JAC Advance Access published online on May 8, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn174
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Original research |
β-Lactam and aminoglycoside resistance rates and mechanisms among Pseudomonas aeruginosa in French general practice (community and private healthcare centres)
1 UMR 5234, CNRS, Université de Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux, France 2 Laboratoire d'Analyses Médicales (LAM), 17 allées de Tourny, 33000 Bordeaux, France 3 LAM, av. du 11 novembre, 64100 Bayonne, France 4 LAM, 114 av. Arès, 33000 Bordeaux, France 5 LAM, Ma campagne Mas de Pierre Levée, 16000 Angoulême, France 6 LAM, 190 crs St Louis, 33300 Bordeaux, France 7 LAM, ZI Dumes, 33000 Bordeaux, France 8 LAM, 64 av. des Pyrénées, 33140 Villenave d'Ornon, France 9 LAM, 89 av. JJ Rousseau, 33160 St Médard-en-Jalles, France
* Corresponding author. Tel: +33-5-57-57-10-75; Fax: +33-5-56-90-90-72; E-mail: veronique.dubois{at}bacterio.u-bordeaux2.fr
Received 30 January 2008; returned 10 March 2008; revised 28 March 2008; accepted 29 March 2008
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Abstract |
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Objectives: The aim of this study was to assess antibiotic resistance rates and mechanisms of β-lactam and aminoglycoside resistance among isolates of Pseudomonas aeruginosa isolated in the extra-hospital setting (community and private healthcare centres).
Patients and methods: During a 4 month period, 226 non-repetitive strains of P. aeruginosa were collected from patients residing in private healthcare centres (73.5%) or at home (26.5%). Resistance rates were evaluated by MIC determination, and β-lactam and aminoglycoside resistance was analysed by phenotypic tests, PCR amplification, cloning and sequencing.
Results: Among the ticarcillin-resistant strains (38.1%), 33.7% overexpressed their chromosomal cephalosporinase, 27.9% produced acquired penicillinases (21 PSE-1, 2 OXA-21 and 1 TEM-2), 4.7% produced extended-spectrum β-lactamases (ESBLs) (3 TEM-21 and 1 SHV-2a) and 45.3% possessed a non-enzymatic resistance (NER). Thus, 88.4% had a single mechanism of resistance, whereas 11.6% cumulated several mechanisms. No carbapenemases were detected among the 6.6% imipenem-resistant strains. With regard to aminoglycosides, 23.0% of the strains exhibited an acquired resistance to gentamicin (GEN), tobramycin (TOB), amikacin (AMK) or netilmicin (NET). Enzymatic resistance was more frequent (71.2%) than NER (34.6%). Various aminoglycoside modifying enzymes were associated with overlapping phenotypes: 36.5% strains produced AAC(6')-I with either a serine (GEN-TOB-NET) or a leucine (TOB-NET-AMK) at position 119, or both variants (GEN-TOB-NET-AMK); 21.2% expressed ANT(2'')-I (GEN-TOB), 7.7% AAC(3)-II (GEN-TOB-NET), 5.8% AAC(3)-I (GEN) and 1.9% AAC(6')-II (GEN-TOB-NET-AMK) or AACA7 (TOB-NET-AMK).
Conclusions: Antibiotic resistance rates in P. aeruginosa were globally similar in general practice as in French hospitals. This first analysis of resistance mechanisms showed an unexpectedly high frequency of ESBLs and an unusual distribution of aminoglycoside modifying enzymes.
Key Words: cephalosporinase , penicillinase , extended-spectrum β-lactamase , aminoglycoside modifying enzymes , non-enzymatic resistance mechanism
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Introduction |
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Multidrug-resistant bacteria, such as extended-spectrum β-lactamase (ESBL)-producing enterobacteria and methicillin-resistant Staphylococcus aureus (MRSA), have emerged in the community.1,2 Their presence in nursing homes has shown that private healthcare centres can act as reservoirs for these organisms.3 The epidemiology of ESBL-producing enterobacteria and MRSA in general practice has been thoroughly investigated2–6 but not that of Pseudomonas aeruginosa.
However, P. aeruginosa, a major nosocomial pathogen, is also responsible for community-acquired infections, generally associated with contaminated water and solutions (folliculitis, otitis and corneal ulcers).7 This organism is intrinsically multidrug-resistant and can acquire additional resistances to the sole naturally active antimicrobial agents, i.e. some β-lactams, aminoglycosides, fluoroquinolones and fosfomycin. Clinical implication, antibiotic susceptibilities and β-lactam resistance mechanisms of P. aeruginosa have been surveyed in hospitals, regularly in France and sporadically in other countries. Aminoglycoside resistance mechanisms have been rarely characterized only among nosocomial strains. In contrast, the distribution of P. aeruginosa-induced infections and the antibiotic resistance rates of the strains have been rarely investigated in general practice. Data available include a recent American study8 that gives some information on the source of P. aeruginosa strains isolated from hospital outpatients and patients admitted from nursing homes. Another study indicates the prevalence of antimicrobial resistance in urinary tract infections occurring in nursing home populations.9 Antibiotic resistance mechanisms have never been analysed in the extra-hospital sector (community and private healthcare centres).
In France, the healthcare sector includes on one hand public hospitals and on the other hand general practice, comprising the community and private facilities divided in clinics, rehabilitation centres and nursing homes. Biological analyses in the extra-hospital setting are ensured by private laboratories. In 1998, we founded a network of private biologists to monitor antibiotic resistance out of the hospital in the Aquitaine region (South-Western France).2,6 In 2000, the survey of the Aquitaine network focused on P. aeruginosa. The aim of the present study is to report the results of this survey and to further analyse the molecular basis of β-lactam and aminoglycoside resistances.
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Patients and methods |
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Collection of bacterial strains, identification, serotyping and culture conditions
Between February and May 2000, eight private laboratories of the Aquitaine network have collected all clinically significant strains of P. aeruginosa and filled simplified identification forms containing clinical and demographic data for the corresponding patients. Strains and forms were regularly forwarded to the coordinating laboratory (Laboratory of Microbiology, University of Bordeaux 2). Identification to the species level was verified by the API 20NE system (bioMérieux, Marcy-l’Étoile, France), and serotyping was performed using commercialized antisera (Bio-Rad, Marnes la Coquette, France). All bacterial strains were routinely cultured at 37°C on Mueller–Hinton (MH) agar medium (Sanofi-Diagnostics Pasteur, Marnes la Coquette, France), or grown in Luria broth (Gibco-BRL, Cergy Pontoise, France) or Trypticase soy broth (Sanofi-Diagnostics Pasteur) and stored at –80°C in glycerol broth.
Antibiotic susceptibility testing
MICs of six β-lactams agents, four aminoglycosides, ciprofloxacin and fosfomycin were determined by a standard agar dilution method (http://www.sfm.asso.fr). Penicillins were tested alone and in combination with a fixed concentration of clavulanic acid (2 mg/L) or tazobactam (4 mg/L). P. aeruginosa ATCC 27853, Escherichia coli ATCC 25922 and S. aureus ATCC 25923 served as controls for MIC determination.
Enzymatic and non-enzymatic resistance (NER) mechanisms towards β-lactams were preliminary differentiated by a phenotypic method using β-lactamase inhibitors.10 Briefly, ticarcillin, piperacillin, cefsulodin, ceftazidime, aztreonam and imipenem susceptibilities were simultaneously determined by the disc diffusion method on three agar media, i.e. MH, and MH containing either tazobactam (40 mg/L) or cloxacillin (500 mg/L). The presence of a carbapenemase was investigated by comparing the imipenem activity by the agar diffusion method with discs supplemented or not with EDTA (750 µg).
β-Lactamase extraction, isoelectric focusing (IEF) and cephalosporinase assay
β-Lactamases produced by P. aeruginosa were released by ultrasonic treatment, and their isoelectric points (pIs) were determined by IEF as described previously.11 β-Lactamases of known pIs including PSE-1 (pI 5.7), CARB-3 (pI 5.75), TEM-8 (pI 5.9) and SHV-4 (pI 7.8) were used as pI markers. Cephalosporinase activities were evaluated by a spectrophotometric assay on lysate supernatants for strains that did not contain additional β-lactamases. Decreased optical density resulting from enzymatic hydrolysis of cefalotin was measured at 262 nm, and protein concentration was determined by the BCATM Protein Assay Kit (Pierce, Rockford, USA). AmpC activities were expressed as µmol of substrate hydrolysed per min and per mg of protein. In preliminary experiments, the cephalosporinase level in wild-type susceptible isolates was found to be comprised between 0.001 and 0.003 U/mg of protein. Consequently, strains producing >0.01 U/mg of protein were considered as cephalosporinase overproducers.
PCR, cloning experiments and digestion by restriction enzymes
Total DNA of P. aeruginosa strains was extracted as described previously,11 and the detection of genes encoding β-lactamases, aminoglycoside modifying enzymes and RNA 16S methylase [blaPSE, blaTEM, blaSHV, blaOXA-1 derivatives, blaOXA-10 derivatives, blaOXA-2, blaOXA-18, aac(3)-Ib, aac(3)-IIc, aac(6')-Ib, aac(6')-Ia, aac(6')-IIa, ant(2'')-Ia, ant(4')-IIa, ant(4')-IIb, aac29 and rmtA] was performed under standard PCR conditions,12 using published11,13–15 or laboratory-designed sets of primers (Table 1). The amplicons were revealed by electrophoresis on a 1.5% agarose gel and subsequent exposure to UV light in the presence of ethidium bromide. Restriction by AcsI enzyme (Roche Applied Sciences, Meylan, France) was performed on blaPSE amplicons to differentiate PSE-1 and CARB-3. For strains resistant to gentamicin, tobramycin, amikacin and netilmicin, the amplified fragment of the aac(6')-Ib gene was ligated into the pGEM-T vector according to the manufacturer's instructions (Promega, Charbonnières, France) and the recombinant plasmid was transformed into E. coli DH5
. The transformants were then selected on MH agar plates containing 100 mg/L ampicillin and 1 mg/L netilmicin. For strains with a still unidentified mechanism of aminoglycoside resistance after PCR amplification, cloning experiments were performed using total DNA partially restricted by Sau3AI and ligated into the BamHI-restricted pBK-CMV phagemid (Stratagene, La Jolla, CA, USA). E. coli XL1Blue strains harbouring the recombinant plasmids were selected on MH agar plates containing 15 mg/L amikacin and 50 mg/L kanamycin.
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DNA sequencing
The TEM, SHV and aac(6')-Ib-positive amplicons were sequenced on both strands using laboratory-designed sequencing primers and the dideoxy-chain termination method with the ‘D Rhodamine dye terminators kit’ (PE, Courtaboeuf, France). Sequences were analysed with an automatic sequencer ABI 377 (PE), using ‘Sequencing Analysis’ and ‘Sequence Navigator’ software. The nucleotide and the deduced protein sequences were analysed using the software available over the Internet at the National Center of Biotechnology Information web site (http://www.ncbi.nlm.nih.gov).
Statistical comparisons were carried out using the 
2 test with the Yates’ correction or the two-tailed Fischer's exact test when necessary. A P value inferior to 0.005 was considered as statistically significant, but P values between 0.005 and 0.05 are indicated when obtained. All statistical analyses were performed with the Epi-Info software (version 6.04, CDC, Stone Mountain, GA, USA).
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Results |
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Origin of the P. aeruginosa strains
A total of 226 consecutive and non-duplicate strains of P. aeruginosa were isolated from 216 patients (43.7% females and 56.3% males). They ranged in age from 7 days to 104 years (mean 70.3 years), including 73% who were 61–90 years old. The isolates were more often collected from patients residing in private healthcare centres (73.5%) than living at home (26.5%) (Table 2). Strains were essentially recovered from urine, pus and respiratory tract samples (93.8%) (Table 2). Among community patients, two-thirds (29 out of 47 for whom this information was available) were hospitalized during the previous year and/or had nursing care at home and 71% received an antibiotic treatment during the 6 preceding months. Serotyping showed that 74.3% of the strains divided into 11 of the 16 detectable serotypes, whereas 25.7% were not typeable, including most of the β-lactam hypersusceptible strains (ticarcillin MIC 
2 mg/L). The serotype O6 (20.8%) was the most frequent followed by the O1, O11, O10, O12, O3, O16 and O9 serotypes (11.9%, 9.3%, 8.0%, 6.6%, 5.3%, 4.9% and 4.0%, respectively). The serotypes O2, O4 and O8 were less represented (1.3%, 1.3% and 0.9%, respectively).
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Antibiotic resistance rates
MIC determination underscored that P. aeruginosa is intrinsically poorly susceptible to most antimicrobial agents. Indeed, the mode MIC values were generally close to the French susceptibility breakpoints (ticarcillin, cefepime, aztreonam, gentamicin and amikacin) and sometimes exceeded them (netilmicin and fosfomycin) (Table 3). On the basis of these guidelines, only 28 strains (12.4%) were susceptible to all major antipseudomonal agents (ticarcillin, piperacillin, ceftazidime, imipenem, tobramycin, amikacin, ciprofloxacin and fosfomycin), and often, fosfomycin resistance was the unique resistance marker (80 strains, 35.4%). Thus, >71% of the isolates were susceptible to piperacillin plus tazobactam, ceftazidime and imipenem, and <14% were resistant to all β-lactams except for imipenem. Some variations according to the origin of the strains were observed (Table 4).
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Mechanisms of β-lactam resistance
Of the 86 ticarcillin-resistant strains, 24 (27.9%) produced an acquired penicillinase as confirmed by IEF, PCR amplification and sequencing data (Table 5). PSE-1 was the most frequent enzyme, occurring in 21 of the 24 strains, whereas OXA-21 was found in two cases and TEM-2 in a single instance. Four strains produced an ESBL, including three TEM-21 and one SHV-2a. The TEM-21 enzyme generated a positive disc synergy test, but the SHV-2a enzyme was only revealed by molecular methods, probably due to the concomitant overexpression of the chromosomal cephalosporinase. No carbapenemases were found either by the EDTA inhibition test or by IEF in the 15 strains exhibiting an imipenem MIC superior to 4 mg/L. Four strains out of the 15 showed resistance to imipenem only, while in the remaining 11 strains the imipenem resistance was associated with the presence of a cephalosporinase (four strains), a penicillinase (three strains) and/or an NER (six strains).
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The determination of the cephalosporinase specific activity in strains without acquired β-lactamase showed that 24 strains (27.9%) overproduced their chromosomal cephalosporinase. This overexpression varied according to the strains from 0.0117 to 9.3413 U/mg protein. The combination with a penicillinase (five strains) precluded the determination of the cephalosporinase specific activity, but overexpression of the chromosomal AmpC was assessed by the phenotypic test using β-lactamase inhibitor10 and IEF (Table 5).
NER mechanisms, including outer membrane impermeability and drug efflux, translate into low-level resistance unchanged by tazobactam or cloxacillin by the phenotypic test. Thus, 34 strains were found to be β-lactam-resistant by NER alone, and 5 strains had an additional enzymatic resistance (Table 5). Almost half of the strains (48.8%) exhibiting β-lactam NER were ciprofloxacin-resistant and two-thirds (66.7%) were cefepime-resistant. Among the 86 strains with an intermediate susceptibility or resistance to cefepime, 20 were susceptible to the other β-lactams except for one strain, which was only resistant to imipenem.
Mechanisms of aminoglycoside resistance
Since the mode MICs were close to or exceeded the susceptibility breakpoints for gentamicin and netilmicin, only strains presenting a high-level resistance to these aminoglycosides (MIC 
512 mg/L) and strains presenting a low-level resistance to all aminoglycosides including apramycin were considered to possess acquired resistances. Among these 52 strains, 6 phenotypes were individualized, including 3 that involved the 4 molecules gentamicin (GEN) tobramycin (TOB), amikacin (AMK) and netilmicin (NET), but differed by the resistance levels, either high or low (indicated by square brackets) (Table 6). Of the 10 genes encoding aminoglycoside resistance mechanisms that were searched, only 4 were detected (Table 6). The aac(6')-Ib gene was the most frequently encountered, in 19 strains (36.5% of the resistant strains), including all strains of serotype O12. The presence of this gene was associated with three different phenotypes: GEN-TOB-NET for 1 isolate, [GEN]-TOB-NET-AMK for 12 and GEN-TOB-NET-AMK for 6. Gene sequencing showed the presence of a leucine at position 119 for the 12 strains exhibiting the [GEN]-TOB-NET-AMK phenotype [aac(6')-Ib] and of a serine at the same position for the strain of phenotype GEN-TOB-NET [aac(6')-Ib']. For the six remaining strains with the GEN-TOB-NET-AMK phenotype, sequencing revealed for three strains the presence of A and C (double peak) for the nucleotide corresponding to the substitution at position 119. Then, cloning of the aac(6')-Ib PCR fragment in the pGEMT vector from the GEN-TOB-NET-AMK-resistant strains confirmed for four strains the presence of both the aac(6')-Ib and aac(6')-Ib' genes. For one strain, apramycin resistance, which is a feature of the aminoglycoside NER, was associated with a unique aac(6')-Ib' gene (serine at position 119, GEN-TOB-NET phenotype), which can explain the GEN-TOB-NET-AMK pattern. Finally, in one strain, a single aac(6')-Ib' gene (GEN-TOB-NET) was detected, which cannot account for the amikacin resistance (MIC = 128 mg/L). The second most frequent gene detected was the ant(2'')-Ia gene found in 11 strains (21.2%), including 9 that showed a GEN-TOB resistance pattern and 2 a GEN-TOB-NET-AMK profile. For the latter strains, cloning experiments showed the presence of an additional aac(6')-IIc or aacA7 gene. The third amplified gene was aac(3)-IIc, detected in four strains (7.7%) exhibiting the expected phenotype GEN-TOB-NET. Finally, the last gene found was aac(3)-Ib, present in three strains (5.8%) exhibiting gentamicin and fortimicin resistances. The remaining 15 resistant strains (28.8%) presented a low-level resistance to all the tested aminoglycosides including apramycin.
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Discussion |
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In the private healthcare sector, P. aeruginosa appears to be primarily isolated from patients residing in institutions. This organism was found to be mainly responsible for urinary tract infections, particularly in nursing homes where patients often carry urinary indwelling catheters.14 As observed for ESBL-producing enterobacteria and MRSA,1,3,5,6 at least part of the P. aeruginosa strains collected in the extra-hospital practice likely had a nosocomial origin. Indeed, patients living in nursing homes are frequently hospitalized, and rehabilitation centres receive patients after their discharge from hospitals. Moreover, a high proportion of the community patients had been hospitalized in the preceding year. The hypothesis of a frequent nosocomial origin is supported by the similarity of the serotype distribution. Indeed, serotypes O6, O1 and O11 predominated, and the classically resistant serotype O12 represented
6% of the strains, as observed in French hospitals during the same period.10,16 Thus, as for ESBL-producing enterobacteria and MRSA, prolonged carriage of hospital-acquired P. aeruginosa strains after discharge may be responsible for infections acquired in the community or in private facilities. The overall resistance rates were similar as in French hospitals for first-line drugs, but significantly lower for ceftazidime and imipenem (17% versus 25%, P < 0.05; 7% versus 17%, P < 0.005),10 which are antibiotics exclusively used in the clinical setting. Resistance rates towards aminoglycosides, ciprofloxacin and fosfomycin were close to the lowest values observed in hospital practice (amikacin, 14% to 38%,10,16–18 ciprofloxacin 32% to 44%10,16–18 and fosfomycin 66% to 67%).10 In addition, differences were observed according to the origin of the patient and resistant strains were more often collected in nursing homes as observed with ESBL-producing enterobacteria.4 Comparison to hospital European data19,20 is complicated by the distinct guidelines used in these studies.
With regard to β-lactams, NER was the most frequent type of resistance, as observed in the hospital, in France (38% to 71.5%) and in other European countries (56.3% and 74.5% in Italy and the UK, respectively).19,20 Among NER mechanisms, overexpression of the major efflux pump MexAB-OprM, extruding β-lactams and fluoroquinolones, is probably often implicated in the light of the frequent cefepime and ciprofloxacin co-resistances. The imipenem resistance observed here probably reflected a specific NER mechanism due to the loss of the OprD porin. Enzymatic resistance associated with an acquired β-lactamase (27.9%) was as frequent as in French hospitals (20.7% to 30%) and much higher than in European surveys (3.5% to 10.5%).19,20 PSE-1 was the most frequent enzyme, in particular present in all strains of serotype O12. The other types of penicillinases detected were OXA-21 and TEM-2, enzymes sometimes reported in surveys in France21 as well as in Europe.19,20 However, ESBL producers were unexpectedly frequent in this extra-hospital survey, since few have been reported in French hospitals and only recently.16,18,21 Furthermore, the ESBLs belonged to the TEM and SHV families widespread among enterobacteria instead of the unusual class A or OXA-type enzymes, as reported in other geographical areas.22 The three TEM-21-producing isolates belonged to the same clonal strain responsible for an outbreak in a nursing home14 where ESBL-producing enterobacteria were endemic. The remaining SHV-2a-expressing strain was isolated in a rehabilitation centre. These data suggest that long-term care facilities may be the place of resistance spread, allowing the emergence of multidrug resistance P. aeruginosa before their occurrence in hospital. Cephalosporinase overexpression accounted for 33.7% of the ticarcillin-resistant strains versus 29% to 54.3% in hospitals in France and 14.5% to 19.7% in the UK and Italy, respectively. Finally, carbapenemases were absent in the general practice in 2000, although they have recently emerged in French hospitals.18,23,24
The aminoglycoside mechanisms of resistance have been rarely explored in P. aeruginosa and, to our knowledge, never in extra-hospital practice. The main study performed by Miller et al.25 brought together several studies carried out worldwide. Results showed that in Europe, between 1988 and 1993, NER was the predominant mechanism (6% to 22% of the aminoglycoside-resistant strains). NER can result from the overexpression of active efflux systems, especially MexXY-OprM,26 decreased outer membrane permeability or reduced transport across the inner membrane. Alternatively, the aminoglycoside resistance was due to the presence of two main enzymes, AAC(6')-II conferring the GEN-TOB-NET profile and ANT(2'')-I responsible for the GEN-TOB pattern (20% to 47% and 7.5% to 25% of the resistant strains, respectively); AAC(6')-I (TOB-NET-AMK) also occurred, but uncommonly (1.3% to 5%). Since this study, in Belgium and the Grand Duchy of Luxembourg, Vanhoof et al.27 have principally detected in clinical isolates of P. aeruginosa collected in 1996–97, the aac(6')-Ib gene (77.3%) followed by ant(2'')-Ia (36.4%) and aac(3)-IIc (4.5%), although NER was very infrequent (4.5%). In our study, a predominance of the latter three enzymes was observed (36.5%, 21.2% and 7.7%, respectively), but the impact of NER (34.6%) was much higher. In addition, our data revealed the presence of the aac(3)-Ib gene (5.8%) leading to the GEN phenotype and the aac(6')-IIc and aacA7 genes (1.9%). AAC(6')-I acetylates kanamycin, tobramycin, netilmicin, sisomicin, amikacin and, to a lesser extent, isepamicin but not gentamicin C1.28–30 However, in P. aeruginosa, the presence of the aac(6')-Ib gene was regularly associated with a decreased gentamicin susceptibility. The resulting [GEN]-TOB-NET-AMK profile was probably due to the poor intrinsic gentamicin susceptibility of P. aeruginosa and to the weak activity of the AAC(6')-Ib enzyme against gentamicin C1a, one of the three components of the commercially available gentamicin drug.30 Moreover, it has been demonstrated that modifications of the amino acid sequence of the AAC(6')-I proteins influence their enzymatic activities. Accordingly, a decisive role was assigned to the amino acid at position 119, a leucine being associated with amikacin resistance and a serine with gentamicin resistance. Our study showed that both AAC(6')-I proteins, harbouring either a leucine or a serine at position 119, frequently occurred and often co-existed in the same strain, conferring the broad resistance profile GEN-TOB-NET-AMK. Thus, different phenotypes might be observed with the same gene, and molecular techniques are indispensable to elucidate the resistance mechanisms. Moreover, in P. aeruginosa, owing to the combination of several mechanisms and variable levels of their expression, the involved mechanisms cannot be easily inferred from the resistance profiles.
In conclusion, P. aeruginosa isolated in the extra-hospital practice is often likely to have a nosocomial origin. Accordingly, the overall resistance rates were similar as those observed in the hospital for the first-line β-lactams, but lower for most other drugs. Although most β-lactam resistance mechanisms were close to those described in the hospital, ESBLs were unexpectedly frequent. Amongst aminoglycoside mechanisms of resistance, aac(6')-Ib was the predominant gene. Interestingly, characterization of aac(6')-Ib variants, often coexisting in the same strain, allowed us to explain complex phenotypes. Continued surveillance of antibiotic resistance rates and mechanisms of P. aeruginosa in the extra-hospital practice is warranted, particularly in the light of their current evolution in the hospital.
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This work was supported by grants from the French Network on β-lactamases study and from the Ministère de l'Education Nationale et de la Recherche (EA-525), Université de Bordeaux 2, Bordeaux, France.
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None to declare.
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References |
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