Antimicrobial resistance in generic Escherichia coli isolated from swine fecal samples in 90 Alberta finishing farms

The objective of this study was to determine the prevalence of antimicrobial resistance in generic Escherichia coli isolates obtained from 90 Alberta finisher swine farms. Up to 5 isolates were obtained from each of 269 pooled fecal samples and were classified as susceptible or resistant according to Clinical and Laboratory Standards Institute guidelines. Of the 1322 isolates, 166 (12.6%) were susceptible to all 15 antimicrobials. No resistance to amikacin, ceftiofur, ceftriaxone, or ciprofloxacin, antimicrobials of importance in human medicine, was observed. Relatively low frequencies of resistance were observed to gentamicin (1.1%), amoxicillin/clavulanic acid (0.7%), and cefoxitin (0.7%). Higher frequencies of resistance were observed for tetracycline (78.9%), sulfisoxazole (49.9%), streptomycin (49.6%), ampicillin (30.6%), chloramphenicol (17.6%), kanamycin (10%), and trimethoprim/ sulfamethoxazole (6.4%). Among the isolates resistant to > or = 2 antimicrobial classes, 20.8%, 20.6%, 18.2%, 7.0%, 1.8%, 0.2%, and 0.2% were resistant to 2, 3, 4, 5, 6, 7, and 8 antimicrobials, respectively. The most common multidrug-resistance patterns (resistance to > or = 2 antimicrobial classes) were streptomycin-tetracycline (9.4%), streptomycin-sulfisoxazole-tetracycline (6.2%), and ampicillin-streptomycin-sulfisoxazole-tetracycline (6.1%). More clustering (higher intra-class correlation coefficients) in antimicrobial resistance was observed for isolates at the same visit than for isolates from different visits in the same farm, indicating that sampling more farms, testing fewer isolates per visits, and taking longer periods between visits may be appropriate and more efficient for a better understanding of potential shifts in resistance over time.     

Longitudinal study of Salmonella species in 90 Alberta swine finishing farms

The aim of this study was to determine the farm prevalence of Salmonella in 90 Alberta finishing swine farms over a 5-month period, to evaluate Salmonella distribution in the farm environment and to describe Salmonella serovar diversity on these farms. Ten veterinary practitioners selected 90 Alberta swine farms based on an annual production of > or =2000 market pigs per farm and the willingness of the producers to participate in the study. Between May and September 2000, twenty samples were collected from finishing swine and the environment of each farm. The annual production of selected farms represented approximately 25% of the market swine production in Alberta. Participating farms were geographically representative of major swine production areas in Alberta. Sixty (66.7%) farms had at least one Salmonella-positive sample, with confidence interval (CI) of 57.1-77.2%. Salmonella were detected in 14.3% of fecal and 20.1% of environmental samples. The number of Salmonella-positive samples per farm ranged from 1 to 19. Among environmental samples, Salmonella were most frequently recovered from boots (38.6%) and the main drain (31.8%). Twenty-two serovars were detected on the 60 Salmonella-positive farms. Serovars Typhimurium (78 isolates), Derby (71 isolates) and Infantis (47 isolates) were the most common. A single serovar was detected on 58 farms, while 2, 3 and >3 serovars were detected on 15, 10 and 7 farms, respectively. The Salmonella farm status changed frequently over the 5-month period indicating the dynamic nature of Salmonella infections on these farms.     

Antimicrobial resistance of Actinobacillus pleuropneumoniae isolated from swine

The aim of this retrospective study was to evaluate the antimicrobial resistance rates and the trend in resistance of Actinobacillus pleuropneumoniae isolated from pigs in Italy from 1994 to 2009. A total of 992 A. pleuropneumoniae isolates were tested for their susceptibility to a panel of antimicrobial agents in a disk diffusion method. Resistance to 7 drugs (amoxicillin, amoxicillin/clavulanic acid, ampicillin, cefquinome, cotrimoxazole, penicillin G and tilmicosin) showed a significant increasing trend over the time, while for 2 drugs (gentamycin and marbofloxacin) a significant decrease was observed. Resistance to the remaining 14 antimicrobial agents tested did not change significantly over the study period. Most of the isolates retained high susceptibility to antimicrobials usually effective against A. pleuropneumoniae such as amphenicols, fluoroquinolones and ceftiofur. However, high rates of resistance were observed for potentiated sulfa drugs, tetracyclines and penicillins which are currently recommended antimicrobials for pig pleuropneumonia therapy. Our results suggest the importance of continued monitoring of A. pleuropneumoniae clinical isolates in order to choose the most appropriate treatment of infections and to control the increase of resistance to currently used antimicrobials.     

Antimicrobial resistance of selected Salmonella isolates from food animals and food in Alberta

Salmonella isolates (n = 209) obtained from food animals and foods in Alberta during 1996 through 1999 were tested for sensitivity to 17 antimicrobials. Of the 3553 antimicrobial susceptibility tests on Salmonella isolates, 11.8% were positive for resistance. These isolates were commonly resistant to tetracycline (35.4%), streptomycin (32.5%), sulfamethoxazole (28.7%), ticarcillin (27.3%), and ampicillin (26.8%). Resistance to at least 1 antimicrobial was observed in 112 isolates (53.6%). Salmonella Typhimurium, S. Typhimurium var. Copenhagen, and S. Heidelberg were the most common serovars among isolates resistant to individual antimicrobials and multiple antimicrobials. The most common profile of multiple-antimicrobial resistance was that which included resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline, and ticarcillin. The proportions of isolates that were resistant to antimicrobials were greater among bovine isolates of Salmonella than among poultry isolates, and this difference was greater among isolates from veterinary diagnostic sources than among those from monitoring sources.     

Antimicrobial resistance in Salmonella isolated from animals and their environment in England and Wales from 1988 to 1999

Resistance to 16 antimicrobial agents was monitored in 109,125 Salmonella cultures isolated from animals, their environment and feedstuffs between 1988 and 1999. The sensitivity of the 6512 isolates of Salmonella enterica enterica serotype Dublin to all the antimicrobial agents tested varied from 98.2 per cent in 1997 to 99.7 per cent in 1990 and 1996. In contrast, among 28,053 isolates of Salmonella enterica enterica serotype Typhimurium, there was a marked decrease in their sensitivity to all the antimicrobial agents tested, from 57.4 per cent in 1992 to 7.6 per cent in 1995, owing to the widespread occurrence in farm animals of S Typhimurium isolates of the definitive type DT104, resistant to ampicillin, sulphonamides, streptomycin, chloramphenicol and tetracyclines, although the percentage of sensitive isolates increased to 18.4 per cent in 1999, when the incidence of DT104 had decreased. Some isolates of DT104 also showed an increase in resistance to potentiated sulphonamides (2.4 per cent in 1989 to 19.2 per cent in 1999) and nalidixic acid (0 per cent in 1992, 3.8 per cent in 1995 to a peak of 16.9 per cent in 1998). In 1996, 5.1 per cent of 1086 isolates of S Typhimurium from cattle and 35.9 per cent of 192 isolates of S Typhimurium from poultry showed resistance to nalidixic acid. Of the other 74,528 Salmonella isolates, the percentage of strains sensitive to all the antimicrobials tested decreased slightly from 88.2 per cent in 1988 to 70.6 per cent in 1996 and then increased slightly to 73.7 per cent in 1999. The commonest of these other Salmonella serotypes was Salmonella Enteritidis (20,982), which remained predominantly susceptible (ranging from 81.4 to 97.4 per cent) during the study period. Few isolates were resistant to commonly used veterinary antimicrobials, for example, furazolidone, the use of which was banned in 1990, and the aminoglycoside, apramycin.     

Antimicrobial resistance of fecal Salmonella spp. isolated from all phases of pig production in 20 herds in Alberta and Saskatchewan

Salmonella spp. (n = 468), isolated from the feces of sows, nursery, and grow-finish pigs in 20 farrow-to-finish herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. No resistance was identified to amikacin, amoxicillin-clavulanic acid, ceftiofur, ceftriaxone, ciprofloxacin or nalidixic acid, and less than 1% of the isolates were resistant to cefoxitin and gentamicin. Isolates were most commonly resistant to tetracycline (35%) and sulfamethoxazole (27%). Overall, 59% of the Salmonella were susceptible to all 16 drugs (pansusceptible). Isolates from sows were more likely to be pansusceptible than isolates from nursery or grow-finish pigs. Resistance to 2 or more drugs occurred in 29% of the isolates and was significantly more likely to occur in Salmonella from nursery pigs than from sows. The odds of resistance to 4 of the drugs, streptomycin, ampicillin, kanamycin and cephalothin, were significantly higher in isolates from nursery pigs than grow-finish pigs, while the odds of resistance to 2 drugs, tetracycline and streptomycin, were higher in Salmonella from nursery pigs than from sows. More age-specific risk factor studies are needed to investigate these differences between production phases.     

Antimicrobial use through feed, water, and injection in 20 swine farms in Alberta and Saskatchewan

Antimicrobial resistance (AMR) is an emerging animal welfare and public health issue linked to antimicrobial use (AMU) in livestock. This study was conducted in 2004 on 20 swine farms in Alberta and Saskatchewan. On-farm records and questionnaires were used to retrospectively describe the antimicrobial exposures of pigs through feed, water, and injection. Antimicrobial use in all production categories was described over 12 months. On-farm records and questionnaires provided sufficient data to describe antimicrobial exposure rates through feed and water. In contrast, on-farm records did not supply sufficient data to describe parenteral antimicrobial exposure rates. Records lacked data on the number of exposures per treatment, therefore parenteral AMU was described as an exposure incidence. Parenteral exposure records were often unavailable for pigs less than 22 kg, in which case questionnaires were used. The incidence of parenteral AMU was significantly higher in herds reporting exposure by questionnaire compared with existing records, suggesting that on-farm records did not reliably describe parenteral AMU. However, because antimicrobial exposures in feed and water were markedly more common than through injection, it was concluded that existing on-farm data would be a valuable resource for investigating AMU and AMR in pigs.     

Characterization of integron mediated antimicrobial resistance in Salmonella isolated from diseased swine

Forty-two Salmonella isolates obtained from diseased swine were genetically characterized for the presence of specific antimicrobial resistance mechanisms. Twenty of these isolates were characterized as S. Typhimurium DT104 strains. Pulsed-field gel electrophoresis was used to determine genetic relatedness and revealed 20 distinct genetic patterns among the 42 isolates. However, all DT104 isolates fell within 2 closely related genetic clusters. Other Salmonella isolates were genetically grouped together according to serotype. All DT104 isolates displayed the penta-resistance phenotype to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline. Resistance to sulfamethoxazole, tetracycline, streptomycin, kanamycin, and ampicillin was most common among the non-DT104 Salmonella isolates. All DT104 strains contained 2 chromosomal integrons of 1000 and 1200 base pairs. The DNA sequencing revealed that the 2 integrons contained genes encoding a resistance to streptomycin and ampicillin, respectively. None of the non-DT104 strains showed the same pattern, although several strains possessed integrons of 1000 base pairs or larger. However, the majority of non-DT104 Salmonella strains did not possess any integrons. Two Salmonella isolates displayed tolerance to the organic solvent cyclohexane, indicating the possibility that they are overexpressing chromosomal regulatory genes marA or soxS or the associated multidrug efflux pump, acrAB. This research suggests that integrons contribute to antimicrobial resistance among specific swine Salmonella serotypes; however, they are not as widely disseminated among non-Typhimurium swine Salmonella serotypes as previously thought.     

Antimicrobial resistance of Salmonella enterica isolates from apparently healthy and clinically ill finishing pigs in Spain

This study was the first conducted in Spain to evaluate the occurrence of antimicrobial resistance and multi-resistance in Salmonella isolates recovered from finishing pigs from Spanish swine farms distributed over the whole country. For this purpose, 290 Salmonella isolates recovered from apparently healthy finishing pigs in a farm-based cross-sectional study and 192 Salmonella isolates recovered from faecal samples of finishing pigs suffering from diarrhoea were investigated. Resistance to a panel of 17 antimicrobials was determined using a broth microdilution technique. Resistance was a common finding and was detected in 90.3% of the Salmonella isolates from apparently healthy finishing pigs and 95.3% of the Salmonella isolates from clinically diseased finishing pigs. Resistance was particularly high among isolates of serogroup B and serovars Typhimurium and its monophasic variant S. 4,5,12:i:-. Higher frequencies of resistance were found to tetracycline, sulphamethoxazole, streptomycin, spectinomycin, ampicillin, chloramphenicol and trimethoprim-sulphamethoxazole. Less than 10% of the isolates were resistant to amoxicillin/clavulanic acid, neomycin, cephalotin, apramycin and gentamicin. Resistance to ciprofloxacin, colistin and ceftiofur was rare (under 1%). Multi-resistance, defined as resistance to four or more drugs, was detected in more than 50% of the isolates. Although multi-resistance was particularly frequent among isolates of S. Typhimurium, it was also high among other serovars as Bredeney and the S. Typhimurium monophasic variant. 4,5,12:i:-.     

Antimicrobial resistance in fecal Escherichia coli isolated from growing chickens on commercial broiler farms

To investigate the effects of rearing practices of commercial broiler chickens on the incidence of antimicrobial resistance in commensal Escherichia coli isolates, fecal E. coli isolates obtained in 4 farms were screened for anitimicrobial resistance. Ten E. coli isolates were recovered from each of the fecal samples collected from 10 birds in the farms at the ages of 2 days, 14-17 days, and 47-50 days. In 2 out of the 4 farms, no antimicrobials were used during the rearing period. In the other two farms, following collection of the fecal samples at 14 and 15 days of age, oxytetracycline (OTC), sulfadimethoxine (SDMX), and tylosin were given to birds on one farm and SDMX was used in the other. Isolates resistant to ampicillin and OTC that were obtained from an untreated flock at different sampling times were closely related to each other by pulsed-field gel electrophoresis patterns (PFGE) of XbaI-digested chromosomal DNA. PFGE analysis together with in vitro conjugation experiments suggested that diversity of resistance phenotypes within a clone may be resulted from the acquisition and loss of R-plasmids in an untreated and a treated flock. The numbers of resistance phenotypes observed among fecal isolates increased during the growth of the chickens in all the farms. The results in the present study suggest that persistence of commensal E. coli strains resistant to antimicrobials even in the absence of antimicrobial administration. It is also hypothesized that horizontal transmission of resistance determinants resulted in the emergence of different resistance phenotypes in those farms.     

Assessment of antibiotic resistance phenotype and integrons in Salmonella enterica serovar Typhimurium isolated from swine

Salmonella enterica serovar Typhimurium (S. Typhimurium) isolated and identified from swine were subjected for the analysis of antibiotic resistance pattern and clinically important class 1 and 2 integrons. In addition, S. Typhimurium isolates exhibiting ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline and florfenicol (ACSSuTF) resistance pattern as described in most Salmonella enterica serotype Typhimurium definitive type 104 (DT104) were characterized by polymerase chain reaction. All the isolates were resistant to more than four antibiotics and showed the highest resistance to streptomycin (94.1%), followed by tetracycline (90.1%), ampicillin (64.7%), chloramphenicol (56.8%) and gentamicin (54.9%). MIC value for the ten isolates ranged between 0.125-2 mug/ml for ciprofloxacin. Among the beta-lactams used, only one of the isolate exhibited resistance to ceftiofur (MIC 8 microg/ml). Sixty eight percent of these multi drug resistance (MDR) S. Typhimurium isolates carried clinically important class 1 integron with 1kb (aadA) and/or 2kb (dhfrXII-orfF-aadA2) resistance gene cassettes. This study reports the increasing trend of multi drug resistance (MDR) S. Typhimurium with clinically important class 1 integron in pigs. In addition, emergence of the ACSSuTF-type resistance in S. Typhimurium PT other than DT104 may limit the use of resistance gene markers in its detection methods by PCR.     

Molecular epidemiology and antimicrobial resistance of Salmonella typhimurium DTI04 on Ontario swine farms.

This study was conducted to examine antimicrobial resistances, plasmid profiles, and pulsed-field gel electrophoresis patterns of 80 Salmonella Typhimurium (including var. Copenhagen) DT104 strains (including DT104a and DT104b) recovered from pig and environmental fecal samples on 17 swine farms in Ontario. No resistance was observed to amoxicillin/clavulanic acid, apramycin, carbadox, cephalothin, ceftriaxone, ceftiofur, cefoxitin, ciprofloxacin, nalidixic acid, trimethoprim, and tobramycin. However, the isolates exhibited resistance against 4 to 10 antimicrobials with the most frequent resistance being to sulfonamides (Su), ampicillin (A), streptomycin (S), spectinomycin (Sp), chloramphenicol (C), tetracycline (T), and florfenicol (F). Thirteen distinct resistance patterns were determined but 88% of isolates shared the typical resistance pattern "ACSpSSuT." Twelve different plasmid profiles were observed; the 62 MDa virulence-associated plasmid was detected in 95% of the isolates. The 2.1 MDa plasmid was the second most frequent one, which was harbored by 65% isolates. The isolates were classified into 23 distinct genotypes by PFGE-SpeI + BlnI when difference in at least one fragment was defined as a distinct genotype. In total, 39 distinct "types" were observed when defining a "type" based on the combination of antimicrobial resistance, plasmid pattern, and PFGE-SpeI + BlnI for each isolate. The highest diversity was 0.96 (95% CI: 0.92, 0.96) for the "type" described above followed by 0.92 (95% CI: 0.88, 0.93) for PFGE-SpeI + BlnI. The diversity of DT104 isolates indicates there might be multiple sources for this microorganism on swine farms. This knowledge might be used to track these sources, as well as to study the extent of human salmonellosis attributed to pork compared to food products derived from other food-producing animals.     

Antimicrobial susceptibility of Brachyspira hyodysenteriae isolated from 21 Polish farms

Swine dysentery (SD) is a common disease among pigs worldwide, which contributes to major production losses. Antimicrobial susceptibility testing of B. hyodysenteriae, the etiological agent of SD, is mainly performed by the agar dilution method. This method has certain limitations due to difficulties in interpretation of results. The aim of this study was the analysis of antimicrobial susceptibility of Brachyspira hyodysenteriae (B. hyodysenteriae) Polish field isolates by broth microdilution procedure. The study was performed on 21 isolates of B. hyodysenteriae, collected between January 2006 to December 2010 from cases of swine dysentery. VetMIC Brachyspira panels with antimicrobial agents (tiamulin, valnemulin, doxycycline, lincomycin, tylosin and ampicillin) were used for susceptibility testing of B. hyodysenteriae. The minimal inhibitory concentration (MIC) was determined by the broth dilution procedure. The lowest antimicrobial activity was demonstrated for tylosin and lincomycin, with inhibition of bacterial growth using concentrations > 128 microg/ml and 32 microg/ml, respectively. In the case of doxycycline, the MIC values were < or = 2.0 microg/ml. No decreased susceptibility to tiamulin was found among the Polish isolates and MIC values for this antibiotic did not exceed 1.0 microg/ml. The results of the present study confirmed that Polish B. hyodysenteriae isolates were susceptible to the main antibiotics (tiamulin and valnemulin) used in treatment of swine dysentery. Further studies are necessary to evaluate a possible slow decrease in susceptibility to tiamulin and valnemulin of B. hyodysenteriae strains in Poland.     

Antimicrobial resistance of fecal Escherichia coli isolated from grow-finish pigs in 20 herds in Alberta and Saskatchewan.

Escherichia coli (n = 1439), isolated from the feces of apparently healthy grow-finish pigs in 20 herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. All isolates were susceptible to amikacin, ceftriaxone, and ciprofloxacin and less than 1% was resistant to amoxicillin-clavulanic acid, cefoxitin, ceftiofur, gentamicin, and nalidixic acid. Resistance was most common to tetracycline (66.8%), sulfamethoxazole (46.0%) and streptomycin (33.4%). Twenty-one percent of the isolates were susceptible to all drugs, while 57% were resistant to 2 or more antimicrobials. Unconditional associations between resistances provided insight into the potential for co-selection. Every resistance-outcome was associated with at least 2 other drug-resistances. These associations illustrate the propensity for resistance phenotypes to occur together and the importance of considering co-selection in antimicrobial use decisions. A 2nd analysis explored the associations between resistance phenotypes in E. coli and Salmonella spp. from the same herd. Only 2 resistances in Salmonella were associated with herd-level E. coli resistance, indicating that E. coli is a poor sentinel for Salmonella AMR within herds. Herd-level management, including antimicrobial use, could affect antimicrobial resistance. The intra-class correlation between isolates within herds ranged from 0.1 to 0.46, which confirmed resistance clustered within herds. This suggests herd-level interventions might mitigate antimicrobial resistance. Overall, these results reflect the on-farm selection pressure for resistance and the potential food-safety risk from near-market animals. These data provide a baseline for comparisons with future on-farm monitoring of antimicrobial resistance in E. coli.     

Comparison of antimicrobial resistance in generic Escherichia coli and Salmonella spp. cultured from identical fecal samples in finishing swine

The objectives of this study were to investigate the associations between antimicrobial resistance patterns in generic Escherichia coli and Salmonella spp. isolates recovered from identical pen pooled fecal samples, and to evaluate potential clustering of multiple isolates of these organisms within identical fecal samples. Up to 5 generic E. coli (n = 922 isolates) and Salmonella spp. (n = 922 isolates) isolates were obtained from each of 188 pen pooled fecal samples that had been collected from 45 finishing swine farms in Alberta in 2000, and tested for susceptibility to 15 antimicrobials. No isolates of either organism were resistant to 3rd generation cephalosporins or fluoroquinolones, which in Canada are considered antimicrobials of very high importance to human health. Approximately twice as many generic E. coli isolates as Salmonella spp. isolates were resistant to at least 1 antimicrobial. In addition, E. coli isolates showed more multidrug-resistance patterns. No significant association was observed between the resistance phenotypes of Salmonella spp. and E. coli at the fecal sample level. More clustering at the sample level was observed for proportions of antimicrobial resistance (AMR) in Salmonella spp. isolates than E. coli indicating that in future studies it might be sufficient to test fewer than 5 Salmonella spp. isolates per sample.