et ai 1992 The problem of purifying the bacteria from tissue culture cells was

Et ai 1992 the problem of purifying the bacteria from

This preview shows page 154 - 156 out of 594 pages.

et ai, 1992). The problem of purifying the bacteria from tissue culture cells was addressed by use of 30% percoll in which bacteriophage-like particles were observed by TEM (Yuksel et ai, 2001) and resolved by use of iodixanol (=Optiprep) as substrate for differential centrifugation gradients which together with DNasel digestion led to sufficiently pure, i.e. 99%, bacteria for DNA work (Henriquez et ai, 2003). Analysis of 16S rRNA revealed that Irish isolates formed two groupings whereas Canadian, Norwegian and Scottish cultures clustered together (Reid et ai, 2004). The possibiHty of genetic differences between isolates was examined with a view to explaining reasons for differences in virulence and mortality rates. By electrophoretic analysis of the internal transcribed spacer region of 11 Chilean isolates, two groupings were recog- nised (Casanova et ai, 2003). Piscirickettsia salmonis The pathogen is a pleomorphic, non-motile. Gram-negative, predominantly coc- coid (and ring forms) organism of variable size (0.5 x 1.5-2.0 |im), occurring intracellularly as individuals, pairs or groups. Electron microscopy reveals that each organism is bound by two membrane layers; a characteristic trait of the Rickettsiales, and possibly the tribe Erlichiae. A single isolate, designated LF-89, was studied in detail by Fryer et al. (1992). The 16S rRNA conformed to the gamma subdivision of the Proteobacteria. Moreover, LF-89 did not show any specific relationship to any of 450 bacterial 16S rRNA
Image of page 154
132 Bacterial Fish Pathogens sequences held on file. Nevertheless, similarities were apparent with Wolbachia persica (similarity = 86.3%) and Coxiella burnetii (similarity = 87.5%) than to repre- sentatives of Ehrlichia, Rickettsia or Rochalimaea. In short, it was deemed that the salmonid pathogen was sufficiently novel to warrant description in a new genus of the family Rickettsiaceae. The organism recovered from white sea bass was reported to have a 96.3-98.7% 16S rDNA homology with Pis. salmonis (Arkush et al, 2005), which is low for a confirmed identity. Rickettsia-like organisms An increasing number of pubHcations have described rickettsia-like organisms (RLO) as causal agents of disease (e.g. Rodger and Drinan, 1993; Chen et al, 1994; Khoo et al, 1995; Palmer et al, 1997; Jones et al, 1998; Corbeil et al, 2005). Whether or not these organisms correspond with Piscirickettsia salmonis has not been always estab- Hshed. For example, an RLO was reported as causing disease in tilapia from Taiwan during October 1992 to February 1993 (Chern and Chao, 1994). The pathogen was described as a Gram-negative rod of 0.86 =b 0.32 x 0.63 =b 0.24 |im in size, and thought likely to be a representative of the Rickettsiaceae (Chern and Chao, 1994). A Tasmanian isolate from Atlantic salmon was distinct from Piscirickettsia in terms of sequence aUgnment of the 16S rRNA, and for the present is regarded as an RLO (Corbeil et aL, 2005).
Image of page 155
Image of page 156

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