Limits of sensitivity of LSplex Next we wished to determine check details the minimum amount of target DNA efficiently supporting the optimized LSplex Go6983 mw amplification protocol. Agarose gel electrophoresis was unable to detect the LSplex amplification

products from templates containing less than 10 ng of DNA (105–106 genomic equivalents) from several bacterial species (not shown). However, after fluorescent labeling of the amplification products followed by microarray hybridization strong signals were readily detected. In fact, LSplex amplification (with 800 primer pairs) of 10 ng and also of 1 ng of DNA template resulted in a find more hybridization pattern mostly identical to the one obtained with 2 μg of genomic DNA, while 10 ng of the same genomic DNA were below the limit of sensitivity of the microarray for pathogen detection (Fig. 3). The hybridization pattern obtained with 100 ng genomic DNA showed 22 mismatches compared to 2 μg. In contrast, LSplex on 1 ng template displayed a hybridization profile comparable to the one obtained with 2 μg of non amplified DNA, although the amplification of certain probes was diminished. For instance, lipase (lip) delta-aminolevulinic acid dehydratase (hemB) and Pantone-Valentine

leukocidin F subunit (lukF) were poorly amplified and fell below detection threshold. Most of the LSplex products amplified from 0.1 ng or 0.01 ng (not shown) template were below the limit of detection of the microarray analysis, making species identification impossible. Thus application of LSplex increases the microarray detection of target templates by a factor of 102 to 103 with >95% fidelity. Figure 3 Enhancement of sensitivity of pathogen DNA detection by microarray by LSplex amplification. Hybridization profile of non-amplified genomic S. aureus DNA (2 μg, 100 ng, 10 ng and 1 ng) and indirectly labelled LSplex amplification product of the same DNA starting from 10 ng, 1 ng and 0.1 ng template (columns). Adenosine triphosphate Each row represents individual S. aureus-specific capture probes as well as positive (16S-derived probes) and negative controls. Fluorescent signals were quantified and classified as positive (black boxes) hybridization or absence of hybridization (white boxes). Specificity of LSplex on several DNA templates In the next step we evaluated if the PCR amplification employing 800 primer pairs results in the generation of nonspecific amplification products cross-hybridizing with non-target species.