Pseudomonas anguilliseptica is a dreadful fish pathogen causing severe problem in olive flounder Paralichthys olivaceus farms in Jeju Island, Korea. Diagnosis of this disease required a time-consuming and labor intensive culturing step. Hence more rapid and sensitive detection methods are needed. In this study, a TaqMan probe real-time PCR-based detection assay targeting the 16S rRNA gene of P. anguilliseptica was developed. This assay was specific for P. anguilliseptica and sensitive in detecting as little as 300 pg P. anguilliseptica genomic DNA and 2.4 × 100 plasmid copie. Challenge experiments of healthy flounder with a virulent strain of P. anguilliseptica confirmed the specificity of the designed molecular probe for detection of P. anguilliseptica. This assay represents a significant approach for diagnosing P. anguilliseptica infection in olive flounder.
luxS-mediated autoinducer-2 (AI-2) directly or indirectly regulates important physiologic function in a variety of bacteria, including bioluminescent effect, antimicrobial resistance, virulence factor control, biofilm structure stability and so on. In this study, the regulation of susceptibility to antimicrobials by luxS/AI-2 was investigated in Streptococcus agalactiae. A luxS- knockout mutant strain named SX1 was constructed by homologous recombination from S. agalactiae CNEP110823 (wild type strain), and a luxS-complementation strain named SX2 was constructed from SX1 through transducing a plasmid with the luxS gene and its promoter. Then the susceptibility to cefradine and norfloxacin of these two strains, SX1 exposed to AI-2 precursor molecule 4,5-dihydroxy-2,3-pentanedione (DPD) and the wild type strain was determined by viable bacterial counting. SX1 decreased susceptibility to cefradine and norfloxacin, SX2 returned the susceptibility to the same level as the wild type strain and DPD restored the susceptibility of SX1. The results indicate that luxS/AI-2 quorum sensing is involved in antimicrobial susceptibility in S. agalactiae, which may provide novel clues for antimicrobial therapy in the infection.
Infection levels of Pekinsus olseni in Manila clam Ruditapes phillipinarum much vary among different locations. In order to know the effects of environmental factors on the infection of the parasite, we maintained Manila clams at different salinities (15, 18, 21 and 30 psu) and temperatures (13°C, 18°C and 23°C) after challenge with parasites and examined the infection intensities in the clams at intervals. In clams maintained at different salinities, no association was detected between salinity and infection intensity except that the intensity was significantly lower at 15 psu than at any other salinities on 54 day post challenge only, when the experiment was terminated. A significant difference was observed in the survival rate of clams between challenged and control groups at 30 psu only, suggesting that the negative effect of P. olseni on the survival of clams was attenuated with decreasing salinity. In clams maintained at different temperatures, the infection intensity little changed at 13°C, although it increased remarkably at 18°C and 23°C. The result indicates that in-vivo propagation is suppressed at 13°C and lower. A significant decrease was observed in the survival of clams at 23°C only, indicating that the virulence of P. olseni depends on temperature.