Screening ofBacterial Isolates forMannose-Specific Lectin Activity byAgglutination ofYeasts

Atotal of393clinical bacterial isolates weretested fortheir ability toagglutinate yeast cells ofeither Saccharomyces cerevisiae orCandidaalbicans. A positive agglutination ofyeasts thatcouldbeprevented bymethyl a-D-mannoside was takenasanindication forthepossible presence ofa mannose-specific lectin (carbohydrate-binding protein) onthesurface ofthetested bacteria. Agglutinationtests onglass slides showedthat38%ofalltheisolates tested werepositive intheir capacity toagglutinate yeasts. Amongthevarious strains tested, all isolates ofSerratia marcescens, Proteus morganii, andCitrobacter diversus, as wellas94%ofKlebsiella pneumontae, werepositive. Ontheotherhand, only 46%oftheEscherichia coli, 48%ofthesalmonellae, 44%oftheCitrobacter freundii, and71%oftheAeromonashydrophila isolates werepositive. A quantitative determination ofthelectin activity donebyobserving theagglutination ofyeasts inmicrotiter plates showedthatS.marcescens isolates werethemost avidbinders totheyeast, whereas Klebsiella andCitrobacter isolates werethe weakest. Theagglutination oferythrocytes byEscherichia coli, Shigella, Salmonella, andKlebsiellahasbeenknownformanyyears(4-6, 12). Hemagglutination insomeinstances hasbeen attributed topili andinseveral caseshasbeen inhibited bymannoseandsomeofits derivatives (13). Escherichia coli hasalsobeenshownto agglutinate Saccharomyces cerevisiae yeast cells thatareknowntocontain mannansontheir cell surface, andthis agglutination wasinhibited bysolutions ofD-mannose(11). Theseearlier findings haveledtotheisolation fromsurfaces ofEscherichia coli ofaprotein (lectin) that has mannose-binding properties (7). Themannosebinding lectin hasbeensuggested tobeoneof themechanisms that mediate theadherence and subsequent colonization ofepithelial cells bythe bacteria (11). Inviewofthepossible importance thatthemannose-binding activity mayhavein thepathogenic pathway, wehavetried tofind outinthepresent workhowprevalent this propertyisbyobserving agglutinating capacities amongclinical bacterial strains isolated from patients ofalarge hospital.