Aeromonas salmonicida subsp. salmonicida, the etiological agent of furunculosis in fish, produces a catecholtype siderophore under iron-limiting conditions. In this study, the Fur titration assay (FURTA) was used to identify a cluster of six genes, asbG, asbF, asbD, asbC, asbB, and asbI, encoding proteins similar to components of the siderophore biosynthetic machinery in other bacteria. Reverse transcriptase PCR analyses showed that this cluster consists of four iron-regulated transcriptional units. Mutants with deletions in either asbD (encoding a multidomain nonribosomal peptide synthetase), asbG (encoding a histidine decarboxylase), or asbC (encoding a predicted histamine monooxygenase) did not grow under iron-limiting conditions and did not produce siderophores. Growth of the ⌬asbG strain under iron starvation conditions was restored by addition of histamine, suggesting that the siderophore in this species could contain a histamine-derived moiety. None of the mutants could grow in the presence of transferrin, indicating that A. salmonicida uses the catechol-type siderophore for removal of iron from transferrin rather than relying on a receptor for this iron-binding protein.All 18 A. salmonicida strains analyzed by DNA probe hybridization were positive in tests for the presence of the asbD gene, and all of them promoted the growth of asbD, asbG, and asbC mutants, suggesting that this siderophore-mediated iron uptake system is conserved among A. salmonicida isolates. This study provides the first description of siderophore biosynthesis genes in this fish pathogen, and the results demonstrate that the asbD, asbG, and asbC genes are necessary for the production of a catecholate siderophore that is essential for the growth of A. salmonicida under iron limitation conditions.

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Aeromonas salmonicida subsp. salmonicida, the causative agent of furunculosis in fish, can use heme as the sole iron source. We applied the Fur Titration Assay to isolate a cluster including six genes hutAZXBCD that showed similarity to heme uptake genes of other Gram-negative bacteria, and three genes orf123 of unknown function. The spatial organization of these nine genes, arranged in five transcriptional units, was similar to that of a homologous cluster in A. hydrophila. When a TonB system was provided, this cluster allowed Escherichia coli 101ESD (an ent mutant, unable to synthesize enterobactin) to utilize hemin and hemoglobin as iron sources. Mutation of hutB, a gene that encodes a predicted periplasmic hemin-binding protein, caused a drastic defect in the ability of A. salmonicida to grow with hemin as unique source of iron. Interestingly, a mutant for hutA gene (encoding the outer membrane hemin receptor) showed initially a reduced ability to grow with hemin as sole iron source, but after 24 h it achieved growth levels similar to parental strain. Thus mutation of hutA could not abolish the growth with hemin as iron source, suggesting that redundant outer membrane heme transport functions might be encoded in the A. salmonicida genome.

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Background: Zoonotic food-borne pathogens such as Salmonella spp., which can be hosted by some raw foods, play a crucial role in ranking the public health of a country Objectives: The present study was conducted to assess the frequency, antibiotic resistance pattern and index of multiple antibiotic resistance (MAR) of Salmonella spp. in chicken meat Methods: A cross-sectional survey was conducted from October 2017 to March 2018.One-hundred and fifty chicken meat samples were collected from meat stores in Zahedan, southeast of Iran and screened for contamination with Salmonella spp. using the polymerase chain reaction assay targeting the inv-A gene. Antimicrobial susceptibility testing was performed against 11 commonly prescribed antimicrobial agents in the veterinary treatment to calculate the MAR index Results: The contamination rate was 2.7% (4/150). The antimicrobial resistance rate was 100% (n = 4) against penicillin, tylosin, tetracycline, erythromycin and tiamulin, 50% (n = 2) against trimethoprim/sulfamethoxazole, difloxacin and lincomycin/spectinomycin and 25% (n = 1) against flumequine and florfenicol. All isolates were sensitive to fosfomycin. Interestingly, all isolates (n = 4) exhibited different MAR patterns. Furthermore, the MAR index ranged from 0.45 to 0.81 Conclusions:In addition to the MAR index, which indicated that the isolate originated from a source where antibiotics were used to a great degree and/or in large amounts, the results showed that the chicken meat hosted resistant strains of Salmonella spp. in the study area. Overall, the findings indicated an important public health problem. To reduce this alarming signal, the poultry industry should implement control measures in the study area.