Genetic diversity of geographically distinct Streptococcus dysgalactiae isolates from fish

Coinfections of Aeromonas spp., Enterococcus faecalis, and Vibrio alginolyticus isolated from farmed Nile tilapia and African catfish in Egypt, with an emphasis on poor water quality

The high mortality rate among Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) polycultured in earthen ponds in Manzala, Egypt, was investigated. Mortality has been linked to poor water quality parameters accompanied with bacterial infections. Moribund farmed fishes exhibited general septicemic signs. Fish from both species (45 each) were sampled and analyzed bacteriologically. Vibrio alginolyticus (32.3%), Enterococcus faecalis (29.4%), Aeromonas caviae (23.5%), and A. veronii (14.7%) were isolated from moribund fishes using selective media and further identified by biochemical tests. 16S rRNA gene sequencing and phylogenetic analysis confirmed the identity of these isolates. Experimental infection of O. niloticus with different bacterial isolates resulted in clinical signs of hemorrhagic septicemia and mortality rates of 80%, 60%, 40%, and 30%, respectively, for E. faecalis, A. veronii, V. alginolyticus, and A. caviae. Water parameter analysis revealed marked divergence from typical values. In addition, different bacterial isolates (including Staphylococcus sciuri, S. aureus, E. faecalis, A. veronii, A. caviae, and V. alginolyticus) were identified and isolated from water samples. BLAST analysis of water bacterial isolates displayed a 100% similarity score with relevant fish isolates, indicating that the water was the likely source of infections. Histopathological examination revealed signs of bacterial infection in both fish species. In addition, common circulatory and degenerative changes with melanophore aggregation, and lymphocytic depletion in hematopoietic organs were recorded.

Streptococcus, Centrocestus formosanus and Myxobolus tilapiae concurrent infections in farmed Nile tilapia (Oreochromis niloticus)

Stress triggered concurrent microbial/parasitic infections are prevalent in earthen pond based farmed Nile tilapia Oreochromis niloticus. In the current study, a total of thirty five O. niloticus were collected from a commercial fish farm with a history of severe mortalities at Port Said, Egypt. Nile tilapia samples were subjected to bacteriological, parasitological and pathological examinations. Twenty one Enterococcus fecalis and 15 Streptococcus agalactiae isolates were presumptively identified utilizing the semi-automated API 20 Strept test kit. The identities of the retrieved bacteria were confirmed by the sequencing of 16 S rRNA gene. Moribund O. niloticus were found to be heavily infected by one or both of Centrocestus formosanus encysted metacercariae (EMC) and/or Myxobolus tilapiae spores presenting a unique form of synergistic and/or symbiotic relationship. The identities of both parasites were confirmed through morphological and molecular characterization. Variable circulatory, degenerative, necrotic and proliferative changes were also noticed in hematopoietic organs. Interestingly, multiple myxobolus spores and EMC were noticed in some histological sections. It was obvious that the current concurrent bacterial and parasitic infections are triggered by the deleterious effects of some stressing environmental conditions. The unfavorable climatic conditions (high temperature and high relative humidity) recorded at the surge of mortalities are probable predisposing stress factors.

Molecular characterization and pathogenicity of Francisella noatunensis subsp. orientalis isolated from cultured tilapia (Oreochromis sp.) in Taiwan

Francisella noatunensis subsp. orientalis is a causative agent of systemic granulomatous disease in tilapia. The present study was designed to understand the genetic and phenotypic diversities among Taiwanese Fno isolates obtained from tilapia (n = 17) and green Texas cichlid (Herichthys cyanoguttatus) (n = 1). The enzymatic profiles of the isolates were studied using the API ZYM system. Phylogenetic tree analysis of the 16S rRNA and housekeeping gene and pulsed-field gel electrophoresis (PFGE) were carried out to determine the genotypic characters of all isolates. The phylogenetic tree showed similarity of 99%-100% nucleotide sequences of 16S rRNA and housekeeping genes compared to the Fno references genes from GenBank database. Comparatively, the results revealed an identical profile of enzymatic and PFGE pattern which was distincted from that of F. philomiragia. To understand the pathogenicity, the isolates were intraperitoneal injected to tilapia the gross lesions were observed concomitant with natural outbreak. Median lethal dose upon Nile tilapia and red tilapia were 9.06 × 10³ CFU/fish and 2.08 × 10² CFU/fish, respectively. Thus, our data provide understanding the epidemiology of Taiwanese Fno isolates, and help in development of future control and prevention.

Identification of protective protein antigens for vaccination against Streptococcus dysgalactiae in cobia (Rachycentron canadum)

Streptococcus dysgalactiae is considered a causative agent of severe infection and economic loss for the cobia industry in Taiwan. In this study, protective antigens of this pathogenic bacterium were identified and screened in cobia (Rachycentron canadum). Outer surface proteins (OMPs) of this pathogen were extracted using mutanolysin digestion. Immunogenic targets were detected by western blot and then subjected to peptide sequencing using NanoLC-MS/MS. Two surface proteins, namely phosphoenolpyruvate protein phosphotransferase (PtsA) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), showed strong reactions with cobia antisera against S. dysgalactiae. Recombinant proteins were produced in Escherichia coli cells and their protective efficacies were investigated in cobia. Fish immunised with recombinant proteins, rPtsA + ISA (ISA 763 AVG) and rGAPDH + ISA, elicited higher levels of specific antibody responses against the recombinant proteins and had high levels of lysozyme activity. Notably, vaccinated fish were protected from lethal challenge with relative percentage of survival (RPS) values for rPtsA + ISA and rGAPDH + ISA groups being 91.67% and 83.33%, while 0% RPS value was found in both ISA injected and control groups. The results presented in the study demonstrate that the GAPDH and PtsA are promising vaccine candidates for preventing S. dysgalactiae disease in cobia.

Septicemia due to Streptococcus dysgalactiae subspecies dysgalactiae in vampire bats (Desmodus rotundus)

Beta-hemolytic Streptococcus dysgalactiae is a well-known pathogen for a wide range of animals and humans. Two subspecies are recognized: (i) equisimilis, associated to disease in horses and humans, and (ii) dysgalactiae mainly isolated from animal illness with only a few humans’ cases. This study describes the isolation and characterization of Streptococcus dysgalactiae subsp. dysgalactiae (SDSD) from vampire bats, maintained in captivity for research proposes. Animals presented neurologic, respiratory and gastroenteric symptoms and sudden death. Beta-hemolytic Gram-positive cocci were isolated in blood agar plates and further characterized as Lancefield group C. All isolates were identified as S. dysgalactiae by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry and subspecies dysgalactiae was confirmed by 16S rRNA sequencing and phylogenetic analysis. Genotyping through SE-ALFP resulted in three profiles (A1–A3) with one bat being infected by profiles A1 and A3. This is the first report of SDSD causing illness in bats and especially in Desmodus rotundus species.

Characterization and identification of streptococci from golden pompano in China

Streptococcal infections cause significant mortality and high economic losses in the fish farm industry worldwide, including in the culture of golden pompano Trachinotus ovatus L., a species gaining popularity in China. A total of 9 streptococcal strains were isolated from cage-cultured diseased golden pompano in Beihai, Zhanjing, and Shenzhen, China, between 2012 and 2014. Conventional and rapid identification systems were used to determine that the isolates were Streptococcus agalactiae, S. iniae, and S. dysgalactiae subsp. dysgalactiae. All isolates were gram-positive cocci cells in pairs or short-chain, non-motile, catalase negative, α or β hemolytic cocci. The results of multiplex PCR assays and 16S rRNA BLAST analysis also showed that the β hemolytic strains were S. agalactiae and S. iniae and the α hemolytic strain was S. dysgalactiae subsp. dysgalactiae, respectively. Pathogenicity assays revealed that S. agalactiae (lethal dose [LD50]: 6.38 × 10(4) CFU ml(-1)) was more virulent for golden pompano than S. iniae (LD50: 1.47 × 10(7) CFU ml(-1)) and S. dysgalactiae subsp. dysgalactiae (LD50: 2.57 × 10(6) CFU ml(-1)) when they were challenged by intraperiotoneal (i.p.) injection. The results of antibiotic susceptibility showed that all strains were extremely susceptible to cefradine, erythromycin, and cefotaxime but resistant to gentamicin, penicillin G, novobiocin, neomycin, ciprofloxacin, roxithromycin, furazolidone, enrofloxacin, norfloxacin, kanamycin, ampicillin, tetracycline, and vancomycin This is the first report of a phenomenon of golden pompano coinfection with S. agalactiae and S. iniae, which will contribute to the diagnosis and prevention of streptococcicosis.

Expression, genetic localization and phylogenic analysis of NAPlr in piscine Streptococcus dysgalactiae subspecies dysgalactiae isolates and their patterns of adherence

Streptococcus dysgalactiae, the long recognized mammalian pathogen, has currently received a major concern regarding fish bacterial infection. Adhesion to host epithelial cells and the presence of wall-associated plasminogen binding proteins are prerequisites to Streptococcus infection. This is the first study of the occurrence of nephritis-associated plasminogen-binding receptor (NAPlr) and α-enolase genes in piscine S. dysgalactiae subspecies dysgalactiae (SDSD) isolates. Further characterization of surface localized NAPlr of fish SDSD revealed a similar immune-reactive band of 43 KDa as that from porcine S. dysgalactiae subsp. equisimilis (SDSE). The phylogenetic analysis revealed that NAPlr of fish SDSD is more associated with those of mammalian SDSE and Streptococcus pyogenes rather than of other streptococci. Our findings warrant public attention to the possible implication of these virulence genes in dissemination of SDSD to different tissues of infected hosts and to get advantage to new niches. The SDSD adherence patterns were also studied to better understand their pathogenicity. The patterns of adherence of SDSD on two different cell lines showed a different pattern of adherence. Such difference gives an insight about the variance in host susceptibility to infection.