Are glycopeptide-resistant enterococci in animals a threat to human beings?
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A rapid and reliable polymerase chain reaction (Specific and Random Amplification (SARA)-PCR) has been developed to identify enterococcal species and to detect the vanA gene in one single reaction. This technique was based on the use of the primer set previously designed to amplify a part of the vanA gene (Dutka-Malen et al., J. Clin. Microbiol., 33 (1995) 24-27). In the chosen low stringency conditions complex patterns were obtained, with a sharp band of approximately 700 bp in cases where the vanA gene was present. Discrimination at the species and strain level was achieved by applying the SARA-PCR assay to a collection of 55 enterococcal isolates and type strains. Simultaneously the vanA gene was detected in all strains showing high resistance to vancomycin.
Enterococcus faecalis FAIR E-239, growing on glucose plus citrate, metabolized citrate at pH 6.5 or 7.5, but only when glucose had been exhausted; it did not metabolize citrate at pH 5.5 or 8.5. When grown on citrate only, the strain metabolized citrate at all pH values, and two growth rates were apparent. Citrate was mainly metabolized during the second, much slower growth rate. Glucose also inhibited citrate metabolism by E. faecalis FAIR E-237 and FAIR E-259 and Enterococcus faecium FAIR E-338 and FAIR E-371. Glucose-grown resting cells were unable to metabolize citrate. Citrate-grown resting cells had a pH optimum of 4.7 for citrate metabolism but also metabolized significant amounts of citrate at pH 4.2 and 6.5. Resting stationary phase cells used citrate more rapidly than resting log phase cells. Citrate metabolism was faster at citrate levels <10 mM than above 10 mM. These results suggest that some form of catabolite repression is occurring.
Particular micro-organisms such as enterococcal strains are used as probiotics in feed. Observations indicate a positive effect of such strains on the gut flora, especially for young animals or during feed transition phases. This favourable effect is perceived by the farmers as a means of maintenance of the health status of the animals (e.g. less diarrhoea) and results in significant improvement of animal performance. Micro-organisms have been used since the end of the 1980s in animal feeds and were strictly regulated in 1993, when they were introduced under the scope of Council Directive 70/524/EEC of 23 November 1970 on additives in animal nutrition on feed additives. After a transition period, which ended in the year 2000, every microbial strain must now be assessed by the EU bodies and authorised by a Commission Regulation, before it can be placed on the market for use in feedingstuffs. Council Directive 70/524/EEC on feed additives is based on three main principles: (1) pre-market authorisation, (2) positive list principle, and (3) thorough risk assessment of the effect of a particular strain on human and animal health as well as on the environment. Therefore, before introducing a new enterococcal strain preparation or promote a new use of an approved product, a dossier has to be submitted to the authorities, following the guidelines, as published in Commission Directive 94/40/EEC [Commission Directive 94/40/EC of 22 July 1994 amending Council Directive 87/153/EEC fixing guidelines for the assessment of additives in animal nutrition]. These guidelines contain detailed evaluation methods. The safety requirements refer to (1) the target animal categories, (2) the consumer and the environment (presence of toxins and virulence factors as well as antibiotic resistance and transferability are assessed), and (3) the workers, based on requirements of Council Directive 89/391/EEC.