negative rods which produce a brown water soluble pigment on tryptone

Negative rods which produce a brown water soluble

This preview shows page 109 - 111 out of 594 pages.

negative rods, which produce a brown, water-soluble pigment on tryptone-containing agar, which do not grow at 37°C, and which produce catalase and oxidase (Table 4.1). The circular chromosome is 4,658 =b 30 kb (Umelo and Trust, 1998). Cells are found in, and are pathogenic to, salmonids and increasingly other fish species. Tradition- ally, the lack of motility has been accepted as one of the rehable diagnostic traits used for the division of the aeromonads. However, this criterion has been challenged by the report of Mcintosh and Austin (1991a) of motility (by polar flagella) in a strain of Aer. salmonicida subsp. salmonicida grown at elevated temperatures, i.e. 30-37°C. The appearance of motility was also accompanied by variation in sugar fermentation patterns, the loss of ability to degrade complex molecules and an increase in antibiotic resistance. Further evidence for a motile mode of existence of Aer. salmonicida was provided by the recovery of eight atypical isolates from ulcers (but not from kidney tissue) on goldfish, carp and roach. The ulcerated fish were obtained from aquaria, garden ponds and rivers in England (Austin, 1993). Interestingly, these isolates did not dissociate into different colony types, but grew at 37°C. Of course, there is always the concern that motile contaminants may have been present in cultures which were predominantly Aer. salmonicida. However, the isolation of flagella genes, flaA and flaB, which coded for unsheathed polar flagella at low frequency, has clinched the argument that Aer. salmonicida can be motile under certain circumstances (Umelo and Trust, 1997). Certain traits, such as pigment production, captured the attention of fisheries scientists particularly because they were readily observable. In an examination of pigment production. Griffin et al. (1953b) showed that its development was depen- dent upon medium composition, insofar as tyrosine or phenylalanine was deemed to be essential. This was confirmed by O'Leary et al. (1956). However, it was initially assumed that this pigment was related to melanin, although subsequent investigation has refuted this possibility. Thus, Donlon et al. (1983) discovered that biosynthesis of the pigment from tyrosine differed substantially from melanogenesis and not 3,4- dihydroxyphenylalanine as would have been expected of melanin synthesis. Although production of the brown, water-soluble pigment constitutes a major diagnostic feat- ure of Aer. salmonicida (Fig. 4.1—see colour section; Martin-Carnahan and Joseph, 2005), caution is advised against relying too heavily on the presence of pigment.
Image of page 109
Characteristics of the pathogens: Gram-negative bacteria 87 Table 4.1. Characteristics of Aeromonas salmonicida^ Character Production of: Brown, diffusible pigment Arginine dihydrolase Catalase P-galactosidase H2S Indole Lysine decarboxylase Ornithine decarboxylase Oxidase Phenylalanine deaminase Phosphatase Fermentative metaboHsm Gluconate oxidation Methyl red test MotiHty Nitrate reduction Voges Proskauer reaction Degradation of: AescuHn Blood (|3-haemolysis) Casein Chitin DNA Elastin Gelatin Lecithin
Image of page 110
Image of page 111

You've reached the end of your free preview.

Want to read all 594 pages?

  • Spring '20
  • Bacteria, representative, gram-negative bacteria

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors