Streptococcus agalactiae and Streptococcus difficile 16S-23S intergenic rDNA: genetic homogeneity and species-specific PCR

Supervivencia observada en tres familias de tilapia del Nilo (Oreochromis niloticus) infectadas con Streptococcus agalactiae

La estreptococosis es una de las principales enfermedades en los peces de agua dulce que causa altas tasas de mortalidad. El objetivo de este estudio fue evaluar la respuesta en la supervivencia a la infección por Streptococcus agalactiae en tres familias de tilapia. El experimento se llevó a cabo en el Laboratorio de Enfermedades de los Peces de la Universidad Federal de Lavras. Se utilizaron peces con un peso de 93,7 ± 5,4 g de tres familias diferentes (FA, FB y FC). Se utilizaron 36 peces en cada unidad experimental, inoculados intraperitonealmente con 107 UFC/mL de Streptococcus agalactiae por peces y un grupo control por familia con 9 peces con 1 mL de caldo BHI (Infusión Cerebro Corazón) evaluados durante 15 días. No hubo mortalidad del grupo control. Se observó la presencia de exoftalmia, coloración oscura en todo el cuerpo, letargo y dilatación abdo­minal antes de la muerte en las tres familias evaluadas expuestas al patógeno. El estimador no paramétrico de Kaplan-Meier se utilizó para observar las curvas de supervivencia. Durante los 15 días del desafío, el tiempo promedio de supervivencia de un individuo en las familias FA, FB y FC fue de 9,4; 6,90 y 8,14 días, respectivamente. Pruebas de Log-rank y Peto & Peto para evaluar la diferencia entre las curvas de supervivencia arrojaron que no hubo diferencias significativas entre las familias evaluadas (P=0,08 y P= 0,09), respectivamente.

Systemic Streptococcus agalactiae infection with meningo-ventriculitis in a Linnaeus's two-toed sloth (Choloepus didactylus)

A captive male Linnaeus's two-toed sloth died without any obvious clinical signs. At necropsy, multifocal ulceration at the lumbar and perianal skin, mitral valve vegetation, and multifocal hemorrhage in the leptomeninges were observed. Histopathologically, suppurative meningo-ventriculitis, dermatitis, and endocarditis characterized by severe neutrophilic infiltration were observed. Gram-positive cocci arranged in pairs or chains were present in these inflammatory lesions. Streptococcus agalactiae gene was detected in the skin, heart, and brain tissues by PCR and sequence analysis. These findings may indicate that S. agalactiae primarily infected the skin and then caused septicemia resulting in endocarditis and meningo-ventriculitis. The present case suggests that S. agalactiae infection can cause severe meningo-ventriculitis in two-toed sloth without any specific clinical signs.

Validation of IgY for the diagnosis of Streptococcus agalactiae-caused endocarditis and bacterial meningitis in Nile tilapia (Oreochromis niloticus)

Streptococcus agalactiae (Sta), which belongs to Lancefield group B, causes sepsis, endocarditis and bacterial meningitis in human neonates and Nile tilapia. Because the pathophysiology of Sta infection is partially similar in both species, the identification of biomarkers for the diagnosis and study of this disease is of importance for human and animal health. Therefore, in the present study, we produced an immunoglobulin Y (IgY) by immunizing laying hens with Sta proteins and evaluated its ability to detect Sta in paraffinized tilapia brain and cardiac tissue by direct immunofluorescence (IMF) and indirect immunohistochemistry (IHC). The IgY produced was effective in the diagnosis of Sta infection in Nile tilapia, justifying the use of this species as a biomodel for the study of this disease.

Eutrophication, Ammonia Intoxication, and Infectious Diseases: Interdisciplinary Factors of Mass Mortalities in Cultured Nile Tilapia

The present study was designed to assess the possible causes of the mass mortalities of Nile Tilapia Oreochromis niloticus at El-Behera Governorate, Egypt, in relationship to environmental and microbiotic factors. Water samples were collected from fish farms at different locations and from Lake Edku to analyze water temperature, water pH, salinity, biological oxygen demand, dissolved oxygen, total ammonia nitrogen, and un-ionized ammonia. A number of moribund and freshly dead fish were sampled and submitted to our laboratory for microbiological, molecular, and histopathological examination. Water analysis of the fish farms revealed noticeable increases in the previously mentioned physicochemical parameters. Clinical examinations of moribund fish showed severe gill rot and massive external and internal hemorrhages. Ordinary and molecular laboratory findings confirmed the presence of Branchiomyces sp. in gill tissue and mixed bacterial fish pathogens (Streptococcus agalactiae, Vibrio alginolyticus, V. parahaemolyticus, Pseudomonas anguilliseptica, and P. aeruginosa) in visceral organs. The histopathological and transmission electron microscopic examinations revealed severe necrosis of gill filaments and blockage of branchial blood vessels and lamellar capillaries with Branchiomyces sp. hyphae and spores mixed with different shapes of bacteria. Severe inflammations were detected in liver, kidney, heart, and brain tissues. Ultimately, we can conclude that the syndrome of mass fish kills in this area is a consequence of ecological damage to the aquatic environment, which is mainly related to natural and anthropogenic factors, as well as to the presence of infectious agents. Received September 30, 2015; accepted April 12, 2016.

Development of a novel PCR assay based on the 16S-23S rRNA internal transcribed spacer region for the detection of Lactococcus garvieae

Lactococcus garvieae is recognized as an emerging pathogen in fish. Several PCR-based methods have been developed for the detection and identification of L. garvieae; however, the sensitivity of these methods is still in question regarding the discrimination of this organism from other closely related species. Two primers, ITSLg30F and ITSLg319R, were designed from the sequence in the 16S-23S internal transcribed spacer (ITS) region and used for the specific detection of L. garvieae. L. garvieae strains including fish isolates were positive by this method. In contrast, previously developed PCR methods showed false-positive results with non-L. garvieae species. Our results indicate that a PCR method using the newly designed ITS primer set provides a sensitive and efficient tool for the detection of L. garvieae in fish and aquaculture environments.

A one-step reaction for the rapid identification of Lactobacillus mindensis, Lactobacillus panis, Lactobacillus paralimentarius, Lactobacillus pontis and Lactobacillus frumenti using oligonucleotide primers designed from the 16S-23S rRNA intergenic sequences

AIMS

Species-specific primers targeting the 16S-23S ribosomal DNA (rDNA) intergenic spacer region (ISR) were designed to rapidly discriminate between Lactobacillus mindensis, Lactobacillus panis, Lactobacillus paralimentarius, Lactobacillus pontis and Lactobacillus frumenti species recently isolated from French sourdough.

METHODS AND RESULTS

The 16S-23S ISRs were amplified using primers 16S/p2 and 23S/p7, which anneal to positions 1388-1406 of the 16S rRNA gene and to positions 207-189 of the 23S rRNA gene respectively, Escherichia coli numbering (GenBank accession number V00331). Clone libraries of the resulting amplicons were constructed using a pCR2.1 TA cloning kit and sequenced. Species-specific primers were designed based on the sequences obtained and were used to amplify the 16S-23S ISR in the Lactobacillus species considered. For all of them, two PCR amplicons, designated as small ISR (S-ISR) and large ISR (L-ISR), were obtained. The L-ISR is composed of the corresponding S-ISR, interrupted by a sequence containing tRNA(Ile) and tRNA(Ala) genes. Based on these sequences, species-specific primers were designed and proved to identify accurately the species considered among 30 reference Lactobacillus species tested.

CONCLUSIONS

Designed species-specific primers enable a rapid and accurate identification of L. mindensis, L. paralimentarius, L. panis, L. pontis and L. frumenti species among other lactobacilli.

SIGNIFICANCE AND IMPACT OF THE STUDY

The proposed method provides a powerful and convenient means of rapidly identifying some sourdough lactobacilli, which could be of help in large starter culture surveys.

Risk factors for group B streptococcal colonization: potential for different transmission systems by capsular type

PURPOSE

Group B Streptococcus (GBS) is a common inhabitant of the bowel and vaginal flora, with known transmission routes including sexual contact and vertical transmission from mother to infant. Food-borne transmission is also possible, as GBS is a known fish and bovine pathogen. We conducted a prospective cohort study in order to identify risk factors for acquisition.

METHODS

We identified risk factors for GBS acquisition among college women (n = 129) and men (n = 128) followed at 3-week intervals for 3 months.

RESULTS

A doubling in sex acts significantly increased incidence of GBS capsular type V by 80% (95% confidence interval [CI]: 1.19, 2.58), and other non-Ia or -Ib types combined by 40% (95% CI: 1.00, 2.06; incidence of capsular type Ia (odds ratio [OR] = 1.2; 95% CI: 0.71, 1.88; p = 0.57) and Ib (OR = 1.5, 95% CI: 0.75, 2.86; p = 0.27) were elevated, although not significantly. After adjustment for sexual activity and sexual history, gender, and eating venue, fish consumption increased risk of acquiring capsular types Ia and Ib combined 7.3 fold (95% CI: 2.34, 19.50), but not of acquiring other capsular types. Beef and milk were not associated with GBS incidence.

CONCLUSIONS

Different GBS capsular types may have different transmission routes.

Diversity of lactic acid bacteria associated with fish and the fish farm environment, established by amplified rRNA gene restriction analysis

Lactic acid bacteria have become a major source of concern for aquaculture in recent decades. In addition to true pathogenic species of worldwide significance, such as Streptococcus iniae and Lactococcus garvieae, several species have been reported to produce occasional fish mortalities in limited geographic areas, and many unidentifiable or ill-defined isolates are regularly isolated from fish or fish products. To clarify the nature and prevalence of different fish-associated bacteria belonging to the lactic acid bacterium group, a collection of 57 isolates of different origins was studied and compared with a set of 22 type strains, using amplified rRNA gene restriction analysis (ARDRA). Twelve distinct clusters were delineated on the basis of ARDRA profiles and were confirmed by sequencing of sodA and 16S rRNA genes. These clusters included the following: Lactococcus raffinolactis, L. garvieae, Lactococcus l., S. iniae, S. dysgalactiae, S. parauberis, S. agalactiae, Carnobacterium spp., the Enterococcus "faecium" group, a heterogeneous Enterococcus-like cluster comprising indiscernible representatives of Vagococcus fluvialis or the recently recognized V. carniphilus, V. salmoninarum, and Aerococcus spp. Interestingly, the L. lactis and L. raffinolactis clusters appeared to include many commensals of fish, so opportunistic infections caused by these species cannot be disregarded. The significance for fish populations and fish food processing of three or four genetic clusters of uncertain or complex definition, namely, Aerococcus and Enterococcus clusters, should be established more accurately.

Isolation and characterization of Streptococcus sp. from diseased flounder (Paralichthys olivaceus) in Jeju Island

Streptococcus sp. is gram-positive coccus that causes streptococcal infections in fish due to intensification of aquaculture and caused significant economic losses in fish farm industry. A streptococcal infection occurred from cultured diseased olive flounder (Paralichthys olivaceus) in May, 2005 at a fish farm in Jeju Island, Korea. The diseased flounder exhibited bilateral exophthalmic eyes and rotten gills; water temperature was 16~18℃ when samples were collected. Of the 22 fish samples collected, 3 samples were identified as Lactococcus garvieae and 18 samples were identified as Streptococcus parauberis by culture-based, biochemical test. Serological methods such as slide agglutination, hemolysis and antimicrobial susceptibility test were also used as well as multiplex PCR-based method to simultaneously detect and confirm the pathogens involved in the infection. S. parauberis and L. garvieae have a target region of 700 and 1100 bp., respectively. One fish sample was not identified because of the difference in the different biochemical and serological tests and was negative in PCR assay. In the present study, it showed that S. parauberis was the dominant species that caused streptococcosis in the cultured diseased flounder.

Rapid differentiation and in situ detection of 16 sourdough lactobacillus species by multiplex PCR

A two-step multiplex PCR-based method was designed for the rapid detection of 16 species of lactobacilli known to be commonly present in sourdough. The first step of multiplex PCR was developed with a mixture of group-specific primers, while the second step included three multiplex PCR assays with a mixture of species-specific primers. Primers were derived from sequences that specify the 16S rRNA, the 16S-23S rRNA intergenic spacer region, and part of the 23S rRNA gene. The primer pairs designed were shown to exclusively amplify the targeted rrn operon fragment of the corresponding species. Due to the reliability of simultaneously identifying Lactobacillus plantarum, Lactobacillus pentosus, and Lactobacillus paraplantarum, a previously described multiplex PCR method employing recA gene-derived primers was included in the multiplex PCR system. The combination of a newly developed, quick bacterial DNA extraction method from sourdough and this multiplex PCR assay allows the rapid in situ detection of several sourdough-associated lactobacilli, including the recently described species Lactobacillus rossii, and thus represents a very useful alternative to culture-based methodologies.

High genetic similarity of Streptococcus agalactiae and Streptococcus difficilis: S. difficilis Eldar et al. 1995 is a later synonym of S. agalactiae Lehmann and Neumann 1896 (Approved Lists 1980)

The genetic relationship betweenStreptococcus agalactiaeandStreptococcus difficiliswas studied.S. difficiliswas originally described as serologically non-typable but was later reported to be a group B, type Ib streptococcus. Upon comparative analysis of five gene sequences, it was found thatS. agalactiaeandS. difficilisare closely related. Sequence similarity values between these two species were 100·0 % for 16S rRNA, 99·6 % forgyrB, 98·6 % forsodA, 99·5 % forgyrAand 99·8 % forparCgenes. These data strongly suggest thatS. agalactiaeandS. difficilisare synonyms. The biochemical characteristics ofS. difficilis, which differ slightly from those of typicalS. agalactiae, are similar to those of other group B, type Ib streptococci isolated from fish and frogs. Whole genome DNA–DNA hybridization values between the type strains of both species were greater than 78·6 %. On the basis of these data, it is proposed thatS. difficilisis a later synonym ofS. agalactiae.

Multiplex PCR assay for detection of bacterial pathogens associated with warm-water Streptococcosis in fish

A multiplex PCR-based method was designed for the simultaneous detection of the main pathogens involved in warm-water streptococcosis in fish (Streptococcus iniae, Streptococcus difficilis, Streptococcus parauberis, and Lactococcus garvieae). Each of the four pairs of oligonucleotide primers exclusively amplified the targeted gene of the specific microorganism. The sensitivity of the multiplex PCR using purified DNA was 25 pg for S. iniae, 12.5 pg for S. difficilis, 50 pg for S. parauberis, and 30 pg for L. garvieae. The multiplex PCR assay was useful for the specific detection of the four species of bacteria not only in pure culture but also in inoculated fish tissue homogenates and naturally infected fish. Therefore, this method could be a useful alternative to the culture-based method for the routine diagnosis of warm-water streptococcal infections in fish.

Development of a PCR assay for Streptococcus iniae based on the lactate oxidase (lctO) gene with potential diagnostic value

Streptococcus iniae is a well-known pathogen of both fish and humans that is difficult to identify by conventional biochemical tests. A PCR assay based on the lactate oxidase (lctO) gene of S. iniae was developed for the rapid and specific detection and identification of this pathogen from different sources. The PCR assay had a detection limit of 62-31 cells, and 25 pg of DNA per PCR reaction mixture. The PCR was also effective in detecting the bacterium from inoculated tissue homogenates, suggesting its potential use for a rapid and accurate diagnosis of S. iniae infections.

rpoB gene sequence-based identification of aerobic Gram-positive cocci of the genera Streptococcus, Enterococcus, Gemella, Abiotrophia, and Granulicatella

We developed a new molecular tool based on rpoB gene (encoding the beta subunit of RNA polymerase) sequencing to identify streptococci. We first sequenced the complete rpoB gene for Streptococcus anginosus, S. equinus, and Abiotrophia defectiva. Sequences were aligned with these of S. pyogenes, S. agalactiae, and S. pneumoniae available in GenBank. Using an in-house analysis program (SVARAP), we identified a 740-bp variable region surrounded by conserved, 20-bp zones and, by using these conserved zones as PCR primer targets, we amplified and sequenced this variable region in an additional 30 Streptococcus, Enterococcus, Gemella, Granulicatella, and Abiotrophia species. This region exhibited 71.2 to 99.3% interspecies homology. We therefore applied our identification system by PCR amplification and sequencing to a collection of 102 streptococci and 60 bacterial isolates belonging to other genera. Amplicons were obtained in streptococci and Bacillus cereus, and sequencing allowed us to make a correct identification of streptococci. Molecular signatures were determined for the discrimination of closely related species within the S. pneumoniae-S. oralis-S. mitis group and the S. agalactiae-S. difficile group. These signatures allowed us to design a S. pneumoniae-specific PCR and sequencing primer pair.

Inter- and intraspecies variations of the 16S-23S rDNA intergenic spacer region of various streptococcal species

The 16S-23S rDNA intergenic spacer regions (ISR) of different streptococcal species and subspecies were amplified with primers derived from the highly conserved flanking regions of the 16S rRNA and 23S rRNA genes. The single sized amplicons showed a uniform pattern for S. agalactiae, S. dysgalactiae subsp. dysgalactiae (serogroup C), S. dysgalactiae subsp. equisimilis (serogroup G), S. dysgalactiae subsp. dysgalactiae (serogroup L), S. canis, S. phocae, S. uberis, S. parauberis, S. pyogenes and S. equi subsp. equi, respectively. The amplicons of S. equi subsp. zooepidemicus, S. porcinus and S. suis appeared with 3, 5 and 3 different sizes, respectively. ISR of selected strains of each species or subspecies investigated were sequenced and multiple aligned. This allowed a separation of ISR into regions, with 7 regions for S. agalactiae, S. dysgalactiae subsp. dysgalactiae (serogroup C), S. dysgalactiae subsp. equisimilis (serogroup G), S. dysgalactiae subsp. dysgalactiae (serogroup L), S. canis, S. phocae, S. pyogenes and S. suis, 8 regions for S. uberis and S. parauberis and mostly 9 regions for S. equi subsp. equi, S. equi subsp. zooepidemicus and S. porcinus. Region 4, encoding the transfer RNA for alanine (tRNA(Ala)), was present and identical for all isolates investigated. The size and sequence of ISR appears to be a unique marker for streptococci of various species and subspecies and could be used for bacterial identification. In addition the size and sequence variations of ISR of S. equi subsp. zooepidemicus, S. porcinus and S. suis allows a molecular typing of isolates of these species possibly useful in epidemiological aspects.