Non-typeable Haemophilus influenzae adhere to and invade human bronchial epithelial cells via an interaction of lipooligosaccharide with the PAF receptor

Adherence and invasion are thought to be key events in the pathogenesis of non-typeable Haemophilus influenzae (NTHi). The role of NTHi lipooligosaccharide (LOS) in adherence was examined using an LOS-coated polystyrene bead adherence assay. Beads coated with NTHi 2019 LOS adhered significantly more to 16HBE14 human bronchial epithelial cells than beads coated with truncated LOS isolated from an NTHi 2019 pgmB:ermr mutant (P = 0.037). Adherence was inhibited by preincubation of cell monolayers with NTHi 2019 LOS (P = 0.0009), but not by preincubation with NTHi 2019 pgmB:ermr LOS. Competitive inhibition studies with a panel of compounds containing structures found within NTHi LOS suggested that a phosphorylcholine (ChoP) moiety was involved in adherence. Further experiments revealed that mutations affecting the oligosaccharide region of LOS or the incorporation of ChoP therein caused significant decreases in the adherence to and invasion of bronchial cells by NTHi 2019 (P < 0.01). Analysis of infected monolayers by confocal microscopy showed that ChoP+ NTHi bacilli co-localized with the PAF receptor. Pretreatment of bronchial cells with a PAF receptor antagonist inhibited invasion by NTHi 2109 and two other NTHi strains expressing ChoP+ LOS glycoforms exhibiting high reactivity with an anti-ChoP antibody on colony immunoblots. These data suggest that a particular subset of ChoP+ LOS glycoforms could mediate NTHi invasion of bronchial cells by means of interaction with the PAF receptor.

Evaluation of the virulence of nontypeable Haemophilus influenzae lipooligosaccharide htrB and rfaD mutants in the chinchilla model of otitis media

Considerable evidence has implicated nontypeable Haemophilus influenzae (NTHi) lipooligosaccharide (LOS) in the pathogenesis of otitis media (OM); however, its exact role has not been conclusively established. Recently, two NTHi LOS-deficient mutants have been created and described. Strain 2019-DK1, an rfaD gene mutant, expresses a truncated LOS consisting of only three deoxy-D-manno-octulosonic acid residues, a single heptose, and lipid A. Strain 2019-B29, an isogenic htrB mutant, possesses an altered oligosaccharide core and an altered lipid A. Each strain's ability to colonize the nasopharynx and to induce OM subsequent to transbullar inoculation was evaluated in the chinchilla model. Nasopharyngeal colonization data indicate that the parent strain and both mutants are able to colonize the nasopharynx and exhibit comparable clearance kinetics. Compared with the parent and each other, however, the mutants demonstrated marked differences in virulence regarding their relative abilities to induce OM and persist in the middle ear post-transbullar inoculation. Strain B29 required a 3-log-greater dose to induce OM than the parent strain and did not exhibit evidence of sustained multiplication but persisted for the same duration as the parent. Conversely, strain-DK1, even when inoculated at a dose 4 logs greater than the parent dose, was eliminated from the middle ear 72 h after challenge. A comparison of the relative pathogenicities of these isolates provides the opportunity to address fundamental questions regarding the contribution of LOS to pathogenesis issues at the molecular level. Specifically, the impact of these LOS gene disruptions on OM pathogenesis can be defined and may thus provide potential new targets for future protection and intervention strategies.

Study of the role of the htrB gene in Salmonella typhimurium virulence

We have undertaken a study to investigate the contribution of the htrB gene to the virulence of pathogenic Salmonella typhimurium. An htrB::mini-Tn10 mutation from Escherichia coli was transferred by transduction to the mouse-virulent strain S. typhimurium SL1344 to create an htrB mutant. The S. typhimurium htrB mutant was inoculated into mice and found to be severely limited in its ability to colonize organs of the lymphatic system and to cause systemic disease in mice. A variety of experiments were performed to determine the possible reasons for this loss of virulence. Serum killing assays revealed that the S. typhimurium htrB mutant was as resistant to killing by complement as the wild-type strain. However, macrophage survival assays revealed that the S. typhimurium htrB mutant was more sensitive to the intracellular environment of murine macrophages than the wild-type strain. In addition, the bioactivity of the lipopolysaccharide (LPS) of the htrB mutant was reduced compared to that of the LPS from the parent strain as measured by both a Limulus amoebocyte lysate endotoxin quantitation assay and a tumor necrosis factor alpha bioassay. These results indicate that the htrB gene plays a role in the virulence of S. typhimurium.

Mutation of the htrB gene in a virulent Salmonella typhimurium strain by intergeneric transduction: strain construction and phenotypic characterization

The htrB gene product of Haemophilus influenzae contributes to the toxicity of the lipooligosaccharide. The htrB gene encodes a 2-keto-3-deoxyoctulosonic acid-dependent acyltransferase which is responsible for myristic acid substitutions at the hydroxy moiety of lipid A beta-hydroxymyristic acid. Mass spectroscopic analysis has demonstrated that lipid A from an H. influenzae htrB mutant is predominantly tetraacyl and similar in structure to lipid IV(A), which has been shown to be nontoxic in animal models. We sought to construct a Salmonella typhimurium htrB mutant in order to investigate the contribution of htrB to virulence in a well-defined murine typhoid model of animal pathogenesis. To this end, an r- m+ galE mutS recD strain of S. typhimurium was constructed (MGS-7) and used in inter- and intrastrain transduction experiments with both coliphage P1 and Salmonella phage P22. The Escherichia coli htrB gene containing a mini-Tn10 insertion was transduced from E. coli MLK217 into S. typhimurium MGS-7 via phage P1 and subsequently via phage P22 into the virulent Salmonella strain SL1344. All S. typhimurium transductants showed phenotypes similar to those described for the E. coli htrB mutant. Mass spectrometric analysis of the crude lipid A fraction from the lipopolysaccharide of the S. typhimurium htrB mutant strain showed that for the dominant hexaacyl form, a lauric acid moiety was lost at one position on the lipid A and a palmitic acid moiety was added at another position; for the less abundant heptaacyl species, the lauric acid was replaced with palmitoleic acid.

Identification of the ADP-L-glycero-D-manno-heptose-6-epimerase (rfaD) and heptosyltransferase II (rfaF) biosynthesis genes from nontypeable Haemophilus influenzae 2019

Haemophilus influenzae is an important human pathogen. The lipooligosaccharide (LOS) of H. influenzae has been implicated as a virulence determinant. To better understand the assembly of LOS in nontypeable H. influenzae (NtHi), we have cloned and characterized the rfaD and rfaF genes of NtHi 2019, which encode the ADP-L-glycero-D-manno-heptose-6-epimerase and heptosyltransferase II enzymes, respectively. This cloning was accomplished by the complementation of Salmonella typhimurium lipopolysaccharide (LPS) biosynthesis gene mutants. These deep rough mutants are novobiocin susceptible until complemented with the appropriate gene. In this manner, we are able to use novobiocin resistance to select for specific NtHi LOS inner core biosynthesis genes. Such a screening system yielded a plasmid with a 4.8-kb insert. This plasmid was able to complement both rfaD and rfaF mutants of S. typhimurium. The LPS of these complemented strains appeared identical to the wild-type Salmonella LPS. The genes encoding the rfaD and rfaF genes from NtHi 2019 were sequenced and found to be similar to the analogous genes from S. typhimurium and Escherichia coli. The rfaD gene encodes a polypeptide of 35 kDa and the rfaF encodes a protein of 39 kDa, as demonstrated by in vitro transcription-translation studies. Isogenic mutants which demonstrated truncated LOS consistent with inner core biosynthesis mutants were constructed in the NtHi strain 2019. Primer extension analysis demonstrated the presence of a strong promoter upstream of rfaD but suggested only a very weak promoter upstream of rfaF. Complementation studies, however, suggest that the rfaF gene does have an independent promoter. Mass spectrometric analysis shows that the LOS molecules expressed by H. influenzae rfaD and rfaF mutant strains have identical molecular masses. Additional studies verified that in the rfaD mutant strain, D-glycero-D-manno-heptose is added to the LOS molecule in place of the usual L-glycero-D-manno-heptose. Finally, the genetic organizations of the inner core biosynthesis genes of S. typhimurium, E. coli, and several strains of H. influenzae were examined, and substantial differences were uncovered.

Anther culture as a probable source of resistance to tobacco black shank caused by Phytophthora parasitica var 'nicotianae'

Anther-derived doubled haploid (ADH) tobacco lines possessing a high level of resistance to tobacco black shank, Phytophthora parasitica (Dast.) var 'nicotianae' (B. de Haan) Tucker (Ppn), have been identified from a cross of two tobacco cultivars susceptible to this disease. The objective of this study was to investigate the origin of black shank resistance in ADH lines developed from two susceptible parental cultivars: 'Ovens 62' and 'Ky 15'. In addition to the ADH lines, sexually-derived F2∶8 lines were produced using the single seed descent (SSD) method. Seventy-five ADH lines and 75 SSD lines along with two black shank resistant and three susceptible controls (including parental cultivars) were evaluated under field conditions for resistance to Ppn in 1989 and 1990. Lines were assigned at random to five sets and were planted in a randomized complete block design with three replications/set. A disease index was computed from weekly stand counts of the number of surviving plants per plot for each tobacco line. The 1989 experiment revealed resistance to Ppn in 8 ADH lines, numbers 29, 31, 32, 40, 68, 69, 74, 76, and 1 SSD line, number 32. The 8 ADH lines continued to show resistance in 1990, but SSD line number 32 exhibited a susceptible reaction. There were no other resistant SSD lines.A second field experiment was conducted in 1990 using the putative resistant ADH lines and SSD line nr. 32, which expressed resistance to black shank in 1989. In addition, 12 randomly selected lines from the original 150 ADH and SSD lines were evaluated along with the same five controls as in the previous experiment to further substantiate the resistance of the ADH lines. Lines were planted in a randomized complete block design with eight replications. ADH lines continued to express resistance. SSD line nr. 32 did not show any resistance nor did any other line derived through the single seed descent procedure.These results support the hypothesis that anther culture can generate a high level of black shank resistance. The basis for this resistance is postulated to be due to gene amplification of factors that regulate host response to the black shank fungus.

Characterization of the type 1 fimbrial subunit gene (fimA) of Serratia marcescens

The nucleotide sequence of a DNA fragment that contains the fimA gene, encoding the major fimbrial subunit, of Serratia marcescens IA506 and associated flanking sequences has been elucidated. In addition, the origin of transcription has been identified and is located 120 base pairs upstream of the fimA initiation codon. The predicted amino acid sequence of the FimA polypeptide exhibits some degree of sequence homology with the fimbrial subunits encoded by the fimA determinants of Klebsiella pneumoniae, Salmonella typhimurium, and Escherichia coli and also to Smf2, the major structural component of mannose-resistant (MR) fimbriae of S. marcescens. The Serratia adhesin that facilitates haemagglutination mediated by type 1 fimbriae is less susceptible to inhibition by D-mannose than has been observed to be the case in other type 1 fimbrial adhesins. The molecule conferring this adherence specificity has been shown to be distinct from the fimA gene product and, therefore, is analogous to the fimbrial systems reported in other species.

A fluoride analysis program to reduce tooth decay in rural children

Daily ingestion of optimal amounts of fluoride has been shown to significantly reduce the incidence of tooth decay in children. Fluoridated drinking water is the most effective and efficient primary source of fluoride. Children who do not drink sufficient fluoridated water should receive supplemental fluoride in the form of drops and tablets. Fluoride supplements beginning with the newborn infant at two weeks of age should be prescribed in accordance with the dosage schedules of the American Academy of Pediatrics and the American Dental Association. Fluoride levels of the drinking water source must be determined before prescribing a fluoride supplement. The Arkansas Department of Health offers dentists and physicians a program to analyze the fluoride content of private well or spring water. The program operates through local County Health Departments. Information about the fluoride level in the drinking water of a CWS is available by contacting either that particular CWS or the Engineer Division, Arkansas Department of Health. Questions about fluoride supplementation and/or optimally fluoridated CWS's should be directed to Dr. Wharton A. Nichols, Office of Dental Health, Arkansas Department of Health, 4815 West Markham, Little Rock, AR 72205, (501) 661-2483.

Expression of type 1 fimbriae and mannose-sensitive hemagglutinin by recombinant plasmids

Deletions within the cloned genes (fimA) encoding the type 1 major fimbrial subunits of two isolates of Klebsiella pneumoniae resulted in a nonfimbriate but hemagglutinating phenotype after transformation of Escherichia coli HB101 or ORN103. Phenotypic expression of type 1 fimbriae could be restored by transformation with plasmids containing the fimA genes of the fimbrial gene clusters from different strains. The surface fimbriae expressed were serologically identical to those of the polymerized product of the introduced fimA gene. The fimA gene products of Salmonella typhimurium and Serratia marcescens could utilize the accessory fimbrial genes of K. pneumoniae to produce surface-associated, hemagglutinating fimbriae. The relatedness of the type 1 fimbrial gene clusters from multiple isolates of members of the family Enterobacteriaceae was examined by DNA hybridization techniques. These analyses demonstrated little nucleotide sequence agreement among distinct genera of the enteric bacteria.