Subtyping of Salmonella typhimurium by pulsed-field gel electrophoresis and comparisons with phage types and resistance types

Prevalence, Distribution, and Diversity of Salmonella Strains Isolated From a Subtropical Lake

This study investigated the prevalence, serovar distribution, antimicrobial resistance, and pulsed field gel electrophoresis (PFGE) typing of Salmonella enterica isolated from Lake Zapotlán, Jalisco, Mexico. Additionally, the association of the presence of Salmonella with physicochemical and environmental parameters was analyzed using Pearson correlation analysis and principal component analysis (PCA). Salmonella spp. were identified in 19 of 63 (30.15%) samples. The prevalence of Salmonella was positively correlated with air temperature, electrical conductivity, pH, and dissolved oxygen and negatively correlated with relative humidity, water temperature, turbidity, and precipitation. The predominant serotype identified was Agona (68.48%), followed by Weltevreden (5.26%), Typhimurium (5.26%), and serogroup B (21.05%). Overall, the highest detected antimicrobial resistance was toward colistin (73.68%), followed by sulfamethoxazole (63.15%), tetracycline (57.89%), nalidixic acid (52.63%), and trimethoprim (52.63%). All Salmonella strains were genetically diverse, with a total of 11 XbaI and four BlnI profiles on PFGE. The use of these two enzymes allowed differentiate strains of Salmonella of the same serotype. The results obtained in this study contribute to a better understanding of the Salmonella spp. ecology in an endorheic subtropical lake and provide information for decision makers to propose and implement effective strategies to control point and non-point sources of pathogen contamination.

[Salmonella enterica serovar typhimurium infection presenting as a retrocecal mass in an 8-year-old child]

Minor salmonellosis is due to Gram-negative bacilli, which usually cause enterocolitis with potentially severe complications. We report on a case of a clinically uncommon presentation of Salmonella enterica serovar typhimurium infection in an 8-year-old child who presented with acute abdominal pain. We discuss clinically uncommon presentations of salmonella disease in children, as well as its pathology and radiology.

Pulsed-Field Gel Electrophoresis Subtyping Database for FoodborneSalmonella entericaSerotype Discrimination

Nontyphoid Salmonella is one of the main causes of bacterial gastroenteritis worldwide and is responsible for 65% of reported outbreaks of foodborne diseases in France. Serotyping is widely used for isolate preliminary identification, but it poorly discriminates strains. Rapid, efficient molecular subtyping tools have therefore been developed for the investigation of outbreaks. We evaluated the performance of the pulsed-field gel electrophoresis (PFGE) method for discrimination of 31 Salmonella serotypes frequently isolated in France. We set up a genomic database of Salmonella strains isolated from food, animals, the environment, and humans to improve the management of contamination and reactions to foodborne disease outbreaks. We studied 1128 isolates by PFGE, according to the standardized PulseNet protocol. We identified 452 PFGE patterns, 67.5% of which corresponded to a single isolate. The ability of this method to distinguish between isolates was estimated by calculating the Simpson index and the 95% confidence interval. Values obtained ranged between 0.33 (0.11-0.54) to 0.99 (0.96-1.00), depending on serotype. Epidemiological information about isolates was used for analyses of intra- and interserotype diversity results and for determining whether PFGE patterns were linked to the source of the isolate. Clustering analysis of the PFGE patterns obtained confirmed that serotype and PFGE genotype were closely linked. Some PFGE patterns were identified as major patterns, each of these patterns being found in at least 10 isolates. The database generated has already proved its effectiveness in epidemiological investigations in livestock production and foodborne outbreaks.

Complete nucleotide sequences of 84.5- and 3.2-kb plasmids in the multi-antibiotic resistant Salmonella enterica serovar Typhimurium U302 strain G8430

The multi-antibiotic resistant (MR) Salmonella enterica serovar Typhimurium phage type U302 strain G8430 exhibits the penta-resistant ACSSuT-phenotype (ampicillin, chloramphenicol, streptomycin, sulfonamides and tetracycline), and is also resistant to carbenicillin, erythromycin, kanamycin, and gentamicin. Two plasmids, 3.2- and 84.5-kb in size, carrying antibiotic resistance genes were isolated from this strain, and the nucleotide sequences were determined and analyzed. The 3.2-kb plasmid, pU302S, belongs to the ColE1 family and carries the aph(3')-I gene (Kan(R)). The 84.5-kb plasmid, pU302L, is an F-like plasmid and contains 14 complete IS elements and multiple resistance genes including aac3, aph(3')-I, sulII, tetA/R, strA/B, bla(TEM-1), mph, and the mer operon. Sequence analyses of pU302L revealed extensive homology to various plasmids or transposons, including F, R100, pHCM1, pO157, and pCTX-M3 plasmids and TnSF1 transposon, in regions involved in plasmid replication/maintenance functions and/or in antibiotic resistance gene clusters. Though similar to the conjugative plasmids F and R100 in the plasmid replication regions, pU302L does not contain oriT and the tra genes necessary for conjugal transfer. This mosaic pattern of sequence similarities suggests that pU302L acquired the resistance genes from a variety of enteric bacteria and underscores the importance of a further understanding of horizontal gene transfer among the enteric bacteria.

Characterization of Salmonella enterica serotype Typhimurium isolates from human, food, and animal sources in the Republic of Ireland

A potential epidemic clone of Salmonella enterica serotype Typhimurium DT104, and the possible emergence of S. enterica serotype Typhimurium DT104b, has been identified from the characterization of 67 S. enterica serotype Typhimurium strains from three sources, human gastroenteritis isolates, isolates from food samples, and veterinary isolates, by antimicrobial resistance profiling, phage typing, and pulsed-field gel electrophoresis. Resistance to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline was found in 77.6% of these strains.

AFLP analysis of Salmonella enterica serovar Typhimurium isolates of phage types DT 9 and DT 135: diversity within phage types and its epidemiological significance

Amplified fragment length polymorphism (AFLP) was applied to 35 and 34 isolates, respectively, of Salmonella enterica serovar Typhimurium phage types DT 9 and DT 135, using eight primer pair combinations. Eight and 17 AFLP types were observed in DT 9 and DT 135, respectively. DT 9 is rare in the UK and common in Australia, but one AFLP form dominated with 28 isolates, comprising 22 of 25 UK isolates, four of five Australian isolates, one Jamaican and one Spanish isolate. Of the others, two UK isolates are closely related to the major form, two from elsewhere are in the major cluster and three isolates from different countries are in a separate cluster. For DT 135, two closely related AFLP types of seven and 11 isolates form the major cluster, which also includes 11 isolates, mostly in single-isolate AFLP types, while five isolates from different countries form a well-separated minor cluster. For both DTs all isolates are grouped together if only the phage type specific bands identified earlier are used, confirming their value for molecular-based 'phage typing'. Polymorphic markers identified in this study could also be used for subtyping within both phage types. The value of AFLP is in locating DNA fragments useful for typing, but implementation of a replacement typing scheme would probably involve multiplex PCR or microarray technologies.

Comparison of phenotypic traits and genetic relatedness of Salmonella enterica subspecies arizonae isolates from a colony of ridgenose rattlesnakes with osteomyelitis

Reptiles are well-known sources of human Salmonella infections; however, little is known about the ability of Salmonella to cause disease in reptiles. Thirty-seven isolates of Salmonella enterica subspecies arizonae (S. arizonae) were obtained from retrospective and prospective studies of a closed colony of ridgenose rattlesnakes (Crotalus willardi) with osteomyelitis. All isolates (N = 7) from bone lesions were of a single serotype, 56:z4,z23, and this serotype was found on only 1 occasion among 8 other serotypes isolated from 21 cloacal and intestinal samples. The remainder (N = 7) of serotype 56:z4,z23 isolates were from other extraintestinal sites, including liver, ovary, blood, and testis. S. arizonae isolates were susceptible to most antimicrobials, and plasmid profiles did not correlate with serotype or antimicrobial resistance. Isolates of the 56:z4,z23 serotype (N = 14) formed a tight cluster with 95% similarity by XbaI macrorestriction analysis. Individual isolates of serotypes, 56:z4,z23, 38:(k)-z35, and 48:i-z invaded HeLa cells but an isolate of serotype 50:r-z did not. The same individual isolates of serotype 56:z4,z23 and 48:i-z also invaded viper heart cells. The Salmonella InvA gene was detected by polymerase chain reaction (PCR) in all S. arizonae serotypes tested, including 5 serotype 56:z4,z23 isolates and individual isolates of serotypes 48:i-z and 50:r-z. A source or possible explanation for increased virulence of S. arizonae serotype 56:z4,z23 in this unique host has not been found.

A comparative study and phage typing of silage-making Lactobacillus bacteriophages

To investigate basic characteristics of 10 virulent phages active on silage-making lactobacilli, morphological properties, host ranges, protein composition and genome characterization were separated into five groups based on host ranges and basic properties. The seven phages of groups I, II and V were active on Lactobacillus plantarum and Lactobacillus pentosus. Phage phiPY4 (group III) infected both L. casei and Lactobacillus rhamnosus. Phage phiPY5 (group IV) specifically infected Lactobacillus casei. Morphologically, three phages of groups I belonged to the Myoviridae family, while seven other phages of groups II, III and V belonged to the Siphoviridae family. SDS-PAGE profiles, restriction analysis, G + C contents of DNA and Dot blot hybridization revealed a high degree of homology in each group. Clustering derived from host range analysis was closely related to results of DNA and protein analyses. These phages may be applicable to phage typing for silage-making lactobacilli.