Analysis of microbial diversity on deli slicers using polymerase chain reaction and denaturing gradient gel electrophoresis technologies

Cross-contamination of pathogenic and spoilage bacteria from food-contact surfaces to food products is a serious public health issue. Bacteria may survive and attach to food-contact surfaces by residual food components and/or background bacteria which may subsequently transfer to other food products. Deli slicers, generally used for slicing ready-to-eat products, can serve as potential sources for considerable bacterial transfer. The objective of this study was to assess the extent and distribution of microbial diversity of deli slicers by identification of pathogenic and background bacteria. Slicer-swab samples were collected from restaurants in Arkansas and Texas in the United States. Ten surface areas for each slicer were swabbed using sterile sponges. Denaturing gradient gel electrophoresis (DGGE) was applied to investigate the fingerprint of samples, and each band was further identified by sequence analysis. Pseudomonads were identified as the dominant bacteria followed by Enterobacteriaceae family, and lactic acid bacteria such as Lactococcus lactis and Streptococcus thermophilus were also found. Bacterial distribution was similar for all surface areas, while the blade guard exhibited the greatest diversity. This study provides a profile of the microbial ecology of slicers using DGGE to develop more specific sanitation practices and to reduce cross-contamination during slicing.

Cleaning and decontamination efficacy of wiping cloths and silver dihydrogen citrate on food contact surfaces

AIMS

  To test the efficacy of four wipe cloth types (cotton bar towel, nonwoven, microfibre and blended cellulose/cotton) with either quaternary ammonia cleaning solution or silver dihydrogen citrate (SDC) in cleaning food contact surfaces.

METHODS

  Swab samples collected from untreated, cloth-treated and cloth disinfectant-treated surfaces were subjected to hygiene monitoring using adenosine triphosphate (ATP) bioluminescence and aerobic total plate counting (TPC) assays.

RESULTS

  Adenosine triphosphate measurements taken after wiping the surfaces showed poor cleaning by nonwoven cloths (2·89 RLU 100 cm(-2) ) than the microfibre (2·30 RLU 100 cm(-2) ), cotton terry bar (2·26 RLU 100 cm(-2) ) and blended cellulose/cotton cloth types (2·20 RLU 100 cm(-2) ). The cellulose/cotton cloth showed highest log reduction in ATP-B RLU values (95%) and CFU values (98·03%) when used in combination with SDC disinfectant.

CONCLUSIONS

  Cleaning effect of wiping cloths on food contact surfaces can be enhanced by dipping them in SDC disinfectant. ATP-B measurements can be used for real-time hygiene monitoring in public sector, and testing microbial contamination provides more reliable measure of cleanliness.

SIGNIFICANCE AND IMPACT OF THE STUDY

  Contaminated food contact surfaces need regular hygiene monitoring. This study could help to estimate and establish contamination thresholds for surfaces at public sector facilities and to base the effectiveness of cleaning methods.

Antimicrobial effect and mode of action of terpeneless cold-pressed Valencia orange essential oil on methicillin-resistant Staphylococcus aureus

AIMS

The objectives of this study were to evaluate the antistaphylococcal effect and elucidate the mechanism of action of orange essential oil against antibiotic-resistant Staphylococcus aureus strains.

METHODS AND RESULTS

The inhibitory effect of commercial orange essential oil (EO) against six Staph. aureus strains was tested using disc diffusion and agar dilution methods. The mechanism of EO action on MRSA was analysed by transcriptional profiling. Morphological changes of EO-treated Staph. aureus were examined using transmission electron microscopy. Results showed that 0·1% of terpeneless cold-pressed Valencia orange oil (CPV) induced the cell wall stress stimulon consistent with the inhibition of cell wall synthesis. Transmission electron microscopic observation revealed cell lysis and suggested a cell wall lysis-related mechanism of CPV.

CONCLUSIONS

CPV inhibits the growth of Staph. aureus, causes gene expression changes consistent with the inhibition of cell wall synthesis, and triggers cell lysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Multiple antibiotics resistance is becoming a serious problem in the management of Staph. aureus infections. In this study, the altered expression of cell wall-associated genes and subsequent cell lysis in MRSA caused by CPV suggest that it may be a potential antimicrobial agent to control antibiotic-resistant Staph. aureus.

Dietary fiber content influences soluble carbohydrate levels in ruminal fluids

The soluble carbohydrate concentration of ruminal fluid, as affected by dietary forage content (DFC) and/or ruminally undegradable intake protein content (UIPC), was determined. Four ruminally cannulated steers, in a 4 × 4 Latin square design, were offered diets containing high (75 % of DM) or low (25 % of DM) DFC and high (6 % of DM) or low (5 % of DM) UIPC, in a 2 × 2 factorial arrangement. Zinc-treated SBM was the primary UIP source. Soluble hexose concentration (145.1 μM) in ruminal fluid (RF) of steers fed low DFC diets exhibited a higher trend (P = 0.08) than that (124.5 μM) of steers fed high DFC diets. UIPC did not modulate (P = 0.54) ruminal soluble hexose concentrations. Regardless of diet, soluble hexose concentration declined immediately after feeding and did not rise until 3 h after feeding (P < 0.0001). Cellobiose (≈90 %) and glucose (≈10 %) were the major soluble hexoses present in RF. Maltose was not detected. Soluble glucose concentration (13.0 μM) was not modified by either UIPC (P = 0.40) nor DFC (P = 0.61). However, a DFC by post-prandial time interaction was detected (P = 0.02). Pentose concentrations were greater (P = 0.02) in RF of steers fed high DFC (100.2 μM) than steers fed low DFC (177.0 μM). UIPC did not influence (P = 0.35) soluble pentose concentration. The identity of soluble pentoses in ruminal fluid could not be determined. However, unsubstituted xylose and arabinose were excluded. These data indicate that: (i) soluble carbohydrate concentrations remain in ruminal fluid during digestion and fermentation; (ii) slight diurnal changes began after feeding; (iii) DFC influences the soluble carbohydrate concentration in RF; and (iv) UIPC of these diets does not affect the soluble carbohydrate concentration of RF.

Assessment of a food microbiology senior undergraduate course as a potential food safety distance education course for poultry science majors

Distance education courses have become popular due to the increased number of commuter students as well as people already in the workforce who need further education for advancement within their careers. A graduate-level Web-based course entitled Special Topics-Poultry Food Safety Microbiology was developed from an existing senior undergraduate advanced food microbiology course in the Poultry Science Department at Texas A&M University. Conversion of standard lecture material into a distance education course can provide unique challenges to maintain comparable course content in an asynchronous manner. The overall objective for this course was to examine bacterial activities including ecology in food, animals, raw and processed meat, eggs, and human pathogenesis. Students were surveyed at the end of the class and the majority agreed that they would be willing to take the course as an online course, although they were not willing to pay an extra fee for an online course. The majority of students used the online version of the course as a supplement to the classroom rather than as a substitute.

Cell yields and fermentation responses of a Salmonella Typhimurium poultry isolate at different dilution rates in an anaerobic steady state continuous culture

The objectives of these studies were to determine cell yield and fermentation responses of a Salmonella enterica serovar Typhimurium poultry isolate using various dilution rates in steady state continuous culture incubations. S. enterica Typhimurium cells were propagated in continuous cultures with a total volume of 0.50 l of Luria Bertani medium containing 0.1% glucose. Dilution rates from 0.0125 to 1.44/h were used. Cell protein concentration generally increased linearly with increased dilution rate up to a rate of 0.54/h and declined at the higher dilution rates. Glucose consumption gave a similar pattern to cell protein concentration by declining at the three highest dilution rates. Short chain fatty acid production was inconsistently influenced by dilution rate. Acetate, the most predominant fatty acid produced, declined at the higher dilution rates, as did propionate. Ammonia production remained stable at the lowest dilution rates, but increased significantly at a dilution rates above 0.27/h.

Ciprofloxacin-sensitive and ciprofloxacin-resistant Campylobacter jejuni are equally susceptible to natural orange oil-based antimicrobials

A total of 10 ciprofloxacin-sensitive (ciprofloxacin minimum inhibitory concentration, MIC < 0.5 micro g/ml) and 10 ciprofloxacin-resistant (MIC 16 to 32 micro g/ml) presumptive C. jejuni were further characterized and evaluated for their inhibition by natural orange oil fractions. Partial species identification was performed by using a hippuricase gene-based polymerase chain reaction (PCR) assay. One of the isolates appeared to be atypical and failed to hydrolyze hippurate. Of the ciprofloxacin-resistant C. jejuni isolates tested, six were found to have their quinolone resistance determined by a C --> T mutation in codon 86 of gyrA. Both groups of ciprofloxacin-sensitive and -resistant C. jejuni isolates were most susceptible to cold-pressed terpeneless Valencia orange oil (C4) which yielded inhibition zones from 44.0 +/- 1.4 to 80 +/- 0.0 mm. Less inhibitory responses were recorded for 5-fold concentrated Valencia orange oil (C3) and distilled d-limonene (C7) which exerted similar effects on both ciprofloxacin-sensitive and -resistant C. jejuni isolates. In general, ciprofloxacin-resistant and -sensitive C. jejuni isolates were equally susceptible to the respective orange oil fractions.

The impact of single antimicrobial intervention treatment with potassium lactate, sodium metasilicate, peroxyacetic acid, and acidified sodium chlorite on non-inoculated ground beef lipid, instrumental color, and sensory characteristics

The effect of using potassium lactate, sodium metasilicate, acidified sodium chlorite, or peroxyacetic acid as a single antimicrobial intervention on ground beef instrumental color, sensory color and odor characteristics, and lipid oxidation was evaluated. Prior to grinding, beef trimmings (90/10) were treated with 3% potassium lactate (KL), 4% sodium metasilicate (NMS), 200-ppm peroxyacetic acid (PAA), 1000-ppm acidified sodium chlorite (ASC), or left untreated (CON). Ground beef under simulated retail display was measured at 0, 1, 2, 3, and 7 of display for instrumental color, sensory characteristics, TBARS values, and pH to evaluate the impact of the treatments. The KL, NMS, PAA, and ASC were redder (a(∗); P<0.05) than CON. All treatments were scored by sensory panelists to have a brighter (P<0.05) red color than CON during days 1-3 of display. All treatments had less (P<0.05) lipid oxidation than CON on days 0, 3, and 7 of display. These results suggest that the use of these antimicrobial compounds on beef trimmings prior to grinding may not adversely affect, and may improve bulk packaged ground beef quality characteristics.

The pre- and post-grinding application of rosemary and its effects on lipid oxidation and color during storage of ground beef

The timing of the application of rosemary extract was evaluated as one-way of minimizing myoglobin and lipid oxidation in ground beef. In experiment 1, rosemary extract was added to beef at four different stages namely trim, cube, coarse, and fine ground beef. The beef was evaluated for color and TBARS values during 144h of storage (4°C). Results showed that when rosemary was added to the pre-grinding treatments of trim and cube, ground beef had the highest a(∗) values (redness), oxymyoglobin content, and lowest TBARS values at 144h. In experiment 2, the effect of rosemary extract was evaluated on the color quality of case ready ground beef inoculated with 10(7)CFU/g Escherichia coli. Microbial counts, color, and TBARS values were measured during 144h of simulated storage. The results showed that both the rosemary treated samples that were inoculated and uninoculated remained redder longer and had lower TBARS values than the untreated inoculated and uninoculated controls. There was no significant inhibition of E. coli by the rosemary extract.