Streptococcus pneumoniae remains a major causative agent of serious human diseases. The worldwide increase of antibiotic resistant strains revealed the importance of horizontal gene transfer in this pathogen, a scenario that results in the modulation of the species-specific gene pool. We investigated genomic variation in 20 S. pneumoniae isolates representing major antibiotic-resistant clones and 10 different capsular serotypes. Variation was scored as decreased hybridization signals visualized on a high-density oligonucleotide array representing 1,968 genes of the type 4 reference strain KNR.7/87. Up to 10% of the genes appeared altered between individual isolates and the reference strain; variability within clones was below 2.1%. Ten gene clusters covering 160 kb account for half of the variable genes. Most of them are associated with transposases and are assumed to be part of a flexible gene pool within the bacterial population; other variable loci include mosaic genes encoding antibiotic resistance determinants and gene clusters related to bacteriocin production. Genomic comparison between S. pneumoniae and commensal Streptococcus mitis and Streptococcus oralis strains indicates distinct antigenic profiles and suggests a smooth transition between these species, supporting the validity of the microarray system as an epidemiological and diagnostic tool.

We studied the prevalence of Tropheryma whipplei in influxes to 46 sewage treatment plants and in stool, mouthwash fluids, and dental plaques of 64 healthy workers in those facilities and 146 disease control patients. T. whipplei was found in sewage water, in stool of healthy individuals, and significantly more often in stool of workers exposed to sewage water.

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A food-grade system for the delivery of desired genes to Lactococcus lactis, their inducible expression, and their transfer to related strains was established. Based on the thermosensitive pG ؉ host replicon, two types of plasmid vectors were constructed which contained sections of either the chromosomal leu operon of L. lactis or the tel operon from the lactococcal sex factor. Genes cloned into the leu or tel sequences of these vectors were delivered to the homologous regions of the chromosome or the sex factor through two single crossovers, leading to integration of the recombinant plasmids and subsequent excision of the vector portions. Inducible transcription of integrated genes was achieved by using the nisin-controlled expression (NICE) system. To establish the signal transduction genes nisRK in L. lactis, the vectors pLNG1363 (targeted to the chromosome) and pUK500 (targeted to the sex factor) were constructed. Fusions of six different peptidase genes (pep) from Lactobacillus delbrueckii with the nisin-inducible promoter P nisA were delivered to the sex factor with derivatives of the vector pUK300. Food-grade recombinants of L. lactis were constructed which had the nisRK genes and individual P nisA ::pep fusions integrated either separately into the chromosome and the sex factor or simultaneously into the sex factor. With both types of recombinants, expression of P nisA ::pep fusions after induction with nisin was demonstrated. Depending on the loci used for integration of nisRK, variable induction rates were observed. Furthermore, an engineered sex factor carrying a P nisA ::pepI fusion was transfered by conjugation between two strains of L. lactis at a frequency of 4 ؋ 10 ؊4