Routine antibiotics susceptibility testing still relies on standardized cultivation-based analyses, including measurement of inhibition zones in conventional agar diffusion tests and endpoint turbidity-based measurements. Here, we demonstrate that common off-line monitoring and endpoint determination after 18–24 h could be insufficient for reliable growth-dependent evaluation of antibiotic susceptibility. Different minimal inhibitory concentrations were obtained in 20- and 48 h microdilution plate tests using an Enterococcus faecium clinical isolate (strain UKI-MB07) as a model organism. Hence, we used an on-line kinetic assay for simultaneous cultivation and time-resolved growth analysis in a 96-well format instead of off-line susceptibility testing. Growth of the Enterococcus test organism was delayed up to 30 h in the presence of 0.25 μg mL-1 of vancomycin and 8 μg mL-1 of fosfomycin, after which pronounced growth was observed. Despite the delayed onset of growth, treatment with fosfomycin, daptomycin, fusidic acid, cefoxitin, or gentamicin resulted in higher maximum growth rates and/or higher final optical density values compared with antibiotic-free controls, indicating that growth stimulation and hormetic effects may occur with extended exposure to sublethal antibiotic concentrations. Whereas neither maximum growth rate nor final cell density correlated with antibiotic concentration, the lag phase duration for some antibiotics was a more meaningful indicator of dose-dependent growth inhibition. Our results also reveal that non-temporal growth profiles are only of limited value for cultivation-based antimicrobial silver nanoparticle susceptibility testing. The exposure to Ag(0) nanoparticles led to plasma membrane damage in a concentration-dependent manner and induced oxidative stress in Enterococcus faecium UKI-MB07, as shown by intracellular ROS accumulation.
The aim of this study was to estimate differences in the prevalence of oral streptococcal species in the subgingival biofilm of patients with aggressive periodontitis and of healthy controls. Thirty-three patients with clinical and radiological proof of aggressive periodontitis and 20 healthy subjects were enrolled in this study. Clinical indices were recorded in a six-point measurement per tooth. Samples of the subgingival biofilm were taken with paper points from four teeth of each individual. Alpha-and non-haemolytic, small and catalase-negative colonies were biochemically identified using a rapid ID 32 STREP system and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. A total of 118 strains of oral streptococci (11 species) were identified and Streptococcus sanguinis was found significantly more often in healthy subjects (P50.001). Conversely, the absence of S. sanguinis was associated with high values of clinical indices (P50.001-0.002). Aggressive periodontitis seems to be associated with a loss of colonization of S. sanguinis. Whether or not S. sanguinis offers protection against aggressive periodontitis needs to be determined. Otherwise, there were no significant differences in the distribution of oral streptococcal species in patients and healthy subjects. INTRODUCTIONHealthy gingivae are associated with a simple supragingival biofilm composition: a few (1-20) layers of oral streptococci, Gram-positive rods and very few Gram-negative cocci. These bacteria are early colonizers that are able to survive in an aerated environment. In contrast, clinical gingivitis is associated with the development of a more organized dental plaque of 100-300 layers, with anaerobic Gram-negative rods and filaments being predominant. The species involved in biofilm formation may vary depending on local environmental characteristics, but the colonization pattern is always the same (Marsh & Bradshaw, 1999;Marsh, 2004).Bacterial communities from dental biofilms tend to be grouped in clusters (complexes) according to nutritional and atmospheric requirements. The initiation and progression of periodontitis is thought to be caused by several species belonging to 'red' and 'orange' complexes (Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola, and Prevotella intermedia and Fusobacterium nucleatum, respectively) . However, according to the 'ecological plaque hypothesis ' (Marsh, 1991), the lack of so-called 'protective bacteria' is also thought to play an important role. These are microbial species that can occupy a niche that could shelter pathogenic organisms or that can inhibit some pathogens through metabolic antagonism or by directly inactivating them (Quirynen et al., 2001). Some of the members of the 'yellow' complex of oral streptococci are candidates for this position. Plaque samples from healthy gingival sulci normally contain a large number of oral streptococci (Theilade et al., 1966). Socransky et al. (1998) previously showed that yellow complexes, as a total, were associate...
The epidemiology of Candida infections has changed over the last two decades: The number of patients suffering from such infections has increased dramatically and the Candida species involved have become more numerous as Candida albicans is replaced as an infecting agent by various non-C. albicans species (NAC). At the same time, additional antifungal agents have become available. The different Candida species may vary in their susceptibility for these various antifungals. This draws more attention to in vitro susceptibility testing. Unfortunately, several different test methods exist that may deliver different results. Moreover, clinical breakpoints (CBP) that classify test results into susceptible, intermediate and resistant are controver- sial between CLSI and EUCAST. Therefore, clinicians should be aware that interpretations may vary with the test system being followed by the microbiological laboratory. Thus, knowledge of actual MIC values and pharmacokinetic properties of individual antifungal agents is important in delivering appropriate therapy to patients
Our results suggest that MALDI-TOF-MS might become a useful method for the identification of anaerobic bacteria, especially for those that cannot be readily identified by biochemical analysis. It may become an attractive system even for the routine identification of clinical isolates.
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