Impact of vacuum cooling on Escherichia coli O157:H7 infiltration into lettuce tissue

Vacuum cooling is a common practice in the California leafy green industry. This study addressed the impact of vacuum cooling on the infiltration of Escherichia coli O157:H7 into lettuce as part of the risk assessment responding to the E. coli O157:H7 outbreaks associated with leafy green produce from California. Vacuum cooling significantly increased the infiltration of E. coli O157:H7 into the lettuce tissue (2.65E+06 CFU/g) compared to the nonvacuumed condition (1.98E+05 CFU/g). A stringent surface sterilization and quadruple washing could not eliminate the internalized bacteria from lettuce. It appeared that vacuuming forcibly changed the structure of lettuce tissue such as the stomata, suggesting a possible mechanism of E. coli O157:H7 internalization. Vacuuming also caused a lower reduction rate of E. coli O157:H7 in stored lettuce leaves than that for the nonvacuumed condition.     

Induction of viable but nonculturable Escherichia coli O157:H7 in the phyllosphere of lettuce: a food safety risk factor

Escherichia coli O157:H7 continues to be an important human pathogen and has been increasingly linked to food-borne illness associated with fresh produce, particularly leafy greens. The aim of this work was to investigate the fate of E. coli O157:H7 on the phyllosphere of lettuce under low temperature and to evaluate the potential hazard of viable but nonculturable (VBNC) cells induced under such stressful conditions. First, we studied the survival of six bacterial strains following prolonged storage in water at low temperature (4°C) and selected two strains with different nonculturable responses for the construction of E. coli O157:H7 Tn7gfp transformants in order to quantitatively assess the occurrence of human pathogens on the plant surface. Under a suboptimal growth temperature (16°C), both E. coli O157:H7 strains maintained culturability on lettuce leaves, but under more stressful conditions (8°C), the bacterial populations evolved toward the VBNC state. The strain-dependent nonculturable response was more evident in the experiments with different inoculum doses (10(9) and 10(6) E. coli O157:H7 bacteria per g of leaf) when strain BRMSID 188 lost culturability after 15 days and strain ATCC 43895 lost culturability within 7 days, regardless of the inoculum dose. However, the number of cells entering the VBNC state in high-cell-density inoculum (approximately 55%) was lower than in low-cell-density inoculum (approximately 70%). We recorded the presence of verotoxin for 3 days in samples that contained a VBNC population of 4 to 5 log(10) cells but did not detect culturable cells. These findings indicate that E. coli O157:H7 VBNC cells are induced on lettuce plants, and this may have implications regarding food safety.     

Transmission of Escherichia coli O157:H7 from contaminated manure and irrigation water to lettuce plant tissue and its subsequent internalization.

The transmission of Escherichia coli O157:H7 from manure-contaminated soil and irrigation water to lettuce plants was demonstrated using laser scanning confocal microscopy, epifluorescence microscopy, and recovery of viable cells from the inner tissues of plants. E. coli O157:H7 migrated to internal locations in plant tissue and was thus protected from the action of sanitizing agents by virtue of its inaccessibility. Experiments demonstrate that E. coli O157:H7 can enter the lettuce plant through the root system and migrate throughout the edible portion of the plant.     

Leaf age as a risk factor in contamination of lettuce with Escherichia coli O157:H7 and Salmonella enterica

Outbreaks of Escherichia coli O157:H7 infections have been linked increasingly to leafy greens, particularly to lettuce. We present here the first evidence that this enteric pathogen can multiply on the leaves of romaine lettuce plants. The increases in population size of E. coli O157:H7 in the phyllosphere of young lettuce plants ranged from 16- to 100-fold under conditions of warm temperature and the presence of free water on the leaves and varied significantly with leaf age. The population size was consistently ca. 10-fold higher on the young (inner) leaves than on the middle leaves. The growth rates of Salmonella enterica and of the natural bacterial microflora were similarly leaf age dependent. Both enteric pathogens also achieved higher population sizes on young leaves than on middle leaves harvested from mature lettuce heads, suggesting that leaf age affects preharvest as well as postharvest colonization. Elemental analysis of the exudates collected from the surfaces of leaves of different ages revealed that young-leaf exudates were 2.9 and 1.5 times richer in total nitrogen and carbon, respectively, than middle-leaf exudates. This trend mirrored the nitrogen and carbon content of the leaf tissue. Application of ammonium nitrate, but not glucose, to middle leaves enhanced the growth of E. coli O157:H7 significantly, suggesting that low nitrogen limits its growth on these leaves. Our results indicate that leaf age and nitrogen content contribute to shaping the bacterial communities of preharvest and postharvest lettuce and that young lettuce leaves may be associated with a greater risk of contamination with E. coli O157:H7.     

Fate of Escherichia coli O157:H7 and Salmonella from contaminated manure slurry applied to soil surrounding tall fescue

Aim:  To investigate the potential transfer of Escherichia coli O157:H7 and Salmonella from contaminated manure slurry into the tissue of tall fescue plants.
Methods and Results:  Tall fescue plants ( n  =   50) were fertilized with a manure slurry inoculated with E. coli O157:H7 and Salmonella . Soil was collected and tall fescue plants ( n  =   10 per day) harvested on day 1, 2, 4, 8, and 14 after manure slurry fertilization. Soil samples were positive for E. coli O157:H7 on all days and on day 1, 2, 8, and 14 for Salmonella . None of the plant tissue samples were positive for E. coli O157:H7 on day 1 or 2; however, 20%, 30% and 40% of plant tissue samples were positive for E. coli O157:H7 on day 4, 8, and 14, respectively.
Conclusions:  It may be possible that E. coli O157:H7 can become transmitted and internalized into tall fescue plant tissue within 4 days after exposure to an E. coli O157:H7-contaminated manure slurry. Salmonella did not appear to be transferred to tall fescue plant tissue.
Significance and Impact of the Study:  Faeces contaminated with E. coli O157:11H7 may be one means by which grazing ruminants spread bacterial pathogens to additional animals.     

A piezoelectric immunosensor for specific capture and enrichment of viable pathogens by quartz crystal microbalance sensor, followed by detection with antibody-functionalized gold nanoparticles

A sensitive bacteria enrichment and detection system for viable Escherichia coli O157:H7 was developed using a piezoelectric biosensor-quartz crystal microbalance (QCM) with antibody-functionalized gold nanoparticles (AuNPs) used as detection verifiers and amplifiers. In the circulating-flow QCM system, capture antibodies for E. coli O157:H7 were first immobilized onto the QCM chip. The sample containing E. coli O157:H7 was circulated through the system in the presence of 10ml of brain heart infusion (BHI) broth for 18h. The cells of E. coli O157:H7 specifically captured and enriched on the chip surface of the QCM were identified by QCM frequency changes. Listeria monocytogenes and Salmonella Typhimurium were used as negative controls. After bacterial enrichment, detection antibody-functionalized AuNPs were added to enhance the changes in detection signal. The use of BHI enrichment further enhanced the sensitivity of the developed system, achieving a detection limit of 0-1log CFU/ml or g. The real-time monitoring method for viable E. coli O157:H7 developed in this study can be used to enrich and detect viable cells simultaneously within 24h. The unique advantages of the system developed offer great potential in the microbial analysis of food samples in routine settings.     

Influence of the plant defense response to Escherichia coli O157:H7 cell surface structures on survival of that enteric pathogen on plant surfaces

Consumption of fresh and fresh-cut fruits and vegetables contaminated with Escherichia coli O157:H7 has resulted in hundreds of cases of illness and, in some instances, death. In this study, the influence of cell surface structures of E. coli O157:H7, such as flagella, curli fimbriae, lipopolysaccharides, or exopolysaccharides, on plant defense responses and on survival or colonization on the plant was investigated. The population of the E. coli O157:H7 ATCC 43895 wild-type strain was significantly lower on wild-type Arabidopsis plants than that of the 43895 flagellum-deficient mutant. The population of the E. coli O157:H7 43895 flagellum mutant was greater on both wild-type and npr1-1 mutant (nonexpressor of pathogenesis-related [PR] genes) plants and resulted in less PR gene induction, estimated based on a weak β-glucuronidase (GUS) signal, than did the 43895 wild-type strain. These results suggest that the flagella, among the other pathogen-associated molecular patterns (PAMPs), made a substantial contribution to the induction of plant defense response and contributed to the decreased numbers of the E. coli O157:H7 ATCC 43895 wild-type strain on the wild-type Arabidopsis plant. A curli-deficient E. coli O157:H7 86-24 strain survived better on wild-type Arabidopsis plants than the curli-producing wild-type 86-24 strain did. The curli-deficient E. coli O157:H7 86-24 strain exhibited a GUS signal at a level substantially lower than that of the curli-producing wild-type strain. Curli were recognized by plant defense systems, consequently affecting bacterial survival. The cell surface structures of E. coli O157:H7 have a significant impact on the induction of differential plant defense responses, thereby impacting persistence or survival of the pathogen on plants.     

Survival and growth of Escherichia coli O157:H7 on salad vegetables.

The influence of modified-atmosphere packaging, storage temperature, and time on survival and growth of Escherichia coli O157:H7 inoculated onto shredded lettuce, sliced cucumber, and shredded carrot was determined. Growth of psychotrophic and mesophilic microorganisms and changes in pH and sensory qualities of vegetables, as judged by subjective evaluation, were also monitored. Packaging under an atmosphere containing 3% oxygen and 97% nitrogen had no apparent effect on populations of E. coli O157:H7, psychotrophs, or mesophiles. Populations of viable E. coli O157:H7 declined on vegetables stored at 5 degrees C and increased on vegetables stored at 12 and 21 degrees C for up to 14 days. The most rapid increases in populations of E. coli O157:H7 occurred on lettuce and cucumbers stored at 21 degrees C. These results suggest that an unknown factor(s) associated with carrots may inhibit the growth of E. coli O157:H7. The reduction in pH of vegetables was correlated with initial increases in populations of E. coli O157:H7 and naturally occurring microfloras. Eventual decreases in E. coli O157:H7 in some samples, e.g., those stored at 21 degrees C, are attributed to the toxic effect of accumulated acids. Changes in visual appearance of vegetables were not influenced substantially by growth of E. coli O157:H7. The ability of E. coli O157:H7 to growth on raw salad vegetables subjected to processing and storage conditions simulating those routinely used in commercial practice has been demonstrated.     

Surface decontamination of beef inoculated with Salmonella Typhimurium DT104 or Escherichia coli O157:H7 using dry air in a novel heat treatment apparatus

AIMS: To determine the effectiveness of a novel dry air decontamination apparatus in the deactivation of Salmonella serotype Typhimurium DT104 or Escherichia coli O157:H7 on beef surfaces. METHODS AND RESULTS: A laboratory scale dry air decontamination apparatus, capable of producing repeatable and known heating time-temperature cycles on food surfaces was used in decontamination trials. Beef samples were surface inoculated with 7-8 log10CFU cm(-2) of S. Typhimurium DT104 or E. coli O157:H7 and heated at 60, 75, 90 and 100 degrees C using fast and slow heating rates and subsequently held at these temperatures for up to 600 s. A substantial reduction in pathogen numbers was achieved at higher temperatures (90 and 100 degrees C, 4.18-6.06 log10CFU cm(-2)) using both heating rates, but cell survival at these temperatures was also observed. At the lower temperatures, deactivation was small at 60 degrees C in particular it was less than one log unit after 3 min heating. No significant differences were observed when total reductions in pathogen counts were compared for all the temperature/heat up time combinations tested. During slow heating at 90 degrees C, and both heating rates at 100 degrees C, the pattern of deactivation of S. Typhimurium DT104 or E. coli O157:H7 was triphasic. CONCLUSIONS: This study has shown that heating meat surfaces with dry air can achieve substantial reductions in S. Typhimurium DT104 or E. coli O157:H7. As surface decontamination of beef surfaces with dry air had a negative effect on beef colour and appearance, such a decontamination apparatus would be unsuitable for producing meat for retail sale but it could be used to produce safer meat for use in the catering trade. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides researchers and food processors with data on the dynamic changes in S. Typhimurium DT104 and E. coli O157:H7 counts on intact beef surfaces during heating with dry air under realistic (time-varying) temperature conditions.     

Viability of Escherichia coli O157:H7 in natural river water determined by the use of flow cytometry

The enzymatic activity and viability of Escherichia coli O157:H7 in natural river water was determined by flow cytometry. River water was collected at two sites (an agricultural area and an industrial area) on the Aigawa River (Osaka, Japan). To facilitate estimation of the physiology of E. coli O157 in natural river water, bacterial cells in the water were stained with 6-carboxyfluorescein diacetate (6CFDA) and propidium iodide (PI). The cells were sorted into two populations, using a flow cytometer, based on their esterase activity. Each population was stained with E. coli O157:H7 fluorescent antibody (FA), and E. coli O157:H7 cells were observed in the esterase-active population. River water samples collected at the same points were incubated with yeast extract containing antibiotics to prevent cell division, and bacterial cells in the incubated samples were stained with PI and FA. Escherichia coli O157:H7 existed in both the viable (elongated and/or fattened) and inactive bacterial population determined by flow cytometry. These results indicate that E. coli O157:H7 may retain metabolic activity and growth potential in the natural aquatic environment.     

Comparison of a membrane surface adhesion recovery method with an IMS method for use in a polymerase chain reaction method to detect Escherichia coli O157:H7 in minced beef

In this study, enrichment procedures and two recovery methods, a membrane surface adhesion technique and an immunomagnetic separation (IMS), were compared for use in conjunction with a multiplex polymerase chain reaction (PCR) method with a view to describing a fast (24 h) and economical test for detection of Escherichia coli O157:H7 in meat samples. The study showed no significant difference between three different enrichment media (BHI, E. coli (E.C.) broth+novobiocin, modified tryptone soya broth (mTSB)+novobiocin) or two incubation temperatures (37 or 41.5 degrees C) for growth of E. coli O157:H7 in minced beef. Minced beef samples inoculated with E. coli O157:H7 at 40 cfu g(-1) were incubated at 37 degrees C for 16 h in E.C. broth+novobiocin reaching numbers of (log(10)7.82-8.70). E. coli O157:H7 were recovered by attachment to polycarbonate membranes immersed in the enriched cultures for 15 min or by immunomagnetic separation. Subsequent treatment of recovered membranes or IMS beads with lysis buffer and phenol/chloroform/isoamyl alcohol was used to extract the DNA from the extracted E. coli O157:H7 cells. The results show when E. coli O157:H7 was present at high levels in the enriched meat sample (log(10)9.6-7.5 cfu ml(-1); >16-h enrichment), the membrane and IMS techniques recovered similar levels of the pathogen and the microorganism was detectable by PCR using both methods. At lower levels of E. coli O157:H7 (log(10)6.4), only the IMS method could recover the pathogen but at levels below this neither method could recover sufficient numbers of the pathogens to allow detection. The conclusion of the study is that with sufficient enrichment time (16 h) the membrane surface adhesion membrane extraction method used in combination with multiplex PCR has the potential for a rapid and economical detection method.     

Influence of indigenous eukaryotic microbial communities on the reduction of Escherichia coli O157:H7 in compost slurry

Compost made from livestock manure is commonly used as a crop fertilizer and serves as a possible vehicle for the transmission of Escherichia coli O157:H7 to fresh produce. In this study, we hypothesized that the indigenous microbial communities present in composts adversely affects the survival of E. coli O157:H7. Escherichia coli O157:H7 was spiked into compost slurry and incubated at 25 °C. Escherichia coli O157:H7 exhibited a c. 4 log(10) reduction over 16 days. When compost was supplemented with the eukaryotic inhibitor cycloheximide, there was a minimal decrease in E. coli O157:H7 counts over the same time period. Analysis of microbial communities present in the compost with denaturing gradient gel electrophoresis (DGGE) suggested minor differences in the fungal communities present in cycloheximide-treated compost, compared with untreated compost over a period of 12 days at 25 °C. However, the DGGE profiles of protists showed drastic differences in community complexity. Clone library sequence analysis of protist populations revealed significantly different species composition between treatment and control samples at different time points. This suggests that predation of E. coli O157:H7 by protists might be a potential mechanism for reducing E. coli O157:H7 in compost materials.     

Reduction of Escherichia coli O157:H7 by stimulated Pediococcus acidilactici

This study was conducted to determine if stimulating the growth of meat starter culture (Pediococcus acidilactici) in a laboratory medium (Brain Heart Infusion broth +2.3% NaCl + 1.5% sucrose; LBHI) and during meat fermentation would control Escherichia coli O157:H7. In LBHI medium without P. acidilactici, the numbers of E. coli O157:H7 increased from 4.00 to 8.34 log10 cfu ml-1, whereas in the presence of P. acidilactici (approximately 6.0 log10 cfu ml-1) in LBHI, LBHIM (LBHI + 0.005% MnSO4), LBHIO (LBHI + 0.3 unit ml-1 Oxyrase), and LBHIMO (LBHI + M + O), the numbers of E. coli O157:H7 increased from 4.00 to 8.05, 7.50, 7.99, and 6.50 log10 cfu ml-1, respectively, after incubation at 40 degrees C for 15 h. During salami fermentation, the numbers of E. coli O157:H7 changed from 7.00 to 6.40 and 5.10 log10 cfu g-1 without and with P. acidilactici (approximately 7.0 log10 cfu g-1), respectively. Stimulated P. acidilactici by M, O, and MO further reduced the number of E. coli O157:H7 from 7.00 to 4.00, 4.80, and 3.65 log10 cfu g-1, respectively. The combination of MO was a better growth stimulator for P. acidilactici, which controlled E. coli O157:H7 in both systems (P < 0.05).     

Differences in growth of Salmonella enterica and Escherichia coli O157:H7 on alfalfa sprouts

Sprout producers have recently been faced with several Salmonella enterica and Escherichia coli O157:H7 outbreaks. Many of the outbreaks have been traced to sprout seeds contaminated with low levels of human pathogens. Alfalfa seeds were inoculated with S. enterica and E. coli O157:H7 strains isolated from alfalfa seeds or other environmental sources and sprouted to examine growth of these human pathogens in association with sprouting seeds. S. enterica strains grew an average of 3.7 log(10) on sprouting seeds over 2 days, while E. coli O157:H7 strains grew significantly less, an average of 2.3 log(10). The initial S. enterica or E. coli O157:H7 inoculum dose and seed-sprouting temperature significantly affected the levels of both S. enterica and E. coli O157:H7 on the sprouts and in the irrigation water, while the frequency of irrigation water replacement affected only the levels of E. coli O157:H7. Colonization of sprouting alfalfa seeds by S. enterica serovar Newport and E. coli O157:H7 strains transformed with a plasmid encoding the green fluorescent protein was examined with fluorescence microscopy. Salmonella serovar Newport colonized both seed coats and sprout roots as aggregates, while E. coli O157:H7 colonized only sprout roots.     

Antibacterial activity of pepsin-digested lactoferrin on foodborne pathogens in buffered broth systems and ultra-high temperature milk with EDTA

AIMS: To evaluate the antimicrobial activity in peptone yeast extract glucose (PYG) broth and ultra-high temperature (UHT) milk of bovine lactoferrin hydrolysate (LFH) with pepsin against the foodborne pathogens Salmonella Stanley, Escherichia coli, Listeria monocytogenes and Staphylococcus aureus. METHODS AND RESULTS: The LFH was suspended in PYG and the minimum inhibitory concentration for each pathogen determined. The LFH was also suspended in UHT milk adjusted to pH 4 or 7, samples incubated at 4 or 35 degrees C and the change in bacterial cell population determined. Experiments in UHT milk were conducted using L. monocytogenes and E. coli O157:H7. At pH 4 LFH reduced the population of E. coli O157:H7 and L. monocytogenes by approx. 2 log; however, only E. coli O157:H7 was inhibited in samples adjusted to pH 7. The addition of EDTA (10 mg ml(-1)) to UHT milk supplemented with LFH did not markedly influence the growth of E. coli O157:H7 or L. monocytogenes. CONCLUSIONS: The results suggest that, under low pH and refrigeration conditions, LFH can limit the growth or reduce the population of pathogenic bacteria in a dairy product. SIGNIFICANCE AND IMPACT OF THE STUDY: Natural preservatives that are active against Gram-negative and Gram-positive bacteria are desirable to the food industry. This study demonstrates that LFH is effective in a complex food system. Moreover, the LFH used was not purified, making its use by industry more attractive.     

Frequency of Escherichia coli O157:H7 isolation from stool specimens

During a 6-month period, 7252 faeces specimens were examined for Escherichia coli serotype O157:H7. Forty-nine specimens (0.7%) from 19 patients yielded this organism. Escherichia coli O157:H7 was the third most frequently isolated bacterial pathogen, following Campylobacter jejuni and (or) Salmonella sp. Although regional variation between laboratories determined whether Campylobacter jejuni or Salmonella was the primary bacterial pathogen isolated, E. coli O157:H7 was consistently isolated more frequently than either Shigella or Yersinia enterocolitica.     

Experimental Escherichia coli O157:H7 carriage in calves.

Nine weaned calves (6 to 8 weeks of age) were given 10(10) CFU of a five-strain mixture of enterohemorrhagic Escherichia coli O157:H7 by oral-gastric intubation. After an initial brief period of pyrexia in three calves and transient mild diarrhea in five calves, calves were clinically normal throughout the 13- to 27-day study. The population of E. coli O157:H7 in the faces decreased dramatically in all calves during the first 2 weeks after inoculation. Thereafter, small populations of E. coli O157:H7 persisted in all calves, where they were detected intermittently in the feces and rumen contents. While withholding food increased fecal shedding of E. coli O157:H7 by 1 to 2 log10/g in three of four calves previously shedding small populations of E. coli O157:H7, the effect of fasting on fecal shedding of E. coli O157:H7 was variable in calves shedding larger populations. At necropsy, E. coli O157:H7 was not isolated from sites outside the alimentary tract. E. coli O157:H7 was isolated from the forestomach or colon of all calves at necropsy. Greater numbers of E. coli O157:H7 were present in the gastrointestinal contents than in the corresponding mucosal sections, and there was no histologic or immunohistochemical evidence of E. coli O157:H7 adhering to the mucosa. In conclusion, under these experimental conditions, E. coli O157:H7 is not pathogenic in weaned calves, and while it does not appear to colonize mucosal surfaces for extended periods, E. coli O157:H7 persists in the contents of the rumen and colon as a source for fecal shedding.     

Recombinant anti-EspA antibodies block Escherichia coli O157:H7-induced attaching and effacing lesions in vitro

Intimin and EspA proteins are virulence factors expressed by attaching and effacing Escherichia coli (AEEC) such as enteropathogenic and enterohaemorrhagic E. coli. The EspA protein makes up a filament structure forming part of the type III secretion system (TTSS) that delivers effector proteins to the host epithelial cell. Bacterial surface displayed intimin interacts with translocated intimin receptor in the host cell membrane leading to intimate attachment of the bacterium and subsequent attaching and effacing lesions. Here, we have assessed the use of recombinant monoclonal antibodies against E. coli O157:H7 EspA and intimin for the disruption of AEEC interaction with the host cell. Anti-gamma intimin antibodies did not reduce either adhesion of E. coli O157:H7 to host cell mono-layers or subsequent host cell actin rearrangement. Anti-EspA antibodies similarly had no effect on bacterial adhesion however they had a marked effect upon E. coli O157:H7-induced host cell actin rearrangement, where both monoclonal and polyclonal antibodies completely blocked cytoskeletal changes within the host cell. Furthermore, these anti-EspA antibodies were shown to reduce actin rearrangement induced by some but not all other AEEC serotypes tested. Both polyclonal and monoclonal antibodies could be used to label E. coli O157 EspA filaments and these immunoreagents did not inhibit the formation of such filaments. This is the first report of monoclonal antibodies to EspA capable of disrupting the TTSS function of E. coli O157:H7.     

Influence of apple cultivars on inactivation of different strains of Escherichia coli O157:H7 in apple cider by UV irradiation

This study examined the effect of different apple cultivars upon the UV inactivation of Escherichia coli O157:H7 strains within unfiltered apple cider. Apple cider was prepared from eight different apple cultivars, inoculated with approximately 10(6) to 10(7) CFU of three strains of E. coli O157:H7 per ml (933, ATCC 43889, and ATCC 43895), and exposed to 14 mJ of UV irradiation per cm(2). Bacterial populations for treated and untreated samples were then enumerated by using nonselective media. E. coli O157:H7 ATCC 43889 showed the most sensitivity to this disinfection process with an average 6.63-log reduction compared to an average log reduction of 5.93 for both strains 933 and ATCC 43895. The highest log reduction seen, 7.19, occurred for strain ATCC 43889 in Rome cider. The same cider produced the lowest log reductions: 5.33 and 5.25 for strains 933 and ATCC 43895, respectively. Among the apple cultivars, an average log reduction range of 5.78 (Red Delicious) to 6.74 (Empire) was observed, with two statistically significant (alpha < or = 0.05) log reduction groups represented. Within the paired cultivar-strain analysis, five of eight ciders showed statistically significant (alpha < or = 0.05) differences in at least two of the E. coli strains used. Comparison of log reductions among the E. coli strains to the cider parameters of (o)Brix, pH, and malic acid content failed to show any statistically significant relationship (R(2) > or = 0.95). However, the results of this study indicate that regardless of the apple cultivar used, a minimum 5-log reduction is achieved for all of the strains of E. coli O157:H7 tested.