Fluoroquinolone resistance: relation between drug use and evolution of resistance in some Units of the “San Bassiano” hospital from 2007 to 2008

There is substantial evidence that the overuse of antibiotics is a major cause for the emergence in antimicrobial resistance. This study analyzes the evolution of antimicrobial resistance to ciprofloxacin and levofloxacin from 2007 to 2008 in some Units of the “San Bassiano” hospital and compares this evolution among the consumption of the same antibiotics. The study involved the collection of all first isolates in blood, urine and transtracheal samples between 2007 and 2008; three microorganisms were chosen: Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Microorganisms investigations concerned Geriatrics, Medicine, Surgery and Intensive Care Unit (ICU) with 48, 48, 44 and 10 beds respectively. Identification and antimicrobial susceptibility testing was performed using the Phoenix automated system (Becton Dickinson). If the ciprofloxacin susceptibility was (S) and levofloxacin susceptibility was (I/R) antimicrobial susceptibility was confirmed by the E-Test method (bioMérieux) on Muller Hilton agar and cell density of 0.5 MacFarland. Control strains were E. Coli ATCC 25922, P. aeruginosa ATCC 27853 and S. aureus ATCC 29213. The antibiotics consumed in the hospital between January 2007 and December 2008 were transformed into Defined Daily Dose (DDD), which corresponds to the quantity of antibiotics consumed by a patient in 24 h. Ciprofloxacin and levofloxacin demonstrated a similar pattern of increasing resistance in some units between 2007 and 2008. Fluoroquinolone resistance increase for E. coli, varies from 10% in Geriatrics to 15% in ICU, for S. aureus varies from 15% in Medicine Unit to 5% in ICU. P. aeruginosa maintained the same percentage of resistance from 2007 to 2008, but there was a significantly increase of strains with intermediate sensitivity (I) up to 30%. The consumption of Ciprofloxacin didn’t increase in any of the units and in some case decreased. The consumption of levofloxacin increased in every units and particularly in ICU it raised from 5100 ev doses in 2007 to 6480 in 2008 and from 0 to 300 doses os (DDD). The increased consumption of levofloxacin in 2008 in ICU could explain the increased of Pseudomonas aeruginosa strains with intermediate sensitivity (I).