Coccoid forms in cultures of a strain of the enteric pathogen Campylobacter jejuni were investigated. A culture containing 100% coccoid forms was non-viable. Coccoid forms had a lesser content of cytoplasmic components and nucleic acids than rods of C. jejuni. During the conversion to coccoid forms nucleotides leaked from the cells. The results of treatments with ionic and non-ionic detergents, and lysozyme and ethylenediaminetetraacetic acid indicated a changed cell wall in coccoid forms compared with rods. Using rate-zonal centrifugation coccoid forms were found to be less dense than rods. The results of this study indicate that the coccoid form of C. jejuni ATCC 29428 is a degenerate cell form which is undergoing cellular degradation.

Conditions influencing the conversion of oxygen into toxic derivatives in media were investigated for their effects on production of coccoid forms in cultures of the enteric pathogen Campylobacter jejuni. Compared with stored media, production of coccoid forms was less on freshly prepared media. Whether freshly prepared or stored before use, brucella agar media produced the fewest coccoid forms under the test conditions. Addition of supplements used as detoxifying agents minimized production of these forms on media but antibiotic formulations used in selective media did not influence production of coccoid forms. Furthermore, the type of incubation atmosphere and the strain of C. jejuni influenced the proportions of coccoid forms in cultures. It was deduced from electron microscopy observations during prolonged incubation of cultures that the process of conversion to coccoid forms involves a loss of spiral morphology, a shortening of the cell and retraction of the cytoplasm towards a cell terminal region. Coccoid forms and some intermediate forms in thin sections were found to lack cell integrity. It is concluded that coccoid form production in cultures is a degenerate response to toxic oxygen derivatives in cultures.

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 ...

Many literature reports have cited the importance of the rehydration conditions of lyophilized cultures in determining viability. The rate of rehydration and the volume of fluid used have been identified as two important factors. One possible means of controlling these is by immobilizing the cells before lyophilization within a gel matrix in which the subsequent rehydration rate and fluid volume would be controlled by the properties of the gel. In this study Lactobacillus plantarum was immobilized and lyophilized in Ca-alginate beads in which 1 M glycerol or 0.75 M adonitol with skim milk were incorporated as a cryoprotectant. The properties of these Ca-alginate beads were examined before and after lyophilization and rehydration. The beads incorporating glycerol were smaller and stronger than those with adonitol. After lyophilization, size decreased and strength increased but to a greater extent in the beads with glycerol, indicating that the microenvironment within the two bead types was probably different. The protective effect of the bead microenvironment on immobilized L. plantarum was also examined. Lyophilization and rehydration within the alginate beads with either polyol yielded higher survival rates than that attained with free cell cultures during rehydration in optimal or suboptimal conditions. During rehydration under suboptimal conditions, the immobilized cell survival was greatest when 0.75 M adonitol was the incorporated cryoprotectant.

Factors influencing the production of coccoid forms in cultures and suspensions of a strain of the enteric pathogen Campylobacter jejuni during storage in air were investigated. Addition of blood or a supplement containing ferrous sulphate, sodium metabisulphite and sodium pyruvate minimized conversion of rods to coccoid forms in cultures. Exposure of cultures to light during storage in air increased the rate of production of coccoid forms. Ultraviolet radiation was shown to effect the viability of cells in suspensions but the increase in production of coccoid forms was low after irradiation. The presence of hydrogen peroxide and its dissociation products in bacterial suspensions increased conversion to coccoid forms. Addition of active superoxide dismutase, a superoxide anion scavenging enzyme, minimized production of coccoid forms in suspensions stored in air. Coccoid forms contained a lower level of superoxide dismutase than rods. It is deduced that a decreased level of the enzyme in cells is linked with production of coccoid forms.