Sensibilità in vitro nei confronti dei principali antibiotici da parte degli agenti di mastite isolati nel Triveneto negli anni 2010-2014.

Introduction - Bovine mastitis represents a major cause of economic loss in dairy production. As well as the financial implication of this disease, the importance of mastitis in public health should not be overlooked. The extensive use of antibiotics in mastitis treatment has possible implications for human health through an increased risk of antibiotic resistant strains that may enter the food chain. Aim - The aim of this study was the assessment of the main antimicrobial-resistance (AMR) patterns of bovine mastitis pathogens isolated in the north-east of Italy from 2010 to 2014 during the usual diagnostic activity. Materials and methods - The isolates tested were identified from individual quarter milk samples, which were collected from cows with clinical and subclinical mastitis and from dairy calves with scour. Milk culture was carried out according to the National Mastitis Council guidelines and the in vitro antimicrobial susceptibility was evaluated using agar disk diffusion method as described by NCLSI guide Vet01-A4. E. coli isolated from calves fecal samples were tested for antimicrobial susceptibility with the same method. All isolates were tested with the following antimicrobials: penicillin, ampicillin, clavulanate-amoxicillin, oxacillin, cefoxitin, cephalothin, cefoperazone, cefquinome, spiramycin, kanamycin, tylosin, tylmicosin, trimethoprim + sulphametoxazole, tetracycline, enrofloxacin, and rifampicin. Results and discussion - In this study, out of 15.926 strains, isolated from bovine milk, 29.5% were Coagulasepositive Staphylococci (CPS), 28.6% Streptococcus uberis and Enterococcus spp., 19.5% Coagulase-negative Staphylococci (CNS), 9.2% E. coli, 7.6% Streptococcus dysgalactiae, 5.6% Streptococcus agalactiae. Overall, more than 90% of isolates were Gram-positive bacteria with significantly (p<0.05) higher average susceptibility percentages than Gram-negative strains (79.8% vs 72.5%). For CPS, the lowest susceptibility values were reported towards betalactams (84.6%), tetracycline (88.7%) and macrolides (89.7%). Within betalactams, the susceptibility range was wide (57.8-99%): penicillin G (57.8%) and ampicillin (65.9%) had the lowest susceptibility values, whereas oxacillin (95.8%), clavulanate-amoxicillin (92.7%) and cephalothin (99%) showed higher susceptibility. For CNS the least effective antibiotics were tetracycline (80.6%), betalactams (82.2%), macrolides (88.8%) and quinolones (90%). Betalactams showed a wide range of susceptibility: penicillin (53%), ampicillin (60.9%), clavulanate-amoxicillin (96.8%), oxacillin (78.1%), cephalothin (97.6%), cefoperazone (95.6%), cefquinome (97.9%). In CNS high in vitro susceptibility was found also towards trimethoprim + sulphametoxazole (95.9%), and aminoglycosides (95.5%). The lowest susceptibility percentages for Streptococcus uberis and Enterococcus spp. were found towards aminoglycosides (19.9%), quinolones (35.5%) and tetracycline (37.2%). Higher percentages were found for macrolides (65.7%) and trimethoprim + sulphametoxazole (76.7%), while the susceptibility patterns towards betalactams members were the following: oxacillin (51.6%), penicillin G (86.3%), ampicillin (82.2%), amoxicillin-clavulanate (98.5%), cephalothin (90.3%), cefoperazone (91.7%) and cefquinome (93.8%). For E. coli the enteric isolates showed lower susceptibility levels compared to mammary ones towards tetracycline (27.3 vs 70.5%), ampicillin (17.4 vs 56.0%), clavulanateamoxicillin (32.3 vs 66.7%), cefquinome (86.1 vs 94.6%) trimethoprim + sulphametoxazole (55 vs 87.3%). Conclusions - The assessment of routine laboratory data can provide useful and costless information in order to improve therapeutic protocols and represents an important surveillance tool to investigate the level of antimicrobial resistance in dairy cows population.

Vengono riportati i risultati dei test di sensibilità in vitro agli antimicrobici (metodo Kirby-Bauer) effettuati su ceppi batterici isolati da casi di mastite nel Triveneto, negli anni 2010-2014. I dati si riferiscono ai seguenti microrganismi: S. aureus e stafilococchi coagulasi-positivi (4694; 29,2%), Streptococcus. uberis ed Enterococcus spp. (4549; 28,3%), stafilococchi coagulasi-negativi (3099; 19,3%), E. coli (1467; 9,1%), Streptococcus dysgalactiae (1218; 7,6%), Streptococcus agalactiae (899; 5,6%). Sono stati presi in considerazione anche 1175 ceppi di E. coli isolati da vitelli con patologia enterica. Per il gruppo degli stafilococchi coagulasi-positivi, i valori più bassi di sensibilità si sono osservati nei confronti dei betalattamici (84,6%), delle tetracicline (88,7%) e dei macrolidi (89,7%). Nel 2014, la sensibilità di questo gruppo verso l’oxacillina (97,5%) è risultata significativamente diversa (p<0,05) rispetto a quella media osservata nel quadriennio precedente (95,5%). Negli streptococchi, le percentuali maggiori di sensibilità si osservano verso betalattamici (75%-93,7%) e rifamicine (82,4%-92,1%). Per E. coli, si osservano percentuali di sensibilità superiori nei ceppi di derivazione mammaria (valori di sensibilità inferiori: 64,7% betalattamici; 70,5% tetracicline) rispetto a quelli isolati da sindrome enterica del vitello (valori di sensibilità inferiori: 27,3% tetracicline; 50,1% chinoloni). Per gli E. coli di origine mammaria, nel 2014 è stata osservata una differenza significativa (p<0,001) della percentuale di sensibilità verso le cefalosporine di I e II generazione (da 20,4% del quadriennio 2010-13 a 34,1%).