Genotypic diversity, and molecular and pathogenic characterization of Photobacterium damselae subsp. piscicida isolated from different fish species in Taiwan

Abstract

Photobacteriosis, caused by Photobacterium damselae subsp. piscicida (Phdp), is a serious disease in marine fish species worldwide. To date, the epidemiological characterization of this pathogen in Taiwan remains limited. In this study, we collected 39 Phdp isolates obtained from different farmed fish for phenotypic and genotypic analysis. Phenotype bioassays using API‐20E and API‐20NE systems showed that the Phdp is a homogeneous group. However, genotyping using the pulsed‐field gel electrophoresis (PFGE) technique revealed genetic variability among Phdp isolates when 13 and 11 different PFGE band patterns were obtained with SmaI and NotI as restriction enzymes, respectively. Phylogenetic analysis using 16S rDNA and the Fur gene clustered Taiwanese isolates and other species of P. damselae in the same clade. In contrast, the ToxR phylogenetic tree, a powerful discriminatory marker, separated the two subspecies. Furthermore, the virulence‐associated genes, AIP56, P55, PDP_0080, Sod and Irp1, were detected from all isolates. Virulence testing with nine representative isolates in cobia (Rachycentron canadum) and Asian sea bass (Lates calcarifer) showed that some were highly pathogenic with 80%–100% mortality rates. This study provides epidemiological data of Phdp infections in farmed fish in Taiwan, which is necessary to develop comprehensive prevention and control strategies for the disease.

Susceptibility of Sea Bream (Sparus aurata) to AIP56, an AB-Type Toxin Secreted by Photobacterium damselae subsp. piscicida

“…However, the screening of 49 Phdp isolates recovered between 2014 and 2020 from diseased sea bream and sea bass in different European countries showed a 100% prevalence of the AIP56-encoding gene. This result, which is in agreement with previous studies reporting a ubiquitous distribution of the aip56 gene in Phdp strains recovered worldwide from different fish species in the last 30 years [18,29,30], suggests the existence of selective pressure to maintain the toxin gene and supports the hypothesis that in the majority of hosts the toxin may be required for virulence. However, it cannot be excluded that, in some hosts, AIP56 may have a less important contribution for virulence and that other virulence determinants, so far unidentified, may assume a more prominent virulence role.…”

Molecular and histopathological characterization of Photobacterium damselae in naturally and experimentally infected Nile tilapia (Oreochromis niloticus)

“…So, the phylogenic tree constructed using 16S rRNA gene can be used to characterize P. damselae but not distinguish their subspecies. Similar findings have been reported previously (Machado & Gram, 2015, 2017; Pham, Cheng, Wang, & Chen, 2020).…”

Phenotype, genotype and pathogenicity of Streptococcus agalactiae isolated from cultured tilapia (Oreochromis spp.) in Taiwan

“…Thus, we could separate the result from the Sma I restriction enzyme cut into 3 clusters, and 10 clusters from the Apa I restriction enzyme. Previous studies have also considered the similarity percentage of each pulsotype (Pham et al., 2020; Tenover et al., 1995). S1/A1 (21/59) was the dominant pulsotype, mostly from Chiayi County, Kaohsiung County and Pingtung County.…”