Myo-inositol as an adjuvant to florfenicol against Aeromonas hydrophila infection in common carp Cyprinus carpio.

Florfenicol, a synthetic drug with chemical structure and spectrum of antibacterial activity similar to chloramphenicol, has been shown to be effective against a number of bacterial pathogens. However, there are increasing signs of florfenicol-resistant bacteria due to the misuse and overuse of florfenicol in aquaculture. In the present study, florfenicol had a higher bactericidal efficacy in the presence of myo-inositol, which may be due to the ability of myo-inositol to increase susceptibility of Aeromonas hydrophila to florfenicol. Furthermore, in two different infected models, co-administration of myo-inositol and florfenicol significantly reduced the bacterial load in the liver, kidney and spleen tissues of A. hydrophila-infected Cyprinus carpio, and greatly increased the survival rate of infected fish. Finally, it was also found that myo-inositol exhibited synergistic action with other antibiotic drugs including neomycin sulfate, ceftriaxone and enrofloxacin. The results obtained in this study suggest that myo-inositol as an efficient adjuvant to antibiotic drugs could be useful in increasing the antimicrobial activity of antibiotic drugs against A. hydrophila infection, and could also be useful to help decrease the occurrence of antibiotic overuse in aquaculture.

L-proline increases survival of tilapias infected by Streptococcus agalactiae in higher water temperature.

Streptococcosis causes massive tilapia kills, which results in heavy economic losses of tilapia farming industry. Out of the Streptococcosis, Streptococcus agalactiae is the major pathogen. The bacterium causes higher mortality of tilapias in higher than lower temperatures. However, effect of temperature on metabolic regulation which is related to the mortality is largely unknown. The present study showed 50% and 70% mortality of tilapias cultured in 25 °C and 30 °C, respectively, in comparison with no death in 20 °C following infection caused by S. agalactiae. Then, GC/MS based metabolomics was used to investigate a global metabolic response of tilapia liver to the two higher water temperatures compared to 20 °C. Thirty-six and forty-five varied abundance of metabolites were identified in livers of tilapias cultured at 25 °C and 30 °C, respectively. More decreasing abundance of amino acids and increasing abundance of carbohydrates were detected in 30 °C than 25 °C groups. On the other hand, out of the pathways enriched, the first five biggest impact pathways belong to amino acid metabolism. Decreasing abundance of l-proline was identified as a crucial biomarker for indexing higher water temperature and a potential modulator to reduce the high death. This was validated by engineering injection or oral addition of l-proline. Exogenous l-proline led to elevated amino acid metabolism, which contributes to the elevated survivals. Our findings provide a potential metabolic modulator for controlling the disease, and shed some light on host metabolic prevention to infectious diseases.