Bovine respiratory disease (BRD) causes high morbidity and mortality in beef cattle worldwide. Antimicrobial resistance (AMR) monitoring of BRD pathogens is critical to promote appropriate antimicrobial stewardship in veterinary medicine for optimal treatment and control. Here, the susceptibility of Mannheimia haemolytica and Pasteurella multicoda isolates obtained from BRD clinical cases (deep lung swabs at post-mortem) among feedlots in four Australian states (2014–2019) was determined for 19 antimicrobial agents. The M. haemolytica isolates were pan-susceptible to all tested agents apart from a single macrolide-resistant isolate (1/88; 1.1%) from New South Wales (NSW). Much higher frequencies of P. multocida isolates were resistant to tetracycline (18/140; 12.9%), tilmicosin (19/140; 13.6%), tulathromycin/gamithromycin (17/140; 12.1%), and ampicillin/penicillin (6/140; 4.6%). Five P. multocida isolates (3.6%), all obtained from NSW in 2019, exhibited dual resistance to macrolides and tetracycline, and a further two Queensland isolates from 2019 (1.4%) exhibited a multidrug-resistant phenotype to ampicillin/penicillin, tetracycline, and tilmicosin. Random-amplified polymorphic DNA (RAPD) typing identified a high degree of genetic homogeneity among the M. haemolytica isolates, whereas P. multocida isolates were more heterogeneous. Illumina whole genome sequencing identified the genes msr(E) and mph(E)encoding macrolide resistance, tet(R)-tet(H) or tet(Y) encoding tetracycline resistance, and blaROB-1 encoding ampicillin/penicillin resistance in all isolates exhibiting a corresponding resistant phenotype. The exception was the tilmicosin-resistant, tulathromycin/gamithromycin-susceptible phenotype identified in two Queensland isolates, the genetic basis of which could not be determined. These results confirm the first emergence of AMR in M. haemolytica and P. multocida from BRD cases in Australia, which should be closely monitored.

In the late 90s, a sharp increase of treatment failures of Trichomonas vaginalis (TV) infections with metronidazole (MTZ) was reported, representing a problem due to limited treatment options. We proposed to review the available evidence on the frequency of MTZ resistance by TV isolates and the relationship between treatment failure and in vitro resistance to MTZ. A systematic review based on the PRISMA guidelines was conducted by searching published studies in three different databases (PubMed, Scopus and Web of Science) up to December 2020. The extracted studies were uploaded to Covidence software; screening was guided based on inclusion and exclusion criteria. Additionally, different articles were included through other sources. For each article, study design, objectives, study population and key outcomes were summarized. We found 403 references from the databases and four extra studies. After duplicate removal and screening of title, abstract and full text, 27 studies were included. The selected studies were published between 1983 and 2019; all except one addressed only vaginal TV infection. We identified four major populations in vitro MTZ resistance: two studies evaluated female adolescents; other two assessed HIV‐positive women. Fifteen studies considered MTZ resistance in newly diagnosed vaginal TV infection. Finally, eight articles studied in vitro susceptibility of isolates from women with clinical resistant trichomoniasis. High level of in vitro MTZ resistance was rare; low‐moderate level was described in most of the cases. Although clinical resistance to MTZ of trichomoniasis was widely reported, there was a paucity of prospective controlled studies. Our review unveiled the need to standardize susceptibility testing, to define breakpoints for detection of MTZ‐resistant isolates and to correlate with clinical outcome. It is important to establish criteria to define clinical resistance to MTZ. Such a consensus would foster the development of surveillance studies about clinical and microbiological response to MTZ treatment.

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