Quantitative detection of streptococcosis infection in dead samples of Nile Tilapia (Oreochromis niloticus)

AIMS

The aims of the study were to evaluate whether epidemic strains of streptococcosis infected tilapia can be isolated and identified from dead fish for epidemiological investigation.

METHODS AND RESULTS

Firstly, tilapias were inoculated with a lethal dose (1 × 10⁸  CFU per fish) of Streptococcus agalactiae and brain tissues were harvested for bacteriological examination and qPCR assay 3, 12, 24 and 48 h postdeath. Streptococcus agalactiae was the only dominant bacterium cultivated on the brain heart infusion (BHI) plate and the bacterial load was about 10⁷  CFU per mg. Secondly, tilapia were killed via ice water shock and immersed either in an aquarium containing 2·27 × 10⁴  CFU per ml S. agalactiae or in a pond with streptococcosis outbreak. Streptococcus agalactiae failed to grow on the BHI plate but were identified (<6 × 10²  CFU per mg) via qPCR assay. Finally, an epidemiological investigation of streptococcosis was conducted in the main tilapia breeding areas of South China. A total of 387 tilapia samples were collected including 24 suspected healthy, 35 moribund and 328 dead fish. The achieved detection rates were 0, 100 and 94·82% via bacteriological examination, and 0, 100 and 98·78% via qPCR assay respectively. The concentration of S. agalactiae in brain tissues ranged between 10⁵ and 10⁷  CFU per mg.

CONCLUSIONS

Streptococcus agalactiae can survive for 48 h in the brain of dead fish. Dead tilapia can be a useful alternative for epidemiological investigation when the diagnostic analysis of moribund fish is unavailable or impractical.

SIGNIFICANCE AND IMPACT OF THE STUDY

This detection method expands the sampling range, reduces the difficulty of sample collection and improves efficiency. Consequently, this method provides an alternative for epidemiological investigation of tilapia streptococcosis.

Genotypes and virulence genes in group B streptococcus isolated in the maternity hospital, Kuwait

OBJECTIVE

To characterize group B streptococcus (GBS) isolates obtained from patients at the Maternity Hospital in Kuwait for their genotypes and carriage of virulence genes.

MATERIALS AND METHODS

A total of 154 GBS isolates were obtained from July 1 to October 31, 2007, from vaginal swabs (n = 95), urine (n = 46), blood (n = 4) and miscellaneous sources (n = 9). Genotypes were obtained by pulsed-field gel electrophoresis (PFGE), following digestion with SmaI or EagI restriction enzymes. PCR was used to screen for the carriage of virulence genes including: surface protein of group B streptococcus (spb1), secreted fibrinogen-binding protein (fbsB), C5a peptidase (scpB), laminin-binding protein (lmb), α- (bca) and β-subunits of the C protein (bac), resistance to protease immunity protein (rib), and phage-associated gene (pag); regulatory protein (dltR), and toxins CAMP factor (cfb), hyaluronidase (hylB) and superoxide dismutase (sodA).

RESULTS

PFGE defined 14 genotypes differentiating isolates with the same serotypes into different genetic backgrounds. All isolates contained genes for virulence factors. However, cfb (99.4%), scpB (88.3%), lmb (88.3%), bca (57.8%), sodA (55.8%) and dltR (53.9%) were the common virulence genes. In total, 144 (90.3%) of the isolates contained 3 or more virulence genes. However, while cfb, lmb and scpB occurred in all genotypes, others occurred in some but not in all genotypes.

CONCLUSIONS

GBS isolates obtained at the Maternity Hospital, Kuwait, belonged to diverse genetic backgrounds with the majority carrying multiple virulence genes.

Multiplex polymerase chain reaction for identification and differentiation of Streptococcus equi subsp. zooepidemicus and Streptococcus equi subsp. equi

The closely related streptococcal species Streptococcus equi subsp. zooepidemicus and S. equi subsp. equi were identified by polymerase chain reaction using oligonucleotide primers designed according to species-specific parts of the superoxide dismutase A encoding gene sodA. A further differentiation of both subspecies could be performed by amplification of the genes seeH and seeI encoding the exotoxins SeeH and SeeI, respectively, which could be detected for S. equi subsp. equi but not for S. equi subsp. zooepidemicus. A further simplification of the identification and differentiation of both subspecies was conducted by sodA-seeI multiplex polymerase chain reaction.

Polymerase chain reaction mediated identification of Streptococcus uberis and Streptococcus parauberis using species-specific sequences of the genes encoding superoxide dismutase A and chaperonin 60*

Streptococcus uberis, a well-known bacterial pathogen associated with bovine mastitis, appears to be biochemically and serologically almost indistinguishable from the closely related species Streptococcus parauberis. In the present study, species-specific oligonucleotide primers were designed using internal parts of the genes sodA, encoding superoxide dismutase A, and cpn60 encoding chaperonin 60 of S. uberis and S. parauberis, respectively. The two oligonucleotide primer pairs allowed a rapid and reliable PCR-mediated identification and differentiation of both species. These studies, performed with S. uberis and S. parauberis reference cultures and clinical isolates from routine diagnostics, revealed that the occurrence of S. parauberis as causative agent of bovine mastitis appears to be rare. In addition the sodA and cpn60 sequence data confirmed that both species could taxonomically be classified to the pyogenic group of genus Streptococcus.

Identification of Streptococcus dysgalactiae strains of Lancefield's group C, G and L by polymerase chain reaction

Streptococcus dysgalactiae serogroup C, G and L strains were investigated by polymerase chain reaction (PCR) using oligonucleotide primers designed according to species-specific parts of the 16S-23S rDNA intergenic spacer region. The oligonucleotide primers with specificity for the 16S-23S rDNA intergenic spacer region allowed a correct identification of all S. dysgalactiae serogroups C, G and L strains investigated. No cross-reactivities could be observed with any of the control strains indicating the usefulness of PCR-technology to identify the serologically heterogeneous species S. dysgalactiae.

Molecular characterization of phenotypically CAMP-negative Streptococcus agalactiae isolated from bovine mastitis

In the present study three phenotypically CAMP-negative Streptococcus agalactiae, isolated from three cows with mastitis, were characterized by molecular analysis. An identification of the S. agalactiae was performed by conventional methods and by PCR amplification of species specific parts of the 16S rRNA gene and the 16S-23S rDNA intergenic spacer region. In addition all three phenotypically CAMP-negative isolates harboured a normal sized CAMP-factor encoding cfb gene indicating a reduced expression of CAMP-factor or a gene defect elsewhere along the pathway of expression. The clonal identity of the three isolates could be demonstrated by macrorestriction analysis of their chromosomal DNA.

Studies on Streptococcus agalactiae isolated from bovine mastitis in Indonesia

All 83 bacterial strains isolated from seven farms in three areas of the island of Java in Indonesia investigated in the present study could be identified as Streptococcus agalactiae. Identification was performed by cultural, biochemical and serological properties and by polymerase chain reaction amplification of species-specific parts of the gene encoding the 16S rRNA, the 16S-23S rDNA intergenic spacer region and the CAMP factor (cfb) gene. All isolates were unpigmented. almost all of the isolates had the serotype pattern II/X. Despite these similarities a macrorestriction analysis of the chromosomal DNA of the bacteria revealed no significant homologies of the DNA-fingerprints of the S. agalactiae from the various areas. This last finding might possibly indicate that a single ancestral unpigmented serotype II/X S. agalactiae clone was responsible for the mastitis situation on Java and had evolved separately in the various farms and regions.