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The addition of Grignard reagents to ketones is a well-established textbook reaction. However, a comprehensive understanding of its mechanism has only recently begun to emerge. X-ray spectroscopy, because of its high selectivity and sensitivity, is the ideal tool for distinguishing between an ensemble of competing pathways. With this aim in mind, we investigated the concerted mechanism of the addition of methylmagnesium chloride (CH 3 MgCl) to acetone in tetrahydrofuran by simulating the X-ray spectra of different molecules in solution. We used electronic structure methods to calculate the X-ray absorption spectra at the Mg K- and L 1 -edges and the X-ray photoelectron spectra at the Mg K-edge for different organomagnesium species, which coexist in solution due to the Schlenk equilibrium. The simulated spectra show that individual species can be distinguished throughout the different stages of the reaction. Each species has a distinct spectral feature which can be used as a fingerprint in solution. The absorption and photoelectron spectra consistently show a blue shift as the reaction progressed from reagents to products., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

We investigate the photoinduced dissociation reaction of NO 2 → NO + O upon electronic excitation of the X̃ 2 A 1 (D 0 ) to the à 2 B 2 (D 1 ) state by femtosecond X-ray absorption spectroscopy at the nitrogen K-edge. We obtain key insight into the chemical bond breaking event and its associated electronic structural dynamics. Calculations of the photoinduced reaction allow to assign the transient absorption features at time scales of 10-50 fs to wave packet motions in the excited D 1 and ground D 0 states, followed by the formation of the NO photoproduct with a 255 ± 23 fs time constant. Our analysis shows that there is no direct correlation between the 1s core levels and the electronic ground and excited states transition energies and the bond elongation of NO 2 , while en route to dissociation toward the NO + O photoproducts, in the transient nitrogen K-edge spectra. However, simulations predict that for a sufficiently short UV pump pulse, the early wave packet dynamics in the D 1 electronic excited state occurring within the first 35 fs along the bending and symmetric stretching modes can be directly mapped in the transient X-ray absorption spectra.

The Bacillus cereus group is comprised of diverse yet closely related species that are ubiquitous in nature. These Gram-positive, spore-forming bacteria are commonly isolated as potential pathogens in environmental and food samples, and they are also beneficially used in industrial applications such as probiotics or agricultural pesticides. Although phylogenetic and genomic analyses identified eight formally recognized species within the Bacillus cereus group, only five members are currently acknowledged using standardized isolation procedures. Therefore, current enumeration procedures may be inadequate and inaccurate in determining the clinical importance of the B. cereus group and their prevalence in food and environmental sources. In this investigation, the R & F® Bacillus cereus Group Chromogenic Plating Medium (BCG) was developed to target the enzyme phosphatidylcholine phospholipase C (PC-PLC) found widely distributed among the B. cereus group species. The performance evaluations of the plating medium demonstrated a 100% plating productivity ratio, inclusivity, and exclusivity when compared with Trypto Soy Agar (TSA). B. cereus group species, including B. anthracis, B. cereus sensu stricto (s.s.), B. cytotoxicus, B. pseudomycoides, B. mycoides, B. thuringiensis, B. toyonensis, B. weidmannii, and B. weihenstephanensis, formed turquoise-colored colonies on the BCG agar, indicating PC-PLC activity after 24-28 h of incubation at the selected optimal temperature of 35 °C. Furthermore, no significant difference was observed between BCG and TSA when enumerating B. cereus s.s. and B. cytotoxicus artificially inoculated in whey protein powder and ultra-high temperature milk after long-term storage., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 R & F Products, Inc. Published by Elsevier Inc. All rights reserved.)

Arcobacters are emerging pathogens that have been underestimated due to a lack of a standardized isolation method. The aim of this research was to evaluate the ability to isolate Arcobacter butzleri, Arcobacter cryaerophilus, and Arcobacter skirrowii using two Arcobacter-specific culture detection systems: (i) the Houf broth and modified charcoal cefoperazone deoxycholate agar supplemented with cefoperazone, amphotericin B, and teicoplanin (HB/mCCDA+CAT), and (ii) the Nguyen-Restaino-Juárez Arcobacter enrichment broth and chromogenic agar (NRJ-B/M). Both detection systems were evaluated for productivity ratio, sensitivity, and specificity. As a result, the productivity ratio for both plating agars were >90%, which indicates that the selective agents used in the two plating agars did not inhibit Arcobacter growth. Moreover, sensitivity evaluations using artificially inoculated retail ground poultry (n = 780) determined that both detection systems were able to isolate A. butlzeri with >95% sensitivity at the 0.1 and 1.0-2.0 CFU/g detection level. The sensitivity in A. cryaerophilus isolation was higher for NRJ-B/M (78.0% at 0.1 CFU/g; 95.1% at 1.0-2.0 CFU/g) when compared with HB/mCCDA+CAT (34.1% at 0.1 CFU/g; 51.2% at 1.0-2.0 CFU/g). Both detection systems resulted in <50% sensitivity when isolating A. skirrowii at 0.1 and 1.0-2.0 CFU/g; however, the sensitivity for NRJ-B/M was significantly higher than HB/mCCDA+CAT. At the detection level of 5.0 CFU/g, both detection systems were able to isolate A. skirrowii with 100% sensitivity. Specificity comparisons using uninoculated ground poultry samples (n = 40) indicated the growth of background microbiota were significantly inhibited or could be easily differentiated on NRJ-B/M (90.0%, specificity) when compared with HB/mCCDA+CAT (30.0%, specificity). Overall, these results show that the NRJ-B/M detection system is a more sensitive and specific detection system when isolating Arcobacter spp. from ground chicken., Competing Interests: Declaration of Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Linear off-resonant x-ray Raman techniques are capable of detecting the ultrafast electronic coherences generated when a photoexcited wave packet passes through a conical intersection. A hybrid femtosecond or attosecond probe pulse is employed to excite the system and stimulate the emission of the signal photon, where both fields are components of a hybrid pulse scheme. In this paper, we investigate how attosecond pulse trains, as provided by high-harmonic generation processes, perform as probe pulses in the framework of this spectroscopic technique, instead of single Gaussian pulses. We explore different combination schemes for the probe pulse as well as the impact of parameters of the pulse trains on the signals. Furthermore, we show how Raman selection rules and symmetry consideration affect the spectroscopic signal, and we discuss the importance of vibrational contributions to the overall signal. We use two different model systems, representing molecules of different symmetries, and quantum dynamics simulations to study the difference in the spectra. The results suggest that such pulse trains are well suited to capture the key features associated with the electronic coherence., (© 2022 Author(s).)

Arcobacter species are ubiquitous emerging pathogens with an impact that has been underestimated due to limitations in isolation and detection methods. Our group recently developed the novel NRJ Arcobacter -detection system, with major improvements in specificity and selectivity compared to other culture-based methods. In this work, the NRJ detection system was evaluated using retail whole broiler chicken carcass. Nanopore 16S rRNA gene amplicon sequencing demonstrated that Arcobacter species are found in very low abundance in retail chicken and that indigenous microbiota could be a major factor interfering with detection. Comparison of the microbiome obtained from modified Houf broth (HB) method, as the standard detection system, and the novel NRJ method, showed Arcobacter abundances of <15% and >97%, respectively. The NRJ system significantly inhibits the growth of non-target microbiota, and specifically allows the multiplication of Arcobacter species. In this report, we describe the gold-standard of Arcobacter -specific culture-based method to test food matrices, which can be used for other applications, such as clinical and environmental sampling., Competing Interests: PN and LR were employed by R & F Products, Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Nguyen, Tuz, Restaino and Juárez.)

Abstract: Arcobacter species are gram-negative rods that have been implicated in food- and waterborne illness. Although various cultural isolation methods have been proposed, the current procedures are unable to fully suppress the growth of background microbiota present in food samples, which inhibits Arcobacter isolation. The purpose of this study was to develop a selective enrichment broth and chromogenic plating medium to detect three Arcobacter species that have been recognized as emerging foodborne pathogens: Arcobacter butzleri, Arcobacter cryaerophilus, and Arcobacter skirrowii. The developed Nguyen-Restaino-Juárez (NRJ) Arcobacter detection system consists of a selective enrichment broth (NRJ-B) and a selective-differential plating medium (NRJ-M). The protocol of the detection method was determined by evaluating the growth of A. butzleri, A. cryaerophilus, and A. skirrowii under various temperatures (30, 35, and 42°C) and incubation (aerobic, microaerophilic, and anaerobic) conditions. Additionally, 47 Arcobacter strains and 39 non-Arcobacter strains were tested in inclusivity and exclusivity evaluations of NRJ-B and NRJ-M. Overall, the study determined that the optimal growth conditions of Arcobacter species using the NRJ Arcobacter detection system were aerobic incubation at 30°C. NRJ-B supported good growth of A. butzleri, A. cryaerophilus, and A. skirrowii while effectively suppressing the growth of non-Arcobacter strains after 48 h. Furthermore, NRJ-M yielded 97.8% inclusivity and 100.0% exclusivity using the tested strains and resulted in salmon-pigmented Arcobacter colonies (1.0 to 1.5 mm in diameter) after 72 h. The novel protocol is the first to develop a chromogenic plating medium for the isolation of Arcobacter species. This simple and accurate test method would greatly contribute to understanding the distribution of pathogenic Arcobacter species in food samples., (Copyright ©, International Association for Food Protection.)

The effects of the substitution on the aryl moiety on the asymmetric oxidation of sulfides mediated by Ti-complexes of chiral 1,2-diarylethane-1,2-diols were investigated. The substitution of the aryl ring of the diol with both EWG and EDG substituents generally decreased the enantioselectivity with respect to the use of unsubstituted 1,2-diphenylethane-1,2-diol (1a). Only in the presence of 1,2-di(4-t-butyl)phenyl-1,2-diol (1g) were higher ee's obtained with aryl methyl and aryl benzyl sulfides affording ee's up to 90 and 99%, respectively. Lower ee's were achieved with larger naphthyl and aryl alkyl sulfides. Contrary to the other Ti-alcoholates used in the oxidation of sulfides, the Ti-complex of diol 1g was soluble in hexane, allowing us to perform the process with high enantioselectivity in this solvent, with great environmental advantages over the commonly used chlorinated solvents., ((c) 2008 Wiley-Liss, Inc.)

A selective and differential plating medium, R & F anthracis chromogenic agar (ACA), has been developed for isolating and identifying presumptive colonies of Bacillus anthracis. ACA contains the chromogenic substrate 5-bromo-4-chloro-3-indoxyl-choline phosphate that upon hydrolysis yields teal (blue green) colonies indicating the presence of phosphatidylcholine-specific phospholipase C (PC-PLC) activity. Among seven Bacillus species tested on ACA, only members of the Bacillus cereus group (B. anthracis, B. cereus, and B. thuringiensis) produced teal colonies (PC-PLC positive) having cream rings. Examination of colony morphology in 18 pure culture strains of B. anthracis (15 ATCC strains plus AMES-1-RIID, ANR-1, and AMED-RIID), with one exception, required 48 h at 35 to 37 degrees C for significant color production, whereas only 24 h was required for B. cereus and B. thuringiensis. This differential rate of PC-PLC synthesis in B. anthracis (due to the truncated plcR gene and PlcR regulator in B. anthracis) allowed for the rapid differentiation on ACA of presumptive colonies of B. anthracis from B. cereus and B. thuringiensis in both pure and mixed cultures. Effective recovery of B. anthracis from a variety of matrices having both high (soil and sewage) and low microbial backgrounds (cloth, paper, and blood) spiked with B. anthracis ANR-1 spores suggests the probable utility of ACA plating for B. anthracis recovery in a diversity of applications.

A chromogenic agar, R&F Enterobacter sakazakii chromogenic plating medium (ESPM), was developed for isolating presumptive colonies of E. sakazakii from foods and environmental sources. ESPM contains two chromogenic substrates (5-bromo-4-chloro-3-indoxyl-alpha-D-glucopyranoside and 5-bromo-4-chloro-3-indoxyl-beta-D-cellobioside), three sugars (sorbitol, D-arabitol, and adonitol), a pH indicator, and inhibitors (bile salts, vancomycin, and cefsulodin), which all contribute to its selectivity and differential properties. On ESPM, 79 pure culture strains of E. sakazakii (10 clinical isolates and others from food and environmental sources) yielded blue-black (three strains were blue-gray) raised colonies, 1 to 2 mm in diameter with and without halos after 24 h at 35 degrees C. Other enteric organisms plus Pseudomonas aeruginosa yielded white, yellow, green, or clear colonies with and without clear halos. Of these genera, only Shigella sonnei and one Pantoea strain produced blue-black to blue-gray colonies. ESPM was used to isolate E. sakazakii from a variety of foods: corn, wheat, and rice flours; powdered infant formula; dairy products (dried milk, whey, and caseinates); cereals; and environmental sources. Most false-positive results on ESPM were eliminated by observing acid production on either sucrose or melibiose after 6 h at 35 degrees C on a R&F E. sakazakii screening medium (ESSM) biplate. In an analysis of 240 samples, the number of samples positive for E. sakazakii by the ESPM-ESSM method and the U.S. Food and Drug Administration protocols (violet red bile glucose agar and tryptic soy agar) were 27 and 16, respectively, with sensitivity and specificity values of 100.0 and 96.9% versus 59.3 and 43.7%, respectively. These data support the fact that E. sakazakii confirmation should be based on more than one confirmation system. Both the API 20E and Biolog Microlog3 4.20 systems should be used for confirmation of E. sakazakii isolates.

Escherichia coli O157:H7 strains ATCC 35150 and ATCC 43894 and five pooled isolates from beef and pork freeze injured at -25 degrees C in beef infusion were used to inoculate ground beef. Samples (25 g each) were added to 225 ml of buffered peptone water with vancomycin, cefsulodin, and cefixime (BPW-VCC), 225 ml of modified EC broth plus novobiocin (mEC+n), and 225 ml of R&F enrichment broth (R&F-EB) and aerobically incubated at 41 to 42 degrees C. After 6, 7, 8, and 24 h of incubation, levels of E. coli O157:H7 recovered from each broth by a PCR assay with the BAX automated system as well as by conventional enrichment with the use of nonaerated mEC+n incubated at 35 degrees C for 24 h were compared with levels recovered by cultural isolation with immunomagnetic separation and plating on BCM E. coli O157:H7 chromogenic agar. For ground beef inoculated with a mean of 4.23 +/- 1.00 total cells (74% freeze injured) per 25 g, after 6 h the PCR assay identified 72.7, 57.6, and 66% of the samples for R&F-EB, BPW-VCC, and mEC+n, respectively, as presumptive positive, whereas the recovery rates after 7 and 8 h exceeded 90%, with the rate for R&F-EB being 100%. For ground beef inoculated with a mean of 1.50 +/- 0.56 total cells (80% freeze injured) per 25 g, after 6 h the PCR assay identified 47.6, 19.1, and 9.5% of the samples for R&F-EB, BPW-VCC, and mEC+n, respectively, as presumptive positive. These values increased to 81.0, 61.9, and 52.4% after 7 h and to 95.2, 61.9, and 71.4% after 8 h. After 24 h, only 55 to 60% of the samples at both inoculum levels tested positive by PCR with conventional enrichment and incubation, whereas >95% of the samples tested positive with R&F-EB aerated at 41 to 42 degrees C. Culture results for R&F-EB and mEC+n after 7 and 8 h of incubation were closely correlated with presumptive positive PCR results.

Five different food types were analyzed by the Reveal for E. coli O157:H7 8-Hour Test System (Reveal 8) and either the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) culture method or the U.S. Department of Agriculture Food Safety Inspection Service (FSIS) culture method for the presence of E. coli O157:H7. A total of 27 laboratories representing academia and private industry in the United States and Canada participated. Food types were inoculated with E. coli O157:H7 at 2 different levels: a high level where predominantly positive results were expected, and a low level where fractional recovery was anticipated. During this study, 1,110 samples and controls were analyzed by both the Reveal 8 and by BAM or FSIS by each of the collaborators (2,220 samples in total). For each set of samples, 740 were artificially inoculated with E. coli O157:H7, and 370 were uninoculated controls. The Reveal 8 detected 528 presumptive positives of which 487 were confirmed positive by the BAM culture method. In comparison, BAM and FSIS detected 489 of the 740 artificially contaminated samples as positive. In an additional in-house study performed only on chilled and frozen raw ground beef, 240 artificially inoculated samples were analyzed by both the Reveal 8 and by FSIS. The Reveal 8 detected and confirmed 104 samples as positive compared to 79 confirmed positive by FSIS.

Four different food types along with environmental swabs were analyzed by the Reveal for E. coli O157:H7 test (Reveal) and the Bacteriological Analytical Manual (BAM) culture method for the presence of Escherichia coli O157:H7. Twenty-seven laboratories representing academia and private industry in the United States and Canada participated. Sample types were inoculated with E. coli O157:H7 at 2 different levels. Of the 1,095 samples and controls analyzed and confirmed, 459 were positive and 557 were negative by both methods. No statistical differences (p <0.05) were observed between the Reveal and BAM methods.

The BCM Listeria monocytogenes detection system (LMDS) consists of a selective preenrichment broth (LMPEB), selective enrichment broth (LMSEB), selective/differential plating medium (LMPM), and identification on a confirmatory plating medium (LMCM). The efficacy of the BCM LMDS was determined using pure cultures and naturally and artificially contaminated environmental sponges. The BCM LMPEB allowed the growth of Listeria and resuscitation of heat-injured L. monocytogenes. The BCM LMSEB, which contains the fluorogenic substrate 4-methylumbelliferyl-myo-inositol-1-phosphate and detects phosphatidylinositol phospholipase C (PI-PLC) activity, provided a presumptive positive test for the presence of pathogenic Listeria (L. monocytogenes and L. ivanovii) after 24 h at 35 degrees C. An initial inoculum of 10 to 100 CFU/ml of L. monocytogenes in BCM LMSEB yielded a fluorogenic response after 24 h. On BCM LMPM, L. monocytogenes and L. ivanovii were the two Listeria species forming turquoise convex colonies (1.0 to 2.5 mm in diameter) from PI-PLC activity on the chromogenic substrate, 5-bromo-4-chloro-3-indoxyl-myo-inositol-1-phosphate. L. monocytogenes was distinguished from L. ivanovii by either its fluorescence on BCM LMCM or acid production from rhamnose. False-positive organisms (Bacillus cereus, Staphylococcus aureus, Bacillus thuringiensis, and yeasts) were eliminated by at least one of the media in the BCM LMDS. Using a pure culture system, the BCM LMDS detected one to two L. monocytogenes cells from a sponge rehydrated in 10 ml of DE neutralizing broth. In an analysis of 162 environmental sponges from facilities inspected by the U.S. Department of Agriculture (USDA), the values for identification of L. monocytogenes by BCM LMDS and the USDA method were 30 and 14 sites, respectively, with sensitivity and specificity values of 85.7 and 100.0% versus 40.0 and 66.1%, respectively. No false-positive organisms were isolated by BCM LMDS, whereas 26.5% of the sponges tested by the USDA method produced false-positive results.

Rapid screening of beef for the presence of Escherichia coli O157:H7 was shown to be feasible using a 10-h enrichment in modified buffered peptone water and the antibody-direct epifluorescent filter technique (Ab-DEFT). The Ab-DEFT involved membrane filtration, fluorescent antibody staining and epifluorescence microscopy and was accomplished in less than 1 h. The procedure allowed detection of the pathogen artificially inoculated into beef patties at 0.1 CFU/g. The 10-h nonselective enrichment broth supported rapid growth, which provided sufficient numbers of cells for a positive determination by the Ab-DEFT after fewer than 10 microscope fields were scanned using a 40× objective lens. Immunomagnetic separation using anti- E. coli O157 Dynabeads ® was used to confirm presumptively positive cultures within 24 h. The ease and rapidity of the Ab-DEFT may provide a substantial time and cost savings to the beef industry for screening beef for the presence of E. coli O157:H7.

The antimicrobial effectiveness of sodium benzoate and potassium sorbate (0.05, 0.10, 0.20 and 0.30%, wt/wt), separately and in equal combinations, were evaluated against the growth of Zygosaccharomyces bailii in an artificially inoculated salsa mayonnaise stored at room temperature (23 to 25°C). Potassium sorbate was able to suppress the growth of Z. bailii significantly ( P < 0.05) more than sodium benzoate did, whereas no significant difference in growth was calculated between potassium sorbate and the combination in equal amounts of the two preservatives. Equal concentrations of the two preservatives were, however, significantly ( P < 0.05) more effective than sodium benzoate in suppressing the growth of the yeast in a salsa mayonnaise. At the investigated concentrations, the preservative systems did not prevent spoilage of the product by Z. bailii . Therefore, the use of yeast-free ingredients, clean and sanitary equipment, and strict adherence to good manufacturing practices during manufacture and packaging is required to produce a salsa mayonnaise free of spoilage microorganisms.

The antimicrobial effects of ozonated water in a recirculating concurrent reactor were evaluated against four gram-positive and four gram-negative bacteria, two yeasts, and spores of Aspergillus niger. More than 5 log units each of Salmonella typhimurium and Escherichia coli cells were killed instantaneously in ozonated water with or without addition of 20 ppm of soluble starch (SS). In ozonated water, death rates among the gram-negative bacteria--S. typhimurium, E. coli, Pseudomonas aeruginosa, and Yersinia enterocolitica--were not significantly different (P > 0.05). Among gram-positive bacteria, Listeria monocytogenes was significantly P < 0.05) more sensitive than either Staphylococcus aureus or Enterococcus faecalis. In the presence of organic material, death rates of S. aureus compared with L. monocytogenes and E. coli compared with S. typhimurium in ozonated water were not significantly (P > 0.05) affected by SS addition but were significantly reduced (P < 0.05) by addition of 20 ppm of bovine serum albumin (BSA). More than 4.5 log units each of Candida albicans and Zygosaccharomyces bailii cells were killed instantaneously in ozonated water, whereas less than 1 log unit of Aspergillus niger spores was killed after a 5-min exposure. The average ozone output levels in the deionized water (0.188 mg/ml) or water with SS (0.198 mg/ml) did not differ significantly (P < 0.05) but were significantly lower in water containing BSA (0.149 mg/ml).

The surface sanitizing properties of a buffered organic acid anionic surfactant (BOAAS) was compared with six traditional sanitizers (organic chlorine - 100 ppm, two iodophors - 25 ppm, peroxyacetic acid - 483 ppm, acid anionic - 230 ppm, and a quaternary ammonium compound - 150 ppm) in its ability to reduce Staphylococcus aureus on an inoculated Formica surface. In the absence of organic material, the traditional sanitizers were not significantly different (P > 0.05) from water in reducing S. aureus at time 0. whereas ≥ 1.2% of the BOAAS reduced a significantly greater (P < 0.05) number of bacteria. When compared with water over 60 min, only the BOAAS significantly reduced (P < 0.05) S. aureus cells. Sixty minutes after exposure, a 1.75% concentration of the BOAAS was > 100× more effective than organic chlorine. Overall, the organic material reduced the effectiveness of the traditional sanitizers and BOAAS. In the presence of 0.5% protein, BOAAS levels ≥ 0.6% significantly (P < 0.05) reduced more S. aureus cells than the quaternary ammonium sanitizer immediately after application. BOAAS concentrations ≥ 0.6% were significantly (P < 0.05) more effective in reducing S. aureus during a 60 min exposure than the organic chlorine sanitizer. In a separate efficacy study, a BOAAS concentration of 0.6% killed >5 logs of S. aureus , Salmonella typhimurium , Pseudomonas aeruginosa and Listeria monocytogenes cells after 30 s exposure.

Peptone tergitol glucuronide (PTG) agar containing 4-methylumbelliferyl-β-D glucuronide (MUG) (for β-glucuronidase activity), the Holbrook, Anderson, Baird-Parker (HABP) method (for detecting indole production), and the standard 3-tube most probable number (MPN) method were compared with plate count agar (PCA) for enumerating three strains of unstressed Escherichia coli artificially inoculated into ground beef and chicken at 1-6 × 10 6 cells/g. No significant difference (P>0.05) was determined between PTG agar and PCA in the recovery of E. coli . The MPN method enumerated a significantly greater (P<0.05) number of E. coli cells than PCA. Compared with PCA, the HABP method recovered a significantly lower (P<0.05) number of E. coli cells from chicken, whereas no significant difference (P>0.05) was obtained with ground beef. When combining all data from chicken and beef, the recovery of E. coli cells by the HABP method was also significantly lower (P<0.05). Overall, based on the enumeration of E. coli on PCA, the HABP method, PTG agar, and MPN method recovered 57, 102, and 144%, respectively.

A 24-h direct plating method for Escherichia coli using the chromogenic substrate 5-bromo-4-chloro-3-indolyl-B-D-glucuronide (X-GLUC) incorporated into a Peptone-tergitol agar base (PTX) was compared with the standard 3-tube Most Probable Number (MPN) method on 50 naturally contaminated ground beef samples. A paired-comparisons t-test showed no significant difference between the two methods. A positive linear correlation between the two methods was observed over the entire range of values. Ninety-seven percent of the positive colonies (blue colonies) on PTX agar were indentified as E. coli , whereas no atypical colonies (nonblue) were characterized as such. Thus, a simple and reliable enumeration of E. coli can be made within 24 h using the X-GLUC substrate in a selective agar as an indicator of B-glucuronidase activity.

Standard Potato Dextrose Agar (PDA) was inferior to PDA/60% sucrose plating medium for enumerating osmotolerant yeasts from a high-sugar food product. The largest disparity in the number of Saccharomyces rouxii cells (>2.00 log number cells/g) recovery by PDA/60% sucrose and standard PDA was during the lag and early log phase. The optimum growth temperatures of S. rouxii propagated in double strength (2X) Potato Dextrose Broth (PDB) were 28°C at 0.995 a w level and 35°C for 0.92 and 0.90 a w levels. No significant (P>0.05) difference was determined between shaking and stomaching for enumeration of S. rouxii , an osmotolerant yeast, from chocolate syrup. Therefore, use of PDA/60% sucrose incubated at 35°C for 5 d is recommended for enumeration of osmotolerant yeasts from a liquid high-sugar product.

The effects of hydrochloric, citric, lactic, phosphoric and malic acids in combination with potassium sorbate on the growth of Saccharomyces bailii , Saccharomyces acidifaciens ( Saccharomyces bailii var. osmophilus ), Saccharomyces rouxii and Saccharomyces bisporus were evaluated. Double strength potato dextrose broth supplemented with 58% (wt/vol) sucrose, 14% (wt/vol) glucose, and 0.2% agar acidulated to a pH of 5.0 to a final a w of 0.88 to 0.89 was used as the growth medium. In general, at 0.05% potassium sorbate, S. rouxii and S. bisporus were more resistant than S. bailii and S. acidifaciens to the antimycotic agent independent of the acid used to acidulate the growth medium, whereas 0.1% potassium sorbate inhibited the growth of the four yeast strains. At 0.05% potassium sorbate, growth occurred (1 log number yeast cells/ml) for S. acidifaciens in the lactic acid/sorbate combination after 36 h of incubation, whereas a bacteriostatic relationship existed for the other acids employed. Citric acid potentiated the antimicrobial effectiveness of 0.05% potassium sorbate at pH 5.0 against the growth of S. rouxii and S. bisporus by either delaying the lag phase or reducing the growth rate.

Antibiotic susceptibility patterns for Yersinia enterocolitica strains involving 10 different serotypes were analyzed and compared. All Y. enterocolitica were susceptible to colistin, gentamicin, kanamycin, neomycin and doxycycline, whereas all isolates displayed resistance to penicillin G, methicillin (derivative of penicillin), novobiocin, and clindamycin. The antibiograms for the Y. enterocolitica isolates were in some instances related to the somatic serotypes, especially serotype 0:8 for which the antimicrobial susceptibility pattern displayed the greatest disparity. By eliminating the antibiograms for the four serotype 0:8 strains, antimicrobial susceptibility patterns for atypical and typical strains were similar.

Growth of total bacteria on fresh meat and heat-processed commodities was analyzed at refrigerated hypobaric and conventional cooler storage. When using the time required for bacterial levels to reach one million/in. 2 as the estimate of the shelf life, the refrigerated hypobaric storage system substantially extended the shelf-life of broiler chickens, pork loins, bone-in heat-processed hams, and lamb and beef carcasses, as compared to storage in conventional coolers. The dominant microorganism isolated from the surface of the bone-in heat-processed hams stored in hypobaric and conventional coolers was a Streptococcus which was resistant to the heat process and tolerant to salt and sodium nitrite. For the fresh meat products, Pseudomonas was the dominant microorganism isolated from these products stored in either hypobaric or conventional coolers.

Effects of preconditioning Saccharomyces rouxii to various sucrose and sorbate concentrations were investigated. Cells were preconditioned to 0 and 60% (wt/vol) sucrose without and with 0. 1% (wt/vol) sorbate by a series of four transfers in potato dextrose broth (PDB). The preconditioned cells were inoculated in growth medium containing 0, 30, or 60% (wt/vol) sucrose with 0. 0.05, or 0.1% (wt/vol) sorbate and in chocolate syrup without and with 0.1% (wt/vol) sorbate. Preconditioning of S. rouxii cells to 0 and 60% sucrose offered no advantage for growth in a medium containing 0, 30 or 60% sucrose. When S. rouxii cells were preconditioned in 0.1% sorbate, an increased resistance to sorbate occurred. S. rouxii cells preconditioned in 60% sucrose/0.1% sorbate were more sensitive to sorbate than cells preconditioned in 0% sucrose/0.1% sorbate. Regardless of the sucrose level, S. rouxii cells, preconditioned in 0. 1% sorbate showed an increased resistance to sorbate when inoculated into the growth medium and the chocolate syrup.

The basic 12-disk Minitek system (14 tests) and the API 20E system were evaluated for identification of Yersinia enterocolitica strains isolated at various locations in the world. The API 20E system correctly identified all the Y. enterocolitica strains while the Minitek system identified 80% (20/25) of the strains. Four of the five cultures misidentified by Minitek were atypical strains isolated from vacuum-packaged meats. These four cultures were identified as Citrobacter freundii by Minitek due to a rhamnose-positive reaction. Minitek and API 20E are rapid and convenient systems which could prove to be beneficial for identifying Y. enterocolitica strains.

Petrifilm ™ violet red bile (PVRB) compared favorably to the most probable number method (MPN) and violet red bile agar (VRBA) methods for enumerating coliforms from frozen raw ground beef. When comparing PVRB and VRBA incubated at 35°C, coliform enumeration displayed a linear relationship (correlation coefficient of 0.932). However, by analyzing 64 ground beef samples, PVRB enumerated 41% more coliforms/g than did VRBA. Two distinct colony types were observed on PVRB: (a) type I (butterfly in appearence) with a colony diameter equal to or greater than 1 mm and gas bubbles 2-4 mm in diameter touching the associated colony; and (b) type II with a colony diameter less than 1 mm in diameter and gas bubbles of the associated colony not necessarily touching the colony but within a colony diameter. The disparity between PVRB and VRBA for enumerating coliforms was attributed to non-coliforms representing approximately 50% of the type II coliform colonies. At 35°C, 83.7% of the type I colonies were Escherichia coli , whereas only 10.9%, of the type II colonies were E. coli . By elevating the incubation temperature from 35°C to 44.5°C, over 90% of the colonies in the counting dilution were type I of which 99.2% were E. coli . At 44.5°C, 39.4% of the type II colonies were E. coli ; however, this colony type represented only 9.5% of the total colonies on PVRB. Therefore, a reliable method for enumerating E. coli from raw meat was developed by counting only the type I colonies on PVRB incubated at 44.5°C.