Genetic recombinants that resulted from lateral gene transfer (LGT) have been detected in sexually transmitted disease isolates of Chlamydia trachomatis, but a mechanism for LGT in C. trachomatis has not been described. We describe here a system that readily detects C. trachomatis LGT in vitro and that may facilitate discovery of its mechanisms. Host cells were simultaneously infected in the absence of antibiotics with an ofloxacin-resistant mutant and a second mutant that was resistant to lincomycin, trimethoprim, or rifampin. Selection for doubly resistant C. trachomatis isolates in the progeny detected apparent recombinant frequencies of 10 ؊4 to 10 ؊3 , ϳ10 4 times more frequent than doubly resistant spontaneous mutants in progeny from uniparental control infections. Polyclonal doubly resistant populations and clones isolated from them in the absence of antibiotics had the specific resistance-conferring mutations present in the parental mutants; absence of the corresponding normal nucleotides indicated that they had been replaced by homologous recombination. These results eliminate spontaneous mutation, between-strain complementation, and heterotypic resistance as general explanations of multiply resistant C. trachomatis that originated in mixed infections in our experiments and demonstrate genetic stability of the recombinants. The kind of LGT we observed might be useful for creating new strains for functional studies by creating new alleles or combinations of alleles of polymorphic loci and might also disseminate antibiotic resistance genes in vivo. The apparent absence of phages and conjugative plasmids in C. trachomatis suggests that the LGT may have occurred by means of natural DNA transformation. Therefore, the experimental system may have implications for genetically altering C. trachomatis by means of DNA transfer.

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Aims: To detect Photobacterium damselae ssp. piscicida using the PCR technique and plating method. Methods and Results: Two strains of P. damselae ssp. piscicida were isolated from cultured cobia (Rachycentron canadum) at two different fish farms in Taiwan. A pair of primers was designed to detect the capsular polysaccharide gene of P. damselae ssp. piscicida by PCR. Reference strains of different genus and different clinical strains were used for this study. The expected product (410 bp) was obtained from both P. damselae ssp. piscicida and P. damselae ssp. damselae, and they were differentiated by culturing on thiosulphate citrate bile salts-sucrose agar (TCBS-1). Photobacterium damselae ssp. damselae grew on TCBS-1 producing green colonies whereas P. damselae ssp. piscicida did not grow. Conclusions: The methods used are cost and labour effective when compared with the other methods and commercially available kits. Significance and Impact of the Study: This work provides an integrated set of methods to identify the species P. damselae and to differentiate P. damselae ssp. piscicida from P. damselae ssp. damselae.

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White spot syndrome virus (WSSV) is the causative agent of white spot syndrome (WSS), a disease that has led to severe mortality rates in cultured shrimp all over the world. The WSSV is a large, ellipsoid, enveloped double-stranded DNA virus with a wide host range among crustaceans. Currently, the main antiviral method is to block the receptor of the host cell membrane using recombinant viral proteins or virus antiserum. In addition to interference with the ligand-receptor binding, disrupting the structure of the virus envelope may also be a means to combat the viral infection. Carbon quantum dots (CQDs) are carbonaceous nanoparticles that have many advantageous characteristics, including small size, low cytotoxicity, cheap, and ease of production and modification. Polyamine-modified CQDs (polyamine CQDs) with strong antibacterial ability have been identified, previously. In this study, polyamine CQDs are shown to attach to the WSSV envelope and inhibit the virus infection, with a dose-dependent effect. The results also show that polyamine CQDs can upregulate several immune genes in shrimp and reduce the mortality upon WSSV infection. This is first study to identify that polyamine CQDs could against the virus. These results, indeed, provide a direction to develop effective antiviral strategies or therapeutic methods using polyamine CQDs in aquaculture.

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The virulence of seven geographic isolates of white spot syndrome virus (WSSV; genus Whispovirus; China [strain CH1995], Nicaragua [strain N2000], Honduras [strain H2000], Ecuador [strains E-L1999 and E-LT2002], and Mexico [strains M-M2001 and M-LP2001]) was compared using a series of challenge experiments, each lasting 10 d. For each isolate, four quantified dilutions (10(-6), 10(7), 10(-8), and 10(-9)) of a viral inoculum were prepared from WSSV-infected shrimp tissue. Each viral inoculum was injected into 10 specific pathogen-free juvenile Pacific white shrimp Litopenaeus vannamei (0.25-1.50 g); controls received injections of marine crustacean physiological saline (3.2%). The minimum dose of viral inoculum that killed 50% of injected shrimp (LD50) was calculated for dilution, tissue concentration, and viral DNA amount. The CH1995 and M-M2001 isolates were the least virulent, with LD50 values of 10(-6) to 10(-7) of viral inoculum. The isolates could be grouped into three virulence clusters (CH1995 and M-M2001; N2000 and E-LT2002; and H2000, E-L1999, and M-LP2001). Virulence clusters were not altered by LD50 values based on viral DNA concentration, although a slight shifting of order in regards to virulence was seen among the three most virulent isolates (E-L1999, H2000, and M-LP2001). Overall, results indicate that there is a measurable virulence difference among WSSV isolates, which may correspond to geographical region.

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