus) with and without invasive group B streptococcal disease

Purpose. Group B Streptococcus (S. agalactiae, GBS) is a Gram-positive opportunistic pathogen that inhabits the respiratory, urogenital and gastrointestinal tracts of humans and animals. Maternal colonization of GBS is a risk factor for a spectrum of clinical diseases in humans and a principle cause of neonatal meningitis and septicaemia.Methodology. We describe polymicrobial sepsis including GBS in two gravid adult female Long-Evans rats experiencing acute mortality from a colony of long-term breeding pairs. Fluorescent in situ hybridization confirmed GBS association with pathological changes in affected tissues, including the heart and uterus.Results. Characterization of seven GBS strains obtained from clinically affected and non-affected animals indicated similar antibiotic resistance and susceptibility patterns to that of human strains of GBS. The rat strains have virulence factors known to contribute to pathogenicity, and shared serotypes with human invasive isolates. Phylogenetic analyses revealed that one rat-derived GBS strain was more closely related to human-derived strains than other rat-derived strains, strengthening the notion that interspecies transmission is possible.Conclusions. To our knowledge, this is the first investigation of genotypic and phenotypic features of rat-derived GBS strains and their comparison to human- and other animal-derived GBS strains. Since GBS commonly colonizes commercially available rats, its exclusion as a potential pathogen for immunocompromised or stressed animals is recommended.

Group B Streptococcal Prosthetic Knee Joint Infection Linked to the Consumption of Raw Fish

Introduction

Group B Streptococcal (GBS) prosthetic joint infections (PJI) are rare, accounting for only 4.6-6% of primary and revision total knee replacements (TKRs). In 2015, there was an outbreak of GBS infections in Singapore with an association confirmed between consumption of Chinese-style raw fish dishes (snakehead fish, Asian bighead carp) and GBS infection, Type III GBS ST283 strain, affecting more than 200 patients in Singapore. This outbreak is the largest of its kind in the world and also the first time that foodborne transmission of GBS has been proven. We present the first reported case in the literature of a confirmed PJI in a TKR related to foodborne transmission of GBS through consumption of raw fish (Snakehead fish).

Case Report

Our patient is a 66-year-old Chinese female admitted with a 24-h history of acute right knee pain and swelling with associated fever in the context of consuming raw fish porridge 3 days before the onset of her symptoms. She had a TKR performed in the same knee 7 years before this presentation. Her GBS PJI was confirmed on both blood and intraoperative tissue/fluid cultures during the outbreak of GBS infections in Singapore. This was managed with debridement, polyethylene liner change, retention of metal prosthesis, and culture-directed antibiotics with good outcomes.

Conclusion

Snakehead fish is a popular dish in the Asian community as a traditional remedy to promote wound healing after surgery. Our paper highlights the link between raw fish consumption and invasive GBS causing PJIs. This can occur in healthy adults, even in the absence of gastrointestinal symptoms, despite being a foodborne transmission. Our paper also highlights that GBS PJIs can be managed with debridement, antibiotic therapy, and implant retention with good outcomes in the setting of acute hematogenous infection. We recommend the inclusion of raw fish consumption on history taking in the workup of suspected PJIs and counseling patients preoperatively on the risk of GBS PJIs with the consumption of raw fish dishes (snakehead fish and Asian bighead carp) to mitigate unnecessary PJI risk.

Population structure and virulence gene profiles of Streptococcus agalactiae collected from different hosts worldwide

Streptococcus agalactiae is a leading cause of morbidity and mortality among neonates and causes severe infections in pregnant women and nonpregnant predisposed adults, in addition to various animal species worldwide. Still, information on the population structure of S. agalactiae and the geographical distribution of different clones is limited. Further data are urgently needed to identify particularly successful clones and obtain insights into possible routes of transmission within one host species and across species borders. We aimed to determine the population structure and virulence gene profiles of S. agalactiae strains from a diverse set of sources and geographical origins. To this end, 373 S. agalactiae isolates obtained from humans and animals from five different continents were typed by DNA microarray profiling. A total of 242 different S. agalactiae strains were identified and further analyzed. Particularly successful clonal lineages, hybridization patterns, and strains were identified that were spread across different continents and/or were present in more than one host species. In particular, several strains were detected in both humans and cattle, and several canine strains were also detected in samples from human, bovine, and porcine hosts. The findings of our study suggest that although S. agalactiae is well adapted to various hosts including humans, cattle, dogs, rodents, and fish, interspecies transmission is possible and occurs between humans and cows, dogs, and rabbits. The virulence and resistance gene profiles presented enable new insights into interspecies transmission and make a crucial contribution to the identification of suitable targets for therapeutic agents and vaccines.

Pathogenicity of Human ST23 Streptococcus agalactiae to Fish and Genomic Comparison of Pathogenic and Non-pathogenic Isolates

Streptococcus agalactiae, or Group B Streptococcus (GBS), is a major pathogen causing neonatal sepsis and meningitis, bovine mastitis, and fish meningoencephalitis. CC23, including its namesake ST23, is not only the predominant GBS strain derived from human and cattle, but also can infect a variety of homeothermic and poikilothermic species. However, it has never been characterized in fish. This study aimed to determine the pathogenicity of ST23 GBS to fish and explore the mechanisms causing the difference in the pathogenicity of ST23 GBS based on the genome analysis. Infection of tilapia with 10 human-derived ST23 GBS isolates caused tissue damage and the distribution of pathogens within tissues. The mortality rate of infection was ranged from 76 to 100%, and it was shown that the mortality rate caused by only three human isolates had statistically significant difference compared with fish-derived ST7 strain (P < 0.05), whereas the mortality caused by other seven human isolates did not show significant difference compared with fish-derived ST7 strain. The genome comparison and prophage analysis showed that the major genome difference between virulent and non-virulent ST23 GBS was attributed to the different prophage sequences. The prophage in the P1 region contained about 43% GC and encoded 28–39 proteins, which can mediate the acquisition of YafQ/DinJ structure for GBS by phage recombination. YafQ/DinJ belongs to one of the bacterial toxin–antitoxin (TA) systems and allows cells to cope with stress. The ST23 GBS strains carrying this prophage were not pathogenic to tilapia, but the strains without the prophage or carrying the pophage that had gene mutation or deletion, especially the deletion of YafQ/DinJ structure, were highly pathogenic to tilapia. In conclusion, human ST23 GBS is highly pathogenic to fish, which may be related to the phage recombination.