Antimicrobial use in agriculture: controlling the transfer of antimicrobial resistance to humans

Chlorophyllin Supplementation of Medicated or Unmedicated Swine Diets Impact on Fecal Escherichia coli and Enterococci

Considering that certain catabolic products of anaerobic chlorophyll degradation inhibit efflux pump activity, this study was conducted to test if feeding pigs a water-soluble chlorophyllin product could affect the antibiotic resistance profiles of select wild-type populations of fecal bacteria. Trial 1 evaluated the effects of chlorophyllin supplementation (300 mg/meal) on fecal E. coli and enterococcal populations in pigs fed twice daily diets supplemented without or with ASP 250 (containing chlortetracycline, sulfamethazine and penicillin at 100, 100 and 50 g/ton, respectively). Trial 2, conducted similarly, evaluated chlorophyllin supplementation in pigs fed diets supplemented with or without 100 g tylosin/ton. Each trial lasted 12 days, and fecal samples were collected and selectively cultured at 4-day intervals to enumerate the total numbers of E. coli and enterococci as well as populations of these bacteria phenotypically capable of growing in the presence of the fed antibiotics. Performance results from both studies revealed no adverse effect (p > 0.05) of chlorophyllin, antibiotic or their combined supplementation on average daily feed intake or average daily gain, although the daily fed intake tended to be lower (p = 0.053) for pigs fed diets supplemented with tylosin than those fed diets without tylosin. The results from trial 1 showed that the ASP 250-medicated diets, whether without or with chlorophyllin supplementation, supported higher (p < 0.05) fecal E. coli populations than the non-medicated diets. Enterococcal populations, however, were lower, albeit marginally and not necessarily significantly, in feces from pigs fed the ASP 250-medicated diet than those fed the non-medicated diet. Results from trial 2 likewise revealed an increase (p < 0.05) in E. coli and, to a lesser extent, enterococcal populations in feces collected from pigs fed the tylosin-medicated diet compared with those fed the non-medicated diet. Evidence indicated that the E. coli and enterococcal populations in trial 1 were generally insensitive to penicillin or chlortetracycline, as there were no differences between populations recovered without or with antibiotic selection. Conversely, a treatment x day of treatment interaction observed in trial 2 (p < 0.05) provided evidence, albeit slight, of an enrichment of tylosin-insensitive enterococci in feces from the pigs fed the tylosin-medicated but not the non-medicated diet. Under the conditions of the present study, it is unlikely that chlorophyllin-derived efflux pump inhibitors potentially present in the chlorophyllin-fed pigs were able to enhance the efficacy of the available antibiotics. However, further research specifically designed to optimize chlorophyll administration could potentially lead to practical applications for the swine industry.

Impact of bee venom supplement on productive performance, health status and economics of weaned male rabbits: Considering breed and dosage factors

The objectives of the present study were to investigate the potential effects of purified bee venom (BV) on various aspects of growth, carcass, antioxidant, intestinal bacterial count and economic considerations in rabbits. A total of 240 male rabbits, comprising two distinct breeds (V-Line and New Zealand White [NZW]), 5 weeks old, with an average live body weight (BW) of 680 ± 20 g, were randomly divided into six groups, each containing 30 rabbits. Each group had five replicates, with six rabbits in each replicate. The allocation of animals to the groups followed a fully factorial design, incorporating two factors: breed (V-Line and NZW) and four levels of purified BV derived from Apis Mellifera. The control group (G1) received a basal diet without additives. The other three groups (G2, G3 and G4) received the basal diet with BV supplementation in their drinking water at 0.5, 1 and 2 mg/L respectively. The study results indicated that NZW rabbits significantly enhanced feed conversion ratio while maintaining consistent carcass attributes compared to the V-Line breed. Despite variations in growth parameters being less pronounced, the supplementation of BV at levels of 1-2 mg/L demonstrated significant improvements in various other parameters. Notably, the interaction between the BV supplement and the breed factor (p < 0.001) yielded notable distinctions in most production metrics, encompassing BW, weight gain, feed conversion, carcass attributes and blood parameters. Increasing levels of BV supplementation, particularly at 1 mg/L, led to substantial improvements in serum and tissue metabolites. Moreover, the levels of total bacterial count and Escherichia coli in the jejunum and colon were significantly diminished, while the population of Lactobacilli in the colon was augmented (p < 0.001) in rabbits from both breeds receiving BV supplementation (1-2 mg/L) compared to the control group. The results underscore the potential of the BV supplement to enhance final weights, bolster antioxidant status and mitigate the presence of pathogenic bacteria, thereby contributing to enhanced economic efficiency in rabbits. Further inquiries are warranted to comprehensively investigate BV supplementation's potential advantages and limitations across different breeds and dosage levels.

Metagenomic insights into microbial contamination in critical healthcare environments and the efficacy of a novel "HLE" disinfectant

BACKGROUND

Bacterial contamination on inanimate clinical surfaces is directly linked to severe health problems, especially those caused by multidrug resistant (MDR) pathogens. Here, we evaluated the microbial burden in these environments and tested the efficacy of a novel HLE disinfectant solution.

METHODS

Microbial contamination of healthcare surfaces [Intensive Care Unit (ICU), Long Period Hospitalization Room (LPHR) and Otolaryngology Consultation (OC)] and the efficacy of HLE disinfectant solution were determined analyzing the viable counts on general and selective media, and also by molecular studies focused on metagenomic and specific qPCR.

RESULTS

Different contamination loads were detected with LPHR showing the highest contamination. Treatment with the HLE disinfectant solution curbed the spread of well-adapted pathogens on touched surfaces (ICU, LPHR and OC). Metagenomic analysis of microbial diversity of the Patient Table (most contaminated surface in LPHR) revealed the presence of mainly A. johnsonii and P. putida. Furthermore, functional annotation of toxin, virulence and antibiotic resistance sequences showed a high diversity of Acinetobacter spp. and Pseudomonas spp. In this context, specific qPCR analysis confirmed the efficacy of HLE disinfectant solution against the most prevalent and critical pathogens Pseudomonas sp. and Acinetobacter sp. achieving their complete eradication.

CONCLUSION

Given the persistence of detrimental resistant pathogens, the application of HLE disinfection solution could be a highly beneficial and effective option -used either alone or in combination-for infection prevention and control with the aim to eliminate microbial pathogens and their genes from contaminated contact-surfaces and thus limit the spread to humans and other ecological niches.

Role of Antimicrobial Resistance in Outcomes of Acute Endophthalmitis

BACKGROUND

This study explores local trends in antimicrobial resistance and its influence on long-term visual outcomes following treatment with broad-spectrum empiric intravitreal antibiotics.

METHODS

All patients undergoing intraocular sampling for endophthalmitis from Auckland between January 2006-May 2023 were included. The impact of antimicrobial resistance on the final visual outcome was analysed using logistic regression models.

RESULTS

389 cases of endophthalmitis were included, and 207 eyes (53.2%) were culture positive. When tested, all Gram-positive microorganisms were fully susceptible to Vancomycin, and all Gram-negative microorganisms demonstrated full or intermediate susceptibility to Ceftazidime. Resistance to at least one antimicrobial agent was present in 89 culture results (43.0%), and multidrug resistance (resistant to ≥3 antimicrobials) in 23 results (11.1%). No increase in resistance was observed over time. The primary procedure was a tap and inject in 251 eyes (64.5%), and early vitrectomy was performed in 196 eyes (50.3%). Severe vision loss (≤20/200) occurred in 167 eyes (42.9%). Antimicrobial resistance was associated with an increased risk of retinal detachment (OR 2.455 p = 0.048) but not vision loss (p = 0.288).

CONCLUSION

High sensitivity to Vancomycin and Ceftazidime was present in our population, reinforcing their role as first-line empiric treatments. Resistant microorganisms were associated with an increased risk of retinal detachment but no alteration in final visual outcome.

Antimicrobial Resistance Genes (ARGs), the Gut Microbiome, and Infant Nutrition

The spread of antimicrobial resistance genes (ARGs) is a major public health crisis, with the ongoing spread of ARGs leading to reduced efficacy of antibiotic treatments. The gut microbiome is a key reservoir for ARGs, and because diet shapes the gut microbiome, diet also has the potential to shape the resistome. This diet-gut microbiome-resistome relationship may also be important in infants and young children. This narrative review examines what is known about the interaction between the infant gut microbiome, the infant resistome, and infant nutrition, including exploring the potential of diet to mitigate infant ARG carriage. While more research is needed, diet has the potential to reduce infant and toddler carriage of ARGs, an important goal as part of maintaining the efficacy of available antibiotics and preserving infant and toddler health.

Effects of antibiotic interaction on antimicrobial resistance development in wastewater

While wastewater is understood to be a critically important reservoir of antimicrobial resistance due to the presence of multiple antibiotic residues from industrial and agricultural runoff, there is little known about the effects of antibiotic interactions in the wastewater on the development of resistance. We worked to fill this gap in quantitative understanding of antibiotic interaction in constant flow environments by experimentally monitoring E. coli populations under subinhibitory concentrations of combinations of antibiotics with synergistic, antagonistic, and additive interactions. We then used these results to expand our previously developed computational model to account for the effects of antibiotic interaction. We found that populations grown under synergistic and antagonistic antibiotic conditions exhibited significant differences from predicted behavior. E. coli populations grown with synergistically interacting antibiotics developed less resistance than predicted, indicating that synergistic antibiotics may have a suppressive effect on resistance development. Furthermore E. coli populations grown with antagonistically interacting antibiotics showed an antibiotic ratio-dependent development of resistance, suggesting that not only antibiotic interaction, but relative concentration is important in predicting resistance development. These results provide critical insight for quantitatively understanding the effects of antibiotic interactions in wastewater and provide a basis for future studies in modelling resistance in these environments.

Effects of Antibiotic Interaction on Antimicrobial Resistance Development in Wastewater

While wastewater is understood to be a critically important reservoir of antimicrobial resistance due to the presence of multiple antibiotic residues from industrial and agricultural runoff, there is little known about the effects of antibiotic interactions in the wastewater on the development of resistance. We worked to fill this gap in quantitative understanding of antibiotic interaction in constant flow environments by experimentally monitoring E. coli populations under subinhibitory concentrations of combinations of antibiotics with synergistic, antagonistic, and additive interactions. We then used these results to expand our previously developed computational model to account for the complex effects of antibiotic interaction. We found that while E. coli populations grown in additively interacting antibiotic combinations grew predictably according to the previously developed model, those populations grown under synergistic and antagonistic antibiotic conditions exhibited significant differences from predicted behavior. E. coli populations grown in the condition with synergistically interacting antibiotics developed less resistance than predicted, indicating that synergistic antibiotics may have a suppressive effect on antimicrobial resistance development. Furthermore E. coli populations grown in the condition with antagonistically interacting antibiotics showed an antibiotic ratio-dependent development of resistance, suggesting that not only antibiotic interaction, but relative concentration is important in predicting resistance development. These results provide critical insight for quantitatively understanding the effects of antibiotic interactions in wastewater and provide a basis for future studies in modelling resistance in these environments.

Importance

Antimicrobial resistance (AMR) is a growing global threat to public health expected to impact 10 million people by 2050, driving mortality rates globally and with a disproportionate effect on low- and middle-income countries. Communities in proximity to wastewater settings and environmentally contaminated surroundings are at particular risk due to resistance stemming from antibiotic residues from industrial and agricultural runoff. Currently, there is a limited quantitative and mechanistic understanding of the evolution of AMR in response to multiple interacting antibiotic residues in constant flow environments. Using an integrated computational and experimental methods, we find that interactions between antibiotic residues significantly affect the development of resistant bacterial populations.

Long-Term Effects of Single-Dose Cephalosporin or Macrolide Use on the Prevalence of AmpC and Extended-Spectrum β-Lactamase Producing Escherichia coli in the Feces of Beef Cattle

Extended-spectrum-β-lactamase (ESBL) and AmpC-lactamase-producing Enterobacteriaceae are serious public health threats. Due to an increasing number of reports of ESBL and AmpC producing Escherichia coli in agricultural settings, it is critical to understand the relationship between the use of two of the highest priority critically important human antibiotics (e.g., third generation cephalosporins [3GC] and macrolides) in food animals and their potential contribution to the selection of ESBL/AmpC E. coli. The objective of our randomized controlled feedlot trial was to measure the effects of ceftiofur crystalline-free acid and tulathromycin on 3GC resistant fecal E. coli populations in cattle before and at various time points after treatment up to and including at slaughter. Multi-level mixed-effects linear regression showed no effect of ceftiofur and tulathromycin on 3GC E. coli CFU counts at slaughter (Day 99); however, a significant (p < 0.05) population shift was observed from susceptible to 3GC resistant E. coli immediately after ceftiofur administration (Day 7). Among 799 fecal samples screened using selective media, 17.7% were ESBL/AmpC E. coli positive, which were further tested for phenotypic antibiotic susceptibility. The majority of the isolates from these plates were multidrug-resistant (94.3%) and expressed either AmpC (78.1%) or ESBL (28.1%) phenotype. A subset of isolates was whole-genome sequenced (n = 20) and identified to harbor chromosomal and/or plasmidal bla genes such as CMY-2, CTX-M, and TEM. Our findings show a time-dependent selection of antibiotics on 3GC-resistant E. coli. High prevalence of multidrug-resistant ESBL/AmpC E. coli found in cattle feces highlights the importance of prudent use of antibiotics in livestock.

Litter Commensal Bacteria Can Limit the Horizontal Gene Transfer of Antimicrobial Resistance to Salmonella in Chickens

Fostering a "balanced" gut microbiome through the administration of beneficial microbes that can competitively exclude pathogens has gained a lot of attention and use in human and animal medicine. However, little is known about how microbes affect the horizontal gene transfer of antimicrobial resistance (AMR). To shed more light on this question, we challenged neonatal broiler chicks raised on reused broiler chicken litter-a complex environment made up of decomposing pine shavings, feces, uric acid, feathers, and feed-with Salmonella enterica serovar Heidelberg (S. Heidelberg), a model pathogen. Neonatal chicks challenged with S. Heidelberg and raised on reused litter were more resistant to S. Heidelberg cecal colonization than chicks grown on fresh litter. Furthermore, chicks grown on reused litter were at a lower risk of colonization with S. Heidelberg strains that encoded AMR on IncI1 plasmids. We used 16S rRNA gene sequencing and shotgun metagenomics to show that the major difference between chicks grown on fresh litter and those grown on reused litter was the microbiome harbored in the litter and ceca. The microbiome of reused litter samples was more uniform and enriched in functional pathways related to the biosynthesis of organic and antimicrobial molecules than that in fresh litter samples. We found that Escherichia coli was the main reservoir of plasmids encoding AMR and that the IncI1 plasmid was maintained at a significantly lower copy per cell in reused litter compared to fresh litter. These findings support the notion that commensal bacteria play an integral role in the horizontal transfer of plasmids encoding AMR to pathogens like Salmonella. IMPORTANCE Antimicrobial resistance spread is a worldwide health challenge, stemming in large part from the ability of microorganisms to share their genetic material through horizontal gene transfer. To address this issue, many countries and international organizations have adopted a One Health approach to curtail the proliferation of antimicrobial-resistant bacteria. This includes the removal and reduction of antibiotics used in food animal production and the development of alternatives to antibiotics. However, there is still a significant knowledge gap in our understanding of how resistance spreads in the absence of antibiotic selection and the role commensal bacteria play in reducing antibiotic resistance transfer. In this study, we show that commensal bacteria play a key role in reducing the horizontal gene transfer of antibiotic resistance to Salmonella, provide the identity of the bacterial species that potentially perform this function in broiler chickens, and also postulate the mechanism involved.

Analysis of Antimicrobial Resistance in Non-typhoidal Salmonella Collected From Pork Retail Outlets and Slaughterhouses in Vietnam Using Whole Genome Sequencing

Non-typhoidal salmonella (TS) remains a significant health burden worldwide. In Vietnam, pork accounts for 70% of the total meat consumed, and contamination with Salmonella is high. High levels of antimicrobial resistance (AMR) have emerged among porcine NTS and of particular concern is the emergence of colistin resistance, a “last defense” antibioic against multi-drug resistant (MDR) Gram-negative pathogens. This study aimed to investigate the antibiotic susceptibility of 69 NTS isolates collected from the pork retail outlets and slaughterhouses in Vietnam during 2014 a nd 2018/19. Phenotypic testing and whole genome sequencing was used to assess the serotype and AMR gene profiles of the 69 NTS isolates. Seventeen different serotypes were identified, of which S. enterica subsp enterica serotype Typhimurium was the most common followed by S. ser. Rissen, S. ser. London, S. ser. Anatum, and S. ser. Derby. Phenotype AMR was common with 41 (59.4%) isolates deemed MDR. MDR strains were most common in slaughterhouses (83%) and supermarkets (75%) and lowest in traditional markets (38%) and convenience stores (40%). Colistin resistance was identified in 18 strains (15 resistant, three intermediate) with mcr-1 identified in seven isolates (S. ser. Meleagridis, S. Rissen, S. Derby) and mcr-3 in two isolates (S. Typhimurium). This includes the first mcr positive S. Meleagridis to our knowledge. Surprisingly, boutique stores had high levels (60%) of MDR isolates including 5/20 isolates with mcr-1. This study demonstrates that pork from modern retail stores classed as supermarkets or boutique (with pork claiming to be high quality, traceable, environmentally friendly marketed toward higher income consumers) still contained NTS with high levels of AMR.

A Bayesian latent class mixture model with censoring for correlation analysis in antimicrobial resistance across populations

Background

The emergence of antimicrobial resistance across populations is a global threat to public health. Surveillance programs often monitor human and animal populations to evaluate trends of emergence in these populations. Many national level antibiotic resistance surveillance programs quantify the proportion of resistant bacteria as a means of monitoring emergence and control measures. The reason for monitoring these different populations are many, including interest in similar changes in resistance which might provide insight into emergence and control options.

Methods

In this research, we developed a method to quantify the correlation in antimicrobial resistance across populations, for the conventionally unnoticed mean shift of the susceptible bacteria. With the proposed Bayesian latent class mixture model with censoring and multivariate normal hierarchy, we address several challenges associated with analyzing the minimum inhibitory concentration data.

Results

Application of this approach to the surveillance data from National Antimicrobial Resistance Monitoring System led to a detection of positive correlation in the central tendency of azithromycin resistance of the susceptible populations from Salmonella serotype Typhimurium across food animal and human populations.

Conclusions

Our proposed approach has been shown to be accurate and superior to the commonly used naïve estimation by simulation studies. Further implementation of this Bayesian model could serve as a useful tool to indicate the co-existence of antimicrobial resistance, and potentially a need of clinical intervention.

Horizontal Gene Transfer Is the Main Driver of Antimicrobial Resistance in Broiler Chicks Infected with Salmonella enterica Serovar Heidelberg

The overuse and misuse of antibiotics in clinical settings and in food production have been linked to the increased prevalence and spread of antimicrobial resistance (AR). Consequently, public health and consumer concerns have resulted in a remarkable reduction in antibiotics used for food animal production. However, there are no data on the effectiveness of antibiotic removal in reducing AR shared through horizontal gene transfer (HGT). In this study, we used neonatal broiler chicks and Salmonella enterica serovar Heidelberg, a model food pathogen, to test if chicks raised antibiotic free harbor transferable AR. We challenged chicks with an antibiotic-susceptible S. Heidelberg strain using various routes of inoculation and determined if S. Heidelberg isolates recovered carried plasmids conferring AR. We used antimicrobial susceptibility testing and whole-genome sequencing (WGS) to show that chicks grown without antibiotics harbored an antimicrobial resistant S. Heidelberg population at 14 days after challenge and chicks challenged orally acquired AR at a higher rate than chicks inoculated via the cloaca. Using 16S rRNA gene sequencing, we found that S. Heidelberg infection perturbed the microbiota of broiler chicks, and we used metagenomics and WGS to confirm that a commensal Escherichia coli population was the main reservoir of an IncI1 plasmid acquired by S. Heidelberg. The carriage of this IncI1 plasmid posed no fitness cost to S. Heidelberg but increased its fitness when exposed to acidic pH in vitro. These results suggest that HGT of plasmids carrying AR shaped the evolution of S. Heidelberg and that antibiotic use reduction alone is insufficient to limit antibiotic resistance transfer from commensal bacteria to Salmonella enterica.

IMPORTANCE The reported increase in antibiotic-resistant bacteria in humans has resulted in a major shift away from antibiotic use in food animal production. This shift has been driven by the assumption that removing antibiotics will select for antibiotic susceptible bacterial taxa, which in turn will allow the currently available antibiotic arsenal to be more effective. This change in practice has highlighted new questions that need to be answered to assess the effectiveness of antibiotic removal in reducing the spread of antibiotic resistance bacteria. This research demonstrates that antibiotic-susceptible Salmonella enterica serovar Heidelberg strains can acquire multidrug resistance from commensal bacteria present in the gut of neonatal broiler chicks, even in the absence of antibiotic selection. We demonstrate that exposure to acidic pH drove the horizontal transfer of antimicrobial resistance plasmids and suggest that simply removing antibiotics from food animal production might not be sufficient to limit the spread of antimicrobial resistance.

Strategies to Improve Poultry Food Safety, a Landscape Review

Food safety remains a significant public health issue for the poultry industry. Foodborne pathogens can be in contact at all phases of poultry production, from initial hatch to processing and ultimately to retail and meal preparation. Salmonella and Campylobacter have been considered the primary foodborne pathogens associated with poultry. Both organisms are major causative agents of human foodborne illness. Limiting these pathogens in poultry production requires identifying their sources and routes of transmission. This involves the ability to isolate and precisely identify them using methodologies capable of discernment at the genome level. Interventions to reduce their occurrence in poultry production employ two basic strategies: prevention of establishment and elimination of already-established pathogens. This review provides an overview of current findings and prospects for further research on poultry food safety issues.

Formic Acid as an Antimicrobial for Poultry Production: A Review

Organic acids continue to receive considerable attention as feed additives for animal production. Most of the emphasis to date has focused on food safety aspects, particularly on lowering the incidence of foodborne pathogens in poultry and other livestock. Several organic acids are currently either being examined or are already being implemented in commercial settings. Among the several organic acids that have been studied extensively, is formic acid. Formic acid has been added to poultry diets as a means to limit Salmonella spp. and other foodborne pathogens both in the feed and potentially in the gastrointestinal tract once consumed. As more becomes known about the efficacy and impact formic acid has on both the host and foodborne pathogens, it is clear that the presence of formic acid can trigger certain pathways in Salmonella spp. This response may become more complex when formic acid enters the gastrointestinal tract and interacts not only with Salmonella spp. that has colonized the gastrointestinal tract but the indigenous microbial community as well. This review will cover current findings and prospects for further research on the poultry microbiome and feeds treated with formic acid.

Prior exposure of agriculture cephalosporin ceftiofur impaired conjugation of blaCTX-M-65 gene-bearing plasmid in Salmonella Saintpaul

AIMS

Although a link between agricultural cephalosporin use and resistance in Salmonella has been demonstrated with the drug ceftiofur, the underlying mechanism of the correlation is unclear. This study investigated the impact of ceftiofur exposure in S. Saintpaul on ceftriaxone resistance, the gene expression and the conjugative transfer of the bla_CTX-M-65 gene.

METHODS AND RESULTS

Prior ceftiofur exposure caused a twofold increase in MIC from 1024 to 2048 µg ml^-1 towards ceftriaxone and increased the enzymatic activity of Bla_CTX-M-65 2·2 folds from 3·46 to 7·67 nmol nitrocefin hydrolysed min^-1 . A threefold upregulation in gene expression of the bla_CTX-M-65 gene was also observed. Donors exposed to ceftiofur subsequently demonstrated a 2·5-fold decrease in transfer efficiency.

CONCLUSIONS

Prior exposure of S. Saintpaul to ceftiofur led to increased phenotypic resistance towards ceftriaxone while its ability to spread the cephalosporin resistance through conjugation, conversely, was impaired.

SIGNIFICANCE AND IMPACT OF THE STUDY

Findings from this study shed light on one possible mechanism in which agricultural cephalosporin exposure in Salmonella may subsequently impact clinical treatment. The finding that cephalosporin exposure in donors may hinder the subsequent spread of resistance instead of aiding it up was counter-intuitive.

Effects of treatment with enrofloxacin or tulathromycin on fecal microbiota composition and genetic function of dairy calves

The increasing concerns with antimicrobial resistance highlights the need for studies evaluating the impacts of antimicrobial use in livestock on antimicrobial resistance using new sequencing technologies. Through shotgun sequencing, we investigated the changes in the fecal microbiome composition and function, with a focus on functions related to antimicrobial resistance, of dairy calves. Heifers 2 to 3 weeks old, which were not treated with antibiotics by the farm before enrollment, were randomly allocated to one of three study groups: control (no treatment), a single treatment of enrofloxacin, or a single treatment of tulathromycin. Fecal samples were collected at days 4, 14, 56 and 112 days after enrollment, and DNA extraction and sequencing was conducted. The effect of antibiotic treatment on each taxon and genetic functional level by time (including Day 0 as a covariate) revealed few changes in the microbiota. At the genus level, enrofloxacin group had higher relative abundance of Blautia, Coprococcus and Desulfovibrio and lower abundance of Bacteroides when compared to other study groups. The SEED database was used for genetic functional analyses, which showed that calves in the enrofloxacin group started with a higher relative abundance of "Resistance to antibiotics and toxic compounds" function on Day 0, however an increase in antibiotic resistance genes after treatment with enrofloxacin was not observed. "Resistance to Fluoroquinolones" and "Erythromycin resistance", of relevance given the study groups, were not statistically different in relative abundance between study groups. "Resistance to fluoroquinolones" increased during the study period regardless of study group. Despite small differences over the first weeks between study groups, at Day 112 the microbiota composition and genetic functional profile was similar among all study groups. In our study, enrofloxacin or tulathromycin had minimal impacts on the microbial composition and genetic functional microbiota of calves over the study period.

Effect of Polymer Demixed Nanotopographies on Bacterial Adhesion and Biofilm Formation

As the current global threat of antimicrobial resistance (AMR) persists, developing alternatives to antibiotics that are less susceptible to resistance is becoming an urgent necessity. Recent advances in biomaterials have allowed for the development and fabrication of materials with discrete surface nanotopographies that can deter bacteria from adhering to their surface. Using binary polymer blends of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polycaprolactone (PCL) and varying their relative concentrations, PS/PCL, PS/PMMA and PCL/PMMA polymer demixed thin films were developed with nanoisland, nanoribbon and nanopit topographies. In the PS/PCL system, PS segregates to the air-polymer interface, with the lower solubility PCL preferring the substrate-polymer interface. In the PS/PMMA and PCL/PMMA systems, PMMA prefers the air-polymer interface due to its greater solubility and lower surface energy. The anti-adhesion efficacy of the demixed films were tested against Pseudomonas aeruginosa (PA14). PS/PCL and PCL/PMMA demixed films showed a significant reduction in cell counts adhered on their surfaces compared to pure polymer control films, while no reduction was observed in the counts adhered on PS/PMMA demixed films. While the specific morphology did not affect the adhesion, a relationship between bacterial cell and topographical surface feature size was apparent. If the surface feature was smaller than the cell, then an anti-adhesion effect was observed; if the surface feature was larger than the cell, then the bacteria preferred to adhere.

Stress tolerance of Staphylococcus aureus with different antibiotic resistance profiles

Staphylococcus aureus (S. aureus) is a zoonotic bacterium and is among the most important pathogens causing bacterial foodborne diseases. In recent years, disease caused by antibiotic-resistant S. aureus is a serious clinical problem that poses a great threat to public health. In this study, we examined the drug-resistance phenotypes and genotypes of 9 S. aureus strains. One strain was obtained from the China Center for Type Culture Collection (CCTCC), and the remaining eight strains were isolated from food. Two common methods (the Kirby-Bauer disk diffusion and broth microdilution methods) were used to detect bacterial drug resistance. Then, we analysed the relationship between the bacterial drug resistance phenotypes and genotypes. We found that some S. aureus strains isolated from food were drug-resistant or even multi-drug resistant and that there was not a perfect match between resistance phenotypes and genotypes. The viabilities of the drug-sensitive (DS), drug-resistant (DR), and multi-drug resistant (MDR) S. aureus strains were also compared when they were exposed to conditions of acid (HCl, pH = 1.5), heat (63 °C), and osmotic pressure (30% NaCl). The results showed that the DR and MDR bacterial strains had survival rates similar to or higher than those of the DS strains under environmental stress.

Screening of crows and waterfowls for Salmonella and Listeria monocytogenes infection

Background and Aim: Wild birds can carry a number of potential human and animal pathogens. These birds can intrude into human habitats giving the opportunity to transmission of such infection. Therefore, the current study was designed to investigate the role of crows and waterfowls as vectors of Salmonella and Listeria monocytogenes and to compare cultivation methods with direct polymerase chain reaction (PCR) for the detection of infection. Materials and Methods: A total of 200 fecal dropping samples were collected. Salmonella was cultivated by three step method (Universal Pre-enrichment Broth [UPB], Rappaport-Vassiliadis Broth, and Xylose Lysine Desoxycholate agar). The recovered isolates were characterized by biotyping, serotyping, and PCR detection of enterotoxin (stn) gene. The antibiogram pattern of isolates against a panel of 8 antibiotics was recorded. L. monocytogenes was cultivated on UPB, then on Listeria Oxford Agar and Listeria CHROMagar. The recovered isolates were characterized by biotyping and PCR detection of listeriolysin (hylA) gene. Results: The percentages of Salmonella infection in crows and waterfowls were 10 and 20, respectively. The most frequently recovered serovars were Typhimurium, Potengi, Enteritidis, and Kentucky. Antimicrobial susceptibility analysis of Salmonella isolates showed that the resistance rates for gentamicin were the highest (92%), followed by amoxicillin (88%) and cefixime (60%). Resistance to 8 antibiotics was recorded in 60% (15/25) of Salmonella isolates. The percentages of L. monocytogenes infection in crows and waterfowls were 1.3 and 2, respectively. Direct PCR applied to UPB revealed that 12% and 3% of samples were positive for Salmonella and L. monocytogenes, respectively, and there was no significant difference between direct PCR and cultivation method for the detection of infection. Conclusion: The present findings indicate that wild birds can harbor zoonotic enteric pathogens and this necessitates monitoring the epidemiologic status of these pathogens among wild birds and humans and applying the appropriate intervention measures to prevent the spread of infection.

Impedance Spectroscopic Detection of Binding and Reactions in Acid-Labile Dielectric Polymers for Biosensor Applications

We synthesized previously unreported copolymers with cleavable acid-labile side chains for use as electrochemical sensing layers in order to demonstrate a novel architecture for a one-step immunosensor. This one-step system is in contrast to most antigen-capture signal amplification methods that involve complicated secondary labeling techniques, or require the addition of redox probes to achieve a sensing response. A series of novel copolymers composed of various trityl-containing monomers were synthesized and characterized to determine their dielectric properties. Results indicate that the thin films of these polymers are stable in water, but some begin to degrade under acidic conditions or upon antigen binding, causing observable changes in the phase angle.

Class 1 integrons and plasmid-mediated multiple resistance genes of the Campylobacter species from pediatric patient of a university hospital in Taiwan

Background

The Campylobacter species usually causes infection between humans and livestock interaction via livestock breeding. The studies of the Campylobacter species thus far in all clinical isolates were to show the many kinds of antibiotic phenomenon that were produced. Their integrons cause the induction of antibiotic resistance between bacterial species in the Campylobacter species.

Results

The bacterial strains from the diarrhea of pediatric patient which isolated by China Medical University Hospital storage bank. These isolates were identified by MALDI-TOF mass spectrometry. The anti-microbial susceptibility test showed that Campylobacter species resistant to cefepime, streptomycin, tobramycin and trimethoprim/sulfamethoxazole (all C. jejuni and C. coli isolates), ampicillin (89% of C. jejuni; 75% of C. coli), cefotaxime (78% of C. jejuni; 100% of C. coli), nalidixic acid (78% of C. jejuni; 100% of C. coli), tetracycline (89% of C. jejuni; 25% C. coli), ciprofloxacin (67% of C. jejuni; 50% C. coli), kanamycin (33% of C. jejuni; 75% C. coli) and the C. fetus isolate resisted to ampicillin, cefotaxime, nalidixic acid, tetracycline, ciprofloxacin, kanamycin by disc-diffusion method. The effect for ciprofloxacin and tetracycline of the Campylobacter species was tested using an E-test. The tet, erm, and integron genes were detected by PCR assay. According to the sequencing analysis (type I: dfr12-gcuF-aadA2 genes and type II: dfrA7 gene), the cassette type was identified. The most common gene cassette type (type I: 9 C. jejuni and 2 C. coli isolates; type II: 1 C. coli isolates) was found in 12 class I integrase-positive isolates.

Conclusions

Our results suggested an important information in the latency of Campylobacter species with resistance genes, and irrational antimicrobial use should be concerned.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-017-0199-4) contains supplementary material, which is available to authorized users.

Comparison of antimicrobial resistant genes in chicken gut microbiome grown on organic and conventional diet

Antibiotics are widely used in chicken production for therapeutic purposes, disease prevention and growth promotion, and this may select for drug resistant microorganisms known to spread to humans through consumption of contaminated food. Raising chickens on an organic feed regimen, without the use of antibiotics, is increasingly popular with the consumers. In order to determine the effects of diet regimen on antibiotic resistant genes in the gut microbiome, we analyzed the phylotypes and identified the antimicrobial resistant genes in chicken, grown under conventional and organic dietary regimens. Phylotypes were analyzed from DNA extracted from fecal samples from chickens grown under these dietary conditions. While gut microbiota of chicken raised in both conventional and organic diet exhibited the presence of DNA from members of Proteobacteria and Bacteroidetes, organic diet favored the growth of members of Fusobacteria. Antimicrobial resistance genes were identified from metagenomic libraries following cloning and sequencing of DNA fragments from fecal samples and selecting for the resistant clones (n=340) on media containing different concentrations of eight antibiotics. The antimicrobial resistant genes exhibited diversity in their host distribution among the microbial population and expressed more in samples from chicken grown on a conventional diet at higher concentrations of certain antimicrobials than samples from chicken grown on organic diet. Further studies will elucidate if this phenomena is widespread and whether the antimicrobial resistance is indeed modulated by diet. This may potentially assist in defining strategies for intervention to reduce the prevalence and dissemination of antibiotic resistance genes in the production environment.

Impact of Timing and Dosage of a Fluoroquinolone Treatment on the Microbiological, Pathological, and Clinical Outcomes of Calves Challenged with Mannheimia haemolytica

The efficacy of an early and low inoculum-adjusted marbofloxacin treatment was evaluated on microbiological and clinical outcomes in calves infected with 4.10⁷ CFU of Mannheimia haemolytica A1. Twenty-two calves were included based on their rectal temperature rise in the 10 h after challenge and allocated in four groups, receiving a single intramuscular injection of saline (CON), 2 mg/kg marbofloxacin 2–4 h after inclusion (early treatment, E2), 2 or 10 mg/kg marbofloxacin 35–39 h after inclusion (late treatments, L2, L10). In CON calves, M. haemolytica DNA loads in bronchoalveolar lavages continuously increased from inclusion to day 4, and were associated with persistent respiratory clinical signs and lung lesions. At times of early and late treatments, M. haemolytica loads ranged within 3.5–4 and 5.5–6 log₁₀ DNA copies/mL, respectively. Early 2 mg/kg marbofloxacin treatment led to rapid and total elimination of bacteria in all calves. The late treatments induced a reduction of bacterial loads, but 3 of 6 L2 and 1 of 6 L10 calves were still positive for M. haemolytica at day 4. Except for CON calves, all animals exhibited clinical improvement within 24 h after treatment. However, early 2 mg/kg treatment was more efficacious to prevent pulmonary lesions, as indicated by the reduction of the extension and severity of gross lesions and by the histopathological scores. These results demonstrated for the first time that a reduced antibiotic regimen given at an early stage of the disease and targeting a low bacterial load could be efficacious in a natural bovine model of pneumonia.

Prevalence of Nontyphoidal Salmonella and Salmonella Strains with Conjugative Antimicrobial-Resistant Serovars Contaminating Animal Feed in Texas

The objective of this study was to characterize 365 nontyphoidal Salmonella enterica isolates from animal feed. Among the 365 isolates, 78 serovars were identified. Twenty-four isolates (7.0%) were recovered from three of six medicated feed types. Three of these isolates derived from the medicated feed, Salmonella Newport, Salmonella Typhimurium var. O 5- (Copenhagen), and Salmonella Lexington var. 15+ (Manila), displayed antimicrobial resistance. Susceptibility testing revealed that only 3.0% (12) of the 365 isolates displayed resistance to any of the antimicrobial agents. These 12 isolates were recovered from unmedicated dry beef feed (n = 3), medicated dry beef feed (n = 3), cabbage culls (n = 2), animal protein products (n = 2), dry dairy cattle feed (n = 1), and fish meal (n = 1). Only Salmonella Newport and Salmonella Typhimurium var. O 5- (Copenhagen) were multidrug resistant. Both isolates possessed the IncA/C replicon and the blaCMY-2 gene associated with cephalosporin resistance. Plasmid replicons were amplified from 4 of 12 resistant isolates. Plasmids (40 kb) were Salmonella Montevideo and Salmonella Kentucky. Conjugation experiments were done using 7 of the 12 resistant isolates as donors. Only Salmonella Montevideo, possessing a plasmid and amplifying IncN, produced transconjugants. Transconjugants displayed the same antimicrobial resistance profile as did the donor isolate. Three isolates that amplified replicons corresponding to IncA/C or IncHI2 did not produce transconjugants at 30 or 37°C. The results of this study suggest that the prevalence of antimicrobial-resistant Salmonella contaminating animal feed is low in Texas. However, Salmonella was more prevalent in feed by-products; fish meal had the highest prevalence (84%) followed by animal protein products (48%). Ten of the 35 feed types had no Salmonella contamination. Further investigation is needed to understand the possible role of specific feed types in the dissemination of antimicrobial resistant bacteria.

Agriculture and food animals as a source of antimicrobial-resistant bacteria

One of the major breakthroughs in the history of medicine is undoubtedly the discovery of antibiotics. Their use in animal husbandry and veterinary medicine has resulted in healthier and more productive farm animals, ensuring the welfare and health of both animals and humans. Unfortunately, from the first use of penicillin, the resistance countdown started to tick. Nowadays, the infections caused by antibiotic-resistant bacteria are increasing, and resistance to antibiotics is probably the major public health problem. Antibiotic use in farm animals has been criticized for contributing to the emergence of resistance. The use and misuse of antibiotics in farm animal settings as growth promoters or as nonspecific means of infection prevention and treatment has boosted antibiotic consumption and resistance among bacteria in the animal habitat. This reservoir of resistance can be transmitted directly or indirectly to humans through food consumption and direct or indirect contact. Resistant bacteria can cause serious health effects directly or via the transmission of the antibiotic resistance traits to pathogens, causing illnesses that are difficult to treat and that therefore have higher morbidity and mortality rates. In addition, the selection and proliferation of antibiotic-resistant strains can be disseminated to the environment via animal waste, enhancing the resistance reservoir that exists in the environmental microbiome. In this review, an effort is made to highlight the various factors that contribute to the emergence of antibiotic resistance in farm animals and to provide some insights into possible solutions to this major health issue.

Strategic measures for the control of surging antimicrobial resistance in Hong Kong and mainland of China

Antimicrobial-resistant bacteria are either highly prevalent or increasing rapidly in Hong Kong and China. Treatment options for these bacteria are generally limited, less effective and more expensive. The emergence and dynamics of antimicrobial resistance genes in bacteria circulating between animals, the environment and humans are not entirely known. Nonetheless, selective pressure by antibiotics on the microbiomes of animal and human, and their associated environments (especially farms and healthcare institutions), sewage systems and soil are likely to confer survival advantages upon bacteria with antimicrobial-resistance genes, which may be further disseminated through plasmids or transposons with integrons. Therefore, antibiotic use must be tightly regulated to eliminate such selective pressure, including the illegalization of antibiotics as growth promoters in animal feed and regulation of antibiotic use in veterinary practice and human medicine. Heightened awareness of infection control measures to reduce the risk of acquiring resistant bacteria is essential, especially during antimicrobial use or institutionalization in healthcare facilities. The transmission cycle must be interrupted by proper hand hygiene, environmental cleaning, avoidance of undercooked or raw food and compliance with infection control measures by healthcare workers, visitors and patients, especially during treatment with antibiotics. In addition to these routine measures, proactive microbiological screening of hospitalized patients with risk factors for carrying resistant bacteria, including history of travel to endemic countries, transfer from other hospitals, and prolonged hospitalization; directly observed hand hygiene before oral intake of drugs, food and drinks; and targeted disinfection of high-touch or mutual-touch items, such as bed rails and bed curtains, are important. Transparency of surveillance data from each institute for public scrutiny provides an incentive for controlling antimicrobial resistance in healthcare settings at an administrative level.

High-level recombinant human lysozyme expressed in milk of transgenic pigs can inhibit the growth of Escherichia coli in the duodenum and influence intestinal morphology of sucking pigs

Lysozyme is often used as a feed additive and acts as an antimicrobial protein that enhances immune function and defends against pathogenic bacteria in pigs. In this study, we genetically added recombinant human lysozyme (rhLZ) to sow milk by somatic cell nuclear transfer and investigated whether the presence of recombinant human lysozyme can influence intestinal microbiota and morphology in sucking pigs. We generated transgenic cloned pigs and the first-generation hybrids (F1) produced high levels of rhLZ in milk. The average concentration of rhLZ was 116.34 ± 24.46 mg/L in the milk of F1 sows, which was 1500-fold higher than that of the native pig lysozyme. In vitro, it was demonstrated that rhLZ in milk of transgenic pigs had enzyme levels at 92,272 ± 26,413 U/mL. In a feeding experiment, a total of 40 newborn piglets were nursed by four transgenic sows and four sibling non-transgenic sows (F1), with five piglets per gilt. The piglets were allowed to nurse for 21 days and the sow milk was the only source of nutrition for the piglets. All piglets were slaughtered on postnatal day 22. Six types of bacteria were cultured and analyzed to detect the impact of rhLZ on gut microbiota. The number of Escherichia coli in the duodenum of piglets reared by transgenic sows was significantly decreased (p<0.001) and their villus height to crypt depth ratio in the intestine were increased due to the significant decrease of crypt depth in the duodenum, jejunum, and ileum (p<0.001). Together, we successfully generated rhLZ transgenic cloned pigs and elevated lysozyme level in nuring piglets. The results of the feeding experiments demonstrated that rhLZ-enhanced milk can inhibit the growth of E. coli in the duodenum and positively influence intestinal morphology without adversely affecting weight gain or piglet growth.

Obesity in the United States - dysbiosis from exposure to low-dose antibiotics?

The rapid increase in obesity prevalence in the United States in the last 20 years is unprecedented and not well explained. Here, we explore a hypothesis that the obesity epidemic may be driven by population-wide chronic exposures to low-residue antibiotics that have increasingly entered the American food chain over the same time period. We propose this hypothesis based on two recent bodies of published reports – (1) those that provide evidence for the spread of antibiotics into the American food chain, and (2) those that examine the relationship between the gut microbiota and body physiology. The livestock use of antimicrobial agents has sharply increased in the US over the same 20-year period of the obesity epidemic, especially with the expansion of intensified livestock production, such as the concentrated animal feeding operations. Observational and experimental studies support the idea that changes in the intestinal microbiota exert a profound effect on body physiology. We propose that chronic exposures to low-residue antimicrobial drugs in food could disrupt the equilibrium state of intestinal microbiota and cause dysbiosis that can contribute to changes in body physiology. The obesity epidemic in the United States may be partly driven by the mass exposure of Americans to food containing low-residue antimicrobial agents. While this hypothesis cannot discount the impact of diet and other factors associated with obesity, we believe studies are warranted to consider this possible driver of the epidemic.

Identification of novel antimicrobial resistance genes from microbiota on retail spinach

BACKGROUND

Drug resistance genes and their mobile genetic elements are frequently identified from environmental saprophytic organisms. It is widely accepted that the use of antibiotics in animal husbandry selects for drug resistant microorganisms, which are then spread from the farm environment to humans through the consumption of contaminated food products. We wished to identify novel drug resistance genes from microbial communities on retail food products. Here, we chose to study the microbial communities on retail spinach because it is commonly eaten raw and has previously been associated with outbreaks of bacterial infections.

RESULTS

We created metagenomic plasmid libraries from microbiota isolated from retail spinach samples. We identified five unique plasmids that increased resistance to antimicrobial drugs in the E. coli host. These plasmids were identified in E. coli that grew on plates that contained ampicillin (pAMP), aztreonam (pAZT), ciprofloxacin (pCIP), trimethoprim (pTRM), and trimethoprim-sulfamethoxazole (pSXT). We identified open reading frames with similarity to known classes of drug resistance genes in the DNA inserts of all 5 plasmids. These drug resistance genes conferred resistance to fluoroquinolones, cephalosporins, and trimethoprim, which are classes of antimicrobial drugs frequently used to treat human Gram negative bacterial infections. These results show that novel drug resistance genes are found in microbiota on retail produce items.

CONCLUSIONS

Here we show that microbiota of retail spinach contains DNA sequences previously unidentified as conferring antibiotic resistance. Many of these novel sequences show similarity to genes found in species of bacteria, which have previously been identified as commensal or saprophytic bacteria found on plants. We showed that these resistance genes are capable of conferring clinically relevant levels of resistance to antimicrobial agents. Food saprophytes may serve as an important reservoir for new drug-resistance determinants in human pathogens.

Comparison of predicted epimerases and reductases of the Campylobacter jejuni D-altro- and L-gluco-heptose synthesis pathways

Uniquely modified heptoses found in surface carbohydrates of bacterial pathogens are potential therapeutic targets against such pathogens. Our recent biochemical characterization of the GDP-6-deoxy-D-manno- and GDP-6-deoxy-D-altro-heptose biosynthesis pathways has provided the foundation for elucidation of the more complex L-gluco-heptose synthesis pathway of Campylobacter jejuni strain NCTC 11168. In this work we use GDP-4-keto,6-deoxy-D-lyxo-heptose as a surrogate substrate to characterize three enzymes predicted to be involved in this pathway: WcaGNCTC (also known as Cj1427), MlghB (Cj1430), and MlghC (Cj1428). We compare them with homologues involved in d-altro-heptose production: WcaG81176 (formerly WcaG), DdahB (Cjj1430), and DdahC (Cjj1427). We show that despite high levels of similarity, the enzymes have pathway-specific catalytic activities and substrate specificities. MlghB forms three products via C3 and C5 epimerization activities, whereas its DdahB homologue only had C3 epimerase activity along its cognate pathway. MlghC is specific for the double C3/C5 epimer generated by MlghB and produces L-gluco-heptose via stereospecific C4 reductase activity. In contrast, its homologue DdahC only uses the C3 epimer to yield d-altro-heptose via C4 reduction. Finally, we show that WcaGNCTC is not necessary for L-gluco-heptose synthesis and does not affect its production by MlghB and MlghC, in contrast to its homologue WcaG81176, that has regulatory activity on d-altro-heptose synthesis. These studies expand our fundamental understanding of heptose modification, provide new glycobiology tools to synthesize novel heptose derivatives with biomedical applications, and provide a foundation for the structure function analysis of these enzymes.

Protective mechanism of curcumin against Vibrio vulnificus infection

Curcumin, a natural polyphenolic flavonoid extracted from the rhizome of Curcuma longa L., has many beneficial biological activities. However, there are relatively few reports of the effects of curcumin on pathogen infections. This study examined the effect of curcumin on a Vibrio vulnificus infection. The cytotoxicity of V. vulnificus to HeLa cells was significantly inhibited by curcumin (at 10 or 30 μM). To further examine the inhibitory mechanism of curcumin against V. vulnificus-mediated cytotoxicity, the level of bacterial growth, bacterial motility, cell adhesion, RTX toxin expression and host cell reactions were evaluated. Curcumin inhibited V. vulnificus growth in HI broth. Curcumin inhibited both bacterial adhesion and RTX toxin binding to the host cells, which can be considered the major protective mechanisms for the decrease in V. vulnificus cytotoxicity. Curcumin also inhibited host cell rounding and actin aggregation, which are the early features of cell death caused by V. vulnificus. In addition, curcumin decreased the V. vulnificus-induced NF-κB translocation in HeLa cells. Finally, curcumin protected mice from V. vulnificus-induced septicemia. In conclusion, curcumin may be an alternative antimicrobial agent against fatal bacterial infections.

Simultaneous analysis of free and conjugated estrogens, sulfonamides, and tetracyclines in runoff water and soils using solid-phase extraction and liquid chromatography-tandem mass spectrometry

The ability to monitor multiple analytes from various classes of compounds in a single analysis can increase throughput and reduce cost when compared to traditional methods of analyses. This method for analyzing free (parent estrogen) and conjugated estrogens (metabolites) along with sulfonamides and tetracyclines utilizes a high pH (10.4) mobile phase with an ammonium hydroxide buffer for both positive- and negative-mode electrospray ionization. A single-step sample preparation by solid-phase extraction (SPE) was used to isolate and concentrate all analytes simultaneously. The analytical method was developed and validated for recoveries at 3 concentration levels for water and soil and produced recoveries of 42-123% and 21-105% respectively. Method detection limits ranged from 0.3 to 1.0 ng/L for water samples and 0.01 to 0.1 ng/g for soils. The method quantification limit ranged from 0.9 to 3.3 ng/L for water samples and 0.06 to 0.7 ng/g for soils. The single-point standard addition calibration procedure was validated across a linear range of MQL to 100 ng/L with ≥82% accuracy against a matrix matched standard curve. Furthermore, sorption of tetracyclines onto glassware was investigated and minimized by 10% using nitric acid-rinsed glassware, while separation parameters were further optimized based on retention time and signal responses. This method has been used for the quantification of estrogens, tetracyclines, and sulfonamides in soil and runoff waters with multiple compounds detected simultaneously in a single analysis.

Dose imprecision and resistance: free-choice medicated feeds in industrial food animal production in the United States

BACKGROUND

Industrial food animal production employs many of the same antibiotics or classes of antibiotics that are used in human medicine. These drugs can be administered to food animals in the form of free-choice medicated feeds (FCMF), where animals choose how much feed to consume. Routine administration of these drugs to livestock selects for microorganisms that are resistant to medications critical to the treatment of clinical infections in humans.

OBJECTIVES

In this commentary, we discuss the history of medicated feeds, the nature of FCMF use with regard to dose delivery, and U.S. policies that address antimicrobial drug use in food animals.

DISCUSSION

FCMF makes delivering a predictable, accurate, and intended dose difficult. Overdosing can lead to animal toxicity; underdosing or inconsistent dosing can result in a failure to resolve animal diseases and in the development of antimicrobial-resistant microorganisms.

CONCLUSIONS

The delivery of antibiotics to food animals for reasons other than the treatment of clinically diagnosed disease, especially via free-choice feeding methods, should be reconsidered.

Development of a DNA microarray for enterococcal species, virulence, and antibiotic resistance gene determinations among isolates from poultry

A DNA microarray (Enteroarray) was designed with probes targeting four species-specific taxonomic identifiers to discriminate among 18 different enterococcal species, while other probes were designed to identify 18 virulence factors and 174 antibiotic resistance genes. In total, 262 genes were utilized for rapid species identification of enterococcal isolates, while characterizing their virulence potential through the simultaneous identification of endogenous antibiotic resistance and virulence genes. Enterococcal isolates from broiler chicken farms were initially identified by using the API 20 Strep system, and the results were compared to those obtained with the taxonomic genes atpA, recA, pheS, and ddl represented on our microarray. Among the 171 isolates studied, five different enterococcal species were identified by using the API 20 Strep system: Enterococcus faecium, E. faecalis, E. durans, E. gallinarum, and E. avium. The Enteroarray detected the same species as API 20 Strep, as well as two more: E. casseliflavus and E. hirae. Species comparisons resulted in 15% (27 isolates) disagreement between the two methods among the five API 20 Strep identifiable species and 24% (42 isolates) disagreement when considering the seven Enteroarray identified species. The species specificity of key antibiotic and virulence genes identified by the Enteroarray were consistent with the literature adding further robustness to the redundant taxonomic probe data. Sequencing of the cpn60 gene further confirmed the complete accuracy of the microarray results. The new Enteroarray should prove to be a useful tool to accurately genotype strains of enterococci and assess their virulence potential.

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.

Antimicrobial resistance in Campylobacter coli selected by tylosin treatment at a pig farm

Limited knowledge is available regarding the dynamics of macrolide resistance under farm conditions with natural Campylobacter populations. We examined the dynamics of antimicrobial resistance in Campylobacter coli at a large pig farm. Faeces were sampled from untreated sows and piglets (n=57), weaned pigs treated with tylosin (n=68) and pigs of the same group 3-5 weeks after withdrawal of tylosin (n=15). Additionally, 48 weaned pigs were sampled after tylosin had not been administered for 7 months at the farm. MICs for seven antimicrobials were determined, isolates were genotyped by PFGE and mutations conferring macrolide resistance were identified. Resistance to at least one antimicrobial agent was higher (P<0.001) in the isolates from the treated pigs (30 of 56) than in those from the untreated animals (2 of 40). Resistance to ciprofloxacin, erythromycin, nalidixic acid and streptomycin was higher (P<0.05) in the isolates from the treated pigs than in those from the untreated animals. All 14 erythromycin-resistant isolates studied (MIC ≥ 512 μg/ml) contained mutation A2075G in 23S rRNA. Resistance against at least one antimicrobial was significantly lower (P<0.05) when tylosin had not been administered for 7 months. Resistance to erythromycin and streptomycin also decreased (P<0.05). PFGE analysis revealed a change of genotypes induced by tylosin treatment. In conclusion, tylosin treatment of pigs selected for a high-level of resistance to erythromycin and resistance to ciprofloxacin, nalidixic acid and streptomycin also increased in C. coli isolates within a few days.

Antibiotic resistance genes in the vaginal microbiota of primates not normally exposed to antibiotics

Previous studies of resistance gene ecology have focused primarily on populations such as hospital patients and farm animals that are regularly exposed to antibiotics. Also, these studies have tended to focus on numerically minor populations such as enterics or enterococci. We report here a cultivation-independent approach that allowed us to assess the presence of antibiotic resistance genes in the numerically predominant populations of the vaginal microbiota of two populations of primates that are seldom or never exposed to antibiotics: baboons and mangabeys. Most of these animals were part of a captive colony in Texas that is used for scientific studies of female physiology and physical anthropology topics. Samples from some wild baboons were also tested. Vaginal swab samples, obtained in connection with a study designed to define the normal microbiota of the female vaginal canal, were tested for the presence of two types of antibiotic resistance genes: tetracycline resistance (tet) genes and erythromycin resistance (erm) genes. These genes are frequently found in human isolates of the two types of bacteria that were a substantial part of the normal microbiota of primates (Firmicutes and Bacteroidetes). Since cultivation was not feasible, polymerase chain reaction and DNA sequencing were used to detect and characterize these resistance genes. The tet(M) and tet(W) genes were found most commonly, and the tet(Q) gene was found in over a third of the samples from baboons. The ermB and ermF genes were found only in a minority of the samples. The ermG gene was not found in any of the specimens tested. Polymerase chain reaction analysis showed that at least some tet(M) and tet(Q) genes were genetically linked to DNA from known conjugative transposons (CTns), Tn916 and CTnDOT. Our results raise questions about the extent to which extensive exposure to antibiotics is the only pressure necessary to maintain resistance genes in natural settings.

Sorption mechanisms of cephapirin, a veterinary antibiotic, onto quartz and feldspar minerals as detected by Raman spectroscopy

Raman spectroscopy was used to investigate sorption mechanisms of cephapirin (CHP), a veterinary antibiotic, onto quartz (SiO(2)) and feldspar (KAlSi(3)O(8)) at different pH. Sorption occurs by electrostatic attraction, monodentate and bidentate complexation. The zwitterion (CHP(o)) adsorbs to a quartz((+)) surface by electrostatic attraction of the carboxylate anion group (-COO(-)) at low pH, but adsorbs to a quartz((-)) surface through electrostatic attraction of the pyridinium cation, and possibly COO(-) bridge complexes, at higher pH. CHP(-) bonds to quartz((-)) surfaces by bidentate complexation between one oxygen of -COO(-) and oxygen from carbonyl of an acetoxymethyl group. On a feldspar((+/-)) surface, CHP(o) forms monodentate complexes between CO, and possible -COO(-) bridges and/or electrostatic attachments to localized edge (hydr)oxy-Al surfaces. CHP(-) adsorbs to feldspar((-)) through monodentate CO complexation. Similar mechanisms may operate for other cephalosporins. Results demonstrate, for the first time, that Raman techniques can be effective for evaluating sorption mechanisms of antibiotics.