Cytotoxicity and calcium-dependent antigen of Yersinia

Intracellular targeting of the Yersinia YopE cytotoxin in mammalian cells induces actin microfilament disruption

Pathogenic Yersinia spp., including the etiological agent of plague, Y. pestis, all carry a common plasmid that encodes a number of essential virulence determinants, the Yop proteins. One of these, YopE, has been shown to be involved in the obstruction of the primary host defense by a molecular mechanism leading to inhibition of phagocytosis (R. Rosqvist, A. Forsberg, M. Rimpiläinen, T. Bergman, and H. Wolf-Watz, Mol. Microbiol. 4:657-667, 1990). Although the Yop proteins are secreted into the culture supernatant in vast amounts, in vitro studies of the function of the Yop proteins have so far been unsuccessful. We show that isolated Yop proteins indeed can cause cytotoxic effects in vitro if the proteins are introduced intracellularly into the eukaryotic cell. Isolated Yop proteins of Yersinia pseudotuberculosis were found to disrupt the microfilament structure when microinjected intracellularly into the host cell. In particular, YopE was demonstrated to be directly involved in the cytotoxic action, whereas YopD seems to have a critical role in translocating the YopE protein through the host cell membrane. These results elucidate the requirement for at least some of the Yop proteins to leave the pathogen during infection.

Identification of hemolytic granules isolated from human myocardial cells

Human myocardial cells from fresh autopsy material contained granules which possessed hemolytic activity against guinea pig and rabbit erythrocytes. The hemolytic granules, which had a density of 1.02 and a diameter of 200-300 nm, were recovered as a microsome fraction from subcellular homogenates of human myocardial cells by differential centrifugation in 300 mM sucrose containing 0.1 mM PMSF and 10 mM EDTA. The membrane lesions caused by the granules were ring-like structures with an internal diameter of about 10-17 nm, analogous to that caused by perforin- and complement-induced lysis. However, the requirement for divalent cation differed from that for perforin-induced lysis, since the microsome-mediated lysis occurred in the presence of EDTA.

Virulence of Yersinia pseudotuberculosis isolated from pork and from the throats of swine

Yersinia pseudotuberculosis was isolated from retail pork and from healthy swine throats. These wild-type strains and their representative cured isogenic strains were tested for the presence of plasmids and several virulence factors, and these characteristics were compared with those of virulent strains from humans. Two pork isolates (serotype IVB) and four swine isolates (serotypes IIB, IIC, III, and IVB) harbored a 42- to 48-megadalton plasmid which had similar fragmentation patterns resulting from digestion with restriction endonuclease. These six strains were lethal for mice via oral challenge and were positive in autoagglutination and calcium dependency tests. They also invaded HeLa cells and induced cytotoxicity. Histopathological examination and indirect fluorescent-antibody staining provided definite evidence of the pathogenicity of these strains when tissue sections from orally infected mice were used. The virulence factors of wild-type pork and swine isolates with the 42- to 48-megadalton plasmid were identical to those of two human isolates (serotypes IVB and VB). Hence, these pork and swine isolates should be considered potentially pathogenic for humans. The finding suggests that retail pork and swine may play an important role in the epidemiology of human infections caused by Y. pseudotuberculosis.

Virulence plasmid-associated HeLa cell induced cytotoxicity of Yersinia pseudotuberculosis

A virulent plasmid-containing strain and an isogenic plasmid-free avirulent derivative strain of Y. pseudotuberculosis were compared with respect to the interaction with cultured HeLa cells. No difference in the ability to adhere to HeLa cells was observed. Both strains invaded the HeLa cells to the same degree. The internalized bacteria did not multiply over a 24-h period. When incubated at 37 degrees C HeLa cells infected with the virulent plasmid-containing strain YPIII(pIB1) showed morphological changes in contrast to the avirulent plasmid-free strain YPIII which showed no such effect. This cytotoxic effect was recorded after about 2 hours of incubation at 37 degrees C. This event could be prevented by addition of gentamicin 1 hour before the predicted time of the morphological changes of the HeLa cells. A number of transposon Tn5 derived plasmid mutants were analyzed and a correlation was found between virulence and ability to induce cytotoxicity. The cytotoxic effect was not absolutely linked to Ca2+-dependence because one Ca2+-independent mutant was found to be cytotoxic. This mutant was able to express the temperature-inducible plasmid-coded outer membrane proteins (YOPs) as well as the V-antigen. On the molecular level a strong correlation was found between expression of some of the YOPs, the V-antigen and the cytotoxic effect. However, one of these YOPs, YOP1, could be eliminated as being an important determinant of cytotoxicity because an insertion mutant of the corresponding structural gene was still able to induce cytotoxicity.