Joseph Odumeru

Irrigation water as source of foodborne pathogens on fruit and vegetables.

Awareness is growing that fresh or minimally processed fruit and vegetables can be sources of disease-causing bacteria, viruses, protozoa, and helminths. Irrigation with poor-quality water is one way that fruit and vegetables can become contaminated with foodborne pathogens. Groundwater, surface water, and human wastewater are commonly used for irrigation. The risk of disease transmission from pathogenic microorganisms present in irrigation water is influenced by the level of contamination; the persistence of pathogens in water, in soil, and on crops; and the route of exposure. Groundwater is generally of good microbial quality, unless it is contaminated with surface runoff; human wastewater is usually of very poor microbial quality and requires extensive treatment before it can be used safely to irrigate crops; surface water is of variable microbial quality. Bacteria and protozoa tend to show the poorest survival outside a human host, whereas viruses and helminths can remain infective for months to years. Guidelines governing irrigation water quality and strategies to reduce the risk of disease transmission by foodborne pathogens in irrigation are discussed.

Development of a Procedure for Discriminating among Escherichia coli Isolates from Animal and Human Sources

ABSTRACT Counts of Escherichia coli cells in water indicate the potential presence of pathogenic microbes of intestinal origin but give no indication of the sources of the microbial pollution. The objective of this research was to evaluate methods for differentiating E. coli isolates of livestock, wildlife, or human origin that might be used to predict the sources of fecal pollution of water. A collection of 319 E. coli isolates from the feces of cattle, poultry, swine, deer, goose, and moose, as well as from human sewage, and clinical samples was used to evaluate three methods. One method was the multiple-antibiotic-resistance (MAR) profile using 14 antibiotics. Discriminant analysis revealed that 46% of the livestock isolates, 95% of the wildlife isolates, and 55% of the human isolates were assigned to the correct source groups by the MAR method. Amplified fragment length polymorphism (AFLP) analysis, the second test, was applied to 105 of the E. coli isolates. The AFLP results showed that 94% of the livestock isolates, 97% of the wildlife isolates, and 97% of the human isolates were correctly classified. The third method was analysis of the sequences of the16S rRNA genes of the E. coli isolates. Discriminant analysis of 105 E. coli isolates indicated that 78% of the livestock isolates, 74% of the wildlife isolates, and 80% of the human isolates could be correctly classified into their host groups by this method. The results indicate that AFLP analysis was the most effective of the three methods that were evaluated.

Assessment of the microbiological quality of ready-to-use vegetables for health-care food services

The microbiological quality of ready-to-use (RTU) vegetables, including chopped lettuce, salad mix, carrot sticks, cauliflower florets, sliced celery, coleslaw mix, broccoli florets, and sliced green peppers was determined before and after processing. Microbial profiles were obtained 24 h after processing and on days 4, 7, and 11 after storage at 4 and 10°C to simulate temperature abuse. In addition, the microbial profiles of four RTU vegetables, coleslaw mix, salad mix, cauliflower florets, and sliced green peppers were determined 7 days after distribution to a select group of Ontario hospitals. RTU vegetables, with the exception of green peppers, showed up to a 1-log decrease in aerobic colony counts after processing. These counts increased to preprocessing levels after 4 days of storage at both 4 and 10°C. RTU vegetables stored at temperature abuse conditions (10°C)had significantly higher counts (P < 0.001) on days 4 to 11 as compared to those stored at 4°C. Green peppers had the highest bacterial counts while cauliflower and chopped lettuce had the lowest counts at both storage temperatures (P < 0.05). Increased levels of Listeria monocytogenes in RTU vegetables were associated with temperature abuse. Levels of >100 MPN/g for L. monocytogenes were detected in 8 of 120 (6.7%) samples stored at 10°C but not in 175 samples stored at 4°C after 7 days (P < 0.05). Overall, L. monocytogenes was detected in 13 of 120 (10.8%) RTU vegetables stored for up to 11 days at 10°C and 5 of 176 (2.8%) samples stored at 4°C (P < 0.05). E. coli was detected in 2 of the 120 (1.7%) processed RTU vegetables after day 7 of storage at 10°C and 1 of the 65 (1.5%) unprocessed vegetables from the same batches of vegetables used for processing. This indicator organism was not detected in RTU vegetable samples stored at 4°C or in any of the RTU vegetable samples obtained from hospital coolers. Other pathogenic bacteria, such as Salmonella spp., Campylobacter spp., Yersinia enterocolitica (serotype O:3) and verocytotoxigenic E. coli (VTEC) were not detected in any of the RTU vegetables tested, Recommendations regarding processing, distribution, and storage of these products are presented.

Survey of Ontario bulk tank raw milk for food-borne pathogens

Raw (unpasteurized) milk can be a source of food-borne pathogens. Raw milk consumption results in sporadic disease outbreaks. Pasteurization is designed to destroy all bacterial pathogens common to raw milk, excluding spore-forming bacteria and possibly Mycobacterium paratuberculosis , but some people continue to drink raw milk, believing it to be safe. Current methods for assessing the bacteriological quality of raw milk, such as aerobic plate counts, are not usually designed to detect specific pathogens. The objective of this study was to estimate the proportion of pick-ups (loads of raw milk from a single farm bulk tank) from Ontario farm bulk tanks that contained Listeria monocytogenes . Salmonella spp., Campylobacter spp., and/or verotoxigenic Escherichia coli (VTEC). Samples from 1,720 pick-ups of raw milk were tested for the presence of these pathogens, and 47 L. monocytogenes , three Salmonella spp., eight Campylobacter spp., and 15 VTEC isolates were detected, representing 2.73, 0.17, 0.47, and 0.87% of milk samples, respectively. Estimates of the proportion of theoretical tanker truck loads of pooled raw milk contaminated with pathogens ranged from a low of 0.51 % of tankers containing raw milk from 3 bulk tanks being contaminated with Salmonella spp. to a high of 34.41 % of tankers containing raw milk from 10 bulk tanks being contaminated with at least one of the pathogens. Associations between the presence of pathogens and raw milk sample characteristics were investigated. The mean somatic cell count was higher among VTEC- or L. monocytogenes -positive samples, and the mean aerobic plate count was found to be higher among L. monocytogenes -positive samples. These results confirm the presence of bacterial food pathogens in raw milk and emphasize the importance of continued diligence in the application of hygiene programs within dairies and the separation of raw milk from pasteurized milk and milk products.

Identification of contamination sources of Bacillus cereus in pasteurized milk

In order to determine the sources of Bacillus cereus in pasteurized milk, a total of 232 milk samples from various sampling points along milk processing lines and 122 environmental swabs were collected in two dairy plants between March and September, 1996. The incidence of B. cereus vegetative cells in raw milk from the plants was low (< or = 10%). However, the incidence and the average counts of B. cereus spores in the raw milk were very high and similar to those of B. cereus vegetative cells in pasteurized milk or final products after enrichment (> 80% and 1.1 x 10(5) cfu ml(-1), respectively). The incidence and average count of both vegetative cells and spores of B. cereus in environmental swabs was low. Using the microbial identification system (MIDI), a library of B. cereus fatty acid profiles comprising 229 B. cereus isolates from milk samples and environmental swabs was constructed using a critical Euclidian distance of 6.0 units as the cut-off value. Using this library, the relationship between 546 B. cereus isolates from the different sampling points along the milk processing lines and the environmental swabs was determined. Most B. cereus isolates obtained from the pasteurized milk and final products belonged to the same sub-groups as the B. cereus strains germinated from spores in raw milk. Furthermore, specific sub-groups were found in pasteurized milk, different dairy plants and at different sampling times. The results suggested that B. cereus spores in raw milk were the major source of B. cereus in pasteurized milk and that post-pasteurization contamination along the milk processing lines was possibly a minor source of B. cereus in pasteurized milk.

Effects of processing and packaging on vitamin C and β-carotene content of ready-to-use (RTU) vegetables.

High pressure liquid chromatographic methods were used for measurement of the concentration of vitamin C and β-carotene in broccoli and green pepper. The effects of processing, packaging and storage on the levels of these nutrients in both unprocessed and processed ready-to-use (RTU) vegetables were determined. Systems investigated included: (a) unpacked and pillow packaged broccoli, and (b) unpacked, pillow, partial vacuum, and total vacuum packaged green pepper. There was a statistically significant decrease in vitamin C over a 10 day storage period of unpacked and packaged vegetables including all four packaging systems (P<0.001, overall average decrease of 11%). The overall loss of β-carotene during the 10 day storage period was not statistically significant (P=0.14). Although there was a significant loss in vitamin C during storage, in most cases there was no difference in loss of vitamin C or β-carotene between the processed and unprocessed vegetables, and the packaging systems.

Microbial Survey of Selected Ontario-Grown Fresh Fruits and Vegetables

Recent produce-related outbreaks have been receiving heightened media coverage, which has increased public concern toward the safety of fresh fruits and vegetables. In response, the microbial contamination of Ontario-grown fresh fruits and vegetables was evaluated by the Ontario Ministry of Agriculture, Food and Rural Affairs during the summer of 2004. Prior to this survey, information specific to the microbial contamination of Ontario-produced fruits and vegetables was limited. This nonregulatory survey had two objectives: (i) to obtain a general microbiological profile of selected fruits and vegetables produced in Ontario and (ii) to use the information and knowledge gained from this survey to direct and support future on-farm food safety research and food safety programs to manage potential risks. In all, 1,183 samples, including muskmelon (151), scallions and green onions (173), leaf lettuce (263), organic leaf lettuce (112), head lettuce (155), parsley (127), cilantro (61), and fresh market tomatoes (141), were collected and analyzed. Samples were analyzed for Salmonella, Shigella, and generic E. coli. Enrichment cultures positive for E. coli were further assessed for verotoxigenicity. One sample each of Roma tomato and organic leaf lettuce were positive for Salmonella, with no samples yielding Shigella or verotoxigenic E. coli. The E. coli prevalence was highest in parsley (13.4%), followed by organic leaf lettuce (11.6%), leaf lettuce (6.5%), scallions (6.4%), cilantro (4.9%), muskmelon (1.3%), head lettuce (0%), and fresh market tomatoes (0%). These findings, in combination with foodborne illness data, will help target those commodities that require more focused risk mitigation efforts.

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.

Antibiotic resistance of Salmonella isolated from hog, beef, and chicken carcass samples from provincially inspected abattoirs in Ontario.

The emergence of antimicrobial-resistant Salmonella organisms, especially Salmonella Typhimurium DT104, has been reported in many countries, including the United States and Canada. The purposes of this study were to determine the antimicrobial resistance patterns of Salmonella isolated from hog, beef, and chicken carcasses from provincially inspected abattoirs in Ontario and to determine the agreement between the agar dilution method and the microbroth dilution method for measurement of antimicrobial resistance of the isolates. Antimicrobial resistance of Salmonella isolates from hogs (n = 71), beef (n = 24), and chicken (n = 295) to amikacin, ampicillin, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, streptomycin, sulfamethoxazole, and tetracycline was determined using the two methods. None of the 390 isolates were resistant to ciprofloxacin at levels of 0.125 microg/ml. All chicken and hog isolates were sensitive to amikacin, whereas all beef isolates were sensitive to both amikacin and gentamicin. Multiple antimicrobial resistance (resistance to more than one antimicrobial) was found in 29% of bovine isolates and 42% of porcine isolates using both methods for testing and in 42% by the agar dilution and 33% by the microbroth dilution methods in the chicken isolates. Overall, there was good agreement between the two test methods for resistance to most of the antimicrobials, with disagreement found in the results in 1.3% of the isolates for ampicillin and sulfamethoxazole, 8.2% for streptomycin, 5.6% for cephalothin, and 1.0% of the isolates for tetracycline. The lack of agreement between the two test methods was found mostly among the chicken isolates.

Antibiotic resistance of Campylobacter jejuni and Campylobacter coli isolated from hog, beef, and chicken carcass samples from provincially inspected abattoirs in Ontario

Campylobacterjejuni is one of the most common causes of bacterial foodborne infection in the United States, and there are reports of resistance of Campylobacter spp. to antimicrobial agents used for the treatment of gastroenteritis. The purpose of this study was to determine the antimicrobial resistance patterns of Campylobacter spp. isolated from hog, beef, and chicken carcasses from provincially inspected abattoirs in Ontario. The agar dilution method was performed to measure antimicrobial resistance of the isolates. Antimicrobial resistance of Campylobacter isolates from hogs (n = 401), beef (n = 21), and chicken (n = 435) to ampicillin, azithromycin, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gentamicin, nalidixic acid, streptomycin, and tetracycline was determined. Resistance of chicken, hog, and beef isolates was 14.3, 18.2, and 9.5% to ampicillin; 17.9, 67.3, and 38.1% to azithromycin; 0, 0.5, and 0% to chloramphenicol; 3.7, 1.2, and 0% to ciprofloxacin; 2.3, 46.6, and 4.8% to clindamycin; 6.7, 43.6, and 4.8% to erythromycin; 0.2, 0, and 0% to gentamicin; 5.1, 10.7, and 0% to nalidixic acid; 13.6, 57.4, and 4.8% to streptomycin; and 52.6, 44.1, 42.9% to tetracycline, respectively. The hog isolates had the greatest resistance to seven of the ten antimicrobials tested. Results of this study confirm the existence of antimicrobial resistance of Campylobacter to various antimicrobial agents,especially ciprofloxacin and erythromycin, commonly used for treatment of campylobacteriosis in humans.