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A BOUT twenty years ago, studies on

An 8-y-old, castrated male Siberian Husky dog was admitted to an emergency clinic with acute collapse and severe swelling of both forelimbs, ventral thorax, and axillary region. The clinical assessment, with laboratory tests and radiologic investigation, confirmed severe subcutaneous emphysema and multi-organ failure. The animal died while receiving emergency treatment. On postmortem examination, Clostridium perfringens was isolated from the subcutaneous fluid and the effusion from the thoracic and abdominal cavities. Relevant histopathology findings included subcutaneous emphysema and multi-organ perivascular and intravascular, intralesional myriad 0.5–3-µm gram-positive rod bacteria, with no associated inflammation. Whole-genome sequencing and phylogenetic analysis identified C. perfringens type A. Virulence genes detected included cpa (alpha toxin), cadA (v-toxin), colA (collagenase A), nagH (hyaluronidase), nanH, nanI, nanJ (sialidases), and pfoa (perfringolysin). These virulence genes have previously been reported to act synergistically with alpha toxin in C. perfringens–mediated gas gangrene.

A 5-year retrospective study was conducted to describe the mastitis-causing organisms isolated from bovine milk samples submitted to four veterinary diagnostic laboratories in Australia. The aim of this study was to identify temporal, geographical, and seasonal patterns of occurrence for the organisms and report the in vitro susceptibility of the most common mastitis-causing pathogens. In total, 22,102 milk samples were submitted between 2015 and 2019. The results were reported as positive growth for at least one significant organism (n = 11,407; 51.6%), no growth (n = 5,782; 26.2%), and mixed/contaminated growth (n = 4,913; 22.2%). Culture results for no growth, gram-negative bacteria, and eukaryotic organisms were combined for each region, and they were accounted for between 23 and 46% of submissions. These results represent a subset of mastitis cases for which the antibiotic treatment may not be warranted. A total of 11,907 isolates were cultured from 11,407 milk samples. The most common isolated organisms were Streptococcus uberis [41.3%; 95% confidence interval (CI): 40.4–42.1%] and Staphylococcus aureus (23.6%; 95% CI: 22.8–24.3%). For S. uberis and S. aureus, there was an association between a positive culture result and the dairy region. All regions except for the Sub-tropical Dairy region were more likely to culture S. uberis compared to the reference, Dairy NSW (P < 0.001). Similarly, for S. aureus, a positive culture result was more likely in all other dairy regions compared to Dairy NSW (P < 0.001). The LISA cluster analysis identified differences between High-High (hotspot) postcodes for S. aureus and S. uberis throughout all the analyzed dairy regions. These results highlight the need for further investigations into specific risk factors, such as environmental factors and herd-level predictors, which may have influenced the observed regional variations. Common mastitis-causing pathogens showed overall good susceptibility to a range of antimicrobials used in the treatment of mastitis. On-going surveillance of mastitis-causing pathogens and their antimicrobial susceptibilities will facilitate targeted mastitis control and treatment programs.

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