A novel phage-encoded endolysin EN534-C active against clinical strain Streptococcus agalactiae GBS.

Streptococcus agalactiae (Group B Streptococcus, GBS) is primarily known as a major neonatal pathogen. In adults, these bacteria often colonize the gastrointestinal and urogenital tracts. Treatment of infections using antibiotics is often complicated by recurrences caused by multi-resistant streptococci. Endolysin EN534 from prophage A2 of human isolate Streptococcus agalactiae KMB-534 has a modular structure consisting of two terminal catalytic domains, amidase_3 and CHAP, and one central binding domain, LysM. The EN534 gene was cloned into an expression vector, and the corresponding recombinant protein EN534-C was expressed in Escherichia coli in a soluble form and isolated by affinity chromatography. The lytic activity of this endolysin was tested on cell wall substrates from different GBS serotypes, B. subtilis, L. jensenii, and E. coli. The enzyme lysed streptococci, but not beneficial vaginal lactobacilli. The isolated protein is stable in a temperature range of 20-37 °C. Calcium ions enhanced the activity of the enzyme in the pH range from 5.0 to 8.0. The exolytic activity of EN534-C was observed by time-lapse fluorescence microscopy on a S. agalactiae CCM 6187 substrate. Recombinant endolysin EN534-C may have the potential to become an antimicrobial agent for the treatment of S. agalactiae infections.

Comparative transcriptome profiling reveals a mechanism of Streptococcus agalactiae resistance to florfenicol.

Florfenicol is widely used to control diseases in aquatic animals, and is used extensively to treat streptococcosis-caused by Streptococcus agalactiae-in the commercially important fish tilapia. There are known issues with the development of florfenicol resistance in Streptococcus agalactiae, but the underlying resistance mechanisms are not clear, a situation currently preventing optimal deployment of antibiotics. Here, we examined the induction of resistance by successively increasing the concentrations of florfenicol, and then used RNA-sequencing (RNA-Seq) to characterize changes in the transcriptomes of a florfenicol-resistant strain (H51-R) and a florfenicol-sensitive strain (H51-S). We obtained a total of 18,418,068 sequence reads in H51-R and 16,070,122 sequence reads in H51-S, from which a total of 1940 unigenes were assembled. In total, 376 unigenes were found to be differently expressed genes (DEGs). After florfenicol treatment, 181 genes were upregulated and 195 genes were downregulated. GO functional analysis of the DEGs indicated that the most strongly enriched GO terms included metabolic process (152 genes), catalytic activity (146), and binding (133), with terms including membrane, membrane part, and transporter activity also showing enrichment. KEGG pathway enrichment analysis highlighted that ribosomes were prominently involved in the transcriptional changes associated with florfenicol resistance. This study demonstrates that florfenicol treatment affects multiple biological functions of Streptococcus agalactiae, suggests that florfenicol resistance in Streptococcus agalactiae is closely related to the reduction of intracellular drug accumulation caused by ATP-binding cassette (ABC) transporters, and highlights the potential involvement of altered ribosomal function in florfenicol resistance.

Genetic and pathogenic difference between Streptococcus agalactiae serotype Ia fish and human isolates.

BACKGROUND: Streptococcus agalactiae (GBS) is a common pathogen to infect newborn, woman, the elderly, and immuno-compromised human and fish. 37 fish isolates and 554 human isolates of the GBS in 2007-2012 were investigated in serotypes, antibiotic susceptibility, genetic difference and pathogenicity to tilapia. RESULTS: PCR serotyping determined serotype Ia for all fish GBS isolates and only in 3.2 % (3-4.2 %) human isolates. For fish isolates, all consisted a plasmid less than 6 kb and belonged to ST7 type, which includes mainly pulsotypes I and Ia, with a difference in a deletion at the largest DNA fragment. These fish isolates were susceptible to all antimicrobials tested in 2007 and increased in non-susceptibility to penicillin, and resistance to clindamycin and ceftriaxone in 2011. Differing in pulsotype and lacking plasmid from fish isolates, human serotype Ia isolates were separated into eight pulsotypes II-IX. Main clone ST23 included pulsotypes II and IIa (50 %) and ST483 consisted of pulsotype III. Human serotype Ia isolates were all susceptible to ceftriaxone and penicillin and few were resistant to erythromycin, azithromycin, clindamycin, levofloxacin and moxifloxacine with the resistant rate of 20 % or less. Using tilapia to analyze the pathogenesis, fish isolates could cause more severe symptoms, including hemorrhage of the pectoral fin, hemorrhage of the gill, and viscous black and common scites, and mortality (>95 % for pulsotype I) than the human isolates (<30 %); however, the fish pulostype Ia isolate 912 with deletion caused less symptoms and the lowest mortality (<50 %) than pulsotype I isolates. CONCLUSION: Genetic, pathogenic, and antimicrobial differences demonstrate diverse origin of human and fish serotype Ia isolates. The pulsotype Ia of fish serotype Ia isolates may be used as vaccine strains to prevent the GBS infection in fish.

Conjugative transfer of resistance determinants among human and bovine Streptococcus agalactiae.

Streptococcus agalactiae (GBS) is a major source of human perinatal diseases and bovine mastitis. Erythromycin (Ery) and tetracycline (Tet) are usually employed for preventing human and bovine infections although resistance to such agents has become common among GBS strains. Ery and Tet resistance genes are usually carried by conjugative transposons (CTns) belonging to the Tn916 family, but their presence and transferability among GBS strains have not been totally explored. Here we evaluated the presence of Tet resistance genes (tetM and tetO) and CTns among Ery-resistant (Ery-R) and Ery-susceptible (Ery-S) GBS strains isolated from human and bovine sources; and analyzed the ability for transferring resistance determinants between strains from both origins. Tet resistance and int-Tn genes were more common among Ery-R when compared to Ery-S isolates. Conjugative transfer of all resistance genes detected among the GBS strains included in this study (ermA, ermB, mef, tetM and tetO), in frequencies between 1.10(-7) and 9.10(-7), was possible from bovine donor strains to human recipient strain, but not the other way around. This is, to our knowledge, the first report of in vitro conjugation of Ery and Tet resistance genes among GBS strains recovered from different hosts.

Conjugative transfer of resistance determinants among human and bovine Streptococcus agalactiae

Streptococcus agalactiae (GBS) is a major source of human perinatal diseases and bovine mastitis. Erythromycin (Ery) and tetracycline (Tet) are usually employed for preventing human and bovine infections although resistance to such agents has become common among GBS strains. Ery and Tet resistance genes are usually carried by conjugative transposons (CTns) belonging to the Tn916 family, but their presence and transferability among GBS strains have not been totally explored. Here we evaluated the presence of Tet resistance genes (tetM and tetO) and CTns among Ery-resistant (Ery-R) and Ery-susceptible (Ery-S) GBS strains isolated from human and bovine sources; and analyzed the ability for transferring resistance determinants between strains from both origins. Tet resistance and int-Tn genes were more common among Ery-R when compared to Ery-S isolates. Conjugative transfer of all resistance genes detected among the GBS strains included in this study (ermA, ermB, mef, tetM and tetO), in frequencies between 1.10-7 and 9.10-7, was possible from bovine donor strains to human recipient strain, but not the other way around. This is, to our knowledge, the first report of in vitro conjugation of Ery and Tet resistance genes among GBS strains recovered from different hosts.

Identification of high immunoreactive proteins from Streptococcus agalactiae isolates recognized by human serum antibodies.

The aim of the studies was to identify immunogenic proteins of Streptococcus agalactiae (group B streptococcus; GBS) isolates. Investigation of the immunoreactivity with human sera allowed us to determine major immunogenic proteins which might be potential candidates for the development of vaccine. For the study, we have selected 60 genetically different, well-characterized GBS clinical isolates. The proteins immunoreactivity with 24 human sera from patients with GBS infections, carriers, and control group without GBS was detected by SDS-PAGE and Western blotting. As a result, some major immunogenic proteins were identified, of which four proteins with molecular masses of about 45 to 50 kDa, which exhibited the highest immunoreactivity features, were analyzed by LC-MS/MS. The proteins were identified by comparative analysis of peptides masses using MASCOT and statistical analysis. The results showed known molecules such as enolase (47.4 kDa), aldehyde dehydrogenase (50.6 kDa), and ones not previously described such as trigger factor (47 kDa) and elongation factor Tu (44 kDa). The preliminary results indicated that some GBS proteins that elicit protective immunity hold promise not only as components in a vaccine as antigens but also as carriers or adjuvants in polysaccharide conjugate vaccines, but more studies are needed.