The prevalence of extended-spectrum β-lactamase (ESBL) in Enterobacteriaceae has been increasing worldwide. The aims of this study were to determine the prevalence of ESBLs among clinical isolates of Escherichia coli obtained from 2000 to 2010 in Japan, and to characterize the sequence type (ST) and antimicrobial susceptibility of the blaCTX-M-carrying strains. The genes for β-lactamases were determined by conventional PCR and sequencing, and the antimicrobial susceptibility test was performed by the broth microdilution method. Among the 948 strains, 35 were judged as ESBL-positive strains. The positive rates ranged from 0.6% to 3.9% until 2008, but surged to 10.3% in 2010. Thirty-three of them carried blaCTX-M, but all were negative for ESBL-type blaTEM and blaSHV. blaCTX-M-14 was the most prevalent (18/33) among blaCTX-M-carrying strains, followed by blaCTX-M-15 (7/33) of which five were isolated in 2008 and 2010. Additionally, blaCTX-M-27 appeared in 2010 for the first time in this study and accounted for more than a third of the blaCTX-M-carrying strains. From the MLST analysis, ST131 known as a world pandemic clone, has been predominantly isolated since 2006. The major types of ESBLs carried by ST131 strains clearly shifted from blaCTX-M-14 to blaCTX-M-15 and/or blaCTX-M-27 between 2006 and 2010. Most of these isolates were still susceptible to doripenem, latamoxef (moxalactam), flomoxef and cefmetazole. Our results suggest that a change of the dominant type of ESBL among Enterobacteriaceae is currently in progress in Japan, and therefore further periodic surveillance is needed.

From October 2010 to September 2011, we collected the specimen from 361 patients with lower respiratory tract infections in 16 institutions in Japan, and investigated the susceptibilities of isolated bacteria to various antibacterial agents and patients’ characteristics. All of 399 strains that were isolated from specimen (mainly from sputum) and assumed to be bacteria causing in infection, were examined. The isolated bacteria were: Staphylococcus aureus 70, Streptococcus pneumoniae 65, Haemophilus influenzae 72, Pseudomonas aeruginosa (non-mucoid) 47, P. aeruginosa(mucoid) 14, Klebsiella pneumoniae 30, and Moraxella catarrhalis 39.

Of 70 S. aureus strains, those with 2 g/mL or less of MIC of oxacillin (methicillinsusceptible S. aureus: MSSA) and those with 4μg/mL or more of MIC of oxacillin (methicillinresistant S. aureus: MRSA) were 45 (64.3%) and 25 (35.7%) strains, respectively. Against MSSA, imipenem had the most potent antibacterial activity and inhibited the growth of all strains at 0.063μg/mL or less. Against MRSA, vancomycin and arbekacin showed the potent activity and inhibited the growth of all the strains at 2μg/mL. Linezolid also showed the great activity and inhibited the growth of all the strains at 2μg/mL. Carbapenems and penems showed the most potent activities against S. pneumoniae and panipenem inhibited the growth of all the strains at 0.125μg/mL. Imipenem and faropenem also had a preferable activity and inhibited the growth of all the strains at 0.5 and 1μg/mL, respectively. In contrast, there were high-resistant strains (MIC: >128μg/mL)for erythromycin(44.6%)and clindamycin(24.6%). Against H. influenzae, levofloxacin showed the most potent activity and its MIC₉₀ was 0.063μg/mL or less. Meropenem showed the most potent activity against P. aeruginosa (mucoid) and its MIC₉₀ was 0.5μg/mL. Against the non-mucoid type of P. aeruginosa, tobramycin had the most potent activity and its MIC₉₀ was 2μg/mL. Against K. pneumoniae, cefozopran had the most potent activity and inhibited the growth of all the strains at 0.063μg/mL or less. All the antibacterial agents except ampicillin generally showed a potent activity against M. catarrhalis and the MIC₉₀ of them were 2μg/mL or less.

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From October 2011 to September 2012, we collected the specimen from 316 patients with lower respiratory tract infections in 16 institutions in Japan, and investigated the susceptibilities of isolated bacteria to various antibacterial agents and patients’ characteristics. All of 357 strains that were isolated from specimen (mainly from sputum) and assumed to be bacteria causing in infection, were examined. The isolated bacteria were: Staphylococcus aureus 51, Streptococcus pneumoniae 73, Haemophilus influenzae 88, Pseudomonas aeruginosa (non-mucoid) 34, P. aeruginosa(mucoid) 9, Klebsiella pneumoniae 21, and Moraxella catarrhalis 33.

Of 51 S. aureus strains, those with 2μg/mL or less of MIC of oxacillin (methicillinsusceptible S. aureus: MSSA) and those with 4μg/mL or more of MIC of oxacillin (methicillinresistant S. aureus: MRSA) were 31(60.8%) and 20(39.2%) strains, respectively. Against MSSA, imipenem had the most potent antibacterial activity and inhibited the growth of all strains at 0.063μg/mL or less. Against MRSA, vancomycin showed the potent activity and inhibited the growth of all the strains at 1μg/mL. Linezolid also showed the great activity and inhibited the growth of all the strains at 2μg/mL. Carbapenems and penems showed the most potent activities against S. pneumoniae and panipenem inhibited the growth of all the strains at 0.125μg/mL. Imipenem and faropenem also had a preferable activity and inhibited the growth of all the strains at 0.5 and 1μg/mL, respectively. In contrast, there were high-resistant strains (MIC: >128μg/mL) for erythromycin (53.4%)...

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