[Evolution of susceptibility to antibiotics of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumanii, in a University Hospital Center of Beirut between 2005 and 2009].

INTRODUCTION: Until recently, multiresistant bacteria were only limited to hospitals. However, they are now responsible for community acquired infections, affecting people who have had no contact with the hospital environment. Several mechanisms are associated with these resistances. The production of betalactamases is however the predominant mechanism and especially the production of extended spectrum beta-lactamases or ESBL by strains of Escherichia coli and Klebsiella pneumoniae, which mediate resistance to third generation cephalosporins and aztreonam (AZT). The association of multiple mechanisms of resistance (efflux pumps, impermeability and enzymatic inactivation) generates multi resistant bacteria such as Pseudomonas aeruginosa MDR and Klebsiella pneumoniae MDR.

AIM OF THE STUDY: The aim of the study was to analyze retrospectively the susceptibility to antibiotics of strains of E. coli, K. pneumoniae, P. aeruginosa and A. baumanii isolated from hospitalized and outpatients in a university hospital center of Beirut over a period of five years from 2005 to 2009.

MATERIALS AND METHODS: Bacterial strains were classified according to their origin (inpatients versus outpatients), their ability to produce or not ESBLs for E. coli and K. pneumonia and if they were MDR for P. aeruginosa and A. baumanii. Antibiotics susceptibilities were retrieved from the informatics database of the hospital. Comparison of susceptibility percentages was done using a unilateral z-test on a computer program.

RESULTS: In 2009, 2541 strains of E. coli were isolated, 773 of which or 30.4 % were ESBL producers while 2031 strains were isolated in 2005, of which 361 or 17.8 % were ESBL producers (p<0.001). We noticed a decrease in hospital strains susceptibility to ceftazidime (CAZ) and AZT, between 2005 and 2009 (p<0.001), and a decrease in community strains susceptibility to triméthoprime/sulfaméthoxazole (SXT) between 2005 and 2009 (p=0.03). We noted however a significant decrease of ESBL producing strains between 2007 and 2009: 33.4 % versus 30.4 % (p=0.03). Among 560 strains of K. pneumoniae isolated in 2009, 178 strains or 31.8 % were ESBL producers in comparison to 23.7 % of the strains isolated in 2005 (p=0.03). We also noticed a decrease in hospital strains susceptibility to piperacilline-tazobactam (TZP), cefotaxime (CTX) and AZT (p<0.001 p=0.03 and p=0.03 respectively) between 2006 and 2009, and a significant increase in ESBL producing strains between 2008 et 2009 (p=0.0001). 26.5 % of P. aeruginosa strains isolated in 2009 were MDR bacteria with no significant change as compared to 26.6 % in 2005 (p=0.5). However, the percentage of MDR strains slightly decreased between 2008 and 2009 (p=0.047). The susceptibility of MDR strains to CAZ and imipenem (IMP) decreased between 2005 and 2009 (p<0.001 and P=0.003 respectively). As for A. baumanii, 77.7 % of strains were MDR in 2009 in comparison to 73.4 % in 2005 (p=0.24) with a dramatic decrease of MDR strains susceptibility to IMP from 92.3 % in 2006 to 30 % in 2009 (p<0.001).

CONCLUSION: Despite restrictions on antibiotics prescriptions and isolation of patients harboring MDR bacteria or bacteria producing ESBL, there has not been satisfactory reduction of multi resistant bacteria and efforts should be made to reduce these bugs from the hospital flora.