Biomedical subjects

Robert E Mandrell

Publications and source records attributed to Robert E Mandrell.

26 records · Page 2Linked to original sources

PubMed2003

Attachment of Listeria monocytogenes to radish tissue is dependent upon temperature and flagellar motility.

Outbreaks of listeriosis and febrile gastroenteritis have been linked to produce contamination by Listeria monocytogenes. In order to begin to understand the physiology of the organism in a produce habitat, the ability of L. monocytogenes to attach to freshly cut radish tissue was examined. All strains tested had the capacity to attach sufficiently well such that they could not be removed during washing of the radish slices. A screen was developed to identify Tn917-LTV3 mutants that were defective in attachment to radish tissue, and three were characterized. Two of the three mutations were in genes with unknown functions. Both of the unknown genes mapped to a region predicted to contain genes necessary for flagellar export; however, only one of the two insertions caused a motility defect. The third insertion was found to be in an operon encoding a phosphoenolpyruvate-sugar phosphotransferase system. All three mutants were defective in attachment when tested at 30 degrees C; the motility mutant had the most severe phenotype. However, not all of the mutants were defective when tested at other temperatures. These results indicate that L. monocytogenes may use different attachment factors at different temperatures and that temperature should be considered an important variable in studies of the molecular mechanisms of Listeria fitness in complex environments.

Bacterial Adhesion↗

PubMed2003

Colonization of Arabidopsis thaliana with Salmonella enterica and enterohemorrhagic Escherichia coli O157:H7 and competition by Enterobacter asburiae.

Enteric pathogens, such as Salmonella enterica and Escherichia coli O157:H7, have been shown to contaminate fresh produce. Under appropriate conditions, these bacteria will grow on and invade the plant tissue. We have developed Arabidopsis thaliana (thale cress) as a model system with the intention of studying plant responses to human pathogens. Under sterile conditions and at 100% humidity, S. enterica serovar Newport and E. coli O157:H7 grew to 10(9) CFU g(-1) on A. thaliana roots and to 2 x 10(7) CFU g(-1) on shoots. Furthermore, root inoculation led to contamination of the entire plant, indicating that the pathogens are capable of moving on or within the plant in the absence of competition. Inoculation with green fluorescent protein-labeled S. enterica and E. coli O157:H7 showed invasion of the roots at lateral root junctions. Movement was eliminated and invasion decreased when nonmotile mutants of S. enterica were used. Survival of S. enterica serovar Newport and E. coli O157:H7 on soil-grown plants declined as the plants matured, but both pathogens were detectable for at least 21 days. Survival of the pathogen was reduced in unautoclaved soil and amended soil, suggesting competition from indigenous epiphytes from the soil. Enterobacter asburiae was isolated from soil-grown A. thaliana and shown to be effective at suppressing epiphytic growth of both pathogens under gnotobiotic conditions. Seed and chaff harvested from contaminated plants were occasionally contaminated. The rate of recovery of S. enterica and E. coli O157:H7 from seed varied from undetectable to 19% of the seed pools tested, depending on the method of inoculation. Seed contamination by these pathogens was undetectable in the presence of the competitor, Enterobacter asburiae. Sampling of 74 pools of chaff indicated a strong correlation between contamination of the chaff and seed (P = 0.025). This suggested that contamination of the seed occurred directly from contaminated chaff or by invasion of the flower or silique. However, contaminated seeds were not sanitized by extensive washing and chlorine treatment, indicating that some of the bacteria reside in a protected niche on the seed surface or under the seed coat.

Arabidopsis↗

PubMed2003

Serotyping of Listeria monocytogenes by enzyme-linked immunosorbent assay and identification of mixed-serotype cultures by colony immunoblotting.

Routine analysis of Listeria monocytogenes by serotyping using traditional agglutination methods is limited in use because of the expense and limited availability of commercially prepared antisera and intra- and interlaboratory discrepancies arising from differences in antiserum preparation and visual determination of agglutination. We have adapted a commercially available set of L. monocytogenes antisera to an enzyme-linked immunosorbent assay (ELISA) format for high-throughput, low-cost serotype determination. Rather than subjective visualization of agglutination, positive antigen and antiserum reactions were scored by a quantitative, colorimetric reaction. ELISA serotyping of 89 of 101 L. monocytogenes isolates agreed with slide agglutination serotyping data, and 100 previously uncharacterized isolates were serotyped unambiguously by the ELISA method. In addition, mixed-serotype cultures of L. monocytogenes were identified by a colony immunoblot procedure, in which serogroup 1/2 and serogroup 4 colonies were discriminated by differential staining.

Agglutination↗

PubMed2003

Antibacterial activities of phenolic benzaldehydes and benzoic acids against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, and Salmonella enterica.

We evaluated the bactericidal activities of 35 benzaldehydes, 34 benzoic acids, and 1 benzoic acid methyl ester against Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica when these compounds were substituted on the benzene ring with 0, 1, 2, or 3 hydroxy (OH) and/or methoxy (OCH3) groups in a pH 7.0 buffer. Dose-response plots were used to determine the percentage of the sample that induced a 50% decrease in CFU after 60 min (BA50). Of the 70 compounds tested, 24 were found to be active against all four pathogens, and additional 4, 10, and 12 were found to be active against three, two, and one of the pathogens, respectively. C. jejuni was approximately 100 times as sensitive as the other three pathogens. The 10 compounds that were most active against the four pathogens (with average BA50 values ranging from 0.026 to 0.166) and are candidates for studies of activity in foods or for disinfections were 2,4,6-trihydroxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 2,3,4-trihydroxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, 2,3-dihydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-2,6-dimethoxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde. and 2-hydroxybenzaldehyde. Comparison of the chemical structures of the test compounds and their activities revealed that (i) the aldehyde (CHO) group was more active than the carboxyl (COOH) group whether or not OH groups were present; (ii) compounds were most active with trisubstituted OH > disubstituted OH > monosubstituted OH; (iii) for disubstituted derivatives, 2-OH enhanced activities were exhibited by benzaldehyde but not by benzoic acid; (iv) compounds were more active with OH than with OCH3, irrespective of the position of substitution on the benzene ring; (v) compounds with mixed OH and OCH3 groups exhibited variable results, i.e., in some cases OCH3 groups enhanced activity and in other cases they did not; (vi) methoxybenzoic acids were largely inactive; and (vii) gallic acid was 20 times as active against S. enterica at pH 7.0 as it was at pH 3.7, suggesting that the ionization of its OH groups may enhance bactericidal activity.

Anti-Infective Agents↗

PubMed2002

Fitness of Salmonella enterica serovar Thompson in the cilantro phyllosphere.

The epiphytic fitness of Salmonella enterica was assessed on cilantro plants by using a strain of S. enterica serovar Thompson that was linked to an outbreak resulting from cilantro. Salmonella serovar Thompson had the ability to colonize the surface of cilantro leaves, where it was detected by confocal laser scanning microscopy (CLSM) at high densities on the veins and in natural lesions. The population sizes of two common colonizers of plant surfaces, Pantoea agglomerans and Pseudomonas chlororaphis, were 10-fold higher than that of the human pathogen on cilantro incubated at 22 degrees C. However, Salmonella serovar Thompson achieved significantly higher population levels and accounted for a higher proportion of the total culturable bacterial flora on cilantro leaves when the plants were incubated at warm temperatures, such as 30 degrees C, after inoculation, indicating that the higher growth rates exhibited by Salmonella serovar Thompson at warm temperatures may increase the competitiveness of this organism in the phyllosphere. The tolerance of Salmonella serovar Thompson to dry conditions on plants at 60% relative humidity was at least equal to that of P. agglomerans and P. chlororaphis. Moreover, after exposure to low humidity on cilantro, Salmonella serovar Thompson recovered under high humidity to achieve its maximum population size in the cilantro phyllosphere. Visualization by CLSM of green fluorescent protein-tagged Salmonella serovar Thompson and dsRed-tagged P. agglomerans inoculated onto cilantro revealed that the human pathogen and the bacterial epiphyte formed large heterogeneous aggregates on the leaf surface. Our studies support the hypothesis that preharvest contamination of crops by S. enterica plays a role in outbreaks linked to fresh fruits and vegetables.

Colony Count, Microbial↗

PubMed2002

Association of Escherichia coli O157:H7 with preharvest leaf lettuce upon exposure to contaminated irrigation water.

Recent foodborne outbreaks have linked infection by enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 to the consumption of contaminated lettuce. Contamination via food handler error and on-the-farm contamination are thought to be responsible for several outbreaks. Though recent studies have examined the application of EHEC to store-bought lettuce, little is known about the attachment of EHEC to growing plants. We investigated the association of lettuce seedlings with EHEC O157:H7 strains implicated in lettuce or fruit outbreaks using hydroponic and soil model systems. EHEC strains that express the green fluorescent protein were observed by stereomicroscopy and confocal laser scanning microscopy to determine adherence patterns on growing lettuce seedlings. Bacteria adhered preferentially to plant roots in both model systems and to seed coats in the hydroponic system. Two of five nonpathogenic E. coli strains showed decreased adherence to seedling roots in the hydroponic system. EHEC was associated with plants in as few as 3 days in soil, and contamination levels were dose-dependent. EHEC levels associated with young plants inoculated with a low dose suggested that the bacteria had multiplied. These data suggest that preharvest crop contamination via contaminated irrigation water can occur through plant roots.

Bacterial Adhesion↗

PubMed2002

Bactericidal activities of plant essential oils and some of their isolated constituents against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, and Salmonella enterica.

An improved method of sample preparation was used in a microplate assay to evaluate the bactericidal activity levels of 96 essential oils and 23 oil compounds against Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica obtained from food and clinical sources. Bactericidal activity (BA50) was defined as the percentage of the sample in the assay mixture that resulted in a 50% decrease in CFU relative to a buffer control. Twenty-seven oils and 12 compounds were active against all four species of bacteria. The oils that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.009) were marigold, ginger root, jasmine, patchouli, gardenia, cedarwood, carrot seed, celery seed, mugwort, spikenard, and orange bitter oils; those that were most active against E. coli (with BA50 values ranging from 0.046 to 0.14) were oregano, thyme, cinnamon, palmarosa, bay leaf, clove bud, lemon grass, and allspice oils; those that were most active against L monocytogenes (with BA50 values ranging from 0.057 to 0.092) were gardenia, cedarwood, bay leaf, clove bud, oregano, cinnamon, allspice, thyme, and patchouli oils; and those that were most active against S. enterica (with BA50 values ranging from 0.045 to 0.14) were thyme, oregano, cinnamon, clove bud, allspice, bay leaf, palmarosa, and marjoram oils. The oil compounds that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.034) were cinnamaldehyde, estragole, carvacrol, benzaldehyde, citral, thymol, eugenol, perillaldehyde, carvone R, and geranyl acetate; those that were most active against E. coli (with BA50 values ranging from 0.057 to 0.28) were carvacrol, cinnamaldehyde, thymol, eugenol, salicylaldehyde, geraniol, isoeugenol, citral, perillaldehyde, and estragole; those that were most active against L monocytogenes (with BA50 values ranging from 0.019 to 0.43) were cinnamaldehyde, eugenol, thymol, carvacrol, citral, geraniol, perillaldehyde, carvone S, estragole, and salicylaldehyde; and those that were most active against S. enterica (with BA50 values ranging from 0.034 to 0.21) were thymol, cinnamaldehyde, carvacrol, eugenol, salicylaldehyde, geraniol, isoeugenol, terpineol, perillaldehyde, and estragole. The possible significance of these results with regard to food microbiology is discussed.

Bacteria↗

PubMed2002

Prevalence of Escherichia coli associated with a cabbage crop inadvertently irrigated with partially treated sewage wastewater.

Preharvest contamination of field crops may have many sources, including feces, soil, and irrigation water. In March 2000, a sewage spill released unchlorinated tertiary-treated effluent into a creek used to irrigate commercial produce. A field of young cabbage transplants was irrigated with creek water as the contaminated water flowed past this land. Cabbage samples were taken from plots within this field, and Escherichia coli was isolated from the roots of these plants but not from the edible portion of the cabbage. No E. coli was isolated from water samples or from control samples taken from a nearby cabbage field watered with chlorinated municipal water. The cabbage field under study had not been fertilized with manure for at least 2 years prior to the contamination incident. Six different E. coli serotypes were identified, although none of them proved to be pathogenic. These serotypes were separated into five groups by a RiboPrinter; the resulting groups correlated well with the serotypes and the locations in the field from which these strains were isolated. We previously found that certain nonpathogenic E. coli strains displayed lower levels of adherence to lettuce seedling roots in a hydroponic adherence assay. The E. coli field strains displayed variable patterns of adherence to lettuce seedlings: strain MW421 showed significantly lower root and shoot adherence levels than did the other field strains, while strains MW423 and MW425 showed significantly higher root and shoot adherence levels. These data suggest that water quality is of paramount importance for the food safety of growing crops.

Bacterial Adhesion↗