Study of pathogenicity and severity of Lactococcus garvieae isolated from rainbow trout (Oncorhynchus mykiss) farms in Kohkilooieh and Boyerahmad province

Abstract

Background: Lactococcus garvieae is one of the most important risk factors in the rainbow trout culture. Therefore, the purpose of this study was to identify and detect strains isolated from rainbow trout suspected of having Lactococcus garvieae using biochemical characteristics and PCR and determination of the degree of severity of isolated strains. Methods: In this study, the cause of lactococcosis in selected rainbow trout farms in Kohkilooieh and Boyerahmad province was assayed. Gram-positive and catalase-negative bacterial isolates were first obtained from selected trout fish farms using conventional biochemical tests and PCR assay. The 10-day LD 50 method (concentration causing 50% mortality in 10 days) was used to determine the severity of the isolated bacteria. Results: One bacterial isolate was detected from all sampled fish which confirmed as Lactococcus garvieae using a specific PCR assay based on the 16S rDNA gene by producing a single band of 1107 bp. Analysis of the rate of mortality showed that the 10-day LD 50 was 4.6 × 10 5 CFU/fish. The results of this study showed that isolated bacteria had high severity for rainbow trout. The presence of bacteria in internal organs of suspected fish showed a severe systemic infection in challenged fish. Antibiogram assay also indicated that the isolated Lactococcus garvieae were resistant to some mostly used antibiotics in rainbow trout. Conclusions: According to current research, it can be concluded that the condition of lactococcosis in the studied area is not suitable, and despite the presence of disease, there is no proper action to control and prevent the disease. Unfortunately, isolated bacteria from the studied area have a very high severity compared to bacteria isolated from other regions of the country or other countries. Therefore, further investigation is needed to determine the cause of this difference and possibly in the design of the vaccine.

Isolation and characterization ofLactococcus garvieaefrom rainbow trout, Onchorhyncus mykiss, from California, USA

“…The highly virulent nature of a Californian trout L. garvieae isolate was confirmed in laboratory-controlled challenges, which determined an LD 50 of ∼20 CFU/mL 21 dpc. Results were similar to the 1.25 × 10 1 CFU/mL reported by Eldar and Gittino (1999), but lower than LD 50 values of 10 2 CFU/mL (Pereira et al, 2004), 7.4 × 10 5 CFU/mL (Karami et al, 2019), 6 × 10 5 CFU/mL (Sharifiyazdi et al, 2010) and 1.7 × 10 5 CFU/mL (Türe et al, 2014) determined for other trout isolates using the same infection route. The differences could be the result of bacterial strain virulence, fish susceptibility (e.g.…”

“…garvieae from Iran, Turkey and Japan likewise show variable sensitivities to antimicrobial agents (Balta & Balta, 2019;Karami et al, 2019;Maki et al, 2008;Sharifiyazdi et al, 2010;Soltani et al, 2008).…”

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

“…The development of a disease depends primarily on the virulence of the bacteria, the characteristics of the host infected, the route of infection, the age of the fish infected, the quality of water, and other environmental factors (Meyburgh et al., 2017; Sudheesh et al., 2012). The pathogenic mechanism underlying L. garvieae infection involves the formation of vascular endothelial lesions that lead to the manifestation of petechiae and disseminated inflammation in fish (Meyburgh et al., 2017), where the severity of infection or symptoms can vary depending on the host organism (Karami et al., 2019). The gross histopathological observation in the present case study were consistent with previous findings of anaemia, pale gills, renomegaly, splenomegaly, congestion and haemorrhages in heart, liver, kidney, spleen and brain, leading to partial degeneration (Chang et al., 2002; Chen et al., 2002; Meyburgh et al., 2017; Shahi et al., 2018).…”

The Opportunistic Pathogen Chryseobacterium balustinum WLT: Pathogenicity and Antibiotic Resistance

“…Generally, the pathogenicity of Chryseobacterium in farmed fish is comparably lower than the major bacterial pathogens (e.g., Flavobacterium and Lactococcus) and earlier studies reported 5 LogCFU/fish as the median lethal dose of Chryseobacterium [33,34]. The LD50 of C. cucumeris in pond loach was 7.8 LogCFU/fish [32], whereas the LD50 of C. indologenes in yellow perch was 8.1 LogCFU/fish [35].…”

“…The C. scophthalmum TPBLGL 18 infection in golden mahseer resulted in median lethal dose of 6.2 LogCFU/fish [36]. Although the pathogenicity of the Chryseobacterium was not much greater than the common pathogens, multidrug-resistant features of the strain WLT may pose a therapeutic challenge [33,34]. Therefore, Chryseobacterium could be considered as a fish pathogenic microoganism in addition to its food spoilage activity.…”