Abstract
Acholeplasma (A.) laidlawii is an opportunistic pathogen with the ability to disseminate resistance determinants to antibiotics; however, its resistance to macrolides has been less studied. The aim of the present study was to characterize the mechanisms responsible for the resistance to macrolides, tiamulin and lincomycin found in a strain of A. laidlawii isolated from a pig with pneumonia. MICs of erythromycin, 15- and 16-membered macrolides, tiamulin and lincomycin were determined by microdilution method with and without reserpine, an inhibitor of ABC efflux pumps and regions of the genome were sequenced. Reserpine only decreased lincomycin MIC but it did not change the MICs of macrolides and tiamulin. The analysis of the DNA sequence of 23S rRNA showed nucleotide substitutions at eight different positions, although none of them were at positions previously related to macrolide resistance. Five mutations were found in the L22 protein, one of them at the stop codon. In addition, two mutations were found in the amino acid sequence of L4. The combination of multiple mutations in the ribosomal proteins L22 and L4 together with substitutions in 23S rRNA DNA sequence was associated with the resistance to macrolides, the pleuromutilin and lincomycin in the studied A. laidlawii strain.
Highlights
Acholeplasma (A.) laidlawii, a species of the class Mollicutes, is universally disseminated, having been first isolated from wastewaters in 1936 [1]
MICs for 470 wild strain of all the 15- and 16-membered macrolides were ≥32 mg/L and erythromycin and lincomycin MICs were 2048 and 4096 mg/L, respectively, whereas MICs of the 15- and 16-membered macrolides and lincomycin ranged < 0.25–1 mg/L for the type strain PG8, with the exception of erythromycin, which produced a similar value to that observed for the wild strain (2048 mg/L)
Reserpine 20 mg/L did not increase the susceptibility of the 470 strain to macrolides, tiamulin and lincomycin (Table 1)
Summary
Acholeplasma (A.) laidlawii, a species of the class Mollicutes, is universally disseminated, having been first isolated from wastewaters in 1936 [1]. It colonizes animals, plants and insects, and it is a frequent contaminant in cell cultures and vaccine preparations [2,3,4,5]. Plants and insects, and it is a frequent contaminant in cell cultures and vaccine preparations [2,3,4,5] It is frequently found as commensal of the mucosa in the upper respiratory and in the urogenital tract in animals, it is able to cause opportunistic infections such as bovine mastitis [6,7,8]. A. laidlawii has been isolated from both normal and pneumonic lungs of pigs [10] and nasal secretion, trachea, and lung of calves [11]
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