Aims: The behaviour of Escherichia coli O157:H7 was studied during the manufacture and ripening of a smear-ripened cheese produced from raw milk. Methods and Results: Cheese was manufactured on a laboratory scale using milk (20 l) inoculated with E. coli O157:H7, and enumeration was carried out using CT-SMAC. From an initial level of 1á52 0á03 log cfu ml ±1 in the milk (34 2 cfu ml ±1 ), the numbers increased to 3á4 0á05 log cfu g ±1 in the cheese at day 1. During ripening, the numbers decreased to <1 cfu g ±1 and <10 cfu g ±1 in the rind and core, respectively, after 21 days, although viable cells were detected by enrichment after 90 days. The presence of E. coli O157:H7 in the cheese was con®rmed by latex agglutination and by multiplex PCR. Conclusions:The results indicate that the manufacturing procedure encouraged substantial growth of E. coli O157:H7 to levels that permitted survival during ripening and extended storage. Signi®cance and Impact of the Study: The presence of low numbers of E. coli O157:H7 in milk, destined for raw milk cheese manufacture, could constitute a threat to the consumer. INTRODUCTIONSince its identi®cation as a human pathogen in 1982 (Riley et al. 1983), Escherichia coli O157:H7 has become a pathogen of major concern for the food and dairy industries because of it's ability to cause severe illness, in particular, haemorrhagic colitis, haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Several well documented food-borne outbreaks, such as that in Scotland in 1996±97, have heightened public awareness of food as a vehicle for transmission of this pathogen.Many outbreaks of E. coli O157:H7-related food-borne illness have been linked with the consumption of contaminated meat, since the intestinal tract of cattle is the primary reservoir for this pathogen (Willshaw et al. 1994;Zhao et al. 1995). Other foodstuffs, however, have been implicated in many outbreaks, including water, lettuce, alfalfa sprouts and apple juice (Buchanan and Doyle 1997). The consumption of unpasteurized milk and dairy products manufactured from unpasteurized milk has also been associated with transmission of E. coli O157:H7 (CDSC 1998; 1999a,b). In 1999, over 11% of the total number of reported cases of infection caused by E. coli O157:H7 in England and Wales were due to dairy products (CDSC 2000). In many parts of Europe, indigenous cheeses manufactured from unpasteurized milk are consumed, giving rise to concern that these products may be a threat to consumer safety as a result of the presence of pathogens such as E. coli O157:H7.The ability of verotoxigenic E. coli to grow and survive during the manufacture of fresh (Arocha et al. 1992), hard (Reitsma and Henning 1996) and Camembert (Ramsaran et al. 1998) cheese has been investigated. In fresh cheese, E. coli O157:H7 grew from an initial level of about 10 5 cfu ml ±1 to ®nal numbers of about 10 7 cfu g ±1 during the manufacture of cottage cheese. However, during the heating phase, total inactivation occurred. During the manufacture ...
Thirty-three putative inhibitor-producing lactic acid bacteria (LAB) were isolated from malted barley based on their ability to inhibit groivth oftioo indicator strains. Eleven of the inhibitorproducing LAB produced an antimicrobial activity which zvas active across a wide pH range, relatively insensitive to heat treatment rohile sensitive to treatment ivith proteolytic enzymes indicating that the inhibitory compounds are proteinaceous in nature and therefore bacteriocinlike inhibitory substances. Ten of these eleven malt isolates were observed to secrete the inhibitory compounds into the cell-free supernatant with optimal production occurring in the late exponential growth phase. The inhibitory spectra of these isolates included various Grampositive bacteria among which a variety of beer-spoiling bacteria.
The direct detection and estimation of concentration of Escherichia coli O157:H7 down to 1 CFU/g of cheese was achieved by conventional plating techniques. Cheese was manufactured with unpasteurized milk inoculated with E. coli O157: H7 at 34 +/- 3 CFU/ml. The numbers of E. coli O157:H7 were monitored during cheese ripening by plating on sorbitol MacConkey agar supplemented with cefixime and potassium tellurite (CT-SMAC) and on CT-O157:H7 ID medium. Using the pour plate method, E. coli O157:H7 colonies could easily be distinguished from non-O157:H7 colonies on CT-O157:H7 ID medium but not on CT-SMAC. Higher numbers of E. coli O157:H7 were detectable with O157:H7 ID medium. Latex agglutination and PCR were used to confirm the identification of typical E. coli O157:H7 colonies, and nontypical colonies as not being E. coli O157:H7. As few as 1 CFU/g of cheese could be detected. E. coli O157:H7 also was detected in deliberately contaminated milk at concentrations as low as 4 CFU/10 ml.
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