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Australia relies on periodic antimicrobial resistance (AMR) surveys to determine trends and changes in AMR in animal production systems. This study is a follow-up to a survey of Escherichia coli from healthy cattle at slaughter conducted in 2013, which provided baseline data on AMR prevalence across cattle groups and production practices. In this study, 591 beef cattle, 194 dairy cattle, and 216 veal calf fecal samples were collected from 25 beef and veal processing establishments in Australia, representing approximately 77% of total export volume. A total of 969 matrix-assisted laser desorption–ionization results confirmed commensal E. coli isolates from 574 beef cattle, 186 dairy cattle, and 209 veal calves were recovered, and antimicrobial susceptibility testing was carried out by microbroth dilution to 16 drugs from 10 classes interpreted against epidemiological cutoff breakpoints. Overall, a high proportion of E. coli isolates (83.8%) were wild type for all antimicrobials assessed. In addition, isolates that were non–wild type (NWT) for three or more classes of antimicrobial did not exceed 4% for any of the cattle groups. The prevalence of E. coli that were NWT for antimicrobials that are critical or of high importance to human health was very low, with 1.4% of all isolates tested determined to be NWT for fluoroquinolones, third-generation cephalosporins, or polymyxins. Genomic analysis of NWT isolates identified one beef cattle isolate (ST-10) harboring blaCMY-2 and a dairy isolate (ST-58) and two veal calf isolates (ST-58 and ST-394) that had qnrS1, which confer resistance to extended-spectrum cephalosporins and fluoroquinolones, respectively. The low levels of AMR reported in this study confirm previous Australian studies, which indicated that there is minimal evidence that specific production practices lead to widespread disproportionate development of NWT isolates. Most E. coli from Australian cattle were determined to be wild type. Cattle production practices are not leading to widespread AMR. Resistance to critical antimicrobials for human health was low. Genomic analysis identified E. coli with blaCMY-2 or qnrS1. [ABSTRACT FROM AUTHOR]

Antimicrobial agents are used in cattle production systems for the prevention and control of bacterial associated diseases. A consequence of their use is the potential development of antimicrobial resistance (AMR). Enterococcus faecium and Enterococcus faecalis that are resistant to antimicrobials are of increased concern to public health officials throughout the world as they may compromise the ability of various treatment regimens to control disease and infection in human medicine. Australia is a major exporter of beef; however it does not have an ongoing surveillance system for AMR in cattle or foods derived from these animals. This study examined 910 beef cattle, 290 dairy cattle and 300 veal calf faecal samples collected at slaughter for the presence of enterococci. Enterococcus were isolated from 805 (88.5%) beef cattle faeces, 244 (84.1%) dairy cattle faeces and 247 (82.3%) veal calf faeces with a total of 800 enterococci subsequently selected for AMR testing. The results of AMR testing identified high levels of resistance to antimicrobials that are not critically or highly important to human medicine with resistance to flavomycin (80.2%) and lincomycin (85.4–94.2%) routinely observed. Conversely, resistance to antibiotics considered critically or highly important to human medicine such as tigecycline, daptomycin, vancomycin and linezolid was not present in this study. There is minimal evidence that Australian cattle production practices are responsible for disproportionate contributions to AMR development and in general resistance to antimicrobials of critical and high importance in human medicine was low regardless of the isolate source. The low level of antimicrobial resistance in Enterococcus from Australian cattle is likely to result from comprehensive controls around the use of antimicrobials in food-production animals in Australia. Nevertheless, continued monitoring of the effects of all antimicrobial use is required to support Australia’s reputation as a supplier of safe and healthy food. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate phenotypic and genotypic AMR characteristics of Salmonella enterica isolates from Australian cattle collected through a structured national survey utilizing 1001 faecal samples collected from healthy cattle at slaughter. A total of 184 Salmonella isolates were subsequently derived and subjected to microbroth dilution to 16 drugs from 11 classes with interpretation of minimum inhibitory concentrations (MICs) using epidemiological cut off (ECOFF) values to distinguish between wild-type and non-wild-type populations. Most isolates were susceptible (wild type) to all antimicrobials tested, with no resistance (non-wild type) detected for colistin, nalidixic acid, meropenem, gentamicin, florfenicol or chloramphenicol. Low rates of resistance were detected for ampicillin (2.2%), cefoxitin (2.2%), ceftiofur (2.2%), ceftriaxone (2.2%), ciprofloxacin (0.5%), streptomycin (3.3%) and tetracycline (0.5%). Isolates resistant to ceftriaxone (a critically important antimicrobial, CIA) carried the extended spectrum cephalosporin gene bla CMY-2 while no known mutation in the QRDR region or qnrS genes were detected for the CIA ciprofloxacin-resistant isolate. Thirty-six serovars were detected among the 184 Salmonella isolates using whole genome sequencing, dominated by Typhimurium (n = 36), Saintpaul (n = 22) and Anatum (n = 16). Genomic analysis clustered the cattle isolates based on serovar, with the majority of serovars containing a single sequence type (ST). Further analysis of the bovine Typhimurium isolates (ST19) and comparison with publicly available data from human Typhimurium isolates from Australia, revealed the majority of cattle isolates were unrelated to human isolates. In conclusion, this study demonstrates the continued low prevalence of AMR among Salmonella within the beef, dairy and veal industries in Australia. Salmonella Typhimurium from cattle were genetically distinct from isolates sourced from human infections. Further investigations are warranted to expand on the potential clinical and public health relevance of these findings to inform risk-management of this key pathogen. • This study reveals ongoing low prevalence of AMR in Salmonella in Australian cattle • Resistance was heighest for streptomycin (3.3%), and ampicillin, cefoxitin, ceftiofur, ceftriaxone, (each 2.2 %) • Thirty-six serovars were detected among the 184 Salmonella isolates dominated by Typhimurium, Saintpaul and Anatum • Genomic analysis revealed clustering based on serovars, with the majority of serovars containing a single sequence type (ST) • Salmonella Typhimurium (ST19) from cattle were genetically distinct and unrelated from isolates sourced from human infections. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to determine the diversity among Campylobacter isolates from Australia (n = 20), Poland (n = 22), and Malaysia (n = 16) with respect to antimicrobial resistance (AMR), the presence of 8 putative virulence markers, flaA-RFLP and flaA-SVR, and a PCR binary typing system (P-BIT). AMR to nine antimicrobials was assessed using the Sensititre® Campylobacter plate. Only two (10%) Australian isolates were resistant, one to tetracycline and one to nalidixic acid. Polish isolates (12; 54.5%) carried multiresistance with the most common pattern (9 strains; 40.9%) ciprofloxacin, nalidixic acid, and tetracycline. All Malaysian strains were resistant to at least three antimicrobials, with 9 isolates carrying multiresistance to 8 antimicrobials. Distribution of the 8 virulence markers tested in this study varied between countries. Differences were noted between countries in the carriage of ciaB and the cdt gene cluster, responsible for invasion and toxin production, respectively. Typing of Campylobacter isolates using the P-BIT, flaA-SVR, and flaA-RFLP approaches revealed 50, 30, and 11 genotypes, respectively. A limited number of overlapping Campylobacter genotypes from different countries irrespective of the typing method used was observed. The combined molecular differentiation strategy gave insight into strain relationships both within and across countries. The resistance patterns identified in the study may lead to a better understanding of antibiotic resistance distribution among Campylobacter in geographically distant countries with different antimicrobial treatment policy. [Copyright &y& Elsevier]