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Investigations on Pseudomonas pseudomallei and melioidosis

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DassanayakeL_1975redux.pdf (71.44Mb)
Date
1975
Author
Dassanyake, Lincoln
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Abstract
 
 
One hundred and sixteen strains of Ps.pseudomallei collected from various countries have been examined. The morphological, cultural and biochemical properties by which the species is usually identified in the clinical laboratory have been evaluated. The tests have not excluded any of the strains examined as Ps.pseudomallei. However, the confusions that may arise in the identification of the species on the basis of •conventional' tests have been highlighted and the need for the inclusion of some of the tests suggested by Wetmore and Gochenour (1956) has been discussed.
 
Colonial dissociation in Ps.pseudomallei has been shown to be a common feature. The number and frequency of such dissociants have approximated those reported for Ps.aeruginosa. A minimum period of incubation of at least 48 hours has been found to be necessary for colony differentiation. The initial recognition of Ps.pseudomallei on the basis of the rugose or ultra-rugose colony character, its •typical' odour and lustre on plate cultures and the pellicle growth in broth, has been questioned.
 
Some morphological and tinctorial properties described by other workers have not been seen or have been seen or occur erratically. Electron microscopy has shown the organism to possess 2-6 flagella at one pole. The bipolar flagellation reported by some workers has not been observed. Structures resembling fimbriae (pili) have been demonstrated.
 
Nine strains of the collection were examined for the presence of heat stable exotoxins.
 
All strains of Ps.pseudomallei have been examined for lysogenicity. The incidence of lysogeny in Ps.pseudomallei has been found to approach as much as 64% when tested against 10 selected indicator strains. That some strains are multiply lysogenic has been suspected. Mutagenic agents such as ultraviolet light and mitomycin have been found to induce the production of phage in lysogenic cultures. Baeteriocinlike inhibitors produced by a large number of these strains have interfered in the attempts to group strains on the basis of lysogenicity. A few propagated phage preparations examined in the electron microscope have shown the existence of four morphological types.
 
That the occurrence of bacteriocin-like inhibitions is due to more than one class of inhibitory or lytic agents including toxic alkaline metabolites and particles resembling phage components, has been considered.
 
Strains of Ps.pseudomallei have been shown to produce an antibacterial agent inhibitory to strains of Ps.aeruginosa and likewise some strains of Ps.aeruginosa produce agents inhibitory to Ps.pseudomallei♦ How these may affect 'pyocin' typing schemes in areas where melioidosis is endemic has been discussed.
 
Ps.pseudomallei, though lacking in the ability to produce any blue-green pigment, has shown a striking similarity to Ps.aeruginosa in inhibiting several gram-positive and grsun-negative bacteria.
 
Phage typing of Ps.pseudomallei strains has resulted in so many over-lapping patterns as to permit only broad groupings which, for the most part, have shown no relationship to the origin and distribution of strains or to any serological group. Much of the failure to obtain clear-cut groups could possibly be due to the phages used in the typing set.
 
The specificity of the propagated phages in attacking 93 of 116 strains of Ps.pseudomallei either strongly or weakly and not attacking any of the strains of Ps.aeruginosa and a number of other bacteria has once again raised the question whether a phage pool of Ps.pseudomallei could be used as an aid in differentiating the species (and if necessary, Ps.mallei) from those organisms with which it may be confused.
 
The fairly uniform and characteristic pattern of sensitivity of Ps.pseudomallei to antimicrobial agents used in the disc-sensitivity test in relation to those observed for Ps.aeruginosa has warranted the suggestion that it may serve as an additional aid to the identifi¬ cation of the species.
 
Since all strains of Ps.pseudomallei have been found to be serologically homogeneous in relation to agglutination tests with antisera prepared against formolised suspensions, this may offer a means of confirming the identification of the species, but the autoagglutinability of rough strains have, on occasions, been found to interfere with the conduct of such tests.
 
Limitations to the identification of the species by means of the agglutination test against unabsorbed sera prepared against the thermostable antigens have been shown. That strains of Ps.pseudomallei may differ in their thermostable antigenic components has been demonstrated by means of agglutinin-absorption, immuno-diffusion and immuno-electrophoresis methods. On this basis, at least 2 distinct sero-groups, one restricted to certain strains from Australia, have been found. Antigenic changes that appear to be due to phage "conversion" have been demonstrated in one instance. Changes in the degree of sensitivity to antimicrobial agents and in the production of haemolysis on blood agar that have occurred through an association with certain phages, have been reported.
 
URI
http://hdl.handle.net/1842/30154
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