Carbapenems such as imipenem and meropenem are the first-line agents for the treatment of serious nosocomial infections caused by multidrug-resistant Enterobacteriaceae clinical isolates (2). However, the phenomenon of carbapenem resistance is emerging among a wide variety of these species (11). Carbapenemases have been widespread in recent years and predominantly contribute to carbapenem resistance among Enterobacteriaceae, especially Klebsiella pneumoniae and Citrobacter freundi (8). For screening of the carbapenem-resistant Enterobacteriaceae clinical isolates, we conducted a surveillance study of carbapenem-resistant Enterobacteriaceae isolates in order to investigate the frequency and prevalence of K. pneumoniae carbapenemase (KPC)-type genes in Huashan Hospital (Fudan University, Shanghai, China), a 1,300-bed tertiary care hospital. We hereby report a high prevalence of carbapenem-resistant K. pneumoniae isolates carrying the KPC-2-type carbapenemase gene or KPC-2-type carbapenemase gene coupled with the CTX-M-type extended-spectrum β-lactamase (ESBL) gene.
From January 2005 to March 2010, 109 nonduplicate Klebsiella pneumoniae isolates with resistance to ertapenem were collected. Antimicrobial susceptibility testing was performed by the agar dilution method, and MICs were interpreted following CLSI (4) or British Society for Antimicrobial Chemotherapy (BSAC) criteria (1). The presence of genes encoding β-lactamases, including metallo-β-lactamases (MBLs), KPC-type and OXA-type carbapenemases, ESBLs, and plasmid-mediated AmpC enzymes were screened by PCR using primers described by Rasheed et al. (10). All amplified products were then subjected to direct nucleotide sequencing. The results were analyzed with the software available on the National Center for Biotechnology Information website (http://www.ncbi.nlm.nih.gov).
The susceptibility rates of 109 K. pneumoniae isolates to imipenem, meropenem, and ertapenem were 4.6%, 2.8%, and 0.0%, respectively (Table 1). Carbapenem-resistant Enterobacteriaceae isolates exhibited high resistance rates against the carbapenem agents tested, with MIC90 values of 128 μg/ml or higher. Totals of 96.3%, 74.3%, 66.1%, and 64.2% of isolates were susceptible to colistin, minocycline, tigecycline, and doxycycline, respectively (Table 1). KPC-2-type carbapenemase was the most predominant carbapenemase, present in 70.6% (77/109) of isolates. KPC-2-type carbapenemase coupled with CTX-M-14- or CTX-M-15-type ESBL accounted for 59.6% (65/109) of isolates. A total of 10.1% (11/109) of KPC-positive isolates were simultaneously producing both CTX-M-14-type ESBL and DHA-1-type plasmid-mediated AmpC enzymes. GIM-1-type or VIM-1-type MBL, OXA-type carbapenemases were detected in 9.2% (10/109) and 10.1% (11/109) of isolates, respectively.
Table 1.
Microbiological activities of various antimicrobial agents against 109 carbapenem-resistant K. pneumoniae isolates
| Drug | MIC (μg/ml)a |
% susceptible | ||
|---|---|---|---|---|
| Range | 50% | 90% | ||
| Imipenem | 0.25–256 | 32 | 128 | 4.6 |
| Meropenem | 0.5–>256 | 64 | 128 | 2.8 |
| Ertapenem | 1–>256 | 128 | >256 | 0.0 |
| Panipenem | 1–>512 | 64 | 256 | |
| Colistin | 0.5–128 | 1 | 2 | 96.3 |
| Tigecycline | 0.25–8 | 1 | 4 | 66.1 |
| Minocycline | 0.06–128 | 2 | 32 | 74.3 |
| Doxycycline | 0.06–64 | 4 | 64 | 64.2 |
| Fosfomycin | 0.5–256 | 128 | 256 | 45.0 |
| Cefepime | 2–256 | 256 | 256 | 1.8 |
| Ceftazidime | 1–>256 | 256 | >256 | 1.8 |
| Cefotaxime | 4–>256 | >256 | >256 | 0.0 |
| Cefoxitin | 0.06–>256 | 128 | >256 | 1.8 |
| Cefoperazone-sulbactam | 2–256 | 256 | 256 | 4.6 |
| Piperacillin-tazobactam | 0.25–256 | 256 | 256 | 1.8 |
| Aztreonam | 16–>256 | >256 | >256 | 0.0 |
| Amikacin | 1–512 | >256 | >256 | 14.7 |
| Ciprofloxacin | <0.06–256 | 256 | 256 | 8.3 |
50% and 90%, MIC50 and MIC90, respectively. According to the British Society for Antimicrobial Chemotherapy (BSAC) criteria (1), a colistin MIC of ≤2 mg/liter indicates susceptible and >2 mg/liter indicates resistant and a tigecycline MIC of ≤1 mg/liter indicates susceptible, 2 mg/liter indicates intermediate, and >2 mg/liter indicates resistant.
In this study, we have reported for the first time the frequency of KPC-2-type carbapenemases with or without CTX-M-type ESBLs among carbapenem-resistant K. pneumoniae isolates in China. In our hospital, the incidence of carbapenem-resistant K. pneumoniae isolates showed a significant increase from 0.9% in 2005 to 12.9% in 2009. These results suggested that the rapidly increased prevalence of carbapenem resistance among K. pneumoniae isolates in our hospital could be the consequence of the failure to control the spread of these strains. Therefore, prompt detection of carbapenemase-producing Enterobacteriaceae isolates, active antibiotic resistance surveillance, and strict implementation of infection control measures are critical to avoid the rapid spread or outbreaks by these multidrug-resistant or pan-drug-resistant isolates in health care-associated facilities (3, 5–7, 9).
Acknowledgments
This work was supported by the Shanghai Municipal Natural Science Foundation (no. 11ZR1404700).
Footnotes
Published ahead of print on 14 February 2011.
Contributor Information
Demei Zhu, Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai 200040, China.
Honghai Wang, State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, 12 Wulumuqi Zhong Road, Shanghai 200433, China.
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