Ribosomal protein L4 of Lactobacillus rhamnosus LRB alters resistance to macrolides and other antibiotics

In Vitro Probiotic Characterization and Safety Assessment of Lactic Acid Bacteria Isolated from Raw Milk of Japanese-Saanen Goat (Capra hircus)

Two novel probiotic strains of lactic acid bacteria were successfully isolated from the raw milk of dairy Japanese-Saanen goats. Selection criteria for positive candidates were grown on de Man-Rogosa-Sharpe or M17 selective medium at 30, 35, or 42 °C anaerobically, and characterized based on Gram reaction, catalase test, and tolerance to low pH and bile salts. Among the 101 isolated positive candidates, two strains, YM2-1 and YM2-3, were selected and identified as Lacticaseibacillus rhamnosus using 16S rDNA sequence similarity. Culture supernatants of the two strains exhibited antipathogenic activity against Salmonella enterica subsp. enterica serovar. Typhimurium, Shigella sonnei, methicillin-resistant Staphylococcus aureus, methicillin-sensitive Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli O157. The antipathogenic activities were retained to some extent after neutralization, indicating the presence of antipathogenic substances other than organic acids in the culture supernatants. The two strains were sensitive with coincidental minimum inhibition concentrations (indicated in the parentheses hereafter) to ampicillin (0.25 μg/mL), chloramphenicol (4 μg/mL), gentamycin (4 μg/mL), kanamycin (64 μg/mL), streptomycin (16 μg/mL), and tetracycline (4 μg/mL). Furthermore, the two strains were resistant to clindamycin (16 μg/mL) and erythromycin (4 μg/mL). In addition, both YM2-1 and YM2-3 strains showed less unfavorable activities, including bile acid bioconversion, carcinogenic-related enzymes, mucin degradation, plasminogen activation, and hemolysis, than the detection limits of in vitro evaluation methods used in this study. In summary, L. rhamnosus YM2-1 and YM2-3 are highly safe and promising probiotic strains applicable in the dairy industry, and were first isolated from the raw milk of Japanese-Saanen goats.

Involvement of ClpE ATPase in Physiology of Streptococcus mutans

Streptococcus mutans, a dental pathogen, harbors at least three Clp ATPases (ClpC, ClpE, and ClpX) that form complexes with ClpP protease and participate in regulated proteolysis. Among these, the function of ClpE ATPase is poorly understood. We have utilized an isogenic clpE-deficient strain derived from S. mutans UA159 and evaluated the role of ClpE in cellular physiology. We found that loss of ClpE leads to increased susceptibility against thiol stress but not to oxidative and thermal stress. Furthermore, we found that the mutant displays altered tolerance against some antibiotics and altered biofilm formation. We performed a label-free proteomic analysis by comparing the mutant with the wild-type UA159 strain under nonstressed conditions and found that ClpE modulates a relatively limited proteome in the cell compared to the proteomes modulated by ClpX and ClpP. Nevertheless, we found that ClpE deficiency leads to an overabundance of some cell wall synthesis enzymes, ribosomal proteins, and an unknown protease encoded by SMU.2153. Our proteomic data strongly support some of the stress-related phenotypes that we observed. Our study emphasizes the significance of ClpE in the physiology of S. mutans. IMPORTANCE When bacteria encounter environmental stresses, the expression of various proteins collectively known as heat shock proteins is induced. These heat shock proteins are necessary for cell survival specifically under conditions that induce protein denaturation. A subset of heat shock proteins known as the Clp proteolytic complex is required for the degradation of the misfolded proteins in the cell. The Clp proteolytic complex contains an ATPase and a protease. A specific Clp ATPase, ClpE, is uniquely present in Gram-positive bacteria, including streptococci. Here, we have studied the functional role of the ClpE protein in Streptococcus mutans, a dental pathogen. Our results suggest that ClpE is required for survival under certain antibiotic exposure and stress conditions but not others. Our results demonstrate that loss of ClpE leads to a significantly altered cellular proteome, and the analysis of those changes suggests that ClpE's functions in S. mutans are different from its functions in other Gram-positive bacteria.