Abstract
BackgroundClassical strains of Salmonella enterica serovar Typhimurium (Typhimurium) predominantly cause a self-limiting diarrheal illness in humans and a systemic disease in mice. In this study, we report the characterization of a strain isolated from a blood-culture taken from a 15-year old woman suffering from invasive severe salmonellosis, refractory to conventional therapy with extended-spectrum cephalosporin (ESC).ResultsThe strain, named 33676, was characterized as multidrug-resistant Salmonella serogroup A by biochemical, antimicrobial and serological tests. Multilocus sequence typing (MLST) and XbaI macrorestrictions (PFGE) showed that strain 33676 belonged to the Typhimurium ST213 genotype, previously described for other Mexican Typhimurium strains. PCR analyses revealed the presence of IncA/C, IncFIIA and ColE1-like plasmids and the absence of the Salmonella virulence plasmid (pSTV). Conjugation assays showed that the ESC-resistance gene blaCMY-2 was carried on the conjugative IncF plasmid, instead of the IncA/C plasmid, as found in previously studied ST213 strains. Although the IncA/C plasmid conferred most of the observed antimicrobial resistances it was not self-conjugative; it was rather able to conjugate by co-integrating with the IncF plasmid. Strain 33676 was fully attenuated for virulence in BALB/c mice infections. Both type-three secretion system (T3SS), encoded in Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2), were functional in the 33676 strain and, interestingly, this strain produced the H2 FljB flagellin instead of the H1 FliC flagellin commonly expressed by S. enterica strains.ConclusionsStrain 33676 showed two main features that differentiate it from the originally described ST213 strains: 1) the blaCMY-2 gene was not carried on the IncA/C plasmid, but on a conjugative IncF plasmid, which may open a new route of dissemination for this ESC-resistance gene, and 2) it expresses the H2 FljB flagella, in contrast with the other ST213 and most Typhimurium reference strains. To our knowledge this is the first report of an IncF blaCMY-2-carrying plasmid in Salmonella.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0633-7) contains supplementary material, which is available to authorized users.
Highlights
Classical strains of Salmonella enterica serovar Typhimurium (Typhimurium) predominantly cause a self-limiting diarrheal illness in humans and a systemic disease in mice
We found that all the multi-drug resistant (MDR) strains with the ESCresistant phenotype carried the blaCMY-2gene on a large plasmid (150 kb) of the IncA/C incompatibility group (IncA/C), and that these strains belonged to a new chromosomal multi-locus genotype, designated in the Multilocus sequence typing (MLST) database as sequence type 213 (ST213) [23, 24]
Strain 33676 was identified as an MDR Salmonella serogroup A 1, 4, 5 (+) We studied a strain isolated from a patient with severe pancolitis and bacteremia
Summary
Classical strains of Salmonella enterica serovar Typhimurium (Typhimurium) predominantly cause a self-limiting diarrheal illness in humans and a systemic disease in mice. Salmonella enterica are Gram-negative flagellated bacteria that cause salmonellosis, a food-borne disease in humans causing gastroenteritis and bacteremia worldwide. The most prevalent Salmonella serovars isolated from humans and other animals are Typhimurium and Enteritidis [1, 2]. Typhimurium strains cause gastroenteritis in humans and several animals, whereas in mice they produce a systemic infection similar to the enteric fever generated by the human-restricted serovar Typhi [3, 4]. In most S. enterica serovars, the antigenic formula is composed by two flagellar phases (H1 and H2). The S. enterica strains express the flagellar H1 phase. The role of flagella in motility, chemotaxis and pathogenesis is recognized, the biological significance of phase variation in Salmonella has been scarcely addressed [3, 6]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
