​cme.​msu.​edu/​index.​jsp). The respective partial 16S rRNA gene OSI-906 in vitro sequences of OMZ 1117 and 1121 [EMBL: FR667951], and of OMZ 1118 and 1120 [EMBL: FR667952] were identical. OMZ 1119 was identified as L. vaginalis [EMBL: FR667953]. Critical importance of several assay parameters Lactobacilli

are difficult targets for FISH because of their cell wall’s resistance to probe see more penetration. The protocol used successfully in the present study to increase cell permeability evolved from the method of Harmsen et al. [9], which we supplemented with achromopeptidase, previously described to open cell walls of Actinomyces strains [23, 24]. Systematic evaluation of this three-enzyme-pretreatment with 12 reference strains from seven Lactobacillus species showed its indispensability. However, a minority of strains proved to be particularly resistant, as up to 20% of the cells recognizable by phase contrast could not be stained. Of course this raised concerns that such false-negative results could also affect analyses of clinical samples. We cannot completely rule out this possibility, but after comprehensive analysis of many plaque samples we would like to hypothesize that there are differences in cell wall permeability between cultured and native lactobacilli and that false-negative cells are primarily seen after FISH with

cultured lactobacilli. With Erastin purchase cell wall permeability remaining a potential reason for concern, maximum fluorescence intensity from penetrated probes is essential. Fluorescence intensity depends on cellular ribosome content, in situ probe accessibility to the probe target region, and rRNA stability [25]. Several procedures to maximize the performance of FISH probes have been described [15, 16, 26, 27]. They alter the 3-dimensional structure of the target region by using helper probes, optimize probe length and hybridization conditions, improve binding affinity by modifying the probes’ backbone with LNA substitutions, or inhibit enzymatic rRNA degradation. In this study we used all four procedures to improve fluorescence intensity of certain Resveratrol probes. For Lfer466, Lreu986, and Lpla990 one or two helper probes binding directly adjacent

to the target site were added to the hybridization solution and in each case a clear-cut improvement of fluorescence intensity was observed. The same was the case when the LNA-substituted probe L-Ssob440-2 was compared to Ssob440. For five other probes the decision to opt for LNA insertions was taken solely based on own and published experience [25], suggesting limited accessibility of the probes’ target site. All these LNA/DNA-probes displayed intensive fluorescence, but required strict adherence of very stringent hybridization conditions for sufficient specificity. Conclusions In this study we have described the application of 20 new phylogenetic group- or species-specific oligonucleotide probes for the single-cell detection of oral LAB in various clinical or experimental biofilms.