Objective  To investigate the distribution and antimicrobial resistance of clinical bacterial isolates from medical wards in Peking Union Medical College Hospital (PUMCH) between January 1, 2011 and December 31, 2012.

  Methods  A total of 2767 non-duplicate clinical isolates were collected. Disc diffusion test (Kirby-Bauer method) and automated systems were employed to study the antimicrobial resistance. The data were analyzed by WHONET 5.6 software according to Clinical and Laboratory Standards Institute (CLSI) 2012 breakpoints.

  Results  Of the 2767 clinical isolates, gram-negative organisms and gram-positive cocci accounted for 65.3%(n=1807) and 34.7% (n=960), respectively. The 10 most common organisms isolated were Pseudomonas aeruginosa (11.5%), Escherichia coli (11.2%), Staphylococcus aureus (10.1%), Klebsiella pneumoniae (9.7%), Acinetobacter baumannii (9.4%), coagulase-negative staphylococci (5.0%), Enterobacter cloacae (4.1%), Enterococcus faecalis (3.8%), Xanthomonas maltophilia (3.6%), and Enterococcus faecalis (3.4%). Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase negative Staphylococcus(MRCNS) accounted for 33.8% and 75.8%, respectively. The resistance rates of methicillin-resistance strains to β-lactams and other antimicrobial agents were much higher than those of methicillin-susceptive strains including methicillin-susceptible Staphylococcus aureus (MSSA)and methicillin-susceptive coagulase-negative Staphylococcus (MSCNS). In addition, 87.2% of MRSA strains were still susceptible to trimethoprim-sulfamethoxazole, while 84.2% of MRCNS strains were susceptible to rifampin. No staphylococcal strains were resistant to vancomycin, teicoplanin, or linezolid. The resistance rates of E. faecalis strains to most of the drugs tested were much lower than those of E. faecium. However, the resistance rate of the E. faecium to chloramphenicol was only 4.7%. Several strains of both E. faecium and E. faecalis were found resistant to vancomycin. Most of the vancomycin-resistant strains were van-A and van-B types based on their phenotypes. No linezolid-resistant strains were found. Extended spectrum β-lactamases(ESBLs)-producing strains accounted for 66.5%, 32.6%, and 30.5% in E. coli, Klebsiella spp (K.pneumoniae and K. oxytoca), and P. mirabilis, respectively. The resistant rates of ESBLs-producing strains were all higher than the corresponding non-ESBLs-producing strains. The Enterbacteriaceae strains were still highly susceptible to carbapenems, with an overall resistance rate of only 0.9%-2.9%. Only one pan-resistant strain of K. pneumoniae (0.4%, 1/267)was identified. The resistance rates of P. aeruginosa to imipenem and meropenem were 23.4% and 17.4%, respectively. However, the P.aeruginosa isolates showed the lowest resistant rate (6.6%) to amikacin. Also, 56.8% and 57.5% of A. baumannii were resistant to imipenem and meropenem. A. baumannii isolates showed the lowest resistant rates 42.1% and 24.0%, respectively, to cefoperazone-sulbactam and minocycline. The prevalences of pan-resistant strains of A. baumannii and P. aeruginosa were 35.9% and 1.6%, respectively. The detection rate of β-lactamase in H. influenzae was 19.4%. More than 94% of S. pneumoniae strains were resistant to erythromycin and clindamycin.

  Conclusion  Regular monitoring of the bacterial resistance to antibiotics is useful to guide the rational use of antimicrobial agents.