Section E. Diseases of dairy cattle. Brucellosis

Abstract

Brucella phage Much of the recent work on brucella phage has been concerned with studies on host range of various phage preparations and some fundamental work on phage-cell interactions. Earlier work has been recently documented by Parnas (1967 a). Phage-cell interactions Calderone & Pickett (1965) studied in detail 11 brucella phages of Russian or Polish origin (including the reference Tb phage). They reported that phage formed 304 W. J. B B I N L E Y MORGAN plaques on B. suis, which could only be seen if a perfectly clear medium was used. These observations have not been confirmed by other workers, e.g. Jones, Merz & Wilson (1968a); Ostrovskaya & Tolmacheva (1968), although Parnas & Sarnecka (1964) claimed that phage lysed and multiplied on B. suis forming a turbid type of plaque (which they described as type 5). Gargani (1965) reported that phages P and Tb lysed some cultures of B. suis; there was little adsorption of phage P but the phage retarded Brucella multiplication. Calderone & Pickett (1965) found that the guanine/cytosine composition of the DNA of 11 phages studied was very similar (45-3-46-7 %) and the average Tm value (C C) was 88-6-89'2; this very close similarity between the phages was also found by antigenic studies using heterologous and homologous antiphage sera. A detailed study of phage-cell interactions was made by Jones et al. (1968 a), involving rates of adsorption, one step growth curves and lysis from without. The highest rate of adsorption occurred with B. abortus (and B. neotomae-see later) and large, clear plaques were produced. The rate of adsorption on to B. suis cells was very low, replication did not occur and plaques were not formed. A high ratio of phage to cells led to a killing of B. suis (lysis from without) confirming observations made previously (Morgan, 1963; Miinter, 1963). That lysis from without was caused by phage particles was confirmed by Jones, Merz & Wilson (19686) by treatment of phage with trypsin and by density gradient centrifugation. Jones et al. (1968 a) found that adsorption of phage took place neither with B. melitensis nor with rough strains of B. abortus, but they reported that occasional cultures of B. melitensis showed lysis with 10* x RTD (routine test dilution) of phage and rightly cautioned that, for this reason, too much reliance should not be placed on the use of phage alone (at both RTD and 10 4 x RTD); furthermore, rough cultures of B. abortus did not show lysis from without, and susceptible cultures of B. abortus of intermediate colonial morphology showed a pattern similar to that of B. suis. Whilst B. neotomae was not lysed at RTD, it showed complete lysis at 10 4 x RTD; Jones et al. (1968a) showed that B. neotomae adsorbed phage at the same rate as B. abortus, but about half the bacterial cells were killed and only some went through an infective cycle, releasing mature phage; the final phage count was always considerably less than the phage input. Merz (1965), Merz & Wilson (1966) and Jones et al. (1968 a) continued their studies on the effect...