1
© Springer International Publishing Switzerland 2016
B. Austin, D.A. Austin, Bacterial Fish Pathogens,
DOI 10.1007/978-3-319-32674-0_1
Chapter 1
Introduction
Abstract There has been a progressive increase in the number of new bacterial
taxa associated with fi sh diseases over the last 20 years, with examples including
Pasteurella skyensis and Francisella noatunensis and the emergence of so-called
unculturables, e.g. Candidatus , intact cells of which have been observed in diseased
tissue but culture has not yet been achieved.
Keywords Introduction • Cultures • Molecular diagnosis • Unculturables • Disease
defi nition
The traditional view of microbiology was that bacteria should be culturable in the
laboratory, although it is now appreciated the many micro-organisms are unable to
grow on artifi cial media. Although most of the recognised bacterial fi sh pathogens
are capable of growth in laboratory media, the value of the cultures to understanding the biology of the organisms may be questioned. Introductory microbiology
courses emphasise that bacteria multiply by binary fi ssion with single cells being
cloned to form visible colonies. Furthermore, there is an assumption that the colony
contains a homogeneous population of cells, i.e. a clone, although this may be challenged because cells may mutate, and swap and/or share genes (e.g. Pennisi 2002 ).
Then, there is the issue about the relationship of cultured cells to those in the natural
environment [= diseased fi sh] from which they were obtained. Cultured cells may
be bigger (Torrella and Morita 1981 ) and have reduced phenotypic abilities (e.g.
Koskiniemi et al. 2012 ), which may refl ect the loss of DNA by gene deletion or
from plasmids and bacteriophages, or the switching off of specifi c genes. Let us not
forget that cells more suited for the laboratory environment may well outcompete
those more closely associated with the disease pathology. The result will be laboratory cultures with limited relationship to the cells in diseased fi sh. Thus, ensuing
studies to include pathogenicity determination would be of limited value in explaining the true role of the organism in fi sh.
Within the realm of fi sh diseases, it is all too apparent that the names of bacterial
species are often used with little supporting evidence to justify the use of those
names. Over the last two decades, there has been a trend away from the conventional
phenotypic approach of characterising fi sh pathogens to molecular methods; and the
description of new taxa is often based on minimal phenotypic data, which poses
© Springer International Publishing Switzerland 2016
B. Austin, D.A. Austin, Bacterial Fish Pathogens,
DOI 10.1007/978-3-319-32674-0_1
Chapter 1
Introduction
Abstract There has been a progressive increase in the number of new bacterial
taxa associated with fi sh diseases over the last 20 years, with examples including
Pasteurella skyensis and Francisella noatunensis and the emergence of so-called
unculturables, e.g. Candidatus , intact cells of which have been observed in diseased
tissue but culture has not yet been achieved.
Keywords Introduction • Cultures • Molecular diagnosis • Unculturables • Disease
defi nition
The traditional view of microbiology was that bacteria should be culturable in the
laboratory, although it is now appreciated the many micro-organisms are unable to
grow on artifi cial media. Although most of the recognised bacterial fi sh pathogens
are capable of growth in laboratory media, the value of the cultures to understanding the biology of the organisms may be questioned. Introductory microbiology
courses emphasise that bacteria multiply by binary fi ssion with single cells being
cloned to form visible colonies. Furthermore, there is an assumption that the colony
contains a homogeneous population of cells, i.e. a clone, although this may be challenged because cells may mutate, and swap and/or share genes (e.g. Pennisi 2002 ).
Then, there is the issue about the relationship of cultured cells to those in the natural
environment [= diseased fi sh] from which they were obtained. Cultured cells may
be bigger (Torrella and Morita 1981 ) and have reduced phenotypic abilities (e.g.
Koskiniemi et al. 2012 ), which may refl ect the loss of DNA by gene deletion or
from plasmids and bacteriophages, or the switching off of specifi c genes. Let us not
forget that cells more suited for the laboratory environment may well outcompete
those more closely associated with the disease pathology. The result will be laboratory cultures with limited relationship to the cells in diseased fi sh. Thus, ensuing
studies to include pathogenicity determination would be of limited value in explaining the true role of the organism in fi sh.
Within the realm of fi sh diseases, it is all too apparent that the names of bacterial
species are often used with little supporting evidence to justify the use of those
names. Over the last two decades, there has been a trend away from the conventional
phenotypic approach of characterising fi sh pathogens to molecular methods; and the
description of new taxa is often based on minimal phenotypic data, which poses