The woodchuck animal model of hepatitis B-like virus infection and disease.

As a model of virus-induced disease, the WHV/woodchuck system is at an early stage of development; yet, much progress has been made and there now exists considerable evidence that WHV causes serious liver disease with major parallels to HBV infection of man. The relatively short interval (4-5 yrs) from infection to end-stage disease in this model provides unique opportunities for definition of the natural history of HBV disease and the evaluation of various intervention strategies (e.g., vaccine prophylaxis and anti-viral therapy). Such studies are currently in progress in a number of laboratories.

Phase transition of gonococci in mammalian cell cultures.

Neisseria gonorrhoeae was cultivated in mammalian cell cultures in an effort to determine if this environment will elicit a T4 --> T1 transition. Of four avirulent (T4) isolates tested, only one, H4, yielded T1 colonies. This change was consistently obtained in HeLa, WI-38, and MK2 cells, even when the multiplicity of the gonococcal infection was less than 1 per culture. Growth of the gonococci took place primarily on the surface of the cells, as demonstrated by light and electron microscopy, but occasional bacteria were undoubtedly intracellular. T1 colonies were seen at 24 h and were the major population at 48 h. This shift was favored by the presence of viable cells, since smaller yields of T1 were obtained when the cells were irradiated or heat inactivated. It was also favored by low pH, since T1 recovery was reduced when the buffering capacity of the medium was increased. Although the results suggest that T1 gonococci derived from H4 have a selective advantage over T4 in cell cultures, this is not true of all T1 and T4 colony types. F62 T4, which does not undergo a T4 --> T1 shift, propagated as well as T1 in HeLa cell cultures. The change in colony type of strain H4 to T1 was accompanied by formation of pili and by gain in capacity for deoxyribonucleic acid-mediated transformation. It is concluded that gonococci can undergo T4 --> T1 phase transition in mammalian cell cultures, but this property is not retained by all strains.

Interaction of gonococci with phagocytic leukocytes from men and mice.

The interaction of human and mouse phagocytic leukocytes with representative virulent (F62-T1) and avirulent (F62-T4, RD-5) strains of Neisseria gonorrhoeae was studied in vitro. Leukocyte monolayers were incubated with gonococci for 30 min at 37 C, washed repeatedly, reincubated with fresh medium, and sampled for viable bacteria at intervals. After the initial incubation period and washing, human leukocytes retained larger numbers of viable T1 than of T4. During the subsequent 120 min of incubation, the numbers of viable T1 remained approximately constant, whereas viable counts of T4 declined by about two-thirds. In contrast, mouse leukocytes under similar conditions destroyed 70% of both types of gonococci. When human bactericidal serum was applied to infected human leukocytes, it had no effect on T4 but inactivated over 50% of T1. It is concluded that T4 are phagocytized by human leukocytes and are thus exposed to internal digestion, but are protected from bactericidal serum. T1, on the other hand, either adhere to the surface of the leukocytes or remain located so that they are neither digested by the leukocytes nor protected from bactericidal serum.

DNA base composition of rickettsiae.

There is a small but distinct difference in DNA base composition between the typhus and spotted fever groups of rickettsiae. The molar percentages of guanine plus cytosine for Rickettsia prowazeki, R. typhi, and R. canada are approximately 30, for R. rickettsi, R. conori, and R. akari they are about 32.5. The percentage for trench fever rickettsia, Rochalimaea quintana, is 38.6.

Factors Affecting Transformation of Pasteurella novicida.

The requirements and characteristics of Pasteurella novicida transformations in liquid suspensions were studied. Transformation frequencies of 0.1 to 0.3% were routinely obtained when recipient cells were harvested from 16-hr agar plates and higher than 1% when logarithmic-phase broth-grown cells were used. Calcium ions were essential for transformations. The deoxyribonucleic acid dose response curve, kinetics of transformation, and pH optimum for transformations were similar to those of other bacterial transformation systems. The genetic relatedness of P. novicida and P. tularensis was established by transforming P. novicida mutants with deoxyribonucleic acid extracted from P. tularensis.

Cotransduction and cotransformation of genetic markers in Bacillus subtilis and Bacillus licheniformis.

Bacteriophage SP-15, a large generalized transducing phage of Bacillus, was compared with phages PBS-1 and SP-10 for the ability to cotransduce pairs of genetic markers exhibiting different degrees of linkage. When auxotrophs of B. subtilis W-23 were used as recipients, SP-15 and PBS-1 effected a much higher frequency of cotransduction than did SP-10 with markers that were not closely linked. With more closely linked loci, the differences were not as great. SP-15 cotransduced linked markers at a higher mean frequency than PBS-1, suggesting that SP-15 is able to transfer a larger fragment of the Bacillus genome than any phage heretofore described. The frequency of the joint transfer of genetic markers in B. licheniformis was lower via transforming deoxyribonucleic acid than by transduction with phage SP-10. The availability of three procedures for genetic exchange-transduction by SP-15 and SP-10 as well as transformation-each of which reveals a different degree of linkage, makes B. licheniformis 9945A especially amenable to genetic analysis.

Transformation of Pasteurella novicida.

Deoxyribonucleic acid from a streptomycin-resistant mutant of Pasteurella novicida transformed portions of P. novicida streptomycin-sensitive populations to streptomycin-resistant. Similarly, mutants auxotrophic for tryptophan or purine biosynthesis were also transformed to nutritional independence.

Sequential replication of the chromosome of Bacillus licheniformis.

A sequential replication map of the chromosome of Bacillus licheniformis was constructed by employing the method of gene-frequency analysis presented by Yoshikawa and Sueoka. Our analysis of 11 genetic markers was based on the hypothesis that the chromosome initiated replication at a fixed origin and proceeded in a linear fashion to the terminus. The proposed locations of markers were validated by cotransformation and cotransduction analyses. Bacteriophage SP-15 cotransduced markers that failed to show linkage by transformation.