Regardless of their targets and modes of action, subinhibitory concentrations of antibiotics can have an impact on cell physiology and trigger a large variety of cellular responses in different bacterial species. Subinhibitory concentrations of β-lactam antibiotics cause reactive oxygen species production and induce PolIV-dependent mutagenesis in Escherichia coli. Here we show that subinhibitor...

The effects of subinhibitory concentrations of azithromycin (CP-62,993) on the piliation and attachment properties of Neisseria gonorrhoeae were examined. Subinhibitory concentrations of azithromycin significantly reduced the percentage of gonococci that expressed assembled pili on their surfaces by decreasing pilin subunit synthesis and substantially decreased gonococcal adherence to human muc...

OBJECTIVES To investigate the effect of subinhibitory concentrations of cell wall active antibiotics on virulence gene expression and biofilm formation in Staphylococcus aureus Newman and in laboratory strains. METHODS Promoter regions of spa, lukE and agr RNAIII were cloned upstream of a modified luxABCDE reporter. Using disc diffusion assays, the effects of antibiotics were observed on gene...

Streptomycin at subinhibitory concentrations was found to inhibit quorum sensing in Acinetobacter baumannii. Conditioned medium prepared by growth of A. baumannii in the presence of subinhibitory concentrations of streptomycin exhibited reduced activation of two quorum-sensing-regulated genes, abaI, encoding an autoinducer synthase, and A1S_0112. The reduced expression of AbaI resulted in great...

Thirty clinical isolates of Mycobacterium tuberculosis, 20 of which were multidrug-resistant (MDR), were tested for susceptibility to different combinations of amoxycillin, clavulanic acid and subinhibitory concentrations of ethambutol. beta-Lactamase production was assessed semiquantitatively with the nitrocefin method and susceptibility testing was performed with the BACTEC method. All isolat...

OBJECTIVES Since biofilm formation is the hallmark of Enterococcus faecalis isolates, the aim of this study was to quantify biofilm formation in the presence of subinhibitory concentrations of tigecycline. METHODS Interference of tigecycline on biofilm formation was spectrophotometrically quantified using 20 biofilm-producing E. faecalis isolates with tigecycline MICs of 0.12 (8 strains) or 0...

OBJECTIVES Large amounts of biocides are used to reduce and control bacterial growth in the healthcare sector, food production and agriculture. This work explores the effect of subinhibitory concentrations of four commonly used biocides (ethanol, hydrogen peroxide, chlorhexidine digluconate and sodium hypochlorite) on the conjugative transposition of the mobile genetic element Tn916. METHODS ...

Nowadays, the emergence and spread of antibiotic resistance have become an utmost medical and economical problem. It has also become evident that subinhibitory concentrations of antibiotics, which pollute all kind of terrestrial and aquatic environments, have a non-negligible effect on the evolution of antibiotic resistance in bacterial populations. Subinhibitory concentrations of antibiotics h...

BACKGROUND Natural compounds with anti-microbial properties are attractive reagents to reduce the use of conventional antibiotics. Carvacrol, the main constituent of oregano oil, inhibits the growth of a variety of bacterial foodborne pathogens. As concentrations of carvacrol may vary in vivo or when used in animal feed, we here investigated the effect of subinhibitory concentrations of the com...