No abstract

Background: The pathogenesis of bacterial vaginosis remains largely elusive, although some microorganisms, including Gardnerella vaginalis, are suspected of playing a role in the etiology of this disorder. Recently culture-independent analysis of microbial ecosystems has proven its efficacy in characterizing the diversity of bacterial populations. Here, we report on the results obtained by combining culture and PCR-based methods to characterize the normal and disturbed vaginal microflora.

Background: The microbiological diagnosis of bacterial vaginosis is usually made using Nugent's criteria, a useful but rather laborious scoring system based on counting bacterial cell types on Gram stained slides of vaginal smears. Ison and Hay have simplified the score system to three categories and added a fourth category for microflora with a predominance of the Streptococcus cell type. Because in the Nugent system several cell types are not taken into account for a final score, we carried out a detailed assessment of the composition of the vaginal microflora in relation to standard Gram stain in order the improve the diagnostic value of the Gram stain. To this purpose we compared Gram stain based categorization of vaginal smears with i) species specific PCR for the detection of Gardnerella vaginalis and Atopobium vaginae and with ii) tDNA-PCR for the identification of most cultivable species.

BackgroundPseudomonas aeruginosa is the major pathogen involved in the decline of lung function in cystic fibrosis (CF) patients. Early aggressive antibiotic therapy has been shown to be effective in preventing chronic colonization. Therefore, early detection is important and sensitive detection methods are warranted. In this study, we used a dilution series of P. aeruginosa positive sputa, diluted in a pool of P. aeruginosa negative sputa, all from CF patients - to mimick as closely as possible the sputa sent to routine laboratories - to compare the sensitivity of three culture techniques versus that of two conventional PCR formats and four real-time PCR formats, each targeting the P. aeruginosa oprL gene. In addition, we compared five DNA-extraction protocols.ResultsIn our hands, all three culture methods and the bioMérieux easyMAG Nuclisens protocol Generic 2.0.1, preceded by proteinase K pretreatment and followed by any of the 3 real-time PCR formats with probes were most sensitive and able to detect P. aeruginosa up to 50 cfu/ml, i.e. the theoretical minimum of one cell per PCR mixture, when taking into account the volumes used in this study of sample for DNA-extraction, of DNA-elution and of DNA-extract in the PCR mixture.ConclusionIn this study, no difference in sensitivity could be found for the detection of P. aeruginosa from sputum between microbiological culture and optimized DNA-extraction and real-time PCR. The results also indicate the importance of the optimization of the DNA-extraction protocol and the PCR format.

During a study examining transmission of Pseudomonas aeruginosa among 76 cystic fibrosis patients in a rehabilitation center, where patients stay in close contact during prolonged periods, several clusters of patients carrying genotypically identical P. aeruginosa, as well as two clusters of 4 and 10 patients, respectively, colonized with genotypically identical Achromobacter xylosoxidans strains, were discovered

Three PCR techniques (amplification of the psaA, ply, and lytA genes) and a commercial kit (AccuProbe [GenProbe, San Diego, Calif.], based on hybridization with the 16S rRNA gene), all four of which claimed to be specific for Streptococcus pneumoniae, were used to identify 49 alpha-hemolytic streptococcal isolates suspected of being pneumococci. The definite phenotypic identification of these organisms as S. pneumoniae was difficult when optochin susceptibility and the presence of a capsule were taken as markers. Furthermore, RsaI digestion of the amplified 16S rRNA gene was applied. All 49 strains were optochin resistant. Eleven of these were encapsulated and were identified as pneumococci by all tests. Twenty of the 38 unencapsulated strains were unambiguously identified as nonpneumococci by all tests. The identities of another 18 unencapsulated strains remained inconclusive due to highly variable reactions for all phenotypic and genotypic techniques applied. The AccuProbe test was positive for seven strains for which the results of the other tests were inconclusive. RsaI restriction of the amplified 16S rRNA gene confirmed the AccuProbe result for all strains, while the result of the psaA-specific PCR was in concordance with encapsulation for all strains. The results presented here indicate that identification problems continue to exist for some strains, despite the application of genotypic and phenotypic tests in combination. We found the psaA-specific PCR to be the genotypic technique best suited for the identification of genuine pneumococci and optochin-resistant pneumococci.Optochin susceptibility and encapsulation are the phenotypic characteristics that are the most frequently used to differentiate between Streptococcus pneumoniae and other streptococci (22). However, optochin-resistant S. pneumoniae strains are being isolated more frequently (2, 29) and are probably largely overlooked, since in many laboratories primary isolation of pneumococci on culture medium relies on optochin susceptibility itself. The occasional occurrence of encapsulated S. mitis and S. oralis strains and the fact that nontypeable, unencapsulated pneumococci have been reported to comprise 2% of the isolates from normally sterile sites (3) and up to 20% of the conjunctival isolates (12) further complicate the identification of pneumococci. Commercial systems like the API 20S and Vitek2 systems occasionally fail to identify pneumococcal isolates or identify other streptococci as pneumococci (4). Thus, even though the phenotypic identification of typical pneumococci is unambiguous, the existence of optochin-resistant isolates may increasingly cause problems in clinical bacteriological laboratories.In the last decade, new gene amplification methods, based on the detection of pneumococcal virulence factors, have been developed to identify pneumococcal strains (18,23,24,34) and to detect pneumococci directly from clinical samples (8, 13, 14, 19, 31-33, 35, 36). Hybridization methods (10, 30) have also been used for the identification ...

Bacterial vaginosis is characterized by an imbalance of the vaginal microbiome and a characteristic biofilm formed on the vaginal epithelium, which is initiated and dominated by Gardnerella bacteria, and is frequently refractory to antibiotic treatment. We investigated endolysins of the type 1,4-beta-N-acetylmuramidase encoded on Gardnerella prophages as an alternative treatment. When recombinantly expressed, these proteins demonstrated strong bactericidal activity against four different Gardnerella species. By domain shuffling, we generated several engineered endolysins with 10-fold higher bactericidal activity than any wild-type enzyme. When tested against a panel of 20 Gardnerella strains, the most active endolysin, called PM-477, showed minimum inhibitory concentrations of 0.13–8 µg/mL. PM-477 had no effect on beneficial lactobacilli or other species of vaginal bacteria. Furthermore, the efficacy of PM-477 was tested by fluorescence in situ hybridization on vaginal samples of fifteen patients with either first time or recurring bacterial vaginosis. In thirteen cases, PM-477 killed the Gardnerella bacteria and physically dissolved the biofilms without affecting the remaining vaginal microbiome. The high selectivity and effectiveness in eliminating Gardnerella, both in cultures of isolated strains as well as in clinically derived samples of natural polymicrobial biofilms, makes PM-477 a promising alternative to antibiotics for the treatment of bacterial vaginosis, especially in patients with frequent recurrence.

Bacteriophages are a promising therapeutic strategy among cystic fibrosis and lung-transplanted patients, considering the high frequency of colonization/infection caused by pandrug-resistant bacteria. However, little clinical data are available regarding the use of phages for infections with Achromobacter xylosoxidans. A 12-year-old lung-transplanted cystic fibrosis patient received two rounds of phage therapy because of persistent lung infection with pandrug-resistant A. xylosoxidans. Clinical tolerance was perfect, but initial bronchoalveolar lavage (BAL) still grew A. xylosoxidans. The patient’s respiratory condition slowly improved and oxygen therapy was stopped. Low-grade airway colonization by A. xylosoxidans persisted for months before samples turned negative. No re-colonisation occurred more than two years after phage therapy was performed and imipenem treatment was stopped. Whole genome sequencing indicated that the eight A. xylosoxidans isolates, collected during phage therapy, belonged to four delineated strains, whereby one had a stop mutation in a gene for a phage receptor. The dynamics of lung colonisation were documented by means of strain-specific qPCRs on different BALs. We report the first case of phage therapy for A. xylosoxidans lung infection in a lung-transplanted patient. The dynamics of airway colonization was more complex than deduced from bacterial culture, involving phage susceptible as well as phage resistant strains.