This study aimed to compare phenotypic and genetic characteristics of Lactobacillus rhamnosus strains isolated at the end of the ripening of Parmigiano Reggiano cheese and to investigate an important prerequisite of probiotic interest, such as the capability to survive at low pH and in presence of bile salts. The use of API 50 CH, RAPD-PCR analysis and species-specific PCR allowed to ascertain the identity of 63 L. rhamnosus strains. Three L. rhamnosus strains isolated from Parmigiano Reggiano cheese, L. rhamnosus ATCC 7469T and the commercial strain L. GG were assayed to estimate the resistance to various stress factors reproducing in vitro some conditions of the gastro-intestinal environment such as low pH and different amounts of bile salts and acids. The behaviour of almost all the tested strains isolated from Parmigiano Reggiano cheese resulted analogous to that showed by L. GG.

-This work aimed to evaluate the antibiotic susceptibility of 63 Lactobacillus rhamnosus strains isolated from Parmigiano Reggiano cheese, of Lactobacillus GG and of the type strain L. rhamnosus DSM 20021. Antimicrobial susceptibility was determined by the disc diffusion method on 41 antibiotics. Inhibition zone diameter was carefully measured and the results (the mean of four determinations) were expressed in terms of resistance or susceptibility. All the strains isolated from cheese showed resistance to six antibiotics (cefixime, vancomycin, neomycin, enoxacin, pefloxacin and sulphamethoxazole plus trimethoprim). The strain DSM 20021 T was resistant to nine antibiotics (the previous six plus cephalexin, bacitracin and lincomycin), while the commercial strain L. GG showed resistance to eighteen antibiotics. A high strain-specific resistance to different antibiotics was ascertained in Lactobacillus rhamnosus isolated from cheese. The results obtained in this study confirm that antibiotic resistance is a very important feature in the selection of potentially probiotic lactic acid bacteria.Lactobacillus rhamnosus / lactic acid bacteria / antibiotic susceptibility / cheese / probiotic Résumé -Sensibilité aux antibiotiques de souches de Lactobacillus rhamnosus isolées du fromage Parmigiano Reggiano. Le but de cette étude était l'évaluation de la sensibilité aux antibiotiques de 63 souches de Lactobacillus rhamnosus isolées du fromage Parmigiano Reggiano, de la souche Lactobacillus GG et de la souche type de L. rhamnosus DSM 20021. La sensibilité ou la résistance à 41 antibiotiques de ces 65 souches de L. rhamnosus a été déterminée avec le test de diffusion de disque en gélose. Les diamètres des zones d'inhibition, mesurés avec précision, ont permis d'individualiser pour chaque antibiotique testé les souches résistantes et celles sensibles. Toutes les souches isolées du fromage se sont avérées résistantes à six antibiotiques (céfixime, vancomycine, néomycine, enoxacine, péfloxacine et triméthoprime + sulfaméthoxazole). La souche type DSM 20021 T était résistante à neuf antibiotiques (les six précédents plus cefalexine, bacitracine et lincomycine), tandis que la souche commerciale L. GG a montré une résistance à 18 antibiotiques. Une résistance souche-spécifique à différents antibiotiques a été montrée pour les souches de Lactobacillus rhamnosus isolées du fromage. Les résultats obtenus dans cette étude ont confirmé que la résistance aux antibiotiques est une caractéristique très importante pour sélectionner les bactéries lactiques potentiellement probiotiques. Lactobacillus rhamnosus

Lactic acid fermentation of cereal flours resulted in a 100 (rye), 95-100 (wheat), and 39-47% (oat) reduction in phytate content within 24 h. The extent of phytate degradation was shown to be independent from the lactic acid bacteria strain used for fermentation. However, phytate degradation during cereal dough fermentation was positively correlated with endogenous plant phytase activity (rye, 6750 mU g(-1); wheat, 2930 mU g(-1); and oat, 23 mU g(-1)), and heat inactivation of the endogenous cereal phytases prior to lactic acid fermentation resulted in a complete loss of phytate degradation. Phytate degradation was restored after addition of a purified phytase to the liquid dough. Incubation of the cereal flours in buffered solutions resulted in a pH-dependent phytate degradation. The optimum of phytate degradation was shown to be around pH 5.5. Studies on phytase production of 50 lactic acid bacteria strains, previously isolated from sourdoughs, did not result in a significant production of intra- as well as extracellular phytase activity. Therefore, lactic acid bacteria do not participate directly in phytate degradation but provide favorable conditions for the endogenous cereal phytase activity by lowering the pH value.

No abstract

One hundred eighty four strains belonging to the species Lactobacillus casei, L. paracasei and L. rhamnosus were screened for their ability to grow under aerobic conditions, in media containing heme and menaquinone and/or compounds generating reactive oxygen species (ROS), in order to identify respiratory and oxygen-tolerant phenotypes. Most strains were able to cope with aerobic conditions and for many strains aerobic growth and heme or heme/menaquinone supplementation increased biomass production compared to anaerobic cultivation. Only four L. casei strains showed a catalase-like activity under anaerobic, aerobic and respiratory conditions and were able to survive in presence of H2O2 (1 mM). Almost all L. casei and L. paracasei strains tolerated menadione (0.2 mM) and most tolerated pyrogallol (50 mM), while L. rhamnosus was usually resistant only to the latter compound. This is the first study in which an extensive screening of oxygen and oxidative stress tolerance of members of the L. casei group has been carried out. Results allowed the selection of strains showing the typical traits of aerobic and respiratory metabolism (increased pH and biomass under aerobic or respiratory conditions) and unique oxidative stress response properties. Aerobic growth and respiration may confer technological and physiological advantages in the L. casei group and oxygen-tolerant phenotypes could be exploited in several food industry applications.