Plasmid-Mediated Quinolone Resistance (PMQR) in Two Clinical Strains of Salmonella enterica Serovar Corvallis

Non-typhoid serovars of Salmonella enterica are one of the main causes of bacterial food-borne infections worldwide. For the treatment of severe cases of salmonellosis in adults, fluoroquinolones are amongst the drugs of choice. They are categorized by the World Health Organization (WHO) as “critically important with highest priority in human medicine”. In the present study, two clinical S. enterica serovar Corvallis isolates (HUA 5/18 and HUA 6/18) from a Spanish hospital, selected on the basis of fluoroquinolone resistance, were characterized. The MICs of ciprofloxacin, determined by E-test, were 0.5 and 0.75 µg/mL for HUA 5/18 and HUA 6/18, respectively, and both were also resistant to pefloxacin but susceptible to nalidixic acid. Whole genome sequencing (WGS) of the isolates was performed with Illumina platform, and different bioinformatics tools were used for sequence analysis. The two isolates belonged to ST1541, and had the Thr57Ser substitution in the ParC protein which is also found in ciprofloxacin susceptible isolates. However, they harbored identical ColE plasmids of 10 kb carrying the qnrS1 gene. In these plasmids, the gene was flanked by defective versions of IS2-like and ISKra4-like insertion sequences. HUA 5/18 and HUA 6/18 were also phenotypically resistant to streptomycin, sulfonamides and tetracycline, with the responsible genes: strA, strB, sul2 and tet(A) genes, being located on a IncQ1 plasmid. ColE plasmids with the qnrS1 gene are widely spread among multiple serovars of S. enterica from different samples and countries. These mobilizable plasmids are playing an important role in the worldwide spread of qnrS1. Thus, their detection in hospitals is a cause of concern which deserves further attention.

Evaluation of antimicrobial resistance among Salmonella and Shigella isolates in the University Hospital "St. George," Plovdiv, Bulgaria

The aim of this work is to study the epidemiology and antimicrobial resistance to the most commonly used antibiotics for the treatment of acute gastroenteritis caused by Salmonella and Shigella at the largest Bulgarian hospital-University Hospital "St. George," Plovdiv-for the period 2009-2013. Two hundred ninety strains were in vitro tested for resistance to 15 antimicrobial agents. The presence of extended-spectrum beta-lactamases (ESBLs) was demonstrated by a variety of specialized tests. For comparison, a collection of 28 strains submitted by the National Reference Laboratory (NRL) "Enteric Infections" at the National Center of Infectious and Parasitic Diseases (NCIPD), Sofia, was also tested for the production of ESBLs. In isolates, phenotypically demonstrated as ESBL producers, polymerase chain reaction (PCR) detection of the genes bla-CTX-M, bla-SHV, and bla-TEM was performed. Among the 290 tested isolates, only two- Salmonella serotype Livingstone and Shigella flexneri-were phenotypically proven to be ESBL producers. Only 4 strains from the collection of 28, submitted from the NRL "Intestinal Infections" in NCIPD, Sofia, were phenotypically confirmed as ESBL producers. The presence of the bla-CTX-M gene was detected in all of the tested strains (4 from NRL, NCIPD, Sofia, and 2 from the University Hospital St. George, Plovdiv), the bla-SHV gene only in strain S. Livingstone from Plovdiv, and the bla-TEM gene in two from Sofia and one (again S. Livingstone) from Plovdiv. In conclusion, Salmonella and Shigella isolates from patients hospitalized at the University Hospital St. George, Plovdiv, with acute gastroenteritis demonstrate good susceptibility to the most commonly used antibiotic agents, including azithromycin.

Prevalence, antimicrobial resistance, and extended-spectrum beta-lactamases characterization of Salmonella isolates in Apulia, southern Italy (2001-2005)

The prevalence, antimicrobial susceptibility, and production of extended-spectrum beta-lactamases (ESBLs) of Salmonella collected from several hospitals in Apulia (southern Italy) were evaluated. The most common Salmonella isolates were Salmonella enterica serovar Typhimurium (44.6%), S. enterica serovar Enteritidis (33.4 %), S. enterica serovar Infantis (3.2 %), S. enterica serovar Typhi (1.5%), and S. enterica serovar Bovismorbificans (1.5%). The other serovars accounted for less than 1% each. Our data show a high resistance to ampicillin, tetracycline, and chloramphenicol. The isolates were pansensitive (53.5%), resistant to one antimicrobial agent (10.5%), resistant to two antimicrobial agents (22.1%), resistant to three antimicrobial agents (10.8%), and to four antimicrobial agents (2.7%). Resistance to more than four antibiotics was observed in 0.5% of strains. The presence of ESBL was found in only one strain of S. enterica serovar Bovismorbificans. The CTX-M-1 type-producing strain was identified by isoelectric focusing and molecular analysis. Results were consistent with the presence of a pI 8.6 ESBL active on cefotaxime, ceftazidime, cefepime, and aztreonam. Mating experiments showed that the CTX-M-1 determinant was transferable. To the best of our knowledge, this is the first report of CTX-M-1 type ESBL in Salmonella serovar Bovismorbificans.