Laboratoire de Bactériologie, Faculté de Médecine, 28, place Henri Dunant, 63001 Clermont-Ferrand Cedex, France
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Abstract |
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Introduction |
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A survey was carried out to assess the recent evolution of antibiotic susceptibility of P. mirabilis isolates, and to determine the level of implication of this species in infections.
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Material and methods |
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The charts of 100 patients were selected using a table of random digits. Infections and their nosocomial character were defined according to the recommendations of the CDC.8 The McCabe score, for severity of underlying illness, was determined from data recorded on the day of isolation, and the severity of sepsis from the criteria of the European Study Group on Nosocomial Infections.9
Statistical analysis was made with SPSS Base 8.0 Software using Fisher's exact test, the median test and 2 test to compare nosocomial (Group I) with community-acquired infections (Group II).
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Results and discussion |
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After exclusion of the repeated isolates of P. mirabilis, 1072 isolates were included. The frequency of amoxycillin-resistant P. mirabilis in this study was 48.5%, higher than the values reported in 19911992 (<32%).11
The ß-lactam resistance phenotypes were wild for 552 isolates (51.5%), penicillinase for 407 isolates (38.0%), ESBL for 74 isolates (6.9%) and inhibitor-resistant ß- lactamase (IRB) for 39 isolates (3.6%) (Table I).
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Of the 1072 isolates, 7.6% were resistant to amikacin, 21.1% to gentamicin, 24.8% to nalidixic acid, 21.7% to pefloxacin and 43.9% to co-trimoxazole (Table II). The resistance to amikacin may be associated with ESBL-producing isolates, which were often resistant to amikacin (85.1%), and the resistance to gentamicin may be associated with penicillinase- and IRB-producing isolates, whose resistance rates to gentamicin were 43.6 and 94.4%, respectively.
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Documented information was obtained for 95 of the 100 randomly selected patients. In 69/95 patients P. mirabilis was implicated in an infection. However, in 29/75 sites (38.7%), it was associated with another microorganism (and in 6/7 in respiratory tract infections), and so it is difficult to determine its significance precisely.
Of the 69 patients, 42 had fever with or without multivisceral failure (n = 1), shock (n = 1) or sepsis (n = 23). In 58 patients, P. mirabilis was implicated in a monomicrobial infection and in 13/58 in sepsis. Some of the infections were notable by their seriousness or location (septicaemia n = 2, pyelonephritis n = 4, maternofetal infection n = 1, coxarthritis n = 1). This underlines the pathogenic potential of P. mirabilis.
In 42 (60.9%) patients this infection was nosocomial (Group I) and in 27 (39.1%) it was community-acquired (Group II). The sex ratio did not differ between the groups (about 59% female). In comparison with those of Group II, the patients of Group I were characterized by a more severe status: 19 versus two patients had a rapidly or ultimately fatal McCabe score (P < 0.005), a median age of 71 versus 41 years (P < 0.005) and a median length of stay of 28 versus 6 days (P < 0.001). Predisposing factors were present in 39/42 (69.0%) versus 3/27 (11.1%) (P < 0.001) patients: indwelling urinary catheter 29/42 (69%) versus 3/27 (11.1%), surgical intervention 19/42 (45.2%) versus 2/27 (7.4%), intravascular catheter 15/42 (35.7%) versus 1/27 (3.7%), respiratory assistance 14/42 (33.3%) versus 0/27 (0.0%) and corticosteroid therapy 9/42 (21.4%) versus 0/27 (0.0%).
All ESBL-producing isolates (n = 7) were from patients with nosocomial infections and the single IRB-producing isolate was from a patient with a community-acquired infection. IRB-producing isolates may have occurred as the result of the selection pressure of amoxycillinclavulanate, an antibiotic widely used in out-patients and in infants, as previously reported for E. coli isolates.
During the 15 days before isolation of P. mirabilis, 21 of the 27 patients on antibiotics were receiving ß-lactams (penicillin n = 13, imipenem n = 2, cephalosporins n = 6).
Of the 57 treated for P. mirabilis infection, 43 (75.4%) were receiving ß-lactams (penicillins n = 26, oxyimino-cephalosporins n = 13, imipenem n = 3, cefoxitin n = 1), seven aminoglycosides (12.3%), 29 quinolones (50.9%) and 15 another antibiotic (26.3%). Microbiological samples were taken 3 days after the first isolation of P. mirabilis in 27 patients. Eradication was obtained in 15 (55.6%). Seven patients died. Death was not related to P. mirabilis infection.
Since 1990 there has been a notable increase in the frequency of resistance of P. mirabilis to ß-lactams, aminoglycosides and quinolones. Although the pathogen is often isolated in combination with another, our report is of clinical relevance, in that P. mirabilis was the sole organism involved in 60% of cases of infection, some of which were severe. These factors should be taken into account in the choice of antibiotic treatment.
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Acknowledgments |
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Notes |
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References |
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Received 30 June 1999; returned 23 September 1999; revised 1 November 1999; accepted 13 December 1999