First report on genetic characterization, cell-surface properties and pathogenicity of Lactococcus garvieae, emerging pathogen isolated from cage-cultured cobia (Rachycentron canadum)

Evaluating the Antimicrobial Efficacy of TroLEAP2 like-27 peptide in golden pompano (Trachinotus ovatus) against Bacterial Pathogens

Amicrobial peptides are crucial components of immune system, acting as the first line of defense against microbial invasion. This study investigated the antimicrobial activity of TroLEAP2 like-27, a novel 27-amino acid peptide derived from golden pompano (Trachinotus ovatus), against Gram-positive Lactococcus garvieae and Staphylococcus epidermidis, and Gram-negative Vibrio alginolyticus and Vibrio harveyi. The 3D structure and helical wheel presentation of TroLEAP2 like-27 were consistent with typical AMP features. The hydrophobic ratio of TroLEAP2 like-27 was 47 %, and its α-helical structure suggested strong antimicrobial potential. The expression levels of the TroLEAP2 like gene in the liver and intestines tissues of T. ovatus were significantly upregulated following infection with L. garvieae and V. harveyi. The peptide induced bacterial agglutination in the presence of Ca2+ and exhibited bactericidal activity with a MIC50 of 60 μM. Transmission electron microscopy (TEM) revealed structural damage to bacterial membranes, while membrane permeability assays showed dose-dependent disruption and depolarization in all tested strains. Additionally, TroLEAP2 like-27 exhibited a potent capacity to interact with and degrade genomic DNA of all tested bacteria. The peptide treatment significantly reduced bacterial loads in the gill, liver, and intestinal tissues of the fish, with histological analysis revealing a remarkable protective effect on the tissues. Furthermore, fish treated with TroLEAP2 like-27 exhibited improved survival rates following bacterial infection. These findings suggest that TroLEAP2 like-27 is a promising antimicrobial peptide with potential therapeutic applications.

Identification, Characterization, and Epidemiological Analysis of Lactococcus garvieae Fish Isolates Obtained in a Period of Eighteen Years

Lactococcosis caused by Lactococcus garvieae is a bacterial infection affecting fish with a considerable economic impact. Recently, L. garvieae has established itself as an opportunistic pathogen in humans. The aim of the current study was to test classical and molecular-biological methods for the identification of L. garvieae and examine antimicrobial susceptibility and capsule production, an important virulence factor. Additionally, tests for differentiation from closely related species, as well as epidemiological typing, were performed. In a period of 18 years (2002-2019), 24 isolates presumptively identified as L. garvieae were collected from Oncorhynchus mykiss and Salmo salar fish obtained either from retail stores or fish farms. In order to confirm the species, optimized PCR-based protocols were used. As a result, 21 of the tested strains were proved to be L. garvieae (n = 21). The remaining three isolates were Lactococcus lactis, Streptococcus iniae, and Enterococcus faecalis. Epidemiological typing by randomly amplified polymorphic DNA was performed. Except for a single KG+ isolate, all other strains belonged to the European capsular serotype KG-. All L. garvieae isolates showed susceptibility to all tested antibiotics with the exception of clindamycin, which was a diagnostic sign. A thorough optimization of diagnostic methods is essential to determining the etiology of specific infections affecting the personnel at risk in fish farms, the food industry, or within the broader community.

Multiplex PCR assay for the accurate and rapid detection and differentiation of Lactococcus garvieae and L. petauri

Lactococcosis is a common bacterial fish disease caused by Lactococcus garvieae, L. petauri and L. formosensis. Although there are different PCR-based techniques to identify the etiological agent, none of these can differentiate these two bacteria without sequencing PCR-amplified fragments. In the present study, we developed a multiplex PCR assay for simultaneous detection and differentiation of L. garvieae and L. petauri. The specificity of the primers was validated against the bacterial DNA of the targeted and non-targeted bacteria. The sizes of the PCR amplicons were obtained as 204 bp for the DUF1430 domain-containing protein gene of L. garvieae, 465 bp for the Lichenan permease IIC component gene of L. petauri, and 302 bp for the teichoic acid biosynthesis protein F gene of both L. garvieae and L. petauri. The PCR amplicons were clearly separated by agarose gel electrophoresis. The multiplex PCR assay did not produce any amplification products with the DNA of the non-targeted bacteria. The multiplex PCR detection limits for L. garvieae and L. petauri were 5 and 4 CFU in pure culture and 50 and 40 CFU/g in spiked tissue samples, respectively. It takes less than 2 h from plate-cultured bacteria and 3 h from tissue samples to get results. In conclusion, the developed multiplex PCR assay is a rapid, specific, accurate, and cost-effective method for the detection and differentiation of L. garvieae and L. petauri and is suitable to be used for routine laboratory diagnosis of L. garvieae and L. petauri.

Changes in blood serum parameters in farmed rainbow trout (Oncorhynchus mykiss) during a piscine lactococcosis outbreak

The aquaculture sector plays a vital role in global food security, yet it grapples with significant challenges posed by infectious diseases. Piscine lactococcosis is one of the significant threats in rainbow trout aquaculture due to its potential to cause severe economic losses through mortalities, reduced growth rates, and increased susceptibility to other pathogens. It poses challenges in disease management strategies, impacting the sustainability and profitability of rainbow trout farming. The current study focuses on the variations in serum blood parameters of farmed rainbow trout Oncorhynchus mykiss during a lactococcosis outbreak caused by Lactococcus garvieae. Blood samples were collected for biochemical analysis, fish were examined for parasites and bacteria, and DNA from bacterial colonies was PCR-amplified and sequenced for identification. Overall, 13 biochemical parameters, including proteins, enzymes, lipids, chemicals, and minerals, were measured in serum blood samples from both diseased and healthy fish. The results indicate significant alterations in the levels of these parameters during the outbreak, highlighting the impact of infections on the blood profile of farmed rainbow trout. Urea levels were significantly higher in diseased fish compared to controls, and creatinine, phosphorus, and magnesium also showed similar trends. Alanine aminotransferase and total protein levels were higher in control fish. Chloride levels differed significantly between groups. Iron levels were higher in controls and lower in diseased fish. No significant differences were found in other parameters. This study reveals significant changes in serum blood parameters of rainbow trout during a lactococcosis outbreak caused by L. garvieae. These changes highlight the potential of these parameters as tools for monitoring health status, stress, and aquaculture management. Continuous monitoring can provide valuable insights into disease severity and overall fish health, aiding in the development of improved management practices. The presented data contribute to understanding the pathophysiology of piscine lactococcosis and developing effective mitigation strategies for farmed rainbow trout.

Characterization of Lactococcus garvieae and Streptococcus agalactiae in cultured red tilapia Oreochromis sp. in Thailand

OBJECTIVE

Acute mortality with clinical symptoms of streptococcal-like infections was observed in red tilapia Oreochromis sp. cultured in floating cages in Prachin Buri Province, Thailand, during May 2023. Herein, we identified an emerging pathogen, Lactococcus garvieae, as the etiological agent.

METHODS

After bacterial isolation from the brain and kidney of diseased fish, identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and the VITEK 2 system. Sequencing of the 16S ribosomal RNA (rRNA) gene and phylogenetic analysis were applied to confirm bacterial species. Antimicrobial susceptibility testing was conducted. Histopathological findings in the brain, kidney, spleen, liver, and heart were evaluated.

RESULT

From 20 fish samples, L. garvieae (n = 18 isolates) and Streptococcus agalactiae (n = 2 isolates) were identified. A phylogenetic tree of the 16S rRNA gene revealed that Thai isolates of either L. garvieae or S. agalactiae clustered with reference piscine isolates from intercontinental locations. Our isolates showed resistance against quinolones while being susceptible to other antimicrobials. Histopathological changes demonstrated severe septicemic conditions, with more invasive lesions-especially in the heart and liver-being apparent in L. garvieae-infected fish compared to S. agalactiae-infected fish.

CONCLUSION

This study represents the first reported outbreak of L. garvieae with a concurrent S. agalactiae infection in farmed red tilapia in Thailand.

First report of a Kudoa lutjanus outbreak in farmed Chicken Grunts Parapristipoma trilineatum

OBJECTIVE

As part of the National Disease Surveillance Program for Taiwanese Aquaculture, we investigated the causative agent of disease outbreaks in farmed Chicken Grunts Parapristipoma trilineatum.

METHODS

In this study, outbreak cases on two separate farms were noticed in coastal Pingtung County, Taiwan. In total, 50 juvenile fish showing clinical signs (such as emaciation and erratic swimming behavior) and broodstock (two females and two males) from both farms were collected to perform gross lesion assessment, histopathological examination, and molecular identification of the pathogen.

RESULT

Clinical symptoms were infected fish exhibited erratic swimming behavior, such as whirling and floating on the surface of the water. In the following months, cumulative mortality had reached 19% and 24%, respectively. The gross lesions in the infected fish included white oval cysts in the muscle, serosa of the internal organs, sclera of the eyes, and cerebral meninges. After conducting a wet mount examination of cysts using a light microscope, we observed a significant quantity of spores with morphological characteristics, suggesting their affiliation with the Myxosporea group. The spores were semiquadrate, with four tiny suture notches at the periphery; the mean spore length was 7.3 μm (SD = 0.5), and the mean spore width was 8.2 μm (SD = 0.6). The mean length and width of the pyriform polar capsules (nematocysts) were 3.6 μm (SD = 0.5) and 2.2 μm (SD = 0.5), respectively. The 18S and 28S ribosomal RNA sequences of these specimens were identical to those of Kudoa lutjanus.

CONCLUSION

As this was the first time an outbreak of K. lutjanus in Chicken Grunts was confirmed, its reappearance with substantial mortality should serve as a warning to the aquaculture industry.

First identification, molecular characterization, and pathogenicity assessment of Lactococcus garvieae isolated from cultured pompano in Taiwan

Lactococcosis, caused by Lactococcus garvieae, is an acute hemorrhagic septicemia in fish recorded in marine and freshwater aquaculture during the summer months. In 2020-2021, several sea cage Pompano farms recorded sudden fish mortality events. Based on the results of phenotypic and biochemical tests, L. garvieae was predicted to be the cause. PCR with L. garvieae specific primers (pLG1 and pLG2) targeting the 16S rRNA region further confirmed the etiological agent as L. garvieae after amplifying an 1100 base pairs (bp) product. Furthermore, the 16S rRNA sequences of the two representative strains (AOD109-196-2B and AOD110-215-2B) shared 99.81% identity with L. garvieae (GenBank accession number: MT597707.1). The genetic profiles of the strains were classified using pulsed-field gel electrophoresis after digestion with SmaI and ApaI, which clustered our strains under the same pulsotype. Multiplex PCR targeting the capsule gene cluster and serotype-specific PCR collectively showed that the strains were non-capsulated; thus, they belonged to serotype I. An experimental infection was designed to fulfil Koch's postulates by infecting healthy Pompano with case-driven L. garvieae strains (AOD109-196-2B and AOD110-215-2B) with a cumulative mortality of 70%. Overall, L. garvieae infection in Pompano emphasizes the need for better monitoring and control procedures in aquaculture settings.

First identification and histopathological analysis of Lactococcus garvieae infection in whiteleg shrimp, Penaeus vannamei cultured in low salinity water

The isolation and characterization of bacterial species Lactococcus garvieae, previously unreported in whiteleg shrimp, Penaeus vannamei, has now been identified in the species. The pathogen was recovered from an affected shrimp farm in southern Taiwan. Bacterial characterization first identified the isolate as Gram-positive cocci, and biochemical profiles demonstrated that the causative agent of mortality was 97% L. garvieae. The bacterial cell DNA resulted in amplification of 1522 bp with 99.6% confirmation by PCR analysis. The phylogenetic tree revealed 100% evolutionary similarity among previously isolated strains. Experimental infection further confirmed higher susceptibility of whiteleg shrimp to L. garvieae in waters of lower salinity, particularly 5 ppt, than in higher salinity. Histopathological analysis showed severely damaged hepatopancreas with necrotized, elongated, collapsed tubules, dislodged membranes and granuloma formation in infected shrimp. Transmission electron microscopy observation indicated a hyaluronic acid capsular layer surrounding bacterial cell which is a virulence factor of L. garvieae and likely responsible for immunosuppression and higher mortality of shrimp cultured in lower salinity. Collectively, these findings report the first isolation of L. garvieae from whiteleg shrimp and shed new light on the disease that threatens the highly valuable species and accentuates the need for finding a solution.

Nocardia seriolae cell wall lipids: An effective protective mechanism in resistance and virulence

Piscine nocardiosis, caused by Nocardia seriolae, is a refractory granulomatous disease in South-East Asian aquaculture. This study investigates the virulence of nocardial lipids essential for pathogenesis among Actinomycetes. Petroleum ether (PE) was used to selectively delipidate two groups of N. seriolae, namely, live cell (LC) and killed cell (KC); resulting in delipidated live cell (DLC) and delipidated killed cell (DKC), respectively. Changes post-delipidation on genus characteristics, such as loss in acid-fast nature and resistance to lysozyme were observed. Transmission electron microscopy revealed notable changes in the lipid layer. Additionally, Lates calcarifer, Asian seabass intraperitoneally injected with LC and DLC had mortality rates of 90% and 50%, respectively, with the latter exhibiting a delay in mortality. Reverse-transcription quantitative PCR (RT-qPCR) analysis of host cytokines from the spleen and head kidney showed delipidation contributed to the induction of an immune response with increased transcriptional levels of interferon-γ (ifn-γ). Histopathological samples collected on day 7 post-inoculation displayed a varied granulomatous response between the treatment groups and scored for pathological changes. These findings affirm that the virulence of the lipids remains independent of the living state of the cell, significantly altering the immune and granulomatous responses in L. calcarifer to N. seriolae.

Genotyping and phenotyping of Lactococcus garvieae isolates from fish by pulse-field gel electrophoresis (PFGE) and electron microscopy indicate geographical and capsular variations

Lactococcus garvieae is the etiological agent of Lactococcosis, an evolving disease affecting many fish species and causing significant economic losses worldwide. Assessing pathogen relatedness and bacterial population structure is critical for determining the epidemiology of L. garvieae infections and in establishing effective pathogen management methods. The previously published morphological and genetic studies point to a clonal population structure, as seen in other fish bacteria. In the present study, the pulsed-field gel electrophoresis (PFGE) method was utilized to define a population of 41 Taiwanese isolates from outbreaks with comparisons to four well-characterized non-Taiwanese isolates previously published. Two restriction enzymes (ApaI and SmaI) were utilized individually for PFGE analysis (cut-off value = 90.0%), revealing genetic heterogeneity across L. garvieae isolates, with ApaI and SmaI yielding 12 and seven distinct PFGE band patterns, respectively. The phylogenic analysis using internal transcribed spacer region clustered all L. garvieae isolates in the same clad. Furthermore, the electron microscopic results confirmed the absence of capsular gene cluster (CGC) in previously characterized Taiwanese vaccine strain (S3) from grey mullet. Overall, our findings emphasize the importance of analysing the morphological and genetic diversity in L. garvieae being correlated for proper taxonomic classification in vaccine strain selection and epidemiological studies.

Sarcodia suiae Water Extract Promotes the Expression of Proinflammatory and Th1-Type Cytokines and Delay the Onset of Mortality in Cobia (Rachycentron canadum) During Photobacterium damselae subsp. damselae Infection

Cobia (Rachycentron canadum) is a marine fish of high economic value that grows at a fast rate. However, intensive fish farming has led to disease outbreaks in cobia cultures, which is highly costly to the industry. The impact of infectious diseases on cobia production has led to the inappropriate and increased use of chemicals and antibiotics, which negatively affects the environment and human health and promotes the spread of drug-resistant pathogens. Hence, prophylactic measurements, such as the use of immunomodulators, are required to improve the health of cultured animals against pathogens. In this study, we examined the effects of Sarcodia suiae water extract (SSWE) in cobia in vitro and in vivo. We found that treatment with SSWE could significantly increase the expression of cytokines (e.g., IL-1β, IL-6, IL-10, IL-12, and TNF-α) and chemokines (e.g., IL-8) in primary cultured head kidney leukocytes. Intraperitoneal injection of SSWE (20 μg/g body weight) promoted higher expression of IL-6, IL-8, IL-10, IL-12, chemokines (e.g., CC1), and antibodies (e.g., IgT) in head kidney and spleen tissues of the fish compared with other dose levels. Additionally, we describe for the second time (only after India) of the isolation of Photobacterium damselae subsp. damselae (Phdd) from a deadly epizootic in cage-farmed cobia. An intraperitoneal inoculation of SSWE before Phdd challenge showed that SSWE treatment could delay the onset of mortality of cobia. Finally, fish that received SSWE intraperitoneally before infection with Phdd exhibited elevated expression of Th1-type cytokines, namely, IL-8, IL-12, TNF-α, and IFN-γ. At the same time, the expression of Th2-related factors (such as IL-10 in the head kidney, and IgM and IgT in the spleen) were lower for the fish that received SSWE instead of PBS before the Phdd challenge. The results indicate that SSWE treatment facilitates the induction of Th1-type cytokines in cobia to fight against Phdd infection and has the potential to be used as an immunostimulant and vaccine adjuvant for fish.