Analysis of trends in P. aeruginosa antibiotic resistance of animal and human isolates: a retrospective observational study in central Italy.

Objectives: Pseudomonas aeruginosa (PA) is a clinically significant pathogen responsible of nosocomial and community infections both in human and veterinary medicine. The high level of acquired resistance as well as the horizontal and clonal spread of resistant PA strains has become a serious problem, representing a limit for adequate antibiotic therapy and resulting in a serious threat to Public Health. A retrospective observational study was carried out to assess the antibiotic resistance trends in PA strains of animal and human origin from 2006 to 2011. Methods: A total of 384 isolates of PA were obtained from different clinical specimens from animals (n=298) and humans (n=86) living in central Italy. The isolates were identified by PCR and were tested against 12 different antibiotics usually active against PA by disk diffusion method (Table 1). The significance of differences in resistance was evaluated using chi squared test (STATA software version 9.1), and P value less than 0.05 was considered statistically significant. Results: The microorganisms were cultured from ear (43%), tonsillar swabs and bronchial alveolar washes (19%), naso-pharyngeal swabs (17%), wound swabs (13%), high vaginal swabs and urine samples (8%). During six-year period, the development of PA resistance to antibiotics is given in Table 1. There was evidence of increased resistance to gentamicin (P=0.0431), fluoroquinolones (P=0.0167), cefalosporins, and carbapenems in human isolates. At the same time, the resistance of PA to amikacin decreased from 6.4% in 2006 to 3.2% in 2011. Similar trends were observed for PA of animal origin: a significant increased resistance was observed for tetracyclines (P=0.0483), and penicillins (P=0.0325). Different trends were obtained for amikacin, cefquinome and carbapenems for which PA animal strains demonstrated a decreased, but not significant, resistance (P>0.05). Conclusion: This study confirms that resistance profile of PA is changing in central Italy, acquiring gradually less antibiotic susceptibility to molecules used both in veterinary and human medicine. Considering the potential role of PA as zoonotic microorganism, due care must be taken in the antibiotic treatment to prevent the increase of the spread of multidrug resistant zoonotic PA. This study confirms that the widespread antibiotic misuse could be the main risk factor for the occurrence of multiresistant PA strains.