Azlin Mustapha

Antibacterial activities of zinc oxide nanoparticles against Escherichia coli O157:H7

Aims:  To investigate antibacterial activities of zinc oxide nanoparticles (ZnO NP) and their mode of action against an important foodborne pathogen, Escherichia coli O157:H7.

Antifungal activity of zinc oxide nanoparticles against Botrytis cinerea and Penicillium expansum

Antifungal activities of zinc oxide nanoparticles (ZnO NPs) and their mode of action against two postharvest pathogenic fungi (Botrytis cinerea and Penicillium expansum) were investigated in this study. ZnO NPs with sizes of 70 ± 15 nm and concentrations of 0, 3, 6 and 12 mmol l(-1) were used. Traditional microbiological plating, scanning electron microscopy (SEM), and Raman spectroscopy were used to study antifungal activities of ZnO NPs and to characterize the changes in morphology and cellular compositions of fungal hyphae treated with ZnO NPs. Results show that ZnO NPs at concentrations greater than 3 mmol l(-1) can significantly inhibit the growth of B. cinerea and P. expansum. P. expansum was more sensitive to the treatment with ZnO NPs than B. cinerea. SEM images and Raman spectra indicate two different antifungal activities of ZnO NPs against B. cinerea and P. expansum. ZnO NPs inhibited the growth of B. cinerea by affecting cellular functions, which caused deformation in fungal hyphae. In comparison, ZnO NPs prevented the development of conidiophores and conidia of P. expansum, which eventually led to the death of fungal hyphae. These results suggest that ZnO NPs could be used as an effective fungicide in agricultural and food safety applications.

Detection of Melamine in Gluten, Chicken Feed, and Processed Foods Using Surface Enhanced Raman Spectroscopy and HPLC

Melamine, a nitrogen-rich chemical, was implicated in pet and human food recalls in 2007, which caused enormous economic losses to the food industry. In this study, melamine concentration in wheat gluten, chicken feed, and processed foods (that is, cake and noodle) was measured by surface enhanced Raman spectroscopy (SERS) in combination with SERS-active substrates. SERS was able to rapidly detect 0.1% melamine in wheat gluten, 0.05% in chicken feed, 0.05% in cakes, and 0.07% in noodle, respectively. A partial least squares (PLS) model was established for the quantification of melamine in foods by SERS: R= 0.90, RMSEP = 0.33. In addition, SERS results were verified by HPLC analysis based on a simplified FDA method. Compared with HPLC, the SERS method is much faster and simpler, requires minimum sample preparation, but still yields satisfactory qualitative and quantitative results. These results demonstrate that it is an applicable approach to use SERS to screen foods, eliminate presumptive negative samples of melamine contamination from the sample population, and then verify presumptive positive samples using HPLC protocols. Combining these 2 methods could provide a more rapid and cost-effective way for monitoring melamine contamination in increasingly large numbers of imported foods and feed products.

Antimicrobial and antioxidant activities of natural extracts in vitro and in ground beef.

Inhibition of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes by grape seed extract (ActiVin) and pine bark extract (Pycnogenol) and the effect of these natural extracts on the oxidative stability of raw ground beef were studied. In an agar dilution test, the MICs of ActiVin and Pycnogenol were determined to be 4.0 mg/ml for 4.43 log CFU per plate of E. coli O157:H7 and 4.0 mg/ml for 4.38 log CFU per plate of L. monocytogenes. In an inhibition curve test, populations of E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes fell to below the detection limit (10 CFU/ml) after 16 h of incubation. The numbers of E. coli O157:H7, L. monocytogenes, and Salmonella Typhimurium declined by 1.08, 1.24, and 1.33 log CFU/g, respectively, in raw ground beef treated with 1% Pycnogenol after 9 days of refrigerated storage. ActiVin (1%) and oleoresin rosemary (1%) resulted in an approximately 1-log CFU/g reduction in the populations of all three pathogens after 9 days. The addition of 1% ActiVin and Pycnogenol contributed to the maintenance of an acidic pH of 5.80 and 5.58, respectively, in raw ground beef. Compared to the control, all treatments increased in L* (lightness), with the exception of ActiVin. ActiVin and oleoresin rosemary had the highest a* (redness) and b* (yellowness) values, respectively. ActiVin most effectively retarded lipid oxidation, followed by Pycnogenol. The results suggest that these natural extracts have potential to be used with other preservative methods to reduce pathogenic numbers, lipid oxidation, and color degradation in ground beef.

Reduction of Listeria monocytogenes and Escherichia coli O157:H7 numbers on vacuum-packaged fresh beef treated with nisin or nisin combined with EDTA

Nisin or nisin combined with EDTA was used to treat fresh beef. Beef cubes (2.5 by 2.5 by 2.5 cm) that were inoculated with approximately 7 log CFU/ml of Listeria monocytogenes Scott A or Escherichia coli O157:H7 505 B were dipped in the following solutions: (i) H2O, (ii) HCl, (iii) nisin, (iv) EDTA, or (v) nisin combined with EDTA, respectively, for 10 min each, with an exception of one set of control beef samples without treatment. Beef samples were then drip-dried for 15 min, vacuum packaged, and stored at 4 degrees C for up to 30 days. The pH on beef after different treatments was not a key factor in preventing bacterial growth. Treatment with nisin or with nisin combined with EDTA reduced the population of L. monocytogenes by 2.01 and 0.99 log CFU/cm2 as compared to the control, respectively, under the conditions of vacuum package and storage at 4 degrees C for up to 30 days. However, the effect of nisin and nisin combined with EDTA against E. coli O157:H7 505 B was marginal at 1.02 log CFU/cm2 and 0.8 log CFU/cm2 reductions, respectively.

Simultaneous Detection of Escherichia coli O157:H7, Salmonella, and Shigella in Apple Cider and Produce by a Multiplex PCR

With three pairs of primers, a multiplex PCR assay was established for the simultaneous detection of Escherichia coli 0157:H7, Salmonella, and Shigella. Under the optimized conditions, the assay yielded a 252-bp product from E. coli O157:H7, a 429-bp product from Salmonella Typhimurium, and a 620-bp product from Shigella flexneri, respectively. When the DNA extraction of multiple target organisms was included in the same reaction, two or three corresponding amplicons of different sizes were observed. In the specificity test, 10 E. coli O157:H7 strains and one E. coli O157:NM strain showed the expected 252-bp amplicon. Seven other E. coli strains yielded no signal. Additionally, the 429-bp amplicon was produced from 20 Salmonella strains covering 16 serotypes, whereas the 620-bp amplicon was generated from 11 Shigella strains covering 4 species. No nonspecific amplification was observed with DNA from 48 other bacterial strains. Following a 24-h enrichment, the developed assay could concurrently detect the three pathogens at initial inoculation levels of approximately 8 x 10(-1) CFU/g (or CFU/ml) in apple cider, cantaloupe, lettuce, tomato, and watermelon and 8 x 10(1) CFU/g in alfalfa sprouts. The whole procedure can be easily completed within 30 h. The multiplex PCR assay can potentially be a simple, rapid, and efficient tool for presumptive and simultaneous screening of apple cider and produce for contamination by E. coli O157:H7, Salmonella, and/or Shigella.

Oral bacterial deactivation using a low-temperature atmospheric argon plasma brush

OBJECTIVE To study the plasma treatment effects on deactivation effectiveness of oral bacteria. METHODS A low temperature atmospheric argon plasma brush were used to study the oral bacterial deactivation effects in terms of plasma conditions, plasma exposure time, and bacterial supporting media. Oral bacteria of Streptococcus mutans and Lactobacillus acidophilus with an initial bacterial population density between 1.0×10(8) and 5.0×10(8)cfu/ml were seeded on various media and their survivability with plasma exposure was examined. Scanning electron microscopy was used to examine the morphological changes of the plasma treated bacteria. Optical absorption was used to determine the leakage of intracellular proteins and DNAs of the plasma treated bacteria. RESULTS The experimental data indicated that the argon atmospheric plasma brush was very effective in deactivating oral bacteria. The plasma exposure time for a 99.9999% cell reduction was less than 15s for S. mutans and within 5 min for L. acidophilus. It was found that the plasma deactivation efficiency was also dependent on the bacterial supporting media. With plasma exposure, significant damages to bacterial cell structures were observed with both bacterium species. Leakage of intracellular proteins and DNAs after plasma exposure was observed through monitoring the absorbance peaks at wavelengths of 280 nm and 260 nm, respectively. CONCLUSION The experimental results from this study indicated that low temperature atmospheric plasma treatment was very effective in deactivation of oral bacteria and could be a promising technique in various dental clinical applications such as bacterial disinfection and caries early prevention.

Survival of Listeria monocytogenes Scott A on Vacuum-Packaged Raw Beef Treated with Polylactic Acid, Lactic Acid, and Nisin

Low-molecular-weight polylactic acid (LMW-PLA) and lactic acid (LA) were used to inhibit growth of Listeria monocytogenes Scott A on vacuum-packaged beef. Nisin was also used simultaneously as an additional hurdle to the growth of this pathogen. Inoculated beef cubes were immersed in a solution of 2% LMW-PLA, 2% LA, 400 IU/ml of nisin, or combinations of each acid and nisin for 5 min and drip-dried for 15 min. The cubes were then vacuum-packaged and stored at 4 degrees C for up to 42 days. Surface pH values of beef cubes treated with 2% LMW-PLA, the combination of 400 IU/ml of nisin and 2% LMW-PLA (2% NPLA), or 400 IU/ml of nisin alone were significantly reduced from 5.59 to 5.18, 5.01, and 5.19, respectively, whereas those decontaminated with 2% LA or 400 IU/ml of nisin and 2% LA (2% NLA) were significantly decreased from 5.59 to 4.92 and 4.83, respectively, at day 0 (P < or = 0.05). The 2% LMW-PLA, 2% LA, 2% NPLA, 2% NLA, and 400 IU/ml of nisin showed immediate bactericidal effects on L. monocytogenes Scott A (1.22-, 1.56-, 1.57-, 1.94-, and 1.64-log10 reduction, respectively) compared with the initial number of 5.33 log10 CFU/cm2 of the untreated control at day 0 (P < or = 0.05). These treatments, combined with vacuum-packaging and refrigeration temperature, succeeded to inhibit growth of L. monocytogenes during storage up to 42 days. At the end of 42 days, the numbers of L. monocytogenes Scott A remaining viable on these samples were 1.21, 0.36, 2.21, 0.84, and 0.89 log10 CFU/cm2, respectively.

Microbial shelf life determination of vacuum-packaged fresh beef treated with polylactic acid, lactic acid, and nisin solutions

The effectiveness of polylactic acid, lactic acid, nisin, and combinations of the acids and nisin on extending the shelf-life of raw beef was determined. Fresh beef pieces (5 by 5 by 2.5 cm) were dipped in a solution of 2% low molecular weight polylactic acid (LMW-PLA), 2% lactic acid (LA), 200 IU of nisin per ml, or the combinations of nisin in either 2% LMW-PLA or 2% LA. The samples were then drip-dried, vacuum-packaged, and stored at 4 degrees C for up to 56 days. The beef surface pH values and numbers of psychrotrophic aerobic bacteria, psychrotrophic and mesophilic Enterobacteriaceae, Pseudomonas, and Lactobacillus were determined weekly for 56 days. The average surface pH values of the beef samples treated with 2% LMW-PLA or the combination of 200 IU of nisin per ml and 2% LMW-PLA were significantly reduced to 5.19 and 5.17, respectively, at day 0 (P < or = 0.05), while those decontaminated with 2% LA or 200 IU of nisin per ml in 2% LA solution were significantly decreased from 5.62 to 4.98 and 4.96, respectively. The 2% LMW-PLA, 2% LA, or the combinations of each acid and nisin showed immediate inhibitory effects on psychrotrophic aerobic bacteria (1.94, 2.36, 2.59, and 1.76 log reduction, respectively), psychrotrophic Enterobacteriaceae (1.37, 1.86, 1.77, and 1.35 log reduction, respectively), mesophilic Enterobacteriaceae (1.00, 1.00, 0.82, and 0.68 log reduction, respectively), and Pseudomonas (1.77, 1.57, 1.76, and 1.41 log reduction, respectively) on fresh beef (P < or = 0.05). The reduction was evident up to 56 days as seen by the numbers of Enterobacteriaceae and Pseudomonas (P < or = 0.05). Because there was no interaction between treatments and storage times, the data in each period were combined and presented as effect of treatments on overall microbial counts of fresh beef. It was found that 2% LMW-PLA, 2% LA, and the combinations of each acid and nisin significantly lowered the population of the above organisms compared with the untreated control, water, or nisin alone (P < or = 0.05).

Effects of cetylpyridinium chloride, acidified sodium chlorite, and potassium sorbate on populations of Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus on fresh beef.

The effects of selected food-grade antimicrobial agents at decreasing the number of pathogenic bacteria on fresh beef were determined. Beef cubes inoculated with Escherichia coli O157:H7, Listeria monocytogenes, or Staphylococcus aureus were sprayed with 0.5% cetylpyridinium chloride (CPC), 0.12% acidified sodium chlorite (ASC), 0.1% potassium sorbate (PS), or an equal mix of any two solutions. The beef samples were placed on absorbent tray pads sprayed with each single or mixed solution, wrapped with polyvinyl chloride film, heat sealed, and stored at 4 degrees C for 2 weeks. Surface sanitization using CPC, ASC, or an equal mix of these two agents effectively reduced microbial numbers on the beef during storage. At day 0, ASC and the CPC-ASC mix reduced the number of E. coli O157:H7 by 2.50 and 1.58 log CFU/cm2, respectively. CPC demonstrated a 3.25-log reduction of L. monocytogenes and a 4.70-log reduction of S. aureus at 14 days. The CPC-PS mix reduced E. coli O157:H7 numbers by 1.46, L. monocytogenes by 2.95, and S. aureus by 4.41 log CFU/cm2 at 14 days. PS alone and the mixed solutions, CPC-ASC, CPC-PS, or ASC-PS, were not as effective as ASC or CPC alone. To effectively reduce E. coli O157:H7, L. monocytogenes, or S. aureus numbers, higher (> 0.1%) concentrations of PS were necessary. Loss of redness and light color of beef surfaces consistently coincided with decreases in pH for ASC-treated beef samples.