Variation in Salmonella enterica serovar typhi IncHI1 plasmids during the global spread of resistant typhoid fever.

A global collection of plasmids of the IncHI1 incompatibility group from Salmonella enterica serovar Typhi were analyzed by using a combination of DNA sequencing, DNA sequence analysis, PCR, and microarrays. The IncHI1 resistance plasmids of serovar Typhi display a backbone of conserved gene content and arrangement, within which are embedded preferred acquisition sites for horizontal DNA transfer events. The variable regions appear to be preferred acquisition sites for DNA, most likely through composite transposition, which is presumably driven by the acquisition of resistance genes.

Using the genome to dissect the molecular basis of drug resistance.

The need to understand the genetic basis of drug resistance in human pathogens has never been greater. The global incidence of drug-resistant organisms, such as those that cause malaria, continues to rise, while the repertoire of effective, inexpensive drugs is declining. Genomic technologies, such as DNA microarrays and full-genome sequencing offer new hope in advancing our understanding of the underlying genetic processes that facilitate a resistance phenotype.

A systematic map of genetic variation in Plasmodium falciparum.

Discovering novel genes involved in immune evasion and drug resistance in the human malaria parasite, Plasmodium falciparum, is of critical importance to global health. Such knowledge may assist in the development of new effective vaccines and in the appropriate use of antimalarial drugs. By performing a full-genome scan of allelic variability in 14 field and laboratory strains of P.

Elucidating genetic diversity with oligonucleotide arrays.

DNA microarrays, initially designed to measure gene expression levels, also provide an ideal platform for determining genetic diversity. Oligonucleotide microarrays, predominantly high-density oligonucleotide arrays, have emerged as the principal platforms for performing genome-wide diversity analysis. They have wide-ranging potential applications including comparative genomics, polymorphism discovery and genotyping.

Vi antigen expression in Salmonella enterica serovar Typhi clinical isolates from Pakistan.

The accurate identification of Salmonella enterica subsp. enterica serovar Typhi variants that fail to express the capsular polysaccharide, Vi, is an important and much discussed issue for medical microbiology. We have tested a multiplex PCR method which shows the presence or absence of the genetic locus required for Vi expression.

The emergence of multidrug resistance to antimicrobial agents for the treatment of typhoid fever.

Resistance to chloramphenicol was reported in Salmonella Typhi in 1950 but it was not until 22 years later that the first outbreaks of chloramphenicol-resistant typhoid fever occurred. Multidrug-resistant (MDR) Salmonella Typhi emerged in the 1980s and today has an almost worldwide distribution. Genome analysis of Salmonella Typhi strain CT18, an MDR isolate from a patient admitted to The Centre for Tropical Diseases, Ho Chi Minh City, Viet Nam, in December 1993 revealed that the resistance plasmid pHCM1 is very closely related to plasmid R27 which was first isolated in 1961.

Molecular analysis of incHI1 antimicrobial resistance plasmids from Salmonella serovar Typhi strains associated with typhoid fever.

The first outbreak of multidrug-resistant (MDR) typhoid fever in Vietnam was in 1993, and by 1995 nearly 90% of cases were MDR. Plasmid HCM1, sequenced in full, is an incHI1 plasmid from Salmonella enterica serovar Typhi strain CT18, isolated in Vietnam in 1993. Restriction analysis shows that pHCM1 shares a restriction fragment length polymorphism (RFLP) pattern with plasmids isolated from the first outbreak and 10 of 17 MDR plasmids isolated from sporadic cases occurring at the same time in Vietnam.

Salmonella typhi, the causative agent of typhoid fever, is approximately 50,000 years old.

A global collection of 26 isolates of Salmonella typhi was investigated by sequencing a total of 3336 bp in seven housekeeping genes. Only three polymorphic sites were found and the isolates fell into four sequence types. These results show that S.

Characterisation and distribution of a cryptic Salmonella typhi plasmid pHCM2.

pHCM2 is a 106 kbp cryptic plasmid harboured by Salmonella typhi CT18, originally isolated from a typhoid patient in Vietnam. The genome of S. typhi CT18, including pHCM2, has recently been completely sequenced and annotated.