Activity of the new cephalosporin CXA-101 (FR264205) against Pseudomonas aeruginosa isolates from chronically-infected cystic fibrosis patients

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1 ORIGINAL ARTICLE BACTERIOLOGY Activity of the new cephalosporin CXA-101 (FR264205) against Pseudomonas aeruginosa isolates from chronically-infected cystic fibrosis patients L. Zamorano 1, C. Juan 1, A. Fernández-Olmos 2,Y.Ge 3, R. Cantón 2 and A. Oliver 1 1) Servicio de Microbiología and Unidad de Investigación, Hospital Son Dureta, Instituto Universitario de Investigación en Ciencias de la Salud (IUNICS), Palma de Mallorca, 2) Servicio de Microbiología, Hospital Universitario Ramón y Cajal and CIBER de investigación en Salud Publica (CIBERESP), Madrid, Spain and 3) Calixa Therapeutics Inc., San Diego, CA, USA Abstract Chronic respiratory infection caused by Pseudomonas aeruginosa is the main driver of morbidity and mortality in cystic fibrosis (CF) patients. The development of resistance to all available antibiotics is a frequent outcome of these infections. The present study aimed to evaluate the activity of the new cephalosporin CXA-101 (FR264205) against a collection of 100 isolates obtained from 50 CF patients from two Spanish hospitals. The collection included the first (early) and the last (late) available isolate from each patient (average interval 68 ± 39 months). The MIC 50 and MIC 90 of CXA-101 were 0.5 and 2 mg/l and the geometric mean MIC was 0.7 mg/l; the MICs for 95% of the isolates were 8 mg/l (tentative breakpoint). Only meropenem yielded comparable results, although the MIC 90 of this antibiotic was significantly higher (8 mg/l). CXA-101 showed conserved activity against a high proportion of isolates resistant to each of the antibiotics tested (ceftazidime, cefepime, piperacillin-tazobactam, imipenem, meropenem, levofloxacin and tobramycin), with MIC 50 values of 1 2 mg/l. Moreover, CXA-101 retained good activity against multidrug-resistant strains, with MIC 50 and MIC 90 values of 2 and 16 mg/l. CXA-101 was also active against late CF isolates (the MIC for 96% was 8 mg/l); it was the only antibiotic tested to which a similar percentage of early and late isolates was susceptible. These results show that, despite a slight increase in MICs, major cross-resistance to CXA-101 did not develop during treatment of CF patients with the currently available antipseudomonal agents. Therefore, CXA-101 is envisaged as a valuable alternative for the treatment of chronic respiratory infection caused by P. aeruginosa in CF patients. Keywords: Antibiotic resistance, cephalosporins, cystic fibrosis, Pseudomonas aeruginosa Original Submission: 10 August 2009; Revised Submission: 20 November 2009; Accepted: 23 November 2009 Editor: J.-M. Rolain Article published online: 7 December 2009 Clin Microbiol Infect 2010; 16: /j x Corresponding author: A. Oliver, Servicio de Microbiología, Hospital Son Dureta, C. Andrea Doria Nº 55, Palma de Mallorca, Spain antonio.oliver@ssib.es Introduction Chronic respiratory infection (CRI) due to Pseudomonas aeruginosa is the main cause of morbidity and mortality in cystic fibrosis (CF) patients [1,2]. One of the most concerning features of these infections is the extraordinary capacity of P. aeruginosa to develop resistance to almost all available antibiotics through the selection of mutations in chromosomal genes [3], facilitated by the very high prevalence of hypermutable (or mutator) strains deficient in the DNA mismatch repair system [4,5]. Indeed, sequential development of multidrug-resistance (MDR) is a frequent outcome [6] that has a major impact on disease progression [7]. Among the mutation-mediated resistance mechanisms, particularly noteworthy are those leading to the repression or inactivation of the porin OprD, conferring resistance to carbapenems [8], or those leading to the hyperproduction of the chromosomal cephalosporinase AmpC, such as the inactivation of AmpD or PBP4 [9,10], thereby determining resistance to currently available penicillins and cephalosporins. Also remarkable is that mutations leading to the up-regulation of one of the several efflux pumps encoded in the P. aeruginosa genome may confer resistance or reduced susceptibility to multiple agents, including most b-lactams, fluor- Journal Compilation ª2010 European Society of Clinical Microbiology and Infectious Diseases

2 CMI Zamorano et al. Activity of CXA-101 against Pseudomonas aeruginosa isolates from cystic fibrosis 1483 oquinolones and aminoglycosides [11,12]. Moreover, multiple antibiotic-resistant variants frequently coexist in the lungs of chronically-infected CF patients [13]. In addition to antibiotic resistance mutations, several other adaptive mutations promote the long-term persistence of CRI, making its eradication with conventional antimicrobial therapy extremely difficult, if not impossible [14,15]. Among those worthy of note are mutations causing the inactivation of muca that leads to alginate hyperproduction [16]. Mucoid variants are found in 80 90% of chronically-infected patients and are associated with a poorer pulmonary outcome [17]. Alginate hyperproduction is known to reduce bacterial clearance and to inhibit phagocytosis, complement activation, antibiotic penetration and neutralization of oxygen radicals [18 21]. Other important adaptive variants frequently found among P. aeruginosa isolates from CRI (up to 50% of CF patients colonized by P. aeruginosa) are the small colony variants (SCV) [22]. These mutants, which are characterized by their reduced colony size (1 3 mm) in agar-based culture media, have been associated with increased antimicrobial resistance, notably to aminoglycosides, and poorer lung function in CF patients [22]. Over the last two decades, there has been very limited progress in developing antipseudomonal antibiotics that can overcome MDR in P. aeruginosa. CXA-101 (former FR254205) is a new cephalosporin antibiotic in phase 2 clinical development by Calixa Therapeutics Inc. (San Diego, CA, USA) that shows promising characteristics for the treatment of P. aeruginosa infections because it appears to be stable against the most common mechanisms of resistance acquired through mutation in this species [23,24]. In the present study, we evaluated the activity of CXA-101 and antipseudomonal comparators against a collection of P. aeruginosa sequential (early and late) isolates, including mucoid and SCV variants, from chronically-infected CF patients in Spain. infection as well as patients with long-term (over 13 years) chronic infection. The isolates were further classified, according to the major CF morphotypes, in mucoid strains [16], SCV [22] and others (non-mucoid non-scv isolates). All patients had received frequent antipseudomonal treatments, including maintenance aerosol therapy (mainly tobramycin) and several intravenous courses with different combinations of b-lactams, aminoglycosides, and fluoroquinoles during acute exacerbations. Susceptibility testing The MICs of CXA-101, ceftazidime (CAZ), cefepime (FEP), piperacillin-tazobactam (PTZ), imipenem (IMP), meropenem (MER), tobramycin (TOB), and levofloxacin (LEV) were determined by standard CLSI broth microdilution (M100- S18) [19]. CXA-101 (Lot 3F02) was provided by Calixa Therapeutics Inc (San Diego, CA, USA). Other antibiotics were purchased from commercial sources. The range of concentrations tested was from 0.12 mg/l to 64 mg/l. The susceptibility breakpoints defined by the CLSI [25] were used for all comparator antibiotics. When specifically indicated, susceptibility data were also analysed applying EUCAST ( breakpoints. The tentative breakpoint considered for CXA-101 was 8 mg/l for the susceptible category, which is the CLSI and EUCAST susceptibility breakpoint used for the other antipseudomonal cephalosporins CAZ and FEP. This tentative breakpoint is further supported by recent pharmacokinetics/pharmacodynamics (PK/ PD) studies [26]. P. aeruginosa reference strains PAO1 and ATCC were tested in parallel for quality control. MDR strains were defined as those nonsusceptible (intermediate or resistant) to at least three of the following four antibiotics: CAZ, IMP, LEV and TOB. Results Materials and Methods Strains A collection of 100 P. aeruginosa isolates obtained from 50 CF patients treated at two different Spanish hospitals (Hospital Universitario Ramón y Cajal in Madrid and Hospital Son Dureta in Palma de Mallorca) was tested. The collection included the first and the last available P. aeruginosa isolates from each of the 50 chronically-infected CF patients. The intervals between the first (early) and last (late) isolates ranged from 2 to 164 months (average 67.6 ± 39.2 months). The collection included patients with incipient P. aeruginosa The distribution of MICs of CXA-101 and comparators for the collection of CF isolates is shown in Table 1. Table 2 contains data on MIC 50, MIC 90, geometric mean of MICs, and the percentage of isolates susceptible and resistant to each of the antibiotics tested. When the complete collection of CF isolates was considered, the MIC 50 and MIC 90 of CXA-101 were 0.5 and 2 mg/ L, respectivey, and the geometric mean MIC was 0.7 mg/l. These values were only comparable to those obtained for MER, although the MIC 90 of this antibiotic was significantly higher (8 mg/l). The MIC 50, MIC 90 and mean MICs of all the other antibiotics tested were significantly higher (Table 2). In terms of susceptibility percentages, using the 8 mg/l break-

3 1484 Clinical Microbiology and Infection, Volume 16 Number 9, September 2010 CMI TABLE 1. Distribution of MICs of CXA-101 and comparators for a collection of 100 P. aeruginosa isolates obtained from 50 chronically-colonized cystic fibrosis patients Number of isolates (%) inhibited at each antibiotic concentration (mg/l) (MIC 50 and MIC 90 are respectively highlighted in light and dark grey) Antibiotic (breakpoints) a CXA CAZ (S 8-R 32) FEP (S 8-R 32) PTZ (S 64-R 128) IMP (S 4-R 16) MER (S 4-R 16) TOB (S 4-R 16) LEV (S 2-R 8) a The CLSI susceptibility and resistance breakpoints (mg/l) are indicated. The tentative susceptibility breakpoint considered for CXA-101 is 8 mg/l. CAZ, ceftazidime; FEP, cefepime; PTZ, piperacillin-tazobactam; IMP, imipenem; MER, meropenem; TOB, tobramycin; LEV, levofloxacin. TABLE 2. Susceptibility data for CXA-101 and comparators in a collection of 100 Pseudomonas aeruginosa isolates, including the first (early) and the last (late) available isolates obtained from 50 cystic fibrosis patients Susceptibility data for the overall collection/early isolates/late isolates Antibiotic (breakpoints) a MIC 50 (mg/l) MIC 90 (mg/l) Mean MIC (mg/l) % Susceptible % Intermediate % Resistant CXA /0.5/1 2/2/4 0.7/0.6/0.9 95/94/96 CAZ (S 8-R 32) 4/4/8 64/64/ /4.7/7.5 75/80/70 6/6/6 19/14/24 FEP (S 8-R 32) 8/8/8 32/32/64 8.1/7.2/9.2 63/66/60 14/14/14 23/20/26 PTZ (S 64-R 128) 4/4/4 128/128/ /4.6/5.1 87/90/84 13/10/16 IMP (S 4-R 16) 4/4/8 64/32/ /4.7/7.7 52/62/42 20/18/22 28/20/36 MER (S 4-R 16) 0.5/0.5/0.5 8/8/ /0.61/ /90/82 7/6/8 7/4/10 TOB (S 4-R 16) 0.5/0.5/1 16/8/64 1.2/0.9/1.7 77/84/70 6/8/4 17/8/26 LEV (S 2-R 8) 2/1/2 16/8/16 1.8/1.5/2.2 67/74/60 11/8/14 22/18/26 a The CLSI susceptibility and resistance breakpoints (mg/l) are indicated and applied. The tentative susceptibility breakpoint considered for CXA-101 is 8 mg/l. CAZ, ceftazidime; FEP, cefepime; PTZ, piperacillin-tazobactam; IMP, imipenem; MER, meropenem; TOB, tobramycin; LEV, levofloxacin. point, CXA-101 was the most active antibiotic (95% of isolates susceptible) followed by PTZ (87%) and MER (86%), whereas the activities of IMP (52%), CAZ (75%), FEP (63%), LEV (67%) or TOB (77%) were significantly lower. Susceptibility percentages for CAZ, FEP, IMP or TOB would not be modified by the application of the EUCAST (instead of the CLSI) breakpoints because both agencies use the same susceptibility breakpoints for these antibiotics. However, the application of EUCAST susceptibility breakpoints for PTZ (S 16 mg/l), MER (S 2 mg/l) and LEV (S 1 mg/l) would significantly reduce the percentages of susceptibility to these antibiotics: 79% for PTZ, 70% for MER and 47% for LEV (data not shown). When the susceptibility of early vs. late colonizing isolates was analysed, as expected, a clear trend for MICs to increase over time (higher MIC 50, MIC 90 and mean MIC) was detected for all the antibiotics tested, including CXA-101. Nevertheless, as for the complete collection, the activity of CXA-101 against late isolates was comparable to that of MER, and significantly more potent than those of all the other antibiotics tested (Table 2). In terms of susceptibility percentages, CXA-101 (96%) was the most active antibiotic against the late CF isolates, followed, by a margin, by PTZ (84%) and MER (82%). The susceptibility to CAZ (70%), FEP (60%), LEV (60%) or IMP (42%) was particularly low against late CF isolates (Table 2). The activity of CXA-101 against isolates nonsusceptible (intermediate or resistant) to the other antibiotics tested is shown in Table 3. CXA-101 was active against the majority of isolates nonsusceptible to each of the other antibiotic tested, with MIC 50 values of 1 2 mg/l. In terms of susceptibility percentages, considering the 8 mg/l breakpoint, CXA-101 showed very good activity against isolates nonsusceptible to IMP (92% susceptible), LEV (91%), FEP (87%), CAZ (84%) and MER (79%). The activity was slightly lower against PTZ nonsusceptible isolates, although nine of the 13 (69%) PTZ resistant isolates were susceptible to CXA-101 (Table 3) By contrast, all isolates (n = 5) showing CXA-101 MICs 8 mg/l were CAZ- and FEP-resistant, and four of the five were also PTZ- and IMP-resistant. Finally, CXA-101 retained good activity against MDR strains, with MIC 50 and MIC 90 values of 2 and 16 mg/l and MICs 8 mg/l for 84% of the isolates.

4 CMI Zamorano et al. Activity of CXA-101 against Pseudomonas aeruginosa isolates from cystic fibrosis 1485 TABLE 3. Activity of CXA-101 against isolates not susceptible to the comparator antibiotics. Nonsusceptible isolates a CXA-101 susceptibility data MIC 50 (mg/l) MIC 90 (mg/l) Geometric Mean MIC (mg/l) n (%) of isolates with CXA-101 MIC 8 mg/l IMP (n = 48) (91.7) FEP (n = 37) (86.5) LEV (n = 33) (90.9) CAZ (n = 25) (84.0) TOB (n = 23) (82.6) MER (n = 14) (78.6) PTZ (n = 13) (69.2) MDR (n = 19) (84.2) a The CLSI intermediate and resistance categories are included. b MDR strains were defined as those not susceptible to at least three of the following four antibiotics: CAZ, IMP, LEV and TOB. IMP, imipenem; FEP, cefepime; LEV, levofloxacin; CAZ, ceftazidime; TOB, tobramycin; MER, meropenem; PTZ, piperacillin-tazobactam; MDR, multidrug-resistance. TABLE 4. Susceptibility data for CXA-101 and comparators in a collection of 100 cystic fibrosis Pseudomonas aeruginosa isolates, according to morphotype Morphotype (number of isolates) % Susceptible/geometric mean MIC (mg/l) a CXA-101 CAZ (S 8) FEP (S 8) PTZ (S 64) IMP (S 4) MER (S 4) LEV (S 2) TOB (S 4) SCV (n = 19) 89/1.1 63/8.0 42/ /4.6 42/8.0 84/0.8 42/3.6 47/5.4 Mucoid (n = 51) 94/0.8 67/7.7 59/9.9 84/6.8 45/7.6 82/1.1 63/2.1 82/1.1 Others b (n = 30) 100/0.4 97/3.2 83/4.0 93/2.8 70/3.3 93/0.4 90/1.0 87/0.6 a The CLSI susceptibility breakpoints are indicated and applied. The tentative susceptibility breakpoint considered for CXA-101 is 8 mg/l. b Non-mucoid, non-small colony variant (SCV). CAZ, ceftazidime; FEP, cefepime; PTZ, piperacillin-tazobactam; IMP, imipenem; MER, meropenem; LEV, levofloxacin; TOB, tobramycin. Of the 100 CF isolates tested, 51 were found to have the mucoid phenotype, whereas 19 were SCV. The activity of CXA-101 and comparators against these major CF morphotypes is shown in Table 4. Both the SCV and mucoid isolates showed significantly lower susceptibility percentages, with increased MICs (two- to ten-fold higher mean MICs) of all antibiotics tested compared to other morphotypes (nonmucoid non-scv isolates). Additionally, SCV were much less frequently susceptible to TOB than mucoid strains (47% vs. 82%), whereas the susceptibility to all other antibiotics was similarly reduced in both morphotypes. Again, CXA-101 and MER were the most potent antibiotics against SCV and mucoid strains, with a mean MIC of approximately 1 mg/l. Moreover, the percentages of susceptibility to CXA-101 were highest, both in the case of SCV (89%) and mucoid strains (94%). Discussion Although P. aeruginosa eradication from the respiratory tract of CF patients, by early aggressive antimicrobial therapy, might still be possible during initial colonization [27], once CRI is fully established, this goal is generally no longer attainable. In any case, effective antibiotic treatments are still greatly needed for CRI to maintain the basal bacterial densities as low as possible and to restore the basal densities as quickly as possible after the frequent acute exacerbations [28]. Antimicrobial therapy of CRI generally includes the use of maintenance tobramycin or colistin inhalation treatments, as well as repeated intravenous courses of b-lactams or fluoroquinoles combined with aminoglycosides for acute exacerbations [28]. Unfortunately, after years of CRI, sequential development of resistance to all the available antibiotics is a frequent outcome. Indeed, antimicrobial resistance rates among CF isolates are significantly higher than those documented in any other type of infection, including those occurring in the intensive care unit setting [4,29]. Moreover, MDR development is a frequent event [6] and has been demonstrated to have a major impact on the progression of the disease [7]. Over the last two decades, very limited progress has been made in developing anti-pseudomonal agents that can overcome MDR in P. aeruginosa. Among the recently introduced antibiotics, only doripenem appears to have slightly enhanced activity against MDR CF isolates [30]. Nevertheless, crossresistance between doripenem and available carbapenems, particularly MER, has been documented [31], potentially limiting the impact of this antimicrobial agent.

5 1486 Clinical Microbiology and Infection, Volume 16 Number 9, September 2010 CMI CXA-101, previously designated FR , is a new cephalosporin with promising characteristics for the treatment of P. aeruginosa infections because it appears to be stable against the most common mechanisms of resistance acquired through mutation in this species [23,24]. In initial studies, Takeda et al. [24] tested 193 P. aeruginosa isolates from Japan, documenting the excellent activity of FR (MIC 50 /MIC 90 = 0.5/1 mg/l), although the collection included only a limited number of cephalosporin (CAZ)-resistant isolates (13/193). These initial studies also showed conserved activity against mutants overexpressing different P. aeruginosa efflux pumps, as well as against simple AmpD mutants showing moderately increased AmpC expression and b-lactam resistance [23,24]. The high stability in the presence of AmpC-mediated resistance was further confirmed in a recent study by our group [32] in which we evaluated the activity of CXA-101 against a highly challenging collection of strains with multiple combinations of mutations leading to different degrees of AmpC overexpression (ampd, ampdh2, ampdh3 and dacb (PBP4)) and porin loss (oprd). Indeed, CXA-101 was found to be the only b-lactam tested (including CAZ, FEP, PTZ, aztreonam, IMP and MER) conserving high activity (MICs 2 mg/l) against strains containing combinations of all of these mutations [32]. We also recently evaluated a collection of non-cf carbapenem-resistant and MDR P. aeruginosa isolates obtained from a multicentre study in Spain [33]; CXA-101 showed good activity against that collection of isolates (MIC 50 /MIC 90 of 1/4 mg/l, 95% MICs 8mg/L) and, interestingly, almost all of the CXA-101-nonsusceptible isolates produced an MBL or ESBL encoded by a horizontally-acquired gene, consistent with the previously observed stability against mutation-mediated resistance mechanisms. Nevertheless, the available information on the activity of CXA-101 against isolates from CF patients is still limited. A single study by Livermore et al. [34] recently evaluated a highly challenging panel of 56 MDR P. aeruginosa isolates from CF patients and found that CXA- 101 was the most active drug. In the same study, the activity of CXA-101 against isolates of Burkholderia cepacia, another relevant (although much less frequent) CF pathogen, was similar to that of CAZ [34]. Moreover, very recent data show that the activity of CXA-101 against Enterobacteriaceae and Gram-positive cocci might be similar to other extendedspectrum cephalosporins [35]. In the present study, we evaluated the activity of CXA-101 and comparators in a collection of 100 sequential (early-late) P. aeruginosa isolates, including mucoid and SCV variants, from 50 chronically-infected CF patients in Spain. The susceptibility profiles observed in this CF collection included, in agreement with data from previous studies [29], an important number of strains resistant to most currently available antipseudomonal agents, particularly among the late CF isolates. The overall activity of CXA-101 against CF isolates (in terms of MICs) was comparable to that of MER, and significantly higher than that of IMP, CAZ, FEP, PTZ, LEV and TOB. CXA-101 showed conserved activity against a high proportion of isolates resistant to each of the antibiotics tested, with MIC 50 values of 1 2 mg/l and, remarkably, retained good activity against MDR strains, with MIC 50 and MIC 90 values of of 2 and 16 mg/l and MICs 8 mg/l for 84% of the isolates. The activity of CXA-101 was also very high against late CF isolates, being the only antibiotic tested to which a similar percentage of early and late isolates was susceptible. Moreover, CXA-101 was highly potent against mucoid and SCV phenotypes (mean MIC = 1 mg/l). These results show that, despite a certain increase in MICs, major cross-resistance to CXA-101 did not develop during treatment of CF patients with the currently available antipseudomonal agents. Therefore, CXA-101 is envisaged as a potentially valuable antibiotic for the treatment of CRI caused by P. aeruginosa in CF patients. Thus, the usefulness of this antibiotic for the treatment of chronic P. aeruginosa infections in CF patients (in terms of efficacy and reduced resistance development) should be evaluated in pertinent clinical trials. Acknowledgements This work was presented at the 49th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC). Abstract F San Francisco, USA, September Transparency declaration This work was supported by a grant from Calixa Therapeutics Inc. and by the Ministerio de Ciencia e Innovación of Spain, Instituto de Salud Carlos III, through the Spanish Network for the Research in Infectious Diseases (REIPI C03/14 and RD06/0008). Y. Ge is an employee of Calixa Therapeutics Inc., and also owns stocks or shares in Calixa Therapeutics Inc. No dual or conflicting interests for the other authors. References 1. Lyczak JB, Cannon CL, Pier GB. Lung infections associated with cystic fibrois. Clin Microbiol Rev 2002; 15:

6 CMI Zamorano et al. Activity of CXA-101 against Pseudomonas aeruginosa isolates from cystic fibrosis Gibson RL, Burns JL, Rammsey BW. Pathophysiology and management of pulmonary infections in cystic fibrosis. Am J Respir Crit Care Med 2003; 168: Livermore DM. Multiple mechanisms of antimicrobial resistance in Pseudomonas aeruginosa: our worst nightmare? Clin Infect Dis 2002; 34: Oliver A, Cantón R, Campo P, Baquero F, Blázquez J. High frequency of hypermutable Pseudomonas aeruginosa in cystic fibrosis lung infection. Science 2000; 288: Ciofu O, Riis B, Pressler P, Poulsen HP, Hoiby N. Ocurrence of hypermutable Pseudomonas aeruginosa in cystic fibrosis patients is associated with the oxidative stress caused by chronic lung inflamation. Antimicrob Agents Chemother 2005; 49: Merlo CA, Boyle MP, Diener-West M, Marshall BC, Goss CH, Lechtzin N. Incidence and risk factors for multiple antibiotic-resistant Pseudomonas aeruginosa in cystic fibrosis. Chest 2007; 132: Leichtzin N, John M, Irizarry R, Merlo C, Diette GB, Boyle MP. Outcomes of adults with cystic fibrosis infected with antibiotic-resistant Pseudomonas aeruginosa. Respiration 2006; 73: Ballesteros S, Fernández-Rodríguez A, Villaverde R, Escobar H, Pérez-Díaz JC, Baquero F. Carbapenem resistance in Pseudomonas aeruginosa from cystic fibrosis patients. J Antimicrob Chemother 1996; 38: Bagge N, Ciofu O, Hentzer M, Campbell JI, Givskov M, Hoiby N. Constitutive high expression of chromosomal b-lactamase in Pseudomonas aeruginosa caused by a new insertion sequence (IS1669) located in ampd. Antimicrob Agents Chemother 2002; 46: Moya B, Döstch A, Juan C et al. B-lactam resistance response triggered by inactivation of a nonessential penicillin-binding protein. PLoS Pathog 2009; 5: e Jalal S, Ciofu O, Hoiby N, Gotoh N, Wretlind B. Molecular mechanisms of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from cystic fibrosis patients. Antimicrob Agents Chemother 2000; 44: Vogne C, Aires JR, Bailly C, Hocquet D, Plesiat P. Role of the multidrug efflux system MexXY in the emergence of moderate resistance to aminoglycosides among Pseudomonas aeruginosa isolates from patients with cystic fibrosis. Antimicrob Agents Chemother 2004; 48: Foweraker JE, Laughton CR, Brown DF, Bilton D. Phenotypic variability of Pseudomonas aeruginosa in sputa from patients with acute infective exacerbation of cystic fibrosis and its impact on the validity of antimicrobial susceptibility testing. J Antimicrob Chemother 2005; 55: Smith EE, Buckley DG, Wu Z et al. Genetic adaptation by Pseudomonas aeruginosa to the airways of cystic fibrosis patients. Proc Natl Acad Sci USA 2006; 103: Mena A, Smith EE, Burns JL et al. Genetic adaptation by Pseudomonas aeruginosa to the airways of cystic fibrosis patients is catalyzed by hypermutation. J Bacteriol 2008; 190: Govan JR, Deretic V. Microbial pathogenesis in cystic fibrosis: mucoid Pseudomonas aeruginosa and Burkholderia cepacia. Microbiol Rev 1996; 60: Parad RB, Gerard CJ, Zurakowski D, Nichols DP, Pier GB. Pulmonary outcome in cystic fibrosis is influenced primarily by mucoid Pseudomonas aeruginosa infection and immune status and only modestly by genotype. Infect Immun 1999; 67: Yu H, Hanes M, Chrisp CE, Boucher JC, Deretic V. Microbial pathogenesis in cystic fibrosis: pulmonary clearance of mucoid Pseudomonas aeruginosa and inflammation in a mouse model of repeated respiratory challenge. Infect Immun 1998; 66: Pedersen S, Kharazmi SA, Espersen F, Hoiby N. Pseudomonas aeruginosa alginate in cystic fibrosis sputum and the inflamatory response. Infect Immun 1990; 58: Hatch RA, Schiller NL. Alginate lyase promotes diffusion of aminoglycosides through the extracellular polysaccharide of mucoid Pseudomonas aeruginosa. Antimicrob Agents Chemother 1998; 42: Simpson JA, Smith SE, Dean RT. Scavenging by alginate of free radicals released by macrophages. Free Radic Biol Med 1989; 6: Häubler S, Tümmler B, Weissbrodt H, Rohde M, Steinmetz I. Small colony variants of Pseudomonas aeruginosa in cystic fibrosis. Clin Infect Dis 1999; 29: Takeda S, Ishii Y, Hatano K, Tateda K, Yamaguchi K. Stability of FR against AmpC b-lactamase of Pseudomonas aeruginosa. Int J Antimicrob Agents 2007; 30: Takeda S, Nakai T, Wakai Y, Ikeda F, Hatano K. In vitro and In vivo activities of a new cephalosporin, FR264205, against Pseudomonas aeruginosa. Antimicrob Agents Chemother 2007; 51: Clinical and Laboratory Standards Institute (CLSI). Performance standards for antimicrobial susceptibility testing, vol. 28, no. 3, 18th informational supplement. M100 S18. Wayne, PA: Clinical and Laboratory Standards Institute, Ge Y, Liao S. CXA-101 (CXA) population PK analysis and Monte Carlo (MC) simulation for PK/PD target attainment and dose regimen selection. 49th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC). Abstract F San Francisco, USA, September Taccetti G, Campana S, Festini F, Mascherini M, Döring G. Early eradication therapy against Pseudomonas aeruginosa in cystic fibrosis patients. Eur Respir J 2005; 26: Cantón R, Cobos N, de Gracia J et al. Antimicrobial therapy for pulmonary pathogenic colonisation and infection by Pseudomonas aeruginosa in cystic fibrosis patients. Clin Microbiol Infect 2005; 11: Henwood CJ, Livermore DM, James D, Warner M, the Pseudomonas study group. Antimicrobial susceptibility of Pseudomonas aeruginosa: results of a UK survey and evaluation of the British Society for Antimicrobial Chemotherapy disc susceptibility test. J Antimicrob Chemother 2001; 47: Chen Y, Garber E, Zhao Q et al. In vitro activity of doripenem (S-4661) against multidrug-resistant gram-negative bacilli isolated from patients with cystic fibrosis. Antimicrob Agents Chemother 2005; 49: Mushtaq S, Ge Y, Livermore DM. Doripenem versus Pseudomonas aeruginosa in vitro: activity against characterized isolates, mutants, and transconjugants and resistance selection potential. Antimicrob Agents Chemother 2005; 48: Moya B, Zamorano L, Juan C, Pérez JL, Ge Y, Oliver A. Activity of a new cephalosporin, CXA-101 (FR264205) against b-lactom-resistant Pseudomonas aeruginosa mutants selected in vitro and after antipseudomonal treatment of Intensive Care Unit patients. Antimicrob Agents Chemother 2010; doi: /AAC Juan C, Zamorano L, Pérez JL, Ge Y, Oliver A, on behalf of the Spanish Group for the Study of Pseudomonas and REIPI. Activity of a new antipseudomonal cephalosporin, CXA-101 (FR264205), against carbapenem-resistant and multidrug-resistant Pseudomonas aeruginosa clinical strains. Antimicrob Agents Chemother 2009; 54: Livermore DM, Mushtaq S, Ge Y, Wagner M. Activity of cephalosporin CXA-101 (FR264205) against Pseudomonas aeruginosa and Burkholderhia cepacia group strains and isolates. Int J Antimicrob Agents 2009; 34: Brown NP, Pillar CM, Sham DF, Ge Y. Activity profile of CXA- 101 and CXA-101/tazobactam against target Gram-positive and Gram-negative pathogens. Abstract F th Interscience Conference on Antimicrobial Agents and Chemotherapy. San Francisco, Ca, 2009.