Abstract:
One hundred seventy-eight mycoplasma strains isolated from South African
poultry flocks between 2003 and 2015 were identified by full-genome sequencing
and phylogenetic analysis of the 16S rRNA gene and were classified as follows: Mycoplasma
gallisepticum (25%), M. gallinarum (25%), M. gallinaceum, (23%), M. pullorum
(14%), M. synoviae (10%), and M. iners (3%), as well as one Acheoplasma laidlawii strain
(1%). MIC testing was performed on the axenic samples, and numerous strains of each
species were resistant to either chlortetracycline or tylosin or both, with variable sensitivity
to enrofloxacin. The strains of all species tested remained sensitive to tiamulin, except
for one M. gallinaceum sample that demonstrated intermediate sensitivity. The mutation
of A to G at position 2059 (A2059G) in the 23S rRNA gene, which is associated
with macrolide resistance, was found in the South African M. gallisepticum and M. synoviae
strains, as well as a clear correlation between macrolide resistance in M. gallinarum
and M. gallinaceum and mutations G354A and G748A in the L4 ribosomal protein and
23S rRNA gene, respectively. No correlation between resistance and point mutations in
the genes studied could be found for M. pullorum. Only a few strains were resistant to
enrofloxacin, apart from one M. synoviae strain with point mutation D420N, which has
been associated with quinolone resistance, and no other known markers for quinolone
resistance were found in this study. Proportionally more antimicrobial-resistant strains
were detected in M. gallinaceum, M. gallinarum, and M. pullorum than in M. gallisepticum
and M. synoviae. Of concern, three M. gallinaceum strains showed multidrug resistance
to chlortetracycline, tylosin, and oxytetracycline.
