Increasing of temperature induces pathogenicity of Streptococcus agalactiae and the up-regulation of inflammatory related genes in infected Nile tilapia (Oreochromis niloticus)

doi:10.1016/j.vetmic.2014.04.013

Veterinary Microbiology

Volume 172, Issues 1–2, 6 August 2014, Pages 265-271

https://doi.org/10.1016/j.vetmic.2014.04.013 Get rights and content

Highlights

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We investigated the effect of temperature on Streptococcus agalactiaeinfection in Nile tilapia.
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Streptococcus agalactiae were grown at 28 and 35 °C.
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Bacterial virulence was increased corresponding with the elevated temperature.
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Infected Nile tilapia showed massive inflammation when kept in high temperature condition.

Abstract

Temperature strongly affects the health of aquatic poikilotherms. In Nile tilapia (Oreochromis niloticus), elevated water temperatures increase the severity of streptococcosis. Here we investigated the effects of temperature on the vulnerability and inflammatory response of Nile tilapia to Streptococcus agalactiae (Group B streptococci; GBS). At 35 and 28 °C, GBS took 4 and 7 h, respectively to reach the log-phase and, when incubated with tilapia whole blood, experienced survival rates of 97% and 2%, respectively. The hemolysis activity of GBS grown at 35 °C was five times higher than that of GBS grown at 28 °C. GBS expressed cylE (β-hemolysin/cytolysin), cfb (CAMP factor) and PI-2b (pili-backbone) much more strongly at 35 °C than at 28 °C. Challenging Nile tilapia reared at 35 and 28 °C with GBS resulted in accumulated mortalities of about 85% and 45%, respectively. At 35 °C, infected tilapia exhibited tremendous inflammatory responses due to a dramatic up-regulation (30–40-fold) of inflammatory-related genes (cyclooxygenase-2, IL-1β and TNF-α) between 6 and 96 h-post infection. These results suggest that the increase of GBS pathogenicity to Nile tilapia induced by elevated temperature is associated with massive inflammatory responses, which may lead to acute mortality.

Introduction

Nile tilapia (Oreochromis niloticus) is a major fresh-water aquaculture species worldwide. In Thailand, tilapia is one of the most valuable cultured fishes (DOF, 2010). Conventional non-intensive farming is presently being replaced with intensive farming in order to meet the expanding of consumer demand. However, tilapia living in the high density are vulnerable to several infectious diseases due to the easy transmission of pathogenic organisms and the high level of stress. Streptococcus agalactiae (also known as Group B Streptococci; GBS) is a common cause of massive mortalities. Streptococcosis associated with GBS has emerged in various countries but especially in tropical regions, including Thailand (Duremdez et al., 2004, Mian et al., 2009, Suanyuk et al., 2008).

A pathogen by itself is insufficient for a disease outbreak, as environmental conditions are also important (Amal and Zamri-Saad, 2011). Environmental fluctuation, which are unavoidable in open-systems, can induce physiological changes in both the host and pathogens that share a common habitat. For example, the occurrence of streptococcosis has been related to stocking densities, pH, salinities, temperature, dissolved oxygen and water quality (Amal and Zamri-Saad, 2011, Bromage and Owens, 2009). In tilapia and barramundi farms, temperature is considered the most important factor as it has been closely related to the incidence of disease (Bromage and Owens, 2009, Mian et al., 2009).

Temperature changes can trigger changes in global gene expression of streptococcus, resulting in modifications of bacterial morphology, metabolism and virulence (Mereghetti et al., 2008). Moreover, temperature changes can be a ‘stress factor’ in poikilotherms. Deviation of the temperature from the normal physiological range of a fish can reduce its immune response and thus lower its resistance to various pathogens (Karvonen et al., 2010). We found that Nile tilapia rearing at 32 °C or higher was highly susceptible to GBS infection (Rodkhum et al., 2011) and that streptococcosis prevalence and mortality usually occurred during the warm season (Bromage and Owens, 2009, Rodkhum et al., 2011). In this study, we examined the adaptive responses of both GBS and Nile tilapia to high water temperature in order to elucidate the factors contributing to streptococcal pathogenesis in cultured tilapia in tropical countries like Thailand.

Section snippets

Bacterial strain

The pathogenic GBS used in this study was originally isolated from a diseased tilapia during streptococcosis outbreak in central region in Thailand in 2010. The bacterial species was identified with standard biochemical assays and the identified was confirmed by GBS-specific PCR targeting 16S rRNA (Martinez et al., 2001). Molecular serotype of this GBS strain was Ia according to a multiplex PCR technique (Imperi et al., 2010). The median lethal dose (LD₅₀) of this GBS strain in 30 g Nile tilapia

Bacterial growth, hemolytic activity and viability in tilapia whole blood

Colonies of GBS grown at 28 °C on TSA with 5% sheep blood were much smaller and had smaller hemolytic zones than colonies grown at 35 °C (supplementary data; Fig. S1). Bacteria grown at 35 and 28 °C entered the log-phase after 4 and 7 h, respectively (Fig. 1). At the late-stationary phase, the concentration of GBS grown at 35 °C was higher than that of GBS grown at 28 °C. In bacteria grown in tilapia whole blood, the hemolytic activity and viability were also higher at 35 °C (P < 0.05; Fig. 1). In

Discussion

Environmental management is widely known as the key to successful aquaculture farming. Among several parameters that affect production, Water temperature is considered one of the most important factors (Bly and Clem, 1992). The optimal temperature for tilapia is 29–31 °C, while stress-associated mortalities may occur when the temperature is higher than 37–38 °C (Lim and Webster, 2006). GBS outbreaks in fish farms frequently occur in summer with high mortalities when water temperature were above

Acknowledgements

The authors thank Chulalongkorn University graduate scholarship to commemorate the 72nd Anniversary of his majesty king Bhumibol Adulyadej, the 90th Anniversary of Chulalongkorn University Fund (Ratchadapiseksomphot Endowment Fund), PhD Scholarship for Research Abroad (D-RSAB) and Thailand Research Fund and office of the higher education commission (Grant no. MRG5080209).

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Increasing of temperature induces pathogenicity of Streptococcus agalactiae and the up-regulation of inflammatory related genes in infected Nile tilapia (Oreochromis niloticus)

Highlights

Abstract

Introduction

Section snippets

Bacterial strain

Bacterial growth, hemolytic activity and viability in tilapia whole blood

Discussion

Acknowledgements

Fish Shellfish Immunol.

Aquaculture

Biochim. Biophys. Acta

J. Microbiol. Methods

Fish Shellfish Immunol.

Int. J. Parasitol.

J. Biol. Chem.

Vet. Microbiol.

Res. Vet. Sci.

Dev. Comp. Immunol.

Dev. Comp. Immunol.

Aquaculture

Streptococcosis in tilapia (Oreochromis niloticus): a review

Pertanika J. Trop. Agric. Sci.

A note on capsule staining

Science

Biological activity of sea bass (Dicentrarchus labrax L.) recombinant interleukin-1β

Mar. Biotechnol.

Anti-stress effects of Glycine tomentella Hayata in tilapia: inhibiting COX-2 expression and enhancing EPA synthesis in erythrocyte membrane and fish growth

J. Agric. Food Chem.

Fisheries Statistics of Thailand 2008