Evaluation of a DNA probe for identifying Salmonella typhi in Peruvian and Indonesian bacterial isolates

Molecular diagnosis of Salmonella typhi and its virulence in suspected typhoid blood samples through nested multiplex PCR

A nested multiplex polymerase chain reaction (PCR) based diagnosis was developed for the detection of virulent Salmonella typhi in the blood specimens from patients suspected for typhoid fever. After the Widal test, two pairs of primers were used for the detection of flagellin gene (fliC) of S. typhi. Among them, those positive for fliC alone were subjected to identification of genes in Via B operon of Salmonella Pathogenesity Island (SPI-7) where four primer pairs were used to detect tviA and tviB genes. Among 250 blood samples tested, 115 were positive by fliC PCR; 22 of these were negative for tviA and tviB. Hence, the method described here can be used to diagnose the incidence of Vi-negative serovar typhi especially in endemic regions where the Vi vaccine is administered.

Rapid diagnosis of typhoid fever by PCR assay using one pair of primers from flagellin gene of Salmonella typhi

Using the polymerase chain reaction (PCR) assay, we developed a rapid diagnosis method for Salmonella typhi infection in blood specimens from patients with typhoid fever. Primers were designed from the flagellin gene sequence, which would give an amplification product of 367 base pairs. In this study, the specificity of the assay, with no amplification, was seen for the other Salmonella strains with the flagellin gene, and not for non- Salmonella bacteria. For the sensitivity test, the protocol described allowed the detection of two to three copies of the Salmonella typhi genome, as determined by serial dilution of genomic DNA from Salmonella typhi. With the PCR technique, genomic DNA of Salmonella typhi was detected in 46 of 73 blood samples collected from patients with clinically suspected typhoid fever who had fever within 3 days of admission to the General Hospital, Makassar, South Sulawesi, Indonesia, and who had had no prior antibiotic treatment. The PCR results (63% positive cases) were compared with those of blood culture (13.7% positive cases) and the Widal test (35.6% positive cases), using the same samples from each of the 73 patients admitted to the General Hospital in Makassar. The time taken for PCR analysis of each sample was less than 12 h, compared with 3 to 5 days for blood or clot culture. The PCR with one pair of primers can be used as a novel, rapid diagnostic method for typhoid fever, particularly when results of standard culture assays are negative.

Detection of Salmonella typhi by polymerase chain reaction: implications in diagnosis of typhoid fever

The present study was conducted to detect Salmonella typhi by polymerase chain reaction (PCR) in a clinical setting. A group of 40 clinically suspected cases of typhoid fever, lasting for about 3-11 days, with or without chills and rigors and hepatosplenomegaly were selected. Of these, 20 were culture positive and the remaining 20 were found to be negative by conventional blood culture technique. Primary PCR was followed by nested PCR using two sets of primers corresponding to flagellar gene of S. typhi strain. Two bands of about 458 and 343 bp were detected in 20 blood culture positive cases and 12 of the 20 culture negative ones. In the simulated group of samples, no amplification was detected. Our results suggest that PCR-based diagnosis is particularly useful for all clinically suspected cases of typhoid fever. The sensitivity of PCR and its potential use in routine diagnosis and epidemiological studies of typhoid fever can be exploited to complement studies by including bone marrow culture, faeces and bile samples.

Early detection of typhoid by polymerase chain reaction

BACKGROUND

Typhoid is a common problem in developing countries. Cultivation of bacteria and serology (especially Widal test) give unacceptable levels of false-negative and false-positive results, respectively.

PATIENTS AND METHODS

In this study, a recently introduced polymerase chain reaction-based technique (which has 100% specificity for Salmonella typhi) was compared with blood culture and Widal test during the first week of illness of 82 suspected cases of typhoid.

RESULTS

The respective figures of positivity for PCR, blood culture and Widal test were 71.95%, 34.1%, and 36.5%. A control group of 20 healthy persons gave figures of 0%, 0%, and 33.3%, respectively.

CONCLUSION

We conclude that this PCR-based technique is not only absolutely specific, but also very sensitive and, therefore, much superior to blood culture and Widal test for the early diagnosis of typhoid.

Distinctive IS200 insertion between gyrA and rcsC genes in Salmonella typhi

While probing the vicinity of ompC, a copy of the IS200 insertion element was found between the gyrA and rcsC genes of Salmonella typhi, the causal agent of typhoid fever. This distinctive feature was conserved throughout 63 S. typhi isolates of different geographical origins and was absent from 46 other Salmonella serotypes, including those most associated with human infections, as well as from 19 other enteric bacteria. Furthermore, the location of this IS200 copy corresponds to a constant band, present throughout the 14 PstI S. typhi IS200 fingerprints, encompassing several Vi phage types. Interestingly, an apparently unrelated serotype not frequently associated with human disease, Salmonella weltevreden, contained an IS200 copy at the same position, although it was accompanied by an additional segment of cryptic DNA. On the basis of these findings, PCR assays were designed for molecular typing of S. typhi, and these are potentially useful in studying the epidemiology of typhoid fever.

Detection of Salmonella typhi in the blood of patients with typhoid fever by polymerase chain reaction

A polymerase chain reaction (PCR)-based test was developed for the detection of Salmonella typhi in the blood specimens from patients with typhoid fever. Two pairs of oligonucleotide primers were designed to amplify a 343-bp fragment of the flagellin gene of S. typhi. Amplified products were analyzed by agarose gel electrophoresis and Southern blot hybridization by using a 32P-labeled 40-base probe internal to the amplified DNA. The nested PCR with two pairs of primers could detect 10 organisms of S. typhi as determined by serial dilutions of DNA from S. typhi. The peripheral mononuclear cells from 11 of 12 patients with typhoid fever confirmed by blood culture were positive for DNA fragment of the flagellin gene of S. typhi, whereas 10 blood specimens of patients with other febrile diseases were negative. With the nested PCR, S. typhi DNAs were detected from blood specimens of four patients with suspected typhoid fever on the basis of clinical features but with negative cultures. We suggest that the PCR technique could be used as a novel diagnostic method of typhoid fever, particularly in culture-negative cases.

Use of a DNA probe to detect Salmonella typhi in the blood of patients with typhoid fever

A DNA probe was used to detect Salmonella typhi from blood samples from 14 of 33 patients with culture-confirmed typhoid fever, using the equivalent of 2.5 ml of blood. In contrast, S. typhi was detected in 17 of the same 33 patients by culture of 8 ml of blood. The probe hybridized to blood samples of 4 of 47 patients from whom S. typhi was not isolated.

Microbial DNA diagnostic technology

The principle objectives when creating a robust DNA diagnostic assay system are sensitivity, specificity and minimal read-time. To meet these ends, depending on the specifically defined test, various aspects of molecular hybridization methodology must be optimized. In particular, among other things, attention has focused on (i) formulating highly specific probes; (ii) devising sensitive nonisotopic detection systems, (iii) minimizing the extent of preparing clinical samples for assaying, (iv) amplifying the target sequence to augment sensitivity and (v) enhancing hybridization kinetics to speed up the reaction period. In this article, some recent studies that are directed to the development of nucleic acid hybridization systems for clinical diagnosis of microorganisms are considered.