Insegnamento di Malattie Infettive, Università di Pisa, Ospedale S. Chiara, 56100 Pisa, Italy
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Abstract |
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Introduction |
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Materials and methods |
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Results and discussion |
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Most of the enterococci were Enterococcus faecalis (1405), 19 were Enterococcus faecium, six were Enterococcus avium and 683 were unspecified Enterococcus spp.
Over 90% of the strains studied were susceptible to nitrofurantoin, ampicillin, piperacillin and imipenem; 79% were susceptible to fosfomycin, 75.1% to penicillin, 74% to ciprofloxacin and norfloxacin, 72.6% to gentamicin, 90.3% to teicoplanin and 89.7% to vancomycin (Table I).
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Of enterococci from inpatients and outpatients, 7.1% and 14%, respectively, were glycopeptide resistant. In 61 outpatients, glycopeptide-resistant enterococci were isolated from vaginal or urethral secretions or seminal fluid.
The sensitivity of vancomycin-resistant enterococci to the other antibiotics is shown in Table II; only nitrofurantoin and imipenem showed good activity (>90% of the strains were sensitive). There was a striking contrast in susceptibility to fosfomycin between vancomycin-susceptible and vancomycin-resistant enterococci (79% versus 7.5%). Similar patterns of activity against the teicoplanin-resistant enterococcal strains were found for the other antibiotics.
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Sensitivity testing demonstrated excellent activity of nitrofurantoin, ampicillin, piperacillin and imipenem (>90% of the strains were sensitive), but poor activity of quinolones and gentamicin (only 7274% of the strains were sensitive). The rates of resistance to vancomycin (10.3%) and teicoplanin (9.7%) are in accordance with the results of a study performed in Pisa in 1997, but significantly higher than those reported in two multicentre Italian studies during 19936 and 199697.7 Our data are similar to those of the National Infections Surveillance System of the USA, which reported in 1996 rates of glycopeptide resistance of about 12% in intensive care units and 10% in other non-intensive care units.8
In our study, glycopeptide-resistant enterococci were more frequently resistant to other antibiotics: only nitrofurantoin and imipenem were active against >90% of the glycopeptide-resistant enterococcal strains. The highest rates of resistance were detected in samples obtained from the urogenital tract (urine, seminal fluid and vaginal secretion) and, unexpectedly, in outpatients. This may be because the patients who undergo more frequent microbiological evaluations of the urogenital tract are those who have chronic or recurrent infections (cystitis, vaginitis or prostatitis), and may have received numerous courses of antibiotics.3 This may also partly explain the low numbers of VRE that were susceptible to ampicillin and penicillin. Enterococci may be resistant to penicillin and ampicillin because of the production of low-affinity penicillin-binding proteins (PBPs) or because of the production of ß-lactamase. The Vitek system we used in this study can detect isolates with altered PBPs, but it may not reliably detect ß-lactamase-producing strains. Based on the decreased susceptibility to ß-lactams observed in our VRE, it is likely that a significant number of the unspecified VRE are E. faecium, rather than E. faecalis, which are generally susceptible to ß-lactams. The very low percentage of VRE fully susceptible to fosfomycin could be explained by the use of this agent to treat recurrent urinary tract infections in our area.
In conclusion, the high frequency of glycopeptide-resistant enterococci that we observed in Pisa was largely unexpected. The cause of these high rates of resistance is not clear, especially if we consider the data reported in other Italian studies. The indiscriminate use of antibiotics may, in part, explain our results. We feel that continued surveillance in both hospital and outpatient settings is mandatory and that the use of glycopeptides needs to be rationalized.
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Notes |
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References |
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2 . Spera, R. V. & Farber, B. F. (1992). Multiply-resistant Enterococcus faecium. The nosocomial pathogen of the 1990s. Journal of the American Medical Association 268, 25634.[ISI][Medline]
3 . Moellering, R. C. (1998). The specter of glycopeptide resistance: current trends and future considerations. American Journal of Medicine 104, 3S6S.[Medline]
4 . Noble, W. C., Virani, Z. & Cree, R. G. (1992). Co-transfer of vancomycin and other resistance genes from Enterococcus faecalis NCTC 12201 to Staphylococcus aureus. FEMS Microbiology Letters 72, 1958.
5 . National Committee for Clinical Laboratory Standards. (1997). Performance Standards for Antimicrobial Susceptibility TestingEighth Informational Supplement: Approved Standards M100-S8. NCCLS, Wayne, PA.
6 . Venditti, M. & Goglio, A. (1996). Vancomycin susceptibility in enterococcal blood isolates in Italy: a multicenter retrospective analysis. Journal of Chemotherapy 8, 336.[ISI][Medline]
7 . Cornaglia, G. & Fontana, R. (1999). Susceptibilities of strains isolated from outpatient urine specimens in Italy. Clinical Microbiology and Infection 5, Suppl. 3, 237.
8 . Centers for Disease Control. (1996). National Nosocomial Infection Surveillance Report. Data summary from October 1986 to April 1996. American Journal of Infection Control 24, 3808.[ISI][Medline]
Received 9 November 1999; returned 21 January 2000; revised 28 February 2000; accepted 20 March 2000