Multidrug resistance in Salmonella enterica serotype Typhimurium from humans in France (1993 to 2003)

Antimicrobial resistance and virulence genes in Salmonella enterica isolates from dairy cows

One hundred sixty Salmonella enterica isolates from clinically healthy dairy cows were assayed for antibiotic susceptibilities, the presence of class 1 integrons, antimicrobial resistance genes and virulence genes, and conjugal transfer of antimicrobial resistance determinants. One hundred nine (68%) of the Salmonella isolates were resistant to at least 1 antibiotic, and 14 isolates (9%) were multiresistant. The most prevalent resistance observed was to streptomycin (64%). Class 1 integrons were detected in only two Salmonella isolates (serovar Singapore and Derby), and both integrons harbored the same cassette content aadA2. The Derby class 1 integrons were associated with Salmonella genomic island 1-A. Most commonly found resistance genes were strA and strB (9.2%). None of class 1 integrons were horizontally transferred, and the resistance genes were successfully transferred from six (5.5%) Salmonella strains. One hundred fifty-nine isolates (98.8%) were positive to the invasion gene invA, whereas the virulence plasmid-associated genes spvC and pefA were found in only two (1.3%) and one (0.6%) Salmonella isolates, respectively.

Antimicrobial resistance, class 1 integrons, and genomic island 1 in Salmonella isolates from Vietnam

Background

The objective was to investigate the phenotypic and genotypic resistance and the horizontal transfer of resistance determinants from Salmonella isolates from humans and animals in Vietnam.

Methodology/Principal Findings

The susceptibility of 297 epidemiologically unrelated non-typhoid Salmonella isolates was investigated by disk diffusion assay. The isolates were screened for the presence of class 1 integrons and Salmonella genomic island 1 by PCR. The potential for the transfer of resistance determinants was investigated by conjugation experiments. Resistance to gentamicin, kanamycin, chloramphenicol, streptomycin, trimethoprim, ampicillin, nalidixic acid, sulphonamides, and tetracycline was found in 13 to 50% of the isolates. Nine distinct integron types were detected in 28% of the isolates belonging to 11 Salmonella serovars including S. Tallahassee. Gene cassettes identified were aadA1, aadA2, aadA5, bla_PSE-1, bla_OXA-30, dfrA1, dfrA12, dfrA17, and sat, as well as open reading frames with unknown functions. Most integrons were located on conjugative plasmids, which can transfer their antimicrobial resistance determinants to Escherichia coli or Salmonella Enteritidis, or with Salmonella Genomic Island 1 or its variants. The resistance gene cluster in serovar Emek identified by PCR mapping and nucleotide sequencing contained SGI1-J3 which is integrated in SGI1 at another position than the majority of SGI1. This is the second report on the insertion of SGI1 at this position. High-level resistance to fluoroquinolones was found in 3 multiresistant S. Typhimurium isolates and was associated with mutations in the gyrA gene leading to the amino acid changes Ser83Phe and Asp87Asn.

Conclusions

Resistance was common among Vietnamese Salmonella isolates from different sources. Legislation to enforce a more prudent use of antibiotics in both human and veterinary medicine should be implemented by the authorities in Vietnam.

CTX-M-2-producing Salmonella Typhimurium isolated from pediatric patients and poultry in Brazil

Ten Salmonella enterica serovar Typhimurium isolates producing CTX-M-2 extended-spectrum beta-lactamase were identified from clinical and poultry sources in two distant cities in Brazil between 2003 and 2004. They included two isolates from pediatric patients and eight isolates from poultry or its environment. All isolates exhibited coresistance to non-beta-lactam antimicrobials including tetracycline and trimethoprim/sulfamethoxazole. The CTX-M-2 gene was located on transferable plasmids with sizes between 90 and 170 kb that also carried other resistance determinants in some isolates. By pulsed-field gel electrophoresis, the genetic similarity of the isolates including clinical and poultry ones ranged from 89% to 100%.

Characterization of Salmonella Typhimurium isolates associated with septicemia in swine

Salmonella Typhimurium is frequently isolated from pigs and may also cause enteric disease in humans. In this study, 33 isolates of S. Typhimurium associated with septicemia in swine (CS) were compared to 33 isolates recovered from healthy animals at slaughter (WCS). The isolates were characterized using phenotyping and genotyping methods. For each isolate, the phage type, antimicrobial resistance, and pulsed-field gel electrophoresis (PFGE) DNA profiles were determined. In addition, the protein profiles of each isolate grown in different conditions were studied by Coomassie Blue-stained sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot. Various phage types were identified. The phage type PT 104 represented 36.4% of all isolates from septicemic pigs. Resistance to as many as 12 antimicrobial agents, including some natural resistances, was found in isolates from CS and WCS. Many genetic profiles were identified among the PT 104 phage types. Although it was not possible to associate one particular protein with septicemic isolates, several highly immunogenic proteins, present in all virulent isolates and in most isolates from clinically healthy animals, were identified. These results indicated that strains associated with septicemia belong to various genetic lineages that can also be recovered from asymptomatic animals at the time of slaughter.

Salmonella entericaserotypes and antibiotic susceptibility in New Zealand, 2002–2007

We analysed the serotypes and antibiotic susceptibility of 1560 human and 1505 non-humanSalmonellaisolated in New Zealand (NZ) between 2002 and 2007. The most common serotypes in humans wereSalmonella entericaserovar Typhimurium,S. Enteritidis,S. Brandenburg andS. Infantis. Over the 6-year period human cases due toS. Agona andS. Enteritidis increased and cases due toS. Typhimurium decreased. The most common serotypes from non-human sources wereS. Typhimurium,S. Brandenberg,S. Hindmarsh andS. Infantis, and there were no significant changes over time. More isolates were non-susceptible to streptomycin than to any other antibiotic. Almost all isolates were susceptible to ciprofloxacin and gentamicin. There were significant trends of increasing non-susceptibility to streptomycin and sulfonamides in isolates from human and non-human sources, while ampicillin, tetracycline and multidrug non-susceptibility also increased in human isolates. Despite these increases, rates of antibiotic non-susceptibility inSalmonellain NZ are still lower than in many international settings.

Clonal diversity of Salmonella enterica serotype Typhi isolated from patients with typhoid fever in Tehran

In this study, antimicrobial susceptibility test and genetic typing were used to characterize 15 Salmonella enterica serotype Typhi (S. Typhi) isolates recovered from sporadic cases of typhoid fever in Tehran, Iran during 2004. Antimicrobial susceptibility test showed that all isolates were susceptible to 20 antimicrobials examined in this study. Analysis of insertion elements showed that 2 IS200 types with 10 and 11 copies were present. 11 of the 15 isolates were found to possess 10 IS200 elements residing on fragments from 23 to 2.3 kb. Comparison of the RiboPrinter (automated ribotyping) patterns of S. Typhi showed that 60% (9/15) of the isolates belonged to a single ribotype. PCR based random amplified polymorphic DNA analysis (RAPD) and enterobacterial repetitive intergenic consensus (ERIC) and pulsed-field gel electrophresis (PFGE) were also performed. ERIC and RAPD-PCR method showed 2 and 3 genotyping patterns amongst the isolates, respectively. The PFGE typing was carried out by using XbaI restriction enzyme, and 7 restriction patterns were observed. Overall, the molecular typing methods applied in this study showed that the isolated S. Typhi populations were highly polyclonal as shown by PFGE.

Minimum inhibitory concentration of carbapenems and tigecycline against Salmonella spp

Antimicrobial resistance in Salmonella spp. is of grave concern, more so in quinolone-resistant and extended-spectrum beta-lactamase (ESBL)-producing isolates that cause complicated infections. The MIC of azithromycin, ciprofloxacin, cefixime, cefepime, ceftriaxone, gatifloxacin, imipenem, levofloxacin, meropenem and ofloxacin (E-test strip) and tigecycline and faropenem (agar dilution) against 210 Salmonella spp. was determined. MIC(90) (defined as the antimicrobial concentration that inhibited growth of 90 % of the strains) of the carbapenems (imipenem and meropenem) for Salmonella Typhi and Salmonella Paratyphi A was 0.064 microg ml(-1). MIC(90) of faropenem was 0.25 microg ml(-1) for S. Typhi, S. Paratyphi A and Salmonella Typhimurium. The MIC(90) of azithromycin for all Salmonella spp. ranged from 8 to 16 microg ml(-1). Tigecycline showed an MIC(90) of 2 microg ml(-1) for S. Typhi, 1 microg ml(-1) for S. Paratyphi A and 4 microg ml(-1) for S. Typhimurium. We concluded that tigecycline and the carbapenems are likely to have roles in the final stage of treatment of quinolone-resistant and ESBL-producing multidrug-resistant salmonellae.

Variation in Antimicrobial resistance in sporadic and outbreak-related Salmonella enterica serovar Typhimurium

The prevalence of different antimicrobial resistance profiles and variants of the Salmonella genomic island 1 (SGI1) was reported for Salmonellaenterica serovar Typhimurium DT104 strains isolated from patients in Denmark. Variation in antimicrobial resistance and corresponding changes of SGI1 were shown among isolates from a foodborne outbreak.

Chromosomal integration of the extended-spectrum beta-lactamase gene blaCTX-M-15 in Salmonella enterica serotype Concord isolates from internationally adopted children

We report the emergence of Salmonella enterica isolates of serotype Concord (and its monophasic variant 6,7:l,v:-) producing the extended-spectrum beta-lactamases (ESBLs) SHV-12 and CTX-M-15 in France and Norway between 2001 and 2006 (43 in France and 26 in Norway). The majority of these isolates were from adopted children from Ethiopia, most of whom were healthy carriers. Several symptomatic secondary cases were found in the adoptive families and health care facilities in France. Serotype Concord isolates collected before 2003 produced SHV-12 encoded on a 340-kb conjugative plasmid of replicon IncI1. Isolates collected after 2003 produced CTX-M-15. We detected two conjugative plasmids carrying bla(CTX-M-15). One plasmid, approximately 300 kb in size, was positive for the IncHI2 replicon and the plasmid-mediated quinolone resistance gene qnrA1. The other plasmid, from one of the earliest CTX-M-15-producing isolates collected, was a fusion plasmid with IncY and IncA/C(2) replicons and was 200 kb in size. However, we showed, using Southern hybridization of I-CeuI-digested chromosomal DNA and S1 nuclease analysis of plasmid DNA, that most isolates had a bla(CTX-M-15) gene located on chromosomal DNA. Analysis of the flanking regions of the chromosomally located bla(CTX-M-15) gene by cloning revealed an ISEcp1 truncated by an intact IS26 upstream from the bla(CTX-M-15) gene and a truncated orf477 gene downstream from bla(CTX-M-15). We found regions beyond the IS26 and the orf477 genes that were derived from IncA/C(2) plasmids, suggesting the chromosomal integration of part of the bla(CTX-M-15)-carrying IncY and IncA/C(2) fusion plasmid from early CTX-M-15-producing isolates.

Characterization of Salmonella enterica isolates from infants and toddlers in Wuhan, China

BACKGROUND

Extended-spectrum cephalosporins and fluoroquinolones are important antimicrobials for treating invasive salmonellosis, and emerging resistance to these antimicrobials is of paramount concern. This study reports on the antimicrobial susceptibility and molecular characterization of Salmonella enterica isolates recovered in 2006 from 0- to 3-year-old outpatients in China.

METHODS

The isolates were subjected to serotyping, antimicrobial susceptibility testing, screening for beta-lactamase genes, mutations in the quinolone resistance determining regions (QRDRs), qnr alleles and aac-(6')-Ib-cr by PCR followed by DNA sequence analysis. All Salmonella Typhimurium isolates and 43 selected non-Typhimurium isolates were further characterized by PFGE to determine the genetic relatedness.

RESULTS

From 3746 paediatric outpatient stool samples, 221 (5.9%) S. enterica isolates of 29 distinct serotypes were recovered. The antimicrobial resistance profiles differed among serotypes. Ciprofloxacin-resistant isolates were concentrated in serotype Typhimurium that were resistant to at least four additional non-quinolone antimicrobials. Nineteen out of 22 ciprofloxacin-resistant Salmonella Typhimurium isolates were grouped into one PFGE cluster. Plasmid-mediated quinolone resistance determinant aac-(6')-Ib-cr was detected in 18 S. enterica isolates and 4 isolates also carried qnr alleles. Plasmid-mediated blaCTX-M-14-like genes were found in seven ceftriaxone-resistant isolates, and two isolates also exhibited reduced susceptibility to ciprofloxacin.

CONCLUSIONS

Based on these results, fluoroquinolones should not be used to treat the invasive Salmonella Typhimurium infections in this local community. The monitoring programme should stay vigilant for ceftriaxone-resistant S. enterica isolates with reduced fluoroquinolone susceptibility.

Surveillance of antibiotic resistance evolution and detection of class 1 and 2 integrons in human isolates of multi-resistant Salmonella Typhimurium obtained in Uruguay between 1976 and 2000

OBJECTIVES

To study the evolution of antibiotic resistance in isolates of Salmonella enterica subspecies enterica serovar Typhimurium (Salmonella Typhimurium) obtained in Uruguay between the years 1976 and 2000, and to determine the incidence of class 1 and 2 integrons in the multi-resistant isolates.

METHODS

We studied 258 strains of Salmonella Typhimurium from various sources, isolated between 1976 and 2000. We determined the evolution of antibiotic resistance and the distribution of class 1 and 2 integrons in all isolates by means of disk diffusion assays and PCR.

RESULTS

During the period 1989-2000 resistance to streptomycin was 56.8%, tetracycline 13.6%, sulfonamides 11.2%, and ampicillin 7.2%. Resistance to gentamicin, kanamycin, chloramphenicol, and nalidixic acid were lower than 5%; no resistance was detected to fluoroquinolones, oxyiminocephalosporins, and amikacin. These results show a dramatic decrease with respect to values found in the period 1976-1988. In this period, resistance to streptomycin was 63.2%, tetracycline 36.8%, sulfonamides 32.3%, and ampicillin 27.8%. Throughout the two periods, 29 multi-resistant Salmonella Typhimurium strains were isolated harboring some class of integron: 15 strains had only intI2, 11 strains presented both intI1 and intI2, and three isolates only intI1.

CONCLUSIONS

Our results show a marked decrease in resistance throughout these years, along with a correlation between resistance to different antibiotics and the presence of integrons.

Prevalence and spread of extended-spectrum beta-lactamase-producing Enterobacteriaceae in Europe

Extended-spectrum beta-lactamases (ESBLs) represent a major threat among resistant bacterial isolates. The first types described were derivatives of the TEM-1, TEM-2 and SHV-1 enzymes during the 1980s in Europe, mainly in Klebsiella pneumoniae associated with nosocomial outbreaks. Nowadays, they are mostly found among Escherichia coli isolates in community-acquired infections, with an increasing occurrence of CTX-M enzymes. The prevalence of ESBLs in Europe is higher than in the USA but lower than in Asia and South America. However, important differences among European countries have been observed. Spread of mobile genetic elements, mainly epidemic plasmids, and the dispersion of specific clones have been responsible for the increase in ESBL-producing isolates, such as those with TEM-4, TEM-24, TEM-52, SHV-12, CTX-M-9, CTX-M-14, CTX-M-3, CTX-M-15 and CTX-M-32 enzymes.

Prevalence and characterization of extended-spectrum cephalosporin-resistant nontyphoidal Salmonella isolates in adults in Saint Petersburg, Russia (2002-2005)

We studied the prevalence of resistance to extended-spectrum cephalosporins (ESC) among 1,078 Salmonella enterica isolates collected from adults admitted to Botkin Hospital, St. Petersburg, Russia, for gastroenteritis between 2002 and 2005. Only two ESC-resistant isolates were detected, giving a low percentage of strains resistant to ESC (0.2%). One multidrug-resistant (MDR) isolate of the Virchow serotype produced a CTXM-3 extended-spectrum beta-lactamase (ESBL). The bla(CTX-M-3) gene was located downstream from an ISEcp1 element, on an 80-kb conjugative plasmid. The Virchow isolate possessed a class 1 integron with a 2.2-kb gene cassette (dhfrXII-orfF-aadA2). The second ESC-resistant isolate belonged to serotype Newport, was also MDR and produced a CMY-2 cephamycinase. This CMY-2-producing isolate (also called Newport MDR-AmpC) possessed a class 1 integron with a 1-kb gene cassette including a new variant of the aadA gene, aadA24. A large plasmid (>125 kb) was involved in transfer of the bla(CMY-2) gene. The ESC-resistant S. enterica isolates detected in this study were different from those (S. enterica serotype Typhimurium DT193 producing CTXM-4 or CTX-M-5 ESBLs) involved in several nosocomial outbreaks between 1994 and 2003 in Russia. This is the first description of both CTX-M-3 ESBL-producing S. enterica and Newport MDR-AmpC in Russia.

Antimicrobial resistance and phage and molecular typing of Salmonella strains isolated from food for human consumption in Spain

The aims of this study were to ascertain the population structure and antimicrobial susceptibility of Salmonella enterica serovars isolated in 2002 from food in 16 Spanish regions. Serovars were characterized by serotyping, phage typing, antimicrobial susceptibility, and pulsed-field gel electrophoresis (PFGE) typing, and 264 nonrelated strains were selected for further analysis. The main sources were eggs and their derivatives (21.6% of strains), poultry and related products (16.6%), and seafood (16.3%). High serotype diversity was detected (51 serotypes); the most common were Enteritidis (n = 96, 36.3%) and Typhimurium (n = 53, 20.1%), followed by a miscellaneous group of 49 different serotypes (n = 115, 43.5%). A 15% increase in Salmonella Enteritidis isolation was observed. Common phage types for Salmonella Enteritidis were PT1 (41.6% of isolates), PT4 (9.4%), PT6 (9.4%), and PT6a (9.4%), and common types for Salmonella Typhimurium were DTU302 (18.8%), DT104 (15.1%), and DT104B (13.2%). Salmonella Enteritidis strains were categorized into eight PFGE types with a similarity of 81 to 96%, and 73.9% of the strains were grouped into just one cluster. Salmonella Typhimurium isolates were divided into 13 PFGE types with a similarity of 64 to 86%, and one predominant clone contained 41.5% of the strains. Resistance rates for Salmonella Enteritidis, Salmonella Typhimurium, and the miscellaneous group were, respectively, 8.3, 69.8, and 13.9% for ampicillin, 3.1, 52.8, and 59% for streptomycin, 40.6, 22.6, and 10.4% for nalidixic acid, 15.6, 71.7, and 31.1% for tetracycline, 7.3, 18.8, and 9.5% for trimethoprim-sulfamethoxazole, 0, 50.9, and 4.3% for chloramphenicol, and 6.2, 71.7, and 17.4% for multiple (at least four) antimicrobials. All the strains remained susceptible to other beta-lactams and fluoroquinolones. Surveillance of S. enterica isolated from food is strongly recommended to reduce community exposure to antimicrobial resistant strains.

Antimicrobial resistance in Salmonella enterica serovar Typhimurium from human and animal sources in Italy

Salmonella Typhimurium strains isolated in Italy in the period 2002-2004 from human and animal sources were examined for their antimicrobial susceptibility. Resistance to tetracycline (T, 73.6%), sulfonamides (Su, 73.3%), ampicillin (A, 67.6%), streptomycin (S, 65.4%) and chloramphenicol (C, 32.3%) were frequently observed. Resistance to ciprofloxacin was only observed in a swine strain, but most human strains resistant to nalidixic acid showed reduced susceptibility to that drug (MIC > or = 0.125 mg/l). Overall, 64% of the strains were resistant to four or more drugs. The most common resistance profiles were ACSSuT, prevalent in strains belonging phage type DT104 and ASSuT, prevalently associated with strains unable to be typed.

Pulsed-Field Gel Electrophoresis Subtyping Database for FoodborneSalmonella entericaSerotype Discrimination

Nontyphoid Salmonella is one of the main causes of bacterial gastroenteritis worldwide and is responsible for 65% of reported outbreaks of foodborne diseases in France. Serotyping is widely used for isolate preliminary identification, but it poorly discriminates strains. Rapid, efficient molecular subtyping tools have therefore been developed for the investigation of outbreaks. We evaluated the performance of the pulsed-field gel electrophoresis (PFGE) method for discrimination of 31 Salmonella serotypes frequently isolated in France. We set up a genomic database of Salmonella strains isolated from food, animals, the environment, and humans to improve the management of contamination and reactions to foodborne disease outbreaks. We studied 1128 isolates by PFGE, according to the standardized PulseNet protocol. We identified 452 PFGE patterns, 67.5% of which corresponded to a single isolate. The ability of this method to distinguish between isolates was estimated by calculating the Simpson index and the 95% confidence interval. Values obtained ranged between 0.33 (0.11-0.54) to 0.99 (0.96-1.00), depending on serotype. Epidemiological information about isolates was used for analyses of intra- and interserotype diversity results and for determining whether PFGE patterns were linked to the source of the isolate. Clustering analysis of the PFGE patterns obtained confirmed that serotype and PFGE genotype were closely linked. Some PFGE patterns were identified as major patterns, each of these patterns being found in at least 10 isolates. The database generated has already proved its effectiveness in epidemiological investigations in livestock production and foodborne outbreaks.

Clonal expansion and microevolution of quinolone-resistant Salmonella enterica serotype typhi in Vietnam from 1996 to 2004

Salmonella enterica serotype Typhi clinical isolates (n = 91) resistant to nalidixic acid (Nal(r)) were collected from sporadic cases and minor outbreaks throughout Vietnam between 1996 and 2004. These isolates were typed and compared by four methods: Vi phage typing, PstI ribotyping, XbaI and SpeI pulsed-field gel electrophoresis (PFGE), and single-nucleotide polymorphism (SNP) analysis. The results indicated that 65% of the isolates were not typeable by Vi phage typing. In contrast, the ribotyping and, with more accuracy, the SNP analysis methods indicated that all Nal(r) isolates belonged to a single clone (ribotype 3a, haplotype H58) that was found previously and that largely consisted of plasmid-encoded multidrug-resistant serotype Typhi isolates. PFGE demonstrated the occurrence of microevolution within this clone. We identified two major combined PFGE profiles: X1-S1 and X3-S6. X3-S6 predominated between 1996 and 2002 but was replaced by X1-S1 after 2002. Nevertheless, PFGE, with a Simpson's index of 0.78, was not considered an optimal discriminatory method for investigating typhoid fever outbreaks in Vietnam. The rate of quinolone resistance increased and the rate of multidrug resistance decreased during the study period. From 2002 to 2004, 80.6% of the isolates from South Vietnam were resistant only to Nal. The mechanism of Nal resistance in most of the isolates (94%) was a mutation in the quinolone resistance-determining chromosomal region of gyrA that led to the amino acid substitution Ser83Phe. No plasmid-located qnrA, qnrB, or qnrS was detected.

Salmonella enterica serotype Typhimurium carrying hybrid virulence-resistance plasmids (pUO-StVR): a new multidrug-resistant group endemic in Spain

The epidemiological impact in Spain of an emerging group of multidrug-resistant Salmonella enterica serotype Typhimurium, characterized by the presence of virulence-resistance hybrid plasmids (termed pUO-StVR) that are related to the S. Typhimurium virulence plasmid pSLT, was evaluated. Adscription to the group was based on detection of the bla(OXA-1) gene (encoding ampicillin resistance) by PCR, and identification of a pUO-StVR plasmid through hybridization with specific probes for virulence (spvC) and resistance (bla(OXA-1)) genes. In this way, 57 out of 134 ampicillin-resistant clinical isolates of S. Typhimurium, collected over 2002-2004 in 21 Spanish cities, were assigned to the group, which can be already regarded as endemic. Most isolates (>89%) shared the following features: (i) resistance to ampicillin, chloramphenicol, streptomycin/spectinomycin, sulfonamides, and tetracycline, encoded by bla(OXA-1)-catA1-aadA1-sul1-tet(B); (ii) a class 1 integron (InH) with the bla(OXA-1)-aadA1 gene cassettes within its variable region of ca. 2000bp; (iii) the spvC, rck, samA, oriT, traT, traX, repA (RepFIIA), and parA/B genes (but not rsk and pefABCD) of pSLT; (iv) a hybrid plasmid of ca. 125kb, termed pUO-StVR2, where the resistance and virulence genes are located. However, intra-group diversity was also detected, since a total of four resistance phenotypes, five resistance genotypes, two integron profiles, five plasmid variants (pUO-StVR2, 4-7, differing in size, restriction profile and/or resistance pattern), 15 XbaI-BlnI combined macrorestriction profiles, and five phage types were identified. Each hybrid plasmid was revealed as a distinctive BlnI band, through hybridization with pUO-StVR2. The genetic markers used, together with the knowledge generated in the present study, could be applied to epidemiological surveillance of S. Typhimurium pUO-StVR worldwide.

Antimicrobial susceptibility phenotypes, resistance determinants and DNA fingerprints of Salmonella enterica serotype Typhimurium isolated from bovine in Southern Japan

A longitudinal study was conducted in cattle to determine the antimicrobial resistance phenotypes, integron elements, resistance genes and pulsed-field gel electrophoresis fingerprints among Salmonella enterica serotype Typhimurium isolates. A total of 33 strains were isolated and categorised into Groups A, B and C during the period 1989-2004. Thirty-one strains (93.9%) showed resistance to ampicillin (A) encoded by bla(OXA-1), bla(TEM) and bla(PSE-1) genes; 84.8% showed resistance to chloramphenicol (C) encoded by floR and catA1; 97.0% were resistant both to streptomycin (S) and sulfamethoxazole (Su), the former encoded by aadA1 and aadA2; 100% were resistant to oxytetracycline (T) encoded by tetA, tetB and tetG; and 42.4% were resistant to kanamycin (Km) encoded by aphA1-Iab. Multidrug resistance types observed were ACSSuT-Km (n=13), ACSSuT (n=15), ASSuT (n=3) and SSuT (n=2). Class 1 integrons ranging from 1.0 kb to 1.9 kb were detected from 54.5% of isolates (18/33). Integrons were not detected initially (1989-1992), then during the 1993-1996 interval a high frequency of 1.0 kb and 1.2kb amplicons were detected and during 2000-2004 the amplicon size increased to 1.7 kb and 1.9 kb. We report evidence of additional integration of resistance gene cassettes as shown by integrons with increased size. Finally, group B strains showed banding patterns indistinguishable from S. Typhimurium DT104 reference strain, indicating that the DT104 lineage existed on the island since 1993.

Prevalence of qnr genes in Salmonella in France

OBJECTIVES

To detect the qnrA, qnrB and qnrS genes among Salmonella isolates received at the French National Reference Centre for Salmonella in Paris, France.

METHODS

Antibiotic susceptibility was determined by disc diffusion for 499 Salmonella isolates including 320 Salmonella Typhimurium, 100 Salmonella Enteritidis and 79 Salmonella Hadar collected in 2002. Amplification with specific primers of qnrA, qnrB and qnrS genes was performed for all Salmonella Typhimurium, Salmonella Enteritidis and Salmonella Hadar isolates resistant to quinolones and for 17 additional isolates that produced expanded-spectrum beta-lactamases (ESBLs).

RESULTS

Prevalence of quinolone resistance was 3.75%, 11% and 79.7% for Salmonella Typhimurium, Salmonella Enteritidis and Salmonella Hadar serovars, respectively. A single isolate (0.2%) was qnrA-positive (QnrA1 determinant) being a Salmonella serovar Concord carrying also the ESBL gene bla(CTX-M-15). This strain was probably from East Africa. No qnrB or qnrS genes were identified.

CONCLUSIONS

Whereas plasmid-mediated quinolone resistance of the Qnr type is emerging in Enterobacteriaceae worldwide, it remains rare in Salmonella in France.