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Salmonella enterica serovar Typhimurium is the most common Salmonella serovar isolated from humans in Australia. The most common definitive phage types (DT) include 9, 64 and 135. Induction of lysogenic phages from DT 64 with mitomycin C followed by cesium chloride gradient purification, resulted in separation of two populations of phage particles. DNA extracted from these particles that was digested with SmaI showed two distinct patterns of banding. Transmission electron microscopy showed that both phage particles belong to the podovirus family of the C1 morphotype. One of the phages, ST64T is capable of mediating both generalized transduction and bacteriophage type conversion. Crude phage lysate induced from S. Typhimurium DT 64 was capable of phage type conversion. S. Typhimurium DT 9 was converted to DT 64 and DT 135 was converted to DT 16. S. Typhimurium DT 41 was also converted to DT 29. Amplified-fragment length polymorphism revealed differences between the original isolates and the convertants. Phage type conversion raises the question of the stability of the bacterial phage types in natural settings and the possibility of its occurrence during an outbreak scenario.

An Australian bovine parvovirus isolate (BPV 267) was found to haemagglutinate human, guinea-pig, rat and dog erythrocytes, out of a range of 16 species of erythrocyte tested. The haemagglutinating activity was generally found to be both pH and temperature dependent. The virus was found to replicate best in intestinal epithelium, macrophage and lung cells, out of 9 bovine cell types tested. Highest yields of virus were obtained by the use of selected cell strains at low-passage levels which were maintained near neutral pH under conditions of high rates of cell growth. Studies of the rates of thermal inactivation with time showed the virus to be relatively stable at 37 degrees C, 56 degrees C and 70 degrees C, the incorporation of serum proteins, 1 M MgCl2 and 2 M NaCl in the medium having no influence on stability at 56 degrees C. The virus was resistant to the action of CHCl3, ether and 1% trypsin, and its replication was inhibited by BUDR, this effect being reversed by thymidine. Actinomycin D was found to inhibit virus replication, but only when applied during the first 8 h post-infection. Density gradient studies showed infective virus to have a density of 1.41 g cm-3; haemagglutinating non-infective virus with defective morphology having a density of 1.31 g cm-3. In addition, a proportion of morphologically-complete haemagglutinating, but non-infective virus particles was found at a density of 1.36 g cm-3. The virus proved to have a mean diameter of 22 nm.

The conjugative plasmids determining sulfonamide resistance in five Shigella strains, each isolated from a different patient, have been characterized. One S. flexneri 2a strain, isolated in 1952, harbored an fi(+) plasmid of molecular weight 53 x 10(6), which specified synthesis of F-like pili and bore determinants for sulfonamide resistance (Su) and bacteriocinogeny (Col). This plasmid was compatible with plasmids of groups F(I), F(II), I(alpha), and P. A second S. flexneri 2a strain isolated in 1952 harbored an fi(-) plasmid of molecular weight 59 x 10(6), bearing the Su determinant and compatible with all plasmids tested. This strain also harbored an fi(+) group-F(II) plasmid of molecular weight 42 x 10(6), which bore the Col determinant and specified synthesis of F-like pili. Three S. dysenteriae 2 strains isolated in 1956 carried apparently identical fi(-) plasmids of molecular weight 58 x 10(6), which bore the Su determinant, could form transconjugants in Pseudomonas but not in Proteus, and were incompatible with the P-group plasmid RP4.

Biophysical studies with Australia complement-fixing (CF) antigen showed it to be a particle with a buoyant density of 1.20 g/cm(3) in CsCl, a sedimentation coefficient of 110, and an average diameter of 25 nm. The CF antigen was not inactivated by ether, 1% deoxycholate, 1% Tween 80 or overnight heating at 56 C. The antigen was unstable when treated with 1% sodium dodecyl sulfate. A procedure is described for the isolation and partial purification of Australia antigen from serum by using isopycnic banding and rate separation techniques. Treatment of the 1.20 g/cm(3) Australia antigen with 1% Tween 80 yielded a minor peak of CF activity with a buoyant density of 1.39 g/cm(3) in CsCl.