Persistence and growth of different Salmonella serovars on pre- and postharvest tomatoes

The interaction of a range of Salmonella serovars with pre- and postharvest tomatoes was evaluated. Serovars were selected on the basis of previous association in tomato-linked outbreaks of salmonellosis (Salmonella Javiana, Salmonella Montevideo, and Salmonella Newport) or those typically isolated from animal or clinical infections (Salmonella Dublin, Salmonella Enteritidis, Salmonella Hadar, Salmonella Infantis, Salmonella Typhimurium, and Salmonella Senftenberg). Salmonella serovars introduced onto the flowers of growing plants were recovered on and within the developing tomato fruit. Of all the Salmonella serovars tested, Montevideo appeared to be more adapted to survival within tomatoes and was recovered from 90% of the fruit screened. All of the Salmonella serovars could persist and grow when introduced onto unripened (green) tomato fruit. In general, growth (internal and external) was promoted at the high incubation temperature (25 degrees C) and high relative humidity (95%), although this was serovar dependent. The growth and persistence of Salmonella introduced on and into ripened (red) tomatoes was serovar dependent. Salmonella serovars Enteritidis, Typhimurium, and Dublin were less adapted to grow in or on intact red tomatoes than were serovars Hadar, Montevideo, or Newport. The results illustrated that a diverse range of Salmonella serovars can become established within and/or on preharvest tomatoes. The majority of Salmonella can grow and become established both on and within unripened tomatoes, but growth on ripened fruit was serovar dependent. The results provide a possible explanation why only a narrow range of Salmonella serovars are associated with foodborne illness outbreaks linked to tomatoes.

Mode of Salmonella and Escherichia coli O157:H7 inactivation by a stabilized oxychloro-based sanitizer

AIM

To determine the mechanisms by which a stabilized oxychloro (SOC)-based sanitizer, applied to decontaminate seeds destined for sprout production, inactivates Escherichia coli O157:H7 ph1 and Salmonella serotype Meleagridis.

MATERIALS AND RESULTS

The action of SOC on the metabolism, membrane and DNA integrity of Salmonella and E. coli O157:H7 was studied. In both pathogens, there was an oxidative burst and depletion of intracellular glutathione (GSH) upon initial exposure to 200 ppm SOC. Metabolic activity, measured via bioluminescence, decreased over a 4-h period in E. coli O157:H7 ph1 cells exposed to SOC. Membrane integrity, assessed through viability staining, decreased progressively over 23 h when exposed to SOC. The appearance of auxotrophic mutants suggested that DNA damage had also occurred. Enzymes rich in disulfide bonds (alkaline phosphatase and protease) were sensitive to the chlorite-based sanitizer. Through challenging other microbial types, it was found that Gram positive had higher tolerance to SOC than Gram negatives with the exception of Salmonella. MS2 bacteriophage was highly sensitive; however, Bacillus endospores were not inactivated by SOC.

CONCLUSIONS

SOC inactivates E. coli O157:H7 and Salmonella through GSH oxidation and disruption of disulfide bonds. Ultimately, membrane damage resulting from prolonged exposure to SOC leads to the loss of cell viability.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results provide a basis for understanding why extended treatment times are required to inactivate bacteria using SOC.

Inactivation of Escherichia coli O157:H7 and Salmonella on artificially or naturally contaminated mung beans (Vigna radiata L) using a stabilized oxychloro-based sanitizer

AIMS

To evaluate the efficacy of a stabilized oxychloro-based (SOC) sanitizer to decontaminate mung beans artificially or naturally contaminated with Escherichia coli O157:H7 or Salmonella.

METHODS AND RESULTS

Naturally contaminated beans were produced by introducing a five-strain cocktail of E. coli O157:H7 or Salmonella onto the flowers of growing mung bean plants. Escherichia coli O157:H7 was only sporadically recovered from sprout lots (three testing positive from 10 tested) derived from harvested beans. In contrast, Salmonella was recovered from 18 of 20 lots screened. Pathogens present on naturally contaminated seed could be successfully inactivated with SOC applied at 200 ppm for 24 h at 28 degrees C. SOC treatment could also decontaminate artificially inoculated mung bean batches containing different levels of contaminated seed. SOC inactivated E. coli O157:H7, but not Salmonella introduced onto damaged (scarified) beans.

CONCLUSIONS

SOC sanitizer could inactivate Salmonella or E. coli O157:H7 naturally or artificially introduced onto mung beans. However, the SOC treatment failed to inactivate Salmonella introduced onto damaged mung beans.

SIGNIFICANCE AND IMPACT OF THE STUDY

SOC sanitizer represents an effective method for decontaminating undamaged mung beans.

Use of microbial antagonism to reduce pathogen levels on produce and meat products: a review

Lactic acid bacteria (LAB) are often utilized to control food-borne pathogens on produce and on cooked, fermented, or refrigerated meats. Most research to date has focused on the inhibition of Listeria monocytogenes, Escherichia coli O157:H7, Salmonella, Clostridium botulinum, and spoilage microorganisms. LAB are excellent candidates for reducing pathogen levels on foods because they inhibit the growth of these microorganisms through various mechanisms without causing unacceptable sensory changes. This review provides an up-to-date look at research directed at maximizing the use of LAB by selecting the most appropriate strains, by learning how to apply them to foods most effectively, and by gaining an understanding of the mechanism by which they inhibit pathogens.Key words: bacterial competition, lactic acid bacteria, food-borne pathogens, meat products, produce.

Inactivation of escherichia coli 0157:H7 and Salmonella on mung beans, alfalfa, and other seed types destined for sprout production by using an oxychloro-based sanitizer

The efficacy of a stabilized oxychloro-based food grade sanitizer to decontaminate seeds destined for sprout production has been evaluated. By using mung bean seeds as a model system, it was demonstrated that the sanitizer could be used to inactivate a five-strain cocktail of Escherichia coli O157:H7 or Salmonella introduced onto beans at 10(3) to 10(4) CFU/g. Salmonella was more tolerant to stabilized oxychloro than was E. coli O157:H7, with sanitizer levels of >150 and >50 ppm, respectively, being required to ensure pathogen-free sprouts. The decontamination efficacy was also found to be dependent on treatment time (>8 h optimal) and the seed-to-sanitizer ratio (>1:4 optimal). Stabilized oxychloro treatment did not exhibit phytotoxic effects, as germination and sprout yields were not significantly (P > 0.05) different as compared with untreated controls. Although human pathogens could be effectively eliminated from mung beans, the aerobic plate count of native microflora on sprouts grown from treated seed was not significantly (P > 0.05) different from the controls. The diversity of microbial populations (determined through 16S rRNA denaturing gradient gel electrophoresis analysis) associated with bean sprouts was not significantly affected by the sanitizer treatment. However, it was noted that Klebsiella and Herbasprillum (both common plant endophytes) were absent in sprouts derived from decontaminated seed but were present in control sprouts. When a further range of seed types was evaluated, it was found that alfalfa, cress, flax, and soybean could be decontaminated with the stabilized oxychloro sanitizer. However, the decontamination efficacy with other seed types was less consistent. It appears that the rate of seed germination and putative activity of sanitizer sequestering system(s), in addition to other factors, may limit the efficacy of the decontamination method.

Application of DNA microarray technology for detection, identification, and characterization of food-borne pathogens

DNA microarrays represent the latest advance in molecular technology. In combination with bioinformatics, they provide unparalleled opportunities for simultaneous detection of thousands of genes or target DNA sequences and offer tremendous potential for studying food-borne microorganisms. This review provides an up-to-date look at the application of DNA microarray technology to detect food-borne pathogenic bacteria, viruses, and parasites. In addition, it covers the advantages of using microarray technology to further characterize microorganisms by providing information for specific identification of isolates, to understand the pathogenesis based on the presence of virulence genes, and to indicate how new pathogenic strains evolved epidemiologically and phylogenetically.

Analysis of the capsule biosynthetic locus of Mannheimia (Pasteurella) haemolytica A1 and proposal of a nomenclature system

A 16-kbp DNA region that contains genes involved in the biosynthesis of the capsule of Mannheimia (Pasteurella) haemolytica A1 has been characterized. The gene cluster can be divided into three regions like those of the typical group II capsule biosynthetic clusters in gram-negative bacteria. Region 1 contains four genes (wzt, wzm, wzf, and wza) which code for an ATP-binding cassette transport apparatus for the secretion of the capsule materials across the membranes. The M. haemolytica A1 wzt and wzm genes were able to complement Escherichia coli kpsT and kpsM mutants, respectively. Further, the ATP binding activity of Wzt was demonstrated by its affinity for ATP-agarose, and the lipoprotein nature of Wza was supported by [(3)H]palmitate labeling. Region 2 contains six genes; four genes (orf1/2/3/4) code for unique functions for which no homologues have been identified to date. The remaining two genes (nmaA and nmaB) code for homologues of UDP-N-acetylglucosamine-2-epimerase and UDP-N-acetylmannosamine dehydrogenase, respectively. These two proteins are highly homologous to the E. coli WecB and WecC proteins (formerly known as RffE and RffD), which are involved in the biosynthesis of enterobacterial common antigen (ECA). Complementation of an E. coli rffE/D mutant with the M. haemolytica A1 nmaA/B genes resulted in the restoration of ECA biosynthesis. Region 3 contains two genes (wbrA and wbrB) which are suggested to be involved in the phospholipid modification of capsular materials.

Using a green fluorescent protein gene-labeled p-nitrophenol-degrading Moraxella strain to examine the protective effect of alginate encapsulation against protozoan grazing

A gfp-labeled p-nitrophenol-degrading Moraxella strain G21 was used to study grazing of a Tetrahymena thermophila strain in liquid medium. This allowed visualization of the feeding process. Under an epifluorescent microscope, individual G21 fluorescent cells could be seen in vacuoles within the protozoans. Most of the G21 cells appeared to be lysed by T. thermophila and green fluorescent protein released from the bacteria yielded brightly fluorescent food vacuoles inside the protozoans, Examination of population dynamics of a mixed culture of T. thermophila and Moraxella sp. G21 showed that the protozoan reduced the bacterial density from 7.6 to 5.8 log CFU/ml in 2 days. Encapsulating the bacteria in alginate prevented grazing by the protozoans and the density of G21 cells in the beads increased steadily from about 8.3 to 8.9 log CFU/ml in 15 days regardless of the presence of the protozoans.

PCR-based quantitation of Cryptosporidium parvum in municipal water samples

A PCR method for the quantitation of Cryptosporidium parvum oocysts in municipal drinking water samples was investigated. Quantitative PCR uses an internal standard (IS) template with unknown target numbers to compare to standards of known concentrations in a standard curve. The IS template was amplified using the same primers used to amplify a portion of a 358 bp gene fragment that encodes a repetitive oocyst wall protein in C. parvum. Municipal water samples spiked with known numbers of C. parvum oocysts were tested by quantitative PCR using the IS and the Digene SHARP Signal System Assay for PCR product detection. The absorbance readings for target DNA and IS templates versus the number of molecules of the target DNA were plotted to generate standard curves for estimating oocyst numbers. The method allowed the quantitation of oocysts from log 3 to log 5 spiked into municipal water samples.

Applications of the green fluorescent protein as a molecular marker in environmental microorganisms

In this review, we examine numerous applications of the green fluorescent protein (GFP) marker gene in environmental microbiology research. The GFP and its variants are reviewed and applications in plant-microbe interactions, biofilms, biodegradation, bacterial-protozoan interactions, gene transfer, and biosensors are discussed. Methods for detecting GFP-marked cells are also examined. The GFP is a useful marker in environmental microorganisms, allowing new research that will increase our understanding of microorganisms in the environment.

Three sample preparation protocols for polymerase chain reaction based detection of Cryptosporidium parvum in environmental samples

Cryptosporidium parvum is a protozoan parasite responsible for an increasing number of outbreaks of gastrointestinal illness worldwide. In this report, we describe development of sample preparation protocols for polymerase chain reaction (PCR)-based detection of C. parvum in fecal material and environmental water samples. Two of these methods were found adequate for isolation of Cryptosporidium DNA from filtered water pellet suspensions. The first involved several filtration steps, immunomagnetic separation and freeze-thaw cycles. The second method involved filtration, addition of EnviroAmp lysis reagent, freeze-thaw cycles and precipitation of the DNA with isopropanol. Using nested PCR, we detected 100 oocysts/ml of filtered water pellet suspension, with either of the above sample preparation procedures. Nested PCR increased sensitivity of the assay by two to three orders of magnitude as compared to the primary PCR. The detection limit for seeded fecal samples was 10-fold higher than for filtered environmental water pellet suspension. Nested PCR results showed 62.4 and 91.1% correlation with immunofluorescence assay (IFA) for fecal samples and filtered environmental water pellet suspensions, respectively. This correlation decreased to 47.2% and 44.4%, respectively, when only IFA positive samples were analyzed. However, in fecal samples contaminated with a high number (> 10(5)/g) of C. parvum oocysts, this correlation was 100%.

Green fluorescent protein as a visual marker in a p-nitrophenol degrading Moraxella sp

The green fluorescent protein gene (gfp) was introduced into a p-nitrophenol-metabolizing strain of Moraxella sp. by chromosomal integration. The gfp-marked transformants, designated Moraxella sp. strains G21 and G25, exhibited green fluorescence under UV light. Molecular characterization by PCR and Southern hybridization showed the presence of gfp in both transformants. Both transformants and the parent strain degraded 720 microM of p-nitrophenol with nitrite release within 4 h after inoculation in minimal medium supplemented with yeast extract. Transformants degraded up to 1440 microM p-nitrophenol and mineralized about 60% of 720 microM p-nitrophenol, both in broth and in soil, to the same extent as the parent strain. Insertion of gfp did not adversely affect the expression of p-nitrophenol-degrading genes in the transformants. Survival studies indicated that individual green fluorescent colonies of transformants can be detected up to 2 weeks after inoculation in soil. These marked strains could be of value in studies on microbial survival in the environment.

Mutational analysis of the role of the conserved lysine-270 in the Pichia stipitis xylose reductase

Xylose reductase catalyzes the NAD(P)H-dependent reduction of xylose to xylitol and is essential for growth on xylose by yeasts. To understand the nature of coenzyme binding to the Pichia stipitis xylose reductase, we investigated the role of the strictly conserved Lys270 in the putative IPKS coenzyme binding motif by site-directed mutagenesis. The Lys270Met variant exhibited lower enzyme activity than the wild-type enzyme. The apparent affinity of the variant for NADPH was decreased 5-16-fold, depending on the substrate used, while the apparent affinity for NADH, measured using glyceraldehyde as the substrate, remained unchanged. This resulted in 4.3-fold higher affinity for NADH over NADPH using glyceraldehyde as the substrate. The variant also showed a 14-fold decrease in Km for xylose, but only small changes were observed in Km values for glyceraldehyde. The wild-type enzyme, but not the Lys270Met variant, was susceptible to modification by the Lys-specific pyridoxal 5'-phosphate. Results of our chemical modification and site-directed mutagenesis study indicated that Lys270 is involved in both NADPH and D-xylose binding in the P. stipitis xylose reductase.

The putative neuraminyllactose-binding hemagglutinin HpaA of Helicobacter pylori CCUG 17874 is a lipoprotein

The ability of certain strains of Helicobacter pylori to cause sialic acid-sensitive agglutination of erythrocytes has been attributed to the HpaA protein (D.G. Evans, T.K. Karjalainen, D. J. Evans, Jr., D. Y. Graham, and C.H. Lee, J. Bacteriol. 175:674-683, 1993), the gene for which has been cloned and sequenced. On the basis of the hydropathy plot of HpaA and the presence of a potential lipoprotein signal sequence and modification site, and because of the similarities of these features with those of the cell envelope lipoprotein Lpp20 of H. pylori, we examined the possibility that HpaA was also a lipoprotein. Posttranslational processing of the HpaA protein expressed by the cloned gene was sensitive to globomycin, an inhibitor of the lipoprotein-specific signal peptidase II. Antibodies raised to the putative sialic acid-binding region of HpaA failed to bind to the surface of H. pylori cells in immunoelectron microscopy but instead were observed to have labeled the cytoplasm when thin sections were examined. This antibody recognized a 29,000-M(r) protein in Western blots (immunoblots) of cell extracts of H. pylori and Escherichia coli cells expressing the cloned hpaA gene. Determination of the sequence of hpaA from strain CCUG 17874 indicated significant differences from that determined by Evans and coworkers in the above-mentioned study, including extension of the gene into the open reading frame 3 downstream of hpaA to produce a protein with an M(r) of 26,414. Localization of HpaA indicated that it was predominantly located in the cytoplasmic fraction of the cell in both E. coli and H. pylori. HpaA was not observed in the sarkosyl-insoluble outer membrane fraction. An isogenic mutant generated by insertional inactivation of hpaA was unaffected in its ability to bind four different human cell lines as well as fixed sections of gastric tissue and had hemagglutination properties identical to those of the wild type. The data collectively suggest that HpaA is a nonessential lipoprotein internal to the H. pylori cell and that it is not involved in adhesion.

Non-motile mutants of Helicobacter pylori and Helicobacter mustelae defective in flagellar hook production

Flagellar hooks were purified from Helicobacter pylori and Helicobacter mustelae. The 70 x 16 nm H. pylori hook was composed of FlgE subunits of 78kDa, while the 72 x 16 nm H. mustelae hook was composed of 87 kDa subunits. N-terminal sequence was obtained for the FlgE proteins of both species, and for an internal H. mustelae FlgE peptide. Degenerate oligonucleotide primers allowed amplification of a 1.2 kb fragment from the H. mustelae chromosome, which carried part of the flgE gene. The corresponding H. pylori gene was cloned by immunoscreening of a genomic library constructed in lambda ZAP Express. The translated H. pylori flgE sequence indicated a protein with limited homology with the hook proteins from Salmonella typhimurium and Treponema phagedenis. Mutants of H. pylori and H. mustelae defective in hook production generated by allele replacement were non-motile and devoid of flagellar filaments but produced both flagellin subunits, which were localized in the soluble fraction of the cell. The level of flagellin production was unchanged in the mutants, indicating that the regulation of flagellin expression in Helicobacter differs from that in the Enterobacteriaceae.

Molecular characterization of a conserved 20-kilodalton membrane-associated lipoprotein antigen of Helicobacter pylori

Antisera raised in rabbits to whole cells of Helicobacter pylori recognized as a major antigen a protein with an apparent molecular weight of 20,000. The antigen was purified by differential solubilization with N-octyl-beta-D-glucopyranoside, urea, and sodium dodecyl sulfate followed by molecular sieving. The mass of the protein, Lpp20, was 18,283 Da as determined by mass spectrometry. The lpp20 gene encoding this protein was cloned in Escherichia coli by using the vector lambda EMBL3, and plasmid subclones expressed the full-length protein from the native H. pylori promoter. lpp20 was mapped to the same 358-kb NruI fragment as flaB. DNA sequence analysis showed that the gene was 525 bp long and encoded a 175-amino-acid protein with a molecular weight of 19,094 containing a 21-residue typical lipoprotein signal peptide and consensus prolipoprotein processing site. The mass of the deduced 154-residue mature protein was 16,865 Da. Growth of E. coli cells expressing the cloned H. pylori lpp20 gene in the presence of [3H]palmitic acid resulted in radiolabelled Lpp20 while treatment of the E. coli cells with globomycin caused accumulation of unprocessed Lpp20, consistent with Lpp20 being a lipoprotein. Lpp20 cofractionated with the cytoplasmic membrane fraction, although a proportion of the protein was also found in the outer membrane. A mutant generated by mutant-allele exchange displayed normal viability, showing that Lpp20 belonged to the nonessential class of lipoproteins.

High-affinity binding of the basement membrane protein collagen type IV to the crystalline virulence surface protein array of Aeromonas salmonicida

The surface of the fish pathogen Aeromonas salmonicida is covered by a paracrystalline array (the A-layer) which is a virulence factor for the organism. Quantification of the ability of A. salmonicida cells to bind collagen types I and IV in a 125I-radiolabelled liquid-phase assay showed that A-layer-positive cells bound high levels of collagen type IV, but significantly lower levels of collagen type I. Collagen type IV binding was confirmed using non-radiolabelled enzyme-linked immunosorbent assays. 125I-Collagen type IV binding was rapid, specific, saturable, high affinity, and essentially irreversible by unlabelled collagen type IV. The A-layer was responsible for collagen type IV binding because binding was inactivated by selective removal of the A-layer at pH 2.2, and neither isogenic A-layer-deficient A. salmonicida mutants nor strains of Aeromonas hydrophila possessing a morphologically similar paracrystalline array bound this basement membrane protein.

Binding of laminin, type IV collagen, and vitronectin by Streptococcus pneumoniae

Forty-three strains of Streptococcus pneumoniae were tested for their ability to bind radiolabelled laminin, collagen types I, II and IV, fibronectin, and vitronectin. Two basement membrane components, laminin and type IV collagen, interacted with many S. pneumoniae strains. All strains bound laminin and 28 (65%) bound collagen type IV. Approximately 60% of the strains bound vitronectin but only a few strains showed low binding of fibronectin and collagen type I and II.

Production of a conserved adhesin by the human gastroduodenal pathogen Helicobacter pylori

An adhesin protein with an approximate subunit molecular weight of 19,600 has been purified from the gastric pathogen Helicobacter pylori. The protein was loosely associated with the cell surface and was removed by gentle stirring or shearing. Released aggregates of the 19.6-kDa protein were removed from suspension by ultracentrifugation and separated from contaminating membranes by washing in 1.0% sodium dodecyl sulfate (SDS). The SDS-insoluble protein was purified further by Mono Q anion-exchange column chromatography. Electron microscopy of the purified adhesin demonstrated that it formed amorphous aggregates similar to the material attached to the bacterial cells and that the aggregates were morphologically distinct from typical fimbriae. Western blot (immunoblot) analysis with antiserum raised against the purified protein from one strain reacted with a protein with a similar subunit molecular weight present in all nine strains of H. pylori examined, but the protein was not present in other Helicobacter species examined. The N-terminal sequences of the 19.6-kDa protein purified from three different strains of H. pylori were identical for the first 28 amino acids, with the 10 amino-terminal residues showing limited sequence homology with the TcpA pilus protein of Vibrio cholerae. The H. pylori 19.6-kDa protein associated both with human and rabbit erythrocytes and with human buccal epithelial cells. Polystyrene microspheres coated with the protein agglutinated human, horse, and rabbit erythrocytes, suggesting that this protein species could mediate adhesion between H. pylori and eucaryotic cells. This ability to act as an adhesin may make this protein an important virulence factor for H. pylori and hence a potential target for a vaccine and therapy.

Antigenic diversity of the S-layer proteins from pathogenic strains of Aeromonas hydrophila and Aeromonas veronii biotype sobria

The antigenic relatedness of paracrystalline surface array proteins with subunit molecular weights of approximately 52,000 from isolates of Aeromonas hydrophila and Aeromonas veronii biotype sobria belonging to a single heat-stable serogroup was examined. Enzyme-linked immunosorbent assay and immunoblotting with two different polyclonal antisera against surface exposed and non-surface-exposed epitopes of the S-layer protein from A. hydrophila TF7 showed that the S-layer proteins of the mesophilic aeromonads were antigenically diverse. NH2-terminal amino acid sequence analysis of four antigenically different proteins showed that while the proteins were structurally related, they differed in primary sequence. Absorption experiments with heterologous live cells showed that cross-reactive epitopes were in non-surface-exposed regions of the S-layer proteins, while absorption with homologous live cells showed that the immunodominant epitopes of the S-layer protein of strain TF7 were strain specific and exposed on the surface of the native, tetragonal array produced by this strain. Proteolytic digestion of the TF7 S-layer protein with trypsin, chymotrypsin, or endoproteinase Glu-C produced an amino-terminal peptide of approximate Mr 38,000 which was refractile to further proteolytic cleavage under nondenaturing conditions. This peptide carried the immunodominant surface-exposed region of the protein, and chemical cleavage with cyanogen bromide further mapped the portion of these surface-exposed epitopes to a peptide of approximate Mr 26,000, part of which maps within the Mr 38,000 protease-resistant NH2-terminal peptide.

Structure of the tetragonal surface virulence array protein and gene of Aeromonas salmonicida

The paracrystalline surface protein array of the pathogenic bacterium Aeromonas salmonicida is a primary virulence factor with novel binding capabilities. The species-specific structural gene (vapA) for this array protein (A-protein) was cloned into lambda gt11 but was unstable when expressed in Escherichia coli, undergoing an 816-base pair deletion due to a 21-base pair direct repeat within the gene. However, the gene was stable in cosmid pLA2917 as long as expression was poor. A-protein was located in the cytoplasmic, inner membrane and periplasmic fractions in E. coli. The DNA sequence revealed a 1,506-base pair open reading frame encoding a protein consisting of a 21-amino acid signal peptide, and a 481-residue 50,778 molecular weight protein containing considerable secondary structure. When assembled into a paracrystalline protein array on Aeromonas the cell surface A-protein was totally refractile to cleavage by trypsin, but became trypsin sensitive when disassembled. Trypsin cleavage of the isolated protein provided evidence that both the NH2- and COOH-terminal regions form distinct structural domains, consistent with three-dimensional ultrastructural evidence. The NH2-terminal 274-residue domain remained refractile to trypsin activity. This segment connects by a trypsin and CNBr-sensitive 78-residue linker region to a COOH-terminal 129-residue fragment which could apparently refold into a partially trypsin-resistant structure after cleavage at residue 323.

Identification, characterization, and spatial localization of two flagellin species in Helicobacter pylori flagella

Flagellar filaments were isolated from Helicobacter pylori by shearing, and flagellar proteins were further purified by a variety of techniques, including CsCl density gradient ultracentrifugation, pH 2.0 acid disassociation-neutral pH reassociation, and differential ultracentrifugation followed by molecular sieving with a Sephacryl S-500 column or Mono Q anion-exchange column, and purified to homogeneity by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transfer to an Immobilon membrane. Two flagellin species of pI 5.2 and with apparent subunit molecular weights (Mrs) of 57,000 and 56,000 were obtained. N-terminal amino acid analysis showed that the two H. pylori flagellin species were related to each other and shared sequence similarity with the N-terminal amino acid sequence of Campylobacter coli, Bacillus, Salmonella, and Caulobacter flagellins. Analysis of the amino acid composition of the predominant 56,000-Mr flagellin species isolated from two strains showed that it was comparable to the flagellins of other species. The minor 57,000-Mr flagellin species contained a higher content of proline. Immunoelectron microscopic studies with polyclonal monospecific H. pylori antiflagellin antiserum and monoclonal antibody (MAb) 72c showed that the two different-Mr flagellin species were located in different regions of the assembled flagellar filament. The minor 57,000-Mr species was located proximal to the hook, and the major 56,000-Mr flagellin composed the remainder of the filament. Western immunoblot analysis with polyclonal rabbit antisera raised against H. pylori or Campylobacter jejuni flagellins and MAb 72c showed that the 56,000-Mr flagellin carried sequences antigenetically cross-reactive with the 57,000-Mr H. pylori flagellin and the flagellins of Campylobacter species. This antigenic cross-reactivity did not extend to the flagellins of other gram-negative bacteria. The 56,000-Mr flagellin also carried H. pylori-specific sequences recognized by two additional MAbs. The epitopes for these MAbs were not surface exposed on the assembled inner flagellar filament of H. pylori but were readily detected by immunodot blot assay of sodium dodecyl sulfate-lysed cells of H. pylori, suggesting that this serological test could be a useful addition to those currently employed in the rapid identification of this important pathogen.

Antigenic differences among Campylobacter fetus S-layer proteins

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of S-layer proteins extracted from Campylobacter fetus strains by using acid glycine buffer showed that the predominant S-layer proteins of different strains had subunit molecular weights in the range of 90,000 to 140,000. Electron microscopy revealed oblique S-layer lattices with a spacing of approximately 5.6 nm (gamma = 75 degrees) on wild-type strains VC1, VC119, VC202, and VC203. Three variants of C. fetus VC119 producing a predominant S-layer subunit protein of different molecular weight (Mr) from that of the parent were also examined. Each variant produced an oblique lattice morphologically indistinguishable from that of the parent. Amino-terminal sequence analysis showed that the S-layer proteins of the VC119 parent and variants were identical up to residue 18 and that this sequence differed from but was related to the first 16 N-terminal residues shared by the S-layer proteins of the three other wild-type C. fetus isolates. Western immunoblot analysis with an antiserum prepared to the VC119 protein and an antiserum prepared to C. fetus 84-40 LP (Z. Pei, R. T. Ellison, R. V. Lewis, and M. J. Blaser, J. Biol. Chem. 263:6416-6420, 1988) showed that strains of C. fetus were capable of producing S-layer proteins with at least four different antigenic specificities. Immunoelectron microscopy with antiserum to the VC119 S-layer protein showed that C. fetus cultures contained cells with immunoreactive oblique S-layer lattices as well as cells with oblique S-layer lattices which did not bind antibody. This suggests that C. fetus S-layer proteins undergo antigenic variation. Thermal denaturation experiments indicated that the antigenicity conferred by the surface-exposed C. fetus S-layer epitopes was unusually resistant to heat, and the thermal stability appeared to be due to the highly organized lattice structure of the S. layer. Protease digestion of purified VC119 S-layer protein revealed a trypsin-, chymotrypsin-, and endoproteinase Glu-C-resistant domain with an apparent Mr of 110,000, which carried the majority of the epitopes of the S-layer protein, and a small enzyme-sensitive domain. The trypsin- and chymotrypsin-resistant polypeptides shared an overlapping sequence which differed from the N-terminal sequence of the intact S-layer protein.

Purification, characterization, and localization of a protein antigen shared by thermophilic campylobacters

A protein antigen with an apparent molecular weight (Mr) of 31,000 was isolated from 0.2 M glycine hydrochloride (pH 2.2) extracts of a typical human fecal isolate, Campylobacter jejuni VC74. The protein was purified to homogeneity on a preparative scale by immunoaffinity chromatography followed by molecular sieving with a Superose 12 column. Isoelectric focusing under nondenaturing conditions indicated a pI of 9.3, and amino acid composition analysis showed that the protein was unusually rich in lysine, containing 14.9 mol% of this basic amino acid. Cysteine and tryptophan were absent. The protein also contained approximately 35% hydrophobic amino acid residues, and N-terminal amino acid analysis showed that 17 of the first 38 residues were hydrophobic. This amino-terminal sequence to residue 22 was virtually identical to that of an antigenically cross-reactive 31,000-Mr protein isolated from another C. jejuni strain belonging to a different heat-labile serogroup. Western blotting (immunoblotting) of glycine extracts of other C. jejuni, Campylobacter coli, and Campylobacter laridis strains belonging to different thermolabile and thermostable serotypes, as well as Campylobacter fetus, with a rabbit polyclonal antiserum raised against the purified C. jejuni VC74 protein showed that all C. jejuni, C. coli, and C. laridis strains tested contained a 31,000-Mr protein with epitopes which were antigenically cross-reactive with the C. jejuni VC74 protein. The antigenically cross-reactive epitopes of this protein were also readily detected by immunodot blot assay of glycine extracts of C. jejuni, C. coli, and C. laridis with monospecific polyclonal antisera to the 31,000-Mr protein, suggesting that this serological test could be a useful addition to those currently employed in the rapid identification of these important pathogens. Slide agglutination reactions, immunofluorescence assay, and immunogold electron microscopy with antisera to purified 31,000-Mr protein and trypsin treatment of whole cells indicated that the cross-reactive epitopes of the 31,000-Mr protein were not exposed on the cell surface. Cell fractionation analysis and immunogold electron microscopy located the protein on the outer surface of the cytoplasmic membrane. This finding suggests that the 31,000-Mr protein is not a good candidate for inclusion in a monovalent subunit Campylobacter vaccine.

Specific binding of collagen type IV to Streptococcus pyogenes

Many strains of Streptococcus pyogenes are capable of binding type IV collagen. In the present study, all 50 S. pyogenes strains isolated from patients with acute glomerulonephritis showed high or moderate affinity for radiolabelled type IV collagen. A majority of strains of other sources, such as reference strains of various M-types and strains isolated from patients with pharyngeal infections also bound type IV collagen; however, a number of weak binders or non-binders were found among those. The collagen type IV binding component(s) on S. pyogenes were susceptible to proteinase K digestion, partially sensitive to trypsin but insensitive to pepsin treatment at pH 5.5. According to tests with three M-positive strains and their M-negative derivatives, the binding was not dependent on M-protein. The binding was saturable with time and inhibited by unlabelled type IV collagen. Partially inhibition was found with type II collagen, gelatin and fibrinogen but not with a number of other serum proteins.