This paper provides the first detailed biochemical profiling and AMOS-PCR characterization of some Brucella spp. isolates from Zimbabwe. The phage sensitivity patterns of all the Brucella spp. isolates were consistent with what has been reported . However, a single isolate of B. abortus (B15) was lysed by R/C phage and this susceptibility could be indicative of the presence of phage attachment sites which are present in the non-smooth phases of brucellae . The B. melitensis (B10) also showed an atypical reaction because it was not lysed by the Iz1 phage which normally lyses smooth strains of this species. However, the examination of single colonies on microscopy by Henry illumination  showed no sign of dissociation and none of the isolates were agglutinated by the R-monospecific antiserum which is an indicator of dissociation. The agglutination reaction by monospecific antisera showed the predominance of A-specific and M-specific epitopes in our B. abortus and the B. melitensis isolate, respectively. All smooth strains of Brucella may possess either the A, M or both A and M antigenic epitopes on the O chains of the lipopolysaccharides .
Although phage typing is used primarily for identification at the nomen species level, some Brucella strains, especially B. melitensis may show deviation from the standard pattern of susceptibility to Bk2, Iz1 and Wb phages . The use of phage typing as a means of differentiating Brucella spp. has become less discriminatory as a typing tool because of the discovery of new strains with atypical sensitivity patterns .
The growth characteristics and the biochemical profiles of the field Brucella spp. isolates (Table 2) were similar to those of the reference strains used in this study. In addition, the results were consistent with what is reported for Brucella spp. and biovars [2, 3, 16]. However, the requirement for CO2 for growth was at variance with reports from literature . Although most strains of B. abortus biovars 1-4 require CO2 for primary isolation, this attribute is quickly lost on repeated subcultures and such isolates will adapt to growing in atmospheres without CO2 [3, 16].
The use of the AMOS-PCR results were consistent with those reported elsewhere . These results confirmed the identity of the Brucella spp. that was obtained using biochemical profiles. The IS711 analysis using AMOS-PCR can identify only three B. abortus biovars, 1, 2 and 4; all three biovars of B. melitensis; biovar 1 of B. suis and B. ovis, but the individual biovars within a species are not differentiated . Therefore, further DNA fingerprinting methods such as the variable number of tandem repeat analysis (VNTR)  could be used to investigate the molecular epidemiology of these Brucella isolates.
Although the B. abortus used in this study originated from five of the eight geographical provinces of Zimbabwe (Table 1), it is difficult to conclude on the spatial distribution due to the limited number of isolates used. These isolates could possibly be restricted to one or a few geographical regions of Zimbabwe from where they have spread through movement of infected cattle. A study of more isolates is required to determine the spatial distribution of B. abortus in Zimbabwe. However, the predominance of B. abortus biovar 1 over biovar 2 suggested that it is the major cause of bovine brucellosis in both commercial and smallholder cattle farms. Another study which used fewer Brucella isolates from commercial dairy farms reported similar findings . Although B. abortus biovar 2 was also detected and originating from both the commercial and smallholder cattle farms, its distribution could be limited to a few isolated areas. Elsewhere in South Africa biovar 1 had been reported to account for about 90% while biovar 2 contributed 10% of all the B. abortus isolates . South Africa, to a large extent, shares similar geographic, climatic and livestock husbandry systems with Zimbabwe. While it is difficult to explain the reasons for the distribution of these B. abortus biovars in the cattle farming sectors, this could largely be influenced by movement of infected cattle between farms. Some farms often purchase cattle from other farms for the purpose of improving the genetics of their herds  or in the case of smallholder farms, to restock their herds which are continuously lost due to infectious diseases and lack of adequate grazing, especially during the drought seasons.
Despite the relatively few isolates studied, our results suggested that B. abortus biovar 3 and indeed other biovars may be rare in Zimbabwe, but this requires further study. B. abortus biovar 3 has been infrequently reported in South Africa, East and North Africa, while there seems to be no reports of isolation of the other biovars [2, 18]. World wide, in countries where bovine brucellosis is endemic, B. abortus biovar 1 is predominant and B. abortus biovar 2 occurs less frequently while the other biovars are rare [2, 18].