Pulsed-field gel electrophoresis (PFGE) of XbaI-digested chromosomal DNA was performed on 133 strains of Salmonella enterica serovar Typhi obtained from Papua New Guinea, with the objective of assessing the temporal variation of these strains. Fifty-two strains that were isolated in 1992 and 1994 were of one phage type, D2, and only two predominant PFGE profiles, X1 and X2, were present. Another 81 strains isolated between 1997 and 1999 have shown divergence, with four new phage types, UVS I (n = 63), UVS (n = 5), VNS (n = 4), and D1 (n = 9), and more genetic variability as evidenced by the multiple and new PFGE XbaI profiles (21 profiles; Dice coefficient, F = 0.71 to 0.97). The two profiles X1 and X2 have remained the stable, dominant subtypes since 1992. Cluster analysis based on the unweighted pair group method using arithmetic averages algorithm identifies two main clusters (at 87% similarity), indicating that the divergence of the PFGE subtypes was probably derived from some genomic mutations of the X1 and X2 subtypes. The majority of isolates were from patients with mild and moderate typhoid fever and had various XbaI profiles. A single isolate from a patient with fatal typhoid fever had a unique X11 profile, while four of six isolates from patients with severe typhoid fever had the X1 pattern. In addition, 12 paired serovar Typhi isolates recovered from the blood and fecal swabs of individual patients exhibited similar PFGE patterns, while in another 11 individuals paired isolates exhibited different PFGE patterns. Three pairs of isolates recovered from three individuals had different phage types and PFGE patterns, indicating infection with multiple strains. The study reiterates the usefulness of PFGE in assessing the genetic diversity of S. enterica serovar Typhi for both long-term epidemiology and in vivo stability and instability within an individual patient.
Matched MeSH terms: Deoxyribonucleases, Type II Site-Specific/metabolism
Nasopharyngeal carcinoma (NPC) is a human epithelial tumour with high prevalence amongst Chinese in Southern China and South East Asia and is associated with the Epstein-Barr virus (EBV). The viral genome harbours an oncogene, namely, the latent membrane protein 1 (LMP1) gene and known variants such as the 30-bp deletion and loss of XhoI restriction site have been found. Less is known about the relationship between these variants and the population characteristics and histological type.
Matched MeSH terms: Deoxyribonucleases, Type II Site-Specific/metabolism*
Nasopharyngeal carcinoma, a malignancy associated closely with Epstein-Barr virus (EBV), is prevalent among Chinese of Southern China origin. Epidemiological studies indicate a high prevalence of EBV in Asia with viral isolates having typical characteristics of the putative viral oncogene, latent membrane protein 1 (LMP-1), such as the loss of the Xho1 restriction site in Exon 1 and the 30-bp deletion in Exon 3. The EBV LMP-1 gene from throat washings of 120 nasopharyngeal carcinoma patients and 14 healthy individuals were analyzed. Similar analyses were also carried out on 30 and 12 postnasal space biopsies from nasopharyngeal carcinoma patients and healthy individuals, respectively. The 30-bp deletion was detected in 20% of nasopharyngeal carcinoma throat washes and in 100% of nasopharyngeal carcinoma postnasal space biopsies. Interestingly, 16% of the nasopharyngeal carcinoma biopsies possessed both the deleted and the undeleted variants, suggestive of dual infections. The notion of dual infections in nasopharyngeal carcinoma was further supported by the coexistence of both "F" and "f" (BamH1F region) EBV variants in 11% of the nasopharyngeal carcinoma biopsies. All of the throat washes and biopsies from the healthy controls showed the undeleted variant. The loss of the Xho1 restriction site was found with higher frequency both in throat washes and biopsies from patients with nasopharyngeal carcinoma. The discrepancy in the frequency of the 30-bp deletion between throat washes (20%) and postnasal space biopsies (100%) was an indication that this deletion is specific for viral isolates from primary tumour sites.
Matched MeSH terms: Deoxyribonucleases, Type II Site-Specific/metabolism