Salmonella in raccoons (Procyon lotor) in southern Ontario, Canada

Numerous serotypes of Salmonella have been detected in a variety of wild animals, including raccoons (Procyon lotor). Raccoons are common, mid-size omnivores that live in close association with people in urban and rural areas in Ontario. Although raccoons are known to shed Salmonella, little is known about their potential long-term role in maintaining Salmonella infections. We sampled feces from raccoons in three areas of Ontario: one primarily urban site around Niagara, one primarily rural site north of Guelph, and the grounds of the Toronto Zoo, in 2007 to identify which serotypes of Salmonella were commonly shed by raccoons in southern Ontario. In addition, we conducted a longitudinal study at the Toronto Zoo site to determine if raccoons remain persistently infected with Salmonella. Salmonella was found in 45% of samples. The prevalence of Salmonella in raccoon feces ranged from 27% at the rural site to 65% at the urban site. We detected 16 serotypes of Salmonella in 83 positive samples. The most common serotype detected in raccoons from the rural and zoo sites was Salmonella enterica serotype Typhimurium, whereas Salmonella Newport was detected most commonly in the urban site. Only one raccoon of 11 that were captured in four or more consecutive trapping sessions shed the same Salmonella serotype for two consecutive months, suggesting that raccoons regularly acquire new Salmonella serotypes from the environment.     

Patterns of antimicrobial resistance observed in Escherichia coli isolates obtained from domestic- and wild-animal fecal samples, human septage, and surface water

A repeated cross-sectional study was conducted to determine the patterns of antimicrobial resistance in 1,286 Escherichia coli strains isolated from human septage, wildlife, domestic animals, farm environments, and surface water in the Red Cedar watershed in Michigan. Isolation and identification of E. coli were done by using enrichment media, selective media, and biochemical tests. Antimicrobial susceptibility testing by the disk diffusion method was conducted for neomycin, gentamicin, streptomycin, chloramphenicol, ofloxacin, trimethoprim-sulfamethoxazole, tetracycline, ampicillin, nalidixic acid, nitrofurantoin, cephalothin, and sulfisoxazole. Resistance to at least one antimicrobial agent was demonstrated in isolates from livestock, companion animals, human septage, wildlife, and surface water. In general, E. coli isolates from domestic species showed resistance to the largest number of antimicrobial agents compared to isolates from human septage, wildlife, and surface water. The agents to which resistance was demonstrated most frequently were tetracycline, cephalothin, sulfisoxazole, and streptomycin. There were similarities in the patterns of resistance in fecal samples and farm environment samples by animal, and the levels of cephalothin-resistant isolates were higher in farm environment samples than in fecal samples. Multidrug resistance was seen in a variety of sources, and the highest levels of multidrug-resistant E. coli were observed for swine fecal samples. The fact that water sample isolates were resistant only to cephalothin may suggest that the resistance patterns for farm environment samples may be more representative of the risk of contamination of surface waters with antimicrobial agent-resistant bacteria.     

High Levels of Antimicrobial Resistance among Escherichia coli Isolates from Livestock Farms and Synanthropic Rats and Shrews in the Mekong Delta of Vietnam

In Mekong Delta farms (Vietnam), antimicrobials are extensively used, but limited data are available on levels of antimicrobial resistance (AMR) among Escherichia coli isolates. We performed a structured survey of AMR in E. coli isolates (n = 434) from 90 pig, chicken, and duck farms. The results were compared with AMR among E. coli isolates (n = 234) from 66 small wild animals (rats and shrews) trapped on farms and in forests and rice fields. The isolates were susceptibility tested against eight antimicrobials. E. coli isolates from farmed animals were resistant to a median of 4 (interquartile range [IQR], 3 to 6) antimicrobials versus 1 (IQR, 1 to 2) among wild mammal isolates (P < 0.001). The prevalences of AMR among farmed species isolates (versus wild animals) were as follows: tetracycline, 84.7% (versus 25.6%); ampicillin, 78.9% (versus 85.9%); trimethoprim-sulfamethoxazole, 52.1% (versus 18.8%); chloramphenicol, 39.9% (versus 22.5%); amoxicillin-clavulanic acid, 36.6% (versus 34.5%); and ciprofloxacin, 24.9% (versus 7.3%). The prevalence of multidrug resistance (MDR) (resistance against three or more antimicrobial classes) among pig isolates was 86.7% compared to 66.9 to 72.7% among poultry isolates. After adjusting for host species, MDR was ∼8 times greater among isolates from wild mammals trapped on farms than among those trapped in forests/rice fields (P < 0.001). Isolates were assigned to unique profiles representing their combinations of susceptibility results. Multivariable analysis of variance indicated that AMR profiles from wild mammals trapped on farms and those from domestic animals were more alike (R² range, 0.14 to 0.30) than E. coli isolates from domestic animals and mammals trapped in the wild (R² range, 0.25 to 0.45). The results strongly suggest that AMR on farms is a key driver of environmental AMR in the Mekong Delta.     

Considerations when using discriminant function analysis of antimicrobial resistance profiles to identify sources of fecal contamination of surface water in Michigan

The goals of this study were to (i) identify issues that affect the ability of discriminant function analysis (DA) of antimicrobial resistance profiles to differentiate sources of fecal contamination, (ii) test the accuracy of DA from a known-source library of fecal Escherichia coli isolates with isolates from environmental samples, and (iii) apply this DA to classify E. coli from surface water. A repeated cross-sectional study was used to collect fecal and environmental samples from Michigan livestock, wild geese, and surface water for bacterial isolation, identification, and antimicrobial susceptibility testing using disk diffusion for 12 agents chosen for their importance in treating E. coli infections or for their use as animal feed additives. Nonparametric DA was used to classify E. coli by source species individually and by groups according to antimicrobial exposure. A modified backwards model-building approach was applied to create the best decision rules for isolate differentiation with the smallest number of antimicrobial agents. Decision rules were generated from fecal isolates and applied to environmental isolates to determine the effectiveness of DA for identifying sources of contamination. Principal component analysis was applied to describe differences in resistance patterns between species groups. The average rate of correct classification by DA was improved by reducing the numbers of species classifications and antimicrobial agents. DA was able to correctly classify environmental isolates when fewer than four classifications were used. Water sample isolates were classified by livestock type. An evaluation of the performance of DA must take into consideration relative contributions of random chance and the true discriminatory power of the decision rules.     

Characterization of Escherichia coli O157:H7 from downer and healthy dairy cattle in the upper Midwest region of the United States

While cattle in general have been identified as a reservoir of Escherichia coli O157:H7, there are limited data regarding the prevalence and clonality of this pathogen in downer dairy cattle and the potential impact to human health that may occur following consumption of meat derived from downer dairy cattle. In the present study, conducted at two slaughter facilities in Wisconsin between May and October of 2001, we established a higher prevalence of E. coli O157:H7 in fecal and/or tissue samples obtained aseptically from intact colons of downer dairy cattle (10 of 203, 4.9%) than in those from healthy dairy cattle (3 of 201, 1.5%). Analyses of 57 isolates, representing these 13 positive samples (one to five isolates per sample), by pulsed-field gel electrophoresis, revealed 13 distinct XbaI restriction endonuclease digestion profiles (REDP). Typically, isolates from different animals displayed distinct REDP and isolates from the same fecal or colon sample displayed indistinguishable REDP. However, in one sample, two different, but highly related, REDP were displayed by the isolates recovered. Antimicrobial susceptibility testing indicated that 10 of the 57 isolates, recovered from 2 (1 downer and 1 healthy animal) of the 13 positive samples, were resistant to at least 1 of 18 antimicrobials tested. However, there was no appreciable difference in the frequency of resistance of isolates recovered from downer and healthy dairy cattle, and not all isolates with the same REDP displayed the same antimicrobial susceptibility profile. Lastly, it was not possible to distinguish between isolates recovered from downer and healthy cattle based on their XbaI REDP or antimicrobial susceptibility. These results indicate that downer cattle had a 3.3-fold-higher prevalence of E. coli O157:H7 than healthy cattle within the time frame and geographic scope of this study.     

Antimicrobial susceptibility and factors affecting the shedding of E. coli O157:H7 and Salmonella in dairy cattle

AIMS: To examine factors affecting faecal shedding of the foodborne pathogens Escherichia coli O157:H7 and Salmonella in dairy cattle and evaluate antimicrobial susceptibility of these isolates. METHODS: Faecal samples were obtained in replicate from lactating (LAC; n = 60) and non-lactating (NLAC; n = 60) Holstein cattle to determine influence of heat stress, parity, lactation status (LAC vs NLAC) and stage of lactation [60 days in milk (DIM)] and cultured for E. coli O157:H7 and Salmonella. A portion of the recovered isolates were examined for antimicrobial susceptibility using the broth microdilution technique. RESULTS: No effects of heat stress were observed. Lactating cows shed more (P < 0.01) E. coli O157:H7 than NLAC cows (43% vs 32%, respectively). Multiparous LAC cows tended to shed more (P = 0.06) Salmonella than primiparous LAC cows (39% vs 27%, respectively). Parity did not influence (P > 0.10) bacterial shedding in NLAC cows. Cows 60 DIM. Seventeen Salmonella serotypes were identified with the most prevalent being Senftenberg (18%), Newport (17%) and Anatum (15%). Seventy-nine of the Salmonella isolates were resistant to at least one of the seven antibiotics. Escherichia coli O157:H7 isolates were resistant to 11 different antibiotics with multiple resistance to nine or more antibiotics observed in five isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated differences in the shedding patterns of foodborne pathogens due to the stage of the milk production cycle and may help identify times when on-farm pathogen control would be the most effective.     

Field trial evaluating the influence of prophylactic and therapeutic antimicrobial administration on antimicrobial resistance of fecal Escherichia coli in dairy calves

The objective of this study was to describe the influence of in-feed and therapeutic antimicrobials on resistance in commensal fecal Escherichia coli isolated from preweaned calves. Four groups of 30, day-old calf-ranch calves were enrolled and raised until 4 weeks of age. Groups 1 to 3 were raised without antimicrobials in the feed. Group 1 was isolated from the other groups and received no antimicrobial therapy. Group 2 was housed on the calf ranch and did not receive antimicrobial therapy, whereas groups 3 and 4 could be treated with antimicrobials. Group 4 was fed neomycin and tetracycline HCl in the milk replacer. Fecal samples were collected from calves on days 1, 14, and 28. Three E. coli isolates per sample were evaluated for susceptibility to 12 antimicrobials. Cluster analysis was used to group isolates having similar susceptibility patterns. Cumulative logistic regression was used to evaluate factors associated with increasing levels of multiple antimicrobial resistance. In-feed antimicrobials were associated with higher levels of multiple antimicrobial resistance in fecal E. coli.f In calves not receiving in-feed antimicrobials, older calves had higher levels of resistance compared to day-old calves. Individual antimicrobial therapy increased resistance in these calves but appeared to be transient. There was no environmental influence on resistance in E. coli populations among study groups.     

Selection of broad‐spectrum cephalosporin‐resistant Escherichia coli in the feces of healthy dogs after administration of first‐generation cephalosporins

Although antimicrobial products are essential for treating diseases caused by bacteria, antimicrobial treatment selects for antimicrobial‐resistant (AMR) bacteria. The aim of this study was to determine the effects of administration of first‐generation cephalosporins on development of resistant Escherichia coli in dog feces. The proportions of cephalexin (LEX)‐resistant E. coli in fecal samples of three healthy dogs treated i.v. with cefazolin before castration and then orally with LEX for 3 days post‐operation (PO) were examined using DHL agar with or without LEX (50 µg/mL). LEX‐resistant E. coli were found within 3 days PO, accounted for 100% of all identified E. coli 3–5 days PO in all dogs, and were predominantly found until 12 days PO. LEX‐resistant E. coli isolates on DHL agar containing LEX were subjected to antimicrobial susceptibility testing, pulsed‐field gel electrophoresis (PFGE) genotyping, β‐lactamase typing and plasmid profiling. All isolates tested exhibited cefotaxime (CTX) resistance (CTX minimal inhibitory concentration ≥4 µg/mL). Seven PFGE profiles were classified into five groups and three β‐lactamase combinations (bla_CMY‐4‐bla_TEM‐1, bla_TEM‐1‐bla_CTX‐M‐15 and bla_TEM‐1‐bla_CTX‐M‐15‐bla_CMY‐4). All isolates exhibited identical PFGE profiles in all dogs on four days PO and subsequently showed divergent PFGE profiles. Our results indicate there are two selection periods for AMR bacteria resulting from the use of antimicrobials. Thus, continuing hygiene practices are necessary to prevent AMR bacteria transfer via dog feces after antimicrobial administration.     

The diversity of Escherichia coli serotypes and biotypes in cattle faeces

AIM: To study the diversity of commensal Escherichia coli populations shed in faeces of cattle fed on different diets. METHODS AND RESULTS: Thirty Brahman-cross steers were initially fed a high grain (80%) diet and then randomly allocated into three dietary treatment groups, fed 80% grain, roughage, or roughage + 50% molasses. Up to eight different E. coli isolates were selected from primary isolation plates of faecal samples from each animal. Fifty-two distinct serotypes, including nine different VTEC strains, were identified from a total of 474 E. coli isolates. Cattle fed a roughage + molasses diet had greater serotype diversity (30 serotypes identified) than cattle fed roughage or grain (21 and 17 serotypes identified respectively). Cluster analysis showed that serotypes isolated from cattle fed roughage and roughage + molasses diets were more closely associated than serotypes isolated from cattle fed grain. Resistance to one or more of 11 antimicrobial agents was detected among isolates from 20 different serotypes. Whilst only 2.3% of E. coli isolates produced enterohaemolysin, 25% were found to produce alpha-haemolysin. CONCLUSIONS: Diverse non-VTEC populations of E. coli serotypes are shed in cattle faeces and diet may affect population diversity. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides new information on the serotype diversity and phenotypic traits of predominant E. coli populations in cattle faeces, which could be sources of environmental contamination.     

Temporal prevalence of antimicrobial resistance in Campylobacter spp. from beef cattle in Alberta feedlots

Antimicrobial resistance (AMR) was temporally assessed in campylobacters isolated from beef cattle (7,738 fecal samples from 2,622 animals) in four commercial feedlots in Alberta. All calves were administered chlortetracycline and oxytetracycline in feed, and a majority of the animals (93%) were injected with long-acting oxytetracycline upon arrival at the feedlot. Fecal samples from individual animals were collected upon arrival (i.e., entry sample), 69 days (standard deviation [SD] = 3 days) after arrival (i.e., interim sample), and 189 days (SD = 33 days) after arrival (i.e., exit sample) at the feedlot. In total, 1,586 Campylobacter isolates consisting of Campylobacter coli (n = 154), Campylobacter fetus (n = 994), Campylobacter jejuni (n = 431), Campylobacter hyointestinalis (n = 4), and Campylobacter lanienae (n = 3) were recovered and characterized. The administration of antimicrobials did not decrease carriage rates of campylobacters, and minimal resistance (< or =4%) to azithromycin, ciprofloxacin, enrofloxacin, gentamicin, and meropenem was observed. In contrast, substantive increases in the prevalence of isolates resistant to tetracycline and doxycycline (56 to 89%) for C. coli, C. fetus, and C. jejuni, as well as in the number of animals (7 to 42%) from which resistant isolates were recovered, were observed during the feedlot period. Increased resistance to erythromycin (total isolates and carriages rates) was also observed in isolates of C. coli over the three isolation times. The majority of C. fetus isolates recovered were resistant to nalidixic acid, but this was independent of when they were isolated. A relatively limited number of multidrug-resistant isolates were recovered and consisted primarily of C. coli resistant to tetracyclines and erythromycin (10% of isolates). Over the course of the feedlot period, considerable increases in antimicrobial resistance were observed in C. coli, C. fetus, and C. jejuni, but with the exception of erythromycin resistance in C. coli, the administration of antimicrobial agents to beef cattle was found to have a minimal impact on resistance to macrolides and fluoroquinolones, the two classes of antimicrobials used to treat campylobacteriosis in humans. However, the widespread use of antimicrobial agents in beef production and the possible horizontal transfer of mobile genetic elements with antimicrobial resistance determinants among Campylobacter and other bacterial taxa emphasize the need to monitor AMR development in bacteria from beef cattle.     

Characterization of antimicrobial resistant Escherichia coli isolated from processed bison carcasses

AIM: To determine the phenotypic and genotypic antimicrobial susceptibility profiles of Escherichia coli from bison carcasses. METHODS AND MATERIALS: The antimicrobial resistance of 138 E. coli isolates recovered from processed bison carcasses was determined by using the National Antimicrobial Resistance Monitoring System panels, polymerase chain reaction assays, plasmid analysis and conjugation studies. RESULTS: Resistance to 14 of the 16 antimicrobials was observed. Twenty-three (16.7%) isolates displayed resistance to at least one antimicrobial agent. The most prevalent resistances were to tetracycline (13.0%), sulfamethoxazole (7.9%) and streptomycin (5.8%). No resistance was observed to amikacin and ciprofloxacin. Further analysis of 23 antimicrobial-resistant E. coli isolates showed the presence of resistance genes corresponding to their phenotypic profiles. Results of conjugation studies carried out showed most isolates tested were able to transfer their resistance to recipients. CONCLUSION: This study indicated that multidrug-resistant E. coli isolates are present in bison. However, the resistance rate is lower than that reported in other meat species. SIGNIFICANCE AND IMPACT OF THE STUDY: The beneficial effects of antimicrobial-free feeding practice in bison may be promoting a reduction in the prevalence of antimicrobial resistance in commensal flora of bison.     

Changes in antimicrobial resistance in fecal bacteria associated with pig transit and holding times at slaughter plants

Fecal coliforms, fecal streptococci, and antimicrobial resistance (AMR) associated with various pig transit and holding times were investigated at slaughter plants. Changes in the relative abundance of two biotypes of Streptococcus faecium were associated with transit and holding of pigs, although approximately 20% of the isolates were unidentified. The greatest variety of coliforms was isolated from porcine feces after short transit (2 h) or holding (3 h) times and was qualitatively similar to those from pigs on farms. Isolates from pigs with longer average transit or holding times were almost all Escherichia coli (four biotypes). Streptococcal resistance to most antimicrobial agents was significantly greater (P less than 0.05) in isolates from live pigs at slaughter plants than in those from pigs at farms and was apparent after a short transit time (2 h). Streptococci from pigs held an average of 15 h were less resistant to most antimicrobial agents than those from pigs held 3 or 43 h. When compared with short transit times, moderate transit times (6 h) were associated with significantly decreased (P less than 0.05) coliform resistance and decreased resistance transfer but a greater diversity of AMR patterns. Holding pigs overnight (14 h) was associated with lowered coliform resistance to several antimicrobial agents, compared with the resistance of isolates from pigs held 3 or 39 h. A substantial increase (18 to 48%) in the ability to transfer streptomycin resistance was demonstrated in coliforms from pigs held 39 h, when compared with those from pigs held 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antimicrobial resistance and virulence genes of Escherichia coli isolates from swine in Ontario

A total of 318 Escherichia coli isolates obtained from diarrheic and healthy pigs in Ontario from 2001 to 2003 were examined for their susceptibility to 19 antimicrobial agents. They were tested by PCR for the presence of resistance genes for tetracycline, streptomycin, sulfonamides, and apramycin and of 12 common virulence genes of porcine E. coli. Antimicrobial resistance frequency among E. coli isolates from swine in Ontario was moderate in comparison with other countries and was higher in isolates from pigs with diarrhea than in isolates from healthy finisher pigs. Resistance profiles suggest that cephamycinases may be produced by > or = 8% of enterotoxigenic E. coli (ETEC). Resistance to quinolones was detected only in enterotoxigenic E. coli (< or = 3%). The presence of sul3 was demonstrated for the first time in Canada in porcine E. coli isolates. Associations were observed among tetA, sul1, aadA, and aac(3)IV and among tetB, sul2, and strA/strB, with a strong negative association between tetA and tetB. The paa and sepA genes were detected in 92% of porcine ETEC, and strong statistical associations due to colocation on a large plasmid were observed between tetA, estA, paa, and sepA. Due at least in part to gene linkages, the distribution of resistance genes was very different between ETEC isolates and other porcine E. coli isolates. This demonstrates that antimicrobial resistance epidemiology differs significantly between pathogenic and commensal E. coli isolates. These results may have important implications with regards to the spread and persistence of resistance and virulence genes in bacterial populations and to the prudent use of antimicrobial agents.     

Changes in antimicrobial resistance in fecal bacteria associated with pig transit and holding times at slaughter plants.

Fecal coliforms, fecal streptococci, and antimicrobial resistance (AMR) associated with various pig transit and holding times were investigated at slaughter plants. Changes in the relative abundance of two biotypes of Streptococcus faecium were associated with transit and holding of pigs, although approximately 20% of the isolates were unidentified. The greatest variety of coliforms was isolated from porcine feces after short transit (2 h) or holding (3 h) times and was qualitatively similar to those from pigs on farms. Isolates from pigs with longer average transit or holding times were almost all Escherichia coli (four biotypes). Streptococcal resistance to most antimicrobial agents was significantly greater (P less than 0.05) in isolates from live pigs at slaughter plants than in those from pigs at farms and was apparent after a short transit time (2 h). Streptococci from pigs held an average of 15 h were less resistant to most antimicrobial agents than those from pigs held 3 or 43 h. When compared with short transit times, moderate transit times (6 h) were associated with significantly decreased (P less than 0.05) coliform resistance and decreased resistance transfer but a greater diversity of AMR patterns. Holding pigs overnight (14 h) was associated with lowered coliform resistance to several antimicrobial agents, compared with the resistance of isolates from pigs held 3 or 39 h. A substantial increase (18 to 48%) in the ability to transfer streptomycin resistance was demonstrated in coliforms from pigs held 39 h, when compared with those from pigs held 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Satellite tracking of gulls and genomic characterization of faecal bacteria reveals environmentally mediated acquisition and dispersal of antimicrobial‐resistant Escherichia coli on the Kenai Peninsula,Alaska

Gulls (Larus spp.) have frequently been reported to carry Escherichia coli exhibiting antimicrobial resistance (AMR E. coli); however, the pathways governing the acquisition and dispersal of such bacteria are not well described. We equipped 17 landfill‐foraging gulls with satellite transmitters and collected gull faecal samples longitudinally from four locations on the Kenai Peninsula, Alaska to assess: (a) gull attendance and transitions between sites, (b) spatiotemporal prevalence of faecally shed AMR E. coli, and (c) genomic relatedness of AMR E. coli isolates among sites. We also sampled Pacific salmon (Oncorhynchus spp.) harvested as part of personal‐use dipnet fisheries at two sites to assess potential contamination with AMR E. coli. Among our study sites, marked gulls most commonly occupied the lower Kenai River (61% of site locations) followed by the Soldotna landfill (11%), lower Kasilof River (5%) and upper Kenai River (<1%). Gulls primarily moved between the Soldotna landfill and the lower Kenai River (94% of transitions among sites), which were also the two locations with the highest prevalence of AMR E. coli. There was relatively high spatial and temporal variability in AMR E. coli prevalence in gull faeces and there was no evidence of contamination on salmon harvested in personal‐use fisheries. We identified E. coli sequence types and AMR genes of clinical importance, with some isolates possessing genes associated with resistance to as many as eight antibiotic classes. Our findings suggest that gulls acquire AMR E. coli at habitats with anthropogenic inputs and subsequent movements may represent pathways through which AMR is dispersed.     

Prevalence, antibiotic susceptibility, and diversity of Escherichia coli O157:H7 isolates from a longitudinal study of beef cattle feedlots

Prevalence, antibiotic susceptibility, and genetic diversity were determined for Escherichia coli O157:H7 isolated over 11 months from four beef cattle feedlots in southwest Kansas. From the fecal pat (17,050) and environmental (7,134) samples collected, 57 isolates of E. coli O157:H7 were identified by use of bacterial culture and latex agglutination (C/LA). PCR showed that 26 isolates were eaeA gene positive. Escherichia coli O157:H7 was identified in at least one of the four feedlots in 14 of the 16 collections by C/LA and in 9 of 16 collections by PCR, but consecutive positive collections at a single feedlot were rare. Overall prevalence in fecal pat samples was low (0.26% by C/LA, and 0.08% by PCR). No detectable differences in prevalence or antibiotic resistance were found between isolates collected from home pens and those from hospital pens, where antibiotic use is high. Resistant isolates were found for six of the eight antibiotics that could be used to treat E. coli infections in food animals, but few isolates were multidrug resistant. The high diversity of isolates as measured by random amplification of polymorphic DNA and other characteristics indicates that the majority of isolates were unique and did not persist at a feedlot, but probably originated from incoming cattle. The most surprising finding was the low frequency of virulence markers among E. coli isolates identified initially by C/LA as E. coli O157:H7. These results demonstrate that better ways of screening and confirming E. coli O157:H7 isolates are required for accurate determination of prevalence.     

Change in antimicrobial susceptibility of Escherichia coli urinary tract isolates at a single institution over a period of 10 years

Urinary tract infections are common. Few published studies have demonstrated the change in Escherichia coli urinary isolate antimicrobial susceptibility over time within a given area and (or) population. The purpose of this study was to evaluate the change in susceptibility of E. coli clinical isolates obtained from urine specimens at a single institution over a period of 10 years. The microbiology laboratory information system at St. Boniface Hospital (Winnipeg, Manitoba, Canada) was searched retrospectively from 1 January 2000 to 31 December 2009, for all E. coli isolates from either a midstream or catheter urine source that had susceptibility testing performed. Only one isolate per patient was included during the entire study period. Antimicrobial susceptibility testing was carried out with either a Microscan instrument (pre-April 2004) or a Vitek instrument (May 2004 onwards). In total, 7353 E. coli urinary isolates were included for evaluation. Ciprofloxacin susceptibility declined significantly, from 99% in 2000 to 85% in 2009 (p < 0.0001). A small but statistically significant decline in susceptibility was also observed for ampicillin, cefazolin, trimethoprim-sulfamethoxazole, gentamicin, and nitrofurantoin. These data suggest that certain antimicrobials recommended for the treatment of urinary tract infections (ciprofloxacin, trimethoprim-sulfamethoxazole) may no longer be optimal.     

Antimicrobial resistance in generic Escherichia coli isolates from wild small mammals living in swine farm, residential, landfill, and natural environments in southern Ontario, Canada

To assess the impacts of different types of human activity on the development of resistant bacteria in the feces of wild small mammals, we compared the prevalences and patterns of antimicrobial resistance and resistance genes in generic Escherichia coli and Salmonella enterica isolates from fecal samples collected from wild small mammals living in four environments: swine farms, residential areas, landfills, and natural habitats. Resistance to antimicrobials was observed in E. coli isolates from animals in all environments: 25/52 (48%) animals trapped at swine farms, 6/69 (9%) animals trapped in residential areas, 3/20 (15%) animals trapped at landfills, and 1/22 (5%) animals trapped in natural habitats. Animals trapped on farms were significantly more likely to carry E. coli isolates with resistance to tetracycline, ampicillin, sulfisoxazole, and streptomycin than animals trapped in residential areas. The resistance genes sul2, aadA, and tet(A) were significantly more likely to be detected in E. coli isolates from animals trapped on farms than from those trapped in residential areas. Three S. enterica serotypes (Give, Typhimurium, and Newport) were recovered from the feces of 4/302 (1%) wild small mammals. All Salmonella isolates were pansusceptible. Our results show that swine farm origin is significantly associated with the presence of resistant bacteria and resistance genes in wild small mammals in southern Ontario, Canada. However, resistant fecal bacteria were found in small mammals living in all environments studied, indicating that environmental exposure to antimicrobials, antimicrobial residues, resistant bacteria, or resistance genes is widespread.     

Effects of Subtherapeutic Administration of Antimicrobial Agents to Beef Cattle on the Prevalence of Antimicrobial Resistance in Campylobacter jejuni and Campylobacter hyointestinalis

The influence of antimicrobial agents on the development of antimicrobial resistance (AMR) in Campylobacter isolates recovered from 300 beef cattle maintained in an experimental feedlot was monitored over a 315-day period (11 sample times). Groups of calves were assigned to one of the following antimicrobial treatments: chlortetracycline and sulfamethazine (CS), chlortetracycline alone (Ct), virginiamycin, monensin, tylosin phosphate, and no antimicrobial agent (i.e., control treatment). In total, 3,283 fecal samples were processed for campylobacters over the course of the experiment. Of the 2,052 bacterial isolates recovered, 92% were Campylobacter (1,518 were Campylobacter hyointestinalis and 380 were C. jejuni). None of the antimicrobial treatments decreased the isolation frequency of C. jejuni relative to the control treatment. In contrast, C. hyointestinalis was isolated less frequently from animals treated with CS and to a lesser extent from animals treated with Ct. The majority (≥94%) of C. jejuni isolates were sensitive to ampicillin, erythromycin, and ciprofloxacin, but more isolates with resistance to tetracycline were recovered from animals fed Ct. All of the 1,500 isolates of C. hyointestinalis examined were sensitive to ciprofloxacin. In contrast, 11%, 10%, and 1% of these isolates were resistant to tetracycline, erythromycin, and ampicillin, respectively. The number of animals from which C. hyointestinalis isolates with resistance to erythromycin and tetracycline were recovered differed among the antimicrobial treatments. Only Ct administration increased the carriage rates of erythromycin-resistant isolates of C. hyointestinalis, and the inclusion of CS in the diet increased the number of animals from which tetracycline-resistant isolates were recovered. The majority of C. hyointestinalis isolates with resistance to tetracycline were obtained from cohorts within a single pen, and most of these isolates were recovered from cattle during feeding of a forage-based diet as opposed to a grain-based diet. The findings of this study show that the subtherapeutic administration of tetracycline, alone and in combination with sulfamethazine, to feedlot cattle can select for the carriage of resistant strains of Campylobacter species. Considering the widespread use of in-feed antimicrobial agents and the high frequency of beef cattle that shed campylobacters, the development of AMR should be monitored as part of an on-going surveillance program.     

A high prevalence of antimicrobial resistant Escherichia coli isolated from pigs and a low prevalence of antimicrobial resistant E. coli from cattle and sheep in Great Britain at slaughter

The incidence of antimicrobial resistance and expressed and unexpressed resistance genes among commensal Escherichia coli isolated from healthy farm animals at slaughter in Great Britain was investigated. The prevalence of antimicrobial resistance among the isolates varied according to the animal species; of 836 isolates from cattle tested only 5.7% were resistant to one or more antimicrobials, while only 3.0% of 836 isolates from sheep were resistant to one or more agents. However, 92.1% of 2480 isolates from pigs were resistant to at least one antimicrobial. Among isolates from pigs, resistance to some antimicrobials such as tetracycline (78.7%), sulphonamide (66.9%) and streptomycin (37.5%) was found to be common, but relatively rare to other agents such as amikacin (0.1%), ceftazidime (0.1%) and coamoxiclav (0.2%). The isolates had a diverse range of resistance gene profiles, with tet(B), sul2 and strAB identified most frequently. Seven out of 615 isolates investigated carried unexpressed resistance genes. One trimethoprim-susceptible isolate carried a complete dfrA17 gene but lacked a promoter for it. However, in the remaining six streptomycin-susceptible isolates, one of which carried strAB while the others carried aadA, no mutations or deletions in gene or promoter sequences were identified to account for susceptibility. The data indicate that antimicrobial resistance in E. coli of animal origin is due to a broad range of acquired genes.