Characterization and application of a murine monoclonal antibody that reacts specifically with the serogroup D1 Salmonella

Probing deoxysugar conformational preference: A comprehensive computational study investigating the effects of deoxygenation

Deoxysugars are intrinsic components in a number of antibiotics, antimicrobials, and therapeutic agents that often dictate receptor binding, improve efficacy, and provide a diverse toolbox in modifying glycoconjugate function due to an extensive number of unique isomers and inherent conformational flexibility. Hence, this work provides a comprehensive examination of the conformational effects associated with deoxygenation of the pyranose ring. Both the location and degree of deoxygenation were evaluated by interrogating the energetic landscape for a number of mono- and dideoxyhexopyranose derivatives using DFT methods (M05-2X/cc-pVTZ(-f)). Both anomeric forms and in some cases, the alternate chair form, have been investigated in the gas phase. As was documented in a preceding study, variation of the C-6 oxidation state has been shown to affect the anomeric preference of select glucose stereoisomers. Similar results were also observed for several deoxysugar isomers in this work, wherein the alternate anomer was favored upon reduction to the 6-deoxyhexose derivative or oxidation to the hexonic acid. Additionally, comparison of relative Gibbs free energies revealed C-3 deoxygenation imparts greater instability compared to C-2 or C-4 deoxygenation, as indicated by an increase in free energy for 3-deoxysugars. A polarizable continuum solvation model was also applied to empirically validate theoretical results for several deoxysugars, wherein good agreement with both carbon (σ = 1.6 ppm) and proton (σ = 0.20 ppm) NMR shifts was observed for the majority of isomers. Solvated and gas phase anomeric ratios were also calculated and compared favorably to reported literature values, although some discrepancies are noted.

Immunosensor for the differentiation and detection of Salmonella species based on a quartz crystal microbalance

Immunosensors based on the microgravimetric quartz crystal microbalance (QCM) technique have been developed for the detection of Salmonella species from serogroups A, B and D. Salmonella serogroup-specific murine monoclonal antibodies, respectively, raised against these serogroups were immobilized onto the silver electrodes of piezoelectric (PZ) crystals by cross-linkage via glutaraldehyde (GA) to the electrode surfaces pre-coated with thin polyethyleneimine (PEI) layer. The specific immunosensors developed gave responses in linear ranges from 10(5) to 5x10(8) cells per ml with no significant interference from other strains of Salmonella and Escherichia coli up to 10(8) cells per ml. They showed good repeatability and excellent linear range, achieving detection limits down to 10(4) cells per ml with ability to distinguish different strains of Salmonella. These biosensors exhibited an exquisite specificity evidenced by their ability to discriminate antigens, the structures of which differ only by the isomeric form of di-deoxyhexose. The antibody-modified crystals showed no loss in activity over 4 days under storage at 4 degrees C.

Evaluation of culture enrichment procedures for use with Salmonella detection immunoassay

To design efficient culture strategies for use with immunoassays to detect Salmonella in food, the growth of these organisms was investigated according to the Bacteriological Analytical Manual (BAM) and enrichment-immunoassay (EI) culture procedures. The cultures were further evaluated using a commercial enzyme-linked immunosorbent assay (ELISA) kit. The BAM procedure includes pre-enrichment in nutrient broth (NB) for 16 h followed by selective enrichment in either Rappaport-Vassiliadis (RV) or tetrathionate brilliant green (TBG) broth for 16 h. The EI procedure includes pre-enrichment in NB for 4 h, selective enrichment in RV for 16 h and post-enrichment in NB for 4 h. The effects of different incubation times for pre- and post-enrichment, and different culture media for selective enrichment (TBG and RV) and post-enrichment in NB and Brain Heart Infusion broth (BHI) on the growth of the bacteria and ELISA titers in the EI procedure were also investigated. Salmonella enteritidis and S. typhimurium inoculated at different initial concentrations between 0.1 and 35 CFU/ml grew to similar concentrations of 10(7) to 10(8) colony forming unit (CFU)/ml in pure culture and generally 2 to 4 fold lower concentrations (P<0.05) in mixed culture using spiked chicken rinse. In the BAM procedure, the concentration of Salmonella cultured in RV was higher (P<0.01) than that in TBG. The cultures in TBG showed positive results for ELISA, but those in RV were generally negative. In the EI procedure, the ELISA titers from cultures post-enriched in NB or BHI were higher (P<0.01) when TBG, as compared to RV, was used for selective enrichment. Post-enrichment in BHI yielded higher numbers of Salmonella and higher ELISA titers than those in NB (P<0.05) for post-enrichment. This study demonstrated that in both culture procedures small numbers of Salmonella could be increased to at least 10(7) CFU/ml which is detectable by most ELISAs, and that the type of the culture media used may have a significant impact on ELISA results.

Detection and serogroup differentiation of Salmonella spp. in food within 30 hours by enrichment-immunoassay with a T6 monoclonal antibody capture enzyme-linked immunosorbent assay

We previously described an antigen capture enzyme-linked immunosorbent assay which makes use of monoclonal antibody T6, which recognizes an epitope on the outer core polysaccharide of Salmonella lipopolysaccharide molecules that is common to almost all Salmonella serovars. In this paper, we show that this assay can detect between 10(5) and 10(7) Salmonella cells per ml even in the presence of excess Escherichia coli. A total of 153 of 154 (99%) serogroup A to E strains and 51 of 78 (71%) serogroup F to 67 strains were reactive as determined by this assay. This corresponds to a detection rate of approximately 98% of all salmonellae known to affect humans. None of the 65 strains of non-Salmonella bacteria tested positive. Taking advantage of the O-factor polysaccharides also present on the antigen captured by the immobilized T6 antibody, we showed that 136 of 154 Salmonella serogroup A to E strains (88%) were correctly differentiated according to their serogroups by use of enzyme conjugates of a panel of O-factor-specific monoclonal antibodies. We evaluated this assay for the detection and serogroup differentiation of salmonellae directly from enrichment cultures of simulated food, eggs, pork, and infant formula milk. All 26 samples which had been contaminated with Salmonella spp. were detected by T6 (100% sensitivity), with only one false-positive result from 101 samples not contaminated by Salmonella spp. (99% specificity). The detection time was substantially reduced to between 17 and 29 h, depending on the enrichment methods used. Since there were no false-negative results, we concluded that this enrichment-immunoassay method can afford rapid screening for Salmonella spp. in food samples.

Characterization of novel fucosyl- and tyvelosyl-containing glycoconjugates from Trichinella spiralis muscle stage larvae

The monosaccharide composition of an affinity-purified family of antigenically-related Trichinella spiralis larval glycoproteins was determined by gas chromatography/mass spectrometry. This group of 6 major glycoproteins, designated TSL-1, originates in the muscle stage (L1) larval stichosome. They are present on the L1 surface and in excretory/secretory products of L1 larvae, are stage-specific, and are highly immunodominant. The glycosyl composition of the TSL-1 antigens was remarkable in 2 respects: (1) fucose accounted for 36 molar percent of the glycosyl residues; and (2) a 3,6-dideoxyhexose was identified, which accounted for at least 24 molar percent of the glycosyl residues. Previously, 3,6-dideoxyhexoses have been found only in certain Gram-negative bacterial lipopolysaccharides and in ascaroside alcohols (ascarylose) of Ascaris eggs. The 3,6-dideoxyhexose found in the TSL-1 antigens also was found in ES. This Trichinella sugar has been chemically identified as a 3,6-dideoxyarabinohexose, the same as found in Ascaris eggs. However, the absolute configuration of the TSL-1 sugar is D-(tyvelose), not L-(ascarylose) as is found in Ascaris eggs. Methylation analysis indicated that the TSL-1 3,6-dideoxy-D-arabinohexose was present entirely as non-reducing terminal residues. Approximately 83% of the fucose was also present as non-reducing terminal residues, with the remaining fucose found as 3,4-linked branched residues.