Objective  To investigate the antimicrobial resistance of clinical bacterial isolates in Peking Union Medical College Hospital (PUMCH) in 2015.

  Methods  A total of 5746 non-duplicate clinical isolates from January 1 to December 31 2015 were collected. Disc diffusion test (Kirby-Bauer method) and automated systems were employed to detect the antimicrobial resistance. The data were analyzed by WHONET 5.6 software according to 2015 edition of antimicrobial susceptibility testing standards issued by The Clinical and Laboratory Standards Institute (CLSI) of the United States.

  Results  Of the 5746 clinical isolates, the 10 most common bacteria were:Escherichia coli (19.4%), Pseudomonas aeruginosa (11.3%), Klebsiella pneumoniae (10.9%), Staphylococcus aureus (9.8%), Acinetobacter baumannii (9.6%), Enterococcus faecalis (6.5%), Streptococcus agalactiae (5.1%), Enterococcus faecium (4.6%), coagulase-negative Staphylococcus(2.7%), and Enterobacter cloacae(2.5%). Gram-negative bacilli and gram-positive cocci accounted for 67.5% and 32.5%, respectively. Among Staphylococcus aureus and Staphylococcus isolates, methicillin-resistant Staphyloccus aureus(MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCNS) accounted for 22.9% and 77.6%, respectively. The resistance rates of MRSA and MRCNS strains to β-lactams and other antimicrobial agents were much higher than those in methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-susceptible coagulase-negatible Staphylococcus (MSCNS) strains. 88.8% of MRSA strains were still susceptible to trimethoprim-sulfamethoxazole, while 81.7% of MRCNS strains were susceptible to rifampin. No staphylococcal strain resistant to vancomycin, teicoplanin, or linezolid was detected. The resistance rate of E. faecalis strains to most of the antimicrobial agents tested (except Chloramphenicol) was much lower than that of E. faecium, while some strains resistant to vancomycin were found in both species. No linezolid-resistant Enterococcus strains was found. 90.8% of β-hemolytic streptococcus strains were susceptible to penicillin. Extended-spectrum β-lactamase (ESBL)-producing strains accounted for 52.3%(582/1112), 28.9%(200/692), and 26.2%(27/103) in E.coli, Klebsiella spp(K.pneumoniae and K.oxytoca), and P.mirabilis, respectively. Enterbacteriaceae strains were still highly susceptible to carbapenems, with an overall resistance rate of ≤ 4.3%. A few extensively-resistant strains of K.pneumoniae (3.0%, 19/630) were identified. About 76.5% and 74.8% of A.baumannii were resistant to imipenem and meropenem, while the resistant rates to cefoperazone-sulbactam (49.8%) and minocycline (21.8%) were the lowest. The resistance rates of P.aeruginosa to imipenem and meropenem were 16.6% and 11.9%, respectively, while the resistant rate (5.2%) to amikacin was the lowest. The prevalence of extensively-resistant strains in A.baumannii and P.aeruginosa were 20.8% (115/553) and 1.8% (12/650), respectively.

  Conclusions  Antibiotic resistance may still pose a serious threat to clinical practice. Rational use of antibiotics should be required to prevent the spread of antimicrobial resistant strains.