The Clinical Aspects of β-Lactam-Resistant Stenotro- phomonas maltophilia

Recent papers argue that major increases in the isolation of multidrug-resistant Gramnegative bacteria have been of some concern in clinical practice. Among these bacteria, Stenotrophomonas maltophilia is an intrinsic producer of β-lactamases, and has been recognized as a nosocomial pathogen. But few reports are available on the impact of the potential risk of mixed infections. The goal of this review is to explore that impact. S. maltophilia is often isolated from the respiratory tract together with other Gram-negative species, and yields at least two β-lactamases. The enzymes show the capacity to hydrolyze a large amount of imipenem and ceftazidime, and exhibit a susceptibility to aztreonam in combination with cefozopran. The last section elaborates on the idea that S. maltophilia can assist in the survival of other imipenem-susceptible bacteria such as Serratia marcescens and Pseudomonas aeruginosa. This theory is also valid for ceftazidime-susceptible P. aeruginosa. The present review confirms the potential threat of S. maltophilia as an indirect pathogen, and brings an often ignored fact to light: even originally fragile bacteria can live through a strong antimicrobial attack in the presence of a helper bacteria such as S. maltophilia. Although it is sometimes difficult to attribute a causative role to this bacterium, in fact, the existence of S. maltophilia is worthy of attention.