Invasive Group B Streptococcus Isolates Showing Reduced Susceptibility to Penicillin in Hong Kong

and Enterobacter spp. isolates were inhibited at MIC values of 1, 2 and 2 mg/L, respectively. For K. pneumoniae, MIC50 and MIC90 values of tigecycline were 0.25 and 2 mg/L, respectively. The Etest results were confirmed by the broth microdilution method. According to US Food and Drug Administration recommendation for tigecycline (susceptible 2 mg/L and resistant 8 mg/L), all isolates were susceptible and only one (1%) K. pneumoniae strain displayed an intermediate MIC of 4 mg/L. When the European Committee on Antimicrobial Susceptibility Testing breakpoint criteria (susceptible 1 mg/L and resistant .2 mg/L) were used, the percentage of tigecycline susceptibility decreased. Only 4 (31%) Enterobacter spp. and 78 (89%) K. pneumoniae isolates tested were susceptible. Furthermore, all S. marcescens were characterized as intermediate. The isolates collected in this study were broadly resistant to b-lactams, fluoroquinolones and variably to aminoglycosides. Currently, multidrug-resistant Gram-negative bacteria remain the most problematic pathogens worldwide, especially in intensive care units. Carbapenem antibiotics were important agents for the management of those infections. Over the past few years, the progressive increase in carbapenem-resistant Gram-negative non-fermentative bacilli as well as the spread of genes encoding carbapenem-hydrolysing enzymes in enterobacterial species is of great concern, leaving limited choices for therapeutic regimens. Tigecycline was active against MBL-producing members of the family Enterobacteriaceae, inhibiting 99% of them at a concentration of 2 mg/L. A recent study demonstrated that tigecycline was effective against multiresistant K. pneumoniae strains producing Klebsiella pneumoniae carbapenemase (KPC), an ESBL belonging to molecular class A enzymes with activity against carbapenems. In addition, it was active against clinical isolates possessing blaVIM, but the number of MBL producers tested was small. Our results confirm the in vitro activity of tigecycline against Enterobacteriaceae possessing carbapenemases. Its broad-spectrum activity combined with its stability against common resistance mechanisms and the lack of crossresistance with other classes of antibiotics make tigecycline a therapeutic agent for the treatment of infection caused by multiresistant microorganisms. However, the in vitro results require support from clinical studies.