Construction and expression of recombinant plasmids encoding type 1 fimbriae of a urinary Klebsiella pneumoniae isolate

Novel aggregative adherence fimbria variant of enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) organisms belong to a diarrheagenic pathotype known to cause diarrhea and can be characterized by distinct aggregative adherence (AA) in a stacked-brick pattern to cultured epithelial cells. In this study, we investigated 118 EAEC strains isolated from the stools of Danish adults with traveler's diarrhea. We evaluated the presence of the aggregative adherence fimbriae (AAFs) by a multiplex PCR, targeting the four known major subunit variants as well as their usher-encoding genes. Almost one-half (49/118) of the clinical isolates did not possess any known AAF major fimbrial subunit, despite the presence of other AggR-related loci. Further investigation revealed the presence of an AAF-related gene encoding a yet-uncharacterized adhesin, termed agg5A. The sequence of the agg5DCBA gene cluster shared fimbrial accessory genes (usher, chaperone, and minor pilin subunit genes) with AAF/III, as well as the signal peptide present in the beginning of the agg3A gene. The complete agg5DCBA gene cluster from a clinical isolate, EAEC strain C338-14, with the typical stacked-brick binding pattern was cloned, and deletion of the cluster was performed. Transformation to a nonadherent E. coli HB101 and complementation of the nonadherent C338-14 mutant with the complete gene cluster restored the AA adhesion. Overall, we found the agg5A gene in 12% of the 118 strains isolated from Denmark, suggesting that this novel adhesin represents an important variant.

Structural and population characterization of MrkD, the adhesive subunit of type 3 fimbriae

Type 3 fimbriae are adhesive organelles found in enterobacterial pathogens. The fimbriae promote biofilm formation on biotic and abiotic surfaces; however, the exact identity of the receptor for the type 3 fimbriae adhesin, MrkD, remains elusive. We analyzed naturally occurring structural and functional variabilities of the MrkD adhesin from Klebsiella pneumoniae and Escherichia coli isolates of diverse origins. We identified a total of 33 allelic variants of mrkD among 90 K. pneumoniae isolates and 10 allelic variants among 608 E. coli isolates, encoding 11 and 9 protein variants, respectively. Based on the level of accumulated silent variability between the alleles, mrkD was acquired a relatively long time ago in K. pneumoniae but recently in E. coli. However, unlike K. pneumoniae, mrkD in E. coli is actively evolving under a strong positive selection by accumulation of mutations, often targeting the same positions in the protein. Several naturally occurring MrkD protein variants from E. coli were found to be significantly less adherent when tested in a mannan-binding assay and showed reduced biofilm-forming capacity. Functional examination of the MrkD adhesin in flow chamber experiments determined that it interacts with Saccharomyces cerevisiae cells in a shear-dependent manner, i.e., the binding is catch-bond-like and enhanced under increasing shear conditions. Homology modeling strongly suggested that MrkD has a two-domain structure, comprising a pilin domain anchoring the adhesin to the fimbrial shaft and a lectin domain containing the binding pocket; this is similar to structures found in other catch-bond-forming fimbrial adhesins in enterobacteria.

Biofilm formation of Klebsiella pneumoniae on urethral catheters requires either type 1 or type 3 fimbriae

Urinary catheters are standard medical devices utilized in both hospital and nursing home settings, but are associated with a high frequency of catheter-associated urinary tract infections (CAUTI). In particular, biofilm formation on the catheter surface by uropathogens such as Klebsiella pneumoniae causes severe problems. Here we demonstrate that type 1 and type 3 fimbriae expressed by K. pneumoniae enhance biofilm formation on urinary catheters in a catheterized bladder model that mirrors the physico-chemical conditions present in catheterized patients. Furthermore, we show that both fimbrial types are able to functionally compensate for each other during biofilm formation on urinary catheters. In situ monitoring of fimbrial expression revealed that neither of the two fimbrial types is expressed when cells are grown planktonically. Interestingly, during biofilm formation on catheters, both fimbrial types are expressed, suggesting that they are both important in promoting biofilm formation on catheters. Additionally, transformed into and expressed by a nonfimbriated Escherichia coli strain, both fimbrial types significantly increased biofilm formation on catheters compared with the wild-type E. coli strain. The widespread occurrence of the two fimbrial types in different species of pathogenic bacteria stresses the need for further assessment of their role during urinary tract infections.

Identification of a conserved chromosomal region encoding Klebsiella pneumoniae type 1 and type 3 fimbriae and assessment of the role of fimbriae in pathogenicity

Type 3 fimbriae are expressed by most clinical Klebsiella pneumoniae isolates and mediate adhesion to host structures in vitro. However, the role of type 3 fimbriae in K. pneumoniae virulence has not been evaluated by use of in vivo infection models. In this study, the type 3 fimbrial gene cluster (mrk) of the clinical isolate C3091 is described in detail. The mrk gene cluster was revealed to be localized in close proximity to the type 1 fimbrial gene cluster. Thus, a 20.4-kb fimbria-encoding region was identified and found to be highly conserved among different K. pneumoniae isolates. Interestingly, a homologue to PecS, known as a global regulator of virulence in Erwinia chrysanthemi, was identified in the fimbria-encoding region. Comparison to the previously characterized plasmid encoded mrk gene cluster revealed significant differences, and it is established here that the putative regulatory gene mrkE is not a part of the chromosomally encoded type 3 fimbrial gene cluster. To evaluate the role of type 3 fimbriae in virulence, a type 3 fimbria mutant and a type 1 and type 3 fimbria double mutant was constructed. Type 3 fimbria expression was found to strongly promote biofilm formation. However, the fimbria mutants were as effective at colonizing the intestine as the wild type, and their virulence was not attenuated in a lung infection model. Also, in a urinary tract infection model, type 3 fimbriae did not influence the virulence, whereas type 1 fimbriae were verified as an essential virulence factor. Thus, type 3 fimbriae were established not to be a virulence factor in uncomplicated K. pneumoniae infections. However, since type 3 fimbriae promote biofilm formation, their role in development of infections in catheterized patients needs to be elucidated.

Genomic diversity of citrate fermentation in Klebsiella pneumoniae

Background

It has long been recognized that Klebsiella pneumoniae can grow anaerobically on citrate. Genes responsible for citrate fermentation of K. pneumoniae were known to be located in a 13-kb gene cluster on the chromosome. By whole genome comparison of the available K. pneumoniae sequences (MGH 78578, 342, and NTUH-K2044), however, we discovered that the fermentation gene cluster was present in MGH 78578 and 342, but absent in NTUH-K2044. In the present study, the previously unknown genome diversity of citrate fermentation among K. pneumoniae clinical isolates was investigated.

Results

Using a genomic microarray containing probe sequences from multiple K. pneumoniae strains, we investigated genetic diversity among K. pneumoniae clinical isolates and found that a genomic region containing the citrate fermentation genes was not universally present in all strains. We confirmed by PCR analysis that the gene cluster was detectable in about half of the strains tested. To demonstrate the metabolic function of the genomic region, anaerobic growth of K. pneumoniae in artificial urine medium (AUM) was examined for ten strains with different clinical histories and genomic backgrounds, and the citrate fermentation potential was found correlated with the genomic region. PCR detection of the genomic region yielded high positive rates among a variety of clinical isolates collected from urine, blood, wound infection, and pneumonia. Conserved genetic organizations in the vicinity of the citrate fermentation gene clusters among K. pneumoniae, Salmonella enterica, and Escherichia coli suggest that the13-kb genomic region were not independently acquired.

Conclusion

Not all, but nearly half of the K. pneumoniae clinical isolates carry the genes responsible for anaerobic growth on citrate. Genomic variation of citrate fermentation genes in K. pneumoniae may contribute to metabolic diversity and adaptation to variable nutrient conditions in different environments.

Characterization of Klebsiella pneumoniae type 1 fimbriae by detection of phase variation during colonization and infection and impact on virulence

Klebsiella pneumoniae is recognized as an important gram-negative opportunistic pathogen. The ability of bacteria to adhere to host structures is considered essential for the development of infections; however, few studies have examined the influence of adhesion factors on K. pneumoniae virulence. In this study, we cloned and characterized the type 1 fimbria gene cluster of a clinical K. pneumoniae isolate. Although this cluster was not identical to the Escherichia coli type 1 fimbria gene cluster, an overall high degree of structural resemblance was demonstrated. Unique to the K. pneumoniae fim gene cluster is the fimK gene, whose product contains an EAL domain, suggesting that it has a role in regulation of fimbrial expression. Like expression of type 1 fimbriae in E. coli, expression of type 1 fimbriae in K. pneumoniae was found to be phase variable, and an invertible DNA element (fim switch) was characterized. An isogenic type 1 fimbria mutant was constructed and used to evaluate the influence of type 1 fimbriae in different infection models. Type 1 fimbriae did not influence the ability of K. pneumoniae to colonize the intestine or infect the lungs, but they were determined to be a significant virulence factor in K. pneumoniae urinary tract infection. By use of a PCR-based assay, the orientation of the fim switch during colonization and infection was investigated and was found to be all "off" in the intestine and lungs but all "on" in the urinary tract. Our results suggest that during colonization and infection, there is pronounced selective pressure in different host environments for selection of either the type 1 fimbriated or nonfimbriated phenotype of K. pneumoniae.

The Distinct Binding Specificities Exhibited by Enterobacterial Type 1 Fimbriae Are Determined by Their Fimbrial Shafts

Type 1 fimbriae of enterobacteria are heteropolymeric organelles of adhesion composed of FimH, a mannose-binding lectin, and a shaft composed primarily of FimA. We compared the binding activities of recombinant clones expressing type 1 fimbriae from Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium for gut and uroepithelial cells and for various soluble mannosylated proteins. Each fimbria was characterized by its capacity to bind particular epithelial cells and to aggregate mannoproteins. However, when each respective FimH subunit was cloned and expressed in the absence of its shaft as a fusion protein with MalE, each FimH bound a wide range of mannose-containing compounds. In addition, we found that expression of FimH on a heterologous fimbrial shaft, e.g. K. pneumoniae FimH on the E. coli fimbrial shaft or vice versa, altered the binding specificity of FimH such that it closely resembled that of the native heterologous type 1 fimbriae. Furthermore, attachment to and invasion of bladder epithelial cells, which were mediated much better by native E. coli type 1 fimbriae compared with native K. pneumoniae type 1 fimbriae, were found to be dependent on the background of the fimbrial shaft (E. coli versus K. pneumoniae) rather than the background of the FimH expressed. Thus, the distinct binding specificities of different enterobacterial type 1 fimbriae cannot be ascribed solely to the primary structure of their respective FimH subunits, but are also modulated by the fimbrial shaft on which each FimH subunit is presented, possibly through conformational constraints imposed on FimH by the fimbrial shaft. The capacity of type 1 fimbrial shafts to modulate the tissue tropism of different enterobacterial species represents a novel function for these highly organized structures.

Construction of an ori cassette for adapting shuttle vectors for use in Haemophilus influenzae

An ori (origin of DNA replication) cassette, pORC, containing the P15a ori and the kanamycin-resistance-encoding gene from Tn5, was constructed. The cassette was used to convert an Escherichia coli promoter selection vector, which gene from Tn5, was constructed. The cassette was used to convert an Escherichia coli promoter selection vector, which contains a promoterless chloramphenicol (Cm) acetyltransferase-encoding gene (cat) downstream from a multiple cloning site (MCS) [Brosius and Lupski, Methods Enzymol. 153 (1987) 54-68], to an E. coli-Haemophilus influenzae shuttle vector. The shuttle vector, pQL1, was shown to transform E. coli and H. influenzae efficiently. H. influenzae promoters were cloned into pQL1 by ligation of Sau3A-digested H. influenzae chromosomal fragments. Selection and semiquantitative analysis of promoter strength were performed on agar plates containing different concentrations of Cm. With the use of pQL1, H. influenzae gene regulation can now be studied in either H. influenzae or E. coli. In addition, elements of pORC can be used to convert other specialized E. coli vectors to E. coli-H. influenzae shuttle vectors.

Type 1 fimbrial shafts of Escherichia coli and Klebsiella pneumoniae influence sugar-binding specificities of their FimH adhesins

The type 1 fimbriae of enterobacteria comprise FimA, which constitutes most of the fimbrial shaft, and a cassette of three minor ancillary subunits including FimH, the mannose-binding moiety. The sugar-binding specificities of Escherichia coli and Klebsiella pneumoniae type 1 fimbriae were examined by determining the relative activities of two aromatic mannosides in inhibiting the yeast aggregation caused by the fimbriated bacteria. 4-Methylumbelliferyl alpha-mannoside (MeUmb alpha Man) was approximately 10-fold more effective than p-nitrophenyl alpha-mannoside (p-NP alpha Man) in inhibiting the yeast aggregation caused by the recombinant expressing native E. coli type 1 fimbriae. In contrast, MeUmb alpha Man was only fourfold more effective than p-NP alpha Man in assays employing the recombinant expressing native K. pneumoniae type 1 fimbriae. In order to elucidate the molecular mechanisms underlying the sugar-binding specificities of type 1 fimbriae in the two species, transcomplementation studies were performed and resulted in the creation of recombinants expressing two types of hybrid fimbriae: one consisting of a cassette of minor subunits of E. coli fimbriae borne on a filamentous shaft of K. pneumoniae FimA subunits and the other consisting of a cassette of K. pneumoniae minor fimbrial subunits borne on a shaft of E. coli FimA subunits. Although the heterologous FimH was incorporated into the fimbrial filaments in amounts comparable to those observed in native fimbriae, the hemagglutination activities of recombinants expressing hybrid fimbriae were significantly lower than those of their counterparts bearing native fimbriae. The sugar-binding specificity of the recombinant expressing hybrid fimbriae consisting of an E. coli shaft bearing K. pneumoniae FimH was different from those of recombinants expressing native K. pneumoniae fimbriae in its affinity for the two aromatic sugars but was remarkably similar to the specificities exhibited by recombinants expressing native E. coli fimbriae. Conversely, the sugar-binding specificity of the recombinant expressing hybrid fimbriae consisting of a K. pneumoniae shaft bearing E. coli FimH was different from that of the recombinant expressing native E. coli fimbriae but was very similar to those of recombinants expressing native K. pneumoniae fimbriae. We conclude that the differences in the sugar-binding specificity between E. coli and K. pneumoniae FimH fimbrial subunits is influenced by the fimbrial shafts which carry the adhesin molecules in a functionally competent form at the distal tips.

Fimbriation, capsulation, and iron-scavenging systems of Klebsiella strains associated with human urinary tract infection

Thirty-two strains of Klebsiella pneumoniae and seven strains of Klebsiella oxytoca isolated from urinary tract infections in elderly adults were analyzed for capsular antigens, iron-scavenging systems, and fimbriation. All strains were capsulated. Twenty-seven different K antigens were identified among the strains, with no particular antigen dominating. All strains produced the iron-scavenging system enterochelin as analyzed by bioassay and DNA hybridization. In contrast, the aerobactin iron-sequestering system was not detected in any of the strains. All strains caused hemagglutination of tannin-treated human erythrocytes and reacted with an anti-type 3 fimbriae antiserum as well as in DNA hybridization with a type 3 fimbria-specific probe, indicating that the Klebsiella strains possessed this fimbrial type. Possession of type 1 fimbriae was analyzed by agglutination tests and by hybridization with DNA probes from two distinct Klebsiella type 1 fimbria gene clusters. Phenotypic expression of the type 1 fimbriae was found in 29 of 32 K. pneumoniae strains, whereas 30 strains reacted with either of the two type 1 fimbrial cluster DNA probes. In K. oxytoca, however, only three of seven strains expressed type 1 fimbriae and reacted with the DNA probes. The type 3 fimbriae were found to bind to a fraction of epithelial cells exfoliated in normal human urine, whereas the type 1 fimbriae bound strongly to urinary slime. No inhibitors of type 3 fimbrial binding were detected in human urine.

Type 1 fimbriae mutants of Escherichia coli K12: characterization of recognized afimbriate strains and construction of new fim deletion mutants

We have used Southern hybridization analysis to characterize the extent of fim homology in recognized type 1 fimbriae mutants of Escherichia coli K12, including strains HB101, P678-54, and VL584. We have found extensive homology in strain HB101, and confirm that P678-54 lacks the majority of fim DNA. Strain VL584 contains a deletion of the entire fim region. We have used a new allelic exchange procedure to generate novel fim deletion derivatives of strains MG1655, MM294, and YMC9. To increase the utility of the new deletion strains we also isolated recA derivatives of each mutant. These strains facilitate the isolation, characterization, and manipulation of cloned fimbriae genes from diverse sources.

Production of type 1 fimbriae by Escherichia coli HB101

Escherichia coli HB101 is frequently used as a host in the cloning of bacterial virulence genes because of its reported lack of virulence determinants such as fimbriae, adhesins and haemagglutinins. However, passage of HB101 in standing broth culture rapidly induced the production of fimbriae which mediated adhesion to HEp-2 cells and mannose-sensitive haemagglutination of human and guinea-pig erythrocytes. Fimbrial serology, morphology and pilin molecular mass of 18 kDa were consistent with those of type 1 fimbriae.

Cloning and expression in Escherichia coli of LKP pilus genes from a nontypeable Haemophilus influenzae strain

Nontypeable Haemophilus influenzae HF0295, isolated by aspiration from the middle ear of a patient with otitis media, expresses long, thick, and hemagglutinating pili of a single serotype (LKP1) on its surface. An intact pilus vaccine consisting of the LKP1 serotype protected chinchillas against experimental otitis media (C. C. Brinton, Jr., M. J. Carter, D. B. Derber, S. Kar, J. A. Kramarik, A. C. C. To, S. C. M. To, and S. W. Wood, Pediatr. Infect. Dis. J. 8:554-561, 1989; R. B. Karasic, D. J. Beste, S. C. M. To, W. J. Doyle, S. W. Wood, M. J. Carter, A. C. C. To, K. Tanpowpong, C. D. Bluestone, and C. C. Brinton, Jr., Pediatr. Infect. Dis. J. 8:562-565, 1989). The genes encoding LKP1 pili were cloned from a genomic library of the clinical strain as a 12.5-kilobase insert on a plasmid vector and inserted into Escherichia coli K-12. Transposon mutagenesis and deletion constructs mapped the pilus-coding region within a 7-kilobase region of insert DNA. The recombinant bacteria were found by electron microscopy to express pili morphologically similar to LKP1 pili. Purified pilus rods from the recombinant and its parental strain were composed of a single detectable protein with an apparent molecular weight of 27,500. Antibodies raised against LKP1 pili purified from H. influenzae immunologically reacted with pili from the recombinant bacteria. Pili from both strains also adhered to human erythrocytes and buccal cells with the same specificity.

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.

Cloning and expression of a Salmonella enteritidis fimbrin gene in Escherichia coli

A gene bank of DNA from a human isolate of Salmonella enteritidis was constructed in the cosmid pHC79 in Escherichia coli HB101. Five clones containing 35- to 45-kilobase inserts of S. enteritidis DNA reacted in colony immunoblot assays with a polyclonal antiserum prepared against purified S. enteritidis fimbriae. Electron microscopy showed that none of the five fimbrin-producing clones produced fimbriae, yet radioimmunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis located the 14,400-molecular-weight S. enteritidis in the outer membrane fraction of three of the clones and in the periplasmic fraction of all five clones. By using an oligonucleotide probe homologous to the 5' region of the fimbrin structural gene, the fimbrin gene was located on a 5.3-kilobase HindIII fragment. In vitro transcription-translation analysis verified that this HindIII fragment subcloned into plasmid pTZ18R produced unprocessed S. enteritidis fimbrin of molecular weight 16,400. Dot blot hybridization against a selection of strains of the family Enterobacteriaceae indicated a limited distribution of the S. enteritidis fimbrin gene.

Characterization of two genes encoding antigenically distinct type-1 fimbriae of Klebsiella pneumoniae

A uropathogenic isolate of Klebsiella pneumoniae was shown to exhibit a mannose-sensitive hemagglutinating phenotype and to produce type-1 fimbriae consisting of subunits with a different electrophoretic mobility than those previously investigated. The gene cluster encoding expression of fimbriae was cloned and the genetic organization of the encoded polypeptides was determined. The gene encoding the major fimbrial subunit was localized and further examined by nucleotide sequence analysis. Comparison of two K. pneumoniae fimbrial genes revealed a nucleotide sequence agreement of 73%, and amino acid sequence agreement of 84% for the mature fimbrial subunits. Predictions of putative antigenic sites were correlated with regions demonstrating amino acid variability. In agreement with these predictions, no serological cross-reactivity between both fimbrial proteins could be demonstrated using an enzyme-linked immunosorbent assay (ELISA).

Nucleotide sequences of the genes encoding type 1 fimbrial subunits of Klebsiella pneumoniae and Salmonella typhimurium

The nucleotide sequences of the genes encoding the subunits of Klebsiella pneumoniae and Salmonella typhimurium type 1 fimbriae were determined. Comparison of the predicted amino acid sequences of the two subunits revealed domains in which the sequences were highly conserved. Both gene products possessed signal peptides, a fact consistent with the transport of the fimbrial subunit across the membrane, but these regions showed no amino acid homology between the two proteins. The predicted N-terminal amino acid sequences of the processed fimbrial subunits were in good agreement with those obtained by purification of the fimbrial subunits.

Characterization of genes encoding type 1 fimbriae of Klebsiella pneumoniae, Salmonella typhimurium, and Serratia marcescens

With a minicell system, the organization of genes encoding type 1 fimbriae of Salmonella typhimurium, Klebsiella pneumoniae, and Serratia marcescens was determined. In all cases multiple gene products were necessary for the phenotypic expression of fimbriae; thus fimbrial expression in these strains is similar to that in Escherichia coli. The type 1 fimbrial subunit gene was detected by the ability of its product to react with specific antiserum. At least six genes were found to be involved in the expression of type 1 fimbriae by S. typhimurium, and at least four genes constituted the fimbrial gene cluster of K. pneumoniae. In the case of S. marcescens, a minimum of three detectable polypeptides was required for the production of fimbriae. Also, a gene probe consisting in part of nucleotide sequences from the E. coli fimbrial subunit gene hybridized to a discrete DNA fragment derived from the plasmid encoding K. pneumoniae fimbriae. Such a fragment was assumed to contain a gene encoding the structural component of the type 1 fimbriae. Each of the three cloned systems encoded a number of polypeptides which varied in size; thus, the organization and molecular weight of fimbrial accessory proteins of each genus were not identical.

Expression of pili from Bacteroides nodosus in Pseudomonas aeruginosa

The pili of Bacteroides nodosus, the causative agent of ovine footrot, constitute the major host-protective immunogen against homologous serotypic challenge. The pilin gene from B. nodosus 198 has been cloned and morphologically expressed as extracellular pili in Pseudomonas aeruginosa by using a plasmid-borne, thermoregulated expression system. B. nodosus pilin could not be detected in cultures of P. aeruginosa grown at 32 degrees C, but after induction at 37 degrees C, B. nodosus pili were expressed on the cell surface of P. aeruginosa to the virtual exclusion of the host cell pili. Pili harvested from induced P. aeruginosa cultures were used to immunize sheep against footrot. The serum agglutinating antibody titers of vaccinated sheep were comparable to those of sheep receiving pili from B. nodosus. Subsequent challenge of the sheep with B. nodosus 198 indicated that the recombinant- DNA-derived pili vaccine and the B. nodosus pili vaccine provided similar levels of protection against footrot.

Complementation analyses of recombinant plasmids encoding type 1 fimbriae of members of the family Enterobacteriaceae

Insertion mutants of recombinant plasmids encoding type 1 fimbriae of four genera of enteric bacteria were used to detect genetic complementation. After transformation by pairs of plasmids, double transformants were screened for their ability to express type 1 fimbriae. Complementation was observed between genes derived from the same genus but was absent with chimeric molecules carrying genetic information from two different genera. The results indicate that diffusible gene products of the fim cluster are necessary for phenotypic expression of type 1 fimbriae.

Salmonella typhimurium strains carrying haemolysin plasmids and cloned haemolysin genes from Escherichia coli

Like all other Salmonella typhimurium strains examined, the smooth variants SF1397 (LT2) and 1366 and also their semi-rough and rough derivatives are non-haemolytic. Nevertheless, two haemolysin (Hly) plasmids of E. coli belonging to the inc groups incFIII,IV (pSU316) and incI2 (pHly152) were able to be introduced into these strains by conjugation and stably maintained. A considerable percentage of the Hly+ transconjugants obtained had lost parts of their O-side chains, a result of selection for the better recipient capability of "semi-rough" variants rather than the direct influence of the Hly+ plasmids themselves. In contrast to the incFIII,IV plasmid pSU316, which exhibited higher conjugation rates with rough recipients, the incI2 plasmid pHly152 was accepted best by smooth strains. Transformation with cloned E. coli haemolysin (hly) determinant was inefficient (less than 10(-6)) for smooth strains, but 10(2) - 10(3) times higher for rough recipients, and was increased by the use of Salmonella-modified DNA. The transformants and transconjugants were relatively stable and showed the same haemolytic activity as the E. coli donor strains. The virulence of the Hly+ smooth, semi-rough and rough S. typhimurium strains was tested in two mouse models, and neither the mortality rate nor the ability to multiply within the mouse spleen was influenced by the hly determinants.

Construction and comparison of recombinant plasmids encoding type 1 fimbriae of members of the family Enterobacteriaceae

The genes encoding type 1 fimbriae of Salmonella typhimurium, Enterobacter cloacae, and Serratia marcescens were cloned in Escherichia coli. All transformants possessing recombinant plasmids were shown to be fimbriate and demonstrated mannose-sensitive hemagglutinating activity. A comparison of the physical maps of these plasmids revealed little similarity among them, although plasmids encoding type 1 fimbriae of Escherichia coli and Klebsiella pneumoniae appeared similar with respect to restriction enzyme sites. The fimbrial gene cluster ranged in size from 5.5 to 9.0 kilobase pairs as determined by transposon mutagenesis. Plasmid-containing E. coli strains were shown to produce species-specific fimbrial antigens with little or no cross-reactivity between genera. Therefore, it was presumed that each plasmid contained the gene encoding the fimbrial subunit. Complementation was not detected between nonfimbriate insertion mutants of different species but was seen with mutants of the same species.

Cloning and expression in Escherichia coli of the gene encoding the structural subunit of Bacteroides nodosus fimbriae

Bacteroides nodosus is the primary causative agent of ovine foot rot. Virulent isolates of this bacterium contain fimbriae which appear to play a major role in both infectivity and protective immunity. This paper presents the cloning and expression in Escherichia coli of the gene encoding the structural subunit of the fimbriae of B. nodosus. Total DNA was isolated from B. nodosus VCS 1001 (serogroup A), digested with HindIII, and inserted into the positive-selection vector pTR262. Recombinant E. coli clones were screened directly with anti-fimbrial antiserum by using a colony immunoassay. Several positive colonies were identified, each of which contained the same 5.5-kilobase HindIII insert. The prototype has been designated pBA101. Some clones also contained additional flanking sequences from the B. nodosus genome. Western transfer analyses verified that the positive clones were producing the B. nodosus fimbrial structural subunit, molecular weight ca. 17,500. The level of expression of the antigen in E. coli was comparable to that in B. nodosus itself and was unaffected by the insertion site or orientation of the cloned fragment, indicating that synthesis was being directed from an internal promoter. Restriction mapping and deletion analyses localized the fimbrial subunit gene to the vicinity of a PvuII site near the central region of the original HindIII insert. The expressed antigen was located in the membrane-cell wall fraction and may be exposed on the surface of the recombinant E. coli cells.

Legionella pneumophila surface antigens cloned and expressed in Escherichia coli are translocated to the host cell surface and interact with specific anti-Legionella antibodies

Escherichia coli clones that express Legionella pneumophila antigens were isolated from a plasmid genomic library, and their antigens were characterized by immunoblotting with rabbit anti-L. pneumophila sera. Because previous studies of L. pneumophila antigens by whole-cell radioimmunoprecipitation suggested that comigrating native antigens were surface localized, we conducted experiments to determine if the cloned antigens were surface expressed in E. coli. Aliquots of antisera were absorbed by intact cells of three representative antigen-producing E. coli clones, and surface-bound antibodies were acid eluted from the intact cells. Immunoblots made with selectively absorbed antisera and eluted antibodies confirmed that reactivity to the homologous cloned antigens could be specifically absorbed from the antisera and then eluted from the cells, demonstrating a surface (antibody-accessible) localization in the cloned state. Antibodies eluted from the surface of an E. coli clone that expressed a 19-kilodalton antigen reacted with the surface of L. pneumophila in a liquid-phase, whole-cell enzyme-linked immunosorbent assay. In addition, intact cells of this clone were used in an enzyme-linked immunosorbent assay to detect serum antibody. E. coli cells that express foreign antigens on their surfaces can be used to develop antigen-specific immunoassays and to affinity purify monospecific antibodies.

Cloning and expression of Legionella pneumophila antigens in Escherichia coli

To isolate and characterize Legionella pneumophila antigens, we constructed a genomic library of L. pneumophila serogroup 1 (strain 130b). L, pneumophila DNA fragments (2.5 to 7.5 megadaltons) obtained by partial digestion with Sau 3A endonuclease and size fractionation on a sucrose density gradient were inserted into the dephosphorylated BamHI site of vector pBR322; CaCl2-treated Escherichia coli cells of strain HB101 were transformed with hybrid plasmids. To detect expression of antigens, 2,559 ampicillin-resistant transformants were transferred to nitrocellulose paper, lysed in situ, and screened by enzyme immunoassay (EIA) with E. coli-absorbed rabbit anti-L. pneumophila sera. A total of 77 (3%) of the colonies were reactive by EIA; 31 (1.2%) were strongly reactive, and 6 were strongly reactive by EIA without colony lysis. Analysis of 29 stable, strongly reactive clones by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electroblotting showed antigenic bands in 18 clones by EIA with E. coli-absorbed antisera. Absorption of antisera with heat- and Formalin-killed L. pneumophila antigen eliminated or diminished the reactivity of the antigenic bands in representative clones. These studies confirm that several L. pneumophila antigens can be cloned and expressed in E. coli.

The use of transposon Tn5 mutagenesis in the rapid generation of correlated physical and genetic maps of DNA segments cloned into multicopy plasmids--a review

The properties of transposon Tn5 that render it useful for in vivo mutagenesis of cloned DNA sequences are reviewed. Transposition frequency, insertional specificity, polarity and stability of Tn5 insertion mutations are among the topics discussed. Examples are cited from the published literature which illustrate the applications of Tn5 mutagenesis to the analysis of cloned prokaryotic and eukaryotic genes. A methods section is included which outlines precisely how to carry out transposon Tn5 mutagenesis analysis of cloned DNA segments.