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\ud strains isolated from Parmigiano Reggiano cheese, of Lactobacillus GG and of the type strain\ud L. rhamnosus DSM 20021. Antimicrobial susceptibility was determined by the disc diffusion\ud method on 41 antibiotics. Inhibition zone diameter was carefully measured and the results (the mean\ud of four determinations) were expressed in terms of resistance or susceptibility. All the strains isolated\ud from cheese showed resistance to six antibiotics (cefixime, vancomycin, neomycin, enoxacin,\ud pefloxacin and sulphamethoxazole plus trimethoprim). The strain DSM 20021T was resistant to\ud nine antibiotics (the previous six plus cephalexin, bacitracin and lincomycin), while the commercial\ud strain L. GG showed resistance to eighteen antibiotics. A high strain-specific resistance to different\ud antibiotics was ascertained in Lactobacillus rhamnosus isolated from cheese. The results obtained\ud in this study confirm that antibiotic resistance is a very important feature in the selection of potentially\ud probiotic lactic acid bacteria

In this study, for the first time, we examined some of the physico-chemical properties of the cell surface of Akkermansia muciniphila DSM 22959, comparing it with those of Lactobacillus rhamnosus GG—one of the most extensively studied probiotic microorganisms. In particular, hydrophobicity, auto-aggregation, co-aggregation, and biofilm formation were investigated. In addition, antibiotic susceptibility, co-culture, and antimicrobial activity of the two strains were compared. Hydrophobicity was evaluated using xylene and toluene, showing that A. muciniphila DSM 22959 possessed moderate hydrophobicity. A. muciniphila showed a faster and higher auto-aggregation ability than Lb. rhamnosus GG, but a lower aptitude in biofilm formation. In the co-aggregation test, the best performance was obtained by Lb. rhamnosus GG. Regarding the susceptibility to antibiotics, the differences between the two strains were remarkable, with A. muciniphila DSM 22959 showing resistance to half of the antibiotic tested. Interesting results were also obtained with regard to the stimulating effect of Lb. rhamnosus GG on the growth of A. muciniphila when co-cultured.