Chitosan can improve antimicrobial treatment independently of bacterial lifestyle, biofilm biomass intensity and antibiotic resistance pattern in non-aureus staphylococci (NAS) isolated from bovine clinical mastitis

BRESER, MARIA LAURA; TISERA, LUCIA; ORELLANO, MARIA SOLEDAD; BOHL, LUCIANA PAOLA; ISAAC, PAULA; BIANCO, ISMAEL; PORPORATTO, CARINA

Frontiers in Microbiology

Frontiers

Año: 2023 vol. 14

Bovine mastitis is the most frequent and costly disease that affects dairy cattle.Non-aureus staphylococci (NAS) are currently one of the main pathogensassociated with difcult-to-treat intramammary infections. Bioflm is an importantvirulence factor that can protect bacteria against antimicrobial treatment andprevent their recognition by the host’s immune system. Previously, we found thatchronic mastitis isolates which were refractory to antibiotic therapy developedstrong bioflm biomass. Now, we evaluated the influence of bioflm biomassintensity on the antibiotic resistance pattern in strong and weak bioflm-formingNAS isolates from clinical mastitis. We also assessed the effect of cloxacillin (Clx)and chitosan (Ch), either alone or in combination, on NAS isolates with differentlifestyles and abilities to form bioflm. The antibiotic resistance pattern was notthe same in strong and weak bioflm producers, and there was a signifcantassociation (p ≤ 0.01) between bioflm biomass intensity and antibiotic resistance.Bacterial viability assays showed that a similar antibiotic concentration waseffective at killing both groups when they grew planktonically. In contrast, withinbioflm the concentrations needed to eliminate strong producers were 16 to128 times those needed for weak producers, and more than 1,000 times thoserequired for planktonic cultures. Moreover, Ch alone or combined with Clx hadsignifcant antimicrobial activity, and represented an improvement over the activityof the antibiotic on its own, independently of the bacterial lifestyle, the bioflmbiomass intensity or the antibiotic resistance pattern. In conclusion, the degreeof protection conferred by bioflm against antibiotics appears to be associatedwith the intensity of its biomass, but treatment with Ch might be able to helpcounteract it. These fndings suggest that bacterial biomass should be consideredwhen designing new antimicrobial therapies aimed at reducing antibioticconcentrations while improving cure rates