Establishment and persistence of Escherichia coli in the intestine of rainbow trout. Oncorhynchus mykiss (Walbaum), was investigated. Infection was achieved by ingestion of contaminated feed but not by bath exposure. At 15°C. E. coli was found to increase in number in the intestine offish after an initial decline, and could still be detected after 4 days. At 6°C it was detected for 2 days but the numbers declined steadily. A similar trend was observed when extracted gut content was inoculated with E. coli in vitro; after an initial decline, bacterial growth recovered. Gut content in vitro also was a suitable environment for plasmid‐mediated transfer of resistance. Oxytetracycline resistance was transferred successfully from Aeromonas salmoniclda to E. coli. This could not be reproduced in vivo, perhaps because the inoculum of A. salmoniclda achieved per fish was not high enough as it did not withstand drying well on the feed pellets. Introduction by gavage was also tried but failed to establish an A. salmonicida infection. These results show that at temperatures around 15°C, the presence of E. coli in fish need not be an indicator of recent passage through polluted waters. It may be a consequence of infection established many days before, and perhaps some distance away. Furthermore, although transfer of antibiotic resistance from a fish pathogen did take place in the environment of fish intestinal content, the likelihood of this being a high‐risk route for acquisition of resistance by bacteria that can affect humans is low.
Between August and December 2013, the offshore cages of a commercial marine farm culturing red drum Sciaenops ocellatus in Campeche Bay Mexico were affected by an outbreak of an ulcerative granulomatous disease with up to 70% cumulative mortality. Thirty‐one adults displaying open ulcers on the skin were submitted for diagnosis. At necropsy, multiple white‐yellowish nodules (0.1–0.5 cm in diameter) were present in all internal organs, where the kidney and the spleen were the most severely affected. Histopathology evinced typical systemic granulomatous formations. Gram and Ziehl–Neelsen stains on tissue imprints, bacterial swabs and tissue sections revealed Gram‐positive, acid‐fast, branching beaded long rod filamentous bacteria. Tissue samples resulted positive for nocardiosis with a Nocardia genus‐specific nested PCR. Definite identification at the species level and taxonomic positioning of the fastidious pathogen were achieved through a specific Nocardia seriolae PCR and by sequencing the gyrB gene of pure isolates. After administration of antibiotics during fry production, a posterior follow‐up monitoring (from 2014 to 2017) detected mild but recurrent outbreaks of the bacteria with no seasonality pattern. To the extent of our knowledge, this is the first report of piscine nocardiosis in Mexico and the first time this disease is detected in red drum.
Establishment and persistence of Escherichia coli in the intestine of rainbow trout. Oncorhynchus mykiss (Walbaum), was investigated. Infection was achieved by ingestion of contaminated feed but not by bath exposure. At 1 5°C, E. coli was found to increase in number in the intestine offish after an initial decline, and could still be detected after 4 days. At 6°C it was detected for 2 days but the numbers declined steadily. A similar trend was observed when extracted gut content was inoculated with E. coli in vitro: after an initial decline, bacterial growth recovered. Gut content in vitro also was a suitable environment for plasmid-mediated transfer of resistance.Oxytetracycline resistance was transferred successfully from Aeromonas saUnonicida to E. coli. This could not be reproduced in vivo, perhaps because the inoculum of A. sahnonicida achieved per fish was not high enough as it did not withstand drying well on the feed pellets. Introduction by gavage was also tried but failed to establish an A. salmonicida infection. These results show that at temperatures around 15°C, the presence of E. coli in fish need not be an indicator of recent passage through polluted waters. It may be a consequence of infection established many days before, and perhaps some distance away. Furthermore, although transfer of antibiotic resistance from a fish pathogen did take place in the environment of fish intestinal content, the likelihood of this being a high-risk route for acquisition of resistance by bacteria that can affect humans is low.
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