OBJECTIVE

To measure the in vitro activity of a panel of antimicrobial agents against gram-negative pathogens collected from the nine census regions of the USA.

METHODS

Isolates were collected from 76 centers between January 2004 and September 2005. In vitro activity was assessed using CLSI guidelines and CLSI or FDA interpretive criteria.

RESULTS

The lowest overall antimicrobial susceptibilities for Acinetobacter calcoaceticus-baumannii complex isolates (n=851) were detected in the Middle Atlantic and East South Central regions. Overall, 29.3% of A. calcoaceticus-baumannii complex isolates were multidrug-resistant (resistant to > or =3 antimicrobial classes). Tigecycline (2 microg/mL) had the lowest MIC90 against this organism. Imipenem, tigecycline, and levofloxacin had low MIC90s (0.25-4 microg/mL) against Enterobacter spp. (n=1557), although the MIC90 for levofloxacin was elevated for East South Central region isolates (> or = 16 microg/mL). Susceptibility to levofloxacin among the E. coli isolates (n=1785) ranged from 71.7% (Pacific) to 88.5% (New England). The prevalence of ESBL-producing K. pneumoniae (126/1460) varied from 1.7% of isolates (Pacific) to 21.2% (Middle Atlantic). ESBL-producing K. pneumoniae MICs were lowest for imipenem and tigecycline.

CONCLUSIONS

Antimicrobial susceptibility varies among the census regions of the USA. The broad-spectrum in vitro activity of tigecycline may make it a suitable candidate for use in the empiric treatment of serious infections.