Studv On The Resistance Mechanisms And Clinical Characteristics Of Muitidrug Clinical Characteristics Of Multidrug Resistant Klebsiella Pneumoniae

Enterobacteriaceae are one kind of the most commonly confronted clinical pathogens, as well as constitutions of normal intestinal flora. The status of antimicrobial resistance in Enterobacteriaceae deteriorated greatly during the last decade, leaving carbapenems such as imipenem and meropenem the first-line therapy for severe infections caused by Enterobacteriaceae producing extended spectrum β lactamases (ESBLs). The emergence of carbapenem-resistant enterobacteria is therefore worrisome, since consequently the antimicrobial treatment options are very restricted. Klebsiella pneumoniae carbapenemase (KPC) is the most frequent class A carbapenemases pervading in carbapenem-resistant Enterobacteriaceae (CRE) so far. KPC-producing enterobacteria are usually resistant to all (3lactams, including carbapenems, as well as many antimicrobials of other classes, leaving few antibiotic-based treatments available.KPC-producing K. pneumoniae (KPC-KP) has been emerging increasingly in our hospital since the first isolate was identified in2007, which was also the first report of KPC in China. Nevertheless, most of them were still susceptible to one or more aminoglycoside antibiotics, making aminoglycosides one of the last potential effective antibiotics. However, aminoglycoside-resistance has emerged and spread in those KPC-KP isolates in our hospital. We conducted this study to elucidate the resistance mechanisms and clinical characteristics of these multidrug isolates. 1. Study on the resistance mechanisms and molecular epidemiology of KPC-KP isolatesA total of84KPC-KP isolates were identified during the study period (from January2010to December2010). Of them,48were confirmed to be rmtB positive (RPKP) by PCR and sequencing and36were negative (RNKP). All KPC-KP isolates were multidrug resistant (Table1). However,98.8%and96.3%of overall isolates were susceptible to colistin and tigecycline, respectively. Compared with RNKP, RPKP isolates displayed a much severer multidrug resistance phenotype. With regard to aminoglycosides, all RPKP showed high-level resistance undoubtedly, whereas a majority of RNKP were still susceptible to at lest one of them (88.9%for amikacin;72.2%for netilmicin;47.2%for gentamicin). In addition, RPKP isolates demonstrated much lower susceptibility rates for fosfomycin (8.5%for RPKP versus88.9%for RNKP, P<0.01) and minocycline (6.7%for RPKP versus52.8%for RNKP, P<0.01), and both the differences were significant. Apart from blaKPC-2in all isolates and rmtB in RPKP, blaCTX-M-14, blaSHV-12and blaTEM-1were revealed in most of KPC-KP isolates. No metallo-(3-lactamases and other16S rRNA methylase-encoding genes were identified. PFGE analysis of all84KPC-KP revealed10different clonal types. The most widely disseminated clonal type was A. A total of10distinct STs were identified and ST11was the predominant sequence type. RPKP and RNKP isolates shared their dominant ST and PFGE type; nonetheless, RNKP isolates were assigned to more variable PFGE profiles and STs, and relateness between their PFGE and MLST typing seemed more complex. Further plasmid analysis of the representative RPKP isolate (KP76, assigned to PFGE A clone and ST11) revealed that it co-carried rmtB, blaKPC, as well as blaCTX-M-14and blaTEM-1on a plasmid.2. Comparative analysis of clinical characteristics between RPKP and RNKP groupA total of64medical records were available, including35copies of patients with RPKP and29of patients with RNKP. Both groups had rather high ratios of male sex (80.0%in RPKP versus72.4%in PNKP); and about half of patients were in ICU when the KPC-producers were isolated. Length of stay before isolation of KPC-KP seemed a little longer in RPKP group (18.7days for RPKP versus16.2days for RNKP), while total length of stay before discharge or death was much longer in RNKP group instead (36.1days for RPKP versus45.7days for RNKP). In both group, a majority of KPC-KP isolates were acquired in our hospital, with only4RPKP (11.4%) and7RNKP (24.1%) imported from the previous hospitals. Respiratory tract was the most common site of infection in both cohorts. The top two therapies received during the past month were third-generation cepholasporins and carbapenems in both cohorts. Crude mortality among patients with RPKP was22.9%, compared with27.6%in patients with RNKP. Nevertheless, no differences between the two groups were of statistical significance.3. Environmental colonization studyIn total,210environmental samples were collected from the general ICU. Of the210samples,17(8.1%) were positive for KPC-KP, including one RPKP only. The positive samples were recovered from mops (2/4,50%), dustbins (1/4,25%), ventilator and masks (5/37,13.5%), beds (including siderails and bed linens)(2/18,11.1%), sputum aspirators (1/9,11.1%), overbed tables (3/29,10.3%), cardiac monitors (1/18,5.6%), and patient charts (1/22,4.5%), with mops ranking first in the positive rates, followed by dustbins. Areas around three of the four infected patients were contaminated, as well as areas around an adjacent patient of them. Noticeably, both the two decontaminated empty beds surveyed were positive as well. All these environmental KPC-KP isolates fell into PFGE type A, and carried resistance determinants including blaCTX-M-14, blaSHV-12and blaTEM-1.Two representative isolates (one RPKP and one RNKP isolate) were both assigned to ST11.The above results showed:1. KPC-KP isolates were multidrug resistant. Nevertheless, RPKP isolates displayed a much severer multidrug resistance phenotype compared with RNKP. rmtB was the only16S rRNA methylase-encoding gene identified in our study. RPKP and RNKP isolates shared their dominant ST (ST11) and PFGE type (clone A), indicating the ongoing spread of both RPKP and RNKP isolates in our hospital mainly attributing to the results of clonal dissemination. The dominant RPKP clone co-carried rmtB and blaKPC as well as blaCTX-M-14and blaTEM-1on a plasmid.2. No significant differences were observed in the clinical characteristics between RPKP and RNKP groups.3. Nosocomial environment may serve as a potential reservoir during the ongoing epidemic of KPC-KP in our hospital. The fact that decontaminated empty beds were also colonized by KPC-KP questioned the effectiveness of decontamination in our hospital.