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.
