Evaluation of an optical microbiological method for rapidly estimating populations of aerobic bacteria, coliforms, and Escherichia coli from ground pork

The BioSys optical methods for estimating populations of aerobic bacteria, coliforms, and Escherichia coli from ground pork were evaluated. Ground pork samples were analyzed immediately, after temperature abuse at 25 degrees C for various periods of time, or after temperature abuse and dilution by mixing with pork that was prepared by grinding whole muscles that had the outer portion excised using a sterile scalpel. Each ground pork sample was tested using standard methods such as aerobic plate counts (APC), violet red bile (VRB) agar plate counts (coliforms), and three-tube most probable numbers (MPN--E. coli). Each sample was tested using the BioSys for total viable counts (TVC) by placing 2 ml of ground pork homogenate (25 g into 225 ml of sterile 1% buffered peptone water) into 8 ml of nutrient medium containing brom-cresol purple in a test vial and monitoring at 35 degrees C. Coliforms were enumerated by placing 5 ml of ground pork homogenate into 5 ml of coliform medium (CM) in a test vial and monitoring at 35 degrees C. E. coli were enumerated by placing 5 ml of ground pork homogenate into 5 ml of double-strength CM with 2% dextrose in a test vial and monitoring at 42 degrees C. The correlation coefficients for the regression lines comparing APC to BioSys TVC detection times (DT), VRB to BioSys coliform DT, and MPN to BioSys E. coli DT were -0.95, -0.94, and -0.93, and the line equations were logl0 CFU/ml = 8.94 - 0.40(DT), log10 CFU/ml = 8.77 - 0.43(DT), and log10 CFU/ml = 8.96 - 0.81(DT), respectively. These methods may allow pork producers to monitor equipment surfaces and products in less than 16 h and obtain microbiological results prior to shipment.     

Campylobacter, Salmonella, Listeria monocytogenes, verotoxigenic Escherichia coli, and Escherichia coli prevalence, enumeration, and subtypes on retail chicken breasts with and without skin

This study examined the prevalence, counts, and subtypes of Campylobacter, Salmonella, Listeria monocytogenes, verotoxigenic Escherichia coli (VTEC), and E. coli on raw retail chicken breast with the skin on versus the skin off. From January to December 2007, 187 raw skin-on chicken breasts and 131 skin-off chicken breasts were collected from randomly selected retail grocery stores in the Region of Waterloo, Ontario, Canada. Campylobacter isolates were recovered from a higher proportion of the skin-off chicken breasts, 55 (42%) of 131, than of the skin-on chicken breasts tested, 55 (29%) of 187 (P = 0.023). There was no difference in the proportion of Salmonella isolates recovered from the two meat types (P = 0.715): 40 (31%) of 131 skin-off chicken breasts versus 61 (33%) of 187 skin-on chicken breasts. L. monocytogenes isolates were recovered from a statistically lower proportion of the skin-off chicken breasts, 15 (15%) of 99, than of the skin-on chicken breasts, 64 (34%) of 187 (P = 0.001). There was no difference in the proportion of E. coli isolates recovered from the skin-off chicken breasts, 33 (33%) of 99, than from the skin-on chicken breasts, 77 (41%) of 187 (P = 0.204). VTEC was detected on a single skin-off chicken breast. Campylobacter jejuni was the most frequent species isolated on both types of chicken meat: skin-on, 48 (87%) of 55, and skin-off, 51 (94%) of 54. Salmonella serotypes Kentucky and Heidelberg and L. monocytogenes serotype 1/2a were the most frequently detected serotypes from both skin-off and skin-on chicken breasts. Although there appeared to be a trend toward higher enumeration values of these pathogens and E. coli on the skin-on chicken, the differences did not exceed 1 log. This study suggested that skin-off chicken breast may represent a higher risk of consumer exposure to Campylobacter, a similar risk for Salmonella, VTEC, and E. coli, and a lower risk for L. monocytogenes than skin-on chicken breast.     

Comparison of an automated most-probable-number technique with traditional plating methods for estimating populations of total aerobes, coliforms, and Escherichia coli associated with freshly processed broiler chickens

An instrument (TEMPO) has been developed to automate the most-probable-number (MPN) technique and reduce the effort required to estimate some bacterial populations. We compared the automated MPN technique with traditional microbiological plating methods and Petrifilm methods for estimating the total viable count of aerobic microorganisms (TVC), total coliforms (CC), and Escherichia coli populations (EC) on freshly processed broiler chicken carcasses (postchill whole carcass rinse [WCR] samples) and cumulative drip-line samples from a commercial broiler processing facility. Overall, 120 broiler carcasses, 36 prechill drip-line samples, and 40 postchill drip-line samples were collected over 5 days (representing five individual flocks) and analyzed by the automated MPN and direct agar plating and Petrifilm methods. The TVC correlation coefficient between the automated MPN and traditional methods was very high (0.972) for the prechill drip samples, which had mean log-transformed values of 3.09 and 3.02, respectively. The TVC correlation coefficient was lower (0.710) for the postchill WCR samples, which had lower mean log values of 1.53 and 1.31, respectively. Correlations between the methods for the prechill CC and EC samples were 0.812 and 0.880, respectively. The estimated number of total aerobes was generally greater than the total number of coliforms or E. coli recovered for all sample types (P < 2e?1?). Significantly more bacteria were recovered from the prechill samples than from the postchill WCR or cumulative drip samples (P < 9.5e?12 and P < 2e?1?, respectively). When samples below the limit of detection were excluded, 92.1% of the total responses were within a single log difference between the traditional plating or Petrifilm methods and the automated MPN method.     

Presence of faecal coliforms, Escherichia coli and diarrheagenic E. coli pathotypes in ready-to-eat salads, from an area where crops are irrigated with untreated sewage water

Consumption of ready-to-eat (RTE) salads has increased worldwide. Consequently, the number of outbreaks caused by food-borne pathogens, including diarrheagenic E. coli pathotypes (DEPs), associated with the consumption of RTE-salads has increased. DEPs include enterotoxigenic (ETEC), typical and atypical enteropathogenic (tEPEC, aEPEC), enteroinvasive (EIEC), enteroaggregative (EAEC), diffuse adherent (DAEC) and Shiga toxin-producing (STEC) E. coli. In less-developed areas of the world, fresh crops continue to be irrigated with untreated sewage water. The aims of this study were to evaluate the microbiological quality and prevalence of DEPs in RTE-salads of raw vegetables, purchased from restaurants at Pachuca-City, Hidalgo, Mexico, where most locally consumed vegetables are irrigated with untreated sewage water. A total of 130 salads were purchased from restaurants of three categories: A) national chain restaurants and B) local restaurants, both with the H distinctive (a recognition that the Secretary of Tourism grants to restaurants that manage supplies with high levels of hygiene); and C) local small inexpensive restaurants without H distinctive. A total of 6 restaurants were included, 2 per category (A(1-2), B(1-2), C(1-2)). Each sample was tested for the presence of faecal coliforms (FC) and E. coli by standard procedures. E. coli strains were further characterized for the presence of DEPs loci by two multiplex polymerase chain reactions. Among the 130 salad samples 99% (129) were contaminated with FC; 85% (110/129) harboured E. coli and 7% (8/110) DEPs. The amount of positive salad samples for FC and E. coli was similar between restaurants and categories. The FC mean (571 FC/g) of all samples was significantly higher (p<0.001) than the E. coli mean (63 E. coli/g). A weak correlation of 7.7% (r(2)=0.077, p=0.003) between median FC and E. coli MPN (most probable number) per sample was found. Of the 8 salad samples contaminated with DEPs, 2 were spinach salads from restaurant A(2) and 3 were (Mixed salad) samples from each C restaurant. Three samples harboured non-O157 STEC strains, 2 EIEC, 1 ETEC and 2 samples had non-O157 STEC and EIEC strains, simultaneously. A significant difference (p=0.008) between the prevalence of E. coli vs. DEPs was observed. Independently of the restaurants' overall hygienic status, most RTE-salads had a poor microbiological quality and some harboured DEPs that have been associated with illness in Mexico. Health authorities should focus on implementing DEPs screening in raw vegetables and enforcing the legislation that forbids irrigation with untreated sewage water of both root and leafy vegetables.     

Effect of fecal contamination and cross-contamination on numbers of coliform, Escherichia coli, Campylobacter, and Salmonella on immersion-chilled broiler carcasses

The effect of prechill fecal contamination on numbers of bacteria on immersion-chilled carcasses was tested in each of three replicate trials. For each trial, 16 eviscerated broiler carcasses were split into 32 halves and assigned to one of two groups. Cecal contents (0.1 g inoculated with Campylobacter and nalidixic acid-resistant Salmonella) were applied to each of eight halves in one group (direct contamination) that were placed into one paddle chiller (contaminated), whereas the other paired halves were placed into another chiller (control). From the second group of eight split birds, one of each paired half was placed in the contaminated chiller (to determine cross-contamination) and the other half was placed in the control chiller. Postchill carcass halves were sampled by a 1-min rinse in sterile water, which was collected and cultured. Bacterial counts were reported as log CFU per milliliter of rinsate. There were no significant statistical differences (paired t test, P < 0.05) from direct contamination for coliforms (mean 3.0 log CFU) and Escherichia coli (mean 2.7 log CFU), although Campylobacter numbers significantly increased from control values because of direct contamination (1.5 versus 2.1 log CFU), and the incidence increased from 79 to 100%. There was no significant effect of cross-contamination on coliform (mean 2.9 log CFU) or E. coli (mean 2.6 log CFU) numbers. Nevertheless, Campylobacter levels were significantly higher after exposure to cross-contamination (1.6 versus 2.0 log CFU), and the incidence of this bacterium increased from 75 to 100%. Salmonella-positive halves increased from 0 to 42% postchill because of direct contamination and from 0 to 25% as a result of cross-contamination after chilling. Water samples and surface swabs taken postchill from the contaminated chiller were higher for Campylobacter than those taken from the control chiller. Immersion chilling equilibrated bacterial numbers between contaminated and control halves subjected to either direct contamination or cross-contamination for coliforms and E. coli. Campylobacter numbers, Campylobacter incidence, and Salmonella incidence increased because of both direct contamination and cross-contamination in the chiller. Postchill E. coli numbers did not indicate which carcass halves were contaminated with feces before chilling.     

Escherichia coli O157 prevalence and enumeration of aerobic bacteria, Enterobacteriaceae, and Escherichia coli O157 at various steps in commercial beef processing plants

The effectiveness of current antimicrobial interventions used in reducing the prevalence or load of Escherichia coli O157 and indicator organisms on cattle hides and carcasses at two commercial beef processing plants was evaluated. Sponge sampling of beef cattle was performed at five locations from the initial entry of the animals to the slaughter floor to the exit of carcasses from the "hotbox" cooler. For each sample, E. coli O157 prevalence was determined and total aerobic bacteria, Enterobacteriaceae, and E. coli O157 were enumerated. E. coli O157 was found on 76% of animal hides coming into the plants, but no carcasses leaving the cooler were identified as contaminated with E. coli O157. A positive relationship was seen between the incidence of E. coli O157 in hide samples and that in preevisceration samples. Aerobic plate counts and Enterobacteriaceae counts averaged 7.8 and 6.2 log CFU/100 cm2, respectively, on hides, and 1.4 and 0.4 log CFU/100 cm2, respectively, on chilled carcasses. Aerobic plate counts and Enterobacteriaceae counts on preevisceration carcasses were significantly related to the respective levels on the corresponding hides; the carcasses of animals whose hides carried higher numbers of bacteria were more likely to carry higher numbers of bacteria. Implementation of the sampling protocol described here would allow processors to evaluate the efficacy of on-line antimicrobial interventions and allow industrywide benchmarking of hygienic practices.     

Enumeration of total aerobic bacteria and Escherichia coli in minced meat and on carcass surface samples with an automated most-probable-number method compared with colony count protocols

An automated most-probable-number (MPN) system for the enumeration of total bacterial flora and Escherichia coli was compared with plate count agar and tryptone-bile-glucuronide (TBX) and ColiID (in-house method) agar methodology. The MPN partitioning of sample aliquots was done automatically on a disposable card containing 48 wells of 3 different volumes, i.e., 16 replicates per volume. Bacterial growth was detected by the formation of fluorescent 4-methylumbilliferone. After incubation, the number of fluorescent wells was read with a separate device, and the MPN was calculated automatically. A total of 180 naturally contaminated samples were tested (pig and cattle carcass surfaces, n = 63; frozen minced meat, n = 62; and refrigerated minced meat, n = 55). Plate count agar results and MPN were highly correlated (r = 0.99), with log MPN = -0.25 + 1.05 x log CFU (plate count agar) (n = 163; range, 2.2 to 7.5 log CFU/g or cm2). Only a few discrepancies were recorded. In two samples (1.1%), the differences were > or = 1.0 log; in three samples (1.7%), the differences were > or = 0.5 log. For E. coli, regression analysis was done for all three methods for 80 minced meat samples, which were above the limit of detection (1.0 log CFU/g): log MPN = 0.18 + 0.98 x log CFU (TBX), r = 0.96, and log MPN = -0.02 + 0.99 x log CFU (ColiID), r = 0.99 (range, 1.0 to 4.2 log CFU/g). Four discrepant results were recorded, with differences of > 0.5 but < 1.0 log unit. These results suggest that the automated MPN method described is a suitable and labor-saving alternative to colony count techniques for total bacterial flora and E. coli determination in minced meat or on carcass surfaces.     

Reduction of E. coli, Salmonella typhimurium, coliforms, aerobic bacteria, and improvement of ground beef color using trisodium phosphate or cetylpyridinium chloride before grinding

The impact of 10% trisodium phosphate (TSP) or 0.5% cetylpyridinium chloride (CPC) applied to beef trimmings either aerobically or under vacuum before grinding on Salmonella typhimurium (ST), Escherichia coli (EC), coliform (CO), aerobic plate count (APC), color and sensory attributes of ground beef through display was studied. For this, beef trimmings were inoculated with ST and EC then treated with either TSP or CPC in vacuum or aerobic conditions. Trimmings were ground, packaged, displayed under simulated retail conditions and sampled on days 0, 1, 2, 3 and 7 for microbial, instrumental color, and sensory color and odor characteristics. Aerobic and vacuum antimicrobial application methods were equally effective (P>0.05) for reducing microorganisms in ground beef. Trisodium phosphate and CPC reduced (P<0.05) all bacterial types monitored. In addition, TSP and CPC improved (P>0.05) ground beef redness (a*), oxymyoglobin stability (630 nm/580 nm) and sensory overall color throughout display without adversely affecting odor characteristics.     

Detection of Campylobacter jejuni and Campylobacter coli from broiler chicken-related samples using BAX PCR and conventional International Organization for Standardization culture

In this study, the conventional International Organization for Standardization (ISO) culture method was compared with the DuPont Qualicon BAX system, a high-throughput, rapid molecular assay that can be used to detect several bacterial species, including Campylobacter jejuni and Campylobacter coli in diverse sample types. Standard enrichment culture is a time-consuming process, taking up to 6 days to obtain a confirmed result. Rapid molecular assays have been developed that provide results within 24 h. Naturally contaminated samples from the poultry production chain were examined for the presence of Campylobacter spp. Samples from broiler chicken ceca (n = 100), fresh chicken carcass rinses (n = 60), and bootsocks (gauze sock walked through a broiler chicken house; n = 50) were enriched according to the ISO 10272 method in Bolton broth specifically designed to detect Campylobacter spp. in complex sample types. Samples were enriched without blood for use with the BAX system using the Campylobacter BAX kits for the detection of C. jejuni and C. coli. Samples also were directly plated onto modified charcoal cefperazone deoxycholate agar, and results were compared with those from the enriched samples for the ability to detect Campylobacter spp. Campylobacter spp. were isolated from 49% of samples with conventional enrichment cultures, from 48% with direct culture, from 68% with the BAX system and enrichment cultures, and from 62% with the BAX system used directly with samples. Overall, the BAX system detected more positive samples than did the conventional culture method and is an effective methodology for the rapid and reliable detection of Campylobacter spp. from diverse sample types.     

应用显色荧光方法检测牛奶或水中大肠菌群和大肠杆菌

研究了一种能同时检测出牛奶和水中大肠菌群和大肠杆菌的培养基和方法。检样和培养基混合后，经37℃，24h培养，呈现蓝色，表明有大肠杆菌存在，在366nm的紫外光下照射，有荧光发出显示检样中有大肠菌群存在。该方法不需验证步骤，研究过程中没有发现假阳性和假阴性现象出现，灵敏度可达到1-5／100mL。5个牛奶检样和4个水质检样中的定性(P／A)及在牛奶中进行大肠菌群和大肠杆菌最可能数(MPN值)的研究显示，新方法与标准方法有一致的结果。     

Campylobacter, Salmonella, Shigella and Escherichia coli in live and dressed poultry from metropolitan accra.

This study on the microbiology of chicken assessed a total of 97 live birds from three selected farms and 87 carcasses/chicken parts from two supermarkets, two open markets and one wholesale outlet (cold store) in the Accra metropolis. Campylobacter spp. were isolated from 14 (14.4%) gut contents of live birds from three farms. None of the frozen birds were positive for Campylobacter spp. These isolates were sensitive to most common antibiotics but not to ampicillin and tetracyclines. Salmonella spp. were isolated from 7 (7.2%) gut contents and 13 (6.8%) carcasses and were resistant to erythromycin. cefotiam, penicillin, ampicillin and cefadroxil. Samonella spp. had varied susceptibilities to nalidixic acid, chloramphenicol and minocyclin. No Shigella spp. was isolated from any of the live birds but 6 (6.9%) of imported chicken samples from the cold store and two markets were positive. Fosfomycin and chloramphenicol were the only antibiotics effective against these isolates. Twelve different Escherichia coli serovars were identified from the total of 21 positive samples. These, in order of magnitude isolated, are E. coli 0158 (14.3%), 0125 (14.3%), 025 (9.5%), 028ac (9.5%), 0159 (9.5%). 015 (9.5%), 0126 (9.5%), 063 (4.8%), 0143 (4.8%), 026 (4.8%), 078 (4.8%), 0164 (4.8%). Cefadroxil, ampicillin, penicillin, cefotiam, tetracycline and erythromycin were ineffective against all strains of E. coli isolated. Minocyclin was effective against all strains with the exception of E. coli 0159, 025, 0164 and 063, which were moderately susceptible. All strains with exception of E. coli 0164 were susceptible to fosfomycin. Nalidixic acid, chloramphenicol, kanamaycin, ceftrioxone and amoxycillin all showed varied effectiveness against the strains isolated. It is concluded that imported and locally produced chicken is a potential source of multiple-antibiotic-resistant enteropathogenic bacteria. Measures to improve the microbial quality of chicken are discussed.     

Effects of postchill application of acidified sodium chlorite to control Campylobacter spp. and Escherichia coli on commercial broiler carcasses

Experiments were performed to assess the reduction of Campylobacter spp. and Escherichia coli in commercial broiler carcasses by postchill dip applications of acidified sodium chlorite. Carcass rinses were collected before the inside-outside-bird washer (IOBW), post-IOBW, postchill, and after the postchill application of acidified sodium chlorite. Prevalence and counts of Campylobacter spp. and E. coli were determined. The mean values for Campylobacter spp. and E. coli counts differed significantly at sampling sites. The IOBW reduced the bacterial counts significantly in only one experiment. The chiller reduced Campylobacter counts significantly in both experiments but failed to significantly reduce the counts of E. coli in one experiment. No major reduction in the prevalence after enrichment for Campylobacter spp. was detected post-IOBW or postchill. However, a significant reduction in Campylobacter spp. and in E. coli counts and Campylobacter spp. prevalence was seen after the postchill application of acidified sodium chlorite. These results demonstrate that the antimicrobial effect of acidified sodium chlorite applied postchill may be used to significantly reduce Campylobacter spp. and E. coli in commercial broiler carcasses. Postchill systems may eventually be used in different applications, such as mist, spray, or bath, which could be applied closer to the final stages in processing.     

Effect of prechill fecal contamination on numbers of bacteria recovered from broiler chicken carcasses before and after immersion chilling

Paired carcass halves were used to test whether fecal contamination of skin during processing of broiler chickens can be detected by increased bacterial counts in samples taken before and after immersion chilling. In each of three trials, six freshly defeathered and eviscerated carcasses were cut in half, and a rectangle (3 by 5 cm) was marked with dots of ink on the breast skin of each half. One half of each pair was chosen randomly, and 0.1 g of freshly collected feces was spread over the rectangle with a spatula. After 10 min, both halves were sprayed with tap water for 10 to 15 s until feces could no longer be seen in the marked area. Both halves were sampled with a 1-min carcass rinse and were then put in a paddle chiller with other eviscerated carcasses for 45 min to simulate industrial immersion chilling. Immediately after chilling, each carcass half was subjected to another 1-min rinse, after which the skin within the rectangle was aseptically removed from the carcass halves and stomached. Rinses of fecally contaminated halves had significantly higher Enterobacteriaceae immediately before chilling, but there were no differences in coliform and Escherichia coli counts. After chilling, there were no differences in Enterobacteriaceae, coliform, and E. coli counts in rinse or skin samples from the paired carcass halves. Correlations were generally poor between counts in rinse and skin samples but were significant between prechill and postchill rinses for both control and fecally contaminated halves. Correlations were also significant between counts in rinses of control and contaminated halves of the same carcass after chilling. Bacterial counts in postchill carcass rinses did not indicate that fecal contamination occurred before chilling.     

Attachment strength to pork skin and resistance to quaternary ammonium salt and heat of Escherichia coli isolates recovered from a pork slaughter line

The aim of this study was to determine whether the attachment strength to pork skin, quaternary ammonium salt resistance, and thermal inactivation kinetics (at 65 degrees C) of a range of Escherichia coli isolates could be correlated with their temporal stability (persistence) within a pork slaughter line. The genetic lineage of the E. coli isolates was determined using enterobacterial repetitive intergenic consensus-PCR. The genotypes were divided into transient and endemic populations based on the number of times they were recovered within and across sampling visits made to a pork slaughterhouse. No significant variation in the D-value at 65 degrees C (0.27 to 0.51 min) was observed among the genotypes tested. However, differences in D-values were found for 100 ppm quaternary ammonium salt (3.0 to 6.0 min). All of the E. coli genotypes attached strongly to pork skin, and a high proportion of cells were irreversibly bound (39 to 42% of the initial inoculum). However, variation among genotypes was found with respect to loose attachment (21 to 33% of inoculated cells). No correlation between persistence of E. coli genotypes within the slaughter line and attachment strength or quaternary ammonium salt resistance was found. Variation in either physiological attribute could not be predicted based on genetic lineage. Additional or alternative factors may contribute to the ability of E. coli populations to become endemic within pork processing facilities. More studies should be conducted to elucidate the underlying factors that promote the formation of endemic populations of E. coli and other enteric bacteria (e.g., Salmonella) within slaughter lines.     

Preharvest evaluation of coliforms, Escherichia coli, Salmonella, and Escherichia coli O157:H7 in organic and conventional produce grown by Minnesota farmers

Microbiological analyses of fresh fruits and vegetables produced by organic and conventional farmers in Minnesota were conducted to determine the coliform count and the prevalence of Escherichia coli, Salmonella, and E. coli O157:H7. A total of 476 and 129 produce samples were collected from 32 organic and 8 conventional farms, respectively. The samples included tomatoes, leafy greens, lettuce, green peppers, cabbage, cucumbers, broccoli, strawberries, apples, and seven other types of produce. The numbers of fruits and vegetables was influenced by their availability at participating farms and varied from 11 strawberry samples to 108 tomato samples. Among the organic farms, eight were certified by accredited agencies and the rest reported the use of organic practices. All organic farms used aged or composted animal manure as fertilizer. The average coliform counts in both organic and conventional produce were 2.9 log most probable number per g. The percentages of E. coli-positive samples in conventional and organic produce were 1.6 and 9.7%, respectively. However, the E. coli prevalence in certified organic produce was 4.3%, a level not statistically different from that in conventional samples. Organic lettuce had the largest prevalence of E. coli (22.4%) compared with other produce types. Organic samples from farms that used manure or compost aged less than 12 months had a prevalence of E. coli 19 times greater than that of farms that used older materials. Serotype O157:H7 was not detected in any produce samples, but Salmonella was isolated from one organic lettuce and one organic green pepper. These results provide the first microbiological assessment of organic fruits and vegetables at the farm level.     

High level of antimicrobial resistance in Campylobacter jejuni isolated from broiler chickens in Estonia in 2005 and 2006

The development of antimicrobial resistance in Campylobacter jejuni and Campylobacter coli is a matter of increasing concern. Because campylobacteriosis is transmitted to humans usually via food of animal origin, the presence of antimicrobial-resistant campylobacters in broiler chickens has important public health implications. The aim of our study was to analyze resistance patterns of C. jejuni isolated from fecal samples collected at a large Estonian chicken farm, from cecal contents collected at slaughterhouses, and from meat samples collected at the retail establishments in 2005 and 2006. A total of 131 C. jejuni isolates were collected over a 13-month period and tested by the broth microdilution VetMIC method (National Veterinary Institute, Uppsala, Sweden) to determine the MICs of various antimicrobials. Resistance to one or more antimicrobials was detected in 104 (79.4%) of the 131 isolates. High proportions of the isolates were resistant to enrofloxacin (73.3%) and nalidixic acid (75.6%). Multidrug resistance (resistance to three or more unrelated antimicrobials) was detected in 36 isolates (27.5%), all of which were resistant to enrofloxacin. Multidrug resistance was significantly associated with enrofloxacin resistance (P < 0.01), and the use of enrofloxacin may select for multiresistant strains.     

Antimicrobial resistance in Campylobacter, Salmonella, and Escherichia coli isolated from retail grain-fed veal meat from Southern Ontario, Canada

This study estimated the prevalence of Salmonella, Campylobacter, and Escherichia coli isolates in fresh retail grain-fed veal obtained in Ontario, Canada. The prevalence and antimicrobial resistance patterns were examined for points of public health significance. Veal samples (n = 528) were collected from February 2003 through May 2004. Twenty-one Salmonella isolates were recovered from 18 (4%) of 438 samples and underwent antimicrobial susceptibility testing. Resistance to one or more antimicrobials was found in 6 (29%) of 21 Salmonella isolates; 5 (24%) of 21 isolates were resistant to five or more antimicrobials. No resistance to antimicrobials of very high human health importance was observed. Ampicillin-chloramphenicolstreptomycin-sulfamethoxazole-tetracycline resistance was found in 5 (3%) of 21 Salmonella isolates. Campylobacter isolates were recovered from 5 (1%) of 438 samples; 6 isolates underwent antimicrobial susceptibility testing. Resistance to one or more antimicrobials was documented in 3 (50%) of 6 Campylobacter isolates. No Campylobacter isolates were resistant to five or more antimicrobials or category I antimicrobials. E. coli isolates were recovered from 387 (88%) of 438 samples; 1,258 isolates underwent antimicrobial susceptibility testing. Resistance to one or more antimicrobials was found in 678 (54%) of 1,258 E. coli isolates; 128 (10%) of 1,258 were resistant to five or more antimicrobials. Five (0.4%) and 7 (0.6%) of 1,258 E. coli isolates were resistant to ceftiofur and ceftriaxone, respectively, while 34 (3%) of 1,258 were resistant to nalidixic acid. Ciprofloxacin resistance was not detected. There were 101 different resistance patterns observed among E. coli isolates; resistance to tetracycline alone (12.7%, 161 of 1,258) was most frequently observed. This study provides baseline prevalence and antimicrobial resistance data and highlights potential public health concerns.     

Characterization of O157:H7 and other Escherichia coli isolates recovered from cattle hides, feces, and carcasses

In a previous study, the seasonal prevalence was reported for stx+ Escherichia coli O157:H7 in feces and on hides and carcasses of cattle at processing. Overall, 1,697 O157:H7 isolates have now been characterized for the incidence of (i) eae(O157), hlyA, stx1, and stx2 in the recovered isolates and (ii) presumptive rough and presumptive nonmotile isolates. Seven O157:H7 isolates (0.4%) lacked stx genes, although they carried eae and hlyA. All but one of the isolates carried both eae and hlyA. Approximately two-thirds of the isolates (64% when one isolate per sample was considered) carried both stx1 and stx2. E. coli O157:H7 cells that harbored both stx1 and stx2 were more often recovered from hides in the fall (79% of the fall hide isolates) and winter (84% of the winter hide isolates) than in the spring (53%) and summer (59%). Isolates recovered from preevisceration carcasses showed a similar but not statistically significant trend. Twenty-three of the 25 O157:H7 isolates carrying stx1 but not stx2 were recovered during summer. Fifteen presumptive rough and 117 presumptive nonmotile stx+ O157:H7 isolates were recovered. Ten (67%) of the presumptive rough isolates were recovered during summer. Ninety-five of the presumptive nonmotile isolates (81%) were recovered during fall. Forty-eight percent of the false-positive isolates (175 of 363) tentatively identified as O157:H7 were O157+ H7- and lacked eae(O157), hlyA, and stx. These data suggest that in beef processing samples (i) there are minor seasonal variations in the prevalence of stx genes among E. coli O157:H7 isolates, (ii) presumptive rough and presumptive nonmotile stx+ O157:H7 isolates are present, (iii) E. coli O157:H7 isolates lacking stx genes may be rare, and (iv) O157+ H7- isolates lacking stx genes can result in many false-positive results.     

Isolation and characterization of Escherichia coli recovered from Maryland apple cider and the cider production environment

Contaminated apple cider has been implicated in several Escherichia coli O157:H7 outbreaks. In an attempt to investigate sources and modes of entry of E. coli into apple cider, samples of fresh apple, pomace, and cider and equipment and mill floor swabs were analyzed for standard plate counts (SPC), total coliforms (TC), fecal coliforms (FC), and E. coli. E. coli was isolated from 14 (33%) of 42 samples of bottled fresh cider, from food equipment in 6 (67%) of 9 mills, and from apples, pomace, or cider in 7 (78%) of 9 mills. Seventy-five E. coli isolates were further characterized for Shiga toxin-producing E. coli (STEC)-associated virulence factors, antimicrobial susceptibility, and pulsed-field gel electrophoresis (PFGE) type. No E. coli O157:H7 or other STEC was identified. Serotyping and PFGE revealed 64 distinct profiles, suggesting that recovered E. coli arose from multiple independent sources. However, on one occasion, E. coli isolated from the source apple sample was closely related to the E. coli identified in the finished cider sample. E. coli isolates were further tested for antimicrobial susceptibility to 17 antimicrobial agents of human and veterinary importance. Fourteen (19%) of the 75 isolates were resistant to at least one of the antimicrobial agents tested, and 9 (12%) were resistant to at least two of these agents. Of the resistant isolates recovered, 64% were resistant to tetracycline and 57% were resistant to streptomycin. Overall, the level of E. coli contamination in source apple samples did not differ significantly from those in samples of pomace, cider at the press, and cider entering the bottling tank; therefore, source apples cannot be dismissed as a potential contributor of E. coli to the cider-making process.     

Reduction of Escherichia coli population following treatment with bacteriocins from lactic acid bacteria and chelators

The inhibitory activity of lactocin 705/AL705 (2133 arbitrary units per ml (AU ml(-1))), two bacteriocins produced by Lactobacillus curvatus CRL705 and nisin (1066AU ml(-1)) produced by Lactococcus lactis CRL1109 in combination with chelating agents against Escherichia coli strains in TSB medium at 21 and 6 degrees C was investigated. Treatment with EDTA (500 and 1000 mm) and Na lactate (800 mm) alone produced a variable effect depending on the strain, Na lactate being inhibitory against E. coli NCTC12900 at both assayed temperatures while EDTA (1000 mm) led to its inactivation only at 6 degrees C. Direct and deferred strategies using EDTA and Na lactate showed that the direct addition of bacteriocins and chelators was not as effective as compared to deferred treatments. When the deferred treatment effectiveness was evaluated at 6 degrees C, the use of EDTA (500 and 1000 mm) and Na lactate (800 mm) in combination with lactocin 705/AL705 demonstrated to be the most inhibitory strategy against both E. coli strains. Nevertheless, treatments with chelators and bacteriocins was highly dependent upon strain sensitivity. Permeabilization of the outer membrane of E. coli strains with EDTA and Na lactate combined with lactocin 705/AL705 showed to be valuable in controlling this foodborne bacteria at low temperatures.