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.

Lactococcus garvieae-associated septicemia in a central bearded dragon

Lactococcus garvieae is the causative agent of lactococcosis in fish and an emerging zoonotic pathogen with high levels of antimicrobial resistance. We report a case of L. garvieae-associated septicemia in a central bearded dragon (Pogona vitticeps) confirmed via whole-blood PCR and direct sequencing. Following a 30-d course of ceftazidime (20 mg/kg IM q72h), the animal's clinical condition had not resolved; leukopenia persisted, with heterophil toxic change. Coelomic ultrasound findings were consistent with preovulatory follicular stasis, folliculitis, and coelomitis. Following surgical ovariectomy and an additional 30-d course of ceftazidime, the animal's behavior and appetite returned to normal, the animal tested negative via whole-blood PCR assay, and the CBC was unremarkable. To our knowledge, L. garvieae with L. garvieae-associated clinical disease has not been reported previously in a bearded dragon. We conclude that L. garvieae should be considered as a possible etiologic agent in cases of septicemia in bearded dragons, with the potential for zoonotic transmission warranting further investigation.

The Characterisation of Lactococcus garvieae Isolated in an Outbreak of Septicaemic Disease in Farmed Sea Bass (Dicentrarchus labrax, Linnaues 1758) in Italy

In aquaculture, Lactococcus garvieae is a common fish pathogen that can cause significant economic losses in several fresh and saltwater species. Despite the extensive range of hosts, L. garvieae infection in sea bass (Dicentrarchus labrax) has rarely been reported. During the summer of 2023, an outbreak occurred in an inland farm in the Gulf of Follonica (Tuscany, Italy). Fish of various sizes were affected, showing apathy, inappetence, erratic swimming and eye lesions, while the mortality was low (2-3% per month). Anatomopathological examinations suggested a septicaemic infection characterised by melanosis, diffuse redness (skin and fins), paleness (gills and internal organs), haemorrhages and splenomegaly. Seventy swabs from the viscera of 14 subjects were collected and colonies similar to Streptococcus spp. grew from all the samples. Lactococcus garvieae was identified via the biochemical tests, API20STREP, MALDI-TOF, 16S rDNA and whole genome sequencing. Genetical characterisation revealed remarkable differences between this isolate and the strains previously isolated in Italian fish farms. Feed treatments with flumequine and erythromycin were ineffective. Considering the limited effects of antimicrobials, preventive measures, such as vaccination and biosecurity, should be implemented.

First Report of Human Urinary Tract Infection Caused by Lactococcus petauri

Lactococcus petauri is a recently described species of the genus Lactococcus. It was reported as an etiological agent of piscine lactococcosis together with Lactococcus garvieae. L. garvieae was already described as an opportunistic pathogen in human infections, with a potential zoonotic role. This paper represents the first report of a human urinary tract infection caused by L. petauri. A 91-year-old man was admitted to the emergency department for a femur fracture consequent to a domestic accident. The fracture was reduced by surgery and a catheterized specimen urine culture revealed a high bacterial load sustained by Gram-positive cocci, identified by Vitek 2 compact as L. garvieae, and subsequently as L. petauri through Internal Transcribed spacer 16S-23S r-RNA amplification. The number of L. petauri infections in humans is expected to rise in the near future mainly due to diagnostic improvement. A dedicated survey on L. garvieae and L. petauri infections in humans should be performed to better understand their role as pathogens and as zoonotic agents.

Detection and virulence of Lactococcus garvieae and L. petauri from four lakes in southern California

OBJECTIVE

The first objective of the study aimed to detect the presence of Lactococcus petauri, L. garvieae, and L. formosensis in fish (n = 359) and environmental (n = 161) samples from four lakes near an affected fish farm in California during an outbreak in 2020. The second objective was to compare the virulence of the Lactococcus spp. in Rainbow Trout Oncorhynchus mykiss and Largemouth Bass Micropterus salmoides.

METHODS

Standard bacterial culture methods were used to isolate Lactococcus spp. from brain and posterior kidney of sampled fish from the four lakes. Quantitative PCR (qPCR) was utilized to detect Lactococcus spp. DNA in fish tissues and environmental samples from the four lakes. Laboratory controlled challenges were conducted by injecting fish intracoelomically with representative isolates of L. petauri (n = 17), L. garvieae (n = 2), or L. formosensis (n = 4), and monitored for 14 days postchallenge (dpc).

RESULT

Lactococcus garvieae was isolated from the brains of two Largemouth Bass in one of the lakes. Lactococcus spp. were detected in 14 fish (8 Bluegills Lepomis macrochirus and 6 Largemouth Bass) from 3 out of the 4 lakes using a qPCR assay. Of the collected environmental samples, all 4 lakes tested positive for Lactococcus spp. in the soil samples, while 2 of the 4 lakes tested positive in the water samples through qPCR. Challenged Largemouth Bass did not show any signs of infection postinjection throughout the challenge period. Rainbow Trout infected with L. petauri showed clinical signs within 3 dpc and presented a significantly higher cumulative mortality (62.4%; p < 0.0001) at 14 dpc when compared to L. garvieae (0%) and L. formosensis (7.5%) treatments.

CONCLUSION

The study suggests that qPCR can be used for environmental DNA monitoring of Lactococcus spp. and demonstrates virulence diversity between the etiological agents of piscine lactococcosis.

Immune profiling of rainbow trout (Oncorhynchus mykiss) exposed to Lactococcus garvieae: Evidence in asymptomatic versus symptomatic or vaccinated fish

Lactococcosis, caused by the Gram-positive bacterium Lactococcus garvieae, is a major concern in rainbow trout (Oncorhynchus mykiss) farms, which are regularly affected by outbreaks especially during the summer/fall months. In these farms, unvaccinated healthy and symptomatic fish can coexist with vaccinated fish. In the present study, innate (leukogram, serum lysozyme activity, peroxidase activity, antiprotease activity, bactericidal activity, total IgM and total proteins), and specific immune parameters (serum antibodies to L. garvieae) were assessed in unvaccinated adult rainbow trout naturally exposed to the pathogen, with or without evidence of clinical signs, or subjected to vaccination. Blood was drawn from all three groups, and blood smears were prepared. Bacteria were found in the blood smears of 70% of the symptomatic fish but not in any of the asymptomatic fish. Symptomatic fish showed lower blood lymphocytes and higher thrombocytes than asymptomatic fish (p ≤ .05). Serum lysozyme and bactericidal activity did not vary substantially among groups; however, serum antiprotease and peroxidase activity were significantly lower in the unvaccinated symptomatic group than in the unvaccinated and vaccinated asymptomatic groups (p ≤ .05). Serum total proteins and total immunoglobulin (IgM) levels in vaccinated asymptomatic rainbow trout were significantly higher than in unvaccinated asymptomatic and symptomatic groups (p ≤ .05). Similarly, vaccinated asymptomatic fish produced more specific IgM against L. garvieae than unvaccinated asymptomatic and symptomatic fish (p ≤ .05). This preliminary study provides basic knowledge on the immunological relationship occurring between the rainbow trout and L. garvieae, potentially predicting health outcomes. The approach we proposed could facilitate infield diagnostics, and several non-specific immunological markers could serve as reliable indicators of the trout's innate ability to fight infection.

16S-23S rRNA Internal Transcribed Spacer Region (ITS) Sequencing: A Potential Molecular Diagnostic Tool for Differentiating Lactococcus garvieae and Lactococcus petauri

Lactococcus garvieae is the etiological agent of lactococcosis, a clinically and economically significant infectious disease affecting farmed rainbow trout. L. garvieae had been considered the only cause of lactococcosis for a long time; however, L. petauri, another species of the genus Lactococcus, has lately been linked to the same disease. The genomes and biochemical profiles of L. petauri and L. garvieae have a high degree of similarity. Traditional diagnostic tests currently available cannot distinguish between these two species. The aim of this study was to use the transcribed spacer (ITS) region between 16S rRNA and 23S rRNA as a potential useful molecular target to differentiate L. garvieae from L. petauri, saving time and money compared to genomics methods currently used as diagnostic tools for accurate discrimination between these two species. The ITS region of 82 strains was amplified and sequenced. The amplified fragments varied in size from 500 to 550 bp. Based on the sequence, seven SNPs were identified that separate L. garvieae from L. petauri. The 16S-23S rRNA ITS region has enough resolution to distinguish between closely related L. garvieae and L. petauri and it can be used as a diagnostic marker to quickly identify the pathogens in a lactococcosis outbreak.

Comparative Evaluation of Booster Vaccine Efficacy by Intracoelomic Injection and Immersion with a Whole-Cell Killed Vaccine against Lactococcus petauri Infection in Rainbow Trout (Oncorhynchus mykiss)

Lactococcus petauri is an important emergent bacterial pathogen of salmonids in the USA. The purpose of this study was to evaluate the protection conferred to rainbow trout (Oncorhynchus mykiss) against L. petauri by formalin-killed vaccines in immersion and injectable forms, as well as the enhanced protection afforded by booster vaccination. In the first challenge, fish were immunized via intracoelomic injection (IC) or immersion (Imm) routes alone. Approximately 418 degree days (Temperature in degree Celsius × days post-immunization) (dd) Imm, or 622 dd IC post-vaccination, fish were challenged via IC with wild-type L. petauri. In the second experiment, initial Imm vaccination was followed by booster vaccination via Imm or IC routes 273 dd post-immunization along with appropriate PBS controls. The various vaccination protocol efficacies were evaluated by challenging fish with L. petauri by cohabitation with diseased fish 399 dd post-booster administration. A relative percent survival (RPS) of 89.5% and 28% was recorded in the IC and Imm single immunization treatments, respectively. In the second study, an RPS of 97.5%, 10.2%, 2.6% and -10.1% plus approximately 0%, 50%, 20%, and 30% bacterial persistence was recorded in the Imm immunized + IC boosted, Imm immunized + mock IC boosted, Imm immunized + Imm boosted, and Imm immunized + mock Imm boosted treatments, respectively. Only the Imm immunized + IC injection boosted treatments provided significant protection when compared to unvaccinated and challenged treatments (p < 0.05). In conclusion, although both Imm and IC vaccines appear safe for trout, the inactivated Imm vaccines seem to provide only mild and temporary protection against lactococcosis; whereas IC immunized trout develop a significantly stronger protective response in both challenges.

Lactococcosis a Re-Emerging Disease in Aquaculture: Disease Significant and Phytotherapy

Lactococcosis, particularly that caused by Lactococcus garvieae, is a major re-emerging bacterial disease seriously affecting the sustainability of aquaculture industry. Medicinal herbs and plants do not have very much in vitro antagonism and in vivo disease resistance towards lactococcosis agents in aquaculture. Most in vitro studies with herbal extractives were performed against L. garvieae with no strong antibacterial activity, but essential oils, especially those that contain thymol or carvacrol, are more effective. The differences exhibited by the bacteriostatic and bactericidal functions for a specific extractive in different studies could be due to different bacterial strains or parts of chemotypes of the same plant. Despite essential oils being shown to have the best anti-L. garvieae activity in in vitro assays, the in vivo bioassays required further study. The extracts tested under in vivo conditions presented moderate efficacy, causing a decrease in mortality in infected animals, probably because they improved immune parameters before challenging tests. This review addressed the efficacy of medicinal herbs to lactococcosis and discussed the presented gaps.

Isolation and characterization of Lactococcus garvieae from rainbow trout, Onchorhyncus mykiss, from California, USA

Lactococcus garvieae is an emergent bacterial pathogen of salmonid fish in North America that causes acute infections particularly at water temperatures above 15°C. During 2020, L. garvieae was detected in rainbow trout, Onchorhyncus mykiss, cultured in Southern California and the Eastern Sierras. Infected fish exhibited high mortalities and nonspecific clinical signs of lethargy, erratic swimming, dark skin pigmentation, and exophthalmia. Macroscopic changes included external and internal hemorrhages, mainly in the eyes, liver, coelomic fat, intestine, and brain. Histological examination revealed splenitis, branchitis, panophthalmitis, hepatitis, enteritis, and coelomitis, with variable degrees of tissue damage among evaluated fish. Pure colonies of L. garvieae were isolated from infected trout and specific PCR primers for L. garvieae confirmed the preliminary diagnosis. Multilocus sequence analysis showed that the strains recovered from diseased trout represent a novel genetic group. Isolates were able to form biofilms within 24 h that increased their resistance to disinfection by hydrogen peroxide. Laboratory challenge methods for inducing lactococcosis in steelhead trout, O. mykiss, were evaluated by intracoelomic injection with serial dilutions of L. garvieae. The median lethal dose 21 days post challenge was ∼20 colony-forming units/fish. Experimentally infected trout presented similar clinical signs, gross changes, and microscopic lesions as those with natural disease, fulfilling Koch's postulates and demonstrating the high virulence of the recovered strains.

Association of a specific major histocompatibility complex class IIβ single nucleotide polymorphism with resistance to lactococcosis in rainbow trout, Oncorhynchus mykiss (Walbaum)

Major histocompatibility complex (MHC) loci encode glycoproteins that bind to foreign peptides and initiate immune responses through their interaction with T cells. MHC class II molecules are heterodimers consisting of α and β chains encoded by extremely variable genes; variation in exon 2 is responsible for the majority of observed polymorphisms, mostly concentrated in the codons specifying the peptide-binding region. Lactococcus garvieae is the causative agent of lactococcosis, a warm-water bacterial infection pathogenic for cultured freshwater and marine fish. It causes considerable economic losses, limiting the profitability and development of fish industries in general and the intensive production of rainbow trout, Oncorhynchus mykiss (Walbaum), in particular. The disease is currently controlled with vaccines and antibiotics; however, vaccines have short-term efficacy, and increasing concerns regarding antibiotic residues have called for alternative strategies. To explore the involvement of the MHC class II β-1 domain as a candidate gene for resistance to lactococcosis, we exposed 400 rainbow trout to naturally contaminated water. One single nucleotide polymorphism (SNP) and one haplotype were associated with resistance (P < 0.01). These results are promising for using MHC class IIβ as a molecular marker in breeding rainbow trout resistant to lactococcosis.

Molecular epidemiology of zoonotic streptococcosis/lactococcosis in rainbow trout (Oncorhynchus mykiss) aquaculture in Iran

BACKGROUND AND OBJECTIVES

Streptococcosis/lactococcosis is a hyperacute systemic disease that can occur in marine and fresh waters of many species of fish. The aim of this work was to study the disease outbreak in the major rainbow trout (Oncorhynchus mykiss) production of Iran.

MATERIALS AND METHODS

108 Gram positive cocci isolates were obtained from diseased trout in seven provinces with major trout production during 2008 till 2009. These bacterial isolates were characterized using phenotypic and molecular studies. The isolates were also analysed phylogeneticaly and compared with the available data.

RESULTS

49 samples (45.37%) were identified as Streptococcus iniae, 37 samples (35.2%) matched with Lactococcus garvieae; and 22 samples (19.43%) were identified as members of Streptooccus genus by culture-based and biochemical tests of API 50 CH, API 20 STREP and rapid 32 STREP systems. Using universal primers for differentiation of Streptococcus sp. and Enterococcus sp, all 108 samples were identified as Streptococcus sp. with a target region of 500 bp. Single specific PCR resulted in identification of 64 (59.2%) isolates as S. iniae and 44 (40.8%) isolates as L. garvieae. The phylogenetic analysis of the S. iniae isolates resulted in maximal similarity to some strains reported from Taiwan and to all Brazilian strains. Also, one strain showed less sequence similarity values with other tested strains although this strain has high similarity with ATCC 29178 strain, all reported Chinese, and some Taiwanian strains. Also, analysis of S. iniae LctO gene sequence showed that this isolate clustered within the S. iniae group. The sequence analysis of L. garvieae strains also showed that they have maximum similarity to all Japanese and Chinese strains, but one strain has lower sequence similarity values with all other recorded strains.

CONCLUSION

[corrected] The results of this study clearly show that trout farming in Iran is severely affected by both species of S. Iniae and L. garvieae and requires serious preventive criteria.