In vitro activity of imipenem ± aminoglycosides against Pseudomonas aeruginosa and Acinetobacter calcoaceticus / baumanii isolated from patients in ICUs in German hospitals (1999–2002)

Objectives

Carbapenems such as imipenem (IM) provide important antimicrobial activities against Pseudomonas aeruginosa (PA) and Acinetobacter calcoaceticus/baumanii (ACB). Additionally co-administration with an aminoglycoside provides broad-spectrum coverage. The current activity of IM, and the activity of IM and gentamicin (GN) or amikacin (AK), considered together, was reviewed by analysis of cross-susceptibility to this combination, as reported to physicians, by clinical microbiology laboratories in Germany.

Methods

Data were analyzed (January 1999-October 2002) from The Surveillance Network^® (TSN) Database Germany, an electronic surveillance system that collects routine susceptibility test results from 169 hospital laboratories distributed throughout the country. Only data from nonrepeat isolates from patients > 17 years of age, located on ICUs, and derived from antibiotics concomitantly tested were included in the analysis. NCCLS (2002) breakpoints were used to interpret the data.

Results

For all PA (n = 1316) isolated from lower respiratory tract infection (LRTI) specimens during 1999–2000, 65.3% were reported susceptible (S) and 20.9% resistant (R) to IM. The following susceptibility and resistance frequencies were found for PA from LRTI, reported by year: 1999 (n = 127; 65.4% S; 31.5% R), 2000 (n = 346; 66.5% S; 28.9% R), 2001 (n = 539; 63.5% S; 15.4% R), and 2002 (n = 304; 67.1% S; 17.1% R). Among PA from blood reported by year: 1999 (n = 7; 85.7% S; 14.3% R), 2000 (n = 20; 80.0% S; 15.0% R), 2001 (n = 31; 74.2% S; 16.1% R), and 2002 (n = 39; 84.6% S; 12.8% R). Considering data of IM combined with an aminoglycoside, for PA from LRTI isolated during 2000–2002, 86.3% of isolates were S (n = 1634; 5.8% R) to both IM and gentamicin (GT), and 93.8% of isolates were S (n = 1171; 2.8% R) to IM and AK. PA isolates from blood were 89.1% S (n = 64; 3.1% R) to the combination of IM and GT, and 100% S (n = 45) to the combination of IM and AK. Overall (2000–2002) for ACB isolated from LRTI, 98.2% were S (n = 225; 0% R) compared with 100% S (n = 25) for blood isolates. For ACB by year, the following IM susceptibility percentages were detected: 90.5% S in 2000 (n = 21; 9.5% R), 99.3% S in 2001 (n = 143; 0.7% R), and 97.5% S in 2002 (n = 163; 0% R).

Conclusions

In Germany, IM susceptibility has remained consistent for PA since 1999 and ACB since 2000, and no increase in resistant phenotypes was detected. Combinations of IM with an aminoglycoside still approach 100% coverage against PA.