| There are numerous traditional fermented foods in China which contain a variety of microbes. Lactic acid bacteria (LAB) are widely used in food fermentations because of their ability to improve the ?avour and nutrition of food, however, recently, their antibiotic resistance (AR) has become a focus in the food safety field all around the world. In this paper, on the basis of LAB isolated from Chinese fermented foods, their AR was investigated systematically first and then functional strains with the capacity to produce highγ-aminobutyric acid or extracellular polysaccharides were screened out respectively. The main research work and results were listed below:Firstly, AR of LAB from11 Chinese fermented foods was fully analyzed. 7 clinically important antibiotics were employed to assess the resistance level of LAB and the ratio of resistant LAB. The result showed that different levels of antibiotic reisitant LAB were observed in various food samples, and their percentage in all LAB strains was dependent on the origin and type of foodstuff, environment and procedure of food processing. Then 14 resistant LAB were chosed for further investigation, and it was proved that all of them possess multi-resistance, and some hyper resistances were revealed. PCR was employed to clone the known genes responsible to those ARs. Some AR genes existed in genome or pasmid DNA within some of the 14 LAB while others were not detected. In addition, some resistant plamid isolated from the 14 strains were proved to have the potential to transfer horizontally between different LAB strains.Secondly, 257 LAB were isolated from 22 Chinese fermented foods and GABA-producing were tested by paper chromatography. 5 GABA-producing LAB were obtained and they were identified to be 1 Lactobacillus fermentium, 1 Enterococcus faecium and 3 Lb. plantarum according to their DNA sequences. Among them, Lb. fermentium MT133 produced the maximun GABA which was 20.57 g/L after 84 h's fermentation. Later, gadB, the key gene in the production of GABA was cloned from Lb. fermentium MT133 and its sequence was further studied.Thirdly, high EPS-producing LAB were screened from 257 LAB strains by colony observation and thread-drawing metherd. After DNA identification, they turned out to be 1 Leuconostosm mesenteroides, 1 Lb. plantarum and 2 Streptococcus thermophilus. Ln. mesenteroides MT257 produced slime around its colony and the other three can produced 5-160 mm ropy strand when tested by thread-drawing metherd. Later, effects of temperature and carbon source on EPS production were studied. All LAB produced the most EPS under optimum growth temperature while ropier EPS formed under low temperature (25℃). The influence of carbon source was much complicated. Lactocse was the best carbon source for MT257, HII050 and HI060 to produce EPS and sucrose was the best for SHC096. The EPS produced by MT257 could reach as many as 350 mg/L. In this paper, we preliminary analyzed the diversity of LAB as well as their functions in different Chinese fermented foods. We found that some LAB acted as health promoter while some could bring hidden dangers to the food safety. All we did provide important theoretical references for safety assessment and microbe improvement of Chinese fermented foods and also has application prospect.
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