Background: The emergence of reduced susceptibility to fluoroquinolones
among Salmonella enterica serotype Typhimurium isolates leading to clinical failure of
treatment poses a great therapeutic challenge.
Methods: The current study is focused on the evaluation of the minimum inhibitory concentration
(MIC) of quinolones in 29 Salmonella typhimurium of 86 Salmonella spp.
strains, obtained from pigs from the State of Mexico. The MIC was performed with the
Kirby-Bauer method. On the other hand, the GyrA gene was sequenced. The present study
was undertaken to describe the resistance profiles and fluoroquinolone resistance mechanism
of Salmonella Typhimurium.
Results: The DNA sequence of the gyrA genes from Salmonella enterica serovar typhimurium
revealed strong similarity between gyrA and its counterpart in Escherichia
coli. The sequencing of quinolone resistance-determining region (QRDR) of the gyrA
gene showed the presence of mutation at either S83 or at D87 in almost all the Salmonella typhimurium isolates.
Conclusion: This mutation, although phenotypically expressed as decreased susceptibility to fluoroquinolones
goes undetected by the disk diffusion method using the present method of Kirby-Bauer. Hence, it can increase
morbidity and mortality due to delay in appropriate antibiotic treatment.