Abstract
The effects of sub-MICs of certain antibiotics, namely, penicillin G, tetracycline, and trimethoprim-sulfamethoxazole, on the cell surface characteristics and the virulences of two toxigenic isolates of Pasteurella multocida representing capsular types A and D were evaluated. Expression of proteins, in particular, outer membrane proteins and iron-regulated proteins, was not affected by exposure of bacterial cells to low concentrations of antibiotics. However, exposition of surface antigens was modified by sub-MICs of the antibiotics tested. The lipopolysaccharide profile of one isolate (capsular type D) was altered by penicillin G. Sub-MICs of penicillin G and tetracycline diminished the virulence of the capsular type A isolate and adherence to porcine tracheal rings of the capsular type D isolate. Production of dermonecrotic toxin was not affected by sub-MICs of the antibiotics tested. Our results indicate that growth of P. multocida in the presence of low concentrations of antibiotics seems to have, depending on the isolate, profound effects on cell surface characteristics, with concomitant effects on adherence or virulence. Our results also indicate that production of dermonecrotic toxin, an important virulence factor of P. multocida isolates associated with porcine atrophic rhinitis, was not affected by sub-MICs of the antibiotics studied.
Highlights
The effects of sub-MICs of certain antibiotics, namely, penicillin G, tetracycline, and trimethoprimsulfamethoxazole, on the cell surface characteristics and the virulences of two toxigenic isolates of Pasteurella multocida representing capsular types A and D were evaluated
We previously reported that the growth and the morphology of P. multocida can be affected by sub-MICs of antibiotics [13]
We found that P. multocida exposed to penicillin G was totally devoid of capsular material and that treatment with penicillin G, tetracycline, or trimethoprimsulfamethoxazole induced filamentation
Summary
The effects of sub-MICs of certain antibiotics, namely, penicillin G, tetracycline, and trimethoprimsulfamethoxazole, on the cell surface characteristics and the virulences of two toxigenic isolates of Pasteurella multocida representing capsular types A and D were evaluated. The isolates of P. multocida implicated in atrophic rhinitis produce a dermonecrotic toxin (DNT) of about 150 kDa [9, 22, 28] which causes characteristic lesions when injected into pigs [30]. Among the variety of antimicrobial agents used in swine, feed medication containing tetracycline alone or in combination with penicillin and sulfonamides can reduce the clinical signs of atrophic rhinitis [25, 29] It is not very clear whether bactericidal drug concentrations are achieved on the mucosae of the upper respiratory tracts of pigs. Sub-MIC antibiotic effects include morphological changes [1, 6, 13, 19], reduction of growth [1, 13, 39], inhibition of enzyme or toxin production [33], and loss of adhesive properties [31, 34]
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