Interactions of organic acids with vancomycin-resistant Enterococcus faecium isolated from community wastewater in Texas.

AIMS: Investigate the interactions of organic acids (OAs), acetic, butyric, citric, formic, lactic and propionic acid against 50 Gram-positive vancomycin-resistant Enterococcus faecium (VRE) strains to determine whether pH, undissociated or dissociated acid forms correlate with bacterial inhibition. METHODS AND RESULTS: Concentrations of undissociated and dissociated OAs at the molar minimum inhibitory concentrations (MICM s) of the VRE were calculated using the Henderson-Hasselbalch equation. The pH at the MICM s of all VRE strains against acetic, butyric, formic and propionic acids was similar, 4·66 ± 0·07, but there was a 1·1 pH unit difference for all six OAs. Inhibition of VRE by all six OAs did not appear to be solely dependent on pH or on the undissociated OA species. The inhibition of VRE by all six dissociated acids was within Δ = 3·1 mmol l-1 . CONCLUSIONS: Vancomycin-resistant Enterococcus faecium inhibition correlated with the dissociated OA species. A small decrease in the concentration of the dissociated OAs from optimum may result in allowing VRE strains to escape disinfection. SIGNIFICANCE AND IMPACT OF THE STUDY: When an OA is used to disinfect VRE strains, the concentration of the dissociated OA should be carefully controlled. A concentration of at least 20 mmol l-1 dissociated OA should be maintained when disinfecting VRE.

Inhibition of multidrug-resistant Staphylococci by sodium chlorate and select nitro- and medium chain fatty acid compounds.

AIMS: Determine the antimicrobial effects of 5 µmol ml-1 sodium chlorate, 9 µmol ml-1 nitroethane or 2-nitropropanol as well as lauric acid, myristic acid and the glycerol ester of lauric acid Lauricidin® , each at 5 mg ml-1 , against representative methicillin-resistant staphylococci, important mastitis- and opportunistic dermal-pathogens of humans and livestock. METHODS AND RESULTS: Three methicillin-resistant Staphylococcus aureus and two methicillin-resistant coagulase-negative staphylococci were cultured at 39°C in 5 µmol ml-1 nitrate-supplemented half-strength Brain Heart Infusion broth treated without or with the potential inhibitors. Results revealed that 2-nitropropanol was the most potent and persistent of all compounds tested, achieving 58-99% decreases in mean specific growth rates and maximum optical densities when compared with untreated controls. Growth inhibition did not persist by cultures treated solely with chlorate or nitroethane, with adaptation occurring by different mechanisms after 7 h. Adaptation did not occur in cultures co-treated with nitroethane and chlorate. The medium chain fatty acid compounds had modest effects on all the staphylococci tested except the coagulase-negative Staphylococcus epidermidis strain NKR1. CONCLUSIONS: The antimicrobial activity of nitrocompounds, chlorate and medium chain fatty acid compounds against different methicillin-resistant staphylococci varied in potency. SIGNIFICANCE AND IMPACT OF THE STUDY: Results suggest that differential antimicrobial activities exhibited by mechanistically dissimilar inhibitors against methicillin-resistant staphylococci may yield potential opportunities to combine the treatments to overcome their individual limitations and broaden their activity against other mastitis and dermal pathogens.

Characterization of antibiotic and disinfectant susceptibility profiles among Pseudomonas aeruginosa veterinary isolates recovered during 1994-2003.

AIMS: To evaluate susceptibility of Pseudomonas aeruginosa veterinary isolates to antibiotics and disinfectants. METHODS AND RESULTS: Pseudomonas aeruginosa isolates collected from dogs (n = 155) and other animals (n = 20) from sixteen states during 1994-2003 were tested for susceptibility. Most isolates were resistant to twenty-one antimicrobials tested, and the highest prevalence of resistance was to ß-lactams (93.8%) and sulphonamides (93.5%). Fluoroquinolone resistance did not increase from 1994 to 2003. Ciprofloxacin and enrofloxacin had a 5 and 16% prevalence of resistance, respectively, while sarafloxacin and nalidixic acid had a prevalence of resistance of 97 and 98%, respectively. Strains were pan-resistant to triclosan and chlorhexidine, were highly resistant to benzalkonium chloride and demonstrated high susceptibility to other disinfectants. Didecyldimethylammonium chloride was the most active ammonium chloride. Inducible resistance was observed to cetyl ammonium halides, chlorhexidine and benzyl ammonium chlorides, which formulate disinfectants used in veterinary clinics and dairies. Organic acid inhibition was associated with the dissociated acid species. CONCLUSIONS: Dissociated organic acids appear able to inhibit Ps. aeruginosa, and rates of fluoroquinolone resistance merit sustained companion animal isolate surveillance. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of Ps. aeruginosa susceptibility to 24 disinfectants and illustrates the high resistance of Ps. aeruginosa to both antibiotics and disinfectants.

Transient gut retention and persistence of Salmonella through metamorphosis in the lesser mealworm, Alphitobius diaperinus (Coleoptera: Tenebrionidae).

AIMS: This study was undertaken to determine the retention of Salmonella through Alphitobius diaperinus metamorphosis and its contribution, through defecation, to external contamination. METHODS AND RESULTS: Insects were exposed to a tagged Salmonella enterica and evaluated for external elimination. (i) Each day for 3 weeks, a filter collected frass from a restrained insect for analysis. (ii) Exposed larvae in a closed container were followed through pupation, and newly emerged adults were examined for their retention of marker bacteria. CONCLUSIONS: Exposed adults and larvae produced Salmonella-positive frass for an average of 8 days, ranging from 6 to 11 days and 6 to 12 days, respectively. Nineteen per cent of the larvae carried Salmonella through metamorphosis and eclosion, with 5% of the pupal exuviae being positive as well. SIGNIFICANCE AND IMPACT OF THE STUDY: Many sources of foodborne pathogens within the poultry production facilities, including reservoir populations, currently go unrecognized. This diminishes the ability of producers to mitigate the transfer of pathogens between animals, humans and the environment. Poultry management standards accept the reutilization of litter. Alphitobius diaperinus survive between flock rotations on the reutilized litter, and it was demonstrated in this study that the Salmonella they carry can survive with them.

Metabolic detoxification: mechanism of insect resistance to plant psoralens.

Larvae of the black swallowtail butterfly, Papilio polyxenes Stoll, forage successfully on plants that contain high levels of photosensitizing psoralens. These insects rapidly detoxify psoralens, particularly in the midgut tissue prior to absorption, with the result that appreciable levels of unmetabolized phototoxin do not enter the body circulation where deleterious light-induced interactions with dermal or subdermal tissues would occur.

The horizontal transfer of Salmonella between the lesser mealworm (Alphitobius diaperinus) and poultry manure.

There is need to determine the nature of enduring reservoirs of Salmonella contributing to perpetual contamination within poultry flocks. The dispersal of Salmonella between birds, litter and the lesser mealworm has been established, but the extent that these act as critical components in the epidemiology of Salmonella infection during broiler grow-out and flock rotation has not been delineated; in particular, the level of participation by the lesser mealworm beetles (LMB) as agents of retention and dispersal. This study defines this route of transmission and provides empirical data on bacterial loads that facilitate Salmonella transfer. Results showed differential Salmonella transfer dependent on bacterial concentration. At 103  cfu/ml, only a small, but not significant, amount of Salmonella was transferred, from the LMB to the manure and back to uninfected LMB; while from 105 to 107  cfu/ml, a significant acquisition and transfer occurred both internally and externally to the LMB over 4 and 24 hr exposures. These data will be used in correlation with facility management practices to develop intervention strategies to mitigate the establishment and spreading of reservoir Salmonella populations contributing to pre-harvest contamination of poultry flocks.

Transferability of antimicrobial resistance from multidrug-resistant Escherichia coli isolated from cattle in the USA to E. coli and Salmonella Newport recipients.

OBJECTIVES: This study aimed to evaluate conjugative transfer of cephalosporin resistance among 100 strains of multidrug-resistant Escherichia coli (MDRE) to Salmonella enterica serotype Newport and E. coli DH5α recipients. METHODS: Phenotypic and genotypic profiles were determined for MDRE as well as for Salmonella Newport (trSN) and E. coli DH5α (trDH) transconjugants. RESULTS: Of 95 MDRE donor isolates, 26 (27%) and 27 (28%) transferred resistance to trSN and trDH recipients, respectively. A total of 27 MDRE (27%) were confirmed as extended-spectrum ß-lactamase (ESBL)-producers based on the double-disk synergy assay and whole-genome sequencing (WGS). WGS was performed on 25 of the ESBL-producing isolates, showing that 2 isolates carried blaCTX-M-6, 22 possessed blaCTX-M-32 and 1 was negative for blaCTX-M genes. Fourteen of the ESBLs sequenced were qnrB19. Differential transfer of IncA/C and IncN from MDRE32 was observed between trSN32 and trDH32. IncN-positive trDH32 displayed an ESBL phenotype, whereas IncA/C-positive trSN32 displayed an AmpC phenotype. The rate of ESBL transfer to trSN and trDH recipients was 11% and 96%, respectively. CONCLUSIONS: Twenty-seven MDRE were phenotypically identified as ESBL-producers. WGS of 25 MDRE revealed that 2 and 22 isolates carried blaCTX-M-6 and blaCTX-M-32, respectively. One multidrug-resistant isolate exhibited conversion from an AmpC phenotype to an ESBL phenotype with the transfer of only the IncN plasmid. The rate of resistance transfer to Salmonella or E. coli recipients was nearly identical. However, the ESBL phenotype was transferred with significantly greater prevalence to E. coli compared with Salmonella Newport (96% and 11%, respectively).

In Vitro Effects of Thymol-ß-D-Glucopyranoside on Salmonella enterica Serovar Typhimurium and Escherichia coli K88.

Although thymol is bactericidal against many pathogens in vitro, its in vivo effectiveness against pathogens in the lower gastrointestinal tract is limited because of its rapid absorption in the proximal gut. Thymol-ß-D-glucopyranoside (ß-thymol), a conjugated form of thymol, can deliver thymol to the lower gastrointestinal tract and has shown antibacterial effects. In the present study, we examined the in vitro effects of ß-thymol on Salmonella enterica serovar Typhimurium (ST) and Escherichia coli K88 (K88). We inoculated one-half strength Mueller-Hinton broth with 5.8 ± 0.09 log CFU/ml novobiocin- and naladixic acid-resistant (NN) ST (NVSL 95-1776) and 5.1 ± 0.09 log CFU ml(-1) NN-resistant K88, with or without porcine feces (0.1% [wt/vol]) (fecal incubations). The resultant bacterial suspensions were distributed under N2 to triplicate sets of tubes to achieve initial concentrations of 0, 3, 6, and 12 mM for ST treatments and 0, 3, 12, and 30 mM for K88 treatments. Samples were incubated at 39°C and then plated onto NN-containing brilliant green agar and NN-containing MacConkey agar; ST and K88 CFU concentrations were determined via 10-fold dilutions, and viable cell counts were performed at 0, 6, and 24 h. No differences in ST CFU counts were observed in ß-thymol-treated tubes without the added porcine feces (i.e., pure culture) at 6 or 24 h. However, in tubes that contained fecal incubations, ST CFU counts were reduced (P < 0.05) from controls at 6 h in tubes treated with 6 and 12 mM ß-thymol, whereas in tubes treated with 3, 6, and 12 mM ß-thymol the CFU counts were reduced (P < 0.05) at 24 h. No differences were observed in K88 CFU counts in pure culture or in fecal incubations at 6 h, but K88 CFU counts were reduced (P < 0.05) in both pure and fecal incubations at 24 h. The results from this study demonstrate that ß-thymol, in the presence of fecal suspensions, has anti-Salmonella and anti-E. coli effects, suggesting a role of ß-glycoside-hydrolyzing microbes for the release of bactericidal thymol from ß-thymol.

Structure-activity relationships for inhibitory insect myosuppressins: contrast with the stimulatory sulfakinins.

Unusual among insect neuropeptides, the decapeptide myosuppressins are capable of inhibiting contractions of visceral muscle, including the isolated cockroach hindgut. The C-terminal pentapeptide Val-Phe-Leu-Arg-Phe-NH2 has been identified as the myosuppressin active core, the minimum number of residues required to elicit hindgut myoinhibitory activity. Activity of the same magnitude as the parent neuropeptide requires the C-terminal heptapeptide fragment Asp-His-Val-Phe-Leu-Arg-Phe-NH2. Evaluation of a series of substitution analogs delineates structural features critical for myoinhibitory activity within this important fragment. The branched, hydrophobic residues in myosuppressin position 6 (Val) and particularly position 8 (Leu), their absence in the myostimulatory sulfakinins, and the different roles played by the shared Asp residue (myosuppressin position 4; leucosulfakinin position 5) in peptide-receptor interaction, account in large degree for the contrasting biological activities elicited by these otherwise structurally similar peptide families. The results may have broad significance for other invertebrate myotropic systems, such as the locust heart and the pharyngeal retractor muscle of the mollusc Helix aspersa.

Diuretic activity of C-terminal group analogues of the insect kinins in Acheta domesticus.

A series of insect kinin analogues, AFFPWG-X, modified at the C-terminal group, were evaluated in a cricket Malpighian tubule secretion bioassay. The results were compared with activity profiles observed in a cockroach hindgut myotropic bioassay for these analogues. Although the replacement of the C-terminal amide group with a negatively charged acid leads to a precipitious drop in diuretic activity, it can be partially restored with the introduction of ester groups such as methyl or benzyl. The presence of branched chain character in the C-terminal group or a C-terminal alpha-carbon-amide distance spanning five methylene group spacers is incompatible with the receptor interaction required for biological activity. Significant diuretic activity is retained with four or fewer methylene groups in this region. C-terminal group analogues containing -SCH3, -NHCH2CH2OCH3, or -OCH2(C6H5) offered the greatest retention of diuretic activity while providing increased hydrophobicity and/or steric bulk. The data are of potential value in the development of mimetic analogues of this insect neuropeptide family. Mimetic analogues are potentially valuable tools to insect neuroendocrinologists studying diuresis and/or engaged in the development of future pest management strategies.

Pseudodipeptide analogs of the pyrokinin/PBAN (FXPRLa) insect neuropeptide family containing carbocyclic Pro-mimetic conformational components.

Three N-terminal amino acid residues of the C-terminal core pentapeptide Phe-X-Pro-Arg-Leu-NH2 (X = Gly, Ser, Thr, Val) of the pryokinin/PBAN insect neuropeptide family were replaced by nonpeptide moieties. To reestablish some of the conformational properties lost upon removal of the peptide bonds and Pro of the three amino acid residue block, carbocyclic Pro-mimetic components were incorporated into pseudodipeptide analogs. The most active analog contained a trans-DL-1,2-cyclopentanedicarboxyl carbocyclic component and proved to be over 3 orders of magnitude more potent than a simple, straight chain pseudodipeptide analog and approached the potency of the pentapeptide core in a cockroach hindgut myotropic bioassay. The pseudodipeptide analog retains a critical carbonyl residue which can participate in a hydrogen bond that stabilizes a beta-turn conformation in the active core region of the pyrokinin/PBAN peptides. This study demonstrates that knowledge of active conformation can be used to enhance the biological potency of pseudopeptide mimetic analogs of insect neuropeptides. The analogs represent a milestone in the development of pseudopeptide and nonpeptide mimetic analogs of this peptide family, which has been associated with such critical physiological processes as hindgut and oviduct contraction, pheromone biosynthesis, diapause induction, and induction of melanization and reddish coloration in a variety of insects. Mimetic analogs are potentially valuable tools to insect neuroendocrinologists studying these physiological processes and/or engaged in the development of future pest management strategies.

Phytophotodermatitis from celery among grocery store workers.

We detected 19 cases of phytophotodermatitis during a cross-sectional epidemiological investigation of two Oregon grocery stores that were part of the same supermarket chain. Outdoor sunlight exposure during the workshift and tanning salon use were identified as risk factors; the most severe cutaneous reactions tended to occur among tanning salon users. Although both stores carried the same brands and varieties of produce, all 19 cases occurred among employees of one store, which had held a celery sale coincident with the outbreak, resulting in a quadrupling of the usual volume of celery sold. We found elevated psoralen levels in two of three celery samples obtained from the affected store; cutaneous provocation tests with trimmed surfaces of these celery samples produced phototoxic reactions. Preliminary experiments with one brand of celery have demonstrated psoralen levels as high as 25 micrograms/cm2 of trimmed surface. These observations suggest that clinical phytophotodermatitis among grocery store workers may be caused by healthy celery and results from a complex interaction of exposure variables, including ultraviolet radiation from tanning salon use, frequency of handling celery, celery brand, and sporadic elevation of psoralen content from environmental stresses.

Occurrence of the toxin dehydroabietic acid in Salmonella typhimurium.

Many strains of Salmonella typhimurium studied in our lab demonstrated marked differences in the pathogenicity for guinea pig, chicken and Hela cells. As a result, a pathogenic strain of S. typhimurium, strain 9SR2, was evaluated for lipophilic components that may be associated with virulence using gas chromatography/mass spectrometry. The hydroxylated fatty acids 2-hydroxytetradecanoic acid (2-OH-14:0) and 3-hydroxytetradecanoic acid (3-OH-14:0) often present in lipid A, a potent endotoxin, were observed as their methyl esters. The cyclic fatty acids methylene-hexadecanoic acid (C17delta) and methyleneoctadecanoic acid (C19delta) also were detected. The nephrotoxic and neurotoxic diterpenoid resin acid, dehydroabietic acid, was observed for the first time from S. typhimurium in both the total lipid and diglyceride fractions and determined as its methyl ester at m/z 314.2246. Due to its previously established toxicity, dehydroabietic acid may be a factor associated with virulence of S. typhimurium.

Isopimpinellin is not phototoxic in a chick skin assay.

Synthetic isopimpinellin (5,8-dimethoxypsoralen), confirmed to contain as impurities only trace quantities at most of psoralen, bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen), is not phototoxic when tested in a chick skin bioassay system. These findings are at variance with earlier studies showing isopimpinellin to be phototoxic against chick skin and support the conclusion that isopimpinellin is photobiologically inactive. As recently proposed by others, the several reports of isopimpinellin photoactivity are most likely attributable to contamination by small amounts of highly active psoralens such as bergapten or xanthotoxin.

Natural pesticides and bioactive components in foods.

In this review, some common food plants and their toxic or otherwise bioactive components and mycotoxin contaminants have been considered. Crucifers contain naturally occurring components that are goitrogenic, resulting from the combined action of allyl isothiocyanate, goitrin, and thiocyanate. Although crucifers may provide some protection from cancer when taken prior to a carcinogen, when taken after a carcinogen they act as promoters of carcinogenesis. The acid-condensed mixture of indole-3-carbinol (a component of crucifers) binds to the TCDD receptor and causes responses similar to those of TCDD. Herbs contain many biologically active components, with more than 20% of the commercially prepared human drugs coming from these plants. Onion and garlic juices can help to prevent the rise of serum cholesterol. Most herbs used in treatments may have many natural constituents that act oppositely from their intended use. Some herbs like Bishop's week seed contain carcinogens, and many contain pyrrolizidine alkaloids that can cause cirrhosis of the liver. The general phytoalexin response in plants (including potatoes, tomatoes, peppers, eggplant, celery, and sweet potatoes) induced by external stimuli can increase the concentrations of toxic chemical constituents in those plants. In potatoes, two major indigenous compounds are alpha-solanine and alpha-chaconine, which are human plasma cholinesterase inhibitors and teratogens in animals. Because of its toxicity, the potato variety Lenape was withdrawn from the market. Celery, parsley, and parsnips contain the linear furanocoumarin phytoalexins psoralen, bergapten, and xanthotoxin that can cause photosensitization and also are photomutagenic and photocarcinogenic. Celery field workers and handlers continually have photosensitization problems as a result of these indigenous celery furanocoumarins. A new celery cultivar (a result of plant breeding to produce a more pest-resistant variety) was responsible for significant incidences of phytophotodermatitis of grocery employees. Since there is no regulatory agency or body designated to oversee potential toxicological issues associated with naturally occurring toxicants, photodermatitis continues to occur from celery exposure. Sweet potatoes contain phytoalexins that can cause lung edema and are hepatotoxic to mice. At least one of these, 4-ipomeanol, can cause extensive lung clara cell necrosis and can increase the severity of pneumonia in mice. Some phytoalexins in sweet potatoes are hepatotoxic and nephrotoxic to mice. The common mushroom Agaricus bisporus contains benzyl alcohol as its most abundant volatile, and A. bisporus and Gyromitra esculenta both contain hydrazine analogues. Mycotoxins are found in corn, cottonseed, fruits, grains, grain sorghums, and nuts (especially peanuts); therefore, they also occur in apple juice, bread, peanut butter, and other products made from contaminated starting materials.(ABSTRACT TRUNCATED AT 400 WORDS)

Production, characterization, and cross-reactivity studies of monoclonal antibodies against the coccidiostat nicarbazin.

A cELISA was developed for the coccidiostat nicarbazin. On the basis of previous computer-assisted molecular modeling studies, p-nitrosuccinanilic acid (PNA-S) was selected as a hapten to produce antibodies to 4,4'-dinitrocarbanilide (DNC), the active component of the coccidiostat nicarbazin. Synthesis is described for the hapten [p-nitro-cis-1,2-cyclohexanedicarboxanilic acid (PNA-C)] used in a BSA conjugate as a plate coating antigen. Monoclonal antibodies (Mabs) were isolated that compete with nicarbazin, having IgM(kappa) isotype. Because of the lack of water solubility of nicarbazin, N,N-dimethylformamide (DMF) (3%, v/v) and acetonitrile (ACN) (10%, v/v) were added to the assay buffer to achieve solubility of nicarbazin and related compounds. The Nic 6 Mabs had an IC(35) value for nicarbazin of 0.92 nmol/mL, with a limit of detection of 0.33 nmol/mL. Nic 6 exhibited high cross-reactivity for PNA-S and PNA-C, and 3-nitrophenol, 4-nitrophenol, and 1-(4-chlorophenyl)-3-(4-nitrophenyl) urea. However, Nic 6 had little or no cross-reactivity with 15 other related compounds.

Development of a monoclonal antibody-based cELISA for the analysis of sulfadimethoxine. 1. Development and characterization of monoclonal antibodies and molecular modeling studies of antibody recognition.

Sulfonamide antibiotics are used to treat a variety of bacterial and protozoan infections in cattle, swine, and poultry. Current residue methods for the analysis of sulfonamides in animal-based food products include bioassays, chromatographic methods (HPLC, GLC), and immunoassays. Most immunoassays have employed highly specific polyclonal antibodies. In this paper, we describe the isolation of monoclonal antibodies against sulfadimethoxine (SDM) that vary in their sensitivities and cross-reactivities against a large number of sulfonamides. The most sensitive monoclonal antibody, designated SDM-18, exhibits an IC(50) value for SDM of 1.53 ppb. Another monoclonal antibody, designated SDM-44, exhibits IC(50) values for six sulfonamides well below the established threshold level of 100 ppb for animal tissues. Molecular modeling studies of the cross-reactive drugs suggest that, depending on the monoclonal antibody, both steric and electronic features govern antibody binding. Due to the diversity of these monoclonal antibodies, it should be possible to design both compound- and class-specific monoclonal antibody-based immunoassays.

Development of a monoclonal antibody-based cELISA for the analysis of sulfadimethoxine. 2. Evaluation of rapid extraction methods and implications for the analysis of incurred residues in chicken liver tissue.

Several rapid extraction methods were evaluated for use with a monoclonal antibody-based competitive inhibition ELISA (cELISA) to detect sulfadimethoxine (SDM) in chicken liver tissue. These methods included extraction of the samples with (1) aqueous buffer with or without ultrafiltration, (2) acetonitrile/water, (3) methanol/water, or (4) acetone. The organic extraction methods were evaluated with or without solvent evaporation prior to dilution into assay buffer for the cELISA. The aqueous-based extraction methods were compatible with the cELISA. However, of the organic extraction methods, only the acetone liver extract with solvent evaporation prior to analysis was compatible with the cELISA. The cELISA method coupled to aqueous- or acetone-based sample extraction as well as an HPLC method was evaluated for the analysis of chicken liver tissues fortified with SDM at levels from 0.2 to 0.025 ppm. Mean SDM recoveries for the HPLC method and for the cELISA method using samples prepared by aqueous extraction, aqueous extraction and ultrafiltration, or acetone extraction, evaporation, and reconstitution were 68.9, 95.7, 60.1, and 52.5%, respectively. For the analysis of samples obtained from an SDM incurred residue study, HPLC and cELISA analysis of the same organic extract gave results that were highly correlated (R(2) = 0.976; p < 0.0001). However, results obtained from the analysis of aqueous extracts by cELISA did not correlate well with those obtained by HPLC (R(2) = 0.61, p > 0. 0006). This was attributed to the coextraction of cross-reactive SDM-related residues that were not quantified by the HPLC method. The presence of these residues should be considered during data interpretation when ELISA methods coupled with rapid aqueous extraction of samples are used in SDM residue monitoring programs.

HPLC analysis of linear furocoumarins (psoralens) in healthy celery (Apium graveolens).

Four linear furocoumarins (psoralen, bergapten, xanthotoxin, and isopimpinellin) were isolated from three varieties of healthy, commercially grown celery (Apium graveolens). Psoralen has not previously been reported to occur in celery. Combined levels of these photomutagenic and photocarcinogenic furocoumarins measured by normal-phase HPLC did not exceed 1.3 ppm in any of the celery varieties studied.

Phototoxic coumarins in limes.

Coumarins in the rind and pulp of Persian and Key limes were quantified. In the rind of Persian limes, coumarin concentrations were in the order: limettin > bergapten > isopimpinellin > xanthotoxin > psoralen. In the rind of Key limes, psoralen and xanthotoxin were analytically absent; limettin was 10 times more concentrated than either bergapten or isopimpinellin, which were equal in concentration. Coumarin content in Persian lime pulp was in the order: isopimpinellin > limettin > bergapten > xanthotoxin > psoralen. For Key lime pulp, the concentrations of limettin, isopimpinellin and bergapten were equal; psoralen and xanthotoxin were not detected. Coumarins in lime pulp were 13 to 182 times less concentrated than those in the peel. Based on the amounts and types of coumarins, Persian limes appear to be potentially more phototoxic than Key limes. Although bergapten may be the main component of limes responsible for phytophotodermatitis, dermatological interaction assays with psoralen, bergapten, xanthotoxin and limettin should be conducted.