Antimicrobial Resistance of Salmonella enterica Serovar Typhimurium in Shanghai, China

Abstract

We aimed to analyze the antimicrobial resistance phenotypes and to elucidate the molecular mechanisms underlying resistance to cephalosporins, ciprofloxacin, and azithromycin in Salmonella enterica serovar Typhimurium isolates identified from patients with diarrhea in Shanghai. The isolates showed high rates of resistance to traditional antimicrobials, and 20.6, 12.7, and 5.5% of them exhibited decreased susceptibility to cephalosporins, ciprofloxacin, and azithromycin, respectively. Notably, 473 (84.6%) isolates exhibited multidrug resistance (MDR), including 161 (28.8%) isolates that showed an ACSSuT profile. Twenty-two MDR isolates concurrently exhibited decreased susceptibility to cephalosporins and ciprofloxacin, and six of them were co-resistant to azithromycin. Of all the 71 isolates with decreased susceptibility to ciprofloxacin, 65 showed at least one mutation (D87Y, D87N, or D87G) in gyrA, among which seven isolates simultaneously had mutations of parC (S80R) (n = 6) or parC (T57S/S80R) (n = 1), while 49 isolates with either zero or one mutation in gyrA contained plasmid-mediated quinolone resistance (PMQR) genes including qnrB, qnrS, and aac(6′)-Ib-cr. Among the 115 cephalosporin-resistant isolates, the most common ESBL gene was blaCTX-M, followed by blaTEM-1, blaOXA-1, and blaSHV -12. Eight subtypes of blaCTX-M were identified and blaCTX-M-14 (n = 22) and blaCTX-M-55 (n = 31) were found to be dominant. To the best of our knowledge, this is the first report of the presence of blaCTX-M-123 and blaCTX-M-125 in S. Typhimurium. Besides, mphA gene was identified in 15 of the 31 azithromycin-resistant isolates. Among the 22 isolates with reduced susceptibility to cephalosporins and ciprofloxacin, 15 contained ESBL and PMQR genes. Coexistence of these genes lead to the emergence of MDR and the transmission of them will pose great difficulties in S. Typhimurium treatments. Therefore, surveillance for these MDR isolates should be enhanced.

Antimicrobial susceptibility and MLVA analysis of S. Typhimurium strains isolated from human and poultry samples in Tunisia

“…The study of the most frequent alleles obtained from the isolates of the different origins and the higher discriminatory index (DI), showed that ST6 was the loci with highest discriminatory index, and it may be of potential use for source attribution. Previous studies supported our results [9,36]. On the other hand, STTR10 and ST8 locus were absent in many strains (46.6% and 48.8%, respectively).…”

“…The most common resistance profile in human origin strains was AMP-TIC-TET-MIN-SXT (26%), and for poultry strains it was TET-MIN (38.8%) and AMP-TIC-TET-MIN (33.3%), suggesting that a possible gene transference of S. Typhimurium strains between these two sources might have happened. The S. Typhimurium exhibited high rates of resistance to traditional antibiotics such as ampicillin, nalidixic acid, tetracycline and sulfamethoxazole-trimethoprim; this is in accordance with the findings of other authors [35,36]. The detection of antimicrobial genes and a strict policy for the rational use of antibiotics for treating animals and humans is needed, if we do not want to have to limit the therapeutical choices for treating salmonellosis [5].…”

Distribution and dissemination of antimicrobial-resistant Salmonella in broiler farms with or without enrofloxacin use

“…In Europe, the first case of failure of AZM treatment of Salmonella infection was reported [49]. Similarly, emergence of clinical AZM-resistant Salmonella isolates was recently reported in Asia [50, 51]; 15.24% of Salmonella isolates from chicken showed resistance to AZM (with an MIC ≥16 μg/mL) in another study [52]. However, reports of AZM resistance in Salmonella isolates from humans or animals in South Korea are rare.…”

Antimicrobial resistance and genetic diversity of Salmonella enterica from eggs

“…In addition, many of the strains were multidrug resistant (MDR) with some even being resistant to more than seven antibiotics. Wang et al also showed that 84.6% of the Salmonella isolates from Shanghai, China, exhibited MDR and proved that resistance genes play an important role in MDR (Wang et al, ). Our findings indicate that it is necessary to continue monitoring the antimicrobial resistance of Salmonella isolates to help determine the appropriate antimicrobial therapy for patients infected with this pathogen.…”