Identification of Shewanella putrefaciens as a novel pathogen of the largemouth bass (Micropterus salmoides) and histopathological analysis of diseased fish

Abstract

The largemouth bass (Micropterus salmoides) is an economically important aquaculture species in China, and its production has increased rapidly in recent years. Although Shewanella putrefaciens is known to infect several fish species, its role in infecting M. salmoides is relatively unknown. Here, we isolated a gram-negative bacterial strain (termed XX2021) from farmed largemouth bass. Based on the results of 16S rRNA sequencing and phylogenetic analyses, the isolate was identified as S. putrefaciens. The virulence of XX2021 was dependent on water temperature, such as the LD50 values were 4.21×104, 7.26×105, and 2.47×106 CFU/g fish weight at 10°C, 18°C, and 25°C, respectively. Four virulent genes—including dksA, hem, lonR, and fur—were screened through a PCR assay. The results of an antibiotic resistance test showed that XX2021 was sensitive to kanamycin, cefotaxime, doxycycline, sulfamethoxazole, florfenicol, tetracycline, and gentamicin; showed intermediate susceptibility to streptomycin, ampicillin, and norfloxacin; and was resistant to nalidixic acid and penicillin. XX2021-infected fish showed clinical symptoms typical of S. putrefaciens infection. In addition, we re-isolated XX2021 from infected fish and confirmed its identity using 16S rRNA sequencing. Histopathological changes were observed in the intestine, head kidney, spleen, and liver of diseased fish. This study presents the first report of the pathogenic effects of S. putrefaciens in farmed largemouth bass. Our findings may help develop effective disease control strategies for aquaculture fish and prevent disease outbreaks under low water temperatures.

Implications of ammonia stress for the pathogenicity of Shewanella spp. in Oreochromis niloticus: effects on hematological, biochemical, immunological, and histopathological parameters

“…Previous studies have proven that ammonia can damage the liver and kidneys, which are essential organs for detoxification and waste removal [ 10 , 12 , 53 ]. Additionally, other studies have shown alterations in liver and kidney function in Shewanella -infected fish, and some have attributed these changes to virulence factors and toxins [ 22 , 25 , 33 ]. Therefore, the combined effects of both ammonia stress and Shewanella infection on O. niloticus may be more severe than the effects of either stressor alone.…”

“…Numerous papers document histopathological changes in the liver and kidney of ammonia-exposed fish, the extent of which these changes vary based on the concentration and exposure period [ 10 , 56 , 98 , 99 ]. Additionally, different kinds of fish exhibit histological changes in their internal organs, mostly in the liver and kidneys [ 24 , 25 , 33 ]. These alterations are mainly due to the enzyme activity of Shewanella infection, ability to adhere to cells, and the release of cytotoxins [ 20 ].…”

Inhibition of biofilm-forming bacteria and probiotic potential of Bacillus spp. isolated from aquaculture ponds

“…Diseased goldfish (Carassius auratus) showed lethargy, ascites and bulging eyes (Altun et al, 2014). There have been reports of the pathogenicity of S. putrfaciens in clownfish (largemouth bass) (Micropterus salmoides) with histopathological changes observed in the intestines, head of kidneys, spleen, and liver of diseased fish (Jiang et al, 2022). In addition, Shewanella algae were found to cause canker disease in American eel (Anguilla rostrata) (Wang et al, 2020) and black spot disease in white-leg shrimp (Penaeus vannamei) (Cao et al, 2010).…”

Shewanella xiamenensis‐associated ulcerative dermatitis in koi carp (Cyprinus rubrofuscus)

“…Prevalence varies; however, it is not unexpected for up to 100% morbidity (Wildgoose, 2001) and 20% mortality (Pękala et al., 2015) to occur, especially if poor water quality and husbandry are co‐factors (Wildgoose, 2001). In recent years, there have been outbreaks of Shewanella putrefaciens ‐associated UD in wild eels (Esteve et al., 2017), barramundi (Erfanmanesh et al., 2019), gilthead seabream (Tapia‐Paniagua et al., 2018), Nile tilapia (Manal, 2017), rabbitfish (Saeed et al., 1990), largemouth bass (Jiang et al., 2022), European sea bass (Korun et al., 2009), rainbow trout (Pękala et al., 2015), common carp (Pękala et al., 2015), and koi carp (Cocchi et al., 2018). In these studies, S. putrefaciens was identified as an opportunistic fish pathogen capable of inducing a range of lesions (particularly UD) during periods of physiological stress or immunocompromise (Kozinska & Pekala, 2004).…”