Novel Tet(L) Efflux Pump Variants Conferring Resistance to Tigecycline and Eravacycline in Staphylococcus Spp

Abstract

Tigecycline is regarded as one of the few important last-resort antibiotics to treat complicated skin and intra-abdominal infections. Members of the genus Staphylococcus are zoonotic pathogens and pose a serious threat to public health. Tigecycline resistance in this species appears to be a rare phenomenon, and the mechanisms underlying tigecycline resistance have not been fully elucidated. Here, we report two novel variants of the tet(L) gene in Staphylococcus spp. from swine in China, designed as tet(L)_F58L and tet(L)_A117V. The tet(L)_F58L was located within a 18,720 bp chromosomal multidrug resistance gene cluster flanked by two copies of IS257 in Staphylococcus cohnii 11-B-312, while the tet(L)_A117V was located on a 6,292 bp plasmid in S. haemolyticus 11-B-93, which could be transferred to S. aureus by electrotransformation. Cloning of each of the two tet(L) variants into S. aureus RN4220 showed 16- or 8-fold increases in the minimal inhibition concentrations (MICs), which can fully confer the resistance to tigecycline (MICs from 0.125 to 2 mg/liter) and eravacycline (MICs from 0.125 to 1 or 2 mg/liter), but no increase in the MICs of omadacycline, compared with the MICs of the recipient strain S. aureus RN4220. In the in vivo murine sepsis and in the murine pneumonia models, an increase in CFU of S. aureus 29213_pT93 carrying the tet(L)_A117V was seen despite tigecycline treatment. This observation suggests that the tet(L)_A117V and its associated gene product compromise the efficacy of tigecycline treatment in vivo and may lead to clinical treatment failure. Our finding, that novel Tet(L) efflux pump variants which confer tigecycline and eravacycline resistance have been identified in Staphylococcus spp., requires urgent attention. IMPORTANCE Tigecycline and eravacycline are both important last-resort broad spectrum antimicrobial agents. The presence of novel Tet(L) efflux pump variants conferring the resistance to tigecycline and eravacycline in Staphylococcus spp. and its potential transmission to S. aureus will compromise the efficacy of tigecycline and eravacycline treatment for S. aureus associated infection in vivo and may lead to clinical treatment failure.

Keywords: Staphylococcus aureus; Staphylococcus spp.; Tet(L); efflux pump; tigecycline; variant.

FIG 1

Genetic structure of the tet(L) variants in this study and its comparison with the similar region in those deposited in GenBank. (a) Genetic structure of the chromosomal tet(L)_F58L in S. cohnii 11-B-312 and its comparison with the similar region in S. aureus NX-T55. (b) Genetic structure of plasmid-borne tet(L)_A117V in transformant and its comparison with the similar regions in other plasmids. The positions and transcriptional directions of the predicted ORFs are indicated by arrows. The antimicrobial resistance genes are colored in red, and insertion sequences in blue. Genes with predicted functions are showed in black. Regions of >99% homology are denoted by gray shading.

FIG 2

Murine sepsis and pneumonia infection models. (a) The schedule for infection, treatment and sacrifice in murine sepsis- and pneumonia- infection models. (b) CFU counts of S. aureus ATCC 29213 and S. aureus 29213_pT93 in the liver, spleen and kidney, respectively, in murine sepsis infection model. CFU counts of S. aureus ATCC 29213 and S. aureus 29213_ pT93 in lung in murine pneumonia model. (c) H&E staining results of tissues (liver, spleen and kidney) from the murine sepsis model after infected with S. aureus ATCC 29213 and S. aureus 29213_ pT93 and their respective tigecycline treatment groups. (d) H&E staining results of tissues (lung) from the murine pneumonia model after infected with S. aureus ATCC 29213 and S. aureus 29213_ pT93 and their respective tigecycline treatment groups. Data are mean ± standard deviation. P values were calculated using an independent two sample T-test for the log-transformed difference in CFU after treatment (***, P < 0.001).