This study was conducted to investigate tiamulin (TML) residues in the edible tissues of orally dosed broiler chickens and to re-establish the withdrawal time (WT). Thirty-six healthy Ross broiler chickens were administered 0.5 (TML-1) and 2.5 kg (TML-2) per ton feed, respectively, of the drug containing TML 78 g/kg for 10 days. Twenty-four tissue samples were collected from 6 chickens in each of the TML-1 and TML-2 groups on 0, 1, 3, and 5 days after drug administration, respectively. The residual concentrations of TML were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The correlation coefficient of the calibration curves was 0.9978 to 0.9998, and the limits of detection and the limits of quantification (LOQ) were in the range of 0.03 to 0.06, and 0.1 to 0.2 µg/kg, respectively. Recoveries ranged between 89.0% to 116.7%, and the coefficients of variation were less than 13.9%. After the drug administration, TML in the TML-1 and TML2 groups was detected above the LOQ in 1 and 6 samples of liver, respectively, at day 0, and in 1 liver sample from both groups on day one. At 3 days after administration, TML was detected below the LOQ in all samples of TML-1 and TML-2. The calculated WT of TML in both TML-1 and TML-2 using the WT calculation program WT 1.4 was 0 days. In conclusion, the developed analytical method is suitable for detection, and the calculated WT of TML in poultry edible tissues is shorter than the current recommended WT of 7 days for TML in broiler chickens.

Susceptibility results for Pasteurella multocida and Streptococcus suis isolated from swine clinical samples were obtained from January 1998 to October 2010 from the Animal Health Laboratory at the University of Guelph, Guelph, Ontario, and used to describe variation in antimicrobial resistance (AMR) to 4 drugs of importance in the Ontario swine industry: ampicillin, tetracycline, tiamulin, and trimethoprim–sulfamethoxazole. Four temporal data-analysis options were used: visualization of trends in 12-month rolling averages, logistic-regression modeling, temporal-scan statistics, and a scan with the “What’s strange about recent events?” (WSARE) algorithm. The AMR trends varied among the antimicrobial drugs for a single pathogen and between pathogens for a single antimicrobial, suggesting that pathogen-specific AMR surveillance may be preferable to indicator data. The 4 methods provided complementary and, at times, redundant results. The most appropriate combination of analysis methods for surveillance using these data included temporal-scan statistics with a visualization method (rolling-average or predicted-probability plots following logistic-regression models). The WSARE algorithm provided interesting results for quality control and has the potential to detect new resistance patterns; however, missing data created problems for displaying the results in a way that would be meaningful to all surveillance stakeholders.

Mycoplasma bovis is a major cause of pneumonia, arthritis, and mastitis in cattle and can lead to significant economic losses. Antimicrobial resistance is a concern and further limits the already short list of drugs effective against mycoplasmas. The objective of this study was to examine changes in in vitro minimum inhibitory concentrations (MICs) of antimicrobials of aminoglycoside, fluoroquinolone, lincosamide, macrolide, pleuromutilin, phenicol, and tetracycline classes for 210 M. bovis isolates collected from 1978 to 2009. The MIC(50) values of the various antimicrobials were also compared. The MIC(50) levels for enrofloxacin and danofloxacin remained low (0.25 μg/mL) across all 3 decades. MIC(50) levels for tetracyclines, tilmicosin, and tylosin tartrate were low in the 1980s, then increased in the 1990s and remained high. In the 1980s, MIC(50) levels were low for clindamycin, spectinomycin, and tulathromycin, increased in the 1990s to 8 μg/mL (clindamycin) and 32 μg/mL (spectinomycin and tulathromycin), then decreased again in the 2000s. Members of the fluoroquinolone class of antimicrobials had the lowest MIC(50) levels across all 3 decades, which suggests in vitro susceptibility of M. bovis to this class of antimicrobials. Statistically significant associations were observed between MIC values for chlortetracycline, oxytetracycline, tylosin tartrate, and tilmicosin; between clindamycin, tulathromycin, spectinomycin, and tiamulin; and between tylosin tartrate and clindamycin. Changes in MIC levels of various antimicrobials over time show the importance of monitoring the susceptibility of mycoplasmas to antimicrobials. The number of antimicrobials that showed elevated MIC(50) levels, and therefore possibly reduced in vitro effectiveness against M. bovis, supports initiatives that promote prudent use of antimicrobials in agriculture.

Objective-To assess antimicrobial resistance and transfer of virulence genes facilitated by subtherapeutic concentrations of antimicrobials in swine intestines. Animals-20 anesthetized pigs experimentally inoculated with donor and recipient bacteria. Procedures-4 recipient pathogenic bacteria (Salmonella enterica serotype Typhimurium, Yersinia enterocolitica, Shigella flexneri, or Proteus mirabilis) were incubated with donor bacteria in the presence of subinhibitory concentrations of 1 of 16 antimicrobials in isolated ligated intestinal loops in swine. Donor Escherichia coli contained transferrable antimicrobial resistance or virulence genes. After coincubations, intestinal contents were removed and assessed for pathogens that acquired new antimicrobial resistance or virulence genes following exposure to the subtherapeutic concentrations of antimicrobials. Results-3 antimicrobials (apramycin, lincomycin, and neomycin) enhanced transfer of an antimicrobial resistance plasmid from commensal E coli organisms to Yersinia and Proteus organisms, whereas 7 antimicrobials (florfenicol, hygromycin, penicillin G, roxarsone, sulfamethazine, tetracycline, and tylosin) exacerbated transfer of an integron (Salmonella genomic island 1) from Salmonella organisms to Yersinia organisms. Sulfamethazine induced the transfer of Salmonella pathogenicity island 1 from pathogenic to nonpathogenic Salmonella organisms. Six antimicrobials (bacitracin, carbadox, erythromycin, sulfathiazole, tiamulin, and virginiamycin) did not mediate any transfer events. Sulfamethazine was the only antimicrobial implicated in 2 types of transfer events. Conclusions and Clinical Relevance-10 of 16 antimicrobials at subinhibitory or subtherapeutic concentrations augmented specific antimicrobial resistance or transfer of virulence genes into pathogenic bacteria in isolated intestinal loops in swine. Use of subtherapeutic antimicrobials in animal feed may be associated with unwanted collateral effects.

<p>A seven week floor pen trial in boxes (1,8 x 1,7 m) were conducted with 648 male and 648 female commercial Ross broilers to determine the effects of association of constant level (60 ppm) of Salinomycin and six levels (0; 10; 15; 20; 30 and 40 ppm) of Tiamulin, in six replications of 36 birds each. The rations for all treatments from 1-11, 12-23, 24-44 and 45-49 days attended the needs according to the NRC-1984 specification. All drugs were withdrawn for the four days pryor to slaughter. Body weights, feed intake and efficiency were recorded at 23 and 49 days of age. Mortality was determined at 49 days of age. When chickens were 1, 35 and 45 days old eighteen birds from each treatment were randomly collected and tested sorologically for <em>Mycoplasma sp. </em>At this same age six birds from each treatment were taked randomly necropsied and submited to score evaluation for macro and microscopic lesions. The differences among treatments were not statistically significant (P&gt;0.05) for any paramethers studies and with the following means: Body weight at 23 days (797.9 g) and 49 days (2,247.0 g). Average daily weight gain (45.0 g). Feed consumption 23 days (1,164 g) and 49 days (4,321 g). Feed efficiency 23 days (1.45) and 49 days (1.92) and mortality 49 days (6.7%). All samples presented no lesions and were negative for <em>Mycoplasma galissepticum </em>rapid soroaglulination. No detrimental effects were observed in broiler performance due to the association of salinomycin (60 ppm) and tiamulin (10 a 40 ppm).</p> | <p>A pesquisa foi conduzida no Aviário Experimental do Departamento de Produção Animal da Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, em Pirassununga, São Paulo, e teve a finalidade de verificar a possível toxicidade do anticoccidiano salinomicina pela administração simultânea do antibiótico tiamulin na ração. Foram utilizados 1.296 pintos de 01 dia, distribuídos em 36 boxes experimentais e submetidos a 6 tratamentos, com 6 repetições de 36 aves cada. O delineamento experimental foi o de blocos casualizados. Para os tratamentos foram empregados 60 ppm de salinomicina e 0; 10; 15; 20; 30 e 40 ppm de tiamulin. Os dados obtidos indicaram não haver depressão no crescimento das aves, nem tampouco no consumo de ração e conversão alimentar. Não ocorreram lesões nos sacos aéreos e os testes de soroaglutinação rápida para <em>Mycoplasma gallissepticum </em>apresentaram resultados negativos. Tendo em vista os resultados obtidos, pode-se dizer que a adição simultânea de tiamulin e salinomicina em rações de aves para corte, nos níveis utilizados, não acarreta toxicidade.</p>