Adherence properties of an mrkD-negative mutant of Klebsiella pneumoniae.

The role of the mrkD gene in attachment by a type 3 fimbriate Klebsiella pneumoniae strain was further characterized. A clinical isolate, K. pneumoniae IA565, was found to contain two copies of the gene encoding the fimbrial subunit, mrkA, and one copy of the gene encoding the adhesin subunit, mrkD. One copy of mrkA was located on the bacterial chromosome, and the other copy was associated with mrkD and located on a plasmid. The plasmid-borne mrk gene cluster was lost when K. pneumoniae IA565 was subcultured serially in broth at 44 degrees C. The resulting mrkD-negative strain, designated K. pneumoniae IApc35, did not exhibit the following adherence characteristics associated with K. pneumoniae possessing MrkD-positive fimbriae: agglutination of tannic acid-treated human erythrocytes and attachment to trypsinized human buccal cells. However, K. pneumoniae IApc35 produced type 3 fimbriae that were composed of the characteristic 21.5-kDa major fimbrial subunit, were reactive with specific serum, and were visualized specifically by immunoelectron microscopy. K. pneumoniae IApc35 retained a copy of the mrkA gene on its chromosome. This mrkA-containing gene cluster could be complemented by a recombinant plasmid carrying only the mrkD gene, resulting in restoration of the K. pneumoniae IA565-like adhesive phenotype and demonstration of type 3 filament-associated MrkD subunits by using colloidal gold labeling and immunoelectron microscopy. These data indicate that K. pneumoniae may contain multiple copies of the mrk genes which may be present simultaneously on both plasmid and chromosomal DNAs and which may encode fimbriae with different binding specificities.

Quantitative cellular cytotoxicity to Brugia malayi microfilariae: in vitro studies of sera from an area endemic for filariasis in Andhra Pradesh, India.

The extent of eosinophil and neutrophil cell-mediated cytotoxicity on Brugia malayi microfilariae by sera from an area endemic for bancroftian filariasis in Andhra Pradesh, India, has been studied in vitro in terms of the clinical status of the subjects. At physical examination, 66 serum samples were collected. Group "A" included patients with various disease manifestations like lymphoedema, hydrocoele, lymphangitis and elephantiasis. Group "B" had microfilaraemia ranging from 1-300/ml of blood. Subjects with no history of infection past or present (endemic normals) were studied as Group "C". Out of 38 sera tested individually with eosinophils, 14/18 of Group A, 10/11 of Group B and 7/9 of Group C promoted higher (21-97%), moderate (18-88%) and highest (51-95%) range of cytotoxicity, respectively. The age, clinical status and duration of disease among the infected subjects appeared to correlate with the microfilarial mortality. In Group B, we observed the highest microfilarial count (16-300/ml) in lower (1-20 yrs) age groups. These individuals promoted higher (77-83%) cytotoxicity compared to the older age group (21-40 or 41-60) with low (1-36/ml) microfilaraemia. Group C sera were highly toxic to microfilariae. All those that were positive promoted greater than 50% mortality. Eighteen nonendemic normal sera had no effect on microfilariae. The overlapping but differential toxicity of the sera indicates that various clinical manifestations are associated with different types of cellular and humoral responses. These studies should help focus identification of the target epitopes of various immune responses of the host.