Antimicrobial resistance of Salmonella serotypes isolated from slaughter-age pigs and environmental samples

The aim of this study was to determine the antimicrobial resistance patterns of Salmonella strains isolated from slaughter-age pigs and environmental samples collected at modern swine raising facilities in Brazil. Seventeen isolates of six serotypes of Salmonella enterica subsp. enterica were isolated out of 1,026 collected samples: Salmonella Typhimurium (1), Salmonella Agona (5), Salmonella Sandiego (5), Salmonella Rissen (1), Salmonella Senftenberg (4), and Salmonella Javiana (1). Resistance patterns were determined to extended-spectrum penicillin (ampicillin), broad-spectrum cephalosporins (cefotaxime and ceftriaxone), aminoglycosides (streptomycin, neomycin, gentamicin, amikacin, and tobramycin), narrow-spectrum quinolone (nalidixic acid), broad-spectrum quinolone (ciprofloxacin and norfloxacin), tetracycline, trimethoprim, and chloramphenicol. Antimicrobial resistance patterns varied among serotypes, but isolates from a single serotype consistently showed the same resistance profile. All isolates were resistant to tetracycline, streptomycin, and nalidixic acid. One isolate, Salmonella Rissen, was also resistant to cefotaxime and tobramycin. All serotypes were susceptible to ceftriaxone, norfloxacin, ciprofloxacin, ampicillin, gentamicin, and chloramphenicol. The high resistance to tetracycline and streptomycin may be linked to their common use as therapeutic drugs on the tested farms. No relation was seen between nalidixic acid and fluoroquinolone resistance.     

Characterization of Salmonella enterica serotype newport isolated from humans and food animals

Salmonella enterica serotype Newport isolates resistant to at least nine antimicrobials (including extended-spectrum cephalosporins), known as serotype Newport MDR-AmpC isolates, have been rapidly emerging as pathogens in both animals and humans throughout the United States. Resistance to extended-spectrum cephalosporins is associated with clinical failures, including death, in patients with systemic infections. In this study, 87 Salmonella serotype Newport strains were characterized by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing and examined for the presence of class 1 integrons and bla(CMY) genes. Thirty-five PFGE patterns were observed with XbaI, and three of these patterns were indistinguishable among isolates from humans and animals. Fifty-three (60%) Salmonella serotype Newport isolates were identified as serotype Newport MDR-AmpC, including 16 (53%) of 30 human isolates, 27 (93%) of 29 cattle isolates, 7 (70%) of 10 swine isolates, and 3 (30%) of 10 chicken isolates. However, 28 (32%) Salmonella serotype Newport isolates were susceptible to all 16 antimicrobials tested. The bla(CMY) gene was present in all serotype Newport MDR-AmpC isolates. Furthermore, the plasmid-mediated bla(CMY) gene was transferable via conjugation to an Escherichia coli strain. The transconjugant showed the MDR-AmpC resistance profile. Thirty-five (40%) of the isolates possessed class 1 integrons. Sequence analyses of the integrons showed that they contained aadA, which confers resistance to streptomycin, or aadA and dhfr, which confer resistance to trimethoprim-sulfamethoxazole. One integron from a swine isolate contained the sat-1 gene, which encodes resistance to streptothricin, an antimicrobial agent that has never been approved for use in the United States. In conclusion, Salmonella serotype Newport MDR-AmpC was commonly identified among Salmonella serotype Newport isolates recovered from humans and food animals. These findings support the possibility of transmission of this organism to humans through the food chain.     

Association between cyclohexane resistance in Salmonella of different serovars and increased resistance to multiple antibiotics, disinfectants and dyes

A panel of 388 salmonellas of animal and human origin, comprising 35 serotypes, was tested for resistance to cyclohexane and to a range of antibiotics, disinfectants and dyes. Cyclohexane resistance was detected in 41 isolates (10.6%): these comprised members of the serovars Binza (1 of 15), Dublin (1 of 24), Enteritidis (1 of 61), Fischerkietz (4 of 5), Livingstone (9 of 11), Montevideo (1 of 32), Newport (4 of 23), Saint-paul (1 of 3), Senftenberg (10 of 24) and Typhimurium (9 of 93). Most (39 of 41) of the cyclohexane-resistant isolates were from poultry. Statistical analysis showed that the cyclohexane-resistant strains were significantly more resistant than the cyclohexane-susceptible strains to ampicillin, chloramphenicol, ciprofloxacin, erythromycin, nalidixic acid, tetracycline, trimethoprim, cetrimide and triclosan. The multiresistance patterns seen were typical of those caused by efflux pumps, such as AcrAB. The emergence of such resistance may play an important role in the overall antibiotic resistance picture of Salmonella, with particular effect on ciprofloxacin.     

High level ciprofloxacin resistance in Salmonella enterica isolated from blood

PURPOSE: Over the last few years, resistance to ciprofloxacin in Salmonella enterica has become a global concern. The present study was undertaken to find out the susceptibility pattern of Salmonella enterica isolates in our hospital. METHODS: Blood cultures were done using BacT/ALERT 3D system. The antimicrobial susceptibility testing was carried out by the Kirby-Bauer disc diffusion method using CLSI breakpoints. Minimum inhibitory concentration was determined for ciprofloxacin-resistant strains using E-test and Vitek-1 automated system. RESULTS: A total of 25,953 samples of blood culture yielded 431 Salmonella enterica serotype Typhi and 198 serotype Paratyphi A isolates. Twenty-two isolates of serotype Typhi were resistant to ciprofloxacin, while two isolates of Typhi and two Paratyphi A were intermediately susceptible to ciprofloxacin. Ciprofloxacin resistance is 5.6% (24 isolates) among Salmonella enterica serotype Typhi. Ampicillin, chloramphenicol and co-trimoxazole resistance in Salmonella enterica serotype Typhi appears to have decreased to 14.9% (64/431) in comparison to the 27% (55/205) during 2003. All isolates were sensitive to ceftriaxone. CONCLUSIONS: Ciprofloxacin can no longer be considered as the drug of choice in treating Salmonella infections. While first-line antimicrobials may still have a role to play in the treatment of enteric fever, ceftriaxone remains the sole defence against ciprofloxacin-resistant Salmonella infections.     

Antimicrobial resistance and serotype distribution among Salmonella spp. in pigs and poultry in Iceland, 2001-2005

Little information is available on antimicrobial resistance of bacteria isolated from animals and animal products in Iceland. The objective of this study was to analyze serotype distribution and antimicrobial resistance patterns of Salmonella spp. isolated from healthy chickens and pigs in Iceland during 2001-2005. A total of 163 Salmonella strains, isolated in the national Salmonella surveillance program, were available for study. Isolates were tested for antimicrobial susceptibility using a microbroth dilution method (VetMIC) and resistant strains were compared using pulsed-field gel electrophoresis (PFGE) and phage typing. The most commonly isolated serotypes were Salmonella Infantis (61%) and S. Typhimurium (33%); other serotypes were less prevalent. The overall prevalence of resistance was 13.6% in chickens and 12.8% in pigs. Twenty one isolates (12.8%) were resistant to one or more antimicrobials, 19 S. Typhimurium strains, one S. Infantis strain, and one S. Worthington strain. Sixteen out of the 19 resistant S. Typhimurium strains were multiresistant (to > or =3 antimicrobial agents), and, of these, 15 had identical or closely related PFGE patterns (previously phage typed as DT104). The prevalence of antimicrobial resistance in Salmonella spp. in pigs and poultry in Iceland is low; however, we found a multiresistant S. Typhimurium clone that causes concern. Continuous resistance surveillance is important, and further research on the source of resistant clones and possible transmission to humans is needed.     

Characteristics of non-typhoidal Salmonella isolates from human and broiler-chickens in southwestern Seoul, Korea

Non-typhoidal Salmonella (NTS) is an important commensal microorganism. The purpose of this study was to determine the epidemiological relation between NTS isolates from livestock and NTS isolates from human by analyzing antimicrobial susceptibilities and performing molecular typing. We determined the serotypes of 36 human clinical isolates and 64 livestock isolates, performed antimicrobial susceptibility testing against 8 antibiotics, and determined the molecular types of isolated NTS spp. by pulsed field gel electrophoresis (PFGE). In human isolates, S. enteritidis was the most common serotype (17 isolates; 47.2%) and S. typhimurium the second most (8 isolates; 22.2%). In livestock isolates, S. typhimurium was the most common serotype (15 isolates; 23.44%), and S. enteritidis was the second most (14 isolates; 21.88%). Ampicillin and tetracycline resistance were 50% (32/64 isolates) each among broiler-chicken NTS isolates. No human or livestock NTS isolates showed resistance to ciprofloxacin, TMP-SMX, or ceftriaxone. However, 19.4% (7/36) and 46.8% (30/64) of the human and livestock NTS isolates were resistant to nalidixic acid (MIC > or = 16 mg/mL), respectively. The presence of the three identical PFGE molecular types from human and broiler-chicken NTS isolates suggests the possibility of transmission from livestock to humans.     

Antimicrobial resistance patterns and serotype distribution among Salmonella enterica strains in Turkey, 2000–2002

Since Turkey currently lacks a national reference center for Salmonella infections, the present study was conducted to document the distribution of serotypes and antimicrobial resistance patterns among Salmonella enterica isolates recovered from clinical samples in ten Turkish provinces over a 2-year period. Among the 620 Salmonella enterica isolates recovered between 1 July 2000 and 30 June 2002, strains belonging to the serotypes Enteritidis (47.7%), Typhimurium (34.7%), Paratyphi B (6.0%), Typhi (2.9%), Paratyphi A (0.2%) and serogroup C (8.5%) were found. Resistance to multiple antimicrobial agents was particularly high among Salmonella Typhimurium isolates (76.7%), and resistance or decreased susceptibility to ciprofloxacin (MIC0.125 mg/l) was demonstrated in Salmonella Paratyphi B, Salmonella Typhimurium and Salmonella Enteritidis strains. All of the Salmonella Typhi isolates were susceptible to ciprofloxacin. The results indicate that decreased susceptibility to ciprofloxacin is an emerging problem in Salmonella enterica in Turkey, particularly in multiresistant strains.     

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

The aim of this study was to determine the distribution of the antimicrobial resistance phenotypes (R types), the phage types and XbaI-pulsed-field gel electrophoresis (PFGE) types, the genes coding for resistance to beta-lactams and to quinolones, and the class 1 integrons among a representative sample of Salmonella enterica serotype Typhimurium isolates collected from humans in 2002 through the French National Reference Center for Salmonella (NRC-Salm) network. The trends in the evolution of antimicrobial resistance of serotype Typhimurium were reviewed by using NRC-Salm data from 1993, 1997, 2000, and 2003. In 2002, 3,998 isolates of serotype Typhimurium were registered at the NRC-Salm among 11,775 serotyped S. enterica isolates (34%). The most common multiple antibiotic resistance pattern was resistance to amoxicillin, chloramphenicol, streptomycin and spectinomycin, sulfonamides, and tetracycline (ACSSpSuTe R type), with 156 isolates (48.8%). One isolate resistant to extended-spectrum cephalosporins due to the production of TEM-52 extended-spectrum beta-lactamase was detected (0.3%), and one multidrug-resistant isolate was highly resistant to ciprofloxacin (MIC > 32 mg/liter). We found that 57.2% of the isolates tested belonged to the DT104 clone. The main resistance pattern of DT104 isolates was R type ACSSpSuTe (83.2%). However, evolutionary changes have occurred within DT104, involving both loss (variants of Salmonella genomic island 1) and acquisition of genes for drug resistance to trimethoprim or to quinolones. PFGE profile X1 was the most prevalent (74.5%) among DT104 isolates, indicating the need to use a more discriminatory subtyping method for such isolates. Global data from the NRC-Salm suggested that DT104 was the main cause of multidrug resistance in serotype Typhimurium from humans from at least 1997 to 2003, with a roughly stable prevalence during this period.     

Ceftriaxone-resistant salmonella infection acquired by a child from cattle

BACKGROUND: The emergence of resistance to antimicrobial agents within the salmonellae is a worldwide problem that has been associated with the use of antibiotics in livestock. Resistance to ceftriaxone and the fluoroquinolones, which are used to treat invasive salmonella infections, is rare in the United States. We analyzed the molecular characteristics of a ceftriaxone-resistant strain of Salmonella enterica serotype typhimurium isolated from a 12-year-old boy with fever, abdominal pain, and diarrhea. METHODS: We used pulsed-field gel electrophoresis and analysis of plasmids and beta-lactamases to compare the ceftriaxone-resistant S. enterica serotype typhimurium from the child with four isolates of this strain obtained from cattle during a local outbreak of salmonellosis. RESULTS: The ceftriaxone-resistant isolate from the child was indistinguishable from one of the isolates from cattle, which was also resistant to ceftriaxone. Both ceftriaxone-resistant isolates were resistant to 13 antimicrobial agents; all but one of the resistance determinants were on a conjugative plasmid of 160 kb that encoded the functional group 1 beta-lactamase CMY-2. Both ceftriaxone-resistant isolates were closely related to the three other salmonella isolates obtained from cattle, all of which were susceptible to ceftriaxone. CONCLUSIONS: This study provides additional evidence that antibiotic-resistant strains of salmonella in the United States evolve primarily in livestock. Resistance to ceftriaxone, the drug of choice for invasive salmonella disease, is a public health concern, especially with respect to children, since fluoroquinolones, which can also be used to treat this disease, are not approved for use in children.     

Quinolone resistance among Salmonella enterica from cattle, broilers, and swine in Denmark

This study was conducted to determine the susceptibility to nalidixic acid and fluoroquinolones of Salmonella Dublin, S. Enteritidis, and S. Typhimurium isolates from cattle, broilers, and pigs over time in Denmark and to characterise the gyrA, gyrB, and parC genes in quinolone-resistant isolates. A total of 584 S. Typhimiurium and 573 S. Dublin isolates from cattle during 1984 through 1999, and 241 S. Enteritidis and 131 S. Typhimurium from broilers and 452 S. Typhimurium from pigs isolated during 1997-1999 were tested. All isolates from cattle from the period 1984 through 1992 were susceptible to quinolones. A single (1.1%) S. Typhimurium isolate from 1995 and three (5.9%) from 1998 were resistant to nalidixic acid. Six (9.0%) S. Dublin isolates from 1996, four (4.2%) from 1997, and one (1.7%) from 1998 were resistant to nalidixic acid. Resistance was not observed among isolates from cattle in 1999. All broiler isolates from 1997 except for one were susceptible to nalidixic acid, whereas seven (6.2%) S. Enteritidis and two (6.3%) of the S. Typhimurium isolates from 1998 and 9 S. Enteritidis (26.5%) from 1999 were resistant. Among isolates from pigs, four isolates from 1997, three from 1998, and one from 1999 were resistant to nalidixic acid. All the nalidixic acid-resistant isolates had reduced susceptibility to fluoroquinolones. Sequence analysis of the gyrA gene in 37 nalidixic-resistant isolates identified two different base substitutions at codon serine-83 and two at aspartate-87. The base substitutions in serine-83 were TCC (Ser)-->TAC (Tyr), and TCC (Ser)-->TTC (Phe). The base substitutions in aspartic-87 were GAC (Asp)-->AAC (Asn), and GAC (Asp)-->GGC (Gly). Sequence analysis of the gyrB and parC genes revealed no mutations in 27 selected isolates. This study showed that quinolone-resistant isolates have emerged in recent years among food-producing animals, especially among S. Enteritidis from broilers in Denmark, and that the resistance mainly is associated with mutations in gyrA.     

DNA sequence-based subtyping and evolutionary analysis of selected Salmonella enterica serotypes

While serotyping and phage typing have been used widely to characterize Salmonella isolates, sensitive subtyping methods that allow for evolutionary analyses are essential for examining Salmonella transmission, ecology, and evolution. A set of 25 Salmonella enterica isolates, representing five clinically relevant serotypes (serotypes Agona, Heidelberg, Schwarzengrund, Typhimurium, and Typhimurium var. Copenhagen) was initially used to develop a multilocus sequence typing (MLST) scheme for Salmonella targeting seven housekeeping and virulence genes (panB, fimA, aceK, mdh, icdA, manB, and spaN). A total of eight MLST types were found among the 25 isolates sequenced. A good correlation between MLST types and Salmonella serotypes was observed; only one serotype Typhimurium var. Copenhagen isolate displayed an MLST type otherwise typical for serotype Typhimurium isolates. Since manB, fimA, and mdh allowed for the highest subtype discrimination among the initial 25 isolates, we chose these three genes to perform DNA sequencing of an additional 41 Salmonella isolates representing a larger diversity of serotypes. This "three-gene sequence typing scheme" allowed discrimination of 25 sequence types (STs) among a total of 66 isolates; STs correlated well with serotypes and allowed within-serotype differentiation for 9 of the 12 serotypes characterized. Phylogenetic analyses showed that serotypes Kentucky and Newport could each be separated into two distinct, statistically well supported evolutionary lineages. Our results show that a three-gene sequence typing scheme allows for accurate serotype prediction and for limited subtype discrimination among clinically relevant serotypes of Salmonella. Three-gene sequence typing also supports the notion that Salmonella serotypes represent both monophyletic and polyphyletic lineages.     

The isolation of antibiotic-resistant salmonella from retail ground meats

BACKGROUND: Salmonella is a leading cause of foodborne illness. The emergence of antimicrobial-resistant salmonella is associated with the use of antibiotics in animals raised for food; resistant bacteria can be transmitted to humans through foods, particularly those of animal origin. We identified and characterized strains of salmonella isolated from ground meats purchased in the Washington, D.C., area. METHODS: Salmonella was isolated from samples of ground chicken, beef, turkey, and pork purchased at three supermarkets. The isolates were characterized by serotyping, antimicrobial-susceptibility testing, phage typing, and pulsed-field gel electrophoresis. The polymerase chain reaction and DNA sequencing were used to identify resistance integrons and extended spectrum beta-lactamase genes. RESULTS: Of 200 meat samples, 41 (20 percent) contained salmonella, with a total of 13 serotypes. Eighty-four percent of the isolates were resistant to at least one antibiotic, and 53 percent were resistant to at least three antibiotics. Sixteen percent of the isolates were resistant to ceftriaxone, the drug of choice for treating salmonellosis in children. Bacteriophage typing identified four isolates of Salmonella enterica serotype typhimurium definitive type 104 (DT104), one of DT104b, and two of DT208. Five isolates of S. enterica serotype agona had resistance to 9 antibiotics, and the two isolates of serotype typhimurium DT208 were resistant to 12 antibiotics. Electrophoretic patterns of DNA that were indistinguishable from one another were repeatedly found in isolates from different meat samples and different stores. Eighteen isolates, representing four serotypes, had integrons with genes conferring resistance to aminoglycosides, sulfonamides, trimethoprim, and beta-lactams. CONCLUSIONS: Resistant strains of salmonella are common in retail ground meats. These findings provide support for the adoption of guidelines for the prudent use of antibiotics in food animals and for a reduction in the number of pathogens present on farms and in slaughterhouses. National surveillance for antimicrobial-resistant salmonella should be extended to include retail meats.     

Resistance to ciprofioxacin in non-typhoidal salmonellas from humans in England and Wales—the current situation

Objective: To report on the prevalence of isolates with ciprofloxacin resistance in non-typhoidal salmonellas from humans in England and Wales in 1997.
Methods: All non-typhoidal salmonellas referred to the Laboratory of Enteric Pathogens in 1997 were screened for resistance to ciprofloxacin at 0.125 and 1.0 mg/L and nalidixic acid at 16 mg/L, and results were compared to those for 1994. Full minimal inhibitory concentrations (MICs) of these antimicrobials were also determined for a selection of isolates resistant to ciprofloxacin at 0.125 mg/L but sensitive at 1.0 mg/L, and for all isolates resistant at 1.0 mg/L.
Results: Since 1994 there have been increases in the occurrence of resistance to ciprofloxacin (MICs: 0.25–1.0 mg/L) in Salmonella enterica serotypes Enteritidis, Typhimurium, Virchow and Hadar. Of particular importance have been increases in the occurrence of resistance in multiresistant S. Typhimurium DT 104, and also in S. virchow, a serotype with a propensity for causing extraintestinal infections in humans. High-level resistance (MIC≥2.0 mg/L) was uncommon and was identified in only a few strains, all from patients with a history of recent foreign travel.
Conclusions: There is a strong temporal association between increases in the occurrence of ciprofloxacin resistance in Salmonella serotypes Typhimurium, Virchow and Hadar from humans in England and Wales and with the licensing for use in food animals in the UK of the related fluoroquinolone antibiotic enrofloxacin; in contrast, for S. enteritidis ciprofloxacin resistance was most common in a phage type associated with foreign travel. It is hoped that recent recommendations for the use of fluoroquinolone antimicrobials in food animals in the UK will result in a reduction in the occurrence of resistance to ciprofloxacin in zoonotic salmonellas causing infections in humans.     

Antimicrobial use and outcomes in patients with multidrug-resistant and pansusceptible Salmonella Newport infections, 2002-2003

Multidrug-resistant Salmonella Newport with decreased susceptibility to ceftriaxone (MDR-AmpC) is becoming increasingly common in its food animal reservoirs and in humans. Few data exist on rates of antimicrobial use or differences in clinical outcomes in persons infected with MDR-AmpC or other Salmonella strains. We conducted a case-comparison analysis of data from a multistate population-based case-control study to identify antimicrobial treatment choices and differences in clinical outcomes in those infected with MDRAmpC compared to pansusceptible S. Newport. Of isolates from 215 laboratory-confirmed S. Newport cases, 54 (25%) were MDR-AmpC, 146 (68%) were pansusceptible, and 15 (7%) had other resistance patterns; 146 (68%) patients with S. Newport were treated with antimicrobial agents and 66 (33%) were hospitalized. Over two-thirds of cases at low-risk for serious complications received antimicrobial therapy, most commonly with fluoroquinolones, to which this strain was susceptible. There were no significant differences in symptoms, hospitalization, duration of illness, or other outcomes between the persons infected with MDR-AmpC and pansusceptible S. Newport. Although currently prevalent MDR-AmpC S. Newport strains remains susceptible to the antimicrobial most commonly prescribed for it, continued efforts to reduce unnecessary use of antimicrobial agents in food animals and humans are critical to prevent further development of resistance to quinolones and cephalosporins, which is likely to lead to substantial adverse outcomes.     

Increasing Incidence and Comparison of Nalidixic Acid-Resistant Salmonella enterica subsp. enterica Serotype Typhimurium Isolates from Humans and Animals

We determined the resistance to quinolone of 309 Salmonella enterica subsp. enterica serotype Typhimurium strains isolated from humans and animals (cattle, pigs, or poultry) in 1995 or 1996. Nalidixic acid resistance increased from 8.5% in 1995 to 18.6% in 1996. The highest resistance levels correlated with a mutation at Ser-83 (or Asp-82). All strains remained ciprofloxacin susceptible. Human and animal isolates were compared by pulsed-field gel electrophoresis, and the banding patterns of the human isolates most closely matched those of the bovine isolates.     

Characterization of Salmonella enterica serovar Agona slaughter isolates from the animal arm of the National Antimicrobial Resistance Monitoring System-Enteric Bacteria (NARMS): 1997 through 2003

A total of 499 Salmonella enterica serovar Agona isolates from cattle, swine, chicken, and turkey samples were assayed for antimicrobial susceptibility and subtyped using pulsed-field gel electrophoresis (PFGE). Salmonella Agona isolates exhibited increased resistance to amoxicillin/clavulanic acid, ampicillin, cefoxitin, ceftiofur, cephalothin, and chloramphenicol, and a single isolate was resistant to ceftriaxone. Multiple drug resistance (MDR; resistance >or= 2 antimicrobials) was exhibited in 57% (n=282/499) of the Salmonella Agona isolates and 22% (n=111/499) of these Salmonella Agona isolates were resistant to five or more antimicrobials. PFGE patterns of 482 Salmonella Agona slaughter samples resulted in 165 unique patterns. Cluster analysis indicated that isolates indistinguishable by PFGE appeared to group according to antimicrobial resistance profiles. These data suggest that Salmonella Agona is increasing in prevalence in U.S. cattle presented for slaughter and should be further monitored.     

Variability in antimicrobial resistance among Salmonella enterica strains from fattening pigs and sows

The aim of this study was to determine the prevalence of antibiotic resistance and different resistance patterns for Salmonella isolates collected from Belgian sows and fattening pigs at different ages and at slaughter. The most frequently isolated serotypes were S. Typhimurium (42.3%), S. Derby (25.1%), S. Goldcoast (7.3%), and S. Infantis (4.8%). All 901 isolates were submitted to antimicrobial susceptibility testing for 14 compounds using the disc agar diffusion test. The highest percentage of resistance was found to oxytetracycline (34.2%), streptomycin (32.5%), sulfamethizole (27.6%), and ampicillin (24.9%). Three of the isolates showed resistance to cephalosporins and none to second-generation fluoroquinolones. Multiresistance (resistance to > or =2 antimicrobials) was observed in 33.2% of the strains. Differences in resistance patterns were observed between and within serotypes as well as genotypes. A significant lower proportion (p < 0.01) of resistant strains was recovered in fecal samples from sows (23/56) than from fattening pigs during the weaning (30/30), growing (79/85), and finishing periods (45/52). The proportion of resistant strains recovered from fecal samples taken at the herd (154/167) was higher than in the samples collected at the slaughterhouse (75/140). When designing antimicrobial resistance surveillance programs for Salmonella in pigs, it is important to take multiple samples within each herd from both sows and fattening pigs at different time points.     

Association between handling of pet treats and infection with Salmonella enterica serotype newport expressing the AmpC beta-lactamase, CMY-2

Resistance to the extended-spectrum cephalosporins can occur in Salmonella species via the production of extended-spectrum and AmpC beta-lactamases. We describe human infections with Salmonella enterica serotype Newport phage type 14 strains resistant to ceftazidime (CAZ) and cefoxitin (FOX) related to the handling of pet treats containing dried beef. These strains were isolated from five patients in Calgary, Alberta, Canada, during 2002 and were compared to a strain cultured from a commercial pet treat present at the property of one of the patients. The strains were resistant to FOX, CAZ, cefpodoxime, ampicillin, and chloramphenicol; intermediate resistant to ceftriaxone and cefotaxime; and sensitive to the aminoglycosides, ciprofloxacin, cefepime, and imipenem. Isoelectric focusing, multiplex PCR, and sequencing of the amplicons showed that all strains produced the plasmid-encoded AmpC beta-lactamase, CMY-2. Restriction analysis of plasmid DNA following transformation demonstrated that bla(CMY-2) was encoded on an approximately 140-kb plasmid. Pulsed-field gel electrophoresis showed the human and pet treat Salmonella strains to be highly related. This study is the first to implicate the transfer of multidrug-resistant Salmonella species through the handling of commercial pet treats containing animal products. In addition to documenting the first cases of human infection caused by CMY-2-producing S. enterica serotype Newport strains in Canada, this study illustrates the necessity of rapid and accurate laboratory-based surveillance in the identification of novel types of antimicrobial resistance.     

Serotype distribution and antimicrobial resistance of Salmonella enterica from patients with gastroenteritis in Crete, Greece

The aim of the present study was to determine the serotype distribution and the evolution of antimicrobial resistance among Salmonella enterica strains isolated from patients with diarrhea in Crete, Greece, during a 5-year period (2000–2004). Among the 401 S. enterica isolates recovered, serotype Enteritidis was the most prevalent (66.6%), followed by serotype Typhimurium (14.2%). The rates of resistance to ampicillin, amoxicillin-clavulanic acid, gentamicin, chloramphenicol, tetracycline, nalidixic acid and trimethoprim-sulfamethoxazole were 8.5, 7, 0.7, 5.4, 14.2, 2.7 and 2.7%, respectively. A marked decrease in resistance was observed during the study period. Resistance and multidrug resistance was most common in serotype Typhimurium. The extended-spectrum beta-lactamase production observed in one strain of S. enterica serotype Virchow and the reduced ciprofloxacin susceptibility detected in 2.7% of the isolates studied are causes of concern.