CHARACTERIZATION OF TRANSFERRIN-BINDING PROTEIN-1 AND PROTEIN-2 IN INVASIVE TYPE-B AND NONTYPABLE STRAINS OF HAEMOPHILUS-INFLUENZAE

Haemophilus influenzae has the ability to obtain iron from human trans ferrin via two bacterial cell surface transferrin binding proteins, Tb p1 and Tbp2. Although a wide array of strains have been shown to expre ss these receptor proteins, two studies have recently identified a ser ies of isolates which appeared to lack the ability to bind transferrin , Included in this group were the members of a cryptic genospecies of nontypeable biotype IV strains which appear to possess a tropism for f emale urogenital tissues and are major etiologic agents of neonatal an d postpartum bacteremia due to H. influenzae. The present study employ ed oligonucleotide primers specific for genes encoding the Tbp protein s of a type b biotype I strain of H. influenzae to probe the genomic D NAs of isolates from the previous studies, The tbpA and tbpB genes whi ch encode Tbp1 and Tbp2, respectively, were detected in all of the str ains tested either by PCR amplification directly or by Southern hybrid ization analysis. All of the strains displayed a transferrin binding p henotype, and affinity isolation of receptor proteins with transferrin -conjugated Sepharose recovered Tbp1 and/or Tbp2 from 11 of 14 strains , including 2 of the nontypeable biotype IV strains. In addition, all of the strains were capable of growing on human transferrin specifical ly, indicating that the mechanism of iron assimilation from transferri n is functional and is not siderophore mediated. These results confirm the presence of tbp genes in all of the invasive H. influenzae isolat es characterized to date, suggesting that Tbp-mediated iron acquisitio n is important in disease which initiates from either the respiratory or urogenital mucosa.