Abstract: BACKGROUND: Periprosthetic joint infection, a serious complication after artificial joint arthroplasty, has always been a thorny problem in clinical practice. At present, the research on the characteristics of the pathogenic bacteria is insufficient, and more research is needed to help clinical diagnosis and treatment. 
OBJECTIVE: To explore the distribution and drug resistance of pathogens in periprosthetic joint infection after knee and hip arthroplasties, and to compare the characteristics of different pathogen culture results. 
METHODS: A retrospective single-center research was used to study the data of 102 cases of periprosthetic joint infection in the Department of Orthopedics, First Affiliated Hospital of Zhengzhou University from September 2013 to September 2020. Pathogen culture results, drug resistance, and other diagnosis and treatment information were collected. According to the results of pathogen culture, the patients were divided into four groups: gram-positive bacteria, gram-negative bacteria, fungi, and negative culture. The differences in general condition, clinical features, operation methods, and infection control were compared among the four groups.
RESULTS AND CONCLUSION: (1) Totally 66 of 102 patients with periprosthetic joint infection were cultured positive for pathogenic bacteria, and 71 strains of pathogenic bacteria were detected. Gram-positive bacteria accounted for 57.8%. Staphylococcus epidermidis (21.1%) and Staphylococcus aureus (15.5%) were the most common. Gram-negative bacteria accounted for 29.6% and Escherichia coli (12.7%) was the most common. Fungi accounted for 12.7%, with Candida parapsilosis (5.6%) being the most common. (2) Gram-positive bacteria had high resistance rates to penicillin G, oxacillin, clindamycin, and erythromycin, and 0% to vancomycin, tigecycline, and linezolid. Gram-negative bacteria had a high resistance rate to antibiotics such as quinolones, gentamicin, ampicillin, and cefazolin; no drug-resistant fungi had been found. (3) There was no significant difference in sex, age, basic disease, operation site, infection type, sinus, operation mode, and infection control rate among the four groups (P > 0.05). In early infection, the C reactive protein in culture negative group was lower than that in gram-positive bacteria group (P < 0.05), and red serum sedimentation rate and white blood cell count in culture negative group were significantly lower than those in gram-negative bacteria group (P < 0.05). Leukocyte, C-reactive protein, and erythrocyte sedimentation rate of hip periprosthetic infection were higher than those of knee periprosthetic infection (P < 0.05). (4) It is concluded that the main pathogen causing periprosthetic joint infection is still gram-positive bacteria, of which Staphylococcus accounts for the largest proportion. The increase of Candida parapsilosis infection is worthy of attention. Multiple pathogenic bacteria have a high drug resistance rate to some conventional antibiotics, so the use of antibiotics should be adjusted in time according to the results of drug susceptibility and efficacy. 

Key words: periprosthetic joint infection, pathogen, drug resistance, gram-positive bacteria, gram-negative bacteria, culture negative, inflammatory index