Sequence comparison of sulphonamide resistance genes from Aeromonas salmonicida, Edwardsiella ictaluri, and Escherichia coli

Isolates of Aeromonas salmonicida, Edwardsiella ictaluri, and Escherichia coli 1898, from different hosts and geographical locations, displayed resistance to Romet, a potentiated sulphonamide. This resistance is encoded on a plasmid (∼55 kb) containing sulphonamide resistance genes, sul I or sul II as demonstrated by polymerase chain reaction (PCR) analysis. PCR products from either sul I (∼900 bp) or sul II (∼400 bp) were sequenced and compared with the National Institutes of Health GenBank database sequences for these genes. The results suggest common environmental sources of this resistance factor related to various bacterial species and geographical areas. Sul I PCR fragments from various species were identical. This consensus sequence was 99.8% similar to the GenBank sul I sequence. Sul II PCR fragments from various species were 95-100% similar, which was 98.5% similar to the GenBank sul II sequence. The above bacterial species possess nearly identical sul I and sul II gene fragments (\u3e95% homology) to GenBank sul I and sul II sequences from a variety of bacterial species representing hosts and geographical locations other than those in the present study

Edwardsiellosis Caused by Edwardsiella ictaluri

We report the first cases of Edwardsiella ictaluri causing epizootics in laboratory populations of Zebrafish Danio rerio. Edwardsiella ictaluri is primarily recognized as a disease of catfish species and is known to cause an economically important bacterial disease of farm-raised catfish in the USA and abroad; however, it has been isolated on occasion from 10 other genera of nonictalurid fishes. We isolated E. ictaluri from moribund Zebrafish held in quarantine at two different universities in two states and from a research facility in a third state between February 23 and December 6, 2011. Edwardsiellosis in Zebrafish can be described as a severe systemic disease characterized by tissue necrosis and the presence of large numbers of extracellular and intracellular bacteria, often within macrophages. The kidneys (pronephros and mesonephros), spleen, nares, and forebrain were the most commonly and severely affected tissues. In outbreaks, mortality was acute and numerous fish died over a 1–2 week period. Mortality continued until the majority of the population was lost, at which time the remaining fish were euthanized. In addition to these cases, four cultures of bacteria isolated from Zebrafish by another diagnostic laboratory were submitted to the Louisiana Aquatic Diagnostic Laboratory for identification and were confirmed as E. ictaluri. In total, eight cultures of E. ictaluri from Zebrafish from Louisiana, Massachusetts, Pennsylvania, and Florida were identified. The isolates were confirmed as E. ictaluri by biochemical phenotype, API 20E (bioMérieux), and amplification and sequencing of a portion of the 16S rRNA gene. Edwardsiella ictaluri isolates from Zebrafish are believed to comprise a unique group and were differentiated from catfish isolates by exhibiting weaker motility, autoaggregation in broth, a different plasmid profile (two plasmids of 4.0 and 3.5 kb), a different API 20E code (4204000), and lack of lipopolysaccharide recognition with Mab Ed9