Outbreak of group B Streptococcus in a neonatal care unit confirmed by whole-genome sequencing

AIM

Clusters of group B Streptococcus (GBS) infections in neonatal intensive care units (NICU) are poorly documented. We aimed to assess GBS cross-transmission during an outbreak of GBS sepsis.

METHODS

The study was carried out between October and November 2021 in a French University Hospital. Neonatal intensive care unit (NICU) patients with GBS sepsis were included. Clinical data were retrieved from electronic patient records. Group B Streptococcus isolates were characterized at the molecular level using capsular genotyping and whole-genome sequencing (WGS).

RESULTS

The outbreak of GBS sepsis affected three very preterm neonates with a gestational age of less than 26 weeks, including one recurrent male index case aged 26 days, and two female secondary cases aged 5 and 17 days. The microbiological investigation identified a GBS isolate of capsular type III and Sequence Type 17 as responsible for the four infectious episodes. Whole-genome sequencing confirmed the identity between the isolates. The outbreak and the results of the microbiological investigations led to an immediate reinforcement of hygiene measures.

CONCLUSION

Clustered cases of GBS infections in NICU and horizontal transmission of the hypervirulent GBS Sequence Type 17 are likely underestimated. Prospective investigation of all nosocomial cases using WGS should contribute to improving vigilance regarding GBS cross-transmission and infection prevention.

In vivo antibacterial activity of medicinal plant Sophora flavescens against Streptococcus agalactiae infection

Streptococcosis disease caused by Streptococcus agalactiae (Group B Streptococcus, GBS) results in a huge economic loss of tilapia culture. It is urgent to find new antimicrobial agents against streptococcosis. In this study, 20 medicinal plants were evaluated in vitro and in vivo to obtain medicinal plants and potential bioactive compounds against GBS infection. The results showed that the ethanol extracts of 20 medicinal plants had low or no antibacterial properties in vitro, with a minimal inhibitory concentration ≥256 mg/L. Interestingly, in vivo tests showed that 7 medicinal plants could significantly inhibit GBS infection in tilapia, and Sophora flavescens (SF) had the strongest anti-GBS activity in tilapia, reaching 92.68%. SF could significantly reduce the bacterial loads of GBS in different tissues (liver, spleen and brain) of tilapia after treated with different tested concentrations (12.5, 25.0, 50.0 and 100.0 mg/kg) for 24 h. Moreover, 50 mg/kg SF could significantly improve the survival rate of GBS-infected tilapia by inhibiting GBS replication. Furthermore, the expression of antioxidant gene cat, immune-related gene c-type lysozyme and anti-inflammatory cytokine il-10 in liver tissue of GBS-infected tilapia significantly increased after treated with SF for 24 h. Meanwhile, SF significantly reduced the expression of immune-related gene myd88 and pro-inflammatory cytokines il-8 and il-1β in liver tissue of GBS-infected tilapia. The negative and positive models of UPLC-QE-MS, respectively, identified 27 and 57 components of SF. The major components of SF extract in the negative model were α, α-trehalose, DL-malic acid, D- (-)-fructose and xanthohumol, while in the positive model were oxymatrine, formononetin, (-)-maackiain and xanthohumol. Interestingly, oxymatrine and xanthohumol could significantly inhibit GBS infection in tilapia. Taken together, these results suggest that SF can inhibit GBS infection in tilapia, and it has potential for the development of anti-GBS agents.

Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract

Type VIIb secretion systems (T7SSb) in Gram-positive bacteria facilitate physiology, interbacterial competition, and/or virulence via EssC ATPase-driven secretion of small ɑ-helical proteins and toxins. Recently, we characterized T7SSb in group B Streptococcus (GBS), a leading cause of infection in newborns and immunocompromised adults. GBS T7SS comprises four subtypes based on variation in the C-terminus of EssC and the repertoire of downstream effectors; however, the intraspecies diversity of GBS T7SS and impact on GBS-host interactions remains unknown. Bioinformatic analysis indicates that GBS T7SS loci encode subtype-specific putative effectors, which have low interspecies and inter-subtype homology but contain similar domains/motifs and therefore may serve similar functions. We further identify orphaned GBS WXG100 proteins. Functionally, we show that GBS T7SS subtype I and III strains secrete EsxA in vitro and that in subtype I strain CJB111, esxA1 appears to be differentially transcribed from the T7SS operon. Furthermore, we observe subtype-specific effects of GBS T7SS on host colonization, as CJB111 subtype I but not CNCTC 10/84 subtype III T7SS promotes GBS vaginal colonization. Finally, we observe that T7SS subtypes I and II are the predominant subtypes in clinical GBS isolates. This study highlights the potential impact of T7SS heterogeneity on host-GBS interactions.

Evaluation of two rapid commercial assays for detection of Streptococcus agalactiae from vaginal samples

INTRODUCTION

Streptococcus agalactiae, also known as group B streptococci (GBS), is associated with invasive infections in neonates. Identification of GBS vaginal colonization in pregnant women before delivery is essential for treatment with antibiotics to prevent intrapartum vertical transmission to the newborn. This study was designed to evaluate applicability of two rapid real-time PCRs in comparison to standard culture identification.

MATERIAL AND METHODS

We compared the Xpert GBS assay, hereafter referred to as Xpert, and GenomEra GBS PCR, hereafter referred to as GenomEra. The standard culture identification consisted of two different agar plates as well as an enrichment broth.

RESULTS

We analyzed vaginal samples of 260 pregnant women; 42 samples were tested GBS-positive by using standard culture as a gold standard, 30 by Xpert, and 37 by GenomEra. Xpert and GenomEra assays performed with sensitivities of 71.4% and 88.1% as well as specificities of 98.6% and 99.1%, respectively. Twelve vaginal samples were false-negative by Xpert and five samples by GenomEra. Interestingly, three negative Xpert results of standard culture-positive samples exhibited high Ct-values indicating the presence of GBS. If higher Ct-values are taken into consideration, the sensitivity of Xpert increases up to 78.6%. Moreover, only three Xpert PCRs had to be repeated, whereas two Genomera were invalid even after repetition and further 15 GenomEra PCRs were repeated because of borderline results or inhibition of the PCR test.

CONCLUSIONS

In this study, GenomEra assay performed with a higher sensitivity than the Xpert PCR. On the other hand, the Xpert assay needs less hands-on-time for a sample preparation and requires approximately four-fold less repetitions as compared to the GenomEra assay. This robust performance of the Xpert assay make it applicable as a rapid intrapartum point-of-care test, although a higher sensitivity would be desirable. Therefore, culture in the 35-37 week of gestation remains the gold standard to detect vaginal colonization.

Streptococcus agalactiae pyomyositis in a patient with primary biliary cholangitis: A case report

Pyomyositis is an uncommon clinical scenario; it is usually associated with predisposing factors, including poorly controlled diabetes mellitus, trauma history, and immunocompromise. We discuss the case of an elderly woman with a 20-year history of diabetes mellitus and remissive breast cancer after modified radical mastectomy and subsequent chemotherapy 28 years previously. The patient presented with severe shoulder pain and gradual swelling. After examination, pyomyositis was diagnosed and debridement surgery was performed. Culture of the wound samples showed the growth of Streptococcus agalactiae. During hospitalization, primary biliary cholangitis (PBC) was diagnosed incidentally, accompanied by poor glycemic control. After treatment with antibiotics for pyomyositis and ursodeoxycholic acid for PBC, the infection resolved in 8 weeks, and her glycemic control was improved after PBC treatment. It is possible that the long-term untreated PBC worsened insulin resistance and aggravated diabetes mellitus in this patient. To the best of our knowledge, this is the first reported case of pyomyositis caused by an unusual pathogen, S. agalactiae, in a patient with newly diagnosed PBC.

Expression profiling and inflammatory activation analysis of high-mobility group box 1 in Schizothorax prenanti

OBJECTIVE

High-mobility group box 1 (HMGB1) is a highly conserved nuclear protein and participates in the immune response to pathogens in bony fish. In this study, the structure and function of HMGB1 in the cyprinid fish Schizothorax prenanti (SpHMGB1) were investigated.

METHODS

The spatial structure of SpHMGB1 was predicted by CPHmodels. Quantitative reverse transcription PCR was used to detect the mRNA of SpHMGB1 in different tissues and Streptococcus agalactiae infection. The macrophage was treated with synthetic SpHMGB1-B box peptide to analyze the inflammatory activity.

RESULT

Structurally, SpHMGB1 had the conserved A box, B box, and acid tail compared with Zebrafish Danio rerio and mice Mus musculus. SpHMGB1 was universally expressed in various tissues, with the highest expression in the middle kidney. In vivo, SpHMGB1 was significantly induced in response to Streptococcus agalactiae infection in the blood and spleen. Synthetic SpHMGB1-B box peptide activated respiratory burst and up-regulated the messenger RNA expression of interleukin-1β, tumor necrosis factor α, interleukin-10, interferon regulatory factor 1, interferon regulatory factor 7, C-X-C motif chemokine ligand 11-1, C-X-C motif chemokine ligand 11-2, and toll-like receptor 4 in macrophages.

CONCLUSION

This study suggested that SpHMGB1 participated in the response to bacterial pathogens and that SpHMGB1-B box peptide played an important role in mediating the immune response of S. prenanti.

Molecular cloning, expressional analyses and functional identification of TRAIL in tilapia, Oreochromis niloticus

The tumour necrosis factor superfamily (TNFSF) plays critical roles in tumour apoptosis, tissue morphogenesis and lineage determination. TNFSF10 (TRAIL or Apol-2) belongs to the tumour necrosis factor (TNF) cytokine family and induces rapid apoptosis in a wide variety of tumour cell lines upon binding to death-inducing signalling receptors. In this study, we identified TNFSF10 from Nile tilapia (Oreochromis niloticus) and found it was most closely related to Japanese pufferfish (Takifugu rubripes) TNFSF10. Amino acid identity between tilapia TNFSF10 and mandarin fish (Siniperca chuatsi) TRAIL was 69.2%. The highest expression of TNFSF10 mRNA was observed in the liver. In vitro studies showed that the mRNA expression of TNFSF10 was significantly stimulated by LPS in head kidney leucocytes, but remarkably inhibited by Poly I:C in spleen leucocytes. In vivo studies showed Streptococcus agalactiae infection significantly induced the mRNA expression of TNFSF10 in both the head kidney and spleen. The soluble recombinant protein Trx-TNFSF10 could induce cytotoxicity and apoptosis in HeLa cells with cycloheximide as a promoter. Taken together, these results in this study indicate that TNFSF10 may play important roles in the immune system of Nile tilapia.

Natural component plumbagin as a potential antibacterial agent against Streptococcus agalactiae infection

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), can infect humans, terrestrial animals and fish. The emergence of bacterial resistance of S. agalactiae to antibiotics leads to an urgent need of exploration of new antimicrobial agents. In the study, the antibacterial activity of natural component plumbagin (PLB) against S. agalactiae was investigated in vitro and in vivo. The results showed that the minimal inhibitory concentration (MIC) of PLB against S. agalactiae was 8 mg/L. The growth curve assay revealed that PLB could inhibit the growth of S. agalactiae. In addition, the time-killing curve showed that S. agalactiae was killed almost completely by 2-fold MIC of PLB within 12 h. Transmission electron microscopy results showed obvious severe morphological destruction and abnormal cells of S. agalactiae after treated with PLB. The pathogenicity of S. agalactiae to zebrafish was significantly decreased after preincubation with PLB for 2 h in vitro, further indicating the bactericidal activity of PLB. Interestingly, PLB could kill S. agalactiae without inducing resistance development. Furthermore, pretreatment and post-treatment assays suggested that PLB also exhibited the antibacterial activity against S. agalactiae infection in vivo by effectively reducing the bacterial load and improving the survival rate of S. agalactiae-infected zebrafish. In summary, PLB had potent antibacterial activity against S. agalactiae in vitro and in vivo, and it could be an excellent antimicrobial candidate to prevent and control S. agalactiae infection.

Streptococcus agalactiae infection caused spinal deformity in juvenile red tilapia (Oreochromis sp.)

A case of juvenile red tilapia (Oreochromis sp.) showing body deformity due to spinal curvature was investigated. Approximately 20% of the crop (4,000 fish/crop) was affected. Bacterial isolation from the kidney and tissue surrounding the spinal lesion of the affected fish was negative. Histopathology revealed granulomatous inflammation and Gram-positive cocci in connective tissues around the bone and notochord. PCR assay confirmed the presence of S. agalactiae in the spinal tissue lesion. Spinal deformity in red tilapia observed in our study may be associated with the inflammatory process and granuloma that compress the skeleton structure. The present study highlights chronic streptococcosis in tilapia culture that may be unnoticed.

Phenotype, genotype and pathogenicity of Streptococcus agalactiae isolated from cultured tilapia (Oreochromis spp.) in Taiwan

Tilapia (Oreochromis spp.) is globally used as an aquaculture fish species due to its high growth rate and disease resistance. However, it faces an increased risk of streptococcosis. Streptococcus agalactiae, also known as group B streptococcus (GBS), is the most important tilapia pathogen in Asia. Studies of Str. agalactiae infection in Taiwan are still unclear. Thus, this study aimed to explore the phenotype, genotype and pathogenicity of Str. agalactiae isolated from cultured tilapia in Taiwan in 2016-2018. The analysis revealed that 85% of the strains displayed β-haemolysis and 15% showed γ-haemolysis, with the same capsule level, and were positive for the CAMP test. The Rapid ID 32 Strep test showed a similarity of Rapid ID 32 Strep is more than 99.5% to GBS. Genotypic distribution by molecular serotyping detected only serotype Ia from all isolates, despite the regional differences. Pulsed-field gel electrophoresis (PFGE) was categorized into 3 and 10 clusters by restriction enzymes SmaI and ApaI, respectively. Virulence genes and antimicrobial resistance genes presented the same profile in all isolates. The challenge test with 10⁶  CFU/fish (LD₅₀ ), administered intraperitoneally, showed that the β-haemolysis strains had a higher mortality rate than γ-haemolysis, although they were from the same cluster from PFGE, year and region.

Characterization and functional analysis of a galectin-related protein B from Nile tilapia involved in the immune response to bacterial infection

Galectin-related protein is a kind of lectin without canonical activity that regulates cell adhesion and cell growth. In this study, a novel galectin-related protein B (OnGRPB) was identified from Nile tilapia (Oreochromis niloticus). The open reading frame of OnGRPB was 438 bp and encoded a peptide of 145 amino acids. The deduced protein sequence of OnGRPB possessed a conserved carbohydrate recognition domain (CRD) with partial sugar binding sites (N-R, V-N and W-E) and shared high identities with other fish GRPB proteins. The qRT-PCR analysis found that OnGRPB was widely distributed in various tissues and monocyte/macrophages (Mo/MΦ) of healthy tilapia. After Streptococcus agalactiae infection, OnGRPB transcripts were significantly up-regulated in liver, spleen, head kidney and Mo/MΦ. The recombinant OnGRPB protein (rOnGRPB) had the binding activity and agglutination ability to bacteria. Also, rOnGRPB could modulate antibacterial activity and inflammatory factor expression of Mo/MΦ. These data collectively indicate that OnGRPB plays roles in the immune response of Nile tilapia against bacterial infection.

CD40 induces an antimicrobial response against the intracellular pathogen Streptococcus agalactiae in Nile tilapia, Oreochromis niloticus

Streptococcus agalactiae is a Gram-positive facultative intracellular bacterium that leads to severe economic loss of tilapia worldwide. Previous studies demonstrated that CD40 contributes to host protection against intracellular injection. In this study, CD40 was characterized from Nile tilapia (Oreochromis niloticus), named OnCD40. Sequence analysis showed that open reading frame of OnCD40 was 933 bp, containing a single peptide, a transmembrane domain and four cysteine-rich domains. The qRT-PCR revealed that OnCD40 was expressed in all examined tissues with the most abundant ones in spleen and thymus. After S. agalactiae stimulation, the expression of OnCD40 was significantly induced in most of the detected organs. Moreover, OnCD40-overexpressing fish elicited significant protection against subsequent S. agalactiae challenge; approximately 10000-fold fewer bacteria were detected in spleen of OnCD40-overexpressing fish in comparison with control fish. Thus, CD40 had protecting function in Nile tilapia against intracellular pathogens.

Isolation and molecular characterization of streptococcal species recovered from clinical infections in farmed Nile tilapia (Oreochromis niloticus) in the Philippines

Streptococcosis cause severe losses for global tilapia farming, especially in developing countries. The aim of this study was to identify and characterize streptococci recovered from Nile tilapia farmed in the Philippines. Moribund and apparently healthy fish were sampled from grow-out cages, ponds and hatcheries. Clinical signs observed included exophthalmia, eye opacity, ascites, lethargy, erratic swimming and haemorrhages. Results showed that both Streptococcus iniae and Streptococcus agalactiae were associated with disease in these sites. Consistent with global reports, including those from South-East Asia, S. agalactiae was more widespread than S. iniae. Molecular serotyping of the S. agalactiae isolates identified the serotype Ia and serotype Ib. Histopathological findings were meningitis, meningoencephalitis and septicaemia. Identical virulence profiles were found for all strains of S. iniae, while S. agalactiae strains were separated into virulence profile I and profile II. All strains were susceptible to the tested antibiotics and resistant to oxolinic acid. Only S. agalactiae serotype Ib showed resistance to sulphamethoxazole-trimethoprim. This is the first study from the Philippines to characterize the streptococci involved in disease outbreaks in tilapia aquaculture. Outputs from this study will promote the development of efficacious disease control strategies in tilapia farming for the Philippines and South-East Asia.

Experimental validation of genetic selection for resistance against Streptococcus agalactiae via different routes of infection in the commercial Nile tilapia breeding programme

The objective of this study was to validate the genetic selection for resistance to streptococcosis under experimental challenge conditions in a commercial population of Nile tilapia. Further, effects of using two different routes of infection of Streptococcus agalactiae; intraperitoneal injection (IP) and cohabitation with the shedder fish (cohab), on the genomic parameters, prediction accuracy and response to selection are compared. The comparison was made between two different lines of fish; one selected for S. agalactiae resistance for one generation and randomly mated for two generations (to mimic the multiplication activities occurring in distribution channels and hatcheries); and the other unselected. 1,500 fish, each from these two lines, were used for the experimental challenge test. Survival analysis using Kaplan-Meier estimators and Hazard's ratio was used to quantify differences in mortality between the two lines. Further genomic analysis was performed with 2,684 fish and 35,745 SNPs using both univariate and bivariate GBLUP models. Genetic selection for resistance to S. agalactiae led to the significant (p < .001) reduction in the risk of death by 65% in the selected line, compared to the unselected line. Similarly, the risk of death via cohabitation route of infection significantly (p < .01) decreased by 80%, compared to IP. The genetic correlation between these two routes of infection was ~0.9. Genetic selection changed the impact of the routes of infection, with the change in the distribution of estimated breeding values and the gain of 3.04 ± 1.25 days as selection response (p < .05).

Clinical features and outcomes of community-acquired late-onset sepsis: Focusing on group B Streptococcus and Escherichia coli

BACKGROUND

Group B Streptococcus (GBS) and Escherichia coli are leading causes of late-onset sepsis (LOS) and bacterial meningitis in neonates and infants. This study aimed to describe clinical characteristics and outcomes of community-acquired (CA) LOS caused by GBS and E. coli.

METHODS

A retrospective observational study was performed in three university hospitals in Korea. All infants aged <90 days who were diagnosed with GBS or E coli CA-LOS from 2011 to 2017 were enrolled. Data on the clinical characteristics and outcomes of GBS and E. coli CA-LOS were compared.

RESULTS

Forty GBS and 43 E. coli CA-LOS cases were identified, which mostly (82/83) included term or near-term infants. Meningitis was identified in 54.1% of GBS CA-LOS cases and in 30.3% of E. coli CA-LOS cases, and 88.4% of E. coli CA-LOS cases involved urosepsis. Ten percent each of GBS and non-uropathogenic E. coli (non-UPEC) meningitis cases and all uropathogenic E. coli (UPEC) meningitis cases were diagnosed by pleocytosis without bacterial growth in the cerebrospinal fluid (CSF). Patients with non-culture-proven meningitis had lower CSF pleocytosis and protein levels and higher CSF/serum glucose ratios than patients with culture-proven meningitis (P < 0.05 for all). One patient died of CA-LOS, which was accompanied by meningitis with extended-spectrum β-lactamase-producing non-UPEC. Neurological complications developed in 22.5% of GBS CA-LOS cases and in 2.3% of E. coli CA-LOS cases.

CONCLUSIONS

Neurological complications were frequently observed in GBS CA-LOS cases, although no mortality was observed. Escherichia coli CA-LOS generally developed as urosepsis, which caused non-culture-proven meningitis and had a favorable outcome.

Selection response for Streptococcus agalactiae resistance in Nile tilapia Oreochromis niloticus

The potential of selection to improve resistance to streptococcosis was evaluated in a commercial population of Nile tilapia in Thailand. The base generation (G0) consisted of offspring from 98 sires and 149 dams using a partly nested design. At 60 days post-hatch, 30 fish from each family were injected intraperitoneally with a Streptococcosis agalactiae solution (1 × 10⁹  CFU/ml) and evaluated for 14 days. Disease resistance was recorded as the number of days from challenge until death (DD) and as a binary (BIN) trait (dead/alive) on day 14. Three models were used for genetic analyses: Cox frailty model for DD; animal model for DD; and animal model for BIN. Age at challenge was fitted as a covariate and contemporary group as fixed or random effect, depending on the model. Fish from the 18 most resistant families were selected to produce the first generation (G1). Heritability estimates for G0 were 0.22, 0.14 ± 0.02 and 0.11 ± 0.02 for the Cox, linear DD and linear BIN models, respectively. Selection response indicated that the risk of death decreased to 54%, survival time increased to 3.4 days and survival rate increased to 21%. These results suggest that genetic improvement is possible for this population.

Morphological characterization of the adherence and invasion of Streptococcus agalactiae to the intestinal mucosa of tilapia Oreochromis sp.: An in vitro model

Streptococcosis in tilapia Oreochromis sp. is possibly the most important bacterial disease for fish production worldwide. In Colombia, streptococcosis is caused by Streptococcus agalactiae (GBS), but in other countries, Streptococcus iniae is also involved. Prevention of streptococcosis is required and must be addressed for economic, social, international trade and public health reasons. This research used an in vitro culture of tilapia intestine to detail the intestinal mucosal response once the pathogen contacts the epithelium. We show that S. agalactiae sheds off its capsule to adhere to the epithelium. The bacterium adheres as a single individuum, in groups or in chains and is able to divide on the apical border of enterocytes. GBS adheres at and invades exclusively through the apical portion of the intestinal folds, using the transepithelial route. Once within the cytoplasm of enterocytes, the bacteria continue to divide. On the basolateral side of the epithelium, the microorganisms leave the cells to reach the propria and travel through the microcirculation. No evidence of an immuno-inflammatory reaction or goblet cell response in the epithelium or the lamina propria was seen during the process of adherence and invasion of the pathogen.

Development of attenuated erythromycin-resistant Streptococcus agalactiae vaccine for tilapia (Oreochromis niloticus) culture

Streptococcus agalactiae is an important pathogen in fish, causing great losses of intensive tilapia farming. To develop a potential live attenuated vaccine, a re-attenuated S. agalactiae (named TFJ-ery) was developed from a natural low-virulence S. agalactiae strain TFJ0901 through selection of resistance to erythromycin. The biological characteristics, virulence, stability and the immunization protective efficacy to tilapia of TFJ-ery were determined. The results indicated that TFJ-ery grew at a slower rate than TFJ0901. The capsule thickness of TFJ-ery was significantly less (p < 0.05) than TFJ0901. When Nile tilapia were intraperitoneally (IP) injected with TFJ-ery, the mortality of fish was decreased than that injected with TFJ0901. The RPS of fish immunized with TFJ-ery at a dose of 5.0 × 10⁷ CFU was 95.00%, 93.02% and 100.00% at 4, 8 and 16 weeks post-vaccination, respectively. ELISA results showed that the vaccinated fish produced significantly higher (p < 0.05) antibody titres compared to those of control at 2 or 4 weeks post-vaccination. Taken together, our results suggest that erythromycin could be used to attenuate S. agalactiae, and TFJ-ery is a potent attenuated vaccine candidate to protect tilapia against S. agalactiae infections.

Bone and joint infections in infants under three months of age

AIM

Studies on bone and joint infections (BJI) in infants under three months are rare. We described the clinical and paraclinical features and outcomes of infants hospitalised with BJI under three months of age.

METHODS

The French National Hospital Discharge Database provided data on BJIs in infants under three months of age from January 2004 to 2015 in three Parisian Paediatric teaching hospitals.

RESULTS

We included 71 infants under three months of age with BJI, the median age was 25 days, and the interquartile range (IQR) was 17-43 days. The most common infection sites were the hip (32%) and knee (32%). Symptoms included pain (94%), limited mobility (87%) and/or fever (52%). There were 11 (15.5%) cases of nosocomial BJI. A pathogen was identified in 51 infants (71.8%), including Streptococcus agalactiae (45%), Staphylococcus aureus (22%) and Escherichia coli (18%). The initial median C-reactive protein test rate was 31 mg/L (IQR 17-68). Of the 34 infants followed for more than one year, four developed severe orthopaedic conditions such as epiphysiodesis, limb length discrepancy, bone necrosis and/or impaired limb function.

CONCLUSION

Streptococcus agalactiae was the most common cause of BJI in infants under three months. Orthopaedic sequelae were rare, but severe, and required long-term follow-up.

Capsular polysaccharide of Streptococcus agalactiae is an essential virulence factor for infection in Nile tilapia (Oreochromis niloticus Linn.)

Streptococcus agalactiae (Group B Streptococcus, GBS) is associated with diverse diseases in aquatic animals. The capsule polysaccharide (CPS) encoded by the cps gene cluster is the major virulence factor of S. agalactiae; however, limited information is available regarding the pathogenic role of the CPS of serotype Ia piscine GBS strains in fish. Here, a non-encapsulated mutant (Δcps) was constructed by insertional mutagenesis of the cps gene cluster. Mutant pathogenicity was evaluated in vitro based on the killing of whole blood from tilapia, in vivo infections, measuring mutant survival in tilapia spleen tissues and pathological analysis. Compared to wild-type (WT) GBS strain, the Δcps mutant had lower resistance to fresh tilapia whole blood in vitro (p < 0.01), and more easily cleared in tilapia spleen tissue, and was highly attenuated in tilapia and zebrafish. Additionally, compared to the Δcps mutant, numerous GBS strains and severe tissue necrosis were observed in the tilapia spleen tissue infected with WT strains. These results indicated that the CPS is essential for GBS pathogenicity and may serve as a target for attenuation in vaccine development. Gaining a better understanding of the role, the GBS pathogenicity in fish will provide insight into related pathogenesis and host-pathogen interactions.

Virulence regulation of cel-EIIB protein mediated PTS system in Streptococcus agalactiae in Nile tilapia

Streptococcus agalactiae is a major pathogen of tilapia causing significant economic losses for the global aquatic industry yearly. To elucidate the role of cel-EIIB protein-mediated phosphotransferase systems (PTS) in the virulence regulation of S. agalactiae, cel-EIIB gene deletion in a virulent strain THN0901 was achieved by homologous recombination. The cellobiose utilization of △cel-EIIB strain was significantly decreased relative to S.a.THN0901 strain incubating in LB with 10 mg/ml cellobiose (p < 0.05). The biofilm formation ability of △cel-EIIB strain was also significantly decreased when cultured in BHI medium (p < 0.05). Under a lower infection dose, the accumulative mortality of tilapia caused by △cel-EIIB strain was dramatically decreased (20%), of which S.a.THN0901 strain and △cel-EIIB::i strain were 53.33% and 50%, respectively. The competition experience using tilapia model indicated the invasion and colonization ability of △cel-EIIB strain was significantly weaker than that of S.a.THN0901 strain (p < 0.05). Compared to △cel-EIIB::i strain, the mRNA expression of csrS, csrR, rgfA, rgfC, bgrR and bgrS was significantly downregulated in △cel-EIIB strain (p < 0.05). In conclusion, cel-EIIB protein-mediated cel-PTS not only contributes to biofilm formation and virulence regulation, but also plays an important role in the invasion and colonization of S. agalactiae.

Characterization of bacteriophage HN48 and its protective effects in Nile tilapia Oreochromis niloticus against Streptococcus agalactiae infections

Streptococcus agalactiae is a causative agent responsible for massive mortalities of tilapia that has led to catastrophic losses to tilapia culture globally. Bacteriophages represent a new class of antimicrobials against bacteria. In this study, we characterized the bacteriophage HN48, which formed small and round-transparent plaques on a double-layer plate. With a hexagonal head and a long tail, this phage may belong to the Caudovirales according to the International Committee on Taxonomy of Viruses. HN48 was found to have a relatively wide and highly specific host range, to be sensitive to high temperature (60-80°C) and low pH (3-5), and to be relatively stable at alkaline pH (8-10). Intraperitoneal injection with HN48 had no adverse effects on tilapia and effectively inactivated the bacteria in the kidney. Fish that received phage therapy had 60% ± 3.3% survival rates and a delayed mean death time of about 3 days when compared to the control group. To the best of knowledge, this is the first study of tilapia streptococcal phage. Overall, the results indicated that phage HN48 could prevent tilapia from experimental S. agalactiae infection, suggesting it has the potential to control this disease.

Roles of water quality and disinfectant application on inactivation of fish pathogenic Streptococcus agalactiae with povidone iodine, quaternary ammonium compounds and glutaraldehyde

Streptococcosis is an important bacterial disease in Nile tilapia causing severe economic losses to tilapia aquaculture worldwide. The effects of water quality (low- [LS] and high-level [HS] soiling, to mimic clean or dirty surface conditions and temperatures) and disinfectant application (diluted concentrations and exposure time) were characterized on the inactivation of Streptococcus agalactiae isolated from diseased tilapia. Five isolates were tested against three commercial disinfectant products with the main ingredients being povidone iodine (Anidine 100™; AD), benzalkonium chloride (Better BKC 80%™; BKC 80), and a mixture of quaternary ammonium compounds and glutaraldehyde (Chloraldehyde™; CR). CR demonstrated highest efficacy to S. agalactiae inactivation, followed by BKC 80 and AD, respectively. Higher-level soiling, low temperature, diluted concentrations and short exposure time all decreased the disinfectant efficacy. CR and BKC 80 provided more than 5-log inactivation at 1-min exposure at 20°C under HS conditions, and also with ten-fold-diluted concentrations at 60-min exposure time at 30°C. However, AD required 10-min exposure to effectively remove bacteria under LS conditions at 30°C. The results could facilitate aquaculture management planning that leads to operating cost reductions and improvements in biosecurity.

Epizootics of Streptococcus agalactiae infection in captive rays from Queensland, Australia

The aim of this study was to describe two epizootics of high mortalities from infection with Streptococcus agalactiae, occurring in captive rays held in a marine display aquarium in south-east Queensland, Australia, in 2009 and 2010. Five different species of rays were affected, including mangrove whiprays (Himantura granulata), estuary rays (Dasyatis fluviorum), eastern shovelnose rays (Aptychotrema rostrata), white-spotted eagle rays (Aetobatus narinari) and blue-spotted mask rays (Neotrygon kuhlii). This report describes the history of both epizootics including collection, quarantine and husbandry of rays, the disease epizootics, clinico-pathological features of the disease, antimicrobial therapy, autogenous vaccine production, and laboratory studies including clinical and histopathology, bacteriology, PCR, molecular serotyping and sequencing of the bacterium S. agalactiae.