Pathological and mortality findings associated withAeromonas hydrophilafrom frog eggs in Al‐Ahsa region of Saudi Arabia

Abstract

Background Amphibians decline globally due to infection with virulent bacteria, despite their vital roles in the ecosystem. The current study aimed at addressing the pathological and bacterial findings of the infected Pelophylax ridibundus indigenous to the Al-Ahsa region. Many clinical signs were observed in the eggs, including discoloration, disintegration of the outer jelly coat; defects in morphology, and mortality were reported. Furthermore, neuromasts lacking apical cilia and microvilli were observed in the cleavage stages of the infected developing egg. Additionally, cutaneous hyperaemia, lethargy, peripheral oedema, subcutaneous haemorrhage and cutaneous ulcerations were observed in the infected P. ridibundus adults. Methods Ribbons of frog eggs were collected from Al-Ahsa oasis, the Eastern region, Kingdom of Saudi Arabia (KSA), and examined under light and scanning electron microscope. The developed eggs and adults were further examined using a dissecting microscope to determine signs of infection. A bacterial strain designated as PRE-1 was isolated from the infected eggs, identified genotypically and then characterized phenotypically. Strain PRE-1 was identified as Aeromonas hydrophila based on the comparative gene sequences of the 16S rRNA gene at identity level of (99.92%). Furthermore, phylogenetic relationship based on the 16S rRNA gene sequences of our strain and other relevant strains Aeromonas spp. showed that PRE-1 formed a cluster with A. hydrophila (99% bootstrap support), providing a robustness to the identification of PRE-1 as A. hydrophila. This bacterium was found to be associated with disease outbursts in the marsh frogs from the Al-Ahsa region. Conclusion It is important to continue monitoring the emerging diseases so that their cause can be discerned, and appropriate protocols can be applied to limit the spread of the loss of amphibians, which are vital for our ecosystem.