Chapter 1 : What Is a Pneumococcus?

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The pneumococcus ( or diplococcus) has been profoundly important in the understanding of the human response to infectious disease, the nature of genetic material, and natural transformation as a means of genetic exchange, as well as in the recognition of bacterial resistance to drugs. To develop effective diagnostic tools for the pneumococcus, one has to understand more about its nearest neighbors and include the breadth of diversity of these organisms in strain panels used to validate diagnostic tools—unfortunately, this tends to be the exception rather than the rule. The pneumolysin and autolysin genes have been flagged as potentially useful targets for molecular diagnostics for the past decade or so, and reports throughout this time have always found typical human clinical pneumococci to possess and . This probable pathogenicity island (PPI-1) represents one example of no doubt other events that will be revealed by comparative genomics, which has contributed to the evolution of the founding pneumococcus from which the extant population has arisen. A hypothesis was constructed to account for these novel phenotypes and the role of in pneumococci. However, the development of a diagnostic test based upon single-target identification might be an ambitious hope given the genetic plasticity of the pneumococcus and its naturally transformable relatives.

Citation: Dowson C. 2004. What Is a Pneumococcus?, p 1-14. In Tuomanen E, Mitchell T, Morrison D, Spratt B (ed), The Pneumococcus. ASM Press, Washington, DC. doi: 10.1128/9781555816537.ch1
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Dendrogram of genetic relationships between streptococcal isolates described by Whatmore et al. ( ) and the presence or absence of characteristic pneumococcal diagnostic features. The dendrogram was constructed from housekeeping gene sequence data () by using the neighbor-joining method. Only bootstrap confidence values exceeding 90% are shown. The scale represents the number of nucleotide substitutions per site. Overall identities of strains clustering together either as atypical organisms, , and are indicated by arrows. Features include optochin susceptibility (?), optochin intermediate resistance (□), bile solubility (insert image), presence of an identified pneumococcal capsule (insert image), presence of the pneumolysin gene (?), and presence of the major autolysin gene (?). Strains deficient in these characteristics are highlighted black. Strains, identified here as using three loci and in a previous study examining nine different loci ( ), arise from a common node with a bootstrap value of 100. Within this group two clusters were identified as a and b. Cluster b isolates, though clearly pneumococci, were all acapsulate, with one isolate exhibiting bile insolubility and another exhibiting intermediate optochin resistance. One acapsulate isolate was identified within cluster a. Atypical organisms, arising at node c, represent a rather diffuse collection of strains but are clearly separated from typical strains of and from strains identified as and . Strains identified as form an ill-defined group the bulk of which arise at node d. Strains identified as form a clearly distinguishable group arising at node e. What is interesting is the genetic conservation within pneumococci, compared to the diversity found among and even greater diversity among isolates of .

Citation: Dowson C. 2004. What Is a Pneumococcus?, p 1-14. In Tuomanen E, Mitchell T, Morrison D, Spratt B (ed), The Pneumococcus. ASM Press, Washington, DC. doi: 10.1128/9781555816537.ch1
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Image of FIGURE 2

Condensed dendrogram of genetic relationships between the strain carrying the proposed Norway 4 mutation (in bold) described by Novak et al. ( ) and a panel of genetically diverse well-characterized strains of (including strains Norway 4[ ] and R6 [ ]) atypical organisms, and ( ). The dendrogram was constructed by the neighbor-joining method using the program within MEGA version 2.1 ( ). The scale represents the number of nucleotide substitutions per site.

Citation: Dowson C. 2004. What Is a Pneumococcus?, p 1-14. In Tuomanen E, Mitchell T, Morrison D, Spratt B (ed), The Pneumococcus. ASM Press, Washington, DC. doi: 10.1128/9781555816537.ch1
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