Isolation and characterization of the aerobic bacterial microbiota of the esophagus and its probable association with obstructive caseous lesions in green turtles (Chelonia mydas)

Abstract

Caseous lesions in the esophagus of green turtles (Chelonia mydas) from the coast of Brazil have been described as obstructive lesions and can lead to the death of these animals. However, their etiology remains unclear. The aim of this study was to isolate and characterize the aerobic bacterial microbiota of the esophagus of green turtles (C. mydas) from the Brazilian coast and to verify its possible participation in the etiology of caseous lesions. For this, 42 animals were used, 33 alive and healthy and 9 naturally dead that had esophageal lesions confirmed by necropsy, from Anchieta and Piúma beaches, Espírito Santo. Microbiological tests and morphological evaluation of the esophagus were performed. We isolated 14 different bacterial agents from healthy animal samples, with the prevalence of Pseudomonas aeruginosa being (36.36%), Staphylococcus aureus (33.33%), Aeromonas hydrophila (27.27%), and Vibrio alginolyticus (24.24%). In dead animals, only three distinct agents were isolated: S. aureus (50.00%), A. hydrophila (25.00%), and V. alginolyticus (25.00%). Morphological evaluation revealed a predominance of the lesions at the gastroesophageal junction, with multifocal-to-coalescent distribution, discrete intensity, and absence of obstruction. Ulcerations and caseous exudates, inflammatory infiltrates, parasitic eggs, and giant foreign body cells were also observed as well as bacterial lumps and glandular alterations, such as necrosis, adenitis, and fragments of adult parasites. There was a positive correlation between bacterial lumps and microbiological culture and a negative correlation between bacterial lumps and microbiological culture with parasites. Thus, it was noted that the esophageal aerobic microbiota of C. mydas was predominantly composed of Gram-negative bacteria such as P. aeruginosa, A. hydrophila, and V. alginolyticus, in addition to several enterobacteria and Gram-positive bacteria, such as S. aureus. These agents are opportunists and may be involved in the etiology of caseous esophagitis in association with other pathogens as co-factors working in association or, even in a secondary way.