The sacT gene which controls the sacPA operon of BaciUlus subtilis encodes a polypeptide homologous to the B. subtilis SacY and the Escherichia coli BglG antiterminators. Expression of the sacT gene is shown to be constitutive. The DNA sequence upstream from sacP contains a palindromic sequence which functions as a transcriptional terminator. We have previously proposed that SacT acts as a transcriptional antiterminator, allowing transcription of the sacPA operon. In strains containing mutations inactivating ptsH or ptsI, the expression ofsacPA and sacB is constitutive. In this work, we show that this constitutivity is due to a fully active SacY antiterminator. In the wild-type sacT+ strain or in the sacT30 mutant, SacT requires both enzyme I and HPr of the phosphotransferase system (PTS) for antitermination. It appears that the PTS exerts different effects on the sacB gene and the sacPA operon. The general proteins of the PTS are not required for the activity of SacY while they are necessary for SacT activity.In Bacillus subtilis, the expression of both the sacPA operon and the sacB gene are induced by sucrose (21). The sacA gene codes for an endocellular sucrase (10,11,22), and sacP is the structural gene of a membrane-associated, specific component of the phosphoenolpyruvate-dependent carbohydrate phosphotransferase system (PTS) for sucrose transport (8, 9). The sacB gene encodes a second sucrosehydrolyzing enzyme called levansucrase (22, 37). Two regulatory loci, sacT and sacS, control the transcription of these genes (21,22). Transcriptional regulation of the sacB gene involves an antitermination mechanism (31, 35): between the promoter and the sacB coding sequence, a region of dyad symmetry acts as a transcriptional terminator. Deletion of this termination structure or single-base changes that modify the dyad symmetry led to constitutive synthesis of levansucrase (34). The regulatory locus sacS was identified by analysis of several constitutive mutants. It contains two genes, sacX and sacY, which seem to form an operon. The sacY gene encodes an antiterminator similar to the bglG gene product of Escherichia coli (2,30,42). The sacX gene encodes an enzyme II-like protein, similar to sacP of B. subtilis, bglF from E. coli, and scrA from E. coli, Streptococcus mutans, and Vibrio alginolyticus (3, 43). A specific component of the PTS is also involved in induction of the bgl operon of E. coli. A model of regulation of the bgl operon has been proposed: the enzyme IlBg1, which is involved in P-glucoside transport, negatively regulates the positive regulator BglG by phosphorylation, and thereby abolishing its activity (1,29).A similar model of regulation was proposed for sacB. In the absence of inducer, the sacB gene is not transcribed.

SUMMARYThe virulence offaecal and urinary Escherichia coli strains was studied in relation to serotype, haemolysin production and haemagglutination pattern. By means of an experimental mouse model E. coli strains can be divided into avirulent (I), mouse nephropathogenic (II), and generally virulent (III) strains. Virulent group II and group III strains were more often haemolytic and haemagglutinating than avirulent group I strains. Presence of K antigen could not be associated with virulence. Discriminant analysis for qualitative variables revealed that no combination of the investigated properties contributed more to a strain's virulence level than did one single property. It is concluded that other virulence factors, apart from haemolysin production in group II strains and haemagglutinins in group III strains, must be involved in the determination of a strain's virulence level.All 02, 06 and 018 ac strains tested were virulent, and by far the most 075 strains were avirulent, whereas other 0 groups were more variable with regard to virulence. Pyelonephritis strains were more often mannose-resistant haemagglutinating than faecal and other urinary isolates, indicating that mannoseresistant adhesins may be important in the pathogenesis of pyelonephritis.

The adherence to human uroepithelial cells of 23 Escherichia coli strains belonging to three groups with different levels of virulence was investigated, and the mechanism of adherence was studied. It was found that strains belonging to the most virulent group adhered better to human uroepithelial cells than did avirulent strains. Adherence of less virulent but supposedly nephropathogenic strains was more variable. These results suggest that adherence is an important virulence factor, especially in the group of strains with the highest but a more general virulence. Piliated strains adhered better than did nonpiliated strains. We found strong evidence for the existence of at least two different mechanisms of adherence: (i) mannose-sensitive adherence by piliated strains, very likely mediated by type I pili because this mannose-sensitive adherence was associated with mannose-sensitive hemagglutination of guinea pig erythrocytes by broth cultures of the strains; (ii) mannose-resistant adherence by piliated strains, very likely mediated by non-type I pili because this mannose-resistant adherence was invariably associated with mannose-resistant hemagglutination of human group A erythrocytes by the strains, whether grown in broth or on plates. Additionally, one strain without pili and without hemagglutinating activity adhered well. Thus in most cases adherence seemed to be mediated by bacterial pili, although different types might be involved.

PLATE XVIIISUMMARY. The influence of haemolysin production on virulence was studied in an experimental mouse model. Urinary strains of Escherichia coli can be divided into three virulence groups by determining their kinetics in the mouse kidney after intravenous injection. Virulent strains of groups I1 and I11 were more often haemolytic than avirulent group-I strains. Haemolytic virulent strains often caused haemoglobinuria in the mice, and killed the mice more rapidly than did non-haemolytic virulent strains. No relationship was found between a-haemolytic activity and virulence in wild-type haemolytic strains. When haemolysin production was reduced or eliminated by treatment with actinomycin-D or rifampicin, six out of seven group-I1 strains tested gave the same results as avirulent group-I strains. However, the kinetics in the mouse kidney of four haemolytic group-I11 strains tested was not changed after reduction or elimination of haemolysin production; only a small decrease in toxicity was observed. It is concluded that haemolysin production by E. coli is a decisive virulence factor in most of the mouse-nephropathogenic group-I1 strains, but not in the virulent group-I11 strains.