Differential Recognition and Hydrolysis of Host Carbohydrate Antigens by Streptococcus pneumoniae Family 98 Glycoside Hydrolases*

The presence of a fucose utilization operon in the Streptococcus pneumoniae genome and its established importance in virulence indicates a reliance of this bacterium on the harvesting of host fucose-containing glycans. The identities of these glycans, however, and how they are harvested is presently unknown. The biochemical and high resolution x-ray crystallographic analysis of two family 98 glycoside hydrolases (GH98s) from distinctive forms of the fucose utilization operon that originate from different S. pneumoniae strains reveal that one enzyme, the predominant type among pneumococcal isolates, has a unique endo-β-galactosidase activity on the LewisY antigen. Altered active site topography in the other species of GH98 enzyme tune its endo-β-galactosidase activity to the blood group A and B antigens. Despite their different specificities, these enzymes, and by extension all family 98 glycoside hydrolases, use an inverting catalytic mechanism. Many bacterial and viral pathogens exploit host carbohydrate antigens for adherence as a precursor to colonization or infection. However, this is the first evidence of bacterial endoglycosidase enzymes that are known to play a role in virulence and are specific for distinct host carbohydrate antigens. The strain-specific distribution of two distinct types of GH98 enzymes further suggests that S. pneumoniae strains may specialize to exploit host-specific antigens that vary from host to host, a factor that may feature in whether a strain is capable of colonizing a host or establishing an invasive infection

Epidémies de peste urbaine à Majunga, côte ouest de Madagascar : résumé

In August 1991, an epidemic of urban plague broke out in Majunga, a port on the western coast of Madagascar. As the first resurgence of the disease in this area in 70 years, the episode was a dramatic reminder of the ubiquity of the disease and layed low the falsely reassuring idea that plague was confined to well known centers of high altitude. After the epidemic had claimed 12 victims, 21 patients suffering from bubonic plague and 7 cases of pneumonic plague, it was brought under control by treating exposed subjects and introducing antivectorial measures. Transmission to man continued in the shape of sporadic cases of bubonic plague until April 1992 and a total number of 41 probable or confirmed bacteriological cases (not counting those deceased) were recorded out of 2020 suspected cases. The history of the disease related almost all these cases to the highly populated and unsanitary neighbourhood of Marolaka, situated on the edge of the Betsiboka estuary, and which has kept semi-rural characteristics. Its murine population had practically disappeared, decimated by an epizootic in early July. Out of the two captured sets of two #Rattus rattus (41 fleas per animal) and two #R. norvegicus each, three were carriers of the bacillus. Numerous shrew-mice (#Suncus murinus) occupied the zone and three tested positive to the direct bacteriological test. For the insectivore, the mean #Xenopsylla cheopis index 4 (n=16), rising to 26 in positive animals. The discovery of a plague infested rat carrying #X. cheopis and the persistence of #P. irritans after insecticide treatments, led us to doubt the efficiency of the antivectorial fight that had been undertaken. Risk of endemization was referred to. After a period of quiet of 3 years, isolated cases were detected in March and May 1995, followed by a new epidemic between July 1995 and March 1996. 617 clinical suspects of bubonic plague were notified... (D'après résumé d'auteur