Bench-to-bedside review: Understanding the impact of resistance and virulence factors on methicillin-resistant Staphylococcus aureus infections in the intensive care unit

Rapid antibiotic susceptibility phenotypic characterization of Staphylococcus aureus using automated microscopy of small numbers of cells

Staphylococcus aureus remains a leading, virulent pathogen capable of expressing complex drug resistance that requires up to 2-4 days for laboratory analysis. In this study, we evaluate the ability of automated microscopy of immobilized live bacterial cells to differentiate susceptible from non-susceptible responses of S. aureus isolates (MRSA/MSSA, clindamycin resistance/susceptibility and VSSA/hVISA/VISA) to an antibiotic based on the characterization of as few as 10 growing clones after 4 h of growth, compared to overnight growth required for traditional culture based methods. Isolates included 131 characterized CDC isolates, 3 clinical isolates and reference strains. MRSA phenotype testing used 1 h of 1 μg/mL cefoxitin induction followed by 3 h of 6 μg/mL cefoxitin. Clindamycin susceptibility testing used 1h of induction by 0.1 μg/mL erythromycin followed by 3h of 0.5 μg/mL clindamycin. An automated microscopy system acquired time-lapse dark-field images, and then computed growth data for individual immobilized progenitor cells and their progeny clones while exposed to different test conditions. Results were compared to concurrent cefoxitin disk diffusion and D-test references. For CDC organisms, microscopy detected 77/77 MRSA phenotypes and 54/54 MSSA phenotypes, plus 53/56 clindamycin-resistant and 75/75 clindamycin susceptible strains. Automated microscopy was used to characterize heterogeneous and inducible resistance, and perform population analysis profiles. Microscopy-based hVISA population analysis profiles (PAPs) were included as an extended proof of concept, and successfully differentiated VSSA from hVISA and VISA phenotypes compared to plate-based PAP.

Infection-induced NETosis is a dynamic process involving neutrophil multitasking in vivo

Neutrophil extracellular traps (NETs) are released, as neutrophils die in vitro, in a process requiring hours, leaving a temporal gap for invasive microbes to exploit. Functional neutrophils undergoing NETosis have not been documented. During Gram-positive skin infections, we directly visualized live PMN in vivo rapidly releasing NETs, which prevented bacterial dissemination. NETosis occurred during crawling thereby casting large areas of NETs. NET-releasing PMN developed diffuse decondensed nuclei ultimately becoming devoid of DNA. Cells with abnormal nuclei displayed unusual crawling behavior highlighted by erratic pseudopods and hyperpolarization consistent with the nucleus being a fulcrum for crawling. A combined requirement of Tlr2 and complement mediated opsonization tightly regulated NET release. Additionally live human PMN developed decondensed nuclei and formed NETS in vivo and intact anuclear neutrophils were abundant in Gram-positive human abscesses. Therefore early in infection, non-cell death NETosis occurs in vivo during Gram-positive infection in mice and humans.

Characterization of the antibiotic compound no. 70 produced by Streptomyces sp. IMV-70

We describe the actinomycete strain IMV-70 isolated from the soils of Kazakhstan, which produces potent antibiotics with high levels of antibacterial activity. After the research of its morphological, chemotaxonomic, and cultural characteristics, the strain with potential to be developed further as a novel class of antibiotics with chemotherapeutics potential was identified as Streptomyces sp. IMV-70. In the process of fermentation, the strain Streptomyces spp. IMV-70 produces the antibiotic no. 70, which was isolated from the culture broth by extraction with organic solvents. Antibiotic compound no. 70 was purified and separated into individual components by HPLC, TLC, and column chromatography methods. The main component of the compound is the antibiotic 70-A, which was found to be identical to the peptolide etamycin A. Two other antibiotics 70-B and 70-C have never been described and therefore are new antibiotics. The physical-chemical and biological characteristics of these preparations were described and further researched. Determination of the optimal growth conditions to cultivate actinomycete-producer strain IMV-70 and development of methods to isolate, purify, and accumulate preparations of the new antibiotic no. 70 enable us to research further the potential of this new class of antibiotics.

Year in review 2009: Critical Care--shock

The research papers on shock that have been published in Critical Care throughout 2009 are related to four major subjects: first, alterations of heart function and, second, the role of the sympathetic central nervous system during sepsis; third, the impact of hemodynamic support using vasopressin or its synthetic analog terlipressin, and different types of fluid resuscitation; as well as, fourth, experimental studies on the treatment of acute respiratory distress syndrome. The present review summarizes the key results of these studies together with a brief discussion in the context of the relevant scientific and clinical background published both in this and other journals.