Yeasts associated with Sardinian ewe's dairy products.

In the present work, the occurrence of yeasts in different types of typical Sardinian ewe's cheeses (32 samples of pecorino, 32 of caciotta, 40 of feta, 56 of ricotta) was determined. For the strains isolated the following properties were studied: proteolytic and lipolytic activities, the ability to grow at different temperatures, different concentrations of salt, and to assimilate and/or ferment compounds like lactate, citrate, lactose, glucose, galactose, lactic acid. Of 160 samples analysed, 76.2% yielded growth of yeasts. Yeast counts showed a certain variability among the samples. The highest levels were observed in caciotta and feta cheeses. A total of 281 strains belonging to 16 genera and 25 species were identified. In general, Debaryomyces hansenii was the dominant species, representing 28.8% of the total isolates. Other frequently appearing species were Geotrichum candidum, Kluyveromyces lactis and K. marxianus. Other genera encountered were Pichia, Candida, Dekkera, Yarrowia and Rhodotorula. With regard to the biochemical and technological properties of the yeasts, only K. lactis, K. marxianus and Dek. anomala assimilated and fermented lactose, whereas the majority of the species assimilated lactic acid. The assimilation of citrate was a characteristic of D. hansenii, R. rubra and Y. lipolytica. On the whole, the yeasts were weakly proteolytic while lipolytic activity was present in several species. A high percentage of strains showed a certain tolerance to low temperatures while only some strains of D. hansenii and K. lactis were able to grow at a 10% NaCl concentration.

The HLA-DPB1--associated component of the IDDM1 and its relationship to the major loci HLA-DQB1, -DQA1, and -DRB1.

The major histocompatibility complex (MHC) HLA region on chromosome 6p21 contains the major locus of type 1 diabetes (IDDM1). Common allelic variants at the class II HLA-DRB1, -DQA1, and -DQB1 loci account for the major part of IDDM1. Previous studies suggested that other MHC loci are likely to contribute to IDDM1, but determination of their relative contributions and identities is difficult because of strong linkage disequilibrium between MHC loci. One prime candidate is the polymorphic HLA-DPB1 locus, which (with the DPA1 locus) encodes the third class II antigen-presenting molecule. However, the results obtained in previous studies appear to be contradictory. Therefore, we have analyzed 408 white European families (200 from Sardinia and 208 from the U.K.) using a combination of association tests designed to directly compare the effect of DPB1 variation on the relative predisposition of DR-DQ haplotypes, taking into account linkage disequilibrium between DPB1 and the DRB1, DQA1, and DQB1 loci. In these populations, the overall contribution of DPB1 to IDDM1 is small. The main component of the DPB1 contribution to IDDM1 in these populations appears to be the protection associated with DPB1*0402 on DR4-negative haplotypes. We suggest that the HLA-DP molecule itself contributes to IDDM1.

Conditional linkage disequilibrium analysis of a complex disease superlocus, IDDM1 in the HLA region, reveals the presence of independent modifying gene effects influencing the type 1 diabetes risk encoded by the major HLA-DQB1, -DRB1 disease loci.

Type 1 diabetes mellitus is a common disease with a complex mode of inheritance. Its aetiology is underpinned by a major locus, insulin-dependent diabetes mellitus 1 (IDDM1) in the human leukocyte antigen (HLA) region of chromosome 6p21, and an unknown number of loci of lesser individual effect. In linkage analyses IDDM1 is a single peak, but it is evident that the linkage is caused by allelic variation of three adjacent genes in a 75 kb region, namely the class II genes, HLA-DRB1, -DQA1 and -DQB1. However, even these three genes may not explain all of the HLA association. We investigated, in the founder population of Sardinia, whether non-DQ/DR polymorphic markers within a 9.452 Mb region encompassing the whole HLA complex further influence the disease risk, after taking into account linkage disequilibrium with the disease loci HLA-DQB1, -DQA1 and -DRB1. We generalized the conditional association test, the haplotype method, to detect marker associations that are independent of the main DR/DQ disease associations. Three regions were identified as risk modifiers. These associations were not only independent of the polymorphic exon 2 sequences of HLA-DQB1, -DQA1 and -DRB1, but also independent of each other. The individual contributions of these risk modifiers were relatively modest but their combined impact was highly significant. Together, alleles of single nucleotide polymorphisms at the DMB and DOB genes, and the microsatellite locus TNFc, identified approximately 40% of Sardinian DR3 haplotypes as non-predisposing. This conditional analysis approach can be applied to any chromosome region involved in the predisposition to complex traits.

Major factors influencing linkage disequilibrium by analysis of different chromosome regions in distinct populations: demography, chromosome recombination frequency and selection.

Linkage disequilibrium (LD) mapping of disease genes is complicated by population- and chromosome-region-specific factors. We have analysed demographic factors by contrasting intermarker LD results obtained in a large cosmopolitan population (UK), a large genetic isolate (Sardinia) and a subisolate (village of Gavoi) for two regions of the X chromosome. A dramatic increase of LD was found in the subisolate. Demographic history of populations therefore influences LD. Chromosome-region-specific effects, namely the pattern and frequency of homologous recombination, were next delineated by the analysis of chromosome 6p21, including the HLA region. Patterns of global LD in this region were very similar in the UK and Sardinian populations despite their entirely distinct demographies, and correlate well with the pattern of recombinations. Nevertheless, haplotypes extend across recombination hot spots indicative of selection of certain haplotypes. Subisolate aside, chromosome-region-specific differences in LD patterns appear to be more important than the differences in intermarker LD between distinct populations.

Confirmation of the DRB1-DQB1 loci as the major component of IDDM1 in the isolated founder population of Sardinia.

There is considerable uncertainty and debate concerning the application of linkage disequilibrium (LD) mapping in common multifactorial diseases, including the choice of population and the density of the marker map. Previously, it has been shown that, in the large cosmopolitan population of the UK, the established type 1 diabetes IDDM1 locus in the HLA region could be mapped with high resolution by LD. The LD curve peaked at marker D6S2444, 85 kb from the HLA class II gene DQB1, which is known to be a major determinant of IDDM1. However, given the many unknown parameters underlying LD, a validation of the approach in a genetically distinct population is necessary. In the present report we have achieved this by the LD mapping of IDDM1 in the isolated founder population of Sardinia. Using a dense map of microsatellite markers, we determined the peak of LD to be located at marker D6S2447, which is only 6.5 kb from DQB1. Next, we typed a large number of SNPs defining allelic variation at functional candidate genes within the critical region. The association curve, with both classes of marker, peaked at the loci DRB1-DQB1. These results, while representing conclusive evidence that the class II loci DRB1-DQB1 dominate the association of the HLA region to type 1 diabetes, provide empirical support for LD mapping.

The inter-regional distribution of HLA class II haplotypes indicates the suitability of the Sardinian population for case-control association studies in complex diseases.

We have analysed HLA class II gene-based substructure of the Sardinian population in order to evaluate the possible influence of this parameter in the mapping of common disease loci using association methods. We first examined the distribution of the HLA-DRB1-DQA1-DQB1 haplotypes in 631 newborns from seven different regions of the island, and found that the most frequent haplotypes were uniformly distributed in all regions, but at frequencies unique to Sardinia. Other haplotypes, common in other white European populations, are consistently rare or absent across the whole island. Analysis of molecular variance (AMOVA) showed a very low degree of genetic differentiation between the coastal regions, which have suffered repeated invasions over many years, and the most internal and isolated part of the island. This suggests that there has been little genetic flow from the various populations that have invaded the island during the last 3000 years and that Sardinia is a relatively homogeneous population. The validity of these unrelated control HLA haplotype frequencies and our claim of homogeneity were established by demonstrating the near identity of the affected family-based control (AFBAC) HLA haplotype frequencies in 243 type 1 diabetes and 495 multiple sclerosis families from Sardinia and those of the unrelated controls. These results indicate that robust case-control studies can be carried out in Sardinia offering cost efficiency over certain family-based designs.

Conditional ETDT analysis of the human leukocyte antigen region in type 1 diabetes.

Several studies have indicated that additional genes in the major histocompatibility complex (MHC) region, other than the class II genes HLA-DQB1 and -DRB1 (the IDDM1 locus), may contribute to susceptibility and resistance to type 1 diabetes. The relative magnitude of these non- DR/DQ effects is uncertain and their map location is unknown owing to the extraordinary linkage disequilibrium that extends over the 3.5 Mb of the MHC. The homozygous parent test has been proposed as a method for detection of additional risk factors conditional on HLA-DQB1 and -DRB1. However, this method is inefficient since it uses only parents homozygous for the primary disease locus, the DQB1-DRB1 haplotype. To overcome this limitation, Conditional ETDT was used in the present report to test for association conditional on the DQB1-DRB1 haplotype, thereby allowing all parents to be included in the analysis. First, we confirm in UK and Sardinian type 1 diabetic families that allelic variation at HLA-DRB1 has a very significant effect on the association of DQB1 and vice versa. The Conditional ETDT was then applied to the HLA TNF (tumour necrosis factor) region and microsatellite marker D6S273 region, both of which have been reported to contribute to IDDM1 independent of the HLA-DQB1-DRB1 genes. We found no evidence for a major role for either of these two regions in IDDM1.

Incidence and biochemical characteristics of Bacillus flora in Sardinian dairy products.

This study was planned to assess the frequency and level of Bacillus spp. contamination in Sardinian dairy products and to evaluate some food-spoilage-related characteristics of the strains isolated. Of the 378 dairy products tested, 265 (70%) were found to contain Bacillus spp. The overall level of contamination ranged from less than 10 cfu per ml or gram up to a maximum of 1200 cfu. A total of 483 strains, belonging to 14 species, have been isolated from the 265 positive samples. The most frequently isolated psychotropic species were B. cereus (18.6% of total isolates), B. coagulans and B. mycoides. B. subtilis, B. licheniformis and B. pumilis were the most common mesophilic strains and B. stearotermophilus was the dominant thermophilic species. Most strains showed strong enzymatic activity, as indicated by the high percentage of isolates capable of hydrolysing casein, gelatin, starch and liquids. As regards possible health hazards. 72% of the B. cereus strains tested showed evidence of toxin production using a reversed passive latex agglutination assay.

[The presence of nucleotide sequences of the hepatitis B virus in peripheral lymphocytes of patients with acute hepatitis B]. / Presenza di sequenze nucleotidiche del virus dell'epatite B nei linfociti periferici di pazienti con epatite acuta di tipo B.

Hepatitis B virus (HBV) DNA sequences were assessed in 26 patients with acute type B hepatitis, using dot-blot hybridization technique from peripheral blood mononuclear cells (PBMC), during different phases of the illness. At clinical presentation, 15% of patients showed HBV-DNA sequences in PBMC, while serum HBV-DNA was detected in 58% of patients. During clinical improvement 50% of patients had HBV-DNA in PBMC but only 11.5% were positive for serum HBV-DNA. Twenty-three (88.5%) patients recovered and cleared HBV-DNA from serum and from PBMC; three (11.5%) patients with acute hepatitis progressing to chronicity showed persistently HBV-DNA sequences in serum and in PBMC. In conclusion, our study shows that HBV-DNA sequences may be found in PBMC, transiently in patients with acute hepatitis followed by recovery, persistently in patients with acute hepatitis progressing to chronicity.