Phenotypic and genotypic characterization of Salmonella Enteritidis isolates

Abstract

In order to study the epidemiology of Salmonella Enteritidis outbreaks and determine the source of contamination so that a recurrence can be avoided, detailed characterization is necessary. Thus, the purpose of this study was to verify whether rep-PCR was able to discriminate among Salmonella Enteritidis isolates. Phage typing, detection of virulence genes and antimicrobial resistance testing were also associated to rep-PCR results. One hundred and two S. Enteritidis isolates from broiler carcasses, food, human, pigs, poultryrelated samples, and nine isolates from other countries were genotypically typed by REP-PCR, ERIC-PCR and BOX-PCR, collectively called rep-PCR. Phage typing, detection of virulence genes and antimicrobial resistance testing were also performed. Only three fingerprinting profiles were obtained with each rep-PCR method, with the majority of isolates belonging to the same profile. No relationship was observed between genotypic profile and year, place of isolation or source of infection. However, the less frequent rep-PCR profiles showed single antimicrobial resistance patterns. Although few strains isolated from swine were analyzed, different antimicrobial resistance patterns were observed. Furthermore, phage type 4 was not found in swine isolates. rep-PCR showed a lower discriminatory power as compared with antimicrobial resistance and phage typing, but the combination of genotypic and phenotypic methods was more discriminatory than any method alone, resulting in 48 different types.

Quantification and molecular characterization of Salmonella isolated from food samples involved in salmonellosis outbreaks in Rio Grande do Sul, Brazil

“…In previous studies conducted in Rio Grande do Sul (26,39), strains isolated from poultry and humans have also demonstrated a clonal relationship, which might contribute to elucidate the origin of salmonellosis cases. Since strains from poultry were reported as clonal due to the possible spread of one clone by international trade of breeding lines (33), a common clone causing foodborne outbreaks transmitted by egg products is not unexpectedly.…”

Genetic diversity of food originated Salmonella isolates

“…PFGE is an efficient sub-typing method and commonly used in outbreak investigations. PFGE produces comparable data of genotypic characteristics of Salmonella strains and it is accepted as the gold standard among molecular methods [12,13]. In addition to this, it has been used in typing Salmonella in human patients, animal sources and foods because of its discriminatory power and high reproducibility [14][15][16].…”

Investigation of a food-borne Salmonella Oranienburg outbreak in a Mexican prison

“…The lack of correlation between genotype and the antibiotic resistance profile pattern we detected has previously been documented for different S. enterica serotypes isolated from humans, animals, and food using the same molecular markers we used [6,56,57,58]. This lack of correlation might be partially explained by the fact that both repetitive and RAPD markers are dispersed throughout the bacterial chromosome, while genetic resistance determinants are allocated in restricted genetic regions, or even outside chromosomes, as in the case of plasmids [53].…”

“…However, other serotypes that were analyzed by techniques similar to the ones we used allow for such comparison. De Oliveira et al [6] assessed the diversity of 111 isolates of serotype Enteriditis associated with a diarrheagenic outbreak using the repetitive elements ERIC, REP, and BOX, for which they calculated the D values of 0.04, 0.05, and 0.04, respectively; these figures are one order of magnitude below our D estimates for ERIC and BOX. In contrast, an analysis of serotype Typhi strains from clinical samples obtained along a period of 20 years estimated a D value of 0.9821 for ERIC [40].…”

“…The gold standard for differentiating epidemiologically related strains of S. enterica is the analysis of polymorphisms through pulsed-field gel electrophoresis (PFGE) [4]. However, analysis of repetitive DNA elements has also been proven to be successful [5,6], and even equally or more effective than PFGE for that purpose [7,8]. Additionally, it has been reported that random amplified polymorphic DNA (RAPD) assays combined with other typing techniques are useful for monitoring outbreaks and clinical cases of gastroenteritis caused by serotypes of S. enterica [9][10][11].…”