Analysis of Salmonella typhi isolates from Southeast Asia by pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) revealed that multiple genetic variants of Salmonella typhi are simultaneously present in Southeast Asia and are associated with sporadic cases of typhoid fever and occasional outbreaks. Comparative analysis of PFGE patterns also suggested that considerable genetic diversity exists among S. typhi strains and that some PFGE patterns are shared between isolates obtained from Malaysia, Indonesia, and Thailand, implying movement of these strains within these regions of Southeast Asia, where they are endemic

Antimicrobial susceptibility and pulsed – Field Gel Electrophoretic analysis of Salmonella in a tertiary hospital in northern Malaysia

SummaryBackground and aimsSalmonella infections remain a major public health problem in developing countries. The occurrence of infections caused by antimicrobial-resistant Salmonella has been on the rise complicating the available therapeutic options. The study aimed to determine the antibiograms and genotypes of prevalent Salmonella serotypes.MethodsA retrospective study involving 80 stool and extra-intestinal Salmonella strains collected over a 18-month period (January 2005–June 2006) from a tertiary hospital in Penang, Malaysia was conducted. Isolates were examined for resistance to 14 antimicrobial drugs and the clonality of the strains was determined by PFGE.ResultsTwenty-one serotypes were identified, the most common being S. enteritidis (42.5%) followed by S. corvallis (11.25%) and S. braenderup (11.25%). S. enteritidis was significantly more common amongst the extra-intestinal isolates compared to stool isolates (74.2% versus 22.4%, p<0.0001). Overall, the highest resistance was observed for tetracycline (66.3%), sulphonamides (56.3%), streptomycin (32.5%), trimethoprim (28.8%) and nalidixic acid (27.5%). Amongst the 31 invasive extra-intestinal isolates, resistance towards therapeutically relevant antibiotics was as follows: co-trimoxazole (38.7%), ampicillin (29%) and ceftriaxone (3.2%). Although there was no detectable resistance towards chloramphenicol and ciprofloxacin, 29% strains showed nalidixic acid resistance. About 41% of the 80 isolates were multidrug-resistant. PFGE subtyped the 78 Salmonella isolates to 33 distinct XbaI-pulsotypes. Isolates within the serotypes S. enteritidis, S. corvallis, S. branderup and S. fasta were more homogeneous while S. typhi and S. weltervden were genetically more diverse.ConclusionsThe high percentage of multidrug-resistant Salmonella strains is worrying and is of public health concern. PFGE was a useful and discriminative method for assessing the genetic diversity of Salmonellae

Application of Ribosomal RNA Gene Restriction Patterns Analysis and Pulsed-Field Gel Electrophoresis in Distinguishing Salmonella Weltevreden Isolates in Malaysia

A representative sample of 20 isolates of Salmonella weltevreden strains from stool cultures of patients admitted at the University Hospital, Kuala Lumpur, Malaysia were analyzed. All the strains were susceptible to ampicillin, ceftriaxone, ciprofloxacin, chloramphenicol, tetracycline, trimethoprim, gentamicin and co-trimoxazole. Ribosomal RNA gene restriction pattern analysis of PstI-digested DNA gave three ribotypes while pulsed-field gel electrophoresis (PFGE) analysis of XbaI-digested DNA gave ten distinct profiles. PFGE was more discriminative than ribotyping in distinguishing the strains. The majority of the strains analyzed were very closely related with similarity coefficient values ranging from 0.8 to 1.0. Both PFGE and ribotyping could distinguish one of the strains which was obtained from a patient following a bone marrow transplant for β-thalassemia major, indicating that this particular strain was unrelated to the rest of the strains from patients with acute gastroenteritis

Multidrug resistant Salmonella enterica Serotype Typhi are genetically homologous and coexist with antibiotic- sensitive strains as distinct independent clones

The goal of this study was to report the molecular analysis of antibiotic-sensitive and multidrug resistant (MDR) strains of Salmonella Typhi, using pulsed-field gel electrophoresis (PFGE), with a particular emphasis on the co-existence of these strains in a typhoid-endemic region of Karachi, Pakistan. One hundred isolates of S. typhi in humans (50 MDR and 50 antibiotic-sensitive isolates) from sporadic cases of typhoid fever were analyzed by Vi-phage typing, antibiogram, and PFGE. The MDR S. typhi strains were resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. Analysis by PFGE showed that 50 MDR isolates of S. typhi had a single, homogeneous PFGE profile, which was distinctly different from that of the 50 antibiotic-sensitive isolates obtained in the same time frame from the same area. This latter group of isolates showed much greater diversity of PFGE profiles, as has been observed in other endemic regions. Multidrug-resistant and antibiotic-susceptible strains of S. typhi can coexist in endemic area as epidemiologically independent pathogens and are not in competition for continued persistence and transmission

Cloning and expression of a Vi mimotope of Salmonella enterica serovar Typhi through nucleotide-nucleotide hybridization approach.l

A recombinant His-Vi protein of Salmonella enterica serovar Typhi was successfully constructed and cloned into an expression vector through a nucleotide-nucleotide hybridization approach. After transformation of the construct into Escherichia coli, the recombinant His-Vi protein with a size of approximately 4 kDa was successfully produced and proven by Western blot analysis. This recombinant protein can be used to detect specific anti-Vi antibody produced by typhoid patients. Overall, the His-Vi recombinant protein could serve as a potential diagnostic reagent to detect S. Typhi infection in an individual

Characterization of Multidrug Resistant ESBL-Producing Escherichia coli Isolates from Hospitals in Malaysia

The emergence of Escherichia coli that produce extended spectrum β-lactamases (ESBLs) and are multidrug resistant (MDR) poses antibiotic management problems. Forty-seven E. coli isolates from various public hospitals in Malaysia were studied. All isolates were sensitive to imipenem whereas 36 were MDR (resistant to 2 or more classes of antibiotics). PCR detection using gene-specific primers showed that 87.5% of the ESBL-producing E. coli harbored the blaTEM gene. Other ESBL-encoding genes detected were blaOXA, blaSHV, and blaCTX-M. Integron-encoded integrases were detected in 55.3% of isolates, with class 1 integron-encoded intI1 integrase being the majority. Amplification and sequence analysis of the 5′CS region of the integrons showed known antibiotic resistance-encoding gene cassettes of various sizes that were inserted within the respective integrons. Conjugation and transformation experiments indicated that some of the antibiotic resistance genes were likely plasmid-encoded and transmissible. All 47 isolates were subtyped by PFGE and PCR-based fingerprinting using random amplified polymorphic DNA (RAPD), repetitive extragenic palindromes (REPs), and enterobacterial repetitive intergenic consensus (ERIC). These isolates were very diverse and heterogeneous. PFGE, ERIC, and REP-PCR methods were more discriminative than RAPD in subtyping the E. coli isolates

Study on intraspecific diversity of Ralstonia solanacearum strains in West Malaysia using whole cell fatty acid analysis

Surveys were conducted between the years of 2005 and 2006 at several locations in the northern, central and southern parts of West Malaysia to study the polymorphism of Ralstonia solanacearum strains. These sites included vegetables and farms with known hosts of the pathogen, such as banana, tomato, eggplant, chili and tobacco. Samples were collected from the suspected wilted plants and weeds, including soil and water samples, in selected areas. The bacterium was isolated in all samples using semi-selective tetrazolium chloride medium (TZC). The bacteria strains were detected by using the BIOLOG identification system and were confirmed by nested-PCR. Fatty Acid Methyl Esters (FAME) profiling was performed to determine polymorphism among 58 bacterial isolates. The results showed that the fatty acid composition varied for all R. solanacearum isolates. Grouping of R. solanacearum isolates by fatty acid composition suggested that the existence of distinct groups that were significantly related to host of bacteria but low correlation between fatty acid profiles and biovar or sampling site was detected. A unique FAME profile was found among the strains that have been isolated from banana