Prevalence and antimicrobial resistance of Campylobacter in antimicrobial-free and conventional pig production systems

Impact of In-Feed versus In-Water Chlortetracycline and Tiamulin Administrations on Fecal Prevalence and Antimicrobial Susceptibilities of Campylobacter in a Population of Nursery Pigs

Antimicrobial resistance (AMR) in bacteria is a major public health concern in the US and around the world. Campylobacter is an important foodborne pathogen that resides in the gut of pigs and is shed in feces, with the potential to be transmitted to humans. In pigs, the oral route, either in-feed or in-water, is by far the most common route of administration of antimicrobials. Because the distribution of the antibiotic in the gut and the dosages are different, the impact of in-feed vs. in-water administration of antibiotics on the development of AMR is likely to be different. Therefore, a study was conducted to compare in-feed vs. in-water administrations of chlortetracycline (CTC) and/or tiamulin on fecal prevalence and AMR profiles of Campylobacter among weaned nursery piglets. A total of 1,296 weaned piglets, allocated into 48 pens (27 piglets per pen), were assigned randomly to six treatment groups: Control (no antibiotic), in-feed CTC, in-water CTC, in-feed tiamulin, in-water tiamulin, or in-feed CTC and tiamulin. Fecal samples were collected randomly from 5 piglets from each pen during the pre-treatment (days 0, 7), treatment (days 14, 21), and post-treatment (days 28, 35) phases. Bacterial isolations and species identifications were conducted by culture and PCR, respectively. The microbroth dilution method with SensititreTM plates was used to determine the antimicrobial susceptibility and resistance of Campylobacter isolates. The results on resistance were interpreted based on the European Committee on Antimicrobial Susceptibility Testing (EUCAST) epidemiological cutoff values for Campylobacter. The overall prevalence of Campylobacter was 18.2% (262/1440). Speciation of Campylobacter isolates by PCR indicated the prevalence of only two species: Campylobacter hyointestinalis (17.9%; 258/1440) and C. coli (0.3%; 4/1440). Campylobacter isolates were resistant to tetracycline (98.5%), ciprofloxacin (89.3%), and nalidixic acid (60.3%). Neither the antibiotic nor the route of administration had an effect (p > 0.05) on the prevalence of AMR Campylobacter in the feces of piglets.

Characterization and antimicrobial resistance of Campylobacter jejuni and Campylobacter coli isolated from chicken and pork

The prevalence and antimicrobial resistance (AMR) profile were investigated in Campylobacter jejuni and Campylobacter coli in chicken and pork in Fukuoka, Japan in 2019. Their AMR profiles were compared with those of C. jejuni and C. coli strains isolated in 2013. A total of 53 chicken and 14 pork samples were collected from different supermarkets in Fukuoka in 2019. Campylobacter spp. were isolated by conventional method and characterized by PCR and MALDI-TOF MS. Among 53 chicken samples tested in 2019, 24.5% and 5.7% were positive for C. jejuni and C. coli, respectively, and three (21.4%) of 14 pork samples were positive for C. coli, but not C. jejuni. From the positive samples, 13 and six strains of C. jejuni and C. coli were isolated, respectively. Antimicrobial susceptibility test against 12 different antimicrobials were performed on 48 isolates (43 C. jejuni and five C. coli) from chicken in 2013 and 19 isolates (13 C. jejuni from chicken, three C. coli from chicken and three C. coli from pork) in 2019 using the disk diffusion method. All the C. jejuni and C. coli isolated in 2013 and 2019 were highly resistant to cefazolin and sulfamethoxazole/trimethoprim. Among the C. jejuni isolates from chickens, 25.6% of 2013 isolates were resistant to nalidixic acid, ciprofloxacin, and levofloxacin, and 7% to ampicillin and minocycline, while 30.8% of the isolates were resistant to minocycline, 23.1% to nalidixic acid, ciprofloxacin, and levofloxacin, and 15.4% to ampicillin in 2019. Among the C. coli isolates, 80% of isolates from chickens in 2013, and 33.3% from chicken and 100% from pork in 2019 were resistant to nalidixic acid, ciprofloxacin, and levofloxacin. The frequency of multi-drug resistant (MDR) C. jejuni and C. coli strains from chickens in 2019 were 30.8% and 33.3%, respectively, which were lower than those isolated in 2013 (37.2% and 100%, respectively). One C. jejuni and two C. coli isolates from 2013 were resistant to six antibiotics. However, two C. jejuni and one C. coli isolate from chickens in 2019 were resistant to seven and five antibiotics, respectively. All the C. coli isolates from pork in 2019 were resistant to five antibiotics. The high frequency of AMR strains in C. coli isolates from pork suggests that appropriate use of antimicrobials is required in swine husbandry.

Antibiotics and Antibiotic Resistance Genes in Animal Manure - Consequences of Its Application in Agriculture

Antibiotic resistance genes (ARGs) are a relatively new type of pollutant. The rise in antibiotic resistance observed recently is closely correlated with the uncontrolled and widespread use of antibiotics in agriculture and the treatment of humans and animals. Resistant bacteria have been identified in soil, animal feces, animal housing (e.g., pens, barns, or pastures), the areas around farms, manure storage facilities, and the guts of farm animals. The selection pressure caused by the irrational use of antibiotics in animal production sectors not only promotes the survival of existing antibiotic-resistant bacteria but also the development of new resistant forms. One of the most critical hot-spots related to the development and dissemination of ARGs is livestock and poultry production. Manure is widely used as a fertilizer thanks to its rich nutrient and organic matter content. However, research indicates that its application may pose a severe threat to human and animal health by facilitating the dissemination of ARGs to arable soil and edible crops. This review examines the pathogens, potentially pathogenic microorganisms and ARGs which may be found in animal manure, and evaluates their effect on human health through their exposure to soil and plant resistomes. It takes a broader view than previous studies of this topic, discussing recent data on antibiotic use in farm animals and the effect of these practices on the composition of animal manure; it also examines how fertilization with animal manure may alter soil and crop microbiomes, and proposes the drivers of such changes and their consequences for human health.

Microbiological Safety of Food of Animal Origin from Organic Farms

The organic food sector and consumer interest in organic products are growing continuously. The safety and quality of such products must be at least equal to those of conventional equivalents, but attaining the same standards requires overcoming a particular problem identified in organic food production systems: the occurrence of bacterial pathogens such as Salmonella, Campylobacter, Listeria monocytogenes, Staphylococcus aureus and pathogenic Escherichia coli. These food-borne microorganisms were detected in the production environments of such food. The prevalence of pathogenic bacteria in organic livestock and products may be higher, but may also be the same as or lower than in like material from conventional farms. Furthermore, the incidence of antimicrobial-resistant bacteria was more often detected in conventional than in organic production. The aim of this review was to present the recent information on the microbiological safety of food of animal origin produced from raw materials from organic farms.

Allium Extract Implements Weaned Piglet's Productive Parameters by Modulating Distal Gut Microbiota

Antimicrobial resistance (AMR) has risen as a global threat for human health. One of the leading factors for this emergence has been the massive use of antibiotics growth-promoter (AGPs) in livestock, enhancing the spread of AMR among human pathogenic bacteria. Thus, several alternatives such as probiotics, prebiotics, or phytobiotics have been proposed for using in animal feeding to maintain or improve productive levels while diminishing the negative effects of AGPs. Reducing the use of antibiotics is a key aspect in the pig rearing for production reasons, as well as for the production of high-quality pork, acceptable to consumers. Here we analyze the potential use of Allium extract as an alternative. In this study, weaned piglets were fed with Allium extract supplementation and compared with control and antibiotic (colistin and zinc oxide) treated piglets. The effects of Allium extract were tested by analyzing the gut microbiome and measuring different productive parameters. Alpha diversity indices decreased significantly in Allium extract group in caecum and colon. Regarding beta diversity, significant differences between treatments appeared only in caecum and colon. Allium extract and antibiotic piglets showed better values of body weight (BW), average daily weight gain (ADG), and feed conversion ratio (FCR) than control group. These results indicate that productive parameters can be implemented by modifying the gut microbiota through phytobiotics such as Allium extract, which will drive to drop the use of antibiotics in piglet diet.

Comparison of different approaches to antibiotic restriction in food-producing animals: stratified results from a systematic review and meta-analysis

BACKGROUND

We have previously reported, in a systematic review of 181 studies, that restriction of antibiotic use in food-producing animals is associated with a reduction in antibiotic-resistant bacterial isolates. While informative, that report did not concretely specify whether different types of restriction are associated with differential effectiveness in reducing resistance. We undertook a sub-analysis of the systematic review to address this question.

METHODS

We created a classification scheme of different approaches to antibiotic restriction: (1) complete restriction; (2) single antibiotic-class restriction; (3) single antibiotic restriction; (4) all non-therapeutic use restriction; (5) growth promoter and prophylaxis restriction; (6) growth promoter restriction and (7) other/undetermined. All studies in the original systematic review that were amenable to meta-analysis were included into this substudy and coded by intervention type. Meta-analyses were conducted using random effects models, stratified by intervention type.

RESULTS

A total of 127 studies were included. The most frequently studied intervention type was complete restriction (n=51), followed by restriction of non-therapeutic (n=33) and growth promoter (n=19) indications. None examined growth promoter and prophylaxis restrictions together. Three and seven studies examined single antibiotic-class and single antibiotic restrictions, respectively; these two intervention types were not significantly associated with reductions in antibiotic resistance. Though complete restrictions were associated with a 15% reduction in antibiotic resistance, less prohibitive approaches also demonstrated reduction in antibiotic resistance of 9%-30%.

CONCLUSION

Broad interventions that restrict global antibiotic use appear to be more effective in reducing antibiotic resistance compared with restrictions that narrowly target one specific antibiotic or antibiotic class. Importantly, interventions that allow for therapeutic antibiotic use appear similarly effective compared with those that restrict all uses of antibiotics, suggesting that complete bans are not necessary. These findings directly inform the creation of specific policies to restrict antibiotic use in food-producing animals.

Examination of unintended consequences of antibiotic use restrictions in food-producing animals: Sub-analysis of a systematic review

Antimicrobial resistance is considered one of the greatest threats to global and public health today. The World Health Organization, the Food and Agriculture Organization, and the World Organisation for Animal Health, known as the Tripartite Collaboration, have called for urgent action. We have previously published a systematic review of 181 studies, demonstrating that interventions that restrict antibiotic use in food-producing animals are associated with a reduction in antibiotic resistant bacterial isolates in both animals and humans. What remains unknown, however, are whether (and what) unintended consequences may arise from such interventions. We therefore undertook a sub-analysis of the original review to address this research question. A total of 47 studies described potential consequences of antibiotic restrictions. There were no consistent trends to suggest clear harm. There may be increased bacterial contamination of food products, the clinical significance of which remains unclear. There is a need for rigorous evaluation of the unintended consequences of antibiotic restrictions in human health, food availability, and economics, given their possible widespread implications.

Prevalence, Persistence, and Antimicrobial Resistance of Campylobacter spp. from Eggs and Laying Hens Housed in Five Commercial Housing Systems

Husbandry practices for laying hens in commercial egg production is a topic of interest from a social, economic, and regulatory standpoint. Animal welfare concerns regarding the use of conventional cages have arisen and consumer perceptions of hen welfare have led to a higher demand for cage-free eggs. The aim of this study was to assess the impact of housing systems on prevalence, persistence, and antimicrobial resistance (AMR) of Campylobacter from laying hens and shell eggs. A total of 425 samples were collected over a 10-month period from the North Carolina Layer Performance and Management Test and Campylobacter isolates were identified by serological, biochemical, and molecular tests. Genetic variability was evaluated using pulsed-field gel electrophoresis (PFGE) and AMR testing was performed. Prevalence of Campylobacter spp. ranged from 11.1% in the enrichable cages to 19.7% in the conventional systems. A greater prevalence of Campylobacter was found in the fecal swab samples from free-range birds compared with those of birds housed in the more intensive housing systems (p > 0.05). Overall, 72 isolates were confirmed as Campylobacter spp. by PCR. More than 90% of the isolates (n = 66) were identified as Campylobacter jejuni, followed by Campylobacter coli (n = 6). C. jejuni isolates displayed high levels of resistance to tetracycline (67%). Genetic variability of Campylobacter was high, with more than 20 PFGE patterns identified. Pattern "a" comprised 42% of isolates from all housing systems and was also the most persistent. This study suggests that housing systems of laying hens used for commercial shell egg production may impact the rate of Campylobacter shedding by layers. Isolation rates and tetracycline resistance levels of this pathogen are still of concern, emphasizing the need for well-implemented biosecurity measures on the farm.

The dynamics of the antibiotic resistome in the feces of freshly weaned pigs following therapeutic administration of oxytetracycline

In this study, shotgun metagenomics was employed to monitor the effect of oxytetracycline, administered at a therapeutic dose, on the dynamics of the microbiota and resistome in the feces of weaned pigs. Sixteen weaning pigs were assigned to one of two treatments including standard starter diet for 21 days or antibiotic-supplemented diet (10 g oxytetracycline/100 kg body weight/day) for 7 days, followed by 14 days of standard starter diet. Feces were collected from the pigs on days 0, 8, and 21 for microbiota and resistome profiling. Pigs receiving oxytetracycline exhibited a significantly greater richness (ANOVA, P = 0.034) and diversity (ANOVA, P = 0.048) of antibiotic resistance genes (ARGs) than the control pigs. Antibiotic administration significantly enriched the abundances of 41 ARGs, mainly from the tetracycline, betalactam and multidrug resistance classes. Compositional shifts in the bacterial communities were observed following 7 days of antibiotic adminstration, with the medicated pigs showing an increase in Escherichia (Proteobacteria) and Prevotella (Bacteroidetes) populations compared with the nonmedicated pigs. This might be explained by the potential of these taxa to carry ARGs that may be transferred to other susceptible bacteria in the densely populated gut environment. These findings will help in the optimization of therapeutic schemes involving antibiotic usage in swine production.

Trends in Antimicrobial Resistance Genes in Manure Blend Pits and Long-Term Storage Across Dairy Farms with Comparisons to Antimicrobial Usage and Residual Concentrations

The use of antimicrobials by the livestock industry can lead to the release of unmetabolized antimicrobials and antimicrobial resistance genes (ARG) into the environment. However, the relationship between antimicrobial use, residual antimicrobials, and ARG prevalence within manure is not well understood, specifically across temporal and location-based scales. The current study determined ARG abundance in untreated manure blend pits and long-term storage systems from 11 conventional and one antimicrobial-free dairy farms in the Northeastern U.S. at six times over one-year. Thirteen ARGs corresponding to resistance mechanisms for tetracyclines, macrolides-lincosamides, sulfonamides, aminoglycosides, and β-lactams were quantified using a Custom qPCR Array or targeted qPCR. ARG abundance differed between locations, suggesting farm specific microbial resistomes. ARG abundance also varied temporally. Manure collected during the winter contained lower ARG abundances. Overall, normalized ARG concentrations did not correlate to average antimicrobial usage or tetracycline concentrations across farms and collection dates. Of the 13 ARGs analyzed, only four genes showed a higher abundance in samples from conventional farms and eight ARGs exhibited similar normalized concentrations in the conventional and antimicrobial-free farm samples. No clear trends were observed in ARG abundance between dairy manure obtained from blend pits and long-term storage collected during two drawdown periods (fall and spring), although higher ARG abundances were generally observed in spring compared to fall. This comprehensive study informs future studies needed to determine the contributions of ARGs from dairy manure to the environment.

A randomized controlled trial to evaluate performance of pigs raised in antibiotic-free or conventional production systems following challenge with porcine reproductive and respiratory syndrome virus

The trial objective was to compare the performance and animal health parameters of pigs raised according to one of 3 antibiotic (AB) protocols: standard AB medication consisting of mass treatment on days 4 and 21 and judicious AB therapy given therapeutically thereafter as group medication in water and feed or by individual injection (group T1, N = 702); modified AB medication identical to group T1 but with mass treatment only on day 4 and without subsequent therapeutic feed medication (group T2, N = 675); or an antibiotic-free (ABF) regimen (group T3, N = 702). All pigs were vaccinated with a modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine 3 days after weaning. Using a seeder pig model to mimic endemic field infection dynamics, pigs were contact-challenged with virulent PRRSV lineage 1 strain 174 four weeks after vaccination. At finishing, average daily gain (ADG) and mean feed conversion ratio (FCR) were significantly better (p ≤ 0.05) for the T1 and T2 groups compared to the T3 group. There were no significant differences in post-weaning ADG and FCR between the T1 and T2 groups. Mortality and removals significantly favored (p ≤0.05) the T1 and T2 groups (20.94% and 24.89%, respectively) versus the T3 group (57.98%). Net revenue per pig was $105.43, $98.79, and $33.81 for the T1, T2 and T3 groups, respectively. Under the conditions of this study, these results indicate that in a PRRSV-endemic setting involving bacterial co-infections, an ABF production strategy may leave pigs at considerable risk of exposure to severe clinical disease and that judicious use of antibiotics can significantly improve animal health.

Prevalence, antibiogram and risk factors of thermophilic Campylobacter spp. in dressed porcine carcass of Chitwan, Nepal

BACKGROUND

Campylobacter is the primary cause of food borne gastroenteritis. Moreover, the emergence of multiple drug resistant campylobacters from poultry and pork has produced a potential threat to public health. Research addressing these issues is sparse in Nepal. So, this cross-sectional study aims at determining the prevalence, antibiogram and risk factors of campylobacters from dressed porcine carcass of Chitwan, Nepal.

RESULTS

We collected 139 samples of dressed porcine carcass from 10 different pork shops located in Chitwan district and processed according to OIE Terrestrial Manual, 2008, chapter 2.8.10. Antibiogram of identified Campylobacter spp. was evaluated against nine commonly used antibiotics by using disc diffusion method following CLSI guidelines. The prevalence of Campylobacter spp. was 38.84% (C. coli 76% and C. jejuni 24%). There was no significant difference (p > 0.05) between the prevalence rate of male (32.4%) and female (41%) carcass. Ampicillin and erythromycin showed the highest resistance (92.59% each) followed by colistin (72.2%), tetracycline (61.1%), nalidixic acid and cotrimoxazole (44.4% each), ciprofloxacin (31.5%) and gentamicin (5.56%). Moreover, 77.8% of the isolates were resistant to more than two antimicrobials. Nalidixic acid and tetracycline showed significant difference (p < 0.05) in the resistivity pattern among different species of Campylobacters. The association between prevalence rate and regular sanitization of slaughter slab equipments was significant (p < 0.05). Similarly, prevalence rate was significantly associated (p < 0.01) with chilling and contamination of intestinal content with carcass.

CONCLUSIONS

The pork meat of Chitwan is highly contaminated with antibiotic-resistant Campylobacters and slaughtering practices play significant role in contamination. It is necessary to train the butchers about hygienic slaughtering practice. The consumers as well as butchers should adopt safety measures to prevent themselves from antibiotic resistant campylobacters. The veterinary practitioners should adopt prudent use of antibiotics in pigs.

Effects of chlortetracycline and copper supplementation on antimicrobial resistance of fecal Escherichia coli from weaned pigs

Feed-grade chlortetracycline (CTC) and copper are both widely utilized in U.S. pig production. Cluster randomized experiment was conducted to evaluate the effects of CTC and copper supplementation in weaned pigs on antimicrobial resistance (AMR) among fecal Escherichia coli. Four treatment groups: control, copper, CTC, or copper plus CTC were randomly allocated to 32 pens with five pigs per pen. Fecal samples were collected weekly from three pigs per pen for six weeks. Two E. coli isolates per fecal sample were tested for phenotypic and genotypic resistance against antibiotics and copper. Data were analyzed with multilevel mixed effects logistic regression, multivariate probit analysis and discrete time survival analysis. CTC-supplementation was significantly (99% [95% CI=98-100%]) associated with increased tetracycline resistance compared to the control group (95% [95% CI=94-97%]). Copper supplementation was associated with decreased resistance to most of the antibiotics tested, including cephalosporins, over the treatment period. Overall, 91% of the E. coli isolates were multidrug resistant (MDR) (resistant to ≥3 antimicrobial classes). tetA and blaCMY-2 genes were positively associated (P<0.05) with MDR categorization, while tetB and pcoD were negatively associated with MDR. tetA and blaCMY-2 were positively associated with each other and in turn, these were negatively associated with both tetB and pcoD genes; which were also positively associated with one another. Copper minimum inhibitory concentration was not affected by copper supplementation or by pcoD gene carriage. CTC supplementation was significantly associated with increased susceptibilities of E. coli to copper (HR=7 [95% CI=2.5-19.5]) during treatment period. In conclusion, E. coli isolates from the nursery pigs exhibited high levels of antibiotic resistance, with diverse multi-resistant phenotypic profiles. The roles of copper supplementation in pig production, and pco-mediated copper resistance among E. coli in particular, need to be further explored since a strong negative association of pco with both tetA and blaCMY-2 points to opportunities for selecting a more innocuous resistance profile.

In-feed use of heavy metal micronutrients in U.S. swine production systems and its role in persistence of multidrug-resistant salmonellae

The study aimed to characterize the role of heavy metal micronutrients in swine feed in emergence of heavy-metal-tolerant and multidrug-resistant Salmonella organisms. We conducted a longitudinal study in 36 swine barns over a 2-year period. The feed and fecal levels of Cu(2+) and Zn(2+) were measured. Salmonella was isolated at early and late finishing. MICs of copper sulfate and zinc chloride were measured using agar dilution. Antimicrobial susceptibility was tested using the Kirby-Bauer method, and 283 isolates were serotyped. We amplified pcoA and czcD genes that encode Cu(2+) and Zn(2+) tolerance, respectively. Of the 283 isolates, 113 (48%) showed Cu(2+) tolerance at 24 mM and 164 (58%) showed Zn(2+) tolerance at 8 mM. In multivariate analysis, serotype and source of isolates were significantly associated with Cu(2+) tolerance (P < 0.001). Fecal isolates were more likely to be Cu(2+) tolerant than those of feed origin (odds ratio [OR], 27.0; 95% confidence interval [CI], 2.8 to 250; P = 0.0042) or environmental origin (OR, 5.8), implying the significance of gastrointestinal selective pressure. Salmonella enterica serotypes Typhimurium and Heidelberg, highly significant for public health, had higher odds of having >20 mM MICs of Cu(2+) than did "other" serotypes. More than 60% of Salmonella isolates with resistance type (R-type) AmStTeKm (32 of 53) carried pcoA; only 5% with R-type AmClStSuTe carried this gene. czcD gene carriage was significantly associated with a higher Zn(2+) MIC (P < 0.05). The odds of having a high Zn(2+) MIC (≥8 mM) were 14.66 times higher in isolates with R-type AmClStSuTe than in those with R-type AmStTeKm (P < 0.05). The findings demonstrate strong association between heavy metal tolerance and antimicrobial resistance, particularly among Salmonella serotypes important in public health.

Development of antibiotic regimens using graph based evolutionary algorithms

This paper examines the use of evolutionary algorithms in the development of antibiotic regimens given to production animals. A model is constructed that combines the lifespan of the animal and the bacteria living in the animal's gastro-intestinal tract from the early finishing stage until the animal reaches market weight. This model is used as the fitness evaluation for a set of graph based evolutionary algorithms to assess the impact of diversity control on the evolving antibiotic regimens. The graph based evolutionary algorithms have two objectives: to find an antibiotic treatment regimen that maintains the weight gain and health benefits of antibiotic use and to reduce the risk of spreading antibiotic resistant bacteria. This study examines different regimens of tylosin phosphate use on bacteria populations divided into Gram positive and Gram negative types, with a focus on Campylobacter spp. Treatment regimens were found that provided decreased antibiotic resistance relative to conventional methods while providing nearly the same benefits as conventional antibiotic regimes. By using a graph to control the information flow in the evolutionary algorithm, a variety of solutions along the Pareto front can be found automatically for this and other multi-objective problems.

Effects of antimicrobials fed as dietary growth promoters on faecal shedding of Campylobacter, Salmonella and shiga-toxin producing Escherichia coli in swine

AIMS

To determine whether antimicrobials commonly used in swine diets affect zoonotic pathogen shedding in faeces.

METHODS AND RESULTS

Barrows (n = 160) were sorted into two treatments at 10 weeks of age (week 0 of the study), and fed growing, grow finishing and finishing diets in 4-week feeding periods. For each feeding phase, diets were prepared without (A-) and with (A+) dietary antimicrobials (chlortetracycline, 0-8 week; bacitracin, 9-12 week) typical of the United States. At week 0, 4, 8, 9, 10 and 12 of the study, faecal swabs or grabs were collected for analyses. Campylobacter spp. was absent at week 0, but prevalence increased over time with most isolates being identified as Campylobacter coli. When chlortetracycline was used in A+ diets (week 4 and 8), prevalence for Campylobacter spp., pathogenic Escherichia coli O26 and stx genes was lower in faeces. On week 12 after the shift to bacitracin, Campylobacter spp. and stx genes were higher in faeces from piglets fed A+ diet. Pathogenic E. coli serogroups O103 and O145 were isolated throughout the study and their prevalence did not differ due to diet. Pathogenic E. coli serogroups O111 and O121 were never found in the piglets, and Salmonella spp. prevalence was low.

CONCLUSIONS

In production swine, growing diets with chlortetracycline may have reduced pathogen shedding compared with the A-growing diets, whereas finishing diets with bacitracin may have increased pathogen shedding compared with the A-finishing diet.

SIGNIFICANCE AND IMPACT OF THE STUDY

Inclusion of antimicrobials in the diet can affect zoonotic pathogen shedding in faeces of swine.

Antimicrobial susceptibility, pulsed-field gel electrophoresis, and multi-locus sequence typing of Campylobacter coli in swine before, during, and after the slaughter process

The objective of this study was to determine persistence of clonal strains from farm to retail by assessing the clonal relatedness of Campylobacter coli isolated on farm, peri-harvest, and at processing from 11 individually identified pigs. Phenotypic (antimicrobial susceptibility) and genotypic (pulsed field gel electrophoresis [PFGE] and multi-locus sequence typing [MLST]) characterization of isolates was conducted. There was high genetic diversity of Campylobacter isolates from on-farm fecal samples. Campylobacter isolates from farm, post-evisceration, hide, and carcass samples showed similar phenotypes and belonged to the same genotypic clusters based on PFGE and sequence types (STs) based on MLST. Five STs that have not been previously reported were identified (ST-4083, ST-4084, ST-4085, ST-4086, ST-4087). Despite high genotypic diversity of C. coli on farm, retail meat products were consistently contaminated with isolates of the same STs, particularly ST854 and ST1056, as isolates collected from previous stages confirming persistence of strains from pre- to post-harvest.

Longitudinal study of the persistence of antimicrobial-resistant campylobacter strains in distinct Swine production systems on farms, at slaughter, and in the environment

The objectives of this study were to compare and characterize the prevalence of antimicrobial-resistant (AR) Campylobacter in conventional and antimicrobial-free (ABF) production systems on farms, at slaughter, and in the environment. Fecal and environmental samples were collected from ABF farms (pigs, 1,239; environment, 797) and conventional farms (pigs, 1,650; environment, 1,325). At slaughter, we collected samples from carcasses, including postevisceration swabs, postchill swabs, and mesenteric lymph nodes from ABF systems (postevisceration swabs, 182; postchill swabs, 199; mesenteric lymph nodes, 184) and conventional systems (postevisceration swabs, 272; postchill swabs, 271; mesenteric lymph nodes, 255) at separate processing facilities. We also sampled the processing plant environment, including truck and lairage floor swab samples (ABF, 115; conventional, 90). Overall, a total of 2,908 Campylobacter isolates, including Campylobacter coli (farm, 2,557, 99.8%; slaughter, 341, 98.3%) and Campylobacter jejuni (farm, 4, 0.2%; slaughter, 6, 1.7%), were isolated in the study. There was no significant difference in the prevalence of Campylobacter between ABF and conventionally raised pigs (farrowing, P = 0.20; nursery, P = 0.06; finishing, P = 0.24) and the environment (P = 0.37). At slaughter, Campylobacter was isolated from all of the stages, including postchill. The highest frequencies of resistance were exhibited against tetracycline (ABF, 48.2%; conventional, 88.3%). Ciprofloxacin-resistant C. coli isolates were observed in conventionally raised (17.1%) and ABF (1.2%) pigs (P = 0.11). Antimicrobial use data from conventional farms indicated significant associations between oxytetracycline use and tetracycline resistance in the nursery pigs (P = 0.01), between tiamulin exposure and azithromycin and erythromycin resistance in nursery (P < 0.01) and finishing (P < 0.01) pigs, and between enrofloxacin exposure and ciprofloxacin and nalidixic acid resistance in farrowing (P < 0.01) and nursery (P < 0.01) pigs. Identical antimicrobial resistance profiles were observed in the pigs and their environments on farms and at slaughter. In summary, our results highlight the persistence and dissemination of AR Campylobacter from farm to slaughter in ABF and conventionally raised pigs and their environments.

Genotypic and phenotypic properties of cattle-associated Campylobacter and their implications to public health in the USA

Since cattle are a major source of food and the cattle industry engages people from farms to processing plants and meat markets, it is conceivable that beef-products contaminated with Campylobacter spp. would pose a significant public health concern. To better understand the epidemiology of cattle-associated Campylobacter spp. in the USA, we characterized the prevalence, genotypic and phenotypic properties of these pathogens. Campylobacter were detected in 181 (19.2%) out of 944 fecal samples. Specifically, 71 C. jejuni, 132 C. coli, and 10 other Campylobacter spp. were identified. The prevalence of Campylobacter varied regionally and was significantly (P<0.05) higher in fecal samples collected from the South (32.8%) as compared to those from the North (14.8%), Midwest (15.83%), and East (12%). Pulsed Field Gel Electrophoresis (PFGE) analysis showed that C. jejuni and C. coli isolates were genotypically diverse and certain genotypes were shared across two or more of the geographic locations. In addition, 13 new C. jejuni and two C. coli sequence types (STs) were detected by Multi Locus Sequence Typing (MLST). C. jejuni associated with clinically human health important sequence type, ST-61 which was not previously reported in the USA, was identified in the present study. Most frequently observed clonal complexes (CC) were CC ST-21, CC ST-42, and CC ST-61, which are also common in humans. Further, the cattle associated C. jejuni strains showed varying invasion and intracellular survival capacity; however, C. coli strains showed a lower invasion and intracellular survival potential compared to C. jejuni strains. Furthermore, many cattle associated Campylobacter isolates showed resistance to several antimicrobials including ciprofloxacin, erythromycin, and gentamicin. Taken together, our results highlight the importance of cattle as a potential reservoir for clinically important Campylobacter.

Antimicrobial resistance in Campylobacter coli isolated from pigs in two provinces of China

The aim of this study was to determine the prevalence, antimicrobial resistance and molecular epidemiology of Campylobacter coli isolated from swine in China. A total of 190 C. coli isolates obtained from two slaughter houses and ten conventional pig farms in Shandong (SD, n=95) and Ningxia (NX, n=95) provinces were tested for their susceptibility to 14 antimicrobials. A high prevalence (>95%) of ciprofloxacin and tetracycline-resistant strains was observed in both SD and NX. The erythromycin and clindamycin resistance rates of C. coli from NX (ERY: 54.7% CLI: 43.2%) were higher than those from SD (ERY: 37.9%, CLI: 35.8%). A significant difference (P<0.05) was observed in erythromycin resistance rate, but not (P>0.05) in clindamycin resistance rate. while the resistance rates of ampicillin and kanamycin in NX (AMP: 34.7%, KAN: 43.2%) were significantly lower (P<0.05) than those in SD (AMP: 51.6%, KAN: 71.6%). None of the tested isolates were resistant to phenicols. The majority of the isolates from both provinces (SD: 80% and NX: 73.7%) showed multi-drug resistance profiles. The point mutations of A2075G in the 23S rRNA and C257T in the gyrA gene were detected in 98% (87/89) of macrolide resistant isolates and all ciprofloxacin resistant isolates, respectively. In addition, all tetracycline-resistant isolates harbored the tet(O) gene. The high prevalence of antimicrobial resistance in C. coli strains derived from pigs in China was observed and was likely due to the extensive use of various antimicrobials. Prudent use of antimicrobial agents on farms should be further emphasized to control the dissemination of antimicrobial resistant C. coli.

Intensive swine production and pork safety

Major structural changes in livestock production in developed countries, particularly intensive confinement production and increases in herd and flock sizes, have raised several societal concerns about the future directions and implications of livestock food production, including the safety of meat products. This review of the major parasitic and bacterial foodborne pathogens associated with pork production indicates that pork safety in the United States has improved demonstrably over recent decades. Most notably, changes in swine production methods have been associated with virtual elimination of risk of the foodborne parasites Taenia solium, Trichinella spiralis, and Toxoplasma gondii from pigs reared on modern intensive farms. This represents a substantial public health achievement that has gone largely unheralded. Regulatory changes have led to demonstrably lower prevalence of Salmonella on pork carcasses, but control of bacterial foodborne pathogens on farms remains a significant challenge. Available evidence does not support the hypothesis that intensive pork production has increased risk for the major bacterial foodborne pathogens that are common commensals of the pig (Salmonella, Campylobacter, Listeria, and Yersinia enterocolitica), or that pigs produced in alternative systems are at reduced risk of colonization with these organisms. However, pigs raised in outdoor systems inherently confront higher risks of exposure to foodborne parasites, particularly T. gondii.

Temperature affects sole carbon utilization patterns of Campylobacter coli 49941

Campylobacter spp. are small, asaccharolytic bacteria exhibiting unique nutritional and environmental requirements. Campylobacter spp. exist as commensal organisms in some animal species, yet are estimated to be the most common causative agents of foodborne illness in humans. C. jejuni is most often associated with poultry, while C. coli are more frequently associated with swine. Temperature has been suggested to trigger potential colonization or virulence factors in C. jejuni, and recent studies have demonstrated temperature-dependent genes are important to colonization. It is possible that temperature-dependent colonization factors are in part responsible for the species-specific colonization characteristics of C. coli also. We determined utilization of 190 different sole carbon substrates by C. coli ATCC 49941 at 37 and 42°C using phenotype microarray (PM) technology. Temperature did affect amino acid utilization. L-asparagine and L-serine allowed significantly (P = 0.004) more respiration by C. coli ATCC 49941 at the lower temperature of 37°C as compared to 42°C. Conversely, L-glutamine was utilized to a significantly greater extent (P = 0.015) at the higher temperature of 42°C. Other organic substrates exhibited temperature-dependent utilization including succinate, D,L-malate, and propionate which all supported active respiration by C. coli to a significantly greater extent at 42°C. Further investigation is needed to determine the basis for the temperature-dependent utilization of substrates by Campylobacter spp. and their possible role in species-specific colonization.

Study of the molecular mechanisms involved in high-level macrolide resistance of Spanish Campylobacter jejuni and Campylobacter coli strains

OBJECTIVES

To investigate the molecular mechanisms involved in the high-level erythromycin resistance of clinical Spanish Campylobacter jejuni and Campylobacter coli strains.

METHODS

Overall susceptibilities of 678 C. jejuni and 119 C. coli strains, collected from 10 Spanish provinces during 2006 and 2007, were determined by Etest. In high-level erythromycin-resistant strains, molecular determinants were studied. The analysis was focused on region V of the 23S rRNA gene, the rplD and rplV ribosomal genes, and the regulatory region of the CmeABC efflux pump.

RESULTS

The global resistance rate to erythromycin was 3.8%. Among the resistant strains, 93% were C. coli and 7% were C. jejuni. The A2075G mutation in the 23S rRNA gene was detected in all of the resistant strains except for two, which carried the A2074G mutation. None of the ribosomal rplD and rplV genes harboured the described mutations that confer resistance to macrolides. Different mutations affecting the regulatory region of the CmeABC efflux pump were also found.

CONCLUSIONS

C. coli strains are clearly more resistant to erythromycin than C. jejuni. The mutation A2075G in the 23S rRNA gene was responsible for the resistance in most of the strains; A2074G was only found in two strains. Further studies are required to ascertain the effect of mutations in the regulatory region of cmeABC. Our data indicate that the rate of resistance was similar to that of other European countries.

Prevalence and patterns of antimicrobial resistance in Campylobacter spp isolated from pigs reared under antimicrobial-free and conventional production methods in eight states in the Midwestern United States

OBJECTIVE

To compare apparent prevalence and patterns of antimicrobial resistance in Campylobacter spp in feces collected from pigs reared with antimicrobial-free versus conventional production methods in 8 states in the Midwestern United States.

DESIGN

Cross-sectional study.

SAMPLE POPULATION

95 swine farms that used antimicrobial-free (n = 35) or conventional (60) production methods.

PROCEDURES

Fecal samples from 15 pigs/farm were collected. Biochemical and multiplex-PCR analyses were used to identify Campylobacter spp. The minimal inhibitory concentrations of erythromycin, azithromycin, ciprofloxacin, nalidixic acid, gentamicin, and tetracycline for these organisms were determined by use of a commercially available antimicrobial gradient strip. The data were analyzed by use of population-averaged statistical models.

RESULTS

Campylobacter spp were isolated from 512 of 1,422 pigs. A subset (n = 464) of the 512 isolates was available for antimicrobial susceptibility testing. The apparent prevalence of Campylobacter spp isolates from pigs on conventional farms (35.8%) and antimicrobial-free farms (36.4%) did not differ significantly. Resistances to azithromycin, erythromycin, and tetracycline were significantly higher on conventional farms (70.0%, 68.3%, and 74.5%, respectively) than antimicrobial-free farms (20.1%, 21.3%, and 48.8%, respectively). Resistances to azithromycin, erythromycin, and tetracycline declined as the number of years that a farm was antimicrobial-free increased.

CONCLUSIONS AND CLINICAL RELEVANCE

Production method did not affect the apparent prevalence of Campylobacter spp on swine farms. However, antimicrobial-free farms had a significantly lower prevalence of antimicrobial resistance. Although cessation of antimicrobial drug use will lower resistance over time, investigation of other interventions designed to reduce resistance levels is warranted.

Food safety in free-range and organic livestock systems: risk management and responsibility

Animal production systems that offer outdoor access to the animals have become increasingly popular in the Western world due to the growing general discontent of consumers with conventional bioindustrial farming practices. These open production systems offer improved animal welfare but may create new problems for animal health, resulting in increased food safety risks from bacterial, viral, or parasitic infections or environmental contaminants. Examples of these new problems include increased Toxoplasma gondii infections in pigs and high dioxin levels in eggs from free-range hens. In this review, the relation between positive and negative points of free-range and organic livestock production systems is discussed with reference to production in The Netherlands. We investigated how proponents of more animal welfare friendly systems deal with potential negative issues in public and whether any risk communication is used. Generally, we found that the existence of a dilemma is disputed or avoided in communication with the consumer. This avoidance could be detrimental for public trust in alternative animal production systems, should problems occur. To prevent future problems, it will be necessary to communicate about the relevant types and sources of the food safety risks to the consumers. The responsibility for protecting food safety should be properly divided among the various parties involved: producers, processors, governments, nongovernmental organizations, and consumers.

Comparison of the prevalence of bacterial enteropathogens, potentially zoonotic bacteria and bacterial resistance to antimicrobials in organic and conventional poultry, swine and beef production: a systematic review and meta-analysis

The prevalences of zoonotic and potentially zoonotic bacteria or bacteria resistant to antimicrobials in organic and conventional poultry, swine and beef production were compared using systematic review and meta-analysis methodology. Thirty-eight articles were included in the review. The prevalence of Campylobacter was higher in organic broiler chickens at slaughter, but no difference in prevalence was observed in retail chicken. Campylobacter isolates from conventional retail chicken were more likely to be ciprofloxacin-resistant (odds ratio 9·62, 95% confidence interval 5·67–16·35). Bacteria isolated from conventional animal production exhibited a higher prevalence of resistance to antimicrobials; however, the recovery of some resistant strains was also identified in organic animal production, where there is an apparent reduced antimicrobial selection pressure. Limited or inconsistent research was identified in studies examining the prevalence of zoonotic and potentially zoonotic bacteria in other food-animal species. There is a need for further research of sufficient quality in this area.

Antibiotic resistance in Campylobacter: emergence, transmission and persistence

Campylobacter is a leading foodborne bacterial pathogen, which causes gastroenteritis in humans. This pathogenic organism is increasingly resistant to antibiotics, especially fluoroquinolones and macrolides, which are the most frequently used antimicrobials for the treatment of campylobacteriosis when clinical therapy is warranted. As a zoonotic pathogen, Campylobacter has a broad animal reservoir and infects humans via contaminated food, water or milk. Antibiotic usage in both animal agriculture and human medicine, can influence the development of antibiotic-resistant Campylobacter. This review will describe the trend in fluoroquinolone and macrolide resistance in Campylobacter, summarize the mechanisms underlying the resistance to various antibiotics and discuss the unique features associated with the emergence, transmission and persistence of antibiotic-resistant Campylobacter. Special attention will be given to recent findings and emphasis will be placed on Campylobacter resistance to fluoroquinolones and macrolides. A future perspective on antibiotic resistance and potential approaches for the control of antibiotic-resistant Campylobacter, will also be discussed.

A metagenomic approach for determining prevalence of tetracycline resistance genes in the fecal flora of conventionally raised feedlot steers and feedlot steers raised without antimicrobials

OBJECTIVE

To compare prevalence of tetracycline resistance genes in the fecal flora of conventionally raised feedlot steers and feedlot steers raised without antimicrobials.

SAMPLE POPULATION

61 fecal samples from conventionally raised steers and 61 fecal samples from steers raised without antimicrobials at a single feedlot.

PROCEDURES

Total DNA was extracted from each fecal sample and analyzed by means of 4 multiplex PCR assays for 14 tetracycline resistance genes.

RESULTS

At least 3 tetracycline resistance genes were identified in all 122 fecal samples. For 5 of the 14 tetracycline resistance genes, the percentage of samples in which the gene was detected was significantly higher for fecal samples from conventionally raised cattle than for fecal samples from antimicrobial-free cattle, and for 1 gene, the percent-age of samples in which the gene was detected was significantly higher for fecal samples from antimicrobial-free cattle than for fecal samples from conventionally raised cattle. The percentage of samples with > or = 11 tetracycline resistance genes was significantly higher for fecal samples from conventionally raised cattle (35/61 [57%]) than for fecal samples from antimicrobial-free cattle (16/61 [26%]).

CONCLUSIONS AND RELEVANCE

Results suggested that the prevalence of tetracycline resistance genes was significantly higher in the fecal flora of conventionally raised feedlot steers than in the fecal flora of feedlot steers raised without antimicrobials and that a metagenomic approach may be useful in understanding the epidemiology of antimicrobial resistance in food animals.

Antimicrobial susceptibility of foodborne pathogens in organic or natural production systems: an overview

Organic and natural food production systems are increasing in popularity, at least partially because consumers perceive that these niche markets provide healthier and safer food products. One major difference between these niche markets and conventional production systems is the use of antimicrobials. Because antimicrobial agents exert selective pressures for antimicrobial resistance, relating antimicrobial susceptibility of foodborne bacteria to niche market production systems is of interest. Other differences between production systems might also influence the susceptibility of foodborne pathogens. The objective of this review is to compare the impact of food animal production systems on the antimicrobial susceptibility of common foodborne bacterial pathogens. Studies comparing the susceptibility of such pathogens were diverse in terms of geographic location, procedures, species of bacteria, and antimicrobials evaluated; thus, it was difficult to draw conclusions. The literature is highly variable in terms of production type and practices and susceptibility associations, although few studies have compared truly organic and conventional practices. When statistical associations were found between production type and minimum inhibitory concentrations or percentage of isolates resistant for a particular pathogen, the isolates from conventionally reared animals/products were more commonly resistant than the comparison group (organic, antibiotic free, etc.). Therefore, further studies are needed to better assess public health consequences of antimicrobial resistance and food animal production systems, specifically organic or natural versus conventional.

Associations between antimicrobial exposure and resistance in fecal Campylobacter spp. from grow-finish pigs on-farm in Alberta and Saskatchewan, Canada

Campylobacter spp. (n = 405), isolated from the feces of apparently healthy grow-finish pigs in 20 herds, were tested for susceptibility to 10 antimicrobials representing seven classes. Twelve percent of the isolates were susceptible to all drugs, while 64% were resistant to two or more antimicrobial classes. Resistance was most common to clindamycin, azithromycin, and erythromycin (71% each), and 10% of the isolates were resistant to ciprofloxacin. An antimicrobial use risk-factor analysis and a variance analysis explored the connection between antimicrobial resistance and the herd. The antimicrobial exposure of each production phase of each herd, through feed and water, was evaluated as a potential risk factor for resistance to macrolides and quinolones. Every 100,000 pig days of macrolide exposure in nursery pigs increased the odds of resistance to macrolides by a factor of 1.3. In contrast, the odds of resistance to a quinolone were nine times higher in Campylobacter from herds without beta-lactam exposure in grow-finish pigs compared with those with exposure. The variance analysis identified remarkably high clustering between isolates within herds; the intraclass correlations for resistances ranged from 0.52 to 0.82. Such extreme clustering demonstrates the potential for herd-level interventions to influence antimicrobial resistance in Campylobacter. The three key findings of this study, i.e., the prevalent resistance to macrolides, the association between macrolide exposure and Campylobacter resistance to macrolides, and the high clustering of resistance within herds, illustrate the need for continued study of antimicrobial-resistant Campylobacter on pig farms and the importance of judicious antimicrobial use in pork production.

Farm-level risk factors for fluoroquinolone resistance in E. coli and thermophilic Campylobacter spp. on finisher pig farms

Logistic regression, supported by other statistical analyses was used to explore the possible association of risk factors with the fluoroquinolone (FQ)-resistance status of 108 pig finisher farms in Great Britain. The farms were classified as 'affected' or 'not affected' by FQ-resistant E. coli or Campylobacter spp. on the basis of isolation of organisms from faecal samples on media containing 1 mg/l FQ. The use of FQ was the most important factor associated with finding resistant E. coli and/or Campylobacter, which were found on 79% (FQ-resistant E. coli) and 86% (FQ-resistant Campylobacter) of farms with a history of FQ use. However, resistant bacteria were also found on 19% (FQ-resistant E. coli) and 54% (FQ-resistant Campylobacter) of farms with no history of FQ use. For FQ-resistant E. coli, biosecurity measures may be protective and there was strong seasonal variation, with more farms found affected when sampled in the summer. For FQ-resistant Campylobacter, the buying-in of grower stock may increase risk and good on-farm hygiene may be protective. The findings suggest that resistant organisms, particularly Campylobacter, may spread between pig farms.

Incidence and ecology of Campylobacter jejuni and coli in animals

Since its initial emergence in the 1970s, Campylobacter has become one of the most common causative agents of bacterial foodborne illness. Campylobacter species readily colonize the gastrointestinal tracts of domestic, feral and wild animals and while they rarely cause clinical disease in food animals, they can produce severe acute gastroenteritis in humans. Prevalence of Campylobacter in food animals can exceed 80% thus challenging processors to employ post-harvest pathogen reduction strategies. Reduction of pathogens before arrival to the abattoir is also of interest because the implementation of pre-harvest interventions may compliment existing post-harvest control techniques to further diminish possible retail sources of infection. Such multiple hurdle approaches that simultaneously utilize pre- and post-harvest control techniques are expected to be the most effective approach for decreasing human illness associated with foodborne pathogens.

Niche marketing production practices for beef cattle in the United States and prevalence of foodborne pathogens

Niche-marketed food products are rapidly gaining market share in today's society. Consumers are willing to pay premium prices for food perceived to be safer, healthier, more nutritious, and better tasting than conventional food. This review outlines typical production practices for niche-market beef production systems in the United States and compares prevalence estimates of foodborne pathogens in animals and produce from conventional and niche-market production systems. The two main niches for food animal production are organic and natural productions. Organic and natural beef productions are becoming increasingly popular and there is high consumer demand. Two major differences between conventional beef production systems and niche-market production systems (natural and organic) are in the use of antimicrobials and growth-promoting hormones. The impacts of these production systems on foodborne pathogens in beef cattle are variable and often data are nonexistent. Studies directly comparing conventional and niche-market production systems for dairy, swine, poultry, and produce have observed that the prevalence of foodborne pathogens was seldom statistically different between production systems, but when differences were observed, prevalence was typically greater for the niche-market production systems than the conventional production system. The published literature suggests that the perception of niche-marketed food products being safer and healthier for consumers with regard to foodborne pathogens may not be justified.

A stochastic assessment of the public health risks of the use of macrolide antibiotics in food animals

Campylobacteriosis is an important food-borne illness with more than a million U.S. cases annually. Antibiotic treatment is usually not required. However, erythromycin, a macrolide antibiotic, is recommended for the treatment of severe cases. Therefore, it is considered a critically important antibiotic and given special attention as to the risk that food animal use will lead to resistant infections and compromised human treatment. To assess this risk, we used a retrospective approach; estimating the number of campylobacteriosis cases caused by specific meat consumption utilizing the preventable fraction. We then determined the number of cases with macrolide resistance Campylobacter spp. based on a linear model relating the resistance fraction to on-farm macrolide use. In this article, we considered the uncertainties in the parameter estimates, utilized a more elaborate model of resistance development and separated C. coli and C. jejuni. There are no published data for the probability of compromised treatment outcome due to macrolide resistance. Therefore, our estimates of compromised treatment outcome were based on data for fluoroquinolone-resistant infections. The conservative results show the human health risks are extremely low. For example, the predicted risk of suboptimal human treatment of infection with C. coli from swine is only 1 in 82 million; with a 95% chance it could be as high as 1 in 49 million. Risks from C. jejuni in poultry or beef are even less. Reduced antibiotic use can adversely impact animal health. These low human risks should be weighed against the alternative risks.

A comparative study on the effects of tylosin on select bacteria during continuous flow culture of mixed populations of gut microflora derived from a feral and a domestic pig

Continuous flow cultures of feral (culture FC) and domesticated (culture RPCF) pig gut microflora were established in steady state. Cultures were continuously infused with 25 or 100 microg tylosin/mL and sampled at intervals to assess effects on total culturable anaerobes, Bacteroides and Enterococcus via plating to agar supplemented without or with 100 microg tylosin/mL, the latter to assess bacterial sensitivity to tylosin. Endogenous tylosin-insensitive anaerobes within the cultures, while similar prior to tylosin administration, responded differently during tylosin administration, with concentrations in RPCF cultures becoming enriched more than in FC cultures. Tylosin-insensitive anaerobes in RPCF cultures persisted at increased concentrations after cessation of tylosin administration whereas concentrations in FC cultures decreased slightly. Concentrations of Bacteroides and endogenous Enterococcus recovered on medium without tylosin decreased to near or below detectable levels in FC cultures administered 25 or 100 microg tylosin/mL. Tylosin-insensitive Bacteroides were enriched to >5 log10 CFU/mL in RPCF cultures after 25 microg tylosin/mL but not at 100 microg tylosin/mL. Populations of endogenous tylosin-insensitive Enterococcus were enriched in RPCF but not FC cultures administered 25 or 100 microg tylosin/mL. In cultures administered 100 microg tylosin/mL, an exogenous-sourced E. faecium possessing tylosin resistance maintained itself only in the presence of tylosin. These results indicate that under the conditions of these tests, antibiotic exposure may enrich for antibiotic-insensitive bacteria populations of endogenous or exogenous origin but that the ability of an exogenous tylosin-resistant E. faecium to persist is reduced in the absence of the antibiotic, likely due to exclusion by native flora.

Antimicrobial resistance of 114 porcine isolates of Campylobacter coli

Campylobacter species were isolated from 24 pig farms in 10 different regions of Korea, and were assayed with regard to their susceptibility to eight antimicrobial agents. A total of 114 Campylobacter isolates from 572 intestinal samples were all identified as C. coli via both classical methods and molecular methods, including 16S rDNA sequence analysis and polymerase chain reactions (PCR) using specific primer sets for the hippuricase gene and the aspartokinase gene, designed to differentiate C. coli from C. jejuni. Minimal inhibitory concentrations of seven antimicrobial agents were determined via agar dilution: the MIC(90)s were 64 microg/ml for ampicillin, 8 microg/ml for chloramphenicol, 64 microg/ml for ciprofloxacin, 16 microg/ml for enrofloxacin, >or=128 microg/ml for erythromycin, >or=128 microg/ml for gentamicin, and >or=128 microg/ml for tetracycline. The proportion of isolates resistant to each antimicrobial agent was as follows: 28.9% for ampicillin, 2.6% for chloramphenicol, 84.2% for ciprofloxacin, 83.3% for enrofloxacin, 46.5% for erythromycin, 20.2% for gentamicin, and 56.1% for tetracycline. All 114 isolates were found to be resistant to at least one antimicrobial agent, and 61 isolates (53.5%) were found to be multi-drug resistant (resistant to more than three antimicrobial agents in different classes).

Development and application of real-time PCR assays for quantification of erm genes conferring resistance to macrolides-lincosamides-streptogramin B in livestock manure and manure management systems

Erythromycin and tylosin are commonly used in animal production, and such use is perceived to contribute to the overall antimicrobial resistance (AR) reservoirs. Quantitative measurements of this type of AR reservoir in microbial communities are required to understand AR ecology (e.g., emergence, persistence, and dissemination). We report here the development, validation, and use of six real-time PCR assays for quantifying six classes of erm genes (classes A through C, F, T, and X) that encode the major mechanism of resistance to macrolides-lincosamides-streptogramin B (MLS(B)). These real-time PCR assays were validated and used in quantifying the six erm classes in five types of samples, including those from bovine manure, swine manure, compost of swine manure, swine waste lagoons, and an Ekokan upflow biofilter system treating hog house effluents. The bovine manure samples were found to contain much smaller reservoirs of each of the six erm classes than the swine manure samples. Compared to the swine manure samples, the composted swine manure samples had substantially reduced erm gene abundances (by up to 7.3 logs), whereas the lagoon or the biofilter samples had similar erm gene abundances. These preliminary results suggest that the methods of manure storage and treatment probably have a substantial impact on the persistence and decline of MLS(B) resistance originating from food animals, thus likely affecting the dissemination of such resistance genes into the environment. The abundances of these erm genes appeared to be positively correlated with those of the tet genes determined previously among these samples. These real-time PCR assays provide a rapid, quantitative, and cultivation-independent measurement of six major classes of erm genes, which should be useful for ecological studies of AR.

Characterization of an antibiotic resistant Clostridium hathewayi strain from a continuous-flow exclusion chemostat culture derived from the cecal contents of a feral pig

The chemostat model has been an important tool in studying intestinal microflora. To date, several competitive exclusion products have been developed from such studies as prophylactic treatment against pathogenic bacteria. A continuous-flow chemostat model of a feral pig was developed using inocula from the cecal contents of a wild boar caught in East Texas. Several strains of antibiotic-sensitive bacteria were isolated including Bacteroides, Lactobacillus, Enterococcus and Clostridium sp. This study reports on the characterization of a multidrug-resistant Clostridium hathewayi strain that was isolated from this feral pig's cecal contents maintained in a continuous-flow chemostat system showing high resistance to carbapenems and macrolides (including the growth promoter tylosin). Clostridium hathewayi has been documented to be pathogenic to both humans and animals. Feral pigs may be an important source of pathogenic and antibiotic resistant bacteria and may pose potential risk to domestic species. Further work is needed to elucidate the prevalence of these reservoirs and assess the contribution these may play in the spread of disease and resistance.