Pseudomonas aeruginosa: Antibiotic susceptibility patterns

Bacteria belonging to the former genus Pseudomonas was recently modified with the creation of several genus including Pseudomonas, Stenotrophomonas, Burkholderia, Ralstonia, Comamonas... The complexity of these novel genus is in fact masked by the predominance of a single bacterial species, P. aeruginosa. Several French and foreign multicentric surveys focused on the importance of Gram-negative and non fermenters bacilli in infections. In the last decade, acquired resistance has been characterized by the emergence of new enzymatic mechanisms, formerly unsuspected, in several countries (among which Turkey and Japan): PER-1 (class A), OXA-11, OXA-14, and OXA-18 (class D), or IMP-1 (class B). These novel beta-lactamases mediate broad resistance to beta-lactams as third generation cephalosporins including ceftazidime, and even carbapenems (IMP-1). Nevertheless, the expression level of resistance may be unsuspected because highly variable. Unfortunately this bacterial species can cumulate other resistance mechanisms to aminoglycosides and fluoroquinolones (single mutation for the corresponding DNA gyrase gene or gyrA or/and topo-isomerase IV gene named parC). Such acquired multiresistance was mainly related to hospital environment, to hospitalization unit, and finally according to the patient's underlying diseases. This is related to selective pressure of antibiotics. In conclusion, choosing the adequate treatment is related to the identification of resistance mechanisms, at least for some antibiotics such as beta-lactams, it is also related to complementary laboratory tests such as killing curves of antibiotic combination.