Purpose: This study aimed to survey current 3rd and 4th year dental students, academic deans, and department chairs within U.S. dental schools to analyze the level of understanding; education; guidelines; and overall awareness regarding antibiotic use within dentistry and antimicrobial resistance. Methods: A 25-question survey intended for 3rd and 4th year dental students and a 20-question survey intended for academic deans and various department chairs of U.S dental schools were each developed utilizing REDCap. The survey invitations were sent via e-mail to the current academic dean of each U.S. dental school for distribution. Results: There were a total of 18 respondents from the academic dean and department chair survey and 172 student respondents. Overall, 71% of students reported that they could benefit from more education regarding antibiotics. The majority of both groups agreed that dentistry should play an important role in reducing antimicrobial resistance, but most dental students were ‘not at all familiar’ with the term antimicrobial stewardship and several were unsure if clinical guidelines were present at their schools. Conclusion: Improvements to the dental educational curriculum regarding the responsible use of antibiotics, along with the implementation of stewardship programs within dentistry are strongly encouraged.

The aim of this study was to examine whether Gram-positive cocci isolated from processed poultry in Western Australia provided a potential risk for the transfer of antimicrobial-resistant organisms to humans via commercially prepared ready-to-eat chicken. Research in this study was conducted in three phases: the characterisation of Gram-positive cocci isolated from poultry, an assessment of the isolates' thermal tolerance and the development of a Hazard Analysis Critical Control Points (HACCP) based food-safety program. In the first phase of the study, three specific objectives were investigated. The first determined the presence of Gram-positive cocci on poultry and on processing equipment from poultry-processing plants. The findings confirm the presence of staphylococci and enterococci on incoming live and slaughtered birds and processed carcasses. The data also indicate that carcasses probably become cross-contaminated during processing, when these bacteria are present on the incoming live birds and equipment. The second objective was to characterise staphylococcal isolates by antimicrobial susceptibility testing, and chromosomal and plasmid DNA analysis. The susceptibility of isolates to antimicrobial agents was tested by the disk diffusion method according to the NCCLS (National Committee for Clinical Laboratory Standards) guidelines. Isolates were typed by contour-clamped homogeneous electric field (CHEF) gel electrophoresis of SmaI digested chromosomal DNA, and plasmids were isolated by the cetyltrimethylammonium bromide (CTAB) method. Approximately 37% of Staphylococcus aureus and 16% of coagulase-negative staphylococcal (CNS) isolates were resistant to six or more of the antimicrobial agents tested. Many isolates exhibited resistance to antibiotics that are commonly used in human medicine and registered for veterinary use in Australia. / Among the S. aureus isolates there were twenty-four epidemiologically unrelated SmaI CHEF groups. All staphylococcal isolates, except three CNS, were found to harbour from one to seven plasmids. Some staphylococcal isolates with epidemiologically related CHEF patterns had similar plasmid profiles and resistance patterns. The third objective was to determine the antimicrobial susceptibility of enterococci isolates to the glycopeptide antibiotics. The isolation of two vancomycin-resistant E. faecalis isolates is the first report of VRE outside the health-care setting in Western Australia. Additionally the detection of the vanA gene in an E. gallinarum isolate, a motile enterococcus, has potentially important implications for infection control practices in hospitals. In the second phase of the study, three specific objectives were established to investigate the practical implications of these findings for the chicken industry. The first objective of this phase of the study was to determine the thermal tolerance (D and Z-values) of antimicrobial-resistant, Gram-positive cocci in ground chicken meat. The results indicate that these isolates do not exhibit enhanced thermal-resistance characteristics compared to antimicrobial-susceptible bacteria. The second objective established the internal time-temperature profiles for cooking commercially prepared chicken and estimated the process lethality (F-values). / From three cooking trials, it was confirmed that the internal temperature of at least 70°C was achieved for at least thirty-eight minutes. The third objective of this phase assessed the effectiveness of the thermal process in reducing the risk of the transfer of antimicrobial-resistant cocci via the food chain. The data confirm that the lethal effect (F-values) of the thermal process destroyed these antimicrobial-resistant cocci in commercially prepared ready-to-eat chicken. In the third phase of the study, the data obtained in the earlier parts of the study was incorporated into a model food-safety program for a fast-food chicken chain. The model was based upon the internationally accepted HACCP system, adopted by the Codex Alimentarius Commission. Mindful that the thermal-process step represents only one critical control point in the safe preparation of chicken, this preventative approach ensures that all hazards are controlled at every other step of the process. The data suggest that antimicrobial-resistant, Gram-positive cocci will be present on some ready-to-cook poultry meat processed in Western Australia. This creates opportunities for the potential spread of resistant strains or resistance genes to humans via the food chain. The information from this study will be useful in providing background data and direction for future planning in preventing antimicrobial-resistant bacteria from poultry meat being transmitted through the food chain. The full implementation of the HACCP program would offer substantial benefits and protection to consumers.

The mutant-prevention concentration (MPC) is a novel susceptibility measurement defined by a concentration threshold that would require cells to contain two concurrent resistance mutations for growth. Pneuococcal pneumonia, infections caused by <i> Pseudomonas aeruginosa</i>, and urinary tract infections caused by Gram-negative bacilli represent three distinct clinical situations for which fluoroquinolone-resistance occurs. MPC results were defined and measured for fluoroquinolones against clinical isolates of <i>Citrobacter freundii, Enterobacter cloacae, Escherichia. coli, Klebsiella pneumoniae, P. aeruginosa,</i> and <i> Streptococus pneumoniae</i>. Against clinical isolates of <i>S. pneumoniae</i>, MPC results for six fluoroquinolones were measured. Based on their potential for restricting the selection of resistant mutants, the six fluoroquinolones, in descending order, were found to be gemifloxacin > moxifloxacin > trovafloxacin > gatifloxacin > grepafloxacin > levofloxacin. For several compounds, 90% of clinical isolates that lacked a known resistance mutation had a MPC value that was close to or below the serum levels that could be attained with a dosing regimen recommended by the manufacturers. These data identify gemifloxacin, moxifloxacin and gatifloxacin as good candidates for determining whether MPC can be used as a guide for choosing and eventually administering fluoroquinolones to significantly reduce the development of fluoroquinolone ¡Vresistant <i>S. pneumoniae</i>. MPC90 results for 155 clinical isolates of <i>P. aeruginosa </i>against ciprofloxacin and levofloxacin were 4 and 16 Ýg/ml, respectively. Serum drug concentrations reported previously for standard doses were above MPC90 for 5.5 hr for ciprofloxacin and 0 hr for levofloxacin. These data suggest that superior clinical performance of ciprofloxacin correlates with activity against resistant mutant subpopulations measured in vitro. MPC results were compared with minimum inhibitory concentrations (MIC) measurements preformed by agar dilution, and microbroth dilution and minimal inhibitory concentrations (MBC) for 100 clinical isolates of <i>C. freundii </i> (n=20), <i>E. cloacae</i> (n=20), <i>E. coli</i> (n=20), <i>K. pneumoniae</i> (n=20), and <i>P. aeruginosa</i> (n=20) for ciprofloxacin, levofloxacin and garenoxacin. MPC results were 2-to-8 fold higher than MIC or MBC results. Ciprofloxacin MPC results for <i>E.coli, C. freundii, E. cloacae, K. pneumoniae</i>, and <i>P. aeruginosa</i> were 0.5, 2, 1, 1, and 4 Ýg/ml, respectively. Levofloxacin, MPC results were were 1, 2, 4, 1, and 16 Ýg/ml, respectively. Garenoxacin, MPC were 1, 8, >8, 4, and >32 Ýg/ml, respectively. Garenoxacin had the highest MIC and MPC results and was the least active compound tested against isolates of <i>C. freundii, E. cloacae</i>, and <i>P. aeruginosa</i>. These data support the rational use of quinolones in the treatments of urinary tract infections and suppression of resistance. Incorporation of the MPC measurement into dosing strategies may preserve the longevity of antimicrobial compounds for future infectious diseases.

The mutant prevention concentration (MPC) is defined as the lowest antimicrobial concentration required to inhibit the growth of the least susceptible bacterial cell based on an inoculum of ≥109 colony forming units (CFUs). The current protocol for MPC testing is technically demanding and time-consuming which limits its implementation into clinical microbiology laboratories. In an attempt to simplify the current MPC protocol we developed a modified MPC method, the microbroth dilution method, which requires two fewer days to complete than the current or traditional method. MPC values were consistent for all organisms and strains tested using both the traditional MPC method and the modified microbroth dilution MPC method.<p> Tigecycline is the first of a new class of compound glycylcyclines- with potent in vitro activity against Gram-positive organisms including penicillin-resistant and multi-drug resistant <i>Streptococcus pneumoniae</i> (SP) and methicillin-resistant <i>Staphylococcus aureus</i> (MRSA). We measured minimum inhibitory concentration (MIC) and MPC values for tigecycline against 47 clinical isolates of SP and found that the MPC90 values were >500 fold higher than the MIC90 values. To determine if MPC testing of tigecycline against SP is impacted by blood in the medium, we developed a new medium able to sustain the growth of SP without the need for blood; solidified Todd-Hewitt broth (sTHB). The MPC90 values of tigecycline against SP on sTHB were only 2 fold higher than the MIC90 values. When blood was added to the sTHB, the MPC90 values again became much greater than the MIC90 values (> 256 fold higher). MPC results for <i>Staphylococcus spp.</i> against tigecycline were not impacted by blood in the medium.<p> Benzalkonium chloride (BAK) is a cationic surface-acting agent that acts on bacterial cells by disrupting the intermolecular interaction of the lipid bilayer. To determine if the <i>fluoroquinolones gatifloxacin</i> (Gfx) and moxifloxacin (Mfx) are more active (lower MIC values) in the presence of BAK, we conducted MIC, MPC, and time-kill assays. MIC testing showed that in the presence of 3.125 to 50 µg/ml of BAK, the MIC of Gfx and Mfx decreased by 8- to 5000-fold against clinical isolates of methicillin-susceptible <i>Staphylococcus aureus</i> (MSSA), MRSA, Coagulase-negative <i>Staphylococci</i>(CNS), SP, <i>Escherichia coli</i> (EC), and <i>Pseudomonas aeruginosa</i> (PA). MPC testing showed that the presence of 7 to 10 µg/ml of BAK, the MPC of Gfx and Mfx decreased by 32- to 1000-fold against clinical isolates of MRSA. Conventional time-kill studies (using a bacterial load of 105 CFUs) showed that the killing activity of Gfx against clinical MRSA isolates was enhanced in the presence of BAK with a log10-reduction (percent kill) of 1.6 (76.08%) for Gfx alone at 180 minutes compared to a log10-redecution (percent kill) of 5.4 (100%) for Gfx plus BAK at 180 minutes.<p> Alexidine (Alx) is a bisbiguanide that has been used as an effective disinfectant in the dental industry and is potentially being developed for use as an antimicrobial agent for ocular infections. We conducted susceptibility testing of Alx using MIC testing, MPC testing, and time-kill assays against Gram-positive and Gram-negative pathogens. MIC testing showed that Alx is more active against Gram-positive pathogens than Gram-negative pathogens and showed better activity than the fluoroquinolones Gfx, Mfx, and levofloxacin (Lfx) against MRSA. The MPC values measured for MRSA and MSSA against Alx were non-reproducible using the traditional MPC method. Using the microbroth dilution MPC method, MPC90 values were found to be 32 fold higher than the MIC90 values. If the experimentally determined MPC values are true MPC values, initial MPC testing indicates that Alx may have a high likelihood for selecting for resistance, however, if the MPC values are not accurate it may be necessary to modify the MPC protocol in order to complete MPC testing of Alx against MRSA and MSSA. Conventional time-kill studies (using a bacterial load of 105 CFUs) measured bactericidal activity (> 3 log10-reduction) against MRSA, MSSA, SP, and PA.

This study presents the spatial and temporal variability of Salmonella enterica in urban and rural streams in a model watershed (Grand River watershed, Ontario, Canada), and examines the antimicrobial resistance (AMR) and genetic diversity of various serotypes. Using a swab collection method and various media types, Salmonella were detected in 78.4% of samples between November 2003 and July 2005. A diverse range of Salmonella serotypes (n=38) were isolated from water. Predominant serotypes and phagetypes (PT), including S. Typhimurium PT 104 and S. Heidelberg PT 19, and the proportion of isolates demonstrating AMR (33%), was similar to those for humans and farm animals locally and across Canada, a trend not commonly reported. There was a greater diversity of serotypes and AMR profiles in isolates from the urban stream compared to the rural/agricultural streams. Plasmid-borne resistance was observed in 28.6% of AMR isolates, with two different plasmids responsible for resistance; the TEM-1 plasmid (8.1Kb plasmids carrying blaTEM-1, responsible for ampicillin resistance) and CMY-2 plasmid (95.5Kb plasmids carrying blaCMY-2, responsible for 3rd generation cephalosporin resistance). CMY-2 plasmids were only found in the urban stream and did not create a biological burden under non-selective conditions, indicating the long-term permanence of these plasmids. Seasonal differences in the overall diversity of serotypes and predominance of serotypes of human health significance (S. Typhimurium and S. Heidelberg) were observed. The lower occurrence of S. Typhimurium and S. Heidelberg in February and March was not the result of lower survival of these serotypes at low temperatures. Peaks in occurrence of S. Typhimurium and S. Heidelberg in the summer and spring, respectively, were pronounced in the rural/agricultural streams, as opposed to the urban stream. Pulsed-field gel electrophoresis and plasmid-typing revealed diversity within multiple drug resistant S. Typhimurium PT 104 isolates, indicating genetic differences among tributaries. The ubiquitous nature of Salmonella in water and the predominance of serotypes/phagetypes of human or veterinary health significance suggest that environmental exposure through consumption or contact with contaminated water is plausible. These streams may act as a vehicle for the dissemination of these organisms and their resistance genes between different hosts or environments.

The mutant-prevention concentration (MPC) is a novel susceptibility measurement defined by a concentration threshold that would require cells to contain two concurrent resistance mutations for growth. Pneuococcal pneumonia, infections caused by <i> Pseudomonas aeruginosa</i>, and urinary tract infections caused by Gram-negative bacilli represent three distinct clinical situations for which fluoroquinolone-resistance occurs. MPC results were defined and measured for fluoroquinolones against clinical isolates of <i>Citrobacter freundii, Enterobacter cloacae, Escherichia. coli, Klebsiella pneumoniae, P. aeruginosa,</i> and <i> Streptococus pneumoniae</i>. Against clinical isolates of <i>S. pneumoniae</i>, MPC results for six fluoroquinolones were measured. Based on their potential for restricting the selection of resistant mutants, the six fluoroquinolones, in descending order, were found to be gemifloxacin > moxifloxacin > trovafloxacin > gatifloxacin > grepafloxacin > levofloxacin. For several compounds, 90% of clinical isolates that lacked a known resistance mutation had a MPC value that was close to or below the serum levels that could be attained with a dosing regimen recommended by the manufacturers. These data identify gemifloxacin, moxifloxacin and gatifloxacin as good candidates for determining whether MPC can be used as a guide for choosing and eventually administering fluoroquinolones to significantly reduce the development of fluoroquinolone ¡Vresistant <i>S. pneumoniae</i>. MPC90 results for 155 clinical isolates of <i>P. aeruginosa </i>against ciprofloxacin and levofloxacin were 4 and 16 Ýg/ml, respectively. Serum drug concentrations reported previously for standard doses were above MPC90 for 5.5 hr for ciprofloxacin and 0 hr for levofloxacin. These data suggest that superior clinical performance of ciprofloxacin correlates with activity against resistant mutant subpopulations measured in vitro. MPC results were compared with minimum inhibitory concentrations (MIC) measurements preformed by agar dilution, and microbroth dilution and minimal inhibitory concentrations (MBC) for 100 clinical isolates of <i>C. freundii </i> (n=20), <i>E. cloacae</i> (n=20), <i>E. coli</i> (n=20), <i>K. pneumoniae</i> (n=20), and <i>P. aeruginosa</i> (n=20) for ciprofloxacin, levofloxacin and garenoxacin. MPC results were 2-to-8 fold higher than MIC or MBC results. Ciprofloxacin MPC results for <i>E.coli, C. freundii, E. cloacae, K. pneumoniae</i>, and <i>P. aeruginosa</i> were 0.5, 2, 1, 1, and 4 Ýg/ml, respectively. Levofloxacin, MPC results were were 1, 2, 4, 1, and 16 Ýg/ml, respectively. Garenoxacin, MPC were 1, 8, >8, 4, and >32 Ýg/ml, respectively. Garenoxacin had the highest MIC and MPC results and was the least active compound tested against isolates of <i>C. freundii, E. cloacae</i>, and <i>P. aeruginosa</i>. These data support the rational use of quinolones in the treatments of urinary tract infections and suppression of resistance. Incorporation of the MPC measurement into dosing strategies may preserve the longevity of antimicrobial compounds for future infectious diseases.

The mutant prevention concentration (MPC) is defined as the lowest antimicrobial concentration required to inhibit the growth of the least susceptible bacterial cell based on an inoculum of ≥109 colony forming units (CFUs). The current protocol for MPC testing is technically demanding and time-consuming which limits its implementation into clinical microbiology laboratories. In an attempt to simplify the current MPC protocol we developed a modified MPC method, the microbroth dilution method, which requires two fewer days to complete than the current or traditional method. MPC values were consistent for all organisms and strains tested using both the traditional MPC method and the modified microbroth dilution MPC method.<p> Tigecycline is the first of a new class of compound glycylcyclines- with potent in vitro activity against Gram-positive organisms including penicillin-resistant and multi-drug resistant <i>Streptococcus pneumoniae</i> (SP) and methicillin-resistant <i>Staphylococcus aureus</i> (MRSA). We measured minimum inhibitory concentration (MIC) and MPC values for tigecycline against 47 clinical isolates of SP and found that the MPC90 values were >500 fold higher than the MIC90 values. To determine if MPC testing of tigecycline against SP is impacted by blood in the medium, we developed a new medium able to sustain the growth of SP without the need for blood; solidified Todd-Hewitt broth (sTHB). The MPC90 values of tigecycline against SP on sTHB were only 2 fold higher than the MIC90 values. When blood was added to the sTHB, the MPC90 values again became much greater than the MIC90 values (> 256 fold higher). MPC results for <i>Staphylococcus spp.</i> against tigecycline were not impacted by blood in the medium.<p> Benzalkonium chloride (BAK) is a cationic surface-acting agent that acts on bacterial cells by disrupting the intermolecular interaction of the lipid bilayer. To determine if the <i>fluoroquinolones gatifloxacin</i> (Gfx) and moxifloxacin (Mfx) are more active (lower MIC values) in the presence of BAK, we conducted MIC, MPC, and time-kill assays. MIC testing showed that in the presence of 3.125 to 50 µg/ml of BAK, the MIC of Gfx and Mfx decreased by 8- to 5000-fold against clinical isolates of methicillin-susceptible <i>Staphylococcus aureus</i> (MSSA), MRSA, Coagulase-negative <i>Staphylococci</i>(CNS), SP, <i>Escherichia coli</i> (EC), and <i>Pseudomonas aeruginosa</i> (PA). MPC testing showed that the presence of 7 to 10 µg/ml of BAK, the MPC of Gfx and Mfx decreased by 32- to 1000-fold against clinical isolates of MRSA. Conventional time-kill studies (using a bacterial load of 105 CFUs) showed that the killing activity of Gfx against clinical MRSA isolates was enhanced in the presence of BAK with a log10-reduction (percent kill) of 1.6 (76.08%) for Gfx alone at 180 minutes compared to a log10-redecution (percent kill) of 5.4 (100%) for Gfx plus BAK at 180 minutes.<p> Alexidine (Alx) is a bisbiguanide that has been used as an effective disinfectant in the dental industry and is potentially being developed for use as an antimicrobial agent for ocular infections. We conducted susceptibility testing of Alx using MIC testing, MPC testing, and time-kill assays against Gram-positive and Gram-negative pathogens. MIC testing showed that Alx is more active against Gram-positive pathogens than Gram-negative pathogens and showed better activity than the fluoroquinolones Gfx, Mfx, and levofloxacin (Lfx) against MRSA. The MPC values measured for MRSA and MSSA against Alx were non-reproducible using the traditional MPC method. Using the microbroth dilution MPC method, MPC90 values were found to be 32 fold higher than the MIC90 values. If the experimentally determined MPC values are true MPC values, initial MPC testing indicates that Alx may have a high likelihood for selecting for resistance, however, if the MPC values are not accurate it may be necessary to modify the MPC protocol in order to complete MPC testing of Alx against MRSA and MSSA. Conventional time-kill studies (using a bacterial load of 105 CFUs) measured bactericidal activity (> 3 log10-reduction) against MRSA, MSSA, SP, and PA.

Antimicrobial resistance (AMR) is a growing problem around the world. To meet the threat of a futurewithout effective treatment of infection, WHO and other authorities have published strategies and actionplans. However, it is unclear to what extent they have been implemented. As the seventh wealthiesteconomy in the world, Brazil could serve as a role model for other fast developing countries in the battleagainst AMR. The objective of this study was to investigate if and how implementation of internationalAMR strategies is addressed in literature, and to describe how such guidelines have been implemented inBrazil. The study was carried out as a literature review of scientific articles and of documents published byBrazilian authorities. In the scientific literature great importance was given to a multidisciplinary approachand to surveillance, with a special emphasis on local data. Brazilian documents showed a focus on healthcare settings and on actions concerning surveillance. Many tools were in place, such as networks and legalframework. Using local data, identifying measures most important for the target group and thenimplementing them, was considered most important. Generally, there was a lack of assessments. Brazil stillhas a long way to go, but has started out well with its focus on surveillance.

This study presents the spatial and temporal variability of Salmonella enterica in urban and rural streams in a model watershed (Grand River watershed, Ontario, Canada), and examines the antimicrobial resistance (AMR) and genetic diversity of various serotypes. Using a swab collection method and various media types, Salmonella were detected in 78.4% of samples between November 2003 and July 2005. A diverse range of Salmonella serotypes (n=38) were isolated from water. Predominant serotypes and phagetypes (PT), including S. Typhimurium PT 104 and S. Heidelberg PT 19, and the proportion of isolates demonstrating AMR (33%), was similar to those for humans and farm animals locally and across Canada, a trend not commonly reported. There was a greater diversity of serotypes and AMR profiles in isolates from the urban stream compared to the rural/agricultural streams. Plasmid-borne resistance was observed in 28.6% of AMR isolates, with two different plasmids responsible for resistance; the TEM-1 plasmid (8.1Kb plasmids carrying blaTEM-1, responsible for ampicillin resistance) and CMY-2 plasmid (95.5Kb plasmids carrying blaCMY-2, responsible for 3rd generation cephalosporin resistance). CMY-2 plasmids were only found in the urban stream and did not create a biological burden under non-selective conditions, indicating the long-term permanence of these plasmids. Seasonal differences in the overall diversity of serotypes and predominance of serotypes of human health significance (S. Typhimurium and S. Heidelberg) were observed. The lower occurrence of S. Typhimurium and S. Heidelberg in February and March was not the result of lower survival of these serotypes at low temperatures. Peaks in occurrence of S. Typhimurium and S. Heidelberg in the summer and spring, respectively, were pronounced in the rural/agricultural streams, as opposed to the urban stream. Pulsed-field gel electrophoresis and plasmid-typing revealed diversity within multiple drug resistant S. Typhimurium PT 104 isolates, indicating genetic differences among tributaries. The ubiquitous nature of Salmonella in water and the predominance of serotypes/phagetypes of human or veterinary health significance suggest that environmental exposure through consumption or contact with contaminated water is plausible. These streams may act as a vehicle for the dissemination of these organisms and their resistance genes between different hosts or environments.

Master of Science / Department of Diagnostic Medicine/Pathobiology / Raghavendra Amachawadi / T.G. Nagaraja / Copper is an essential micronutrient that is supplemented in swine diets as a growth promoter. Previous studies suggest a link between copper supplementation and co-selection of antimicrobial resistance (AMR) in Enterococcus, but the data are inconsistent. Therefore, the objective of this study was to assess the impact of copper supplementation, alone or with chlortetracycline (CTC), on prevalence and concentration of copper resistance gene, tcrB, prevalence of tetracycline [tet(M)] and macrolide resistance [erm(B)] genes, and AMR in fecal enterococci of weaned piglets. A total of 320 weaned piglets at 21 days of age were allocated into 64 individual pens distributed equally among two barns. Pen-pair was the experimental unit (n=32). Four treatments were used: a basal diet as the control, a basal diet with 200 ppm of copper as copper sulfate, a basal diet with chlortetracycline (CTC) at 400 g/ton of feed, and a basal diet with 200 ppm of copper and CTC at 400 g/ton of feed. The study period was 35 days with days -7 to -1 as an acclimation period and days 0 to 28 as the treatment period. Direct fecal samples were collected on days 0, 14, and 28. Prevalence of tcrB-positive enterococci was not affected by copper and or CTC supplementation (P > 0.05). Prevalence of tcrB-positive enterococci was higher on day 14 than other sampling days (P = 0.002). Prevalence of tet(M)-positive enterococci was not affected by treatment group or sampling day (P > 0.05). Prevalence of erm(B)-positive enterococci had a significant treatment and sampling day interaction (P = 0.0213). The total copy number of the tcrB gene was quantified as a percent of total bacterial cells in the feces. The median copper MIC of tcrB-negative and -positive isolates was 3 mM and 20 mM, respectively (P < 0.0001). For day 0 (n=64) and day 28 (n=63), all Enterococcus isolates were susceptible to gentamicin, kanamycin, streptomycin, daptomyicin, and tigecycline, with majority of isolates resistant to chloramphenicol, erythromycin, lincomycin, linezolid, tetracycline, tylosin tartrate, and synercid. For day 0 (n=64) and day 28 (n=63), respectively, a total of 61 (95.3%) and 47 (74.6%) isolates were resistant to erythromycin, 51 (79.7%) and 41 (65.1%) to tylosin, and 60 (93.8% and 95.2%) to tetracycline. The results of this study show that supplementing copper, with or without a selection pressure of chlortetracycline, did not increase copper-resistant enterococci and did not co-select resistance to any other antibiotics. Liver abscesses in feedlot cattle have a significant economic impact because of reduction in cattle performance, and carcass yield and liver condemnation at harvest. Fusobacterium necrophorum is the primary causative agent of the liver abscesses. Recently, Salmonella enterica has been isolated from liver abscesses of cattle. Our objectives of this study were to determine prevalence of Salmonella, compare conventional (serological) and commercially available Check &Trace serotyping methods, and to describe the antimicrobial susceptibility patterns of Salmonella isolated from liver abscesses of feedlot cattle. In the 2014 study, the number of liver abscesses positive for Salmonella were higher (P < 0.05) in cattle fed no tylosin in the diet (66/200; 33%) compared to tylosin-fed cattle (31/183; 16.9%). In the 2015 study, Salmonella prevalence tended to be higher in liver abscesses categorized as severe (29/106; 27.4%) compared to mild liver abscesses (38/174; 21.8%), but the difference was not significant. Out of the 164 Salmonella isolated, 152 (92.7%) were used for serotyping and 164 strains were used for antimicrobial susceptibility testing. Serotyping was done by serological method, which is considered as the gold standard, and the commercial Check & Trace method, which is a molecular method based on differences in their DNA sequence. A total of 11 serotypes were identified with Lubbock (66/152; 43.4%) being the predominant serotype, followed by Agona (24/152; 15.8%), Anatum (20/152; 13.2%), and Montevideo (18/152; 11.8%). The commercial identified only a few serotypes correctly suggesting that the method requires further validation. Antimicrobial susceptibility testing was done by microbroth dilution method according to Clinical Laboratory Standards Institute guidelines. A majority of the Salmonella strains were pansusceptible to the antimicrobials included in the panel. Overall, 10 strains (10/164; 6.1%) were resistant to one or more antibiotics and belonged to serotypes Agona, Anatum, Cerro, Lubbock, Mbandaka, and Reading. The top three of nine resistant antibiotics were chloramphenicol (5/10; 50%), streptomycin (5/10; 50%), and tetracycline (6/10; 60%). Whether Salmonella contributes to liver abscess formation or just happen to survive in an abscess initiated by the primary etiologic agent, Fusobacterium necrophorum, remains to be determined.