Chitosan and cloxacillin combination improve antibiotic efficacy against different lifestyle of coagulase-negative Staphylococcus isolates from chronic bovine mastitis

María L Breser,María S Orellano,Luciana P Bohl,Agustín Conesa,Carina Porporatto,Silvia G Correa,Virginia E Rivero,Verónica Felipe,Paula Isaac,Ismael D Bianco

doi:10.1038/s41598-018-23521-0

Abstract

Bovine mastitis affects the health of dairy cows and the profitability of herds worldwide. Coagulase-negative staphylococci (CNS) are the most frequently isolated pathogens in bovine intramammary infection. Based on the wide range of antimicrobial, mucoadhesive and immunostimulant properties demonstrated by chitosan, we have evaluated therapy efficiency of chitosan incorporation to cloxacillin antibiotic as well as its effect against different bacterial lifestyles of seven CNS isolates from chronic intramammary infections. The therapeutic effects of combinations were evaluated on planktonic cultures, bacterial biofilms and intracellular growth in mammary epithelial cells. We found that biofilms and intracellular growth forms offered a strong protection against antibiotic therapy. On the other hand, we found that chitosan addition to cloxacillin efficiently reduced the antibiotic concentration necessary for bacterial killing in different lifestyle. Remarkably, the combined treatment was not only able to inhibit bacterial biofilm establishment and increase preformed biofilm eradication, but it also reduced intracellular bacterial viability while it increased IL-6 secretion by infected epithelial cells. These findings provide a new approach to prophylactic drying therapy that could help to improve conventional antimicrobial treatment against different forms of bacterial growth in an efficient, safer and greener manner reducing multiresistant bacteria generation and spread.

Highlights

Mastitis is the most prevalent and costly disease in dairy cattle around the world[1,2]
Our results show that chitosan addition to cloxacillin therapy significantly reduced antibiotic concentration to improve bacterial killing against planktonic cultures, preformed biofilms and intracellular growth, compared to conventional antibiotic treatment
Antibiogram tests showed that Coagulasenegative staphylococci (CNS) isolates from chronic bovine mastitis (CM-CNS) exhibited 85%, 57% and 42% resistance to penicillin, ampicillin and methicillin, respectively (Table 1)

Summary

Introduction

Mastitis is the most prevalent and costly disease in dairy cattle around the world[1,2]. Biocompatible, bioadhesive, bioactive and non-toxic, and has been proposed to different therapeutic applications in a wide range of administration routes[30,31] Antimicrobial activity of this biopolymer is based on its physical properties, and it is more difficult to develop or transfer resistance[31]. Our results show that chitosan addition to cloxacillin therapy significantly reduced antibiotic concentration to improve bacterial killing against planktonic cultures, preformed biofilms and intracellular growth, compared to conventional antibiotic treatment. These findings may contribute to understand the influence of different bacterial lifestyle and antibiotic resistance and provide bases for new strategies to be applied during the drying period to control persistent intramammary infections and prevent the development and spread of multiresistant bacteria

Methods

Results

Conclusion