A series of 3-oxo-C12-HSL, tetramic acid, and tetronic acid analogues were synthesized to gain insights into the structural requirements for quorum sensing inhibition in Staphylococcus aureus. Compounds active against agr were noncompetitive inhibitors of the autoinducing peptide (AIP) activated AgrC receptor, by altering the activation efficacy of the cognate AIP-1. They appeared to act as negative allosteric modulators and are exemplified by 3-tetradecanoyltetronic acid 17, which reduced nasal cell colonization and arthritis in a murine infection model.

The bovine pathogen Streptococcus uberis was assessed for biofilm growth. The transition from planktonic to biofilm growth in strain 0140J correlated with an upregulation of several gene products that have been shown to be important for pathogenesis, including a glutamine ABC transporter (SUB1152) and a lactoferrin binding protein (gene lbp; protein SUB0145).Approximately 33% of bovine mastitis cases within the United Kingdom are attributable to Streptococcus uberis, and infections can be both persistent and resistant to antimicrobial treatment (10,17). In this study, we assess the ability of S. uberis to form biofilms in vitro. We also analyze the S. uberis clinical isolate 0140J under planktonic and biofilm growth conditions in vitro by using gel electrophoresis liquid chromatography (GeLC)-tandem mass spectrometry (MS/MS) and demonstrate that the changes that 0140J undergoes in the transition from planktonic to biofilm growth include factors strongly implicated in pathogenesis.Biofilm formation by S. uberis isolates. To establish biofilm formation among different strains of S. uberis, we analyzed S. uberis isolates 0140J (a strain of high virulence for the lactating bovine mammary gland), EF20, Y38, C197C, C221, and C198 (a strain obtained from a healthy bovine mammary gland and not associated with pathogenesis) (see Table S1 in the supplemental material) in TSBM medium {tryptic soy broth without dextrose [Difco Labs], supplemented with 10 mM PIPES [piperazine-N,NЈ-bis(2-ethanesulfonic acid)], pH 6.6, and 20% [vol/vol] sterile skim milk}, using a microtiter plate biofilm formation assay (4). All isolates formed biofilms in vitro, with C198 forming the smallest biomass (Fig. 1).A previously elucidated difference between strain C198 and all other strains tested is that C198 lacks the hasAB gene cluster and is, as a consequence, acapsular (J. Leigh, personal communication). In support of capsule production being involved in 0140J biofilm growth in vitro, S. uberis capsule size has been shown to increase in the presence of bovine milkrelated constituents (12) and the addition of 20% (vol/vol) bovine milk to medium was found to promote 0140J biofilm formation in vitro (data not shown). Biofilms were grown in tube reactors (1) that were initially inoculated with S. uberis strain 0140J in TSBM for 1 h under no-flow conditions. Both biofilm and planktonic cells were grown at 37°C in TSB supplemented with 10% (vol/vol) lactose (46 g/liter). Protein extraction was carried out essentially as previously described (6). Protein samples (30 ng) were loaded onto 10% acrylamide gels (Protean III system; Bio-Rad) and stained (GelCode blue; Pierce) according to manufacturer's instructions. Gel lanes were cut into 13 to 15 equal-size gel Differential proteomic analysis of