To determine the association of tetracycline resistance determinants with 
tigecycline sensitivity, tetracycline-resistant Salmonella spp. isolated from 
clinical and food samples were tested for the presence of tetracycline 
resistance determinants, tigecycline sensitivity, and the impact of tetA on 
tigecycline resistance. In addition, the impacts of multiple resistance 
mechanisms on tigecycline resistance were determined using an isolate with ramR 
mutation. Of the 49 tetracycline-resistant Salmonella isolates screened, 32 were 
positive for tetA, 13 were positive for tetB, 2 were positive for tetC and 1 
isolate was positive for both tetA and tetB. The minimum inhibitory 
concentration (MIC) of tigecycline for tetA-carrying isolates ranged from 0.19 
mg/L to 3mg/L (mode 0.75 mg/L), whereas the MIC of tigecycline for tetB-carrying 
isolates ranged from 0.064 mg/L to 0.5mg/L (modes 0.25mg/L and 0.38 mg/L, 
excluding the isolate with both tetA and tetB). Double frameshift mutations in 
codons 201, 202 and 203 were observed in partial sequences of the tetA genes in 
these strains and the majority of published tetA gene sequences. Curing of the 
tetA genes from three isolates reduced the tigecycline MICs, whilst deletion of 
ramR increased tigecycline MICs. This study indicates that the tetA gene 
decreases sensitivity to tigecycline in Salmonella spp. at a low level. With 
additional resistance mechanisms, tetA-carrying strains can reach the breakpoint 
for tigecycline resistance.