JAC Advance Access originally published online on June 18, 2007
Journal of Antimicrobial Chemotherapy 2007 60(2):452-454; doi:10.1093/jac/dkm214
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Correspondence |
Surveillance of antimicrobial susceptibility of Pseudomonas aeruginosa clinical isolates from a central hospital in Portugal
1 Laboratory of Microbiology, Centro de Estudos Farmacêuticos, Faculty of Pharmacy, University of Coimbra, Coimbra, Portugal 2 Laboratory of Microbiology, Centro Hospitalar de Coimbra, Coimbra, Portugal
* Corresponding author. Tel/Fax: +351-239-852569; E-mail: ocardoso{at}ci.uc.pt
Keywords: nosocomial infections , empirical therapy , resistance
Pseudomonas aeruginosa is one of the leading causes of nosocomial infections. Initiation of antimicrobial therapy is often empirical; therefore, it is important to know the susceptibility profile of pathogens in order to select the most appropriate antibiotic. This underscores the importance of using current surveillance data in order to develop rational empirical antimicrobial therapy recommendations.1
The aim of this study was to carry out surveillance of antimicrobial susceptibility of P. aeruginosa clinical isolates in Centro Hospitalar de Coimbra (CHC) to ascertain resistance patterns in order to assist in the determination of guidelines for empirical regimens and prompt enforcement of infection control measures. CHC is a 600 bed, central hospital comprising a general, maternity and paediatric hospital, situated in the centre of Portugal, a highly populated region.
The collection period was from April 2003 to April 2006, and only one isolate per patient was included. Isolates were from inpatients with community-acquired infections (n = 414) or nosocomial infections (n = 685).
Identification and determination of antimicrobial susceptibilities were performed in CHC using MicroScan WalkAway (Dade Behring) and CLSI (formerly NCCLS) breakpoints.2 Isolates with intermediate susceptibility were considered resistant in order to match better treatment decisions in clinical settings.
A multidrug-resistant (MDR) P. aeruginosa was defined as an isolate that was resistant to three or four of the following: piperacillin, ceftazidime, imipenem and ciprofloxacin.
During collection, a total of 1099 P. aeruginosa isolates were obtained in CHC, from nosocomial and community-acquired infections from different clinical specimens, including urine (17.1% and 35.5%, respectively), sputum (46.3% and 30.9%, respectively), exudates (15.6% and 13.5%, respectively), blood (4.5% and 4.6%, respectively) and other sources (16.5% and 15.5%, respectively).
Overall, susceptibility to the most commonly used antipseudomonal drugs was as follows: meropenem, 90.0%; piperacillin plus tazobactam, 89.0%; piperacillin, 86.2%; amikacin, 85.6%; ceftazidime, 85.0%; imipenem, 82.4%; aztreonam, 81.7%; ciprofloxacin, 69.2% and gentamicin, 65.9%.
Among hospital isolates, piperacillin plus tazobactam was the most potent agent (85.1% susceptible), followed by meropenem (84.8%), piperacillin (81.5%), ceftazidime (79.4%) and aztreonam (75%), and the least potent ß-lactam was imipenem (74.7%). Amikacin demonstrated good activity (81.3%), but gentamicin showed poor activity (58.1%). Ciprofloxacin was only moderately active (64.2%). Community isolates were >90% susceptible to most antibiotics except for ciprofloxacin (77.3%) and gentamicin (78.7%). Meropenem was the most potent agent (98.6%) followed by piperacillin plus tazobactam (95.4%), imipenem (95.2%), ceftazidime (94.2%), piperacillin (94.0%), aztreonam and amikacin (92.8%) (Figure 1).
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MDR was recognized in 100 isolates (9.1%). Twenty isolates (20%) were resistant to all antibiotics tested. All these were from nosocomial infections from the principal wards and 70% were from respiratory sources. Among isolates resistant to piperacillin, ceftazidime and imipenem, ciprofloxacin demonstrated some activity (32.9%, 33.8% and 31.8%, respectively). Some ciprofloxacin-resistant isolates (27.4%) were susceptible to ceftazidime (Table 1).
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Studies of susceptibility held in Europe by MYSTIC and SENTRY demonstrated superior activity of meropenem and piperacillin plus tazobactam.3,4 In our work, among nosocomial isolates, piperacillin plus tazobactam showed the best activity followed by meropenem. In CHC, imipenem was the worst among the ß-lactams, with decreased activity over the 3 years of this study (10.9% decrease in susceptibility).
A study by European Surveillance of Antimicrobial Consumption demonstrated that Portugal (with Spain and Italy) was the European country with the highest fluoroquinolone use.5 Misuse of fluoroquinolones may, therefore, explain the low susceptibility of our isolates, whether they were from community (77.2% susceptible) or from hospital (64.2%). MYSTIC and SENTRY studies also revealed low susceptibility to these agents.3,4
Incidence of MDR isolates was high, but within the results observed in Europe.6
Choices of antimicrobial agents for empirical therapy for possible pseudomonal infections must be influenced by regional information as well as by changing local patterns of resistance.4 Since none of the antibiotics tested among nosocomial isolates reached 90% susceptibility, recommendations for empirical treatment are difficult to give, although piperacillin plus tazobactam and meropenem seem a good choice for initial therapy. Monotherapy carries the risk of possible emergence of antibiotic-resistant bacteria during treatment, and combination therapy, including a ß-lactam (carbapenem or piperacillin plus tazobactam) and an aminoglycoside (amikacin), may be a prudent option, especially in cases of severe infection.1 Among community isolates, all ß-lactams would be useful as, in this study, P. aeruginosa was in general susceptible to these agents.
In conclusion, surveillance of antimicrobial susceptibility is important for developing rational empirical therapy guidelines and for guiding efforts to control and prevent spread of resistant microorganisms, especially if, like P. aeruginosa, they show particular propensity for the development of resistance and are a recognized public health threat.
None to declare.
Acknowledgements
We thank Trindade Marques and Jorge Marques for assistance with data management. We thank FCT through POCTI (FEDER) for financial support.
References
1 Fluit A, Verhoef J, Schmitz F. Antimicrobial resistance in European isolates of Pseudomonas aeruginosa. Eur J Microbiol Infect Dis (2000) 19:370–4.[CrossRef]
2 National Committee for Clinical Laboratory Standards. Performance Standards for Antimicrobial Susceptibility Testing Twelfth Informational Supplement M100-S13 (2003) Wayne, PA, USA: NCCLS.
3 Mendes C, Turner P, MYSTIC Study Group (Europe). Unit differences in pathogen occurrence arising from MYSTIC Program European database (1997–2000). Diagn Microbiol Infect Dis (2001) 41:191–6.[CrossRef][Web of Science][Medline]
4 Jones R, Kirby J, Beach M, et al. Geographic variations in activity of broad-spectrum ß-lactams against Pseudomonas aeruginosa: summary of the worldwide SENTRY antimicrobial surveillance program (1997–2000). Diagn Microbiol Infect Dis (2002) 43:239–43.[CrossRef][Web of Science][Medline]
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Ferech M, Coenen S, Malhotra-Kumar S, et al. European surveillance of antimicrobial consumption (ESAC): outpatient quinolone use in Europe. J Antimicrob Chemother (2006) 58:423–7.
6 Desphande L, Fritsche T, Jones R. Molecular epidemiology of selected multidrug-resistant bacteria: a global report from the SENTRY Antimicrobial Surveillance Program. Diagn Microbiol Infect Dis (2004) 49:231–6.[CrossRef][Web of Science][Medline]
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