Residues of chlortetracycline, doxycycline and sulfadiazine-trimethoprim in intestinal content and feces of pigs due to cross-contamination of feed.

BACKGROUND: Cross-contamination of feed with low concentrations of antimicrobials can occur at production, transport and/or farm level. Concerns are rising about possible effects of this contaminated feed on resistance selection in the intestinal microbiota. Therefore, an experiment with pigs was set up, in which intestinal and fecal concentrations of chlortetracycline (CTC), doxycycline (DOX) and sulfadiazine-trimethoprim (SDZ-TRIM) were determined after administration of feed containing a 3 % carry-over level of these antimicrobials. RESULTS: The poor oral bioavailability of tetracyclines resulted in rather high concentrations in cecal and colonic content and feces at steady-state conditions. A mean concentration of 10 mg/kg CTC and 4 mg/kg DOX in the feces was reached, which is higher than concentrations that were shown to cause resistance selection. On the other hand, lower mean levels of SDZ (0.7 mg/kg) and TRIM (< limit of detection of 0.016 mg/kg) were found in the feces, corresponding with the high oral bioavailability of SDZ and TRIM in pigs. CONCLUSIONS: The relation between the oral bioavailability and intestinal concentrations of the tested antimicrobials, may be of help in assessing the risks of cross-contaminated feed. However, future research is needed to confirm our results and to evaluate the effects of these detected concentrations on resistance selection in the intestinal microbiota of pigs.

Using a Stakeholder Analysis to Implement the Belgian One Health National Report for Antimicrobial Use and Resistance.

(1) Background. Antimicrobial resistance (AMR) poses a substantial global health threat with profound economic implications. Acknowledging the imperative for a One Health (OH) strategy to combat this menace, Belgium introduced an annual national OH report, known as the "BELMAP report," encompassing antimicrobial use (AMU) and AMR, with the first edition completed in 2021. The integration of innovations for the healthcare system demands a meticulously planned process. (2) Methods. We introduced a three-step stakeholder analysis (SA) as a prospective framework for navigating this new report process, fostering complementary collaboration, pinpointing obstacles, suggesting approaches to overcome them, and facilitating national policy development. The SA unfolds in three steps: stakeholders identify and list their relevant activities, assess their positions regarding the BELMAP report, and complete "actor mapping" of national AMR and AMU stakeholders. (3) Results. Stakeholder identification reveals a fragmented landscape of AMR and AMU activities across Belgium. Assessment of stakeholder positions uncovers diverse expectations, collaborative challenges, and resource considerations. "Actor mapping" identifies key stakeholders, emphasizing the importance of high-interest and high-power actors. (4) Conclusions. This SA approach not only provides insights into the present stakeholder landscape in Belgium, it can also serve as a blueprint for other countries in the process of developing OH reports.

Identification and typing of Salmonella enterica serotypes isolated from guinea fowl (Numida meleagris) farms in Benin during four laying seasons (2007 to 2010).

The main problem for the local guinea fowl (Numida meleagris) traditional farming and raising system in north-east Benin is the high mortality rate of the keets (up to 70%) due to a combination of climatic, nutritional, hygienic and infectious causes. The present study was carried out to identify and compare the isolates of Salmonella enterica from necropsied keets, laying guinea fowl, surrogate hen mothers, other contact animal species and farmers during four laying seasons (2007 to 2010). S. enterica belonging to eight different serotypes (Adelaide, Farakan, Kingston, Legon, Luke, Oakland, Sangalkam and Teshie) and one untypable isolate were isolated from 13 to 19% of the necropsied keets. The serotypes Adelaide, Farakan, Luke, Sangalkam and Teshie and the untypable isolate were isolated in only one township during 1 year of sampling, while serotypes Oakland, Legon and Kingston were present in two to three townships for 2 to 3 years of sampling. Serotypes Farakan, Kingston, Legon, Oakland and Sangalkam were also isolated from faecal samples of laying guinea fowl and/or surrogate domestic fowl hen mothers. Further comparison by pulsed-field gel electrophoresis and virulotyping provided evidence for their clonality within each of those five serotypes and therefore for the adult guinea fowl and/or hens as the most probable origin of contamination of the keets. The antibiotic resistance profiles, with all isolates resistant to oxacillin, sulfamethoxazol and colistin, emphasize the rise of antibiotic resistance in salmonellas from guinea fowl in this area and the need for alternative therapy policies for these birds.

Several enteropathogens are circulating in suckling and newly weaned piglets suffering from diarrhea in the province of Villa Clara, Cuba.

Intestinal contents of suckling (n = 45) and newly weaned (n = 45) piglets, suffering from diarrhea in the province of Villa Clara in Cuba, were tested for viral, bacterial, and parasitic enteropathogens from May to June 2008. At least one enteropathogen was identified in 53.3 % of piglets and enterotoxigenic Escherichia coli (ETEC; 25.6 %) was the major pathogen; mostly STa(+)/STb(+) or F4(+)/STa(+)/STb(+) ETEC were isolated. The overall occurrence of the rest of pathogens was 10 % for transmissible gastroenteritis virus (TGEV) and Cryptosporidium parvum, 6.7 % for rotavirus A and Isospora suis, 5.6 % for α-toxigenic Clostridium perfringens, 3.3 % for verotoxigenic E. coli (VTEC), and 2.2 % for Salmonella enterica subspecies enterica serovar Newport. TGEV and α-toxigenic C. perfringens were only identified in suckling piglets, while Salmonella Newport and VTEC were only detected in weaned pigs. Porcine epidemic diarrhea virus (PEDV), ß-toxigenic C. perfringens, Eimeria spp., and helminths were not identified. Eight kinds of mixed infections were detected in 25 % of enteropathogen positive piglets. ETEC was present in 10 of 12 mixed infections, and TGEV infections were never combined. This survey demonstrates that several enteropathogens are circulating in piggeries located in the province of Villa Clara in Cuba, and that is necessary to improve surveillance, prevention, and control of enteric infections in order to increase production efficiency.

A multi-country One Health foodborne outbreak simulation exercise: cross-sectoral cooperation, data sharing and communication.

Introduction: The awareness of scientists and policy makers regarding the requirement for an integrated One Health (OH) approach in responding to zoonoses has increased in recent years. However, there remains an overall inertia in relation to the implementation of practical cross-sector collaborations. Foodborne outbreaks of zoonotic diseases continue to affect the European population despite stringent regulations, evidencing the requirement for better 'prevent, detect and response' strategies. Response exercises play an essential role in the improvement of crisis management plans, providing the opportunity to test practical intervention methodologies in a controlled environment. Methods: The One Health European Joint Programme simulation exercise (OHEJP SimEx) aimed at practicing the OH capacity and interoperability across public health, animal health and food safety sectors in a challenging outbreak scenario. The OHEJP SimEx was delivered through a sequence of scripts covering the different stages of a Salmonella outbreak investigation at a national level, involving both the human food chain and the raw pet feed industry. Results: A total of 255 participants from 11 European countries (Belgium, Denmark, Estonia, Finland, France, Italy, Norway, Poland, Portugal, Sweden, the Netherlands) took part in national level two-day exercises during 2022. National evaluations identified common recommendations to countries aiming to improve their OH structure to establish formal communication channels between sectors, implement a common data sharing platform, harmonize laboratory procedures, and reinforce inter-laboratory networks within countries. The large proportion of participants (94%) indicated significant interest in pursuing a OH approach and desire to work more closely with other sectors. Discussion: The OHEJP SimEx outcomes will assist policy makers in implementing a harmonized approach to cross-sector health-related topics, by highlighting the benefits of cooperation, identifying gaps in the current strategies and suggesting actions required to better address foodborne outbreaks. Furthermore, we summarize recommendations for future OH simulation exercises, which are essential to continually test, challenge and improve national OH strategies.

Molecular characterization of Salmonella Enteritidis: comparison of an optimized multi-locus variable-number of tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis.

Salmonella Enteritidis (SE) is a genetically homogenous serovar, which makes optimal subtype discrimination crucial for epidemiological research. This study describes the development and evaluation of an optimized multiple-locus variable number tandem-repeat assay (MLVA) for characterization of SE. The typeability and discriminatory power of this MLVA was determined on a selected collection of 60 SE isolates and compared with pulsed-field gel electrophoresis (PFGE) using restriction enzymes XbaI, NotI, or SfiI. In addition, the estimated Wallace coefficient (W) was calculated to assess the congruence of the typing methods. Selection of epidemiologically unrelated isolates and more related isolates (originating from layer farms) was also based on the given phage type (PT). When targeting six loci, MLVA generated 16 profiles, while PFGE produced 10, 9, and 16 pulsotypes using XbaI, NotI, and SfiI, respectively, for the entire strain collection. For the epidemiologically unrelated isolates, MLVA had the highest discriminatory power and showed good discrimination between isolates from different layer farms and among isolates from the same layer farm. MLVA performed together with PT showed higher discriminatory power compared to PFGE using one restriction enzyme together with PT. Results showed that combining PT with the optimized MLVA presented here provides a rapid typing tool with good discriminatory power for characterizing SE isolates of various origins and isolates originating from the same layer farm.

Comparison of Salmonella enteritidis phage types isolated from layers and humans in Belgium in 2005.

OBJECTIVES: The aim of this study was to investigate the available results for Belgium of the European Union coordinated monitoring program (2004/665 EC) on Salmonella in layers in 2005, as well as the results of the monthly outbreak reports of Salmonella Enteritidis in humans in 2005 to identify a possible statistical significant trend in both populations. MATERIALS AND METHODS: Separate descriptive statistics and univariate analysis were carried out and the parametric and/or non-parametric hypothesis tests were conducted. A time cluster analysis was performed for all Salmonella Enteritidis phage types (PTs) isolated. The proportions of each Salmonella Enteritidis PT in layers and in humans were compared and the monthly distribution of the most common PT, isolated in both populations, was evaluated. RESULTS: The time cluster analysis revealed significant clusters during the months May and June for layers and May, July, August, and September for humans. PT21, the most frequently isolated PT in both populations in 2005, seemed to be responsible of these significant clusters. PT4 was the second most frequently isolated PT. No significant difference was found for the monthly trend evolution of both PT in both populations based on parametric and non-parametric methods. DISCUSSION AND CONCLUSION: A similar monthly trend of PT distribution in humans and layers during the year 2005 was observed. The time cluster analysis and the statistical significance testing confirmed these results. Moreover, the time cluster analysis showed significant clusters during the summer time and slightly delayed in time (humans after layers). These results suggest a common link between the prevalence of Salmonella Enteritidis in layers and the occurrence of the pathogen in humans. Phage typing was confirmed to be a useful tool for identifying temporal trends.

Lessons learned from the management of a national outbreak of Salmonella ohio linked to pork meat processing and distribution.

During the summer of 2005, an increase in reports of human cases of Salmonella enterica serovar Ohio infection was observed in Belgium. During 11 weeks, between 1 July and 13 September, 60 cases of laboratory-confirmed Salmonella Ohio infection were reported to the National Reference Centre for Salmonella, with a peak onset of symptoms in the third week of July. All clinical isolates caused self-limiting gastroenteritis; both genders (32 males and 28 females) and all age groups (three children <5 years of age, three children 5 to 14 years of age, 32 adults 15 to 64 years of age, and 22 adults >65 years of age) were affected. The isolates were distributed throughout Belgium but a cluster of several cases was observed around Brussels. At the same time, an increase in the incidence of this serovar was observed in the Salmonella isolates originating from the official surveillance campaign conducted by the Federal Agency for the Safety of the Food Chain, which identified pork as a likely source of the outbreak strain. Pulsed-field gel electrophoresis typing confirmed the clonal relationship between the human isolates, the isolates from samples collected in the cutting plants, and the isolates from pork meat in distribution. Further epidemiological investigations indicated that one particular slaughterhouse was involved. In that slaughterhouse, the carcasses were contaminated during the evisceration process because of contaminated equipment and uncontrolled environmental conditions. This study highlights the importance of a centralized surveillance laboratory in the management of outbreaks and the need of strict implementation of hygienic rules to avoid this type of outbreak.

Evidence-based semiquantitative methodology for prioritization of foodborne zoonoses.

OBJECTIVES: To prioritize an extended list of food- and water-borne zoonoses to allow food safety authorities to focus on the most relevant hazards in the food chain. METHODS: An evidence-based semiquantitative methodology was developed. Scores were given by 35 scientific experts in the field of animal and public health, food, and clinical microbiology and epidemiology to 51 zoonotic agents according to five criteria related to public health (severity and occurrence in humans), animal health (severity of disease coupled with economic consequences and occurrence in animals), and food (occurrence in food). The scoring procedure was standardized and evidence-based as experts were provided, for each zoonotic agent, a same set of up-to-date help information data related to the five criteria. Independently, the relative importance of the five criteria was weighted by seven food chain risk managers. The zoonotic agents were ranked based on overall weighted scores and were grouped in four statistically different levels of importance. RESULTS: The following foodborne zoonotic pathogens were classified as "most important": Salmonella spp., Campylobacter spp., Listeria monocytogenes, and verocytotoxigenic Escherichia coli. A second group of "significant importance" included Toxoplasma gondii, the agent of bovine spongiform encephalopathy, Clostridium botulinum, Staphylococcus aureus, Cryptosporidium parvum, Mycobacterium bovis, Echinococcus granulosus, Streptococcus spp., Echinococcus multilocularis, Yersinia enterocolitica, Mycobacterium avium, Fasciola hepatica, Giardia intestinalis, and Rotavirus. CONCLUSIONS: This methodology allowed to rank 51 zoonotic agents with objectivity and taking account of a combined input from risk assessors and risk managers. APPLICATIONS: These results support food safety policy makers to establish the multiannual monitoring program of foodborne zoonoses. They also enable to identify knowledge gaps on specific zoonotic agents and to formulate key research questions. Principally, this method of prioritization is of general interest as it can be applied for any other ranking exercise and in any country.

Comparison of classical serotyping and PremiTest assay for routine identification of common Salmonella enterica serovars.

The commercial PremiTest Salmonella kit uses a multiplexed DNA typing test aimed at identifying common serovars of Salmonella enterica. It was used in assays over a 9-month period in the Belgian reference laboratory that performs the routine identification of Salmonella strains of animal origin. A blind analysis of 754 strains was conducted in parallel by classical serotyping and the PremiTest assay. Full results were available for 685 strains (90.8%) by serotyping, while the remaining 69 strains were found to be nontypeable due to either a lack of surface antigen expression or autoagglutination properties. When the PremiTest assay (version 4.2) was performed with crude bacterial extracts, it identified 658 strains (87.3%), including most strains found to be nontypeable by serotyping. In contrast, it gave no, wrong, dual, or noninterpretable results for 96 strains, for which 23 were caused by assay failures. When purified DNA instead of crude extracts were tested, the number of strains successfully identified to the serovar level increased to 714 (94.7%), while all assay failures were cleared. Our conclusion is that, in its actual development stage, the application of the investigated kit to purified DNA samples offers a valuable alternative to classical serotyping for laboratories performing the routine identification of Salmonella strains belonging to commonly encountered serovars and isolated from a given geographical area, assuming that the system has been validated beforehand with a significant number of strains originating from that particular area.

Occurrence and genetic diversity of Bacillus anthracis strains isolated in an active wool-cleaning factory.

Culturable microorganisms from various samples taken at an active factory performing wool and goat hair cleaning were isolated and analyzed. Bacillus anthracis was found in air filter dust, wastewater, and goat hairs, where it accounted for approximately 1% of the total counts of viable bacteria. Consistent with the countries of origin of the processed material (South Caucasian and Middle Eastern), all B. anthracis isolates belonged to the same phylogenetic cluster, as determined by variable-number tandem repeat (VNTR) typing at eight loci. Within this cluster, five closely related VNTR subtypes could be identified, of which two were previously unreported. Additional diversity was observed when more sensitive genetic markers were assayed, demonstrating the multifocal nature of goat hair contamination. Goat hair originating from areas where anthrax is endemic remains a material with high biological risk for modern woolworkers.

Evaluation of the Premi Test Salmonella, a commercial low-density DNA microarray system intended for routine identification and typing of Salmonella enterica.

A new commercial system based on genetic profiling and aimed at identifying Salmonella enterica serovars was evaluated by comparing its performance with classical serotyping on 443 strains. Within 62 serovars represented, 60 gave unique genetic profiles while 2 were undistinguishable. Results were obtained within 8 h, were reproducible and clear-cut. The system allowed single-tube processing of the samples and required no peculiar technical skill. It showed interesting potential for routine laboratory testing.

Salmonella in Belgian laying hens: an identification of risk factors.

Since the 1980s, the prevalence of Salmonella in Belgian poultry layers and broilers has greatly fluctuated with a rise observed in 2003 and a significant decrease in 2005. In order to alleviate the risk at egg consumer level, it is crucial to understand the factors which influence the contamination and the spread of Salmonella in laying hens. To study such determinants we explored the Belgian data from the 2005 baseline study on the prevalence of Salmonella in laying flocks of Gallus gallus in the European Union. The response variables corresponded to presence or absence of Salmonella from dust and faecal samples taken from the environment of a Belgian layer flock. The explanatory variables included: region of Belgium, sampling time (month the flock was sampled), production type (cage or barn and free range), Salmonella vaccination status, flock age and flock size. Analyses of these data were performed using a bivariate logistic regression model assuming independence between the two responses and bivariate generalized estimating equations model, which incorporates the correlation between the two responses on the same flock. The main risk factor that was identified was rearing flocks in cages compared to barns and free-range systems. The results also showed a significant higher risk for Salmonella for a 1 week increase in flocks' age as well as with a unit increase in the size of the flock.

Effect of residual doxycycline concentrations on resistance selection and transfer in porcine commensal Escherichia coli.

Pig feed may contain various levels of antimicrobial residues due to cross-contamination. A previous study showed that a 3% carry-over level of doxycycline (DOX) in the feed results in porcine faecal concentrations of approximately 4 mg/L. The aim of this study was to determine the effect of residual DOX concentrations (1 and 4 mg/L) in vitro on selection of DOX-resistant porcine commensal Escherichia coli and transfer of their resistance plasmids. Three different DOX-resistant porcine commensal E. coli strains and their plasmids were characterised. These strains were each brought in competition with a susceptible strain in a medium containing 0, 1 and 4 mg/L DOX. Resistant bacteria, susceptible bacteria and transconjugants were enumerated after 24 h and 48 h. The tet(A)-carrying plasmids showed genetic backbones that are also present among human E. coli isolates. Ratios of resistant to susceptible bacteria were significantly higher at 1 and 4 mg/L DOX compared with the blank control, but there was no significant difference between 1 and 4 mg/L. Plasmid transfer frequencies were affected by 1 or 4 mg/L DOX in the medium for only one of the resistance plasmids. In conclusion, DOX concentrations of 1 and 4 mg/L can select for resistant E. coli in vitro. Further research is needed to determine the effect of these concentrations in the complex environment of the porcine intestinal microbiota.

Protection of rabbits against enteropathogenic Escherichia coli (EPEC) using an intimin null mutant.

BACKGROUND: Diarrhea and mortality resulting from infections with enteropathogenic Escherichia coli (EPEC) are of major economic importance in the rabbit meat industry. There is a growing need for an effective vaccine to cope with these problems and to reduce the use of antibiotics. EPEC are characterized by an attaching and effacing virulence mechanism. This is partly mediated by the intimate binding between an adhesin, called intimin, and a translocated receptor (Tir) of prokaryote origin. We constructed an intimin deletion mutant of the rabbit EPEC (REPEC) wild-type strain 97/241.6 (bio-/serogroup 3-/O15) and examined its protective capacity. RESULTS: After verifying its complete loss of virulence, we used the attenuated strain in vaccination-challenge experiments in which complete protection against a homologous, but virulent, strain was observed. The attenuated strain was able to persist in the intestinal lumen, where it elicited an immune response against EPEC-related virulence proteins, as was shown using an EspB-specific ELISA. Despite the priming of an immune response and the generation of specific antibodies, the intimin mutant was not able to fully protect rabbits against challenges with REPEC strains of other bio-/serogroups. CONCLUSION: These data indicate that protection against REPEC infections is at least partly bio-/serogroup dependent and a multivalent vaccine may be needed for protection against the full range of REPEC types. Such a combination vaccine may be developed using intimin null mutants, as the latter were clearly shown to be safe and effective against homologous infections.

Risk of cross-contamination due to the use of antimicrobial medicated feed throughout the trail of feed from the feed mill to the farm.

The cross-contamination of non-medicated feed with residues of antimicrobials causes an animal and public health concern associated with the potential for the selection and dissemination of resistance in commensal bacteria and potentially zoonotic bacteria. To identify the extent of this situation, we built a risk model that provides a way to estimate the percentage of cross-contaminated feed in total and at the different levels at which cross-contamination may occur (i.e. the feed mill, the transport truck, the farm), for different levels of antimicrobial medicated feed produced in a country per year. The model, estimated that when antimicrobial medicated feed represents a hypothetical xi = 2% of the total feed produced in a country per year, then 5.5% (95% CI = 3.4%; 11.4%) of the total feed produced in a year could be cross-contaminated with different levels of antimicrobials due to practices related to medicated feed. In detail, 1.80% (95% CI = 0.2%; 7.7%) of the total feed produced in such a country would be cross-contaminated due to antimicrobial carryover occurring at the feed mill level, 1.83% (95% CI = 1.3%; 2.0%) at the transport truck level and 1.84% (95% CI = 1.2%; 2.0%) at the farm level. The model also demonstrated that even in cases where antimicrobial medicated feed would be produced in end-of-line mixers or a fine dosing system on trucks, the risk of cross-contamination would not be negligible; the percentage of cross-contaminated feed produced in a country (where xi = 2%) per year would be 3.7% (95% CI = 2.9%; 4.0%) and 2.4% (95% CI = 1.6%; 2.7%), respectively. It is hard to reduce the risk to zero as it is the result of factors occurring at different levels. Thus, the use of antimicrobial medicated feed should be avoided as much as possible to reduce selection pressure.

Measuring general animal health status: Development of an animal health barometer.

The development of an animal health barometer, an instrument to measure the general health of the Belgian livestock population on a yearly basis and to monitor its evolution over time, is described. The elaboration of a set of 13 animal health indicators (AHIs) as the basis for the animal health barometer is discussed. These indicators were weighted by experts - including scientists, policy makers and agro-industrial representatives - to determine their relative weight in the barometer. The result of the barometer is expressed as a comparison with a previous year. Based on the results of the 13 AHIs, it is concluded that general animal health in Belgium shows a positive evolution since 2008. The animal health barometer provides a composite view of the status of livestock health in Belgium and is a tool to communicate in an intelligible, comprehensible manner on aspects of animal health to consumers and professional stakeholders in the animal production and food chain. Together with the food safety barometer (Baert et al., 2011. Food Res. Int. 44, 940) and the plant health barometer (Wilmart et al., 2014. Eur. J. Plant Pathol. doi: 10.1007/s10658-014-0547-x), the animal health barometer is one of the three instruments to provide a holistic view on the overall status of the safety of the food chain in Belgium.

A trend analysis of antimicrobial resistance in commensal Escherichia coli from several livestock species in Belgium (2011-2014).

A temporal trend analysis was performed on antimicrobial resistance data collected over 4 consecutive years (2011-2014) in the official Belgian antimicrobial resistance monitoring programme. Commensal Escherichia coli strains were isolated from faecal samples of four livestock categories (veal calves, young beef cattle, broiler chickens and slaughter pigs) and the trends of resistance profiles were analysed. The resistance prevalence remained high (>50%) during the study period for ampicillin in veal calves and chickens, for ciprofloxacin and nalidixic acid in chickens, for sulfamethoxazole in veal calves, chickens and pigs and for tetracycline in veal calves. Using logistic regression and Generalized Estimating Equation and after p value adjustment for multiple testing (Linear step-up method), statistically significant decreasing temporal trends were observed for several of the 11 tested antimicrobials in several livestock categories: in veal calves (10/11), in chickens (6/11) and in pigs (5/11). A significant increasing trend was observed for the prevalence of resistance to ciprofloxacin in chickens. Multi-resistance, considered as the resistance to at least three antimicrobials of different antibiotic classes, was observed in the four livestock categories but was significantly decreasing in veal calves, chickens and pigs. Overall, the prevalence of resistance and of multi-resistance was lowest in the beef cattle livestock category and highest in broiler chickens. These decreasing temporal trends of antimicrobial resistance might be due to a decrease of the total antimicrobial consumption for veterinary use in Belgium which was reported for the period between 2010 and 2013. The methodology and statistical tools developed in this study provide outputs which can detect shifts in resistance levels or resistance trends associated with particular antimicrobial classes and livestock categories. Such outputs can be used as objective evidence to evaluate the possible efficacy of measures taken by animal health authorities and stakeholders in the livestock sector to limit antimicrobial resistance occurrence.

The AcrB multidrug transporter plays a major role in high-level fluoroquinolone resistance in Salmonella enterica serovar typhimurium phage type DT204.

Salmonella enterica serovar Typhimurium phage type DT204 strains isolated from cattle and animal feed in Belgium were characterized for high-level fluoroquinolone resistance mechanisms [MICs to enrofloxacin (Enr) and ciprofloxacin (Cip), 64 and 32 microg/ml, respectively]. These strains isolated during the periods 1991-1994, and in 2000 were clonally related as shown by pulsed-field gel electrophoresis (PFGE). Selected strains studied carried several mutations in the quinolone target genes, i.e., a double mutation in the quinolone resistance-determining region (QRDR) of gyrA leading to amino acid changes Ser83Ala and Asp87Asn, a single mutation in the QRDR of gyrB leading to amino acid change Ser464Phe, and a single mutation in the QRDR of parC leading to amino acid change Ser80Ile. Moreover, Western blot analysis showed overproduction of the AcrA periplasmic protein belonging to the AcrAB-ToIC efflux system. This suggested active efflux as additional resistance mechanism resulting in a multiple antibiotic resistance (MAR) phenotype, which was measurable by an increased level of resistance to the structurally unrelated antibiotic florfenicol in the absence of the specific floR resistance gene. The importance of the AcrAB-TolC efflux system in high-level fluoroquinolone resistance was further confirmed by inactivating the acrB gene coding for the multidrug transporter. This resulted in a 32-fold reduction of resistance level to Enr (MIC = 2 microg/ml) and actually in a susceptible phenotype according to clinical breakpoints. Thus, AcrB plays a major role in high-level fluoroquinolone resistance, even when multiple target gene mutations are present. The same effect was obtained using the recently identified efflux pump inhibitor (EPI) Phe-Arg-naphthylamide also termed MC207,110. Among several fluoroquinolones tested in combination with EPI, the MIC of Enr was reduced most significantly. Thus, using EPI together with fluoroquinolones such as Enr may be promising in combination therapy against high-level fluoroquinolone-resistant S. enterica serovar Typhimurium.

Antimicrobial resistance in the food chain: a review.

Antimicrobial resistant zoonotic pathogens present on food constitute a direct risk to public health. Antimicrobial resistance genes in commensal or pathogenic strains form an indirect risk to public health, as they increase the gene pool from which pathogenic bacteria can pick up resistance traits. Food can be contaminated with antimicrobial resistant bacteria and/or antimicrobial resistance genes in several ways. A first way is the presence of antibiotic resistant bacteria on food selected by the use of antibiotics during agricultural production. A second route is the possible presence of resistance genes in bacteria that are intentionally added during the processing of food (starter cultures, probiotics, bioconserving microorganisms and bacteriophages). A last way is through cross-contamination with antimicrobial resistant bacteria during food processing. Raw food products can be consumed without having undergone prior processing or preservation and therefore hold a substantial risk for transfer of antimicrobial resistance to humans, as the eventually present resistant bacteria are not killed. As a consequence, transfer of antimicrobial resistance genes between bacteria after ingestion by humans may occur. Under minimal processing or preservation treatment conditions, sublethally damaged or stressed cells can be maintained in the food, inducing antimicrobial resistance build-up and enhancing the risk of resistance transfer. Food processes that kill bacteria in food products, decrease the risk of transmission of antimicrobial resistance.