| Staphylococci,especially Staphylococcus aureus,are the main cause of skin and soft tissue infections,and have become one of the important pathogens of nosocomial infections.Staphylococci have diverse pathogenicity and can cause a variety of infectious diseases,such as soft tissue infection,endocarditis,pneumonia.Tigecycline is one of the limited options for the treatment of methicillin-resistant Staphylococcus aureus,vancomycin-resistant enterococci and other infections,and is mainly used to treat complex skin and intra-abdominal infections in clinical practice.With the widespread use of tetracycline in farm,some drug-resistant strains,including tigecycline-resistant staphylococci,have been generated in veterinary clinics.At present,there are few reports on the drug resistance of staphylococci to tigecycline,and the related resistance mechanism has not been fully elucidated.Therefore,this study deeply explores the mechanism of tigecycline resistance from staphylococci in swine,which is of great significance to scientific prevention and control of tigecycline resistance transmission and veterinary public health.In this study,the isolation and identification of staphylococci in swine,antimicrobial susceptibility testing,electrotransformation experiments,whole genome sequencing and bioinformatics analysis,gene cloning and functional analysis,murine sepsis and pneumonia model,in vivo experimental treatment and other experiments to further explore the resistance mechanism of tigecycline in staphylococci from swine.In this study,362 strains of staphylococci were isolated and identified from swine farms in some areas of Henan province,and two strains of tigecycline-resistant staphylococci were identified,which were Staphylococcus hemolyticus 11-B-93 and Staphylococcus cohnii 11-B-312.The results of whole genome sequencing showed that two tet(L)variants were found in the two staphylococci strains,named tet(L)A117V and tet(L)F58L,respectively.The results of gene cloning and functional analysis showed that two tet(L)variants could confer to the resistance phenotype of staphylococci to tigecycline(16-fold increase in MIC)and eravacycline(8-16-fold increase in MIC).Genetic environment analysis shows that tet(L)F58L is located in the 18720 bp multidrug resistance gene cluster in S.cohnii 11-B-312 chromosome,which also includes resistance genes: aad D1,lnu(B),lsa(E),spw and aad E,flanked by two IS257 in the same direction;tet(L)A117V is located in a 6292 bp plasmid in S.hemolyticus 11-B-93 and also includes the resistance gene erm(T),which can be transferred horizontally.In vivo experimental treatment with tigecycline results show that the presence of tet(L)A117V affects the therapeutic effect of tigecycline and may lead to tigecycline treatment failure.In conclusion,this study identified two novel tet(L)variants in Staphylococcus spp.,both of which contributed to full resistance to tigecycline and eravacycline in staphylococci,and expanded understanding of the mechanism of tigecycline resistance in gram-positive bacteria.Moreover,In vivo experimental treatment with tigecycline showed that the presence of the tet(L)gene variant resulted in a decrease in the therapeutic efficacy of tigecycline and even failure of clinical treatment.Therefore,measures to monitor and control the dissemination of the novel tet(L)variants in both animal and human clinical strains are needed. |
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