ABSTRACT
Objective To investigate the resistance profile of Klebsiella pneumoniae isolates in Huashan Hospital, Fudan University. Methods The MICs of fluoroquinolones were determined by agar dilution method against 112 clinical strains of K. pneumoniae. Multilocus sequence typing (MLST) were applied to 48 K. pneumoniae strains. The characteristic sequence type (ST) associated with antibiotic resistance was identified by PCR. Results Lower percentage (＜40％) of K. pneumoniae strains were susceptible to fluoroquinolones. Majority (86.2％) of ciprofloxacin non-susceptible K. pneumoniae strains belonged to CC1 (ST11), ST494 or CC4 (ST15 and ST655), indicating the potential of clonal dissemination. ST494 (18.8％) was the second commonest sequence type, next only to ST11. ST494 strains harbored the genes encoding beta-lactamases, oqxAB, qnrD, aac-(6')-lb-cr and armA and had a single point mutation in gyrA. Therefore, ST494 strains were highly resistant to cephalosporins, fluoroquinolones and aminoglycosides and 22％ of the strains were resistant to carbapenems. However, all the ST494 strains were susceptible to tigecycline and tetracycline. Conclusions ST11 and ST494 are the commonest STs of K. pneumoniae conferring multidrug resistance in this hospital. These STs may contribute to the high resistance rates of K. pneumoniae to fluoroquinolones. The susceptibility of ST494 strains to tigecycline and tetracycline allows us to consider the promising potential of such drugs in managing K. pneumoniae infections.
ABSTRACT
Objective To profile 16S rRNA methylase genes and the flanking sequences in extensively drug resistant (XDR) Pseudomonas aeruginosa. Methods A total of 59 strains of XDR P. aeruginosa were collected. MICs of antimicrobial agents against these strains were determined by agar dilution method. The genes encoding 16S rRNA methylase (armA, rmtA, rmtB, rmtC, rmtD, rmtE, and npmA) were analyzed by PCR. The homology of strains was studied by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR). The structure of armA and rmtB flanking regions were characterized. Results The overall prevalence of armA or rmtB genes was 62.7％ (37/59) in XDR P. aeruginosa isolates, specifically armA positive in 17 strains and rmtB positive in 22 strains. The rmtA, rmtC, rmtD, or npmA gene was not identified in any strain. ERICPCR generated 19 types (or clones) from the 59 strains. The 17 armA-positive strains were distributed in 3 clones, and 88.2％ of the armA-positive strains (15) belonged to clone D. The rmtB gene was dispersed in 9 clones. Flanking sequence analysis demonstrated that armA gene was located in a mobile element carrying multiple transposases. The sequence of the mobile element showed 99％ similarity with the sequence of armA-positive plasmid carried by E. coli and A. baumannii. The rmtB gene was also located in a mobile element containing multiple transposases. The sequence of the mobile element was highly consistent with that of rmtB-positive plasmid carried by E. coli and K. pneumoniae. Conclusions The genes encoding 16S rRNA methylase are prevalent in XDR P. aeruginosa strains. All the genes were identified in high-level gentamicin-resistant strains. Clonal dissemination may explain the spread of armA among P. aeruginosa isolates.
ABSTRACT
Objective. To understand drug susceptibilities to common antibacterials, resistance mechanism to β-lactams and quinolones and the clonal spread of resistant stains of Haemophilus influenzae (H. influenzae) and Haernophilus parainfluenzae (H. parainfluenzae) isolated from some hospitals in Shanghai. Methods The in vitro antimicrobial susceptibilities to 13 antibacterials, such as ampicillin, of 156 Haemophilus strains collected from 5 hospitals of Shanghai in 2006 were tested by agar dilution method. The β-lactamase production was determined by chromogenic cephalosporin test. TEM and ROB type of β-lactamase genes and quinolone resistance determining regions (QRDR) of ciprofloxacin-resistant strains were detected by polymerase chain reaction (PCR) amplification. The homology of H. influenzae strains were analyzed by enterobacterial repetitive intergenic consensus (ERIC)-PCR. Results The susceptible rate of 109 strains H. influenzae to ampicillin was 74.3%, while those to ampicillin-sulbactam, cephatosporins and fluoroquinolones were all 100.0%. The β-lactamases-producing rates of 109 strains H. influenzae and 47 strains H. parainfluenzae were 25.7% and 19.1% (χ2=0.776,P=0.378), respectively. TEM gene was detected in all β-lactamases-producing strains. Of 109 H. influenzae isolates, only one was resistant to ciprofloxacin, and Ser84Leu mutation was detected in gyrA gene and Gly206Arg mutation in parC gene. The results of ERIC-PCR showed that 106 H. influenzae strains were clustered into 73 groups with similarity level of 85%. Conclusions Clinical isolates of H. influenzae from hospitals in Shanghai remain highly susceptible to common antimicrobial agents except ampicillin. TEM type of β-lactamase production is the main ampicillin-resistant mechanism of the tested stains. The clonal spread of H. influenzae, including ampicillin-resistant strains, is not prevalent.