A. Aladueña

Mechanism of Resistance to Several Antimicrobial Agents in Salmonella Clinical Isolates Causing Traveler's Diarrhea

ABSTRACT The evolution of antimicrobial resistance in Salmonella isolates causing travelers diarrhea (TD) and their mechanisms of resistance to several antimicrobial agents were analyzed. From 1995 to 2002, a total of 62 Salmonella strains were isolated from stools of patients with TD. The antimicrobial susceptibility to 12 antibiotics was determined, and the molecular mechanisms of resistance to several of them were detected as well. The highest levels of resistance were found against tetracycline and ampicillin (21 and 19%, respectively), followed by resistance to nalidixic acid (16%), which was mainly detected from 2000 onward. Molecular mechanisms of resistance were analyzed in 16 isolates. In these isolates, which were resistant to ampicillin, two genes encoding β-lactamases were detected: oxa-1 (one isolate) and tem-like (seven isolates [in one strain concomitantly with a carb-2]). Resistance to tetracycline was mainly related to tetA (five cases) and to tetB and tetG (one case each). Resistance to chloramphenicol was related to the presence of the floR and cmlA genes and to chloramphenicol acetyltransferase activity in one case each. Different genes encoding dihydrofolate-reductases (dfrA1, dfrA12, dfrA14, and dfrA17) were detected in trimethoprim-resistant isolates. Resistance to nalidixic acid was related to the presence of mutations in the amino acid codons 83 or 87 of the gyrA gene. Further surveillance of the Salmonella spp. causing TD is needed to detect trends in their resistance to antimicrobial agents, as we have shown in our study with nalidixic acid. Moreover, such studies will lead to better treatment and strategies to prevent and limit their spread.

Antibiotic Resistance of Salmonella spp. from Animal Sources in Spain in 1996 and 2000

Emergence of resistant and multiresistant bacteria has become an important worldwide sanitary problem. International agencies recommend improving resistance surveillance studies in not only human but also animal origin strains. Because of its ubiquitous characteristics and zoonotic agent consideration, Salmonella spp. can be used as a good indicator microorganism for resistance surveillance studies. Salmonella spp. strains from animal sources isolated in 1996 (107) and 2000 (474) in Spain were tested against 12 different antimicrobials agents, using the disc diffusion method. Results were interpreted following the NCCLS criteria. Data showed that Salmonella spp. strains (61.7% in 1996 and 81.5% in 2000) were resistant to at least one antibiotic. Pig-related strains were considerably more resistant than strains from other sources. Enteritidis serotype was less resistant than other serotypes, except for ampicillin in 1996 (50% resistant) and nalidixic acid in 2000 (65.1% resistant). An emergent monophasic serotype, 4,5,12:i:-, first detected in 1997 in Spain was 100% resistant and 90% multiresistant. Typhimurium serotype was the most common Salmonella serotype from animal sources in both years. It was widely distributed among animals and was among the serotypes with a higher degree of resistance. The ampicillin, chloramphenicol, sulfonamides, streptomycin, and tetracycline resistance pattern, commonly associated with Salmonella serotype Typhimurium DT 104, had spread among other Typhimurium phage types and other Salmonella serotypes. Salmonella spp. strains isolated from feeding stuffs were considerably more susceptible than animal source strains, suggesting that the high Salmonella spp. resistance percentage was probably due to the use of antibiotics in animal farms rather than the consumption of contaminated feeding stuffs.

Salmonella enterica Infections in Spanish Swine Fattening Units

The present study is the first conducted in Spain to estimate the bacteriological herd prevalence of Salmonella enterica in fattening units and to describe the Salmonella serovar diversity on these farms using a sample representative of the entire swine population. For this purpose, 10 faecal samples were collected from 10 different pens containing pigs close to market weight in a total of 232 fattening units. Total sample size was proportionally distributed according to the fattener census in each of the regions of the country and all the samples were examined by culture of 25 g of faecal material. One hundred (43.1%) farms had at least one Salmonella‐positive sample (95% CI: 37–49.1%). Salmonella enterica was detected in 290 (12.5%) pooled faecal floor samples (95% CI: 11.2–13.8%). The apparent herd prevalence of salmonellosis was similar among multi‐site, finishing and farrow to finish farms. Overall, 24 different serovars were identified, with S. Typhimurium, S. Rissen and S. Derby being the most common both at herd and sample level. Results of phage typing were available for the 91 isolates of S. Typhimurium. A total number of 10 different phage types were identified, with DT 193 being the most frequent. Phage types DT 104, DT 104b and DT U302, which have been associated with several multi‐resistant patterns, accounted for 23% and 29% of the Typhimurium total isolates or Typhimurium infected farms respectively.

Distribución de los serotipos y fagotipos de Salmonella de origen humano aislados en España en 1997-20

Introduccion. La salmonelosis continua siendo una de las causas principales de gastroenteritis en Espana, siendo la serotipificacion el marcador epidemiologico universalmente utilizado para la caracterizacion de los aislamientos de Salmonella spp. Algunos serotipos se identifican muy frecuentemente, reduciendo el poder de discriminacion de esta tecnica. Por ello, para el estudio epidemiologico de las salmonelosis producidas por estos serotipos es necesario utilizar marcadores complementarios como la fagotipificacion. Metodos. Se serotipificaron, por aglutinacion directa, las cepas de Salmonella spp. de origen humano recibidas en el Laboratorio Nacional de Referencia de Salmonella y Shigella (LNRSSE) entre los anos 1997 y 2001 y se fagotipificaron, segun esquemas internacionales, las cepas de los serotipos Enteritidis, Typhimurium, Hadar, Virchow y Typhi. Resultados. Se analizaron 30.856 cepas de Salmonella spp. procedentes de la mayoria de las Comunidades Autonomas. Los serotipos Enteritidis (51%) y Typhimurium (24%) fueron los mayoritarios. Las combinaciones serotipo/fagotipo mas frecuentes fueron: Enteritidis/FT1 (18%), Enteritidis/FT4 (15%), Enteritidis/FT6a (5%), Typhimurium/FT104 (5%) y Enteritidis/FT6 (3%). Las cepas del serotipo Enteritidis/FT1 tuvieron el mayor aumento en este periodo de tiempo, pasando del 11,61% en 1997 al 24,74% en 2001. Conclusiones. La utilizacion jerarquica de la serotipificacion y posteriormente de la fagotipificacion en cepas de Salmonella spp. de los serotipos mas frecuentes aumento enormemente el poder de discriminacion de la serotipificacion. Su aplicacion en estudios epidemiologicos es de gran utilidad en la caracterizacion temprana de cepas relacionadas.