Ziel dieser Studie war es, die in-vitro-Empfindlichkeit von Mastitis-assoziierten Escherichia (E.) coli-Isolaten gegenüber ausgewählten und in der Praxis einsetzbaren veterinärmedizinisch relevanten Wirkstoffen zu untersuchen, um eventuelle Alternativen zu den Cephalosporinen der 3. und 4. Generation bzw. den Fluorchinolonen aufzuzeigen. Dazu wurden im Milchlabor des klinischen Zentrums für Wiederkäuer- und Kamelidenmedizin der Vetmeduni Vienna 154 E. coli-Isolate aus Viertelgemelksproben von Kühen mit Mastitis sowohl mittels Agardiffusionstest (ADT) als auch mittels Bouillon-Mikrodilutionsverfahren (MICRONAUT-S Mastitis 3, Bruker Corporation, Billerica, Massachusetts, USA) untersucht. Zur Identifizierung von ESBL/AmpC β-Laktamase positiven E. coli-Isolate wurde ein spezielles Testverfahren (D68C MASTDISCS, Mast Group Ltd, UK) verwendet. Beim Agardiffusionstest sowie beim Bouillon-Mikrodilutionstest konnte eine hohe in-vitro-Wirksamkeit von Chinolonen/Fluorchinolonen, Cephalosporinen der 3. Generation und von Amoxicillin/Clavulansäure gegenüber den getesteten E. coli-Isolaten nach den CLSI-Standards nachgewiesen werden. Hohe Resistenzraten wurden hingegen gegenüber Trimethoprim/Sulfamethoxazol (24,0%), Tetracyclin (17,5%) und Ampicillin (ADT 19,5%) ermittelt. Dreißig von 154 Isolaten wiesen Mehrfachresistenzen auf. Unter den Reserveantibiotika (Ciprofloxacin, Cefoperazon) waren 11 gegenüber Ciprofloxacin, 6 gegenüber Cefoperazon resistent. Vier von 30 mehrfachresistenten Isolaten zeigten eine ESBL-Aktivität, keines der Isolate zeigte eine AmpC-Aktivität. E. coli ist einer der wichtigsten umweltassoziierten Mastitis-Erreger weltweit. Die antimikrobielle Therapie bei schweren klinischen Mastitisverläufen wird häufig parenteral mit Wirkstoffen durchgeführt, die in der Veterinärmedizin als Reserveantibiotika (Cephalosporine der 3. und 4. Generation und Fluorchinolone) klassifiziert sind. Auf Basis der in-vitro-Ergebnisse stellt Amoxicillin/Clavulansäure eine alternative antimikrobielle Therapiemöglichkeit zu den High Priority Critically Important Antimicrobials (Cephalosporine der 3. und 4. Generation bzw. Fluorchinolone) für eine Score 3 E. coli-Mastitis dar. Escherichia (E.) coli is one of the most important environmentally associated mastitis pathogens worldwide. Gram-negative bacteria can cause numerous clinical symptoms. Lipopolysaccharide (cell wall component of gram-negative bacteria) triggers an immune reaction in the mammary gland. Individual cow-associated factors such as lactation stage and age also play a major role. Due to the different forms of mastitis, there are also different therapeutic approaches. Severe cases of mastitis are treated with systemic antimicrobial therapy. Antimicrobial susceptibility testing in compliance with international standards is essential for this approach. One major focus is a more targeted use of antimicrobials and a reduction of critically important antimicrobials in practice to avoid development of multidrug resistant bacteria. To determine the antimicrobial susceptibility of mastitis-associated E. coli, isolates originating from quarter milk samples of cows with mastitis were tested using different phenotypic methods. The antimicrobial resistance was tested using agar disk diffusion test (ADD, ampicillin, cefoperazone, amoxicillin/clavulanic acid, kanamycin/cefalexin, ciprofloxacin, cefepime, gentamicin, kanamycin, tetracycline, and trimethoprim/sulfamethoxazole) and a commercially available broth microdilution method (MICRONAUT-S Mastitis 3, Bruker Corporation, Billerica, Massachusetts, USA) for determination of the minimum inhibitory concentration (MIC, ampicillin, cefazolin, cefoperazone, cefquinom, amoxicillin/clavulanic acid, kanamycin/cefalexin, and marbofloxacin). To investigate extended-spectrum β-lactamase (ESBL) production and AmpC-producing the Mast D68C test (D68C MASTDISCS, Mast Group Ltd, UK) was used. In both methods isolates showed a high in vitro susceptibility to quinolones and fluoroquinolones, 3^rd and 4^th generation cephalosporins and amoxicillin/clavulanic acid. In contrast, high resistance rates were found against trimethoprim/sulfamethoxazole (24.0%), tetracycline (17.5%) and ampicillin (ADD 19.5%). Four isolates were phenotypically ESBL positive; none of the isolates showed phenotypically AmpC β-lactamase activity. Based on the results, amoxicillin/clavulanic acid can be considered an alternative option for antimicrobial treatment of E. coli mastitis in bovines. However, further studies are necessary to confirm in vivo efficacy. The targeted use of antimicrobial substances in human and veterinary medicine is essential to restrain the development of ESBL -producing bacteria. Received: 24 October 2024 Accepted after revision: 04 April 2025 Article published online: 15 October 2025 © 2025. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany

The objective of this retrospective case-control study was to examine the relationship between E. coli-induced mastitis and acute laminitis in dairy cows. Correspondingly, the medical records of 93 cows diagnosed with E. coli mastitis between 2012 and 2023 were analysed. The cows were categorised into three groups: (1) cows with mastitis scores of 1 or 2 without signs of acute laminitis; (2) cows with a mastitis score of 3 without signs of acute laminitis; (3) cows with a mastitis score of 3 and exhibiting symptoms of acute laminitis. Out of the 93 cows with E. coli mastitis, 19 were assigned to group 1 (20.4%), 46 to group 2 (49.5%), and 28 to group 3 (30.1%). A total of 74 cows (79.6%) scored 3 for mastitis, but 28 cows (37.8%) were also diagnosed with acute laminitis. A higher mastitis score was significantly associated with a higher incidence of acute laminitis (p = 0.0004). E. coli mastitis showed a higher incidence in parity ≥ 3 (73.3% to 78.6%) and occurred in cows of all three groups mainly during the first third of lactation (53.6% to 75.6%). Cows in group 1 had a median survival time of 512 days, while for cows in groups 2 and 3, these values were 93 and 178 days, respectively. Regarding survival times, only a trend but no statistically significant difference (p = 0.221) was found among the cows in the three groups. This could possibly be explained by the fact that additional comorbidities were diagnosed in 53.6% to 65.2% of the cows from all three groups. It is concluded that cows with severe coliform mastitis have a higher risk of developing acute laminitis, and that a thorough clinical examination of the claws should always be performed to avoid overlooking acute laminitis, which accompanied the E. coli mastitis in approximately 38% of cases.