Pseudomonas aeruginosa clones disseminated among patients in a tertiary care teaching hospital in Greece during a two-year period

Abstract number: P1501

Koutsogiannou M., Drougka E., Anastassiou E.D., Christofidou M., Spiliopoulou I.

Objective:Pseudomonas aeruginosa is a cause of a wide diversity of infections in immunocompromised hosts. The high level of antibiotic resistance combined with the frequent spread of epidemic strains make P. aeruginosa one of the major nosocomial pathogens. Antibiotic resistance patterns, serotypes and clones were determined in P. aeruginosa isolates recovered from clinical samples of different hospitalised patients during a two-year period.

Methods: A total of 220 P. aeruginosa isolates recovered from inpatients during 2006–2007 were identified at species level by standard methods (Oxiferm, BD, BBL). Antibiotic susceptibility testing was performed by the agar disk diffusion method according to CLSI guidelines. MIC of colistin (CL) was determined by the Etest (AB Biodisk) and the production of metallo-b-lactamases (MBL) was tested by the double strip Etest. Serotyping was performed by 17 monovalent antisera against the O antigen according to the International Antigenic Typing Scheme. Clones were defined by PFGE of chromosomal DNA SpeI digests.

Results: Eighty-four isolates were recovered from patients hospitalised in the Intensive Care Unit (ICU), followed by the Departments of Internal Medicine (74), Surgery (23), Paediatrics (20) and Outpatients (19). Sixty-one P. aeruginosa were isolated from respiratory tract samples from the ICU, followed by wounds' infections (56), bacteraemias (37), urinary tract (37), catheters (12) and stool specimens (17). Multi-resistant isolates were 52% and 61% in 2006 and 2007 respectively; MBL-positive isolates were 42 (19%), while no isolate was resistant to colistin. The predominant serotype was O:11 (112 isolates), followed by O:1 (18). Eighty clones were identified by PFGE, with five predominant: A (74 strains), B (9 strains), C (6 strains), D (28 strains) and S (5 strains). Four out of five clone S strains were recovered from children. These clones were dominant in the hospital during the two-year period. Serotype O:11 strains were classified into clones A and D, isolated mainly from the ICU. Among MBL-positive strains 16 belonged to clone D and were serotype O:11, six to clone A and four to clone B.

Conclusions: Multi-resistant P. aeruginosa strains are disseminated in our hospital, mainly among ICU patients. Polyclonality combined with the spread of certain dominant clones including multi-resistant strains, indicate the need of appropriate antibiotic policy and continuous infection control measures.