Distribution and genetic determinants of tetracycline resistance in Laribacter hongkongensis isolates from humans and fish
Abstract number: p1604
Lau S.K.P., Woo P.C.Y., Li M.W.S., Wong G.K.M., Yuen K.Y.
To study the distribution of tetracycline resistance and to clone and characterize a tetracycline resistance determinant in Laribacter hongkongensis, a recently discovered bacterial genus and species associated with community-acquired gastroenteritis.
Twenty-four L. hongkongensis strains isolated from patients with community-acquired gastroenteritis and 24 L. hongkongensis strains isolated from freshwater fish in Hong Kong were used in this study. Genetic determinants for tetracycline resistance were looked for by screening a genomic DNA library of L. hongkongensis. The prevalence of tetA gene in other strains of L. hongkongensis was studied by PCR using laboratory-designed primers. The presence of the tetracycline resistance determinants in plasmid was examined by Southern blot analysis.
Among 24 human and 24 fish isolates tested, 3 human and 1 fish isolates were tetracycline-resistant. A 3566-bp gene cluster, which consists of 2 putative transposases, a tetR and a tetA gene, was cloned by inserting restriction fragments of genomic DNA from a resistant strain, HLHK5, into pBK-CMV. The 1266-bp tetA and 636-bp tetR genes shared significant nucleotide sequence homology with known tetA and tetR genes. While the flanking regions and 3' end of the tetA were identical to the corresponding regions of a tetC island in Chlamydia suis, the tetA was almost identical to that of transposon Tn1721 and plasmids found in many gram-negative bacteria, suggesting that illegitimate recombination may have occurred to produce the present tetracycline resistant determinant. Southern hybridization suggested that the tetA gene of HLHK5 was plasmid-encoded. The tetracycline resistance in L. hongkongensis was associated with tetA. PCR amplification of the tetA gene in the 48 isolates of L. hongkongensis, including HLHK5, showed the presence of tetA in all the four tetracycline resistant isolates but none of the tetracycline susceptible ones. In contrast to strain HLHK5, the tetA of two strains were identical to that of Tn1721, while that of the other strain was more closely related to other gram-negative bacteria plasmids.
Our results indicate that horizontal transfer of genes, especially through Tn1721 and related plasmids, between L. hongkongensis and other gram-negative bacteria is probably a frequent event and is an important mechanism for acquisition and dissemination of tetracycline resistance in L. hongkongensis.
|Session name:||XXIst ISTH Congress|
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