Antibacterial activity of selected plant essential oils against Escherichia coli O157:H7.

AIMS: To quantify the antibacterial properties of five essential oils (EO) on a non-toxigenic strain of Escherichia coli O157:H7 in the presence and absence of a stabilizer and an emulsifier and at three different temperatures. METHODS AND RESULTS: Five EOs known to exhibit antibacterial properties were screened by disc diffusion assay and the most active were selected for further study in microdilution colorimetric assays. Oregano (Origanum vulgare) and thyme (Thymus vulgaris; light and red varieties) EO had the strongest bacteriostatic and bactericidal properties, followed by bay (Pimenta racemosa) and clove bud (Eugenia caryophyllata synonym: Syzygium aromaticum) EO. Oregano oil was colicidal at 625 microl l(-1) at 10, 20 and 37 degrees C. The addition of 0.05% (w/v) agar as stabilizer reinforced the antibacterial properties, particularly at 10 degrees C, whereas 0.25% (w/v) lecithin reduced antibacterial activity. Scanning electron micrographs showed extensive morphological changes to treated cells. CONCLUSIONS: Oregano and thyme EO possess significant in vitro colicidal and colistatic properties, which are exhibited in a broad temperature range and substantially improved by the addition of agar as stabilizer. Bay and clove bud EO are less active. Lecithin diminished antibacterial properties. The bactericidal concentration of oregano EO irreversibly damaged E. coli O157:H7 cells within 1 min. SIGNIFICANCE AND IMPACT OF THE STUDY: Oregano and light thyme EO, particularly when enhanced by agar stabilizer, may be effective in reducing the number or preventing the growth of E. coli O157:H7 in foods.

Comparison of the sensitivity of manual and automated immunomagnetic separation methods for detection of Shiga toxin-producing Escherichia coli O157:H7 in milk.

AIM: To determine the sensitivity of methods for detection of injured and uninjured Escherichia coli O157:H7 (E. coli O157) in raw and pasteurized milk. METHODS AND RESULTS: Raw milk, pasteurized milk with 1.5% fat content and pasteurized milk with 3.5% fat content were spiked with E. coli O157 at low levels. The samples were enriched in modified tryptone soya broth with novobiocin (mTSBn) at 37 degrees C. Aliquots of the enriched culture were analysed either by manual immunomagnetic separation (MIMS) and culturing on sorbitol MacConkey agar with or without cefixime and potassium tellurite (SMACct or SMAC), or by automated immunomagnetic separation and integrated ELISA (EiaFosstrade mark). Uninjured E. coli O157 organisms were detected in milk by both methods at 1 cfu 10 ml-1 sample). Injured organisms were detected at levels of about 4 cfu 10 ml-1 sample. Direct enrichment in mTSBn (22 h incubation) showed better sensitivity for injured cells than enrichment in buffered peptone water (BPW, 22 h incubation), or in a two-step enrichment consisting of BPW (6 h, 37 degrees C) and mTSBn (16 h, 37 degrees C), successively. CONCLUSIONS: The methods showed equal sensitivity in that they were both able to detect 1 cfu 10 ml-1 milk sample. Injured organisms can be detected and isolated at a level almost as low as this. A resuscitation step is not recommended for the detection and isolation of injured and non-injured E. coli O157 from milk. SIGNIFICANCE AND IMPACT OF THE STUDY: Due to the dilution of contamination in the bulk tank, analysis of milk for the presence of E. coli O157 requires a very sensitive method. Both methods described here are useful for such analysis.

Control of VTEC in Dutch livestock and meat production.

The Dutch government and the meat industry, recognising VTEC as having important public health, meat quality and economic implications, have taken a number of initiatives within the last 5 years to control VTEC in livestock and meat. These initiatives, brought together last year in a 'Masterplan VTEC', include short-, middle- and long-term priorities. Short-term priorities include advice on interventions in the cases of an outbreak of VTEC associated with a cattle herd, the implementation of handbooks for Good Manufacturing Practice (GMP) in slaughterhouses and deboning plants, and the execution of an action programme on zero-tolerance to faecal contamination of carcasses. Mid-term activities include surveillance of the occurrence of VTEC and other enteropathogens in livestock and meat, and the investigations of VTEC population dynamics in dairy farms, transportation and farm hygiene. In the longer term, this programme aims to produce a system of Integrated Quality Assurance, consolidating effective measures to control VTEC in Dutch livestock and meat, and integrating emerging means for control and prevention.

Survival of Escherichia coli O157:H7 ATCC 43895 in a model apple juice medium with different concentrations of proline and caffeic acid.

The effects of proline and caffeic acid on the survival of Shiga toxin-producing Escherichia coli (STEC) O157:H7 strain ATCC 43895 in a model apple juice medium were studied. It is hypothesized that the inhibitory effect of caffeic acid may explain why almost all outbreaks of STEC O157:H7 infections linked to apple juice or cider have occurred in October or November.

Use of 8-hydroxyquinoline-beta-D-glucuronide for presumptive identification of Shiga toxin-producing Escherichia coli O157.

8-hydroxyquinoline-beta-D-glucuronide (HQG) was used to improve the presumptive identification of Shiga toxin-producing Escherichia coli O157 (STEC O157) on sorbitol MacConkey agars (SMAC). Advantages of HQG are (i) that it is less expensive than 5-bromo-4-chloro-3-indoxyl-glucuronide; (ii) that it is visible in normal daylight and (iii) that it does not diffuse into the agar like 4-methylumbelliferryl-beta-D-glucuronide (MUG). Sixteen STEC O157 isolates, 91 bovine mastitis-associated E. coli isolates and 222 faecal E. coli isolates from apparently healthy cattle were used in this study. 4-methylumbelliferryl-beta-D-glucuronide detected beta-glucuronidase activity in more isolates than HQG (P < 0.05). On SMAC with HQG, cefixime and tellurite all STEC O157 isolates grew as cream-coloured colonies (100% sensitivity), whereas all non-STEC O157 E. coli except one grew either not at all or as purple or black colonies (99.7% specificity). No difference was found between faecal and mastitis isolates for the proportion of isolates that hydrolysed HQG or MUG or fermented sorbitol. However, significantly more mastitis isolates were able to grow in the presence of the cefixime-tellurite supplement. 8-Hydroxyquinoline-beta-D-glucuronide is a useful substrate for the identification of STEC O157 on SMAC.

Campylobacter infections in fattening pigs; excretion pattern and genetic diversity.

The excretion of campylobacter by eight individually housed fattening pigs was monitored during 15 weeks. Rectal faeces samples were collected six times from these pigs and twice from their mothers (seven sows). Campylobacter was cultured from these samples on Preston medium. In some pigs, samples positive for campylobacter alternated with negative samples. Campylobacter was detected in at least four of the six samples collected per fattening pig. The average campylobacter count per sampling showed a decreasing trend (P < 0.001). Of the seven sows, six were shown to excrete campylobacter. Campylobacter isolates of pigs and sows were typed using the Enterobacterial Repetitive Intergenic Consensus Polymerase Chain Reaction (ERIC-PCR); 28 different campylobacter types were distinguished. Up to five different types were isolated from single faeces samples. Individual porkers could harbour up to eight types during their fattening period. The three types most frequently isolated from the fattening pigs were also present in the sows.