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The mesopelagic calanoid copepod Cephalophanes reflugens is characterized by its large eyes with semi-parabolic reflectors. It is hypothesized that the eyes aid in finding crustacean carcasses as food in poor deep-sea light and oligotrophic conditions. Here, the crustacean carcasses-associated luminous, chitin-degrading bacteria may play a vital role in detecting and digesting foods by the copepod. In this study, we collected adult female C. reflugens (n  = 9) from the mesopelagic layers off southwestern Japan in the Pacific Ocean and obtained a total of 47 bacterial isolates from the gut contents. None of the isolates were luminescent, but almost half of the isolates were chitinolytic. Based on the 16S rRNA gene sequences, these chitinolytic bacteria were identified as members of the genus Vibrio , Photobacterium and Pseudoalteromonas. In culture experiments at 15°C, most of the chitinolytic isolates efficiently utilized colloidal chitin as the sole carbon source and degraded the carapace strip of shrimp (Litopenaeus vannamei). Some isolates showed these chitinoclastic activities even at low temperatures (<5°C), equivalent to that of the deep-sea waters. The present results imply that chitin-degrading bacteria significantly contribute to chitin digestion in the gut of C. reflugens , whereas the involvement of luminous bacteria in the feeding mechanism remains unidentified. [ABSTRACT FROM AUTHOR]

Histamine poisoning has been reported worldwide. Improvements in refrigeration technology have led to a reduction in this food, poisoning; however, it continues to occur. Misdiagnosis of fish allergies has compounded this problem and the number of patients subjected to histamine poisoning that are transported to the emergency ward because of anaphylactic shock-like symptoms should not be underestimated. We investigated incidents of histamine food poisoning in Japan from 1998 to 2020, and found that there were a mean 9.7 incidents/year and 195.3 cases/year. Facility-wise occurrence of the incidents per year was the highest in restaurants followed by lunch facilities, and these together accounted for approximately 70% of the incidents. Facility-wise total number of cases was the highest in lunch facilities followed by restaurants, and these together accounted for 80% of the cases. Fish associated with histamine poisoning were mainly tuna, marlin, and mackerel. Based on the current literature review, 23 genera of histamine-producing bacteria were isolated from fish purchased in Japan. The most frequently reported bacteria were Morganella morganii and Photobacterium damselae. Psychrophilic bacteria such as Morganella psychrotolerans and Photobacterium phosphoreum were also isolated. To prevent histamine poisoning, freezing or fast handling of fish and the products during processing and consuming is important because only refrigeration of fish is enough. [ABSTRACT FROM AUTHOR]

A pseudotuberculosis pathogen, Photobacterium damselae subsp. piscicida (Pdp), has caused enormous economic damage to yellowtail aquaculture in Japan. The Ivy gene has been discovered in plasmid of Pdp , and it has been proposed that it may help bacteria evade lysozyme-mediated lysis during interaction with an animal host. However, the lysozyme-inhibiting activity of Pdp -derived Ivy (Ivy-Pdp) is unknown, and it is unclear whether it acts as a virulence factor for host biophylaxis. In this study, the inhibitory effect of Ivy-Pdp on lysozyme was evaluated by expressing and purifying the recombinant Ivy-Pdp protein (rIvy-Pdp). The rIvy-Pdp protein inhibited hen egg white lysozyme activity in an rIvy-Pdp-concentration-dependent manner, and its inhibitory effect was similar under different temperature and pH conditions. The serum and skin mucus of the yellowtail (which is the host species of Pdp), Japanese flounder, and Nile tilapia showed bacteriolytic activity. In contrast, the addition of rIvy-Pdp inhibited the lytic activity in the serum of these fish species. In particular, it significantly inhibited lytic activity in the serum and skin mucus of Nile tilapia. On the basis of these results, we suggest that Ivy-Pdp is a temperature- and pH-stable lysozyme inhibitor. Additionally, Ivy-Pdp inhibited the lytic activity of lysozyme, which is involved in host biophylaxis. In summary, we inferred that Ivy-Pdp is an important factor that diminishes the sterilization ability of C-type lysozyme when Pdp infects the host. • Ivy-Pdp highly preserved the CKPHDC motif, as with Ivy derived from known pathogenic bacteria. • Ivy-Pdp inhibited HEWL lytic activity, regardless of temperature and pH. • Ivy-Pdp inhibited lytic activity of yellowtail and Nile tilapia serum. [ABSTRACT FROM AUTHOR]

The marine bacterium Photobacterium damselae subsp. damselae is a pathogen that causes disease in diverse marine animals, and is also a serious opportunistic human pathogen that can cause fatal infections. Strains of this pathogen isolated from diseased European sea bass in aquaculture facilities in the Turkish coast of the Black Sea were found to exhibit reduced sensitivity to multiple antimicrobials. Selected representative strains were subjected to complete genome sequencing and plasmid characterization. It was found that multidrug resistant (MDR) isolates harboured large conjugative plasmids sharing part of their sequence backbone with pAQU-group plasmids, hitherto reported exclusively in China and Japan. Four new pAQU-group versions of plasmids were identified in the present study, containing distinct combinations of the resistance determinants tetB, floR, sul2, qnrVC, dfrA and strAB. Conjugative transfer of pPHDD2-OG2, a representative plasmid of 170,998 bp, occurred at high frequencies (2.2 × 10-2 transconjugants per donor cell), to E. coli and to pathogenic P. damselae subsp. damselae and subsp. piscicida strains. Upon transfer, pPHDD2-OG2 conferred reduced susceptibility to a number of antimicrobials to the recipient strains. Comparative genomics analysis of host strains suggested that these MDR plasmids of the pAQU-group were acquired by different genetic lineages of Pdd. This study provides evidence that P. damselae subsp. damselae isolated from diseased fish constitute a reservoir for conjugative MDR pAQU-group plasmids in the Mediterranean basin, and have the potential to spread to diverse bacterial species. [ABSTRACT FROM AUTHOR]

All organisms depend on symbiotic associations with bacteria for their success, yet how these interspecific interactions influence the population structure, ecology, and evolution of microbial symbionts is not well understood. Additionally, patterns of genetic variation in interacting species can reveal ecological traits that are important to gene flow and co-evolution. In this study, we define patterns of spatial and temporal genetic variation of a coral reef fish, Siphamia tubifer , and its luminous bacterial symbiont, Photobacterium mandapamensis in the Okinawa Islands, Japan. Using restriction site-associated sequencing (RAD-Seq) methods, we show that populations of the facultative light organ symbiont of S. tubifer exhibit genetic structure at fine spatial scales of tens of kilometers despite the absence of physical barriers to dispersal and in contrast to populations of the host fish. These results suggest that the host's behavioral ecology and environmental interactions between host and symbiont help to structure symbiont populations in the region, consequently fostering the specificity of the association between host generations. Our approach also revealed several symbiont genes that were divergent between host populations, including hfq and a homolog of varS , both of which play a role in host association in Vibrio cholerae. Overall, this study highlights the important role that a host animal can play in structuring the distribution of its bacterial symbiont, particularly in highly connected marine environments, thereby promoting specificity of the symbiosis between host generations. [ABSTRACT FROM AUTHOR]

Cases of histamine fish poisoning (HFP) have been reported worldwide. Although most cases of HFP are caused by mesophilic histamine-producing bacteria (HPB) when temperature abuse occurs, HFP could also be caused by psychrophilic HPB when fish are stored at low temperatures. In this study, mesophilic and psychrophilic HPB were isolated from a wide range of fish samples and identified by 16S rRNA and gyrB sequencing. Most of the mesophilic isolates were Photobacterium damselae subsp. damselae (42.7%) and Morganella morganii (24.0%), and most of the psychrophilic HPB were Photobacterium (94.9%). Whereas 76.0% of the mesophilic HPB produced more than 500 mg/kg of histamine (Hm), psychrophilic HPB generally produced lower Hm level, but 43.2% of these isolates still produced more than 500 mg/kg Hm. This study showed the importance of investigating not only mesophilic but psychrophilic HPB as well. [ABSTRACT FROM AUTHOR]

Aims: To investigate the antimicrobial susceptibility and genetic characteristics of Photobacterium damselae ssp. piscicida isolates obtained from cultured Seriola in Japan. Methods and Results: Minimal inhibitory concentrations of 14 antimicrobials for 74 isolates from Seriola in Japan in 2002 were determined. Isolates showed high frequencies of resistance to sulfamonomethoxine (SMMX) (97·3%), oxytetracycline (OTC) (77·0%), flumequine (FMQ) (77·0%), chloramphenicol (CP) (75·7%), kanamycin (KM) (63·5%) and oxolinic acid (OA) (62·0%), but low to ampicillin (ABPC) (2·8%). All isolates were susceptible to bicozamycin (BCM), fosfomycin (FOM) and florfenicol (FF). Of these isolates, 45 (60·8%) showed same resistance pattern (SMMX-OTC-FMQ-OA-CP-KM). In random amplified polymorphic DNA (RAPD) analysis, no difference was observed among our 74 field isolates and ATCC51736 isolated from Seriola in 1974 in Japan, but different from ATCC 17911 isolated from white perch in USA. Conclusions: FF, BCM, FOM and ABPC were useful antimicrobials for treating pseudotuberculosis. However, the frequency of multidrug resistance was high. RAPD analysis showed homogeneity of isolates from Seriola in Japan. Significance and Impact of the Study: This study demonstrates that some antimicrobials were still useful for treating pseudotuberculosis and that P. damselae ssp. piscicida strains of same origin might have spread among Seriola in Japan since 1974. [ABSTRACT FROM AUTHOR]

To rapidly identify natural isolates of marine bioluminescent bacteria, we developed amplified ribosomal DNA restriction analysis (ARDRA) methods. ARDRA, which is based on the restriction patterns of 16S rRNA gene digested with five enzymes ( EcoRI, DdeI, HhaI, HinfI, RsaI), clearly distinguished the 14 species of marine bioluminescent bacteria currently known, which belong to the genera Vibrio, Photobacterium, and Shewanella. When we applied ARDRA to 129 natural isolates from two cruises in Sagami Bay, Japan, 127 were grouped into six ARDRA types with distinctive restriction patterns; these isolates represented the bioluminescent species, P. angustum, P. leiognathi, P. phosphoreum, S. woodyi, V. fischeri, and V. harveyi. The other two isolates showing unexpected ARDRA patterns turned out to have 16S rRNA gene sequences similar to P. leiognathi and P. phosphoreum. Nevertheless, ARDRA provides a simple and fairly robust means for rapid identification of the natural isolates of marine bioluminescent bacteria, and is therefore useful in studying their diversity. [ABSTRACT FROM AUTHOR]

Occurrence of tetracycline resistance genes encoding ribosomal protection proteins was examined in 151 tetracycline-resistant bacterial isolates from fish and seawater at coastal aquaculture sites in Japan and Korea. The tet(M) gene was detected in 34 Japanese and Korean isolates, which included Vibrio sp., Lactococcus garvieae, Photobacterium damsela subsp. piscicida, and unidentified Gram-positive bacteria. The majority of these bacterial isolates displayed high-level resistance with a minimum inhibitory concentrations (MICs) equal to or greater than 250 μg/ml of oxytetracycline and only four isolates had MICs less than 31.3 μg/ml. 16S rDNA RFLP typing of tet(M)-positive Vibrio isolates suggests that these are clonal populations of the same phylotype specific to a particular location. One Vibrio clone (phylotype III), however, is widely disseminated, being detected during different sampling years, at different locations, and in different fish species in both Japan and Korea. The tet(S) gene was detected in L. garvieae from yellowtail in Japan and in Vibrio sp. from seawater in Korea. This is the first report of tet(S) occurrence in Gram-negative facultative anaerobes. These results suggest that tet(M) and tet(S) genes are present in fish intestinal and seawater bacteria at aquaculture sites and could be an important reservoir of tetracycline resistance genes in the marine environment. [Copyright &y& Elsevier]

We report a case of fatal acute renal failure due to Photo-bacterium damsela infection of the hand. Although the patient received intensive medical care and surgical treatment, he died 8 h after arrival at the hospital. This is the first case of P. damsela sepsis proven by blood culture in Japan. [ABSTRACT FROM AUTHOR]