Survival of Enterobacter sakazakii in infant cereal as affected by composition, water activity, and temperature

Enterobacter sakazakii infections in preterm neonates and infants have been epidemiologically associated with consumption of reconstituted powdered infant formula. The bacterium has been isolated from grain, infant cereals, and cereal factory environments. A study was done to determine the survival characteristics of E. sakazakii initially at populations of 0.31 and 5.03 logCFU/g of infant rice cereal (a(w) 0.30, 0.45-0.46, and 0.68-0.69). Cereal was stored at 4, 21, and 30 degrees C and populations were monitored for up to 12 months. Survival of the pathogen in infant rice, barley, oatmeal, and mixed grain cereals (a(w) 0.63-0.66, 0.76, or 0.82-0.83) initially containing a population of 4.93-5.64 logCFU/g and held at 4, 21, and 30 degrees C up to 24 weeks was determined. Populations decreased significantly (p < or = 0.05) in all cereals stored at 21 and 30 degrees C regardless of a(w). Increases in a(w) or storage temperature accelerated the rate of death of E. sakazakii in dry infant cereals. However, at an initial population of 0.31 logCFU/g, E. sakazakii survived in rice cereal (a(w) 0.30-0.69) for up to 12 months at all storage temperatures. Survival of E. sakazakii was not affected by the composition of dry infant rice, barley, mixed grain, and oatmeal cereals (initial a(w) 0.63-0.83) stored for up to 24 weeks at 4, 21, or 30 degrees C. This study demonstrated that E. sakazakii can survive for up to 12 months in infant cereals having a wide range of a(w) when storage is at temperatures simulating those to which they may be exposed during distribution, at retail, and in the home.     

Model of inactivation of Campylobacter jejuni in poultry scalding

The purpose of this study was to develop a model of inactivation of Campylobacter jejuni in industrial scalding of chickens. Models can be used as a guide for broiler slaughterhouse operations for reducing levels of C. jejuni contamination on broiler carcasses. Mean concentrations of C. jejuni in terms of colony forming units (CFU) in scald tank water and in carcass rinse solution after scalding were 2.90 ± 0.07 and 3.86 ± 0.11 LogCFU/mL, respectively. Scald tank water temperature, flow rate, pH, and total solids in scalding process water were 54.15 ± 0.2 °C, 172.0 ± 8.4 L/min, 8.0 ± 0.01, and 2565 ± 114.3 mg/L, respectively. Inactivation models were developed by using mass balances and literature data for inactivation kinetics, of Campylobacter and the Arrhenius equation. Results of the inactivation models of scalding process indicate that high temperature and short time (less than 2 min) of scalding process were effective in reducing the number of viable cells. For this experimental data more than 50% of the Campylobacter are inactivated on surfaces of the chickens. The model fits the experimental data well and the values of the estimated parameters provide insight for this process. The model can be used for process design and potential process modifications.     

Combined effects of chlorine dioxide, drying, and dry heat treatments in inactivating microorganisms on radish seeds

We determined the combined effectiveness of ClO₂ (200 and 500 μg/ml, 5 min), air drying [25 °C, 40% relative humidity (RH), 2 h], and mild dry heat (55 °C, 23% RH, up to 48 h) treatments in killing total aerobic bacteria (TAB), Escherichia coli O157:H7, and molds and yeasts (MY) on radish seeds. A 5.1-log reduction in the number of TAB was achieved on radish seeds treated with 200 or 500 μg/ml ClO₂ followed by air drying for 2 h and dry heat treatment for 48 h or 24 h, respectively. When radish seeds were treated with 200 and 500 μg/ml ClO₂, air dried, and heat treated for 12 h and 6 h, respectively, the initial population of E. coli O157:H7 (5.6 log CFU/g) on seeds was reduced to an undetectable level (<0.8 log CFU/g). However, the pathogen was detected in 5-day-old sprouts. The reduction of MY (1.2-1.0 log CFU/g) on radish seeds under similar experimental conditions was not changed significantly during subsequent heat treatment up to 48 h. Results show that treating radish seeds with 500 μg/ml ClO₂, followed by air dried at 25 °C for 2 h and heat treatment at 55 °C for 36 h achieved a >5-log CFU/g reduction of TAB and E. coli O157:H7. These observations will be useful when developing effective strategies and practices to enhance the microbiological safety of radish sprouts.     

Lethality of chlorine, chlorine dioxide, and a commercial fruit and vegetable sanitizer to vegetative cells and spores of Bacillus cereus and spores of Bacillus thuringiensis

Chlorine, ClO2, and a commercial raw fruit and vegetable sanitizer were evaluated for their effectiveness in killing vegetative cells and spores of Bacillus cereus and spores of Bacillus thuringiensis. The ultimate goal was to use one or both species as a potential surrogate(s) for Bacillus anthracis in studies that focus on determining the efficacy of sanitizers in killing the pathogen on food contact surfaces and foods. Treatment with alkaline (pH 10.5 to 11.0) ClO2 (200 microg/ml) produced by electrochemical technologies reduced populations of a five-strain mixture of vegetative cells and a five-strain mixture of spores of B. cereus by more than 5.4 and more than 6.4 log CFU/ml respectively, within 5 min. This finding compares with respective reductions of 4.5 and 1.8 log CFU/ml resulting from treatment with 200 microg/ml of chlorine. Treatment with a 1.5% acidified (pH 3.0) solution of Fit powder product was less effective, causing 2.5- and 0.4-log CFU/ml reductions in the number of B. cereus cells and spores, respectively. Treatment with alkaline ClO2 (85 microg/ml), acidified (pH 3.4) ClO2 (85 microg/ml), and a mixture of ClO2 (85 microg/ml) and Fit powder product (0.5%) (pH 3.5) caused reductions in vegetative cell/spore populations of more than 5.3/5.6, 5.3/5.7, and 5.3/6.0 log CFU/ml, respectively. Treatment of B. cereus and B. thuringiensis spores in a medium (3.4 mg/ml of organic and inorganic solids) in which cells had grown and produced spores with an equal volume of alkaline (pH 12.1) ClO2 (400 microg/ml) for 30 min reduced populations by 4.6 and 5.2 log CFU/ml, respectively, indicating high lethality in the presence of materials other than spores that would potentially react with and neutralize the sporicidal activity of ClO2.     

Viability of acid-adapted Escherichia coli O157:H7 in ground beef treated with acidic calcium sulfate

The effects of lactic acid, acetic acid, and acidic calcium sulfate (ACS) on viability and subsequent acid tolerance of three strains of Escherichia coli O157:H7 were determined. Differences in tolerance to acidic environments were observed among strains, but the level of tolerance was not affected by the acidulant to which cells had been exposed. Cells of E. coli O157:H7 adapted to grow on tryptic soy agar acidified to pH 4.5 with ACS were compared to cells grown at pH 7.2 in the absence of ACS for their ability to survive after inoculation into ground beef treated with ACS, as well as untreated beef. The number of ACS-adapted cells recovered from ACS-treated beef was significantly (alpha = 0.05) higher than the number of control cells recovered from ACS-treated beef during the first 3 days of a 10-day storage period at 4 degrees C, suggesting that ACS-adapted cells might be initially more tolerant than unadapted cells to reduced pH in ACS-treated beef. Regardless of treatment of ground beef with ACS or adaptation of E. coli O157:H7 to ACS before inoculating ground beef, the pathogen survived in high numbers.     

Efficacy of chlorine and a peroxyacetic acid sanitizer in killing Listeria monocytogenes on iceberg and Romaine lettuce using simulated commercial processing conditions

The efficacy of chlorine (100 microg/ml) and a peroxyacetic acid sanitizer (80 microg/ml; Tsunami 100) in killing Listeria monocytogenes inoculated at populations of 1 to 2, 2 to 3, and 4 to 5 log CFU/g of iceberg lettuce pieces, shredded iceberg lettuce, and Romaine lettuce pieces was determined by treatment conditions simulating those used by a commercial fresh-cut lettuce processor. The lettuce/treatment solution ratio was 1:100 (wt/vol), treatment temperature was 4 degrees C, and total treatment time was 30 s. Compared with washing in water, treatment of iceberg lettuce pieces containing all levels of inoculum and shredded iceberg lettuce containing 2 to 3 or 4 to 5 log CFU/g with chlorine or Tsunami resulted in significant reductions (P < or = 0.05) of pathogen populations. Populations recovered from Romaine lettuce pieces treated with chlorine or Tsunami were not significantly different from populations recovered from pieces washed with water, regardless of the inoculum level. Within lettuce type and inoculum level, in no instance was the number of L. monocytogenes recovered from lettuce treated with chlorine or Tsunami significantly different. The rate of decrease in free chlorine concentration in treatment solution as affected by the weight/volume ratio (1:100, 1:10, 2:10, and 4:10) of lettuce and solution was determined. The rate of reduction increased as the ratio decreased. The overall order of magnitude of reduction was shredded iceberg lettuce > iceberg pieces > Romaine pieces. The highest reductions in free chlorine concentration in solutions used to treat shredded lettuce are attributed to the release of tissue juices, which increases the concentration of soluble organic materials available for reaction with chlorine.     

Factors affecting survival, growth, and retrieval of Salmonella Poona on intact and wounded cantaloupe rind and in stem scar tissue

Studies were done to determine the survival and recovery of Salmonella enterica serotype Poona from cantaloupe rind as affected by environmental conditions between the time of contamination and analysis. Detection and enumeration of the pathogen as influenced by analytical methods were also investigated. Combinations of preenrichment broth (lactose broth or universal preenrichment broth), enrichment broth (Rappaport–Vassiliadis broth or tetrathionate broth), and selective agar medium (bismuth sulfite agar or xylose lysine desoxycholate agar) for detecting S. Poona on inoculated cantaloupes stored at 4°C for 7 days or 21°C for 3 days were equivalent in performance. The use of nalidixic acid resistance as a marker in S. Poona and nalidixic acid in media used to enhance detection or enumeration of the pathogen by inhibiting background micro-flora in sanitizer efficacy studies, for example, would not adversely affect its survival on or recovery from cantaloupes. Overall, the composition of the carrier (water or 5% horse serum, a high organic matrix) used to prepare inocula did not influence the number of S. Poona recovered from the intact rind surface, wounds in the surface, or the stem scar tissue. Regardless of inoculation site or composition of the carrier, populations on spot inoculated melons stored at 4°C remained constant between 2 and 24 h after inoculation. The pathogen grew within 24 h in wounds of spot- and dip-inoculated cantaloupes stored at 21°C and 37°C. The addition of up to 1.0% Tween 80 to 0.1% peptone used to remove S. Poona from the rind surface did not adversely affect viability and may have enhanced detachment. Consideration of these observations is recommended when developing a method to test the efficacy of sanitizers in killing salmonellae on the rind surface of inoculated cantaloupes and to detect or enumerate salmonellae that may be natural contaminants.     

Survival and growth of alkali-stressed Listeria monocytogenes on beef frankfurters and thermotolerance in frankfurter exudates

Cells of Listeria monocytogenes exposed at 4 degrees C to 1% solutions of two alkaline cleaners or alkali-adapted in tryptose phosphate broth (pH 10.0) at 37 degrees C for 45 min, followed by 4 degrees C for 48 h, were inoculated onto beef frankfurters containing high fat (16 g) and high sodium (550 mg) or low fat (8 g) and low sodium (250 mg) per 57-g serving. Frankfurters were surface inoculated (2.0 log10 CFU/g), vacuum packaged, stored at -20, 4, or 12 degrees C, and analyzed for populations of L. monocytogenes at 2-day to 2-week intervals. Populations did not change significantly on frankfurters stored at -20 degrees C for up to 12 weeks. After storage at 4 degrees C for 6 weeks (I week before the end of shelf life), populations of control cells and cells exposed to alkaline cleaners were ca. 6.0 log10 CFU/g of low fat, low sodium (LFLS) frankfurters and ca. 3.5 log10 CFU/g of high fat, high sodium (HFHS) frankfurters. Growth of alkali-adapted cells on both types of frankfurters was retarded at 4 degrees C. Growth of L. monocytogenes on frankfurters stored at 12 degrees C was more rapid than at 4 degrees C, but a delay in growth of alkali-adapted cells on HFHS and LFLS frankfurters was evident during the first 9 and 6 days, respectively. Alkali-adapted cells had a significantly (P < or = 0.05) lower logistic D59 degrees C-value (decimal reduction time) than alkaline cleaner-exposed cells, but the D59 degrees C-value was not different from that of control cells. Cells exposed to a nonbutyl alkaline cleaner, and then heated in LFLS frankfurter exudates, had a significantly lower D62 degrees C-value than cells that had been exposed to some of the other treatments. Growth characteristics of L. monocytogenes inoculated onto the surface of frankfurters may be altered by previous exposure to alkaline environments. Differences in growth characteristics of L. monocytogenes on HFHS versus LFLS beef frankfurters stored at refrigeration temperatures indicate that composition influences the behavior of both alkaline-stressed and control cells.     

The cohesion of previously fractured Fcc metals in ultrahigh vacuum

The cohesion of clean surfaces of the fcc metals Ag, Al, Cu, and Ni was investigated using the technique of cold welding specimens previously fractured in an ultrahigh vacuum. The cohesive strength of the weld increased with compressive load, all data falling on a single curve with slight positive curvature when the cohesive strength and compression load were normalized through the initial fracture strength of each metal. The cohesion coefficients ranged from 0.62 to 1.15 and were in accord with those obtained using more elaborate techniques of surface preparation and testing. It is proposed that the essentially constant cohesion coefficient obtained for all the unalloyed fcc metals resides in the fact that the area of contact produced by a given compressive load is inversely proportional to the fracture stress of the metal and the cohesive strength is directly proportional to this fracture stress. A lowered cohesion coefficient was observed for copper specimens which had recrystallized in the vicinity of the interface either during the cold welding or as the result of a subsequent heat treatment.     

Bromate Destruction by UV Irradiation and Electric Arc Discharge

Bromate ion destruction by UV irradiation using either a low pressure mercury lamp or a medium pressure mercury lamp has been evaluated. A low pressure lamp which emits radiation predominantly at < 200 nm was more effective than the UV lamp which emits radiation at 254 nm, since bromate ion has a peak absorbance of about 195 nm. Bromate ion was shown to be reduced to bromide ion with bromine as an intermediate. Bromate ion destruction using a low pressure mercury lamp (< 200 nm) ranged from 3 to 38% for doses ranging from 23 to 228 mW-s/cm²; 7-46% destruction was achieved using a medium pressure lamp with initial bromate ion concentrations of 11-38 μg/L and doses ranging from 60 to 550 mW-s/cm². A new innovative electric arc discharge method also has been evaluated and compared with UV irradiation. The electric arc discharge method destroyed 12-45% bromate ion for doses ranging from 130 to 1300 mW-s/cm².