COLIFORM CONTENT OF FROZEN BLANCHED VEGETABLES PACKED IN THE UNITED STATES

Microbiological and metal contamination of watercress in the Wellington region, New Zealand-2000 survey

OBJECTIVES

To investigate potential microbiological and metal contamination of watercress and to assess the public health risks associated with harvesting and consumption of watercress.

METHOD

During March and April 2000, samples were taken from 11 known or potential watercress collection sites in the Wellington region. Microbiological testing included bacterial counts for presumptive and faecal coliforms (watercress); total coliforms (growing water); and Escherichia coli (E. coli) and presence/absence tests for Campylobacter species (growing water and watercress). Watercress concentrations of a range of metals were also measured.

RESULTS

All of the sites showed significant levels of E. coli in samples of both watercress and water. The E. coli levels in water were well above recommended freshwater recreational contact safety guidelines at most sites. Campylobacter was detected in the growing waters at all sites (80% of the samples) and in 11% of the watercress samples. Mean metal concentrations in watercress did not exceed the NZ Food Regulations (1984) levels at any of the sites. However, lead concentrations at the urban sites and one of the semi-urban sites would have exceeded the new Australia New Zealand Food Standards Code maximum levels (2003).

CONCLUSIONS AND IMPLICATIONS

The consumption of raw watercress contaminated with enteric pathogens could potentially cause serious gastrointestinal illness (e.g. campylobacteriosis) and people gathering watercress could also be at risk of infection from contact with contaminated surface waters.

A study of U.S. orchards to identify potential sources of Escherichia coli O157:H7

The association of unpasteurized apple cider with Escherichia coli O157:H7 foodborne illness has led to increased interest in potential reservoirs of this pathogen in the orchard. Fourteen U.S. orchards were surveyed in autumn 1999 to determine the incidence and prevalence of E. coli O157:H7, E. coli, total aerobic microflora, and yeasts and molds. Fruit samples (n = 63) (eight apple and two pear varieties) and soil, water, and fecal samples were collected. Samples were plated on (i) tryptic soy agar for total mesophilic aerobic count, (ii) E. coli and coliform Petrifilm for total coliforms and E. coli, and (iii) yeast and mold Petrifilm. Samples positive for coliforms and E. coli were enriched and tested for E. coli O157:H7. Fruit was also tested for internalization of microflora by aseptically removing the core, stem, and calyx areas, and the individual sections were assessed for the categories of microflora listed above. E. coli was detected in soil and water and in 6% of fruit samples (three pear samples and one apple sample), generally collected from areas previously designated as high risk in this study. However, no E. coli O157:H7 was found. Coliforms were found in 74% of fruit samples and were internalized in the cores of 40% of fruit tested. Yeasts and molds were internalized in 96.7% of samples and aerobic bacteria in 89.6%. E. coli was not found to be internalized. Total aerobic counts and total coliforms were higher in dropped and damaged fruit (P < 0.05). Findings suggest that dropped or damaged fruit should not be included in fruit designated for the production of unpasteurized juice or for the fresh or fresh-cut market. In addition, orchards should be located away from potential sources of contamination, such as pastures.

Coliforms in processed mango: significance and control

The aims of this investigation were to enumerate coliforms in fresh mangoes, puree, cheeks, and cheeks-in-puree in order to determine the source of these organisms in the processed products, to determine methods for their control, and to identify coliforms isolated from cheeks-in-puree to determine whether they have any public health significance. Product from four processors was tested on two occasions. The retail packs of cheeks-in-puree having the highest coliform counts were those in which raw puree was added to the cheeks. Coliform counts in these samples ranged between 1.4 x 10(3) and 5.4 x 10(4) cfu/g. Pasteurisation reduced the coliform count of raw puree to < 5 cfu/g. Forty-seven percent of the 73 colonies, isolated as coliforms on the basis of their colony morphology on violet red bile agar, were identified as Klebsiella pneumoniae using the ATB 32E Identification System. Klebsiella strains were tested for growth at 10 degrees C, faecal coliform response, and fermentation of D-melizitose, to differentiate the three phenotypically similar strains, K. pneumoniae, K. terrigena and K planticola. Results indicated that 41% of K. pneumoniae isolates gave reactions typical of K. pneumoniae. A further 44% of strains gave an atypical reaction pattern for these tests and were designed 'psychrotrophic' K. pneumoniae. Klebsiella pneumoniae counts of between 2.1 x 10(3) and 4.9 x 10(4) cfu/g were predicted to occur in the retail packs of mango cheeks-in-puree produced by the processors who constituted this product with raw puree. In view of the opportunistic pathogenic nature of K. pneumoniae, its presence in these products is considered undesirable and steps, such as pasteurisation of puree, should be taken in order to inactivate it.

Microbiological quality of frozen cauliflower, corn, and peas obtained at retail markets

The microbiological quality of blanched frozen cauliflower, cut corn, and peas at the retail level was determined. At 35 degrees C, mean aerobic plate count (APC) values for cauliflower, corn, and peas, respectively, were 30,000, 6,100, and 4,700 per g; at 30 degrees C, the mean APC values were 45,000, 8,500, and 6,800 per g, respectively. Geometric means for coliform, Escherichia coli, and Staphylococcus aureus counts for all three vegetables were less than 10 per g.