Morganella morganii has been identified as a causative agent of opportunistic infections and histamine poisoning. Bacteriophage is a virus and has recently been considered an alternative agent to antibiotics for the control of bacteria that have developed antibiotic resistance. In this study, a novel M. morganii bacteriophage isolated from river water was characterized. The isolated phage, termed FSP1, was purified by polyethylene glycol precipitation followed by cesium chloride density-gradient centrifugation. FSP1 has infectivity against only M. morganii and was identified as a Myoviridae bacteriophage through morphological analysis with transmission electron microscopy. According to the one-step growth curve, the FSP1 latent period, eclipse period, and burst size were 30, 20 min, and 42 PFU infected cell(-1) , respectively. The genome size of FSP1 was estimated to be c. 45.6-49.4 kb by restriction endonuclease analyses. Moreover, challenge testing against M. morganii in vitro revealed that FSP1 had high lytic activity and that the viable cell count of M. morganii was reduced by 6.12 log CFU mL(-1) after inoculation with FSP1 at a multiplicity of infection (MOI) = 10. These results suggested that FSP1 could be used as a biocontrol agent against M. morganii for treatment of infectious disease treatment or food decontamination.

Histamine food poisoning is a major safety concern related to seafood consumption worldwide.Morganella psychrotolerans is a novel psychrotolerant histamine-producer. In this study, the histamine production behaviors of M. psychrotolerans and two other major histamine-producers, mesophilic Morganella morganii and psychrotrophic Photobacterium phosphoreum, were compared in seafood products, and histamine accumulation by M. psychrotolerans was characterized at various pH and temperature levels in culture broth. The growth of M. psychrotolerans and P. phosphoreum increased similarly at 4°C in canned tuna, but M. psychrotolerans produced much higher levels of histamine than P. phosphoreum. Histamine accumulation by M. psychrotolerans was induced at lower environmental pH condition at 4 and 20 °C. The optimal temperature and pH for producing histamine by crude histidine decarboxylase of M. psychrotolerans was 30 °C and pH 7, respectively. The activity of the crude HDC extracted from M. psychrotolerans cells at 10 °C retained 45% of the activity at 30°C. Histidine decarboxylase gene expression of M. psychrotolerans was induced by low pH conditions. These results suggest that M. psychrotolerans are also a very important histamine-producer leading to histamine poisoning associated with seafood below the refrigeration temperature.

This is the first description of a bacteriophage specifically infecting P. damselae subsp. damselae and its potential applications. Bacteriophage therapy could prove useful in the prevention of histamine poisoning.

In this study, we aimed to investigate the sanitizing effects of peracetic acid (PAA), and the underlying mechanism of its antimicrobial action against Morganella psychrotolerans. The exposure of M. psychrotolerans to 20 ppm PAA for 5 min led to its decrease below the detection level, indicating that PAA has a significant antibacterial effect against M. psychrotolerans in vitro. Moreover, the viable counts of M. psychrotolerans on saury (Cololabis saira) surface were showed a reduction of 1.40 and 2.23 log CFU/cm 2 upon treatment with 80 ppm PAA for 1 and 5 min, 18 respectively. Further, PAA treatment delayed the growth of M. psychrotolerans on 19 saury surface during storage at 4°C. Next, the antimicrobial mechanism of PAA against M. psychrotolerans cells was investigated, and the damage to the cell membrane and cell surface upon PAA treatment was observed using scanning electron microscopy (SEM) and epifluorescence microscopy. The chromosomal DNA and the protein profiles after PAA treatment were also analyzed. Form our results, we hypothesized that the bactericidal effect of PAA treatment was mainly attributed to damage the bacterial cell membrane. These results indicate that PAA may be an efficient disinfectant against M. psychrotolerans and has applications in seafood processing and storage.

Histamine poisoning is a common seafood-borne illness worldwide, and Morganella morganii subsp. morganii is one of the most probable histamine producers. Bacteriophages are bacterial viruses that kill the host cell after infection. In this study, we evaluated the effect of M. morganii phage FSP1 treatment on histamine accumulation by M. morganii in raw tuna meat. M. morganii was inoculated to tuna meat and incubated at 4, 12 and 20℃ to evaluate the inhibitory effects of FSP1 on the growth and histamine accumulation of M. morganii. Viable M. morganii counts were decreased significantly in response to FSP1 treatment under all conditions. Furthermore, histamine concentrations in phage-treated samples were significantly lower than those of control samples. FSP1-resistant M. morganii did not develop after FSP1 treatment. These results suggest that phage treatment might be an effective tool to reduce the risks of histamine poisoning by M. morganii in fisheries products.