Antimicrobial resistance pattern and plasmid profile of Salmonella typhi isolated from an outbreak in Tehran province

Prevalence of fluoroquinolone-resistant Salmonella serotypes in Iran: a meta-analysis

The present study was conducted to investigate the antimicrobial susceptibility profiles of Salmonella serotypes, especially fluoroquinolone-resistant strains, recovered from clinical samples in Iran. A full electronic search using related keywords was conducted in Persian and English languages in ISI Web of Knowledge, PubMed, Scopus, Google Scholar and the Scientific Information Database (SID) search engines to find papers published between 1983 and 1 July 2019. According to the inclusion and exclusion criteria, 46 eligible articles were selected for the final analysis out of the initial 13,186 studies retrieved. The pooled prevalence of quinolone-resistant Salmonella serotypes in clinical specimens in Iran was 2.9% to ciprofloxacin and 48.1% to nalidixic acid. Additional data on antibiotic resistance was as follows: 54.3% to tetracycline, 50.6% to ceftizoxime, 50.2% to streptomycin, 37.9% to ampicillin, 36.5% to kanamycin, 33.5% to trimethoprim-sulfamethoxazole, 27.2% to chloramphenicol, 19.1% to cephalothin, 8.8% to ceftriaxone, 7.6% to cefotaxime, 7.4% to aztreonam, 7.2% to gentamicin, 7% to cefepime, 6.8% to ceftazidime, 5.8% to cefixime, 2.7% to imipenem and 2.2% to meropenem. Findings of the present study showed a rising trend of resistance to the drugs of choice for the treatment of Salmonella infections, i.e. ampicillin, chloramphenicol and trimethoprim-sulfamethoxazole in Iran. However, ciprofloxacin, third-generation cephalosporins and carbapenems are still effective antibiotics especially against multi-drug resistant strains in Iran.

Instability of Escherichia coli R-factors in Salmonella enterica serovar Typhi involves formation of recombinant composite plasmid structures

In spite of a well-documented ability of Samonella enterica Typhi strains to receive R factors from Escherichia coli and other enterobacteria, epidemiological data show that Typhi is a rather poor host of antibiotic-resistance genes and in fact, of plasmids, suggesting that most of the plasmids naturally acquired by Typhi strains become unstable and eventually segregate. We have previously reported evidence that each of three plasmids conjugatively transferred to S. enterica Typhi experienced deletion-mediated loss of a resistance determinant before plasmid segregation occurred. We now report that in Typhi strains containing these unstable plasmids a superhelical DNA species of lower mobility is detected, probably representing plasmid dimer structures. Plasmid deletion is a RecA-dependent process since it is not detected in derivatives of a recA1 S. enterica Typhi strain containing the corresponding plasmids, and in such strains we were unable to detect either the low-mobility species. We propose that the deletable segments contain key information for plasmid stability in S. enterica Typhi, possibly a multimer resolution system.

Extended-spectrum-beta-lactamase production in a Salmonella enterica serotype Typhi strain from the Philippines

A Salmonella enterica serotype Typhi strain was cultured from blood and fecal samples from a 54-year-old man with fever and diarrhea. He had returned from travel to the Philippines a few days earlier. Phenotypic and genotypic analysis confirmed the production of the SHV-12 extended-spectrum beta-lactamase.

Typhoid and paratyphoid fever

Typhoid fever is estimated to have caused 21.6 million illnesses and 216,500 deaths globally in 2000, affecting all ages. There is also one case of paratyphoid fever for every four of typhoid. The global emergence of multidrug-resistant strains and of strains with reduced susceptibility to fluoroquinolones is of great concern. We discuss the occurrence of poor clinical response to fluoroquinolones despite disc sensitivity. Developments are being made in our understanding of the molecular pathogenesis, and genomic and proteomic studies reveal the possibility of new targets for diagnosis and treatment. Further, we review guidelines for use of diagnostic tests and for selection of antimicrobials in varying clinical situations. The importance of safe water, sanitation, and immunisation in the presence of increasing antibiotic resistance is paramount. Routine immunisation of school-age children with Vi or Ty21a vaccine is recommended for countries endemic for typhoid. Vi vaccine should be used for 2-5 year-old children in highly endemic settings.

Emergence of multidrug-resistant Salmonella enterica serovar typhi in Korea

A chloramphenicol-resistant strain of Salmonella enterica serovar Typhi was first noted in Korea in 1992, when a resistant isolate was detected in a returned traveler. Continued isolation of multidrug-resistant (MDR) strains thereafter in other settings prompted a retrospective analysis of laboratory records and phenotypic and genotypic analyses of 12 chloramphenicol-resistant isolates. Among these, one isolate was resistant only to chloramphenicol, and the other isolates were also resistant to ampicillin and co-trimoxazole. MDR was transferred by conjugation from 9 of the 11 isolates. PCR showed that all isolates had an incompatible group HI1 plasmid, and oriT was detected in 10 isolates, which included strains with an unsuccessful transfer of resistance. All of the ampicillin-resistant isolates had a beta-lactamase band of pI 5.4 and bla(TEM) alleles. A PCR amplicon from an isolate showed that the sequences were identical to those of bla(TEM-1), suggesting that all isolates had a TEM-1 beta-lactamase. All isolates had class 1 integrons: 10 isolates had integrons of ca. 1.2 kb with dhfr7 gene cassettes, and 1 isolate had an integron of ca. 2.3 kb with aacA4 and bla(OXA-1)-like gene cassettes. The pulsed-field gel electrophoresis patterns of 7 of 11 MDR isolates were identical and indistinguishable from those reported for isolates in India and Indonesia. In conclusion, some of the MDR strains in Korea are related to those in other Asian countries. Susceptibility testing became necessary for selection of antimicrobial agents for the optimal treatment of patients with the emergence of MDR Salmonella serovar Typhi in Korea.

Epidemiology of emerging/re-emerging antimicrobial-resistant bacterial pathogens

The rapid global expansion of bacteria resistant to antimicrobials is the most important development over the past year in emerging bacterial diseases. The critical events are the emergence of Staphylococcus aureus with decreased sensitivity to vancomycin, worldwide resistance to penicillin in Streptococcus pneumoniae, and the remorseless progression of multiply-resistant Mycobacterium tuberculosis. Most startling was the isolation from a human in Madagascar of a plague bacillus possessing a plasmid readily transferable to Escherichia coli, which confers multiple antibiotic resistance. The hospital environment continues to see the transmission of resistant organisms, notably vancomycin-resistant enterococci. Finally, as food markets become more open around the world, food-borne outbreaks of E. coli O157 and cholera demonstrate how difficult it can be to establish effective health and safety barriers.