Comprehensive analysis of Salmonella sequence polymorphisms and development of a LDR-UA assay for the detection and characterization of selected serotypes

A dual RPA-LFD assay for the simultaneous detection of Salmonella typhimurium and Salmonella enteritidis

Introduction: Salmonella was one of the most common bacteria that caused foodborne illness, with S. typhimurium (Salmonella typhimurium) and S. enteritidis (Salmonella enteritidis) infections accounting for more than 75% of human salmonella infections. Methods: In this study, we developed a method of dual recombinase polymerase amplification (RPA) combined with a lateral flow dipstick for the rapid detection of S. typhimurium and S. enteritidis in clinical specimens (stool). Results: The entire reaction process, including amplification and result reading, could be completed within 65 min. The detection limits of S. typhimurium and S. enteritidis in pure culture samples were 5.23 × 101 CFU/mL and 3.59 × 101 CFU/mL, respectively. The detection limits of S. typhimurium and S. enteritidis in artificially contaminated samples were 8.30 × 101 CFU/mL and 2.70 × 102 CFU/mL, respectively. In addition, the method had no cross-reaction with other pathogenic microorganisms. The results in clinical samples were fully consistent with those obtained using Bacterial Analysis Manual, with sensitivity and specificity were 100% (8/8) and 100% (17/17) for S. typhimurium and 100% (4/4) and 100% (21/21) for S. enteritidis, respectively. Discussion: The detection limits of S. typhimurium and S. enteritidis in artificially contaminated samples were higher than those in pure culture samples, which might be attributed to the inherent complex composition of artificially contaminated samples. In addition, the detection limits of S. typhimurium and S. enteritidis in the same sample were also different, which might be attributed to different amplification efficiency of two target genes in the same reaction system. Conclusion: This assay had potential application outdoors, as it could be performed within 1 h at 38°C without a complex instrument, and the results could be observed with the naked eye. In conclusion, the dual RPA-LFD assay established in this study had practical significance for the rapid detection of S. typhimurium and S. enteritidis in the future.

Magnitude, risk factors and antimicrobial susceptibility pattern of Shigella and Salmonella, among children with diarrhea in Southern Ethiopia: A Cross-sectional Study

Objective:

This study was aimed at identifying Shigella and Salmonella infection, their antibiotic susceptibility pattern and associated risk factors among children with diarrhea who attended Alamura Health Center.

Method:

A facility-based cross-sectional study was conducted on 263 children aged below 14 years with diarrhea. A structured questionnaire was used to collect socio-demographic and clinical data after obtaining the necessary consent from their parents or caretakers. The culture and sensitivity tests were performed using the standard operating procedure of the microbiology laboratory.

Results:

Accordingly, 20/263 (7.6%), 95% confidence interval: 4.4%–11.4% Shigella and 1/263 (0.38%), 95% confidence interval: 0.0%–1.1% Salmonella were isolated. Shigella dysenteriae was dominant 11 (4.2%), followed by Shigella spp. 9 (3.42%) and Salmonella typ 1 (0.38%). The isolates showed 71.4% overall resistance to ampicillin and 61.9% for augmentin and tetracycline, whereas 95.2% of the isolates were sensitive to ciprofloxacin, 85.9% to ceftriaxone and ceftazidime, 81% to gentamycin, 76.2% to chloramphenicol, 66.7% to cefuroxime and 52.4% to cotrimoxazole. The habit of washing hands after toilet use for a while (adjusted odds ratio: 235.1, 95% confidence interval: 20.9–2643.3, p < 0.000) and storing cooked food in an open container for later use (adjusted odds ratio: 36.44, 95% confidence interval: 5.82–228.06, p < 0.000) showed a statistically significant association.

Conclusion:

High level of Shigella and single Salmonella was isolated. Ampicillin, augmentin and tetracycline were resistant and ciprofloxacin, ceftriaxone, ceftazidime, gentamycin, chloramphenicol, cefuroxime and cotrimoxazole were relatively sensitive. Hand-washing after defecation for some time and storing of foods for later use in an open container were statistically associated. Therefore, to alleviate this infection, the concerned body should focus on imparting health education for hand-wash after defecation and storing food in a closed container for later use is mandatory.

Development and Application of an Immunocapture PCR Diagnostic Assay Based on the Monoclonal Antibody for the Detection of Shigella

Background:

Shigella is among the most important human pathogenic microorganisms, infecting both humans and nonhuman and causing clinically severe diarrhea. Shigella must be enriched before detection, which is time-consuming.

Objectives:

To develop a sensitive, rapid, and specific method for Shigella detection.

Materials and Methods:

Shigella was used as an antigen to generate monoclonal antibodies (mAbs). mAbs were screened via indirect enzyme-linked immunosorbent assay (ELISA) and western blot, and two mAbs were selected. The mAb A3 showed high affinity and specificity and was used to develop immune magnetic beads (IMBs) for Shigella enrichment. An immunocapture (IC)-PCR primer was designed from the ipaH gene, and IC-PCR was developed based on the IMBs and PCR.

Results:

This system shortened the Shigella detection time to 70 min. The sensitivity of the IC-PCR was 9 colony-forming units.mL^-1 in artificial milk. The accuracy of the IC-PCR was confirmed using 46 clinical samples collected from monkeys. The IC-PCR results were consistent with the serological and biochemical assays.

Conclusion:

The IC-PCR described herein accurately detected Shigella from milk samples, monkeys and can thus be used to complement classical detection methods.

Detection of Shigella in Milk and Clinical Samples by Magnetic Immunocaptured-Loop-Mediated Isothermal Amplification Assay

Shigella is an important human food-borne zoonosis bacterial pathogen, and can cause clinically severe diarrhea. There is an urgent need to develop a specific, sensitive, and rapid methodology for detection of this pathogen. In this study, loop-mediated isothermal amplification (LAMP) combined with magnetic immunocapture assay (IC-LAMP) was first developed for the detection of Shigella in pure culture, artificial milk, and clinical stool samples. This method exhibited a detection limit of 8.7 CFU/mL. Compared with polymerase chain reaction, IC-LAMP is sensitive, specific, and reliable for monitoring Shigella. Additionally, IC-LAMP is more convenient, efficient, and rapid than ordinary LAMP, as it is more efficiently enriches pathogen cells without extraction of genomic DNA. Under isothermal conditions, the amplification curves and the green fluorescence were detected within 30 min in the presence of genomic DNA template. The overall analysis time was approximately 1 h, including the enrichment and lysis of the bacterial cells, a significantly short detection time. Therefore, the IC-LAMP methodology described here is potentially useful for the efficient detection of Shigella in various samples.

A liquid bead array for the identification and characterization of fljB-positive and fljB-negative monophasic variants of Salmonella Typhimurium

Salmonella1,4,[5],12:i:- accounts currently for one of the most common serotypes observed worldwide. These isolates do not express the FljB flagellin and mostly derive from Salmonella Typhimurium. They are therefore termed Salmonella Typhimurium monophasic variants (STMV) and are considered of comparable public health risk. Since serological identification of the somatic and flagellar antigens of STMV is not sufficient to demonstrate relatedness with Salmonella Typhimurium, additional assays detecting genetic markers unique to Salmonella Typhimurium are required. In addition, identification of the mutations affecting expression of the flagellar gene fljB can be useful to support the monophasic character observed phenotypically. Finally, genetic subtyping of the various mono- and biphasic Salmonella Typhimurium clonal groups can facilitate their epidemiological follow-up. Here, we present a home-made liquid bead array able to fulfill these requirements. This array confirmed the monophasic character of 240 STMV isolates collected in Belgium during 2014-2015 and identified 10 genetic subtypes. Microevolution in and around the fljB locus linked to IS26 insertions is probably one of the driven force accounting for STMV population diversity. Thanks to its open design, other genetic signatures could later be merged to the assay to subtype additional STMV clonal groups and to detect rare mutations.

Rapid and Sensitive Detection of Shigella spp. and Salmonella spp. by Multiple Endonuclease Restriction Real-Time Loop-Mediated Isothermal Amplification Technique

Shigella and Salmonella are frequently isolated from various food samples and can cause human gastroenteritis. Here, a novel multiple endonuclease restriction real-time loop-mediated isothermal amplification technology (MERT-LAMP) were successfully established and validated for simultaneous detection of Shigella strains and Salmonella strains in only a single reaction. Two sets of MERT-LAMP primers for 2 kinds of pathogens were designed from ipaH gene of Shigella spp. and invA gene of Salmonella spp., respectively. Under the constant condition at 63°C, the positive results were yielded in as short as 12 min with the genomic DNA extracted from the 19 Shigella strains and 14 Salmonella strains, and the target pathogens present in a sample could be simultaneously identified based on distinct fluorescence curves in real-time format. Accordingly, the multiplex detection assay significantly reduced effort, materials and reagents used, and amplification and differentiation were conducted at the same time, obviating the use of postdetection procedures. The analytical sensitivity of MERT-LAMP was found to be 62.5 and 125 fg DNA/reaction with genomic templates of Shigella strains and Salmonella strains, which was consist with normal LAMP assay, and at least 10- and 100-fold more sensitive than that of qPCR and conventional PCR approaches. The limit of detection of MERT-LAMP for Shigella strains and Salmonella strains detection in artificially contaminated milk samples was 5.8 and 6.4 CFU per vessel. In conclusion, the MERT-LAMP methodology described here demonstrated a potential and valuable means for simultaneous screening of Shigella and Salmonella in a wide variety of samples.

Genome Sequence of the Salmonella enterica subsp. enterica Serovar Namur Strain 05-2929, Lacking the Salmonella Atypical Fimbrial Operon

This paper announces the genome sequence and annotation of Salmonella enterica subsp. enterica serovar Namur strain 05-2929. S. Namur is a new serovar (39:z4,z23:-) that was isolated from a patient with salmonellosis in 2005 in Namur, Belgium, and has been identified as lacking the Salmonella atypical fimbrial (saf) operon.

Identification of common, non-typable and autoagglutinating Salmonella strains with Premi®Test Salmonella assay

Since Salmonella serotyping according to the White-Kauffmann-Le Minor scheme fails to identify rough and atypical serological variants, this study aimed at improving serovar identification with the commercially available Premi®Test Salmonella Assay. The array was validated against a set of Salmonella reference strains (n = 27) and field isolates of known serological structure (n = 112) showing up to 97.8% congruent results. Its diagnostic suitability was further verified with random field isolates (n = 52; 100% congruence). For 'rough' isolates (n = 54) and those with antigen expression failure (n = 19) the assay showed, respectively, 98.1% and 73.7% of serovar recognition. It considerably improved diagnostic capacity while typing troublesome isolates such as those failing to express flagellar antigens or showing autoagglutination. The method offers lower labour time compared to the traditional serotyping and does not require a broad range of diagnostic sera.

Combined genomarkers approach to Salmonella characterization reveals that nucleotide sequence differences in the phase 1 flagellin gene fliC are markers for variation within serotypes

The characterization and tracking of pathogenic micro-organisms in the clinical laboratory and public health environment demand schemes that are easy to standardize and use, are automated and high-throughput, and provide portable data. A combined genomarkers approach for Salmonella enterica based on comparative sequence analysis by mass spectrometry has been developed. The scheme targets genes encoding synthesis and assembly of antigens, metabolic pathway enzymes, virulence factors and fluoroquinolone resistance, covering the essential sequences that distinguish between and identify variation within serotypes. This study demonstrated how this single method could replace the combination of methods currently required to determine serotypes, subtypes, antibiotic resistance profiles and the genomic relatedness of Salmonella isolates. The results revealed genomic variation within seven serotypes previously unreported. This variation can be detected by using nucleotide sequence differences in the Salmonella flagellin gene fliC as markers that are not detected by traditional serotyping methods.