White feces syndrome (WFS), a gastrointestinal disorder of cultivated penaeid shrimp, causes severe economic and production losses worldwide. Shrimp with WFS usually show a reduced feed consumption and growth rate, hepatopancreatic discoloration, and loose shells. Recently, WFS has been said to be related to an infection with Enterocytozoon hepatopenaei (EHP), a microsporidian parasite, and other opportunistic bacteria, such as the Vibrio species. Vibrio spp. may play an important role in WFS occurrence; nevertheless, Vibrio sp., as a single pathogen, cannot reproduce this syndrome under laboratory conditions. To date, no novel treatment has been found for WFS; therefore, preventive measures, such as strict biosecurity systems to eliminate or inactivate EHP spores and limit the total Vibrio number, have been suggested. This review summarizes the information regarding the association between WFS and water parameters, gut microbiomes, EHP and Vibrio, and disease control strategies.

We developed a qPCR assay based on the β-tubulin gene sequence for the shrimp microsporidian parasite Enterocytozoon hepatopenaei (EHP). This assay reacted with the hepatopancreas (HP) of EHP-infected shrimps, and the highest copy numbers were found in HP and feces samples from Southeast Asian countries (10⁶–10⁸ copies mg⁻¹), while HP samples from Latin America, Artemia, and EHP-contaminated water showed lower amounts (10¹–10³ copies mg⁻¹ or mL⁻¹ of water). No false positive was found with the normal shrimp genome, live feeds, or other parasitic diseases. This tool will facilitate the management of EHP infection in shrimp farms.

We report here the complete genome sequence of Vibrio campbellii , isolated from Penaeus vannamei cultured in a Latin American country. The Tn 3 -like transposon and pirAB genes were encoded on the plasmid pLA16-2. These data support the geographical variations in the virulence plasmid found among acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio isolates from Latin America and Asia.

The emergence of antimicrobial resistant (AMR) strains of Morganella morganii is increasingly being recognized. Recently, we reported a fatal M. morganii infection in a captive bottlenose dolphin (Tursiops truncatus) bred at a dolphinarium in South Korea. According to our subsequent investigations, the isolated M. morganii strain KC-Tt-01 exhibited extensive resistance to third-generation cephalosporins which have not been reported in animals. Therefore, in the present study, the genome of strain KC-Tt-01 was sequenced, and putative virulence and AMR genes were investigated. The strain had virulence and AMR genes similar to those of other M. morganii strains, including a strain that causes human sepsis. An amino-acid substitution detected at the 86th residue (Arg to Cys) of the protein encoded by ampR might explain the extended resistance to third-generation cephalosporins. These results indicate that the AMR M. morganii strain isolated from the captive dolphin has the potential to cause fatal zoonotic infections with antibiotic treatment failure due to extended drug resistance, and therefore, the management of antibiotic use and monitoring of the emergence of AMR bacteria are urgently needed in captive cetaceans for their health and conservation.

The emergence and spread of antibiotic-resistant Aeromonas spp. is a serious public and animal health concern. Wild animals serve as reservoirs, vectors, and sentinels of these bacteria and can facilitate their transmission to humans and livestock. The nutria (Myocastor coypus), a semi-aquatic rodent, currently is globally considered an invasive alien species that has harmful impacts on natural ecosystems and carries various zoonotic aquatic pathogens. This study aimed to determine the prevalence of antibiotic-resistant zoonotic Aeromonas spp. in wild invasive nutrias captured in Korea during governmental eradication program. Three potential zoonotic Aeromonas spp. (A. hydrophila, A. caviae, and A. dhakensis) were identified among isolates from nutria. Some strains showed unexpected resistance to fluoroquinolones, third-generation cephalosporins, and carbapenems. In carbapenem-resistant isolates, the cphA gene, which is related to intrinsic resistance of Aeromonas to carbapenems, was identified, and phylogenetic analysis based on this gene revealed the presence of two major groups represented by A. hydrophila (including A. dhakensis) and other Aeromonas spp. These results indicate that wild nutrias in Korea are a potential reservoir of zoonotic and antibiotic-resistant Aeromonas spp. that can cause infection and treatment failure in humans. Thus, measures to prevent contact of wild nutrias with livestock and humans are needed.