non-CF Strains Research Articles

Staphylococcus aureus and Pseudomonas aeruginosa Isolates from the Same Cystic Fibrosis Respiratory Sample Coexist in Coculture.

ABSTRACTRespiratory infections with bacterial pathogens remain the major cause of morbidity in individuals with the genetic disease cystic fibrosis (CF). Some studies have shown that CF patients that harbor both Staphylococcus aureus and Pseudomonas aeruginosa in their lungs are at even greater risk for more severe and complicated respiratory infections and earlier death. However, the drivers for this worse clinical condition are not well understood. To investigate the interactions between these two microbes that might be responsible for their increased pathogenic potential, we obtained 28 pairs of S. aureus and P. aeruginosa from the same respiratory samples from 18 individuals with CF. We compared the survival of each S. aureus CF isolate cocultured with its corresponding coinfecting CF P. aeruginosa to when it was cocultured with non-CF laboratory strains of P. aeruginosa. We found that the S. aureus survival was significantly higher in the presence of the coinfecting P. aeruginosa compared to laboratory P. aeruginosa strains, regardless of whether the coinfecting isolate was mucoid or nonmucoid. We also tested how a non-CF S. aureus strain, JE2, behaved with each P. aeruginosa CF isolate and found that its interaction was similar to how the CF S. aureus isolate interacted with its coinfecting P. aeruginosa. Altogether, our work suggests that interactions between S. aureus and P. aeruginosa that promote coexistence in the CF lung are isolate-dependent and that this interaction appears to be driven mainly by P. aeruginosa.IMPORTANCE Previous studies have shown that in laboratory settings, Pseudomonas aeruginosa generally kills Staphylococcus aureus. However, these bacteria are often found coinfecting the lungs of cystic fibrosis (CF) patients, which has been associated with worse patient outcomes. To investigate the interactions between these two bacteria, we competed 28 coinfection pairs obtained from the same lung samples of 18 different CF patients. We compared these results to those we previously reported of each CF S. aureus isolate against a non-CF laboratory strain of P. aeruginosa. We found that S. aureus survival against its corresponding coinfection P. aeruginosa was higher than its survival against the laboratory strain of P. aeruginosa. These results suggest that there may be selection for coexistence of these microbes in the CF lung environment. Further understanding of the interactions between P. aeruginosa and S. aureus will provide insights into the drivers of coexistence and their impact on the host.

Effects of the Sex Steroid Hormone Estradiol on Biofilm Growth of Cystic Fibrosis Pseudomonas aeruginosa Isolates.

Women with cystic fibrosis (CF) have a significantly lower life expectancy compared to men, which is indicated by an earlier impairment of lung function due to chronic colonization with biofilm formed by Pseudomonas aeruginosa. There is growing evidence that blood serum concentrations of the steroid sex hormone estradiol (E2) correlate with the occurrence of pulmonary exacerbations in CF but also play a role in the mucoid switch of P. aeruginosa. This study aims to shed light on possible microbiological reasons for sexual dimorphism in CF by investigating the influence of E2 on biofilm formation of P. aeruginosa CF isolates. For this purpose, 10 CF isolates of the respiratory tract derived from different CF patients have been treated with E2 in a microtiter plate biofilm model. Biofilms have been examined by crystal violet assays, field emission scanning electron microscopy (FE-SEM), 3D laser scanning microscopy (LSM), and quorum sensing (QS) reporter assays of the supernatants taken from biofilms. This allowed us to simultaneously investigate the effects of E2 on attached biofilm mass, biofilm ultrastructure, and QS activity. Upon E2 treatment, six out of 10 investigated CF isolates showed an increase of attached biofilm mass, whereas biofilms from two tested non-CF laboratory strains (PAO1 and ATCC19660) did not. Moreover, FE-SEM and 3D LSM analyses of the E2 responsive CF biofilms revealed ultrastructural remodeling of biofilm structure at different scales with increased formation of prominent biofilm spots, enhanced coverage with extracellular polymeric substance (EPS), and extended average surface roughness. QS activity measurements performed in biofilm supernatants via luminescence acyl homoserine lactone (AHL) reporter assays further showed that E2 treatment may also modulate QS signaling, as shown in an E2 sensitive CF isolate. Together, our results suggest the biofilm modulating effects of E2 on various clinical CF isolates that are documented by both biomass and ultrastructural changes of biofilms. The gained new insight into the influence of steroid hormones on P. aeruginosa biofilm phenotypes might pave the way for novel future approaches in personalized medicine based on the patients’ sex and hormonal status.

Clonal Diversity, Biofilm Formation, and Antimicrobial Resistance among Stenotrophomonas maltophilia Strains from Cystic Fibrosis and Non-Cystic Fibrosis Patients.

The intrinsic antibiotic resistance of Stenotrophomonas maltophilia, along with its ability to form biofilm both on abiotic surfaces and host tissues, dramatically affects the efficacy of the antibiotic therapy. In this work, 85 S. maltophilia strains isolated in several hospital of central Italy and from several clinical settings were evaluated for their genetic relatedness (by pulsed-field gel electrophoresis, PFGE), biofilm formation (by microtiter plate assay), and planktonic antibiotic resistance (by Kirby–Bauer disk diffusion technique). The S. maltophilia population showed a high genetic heterogeneity: 64 different PFGE types were identified, equally distributed in cystic fibrosis (CF) and non-CF strains, and some consisted of multiple strains. Most of the strains (88.2%) were able to form biofilm, although non-CF strains were significantly more efficient than CF strains. CF strains produced lower biofilm amounts than non-CF strains, both those from respiratory tracts and blood. Non-CF PFGE types 3 and 27 consisted of strong-producers only. Cotrimoxazole and levofloxacin were the most effective antibiotics, being active respectively against 81.2% and 72.9% of strains. CF strains were significantly more resistant to piperacillin/tazobactam compared to non-CF strains (90% versus 53.3%), regardless of sample type. Among respiratory strains, cotrimoxazole was more active against non-CF than CF strains (susceptibility rates: 86.7% versus 75%). The multidrug resistant phenotype was significantly more prevalent in CF than non-CF strains (90% versus 66.7%). Overall, the multidrug-resistance level was negatively associated with efficiency in biofilm formation. Our results showed, for the first time, that in S. maltophilia both classical planktonic drug resistance and the ability of biofilm formation might favor its dissemination in the hospital setting. Biofilm formation might in fact act as a survival mechanism for susceptible bacteria, suggesting that clinical isolates should be routinely assayed for biofilm formation in diagnostic laboratories.

Epidemiology and natural history of Pseudomonas aeruginosa airway infections in non-cystic fibrosis bronchiectasis.

The natural history and epidemiology of Pseudomonas aeruginosa infections in non-cystic fibrosis (non-CF) bronchiectasis is not well understood.As such it was our intention to determine the evolution of airway infection and the transmission potential of P. aeruginosa in patients with non-CF bronchiectasis.A longitudinal cohort study was conducted from 1986–2011 using a biobank of prospectively collected isolates from patients with non-CF bronchiectasis. Patients included were ≥18 years old and had ≥2 positive P. aeruginosa cultures over a minimum 6-month period. All isolates obtained at first and most recent clinical encounters, as well as during exacerbations, that were morphologically distinct on MacConkey agar were genotyped by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). A total of 203 isolates from 39 patients were analysed. These were compared to a large collection of globally epidemic and local CF strains, as well as non-CF isolates.We identified four patterns of infection in non-CF bronchiectasis including: 1) persistence of a single strain (n=26; 67%); 2) strain displacement (n=8; 20%); 3) temporary disruption (n=3; 8%); and 4) chaotic airway infection (n=2; 5%). Patterns of infection were not significant predictors of rates of lung function decline or progression to end-stage disease and acquisition of new strains did not associate with the occurrence of exacerbations. Rarely, non-CF bronchiectasis strains with similar pulsotypes were observed in CF and non-CF controls, but no CF epidemic strains were observed. While rare shared strains were observed in non-CF bronchiectasis, whole-genome sequencing refuted patient–patient transmission.We observed a higher incidence of strain-displacement in our patient cohort compared to those observed in CF studies, although this did not impact on outcomes.

Mutations in Gene fusA1 as a Novel Mechanism of Aminoglycoside Resistance in Clinical Strains of Pseudomonas aeruginosa.

Resistance of clinical strains of Pseudomonas aeruginosa to aminoglycosides can result from production of transferable aminoglycoside-modifying enzymes, of 16S rRNA methylases, and/or mutational derepression of intrinsic multidrug efflux pump MexXY(OprM). We report here the characterization of a new type of mutant that is 4- to 8-fold more resistant to 2-deoxystreptamine derivatives (e.g., gentamicin, amikacin, and tobramycin) than the wild-type strain PAO1. The genetic alterations of three in vitro mutants were mapped on fusA1 and found to result in single amino acid substitutions in domains II, III, and V of elongation factor G (EF-G1A), a key component of translational machinery. Transfer of the mutated fusA1 alleles into PAO1 reproduced the resistance phenotype. Interestingly, fusA1 mutants with other amino acid changes in domains G, IV, and V of EF-G1A were identified among clinical strains with decreased susceptibility to aminoglycosides. Allelic-exchange experiments confirmed the relevance of these latter mutations and of three other previously reported alterations located in domains G and IV. Pump MexXY(OprM) partly contributed to the resistance conferred by the mutated EF-G1A variants and had additive effects on aminoglycoside MICs when mutationally upregulated. Altogether, our data demonstrate that cystic fibrosis (CF) and non-CF strains of P. aeruginosa can acquire a therapeutically significant resistance to important aminoglycosides via a new mechanism involving mutations in elongation factor EF-G1A.

Temperature, pH and Trimethoprim-Sulfamethoxazole Are Potent Inhibitors of Biofilm Formation by Stenotrophomonas maltophilia Clinical Isolates.

Stenotrophomonas maltophilia, an opportunistic pathogen usually connected with healthcare-associated infections, is an environmental bacterium. Intrinsic resistance to multiple antibiotics, with different virulence determinants in the last decade classified this bacterium in the group of global multiple drug resistant (MDR) organism. S. maltophilia clinical isolates, were collected from tertiary care pediatric hospital in Belgrade, Serbia to investigate influence of different factors on biofilm formation, kinetics of biofilm formation for strong biofilm producers and effect of trimethoprim-sulfamethoxazole (TMP/SMX) on formed biofilm. Most of the isolates (89.8%) were able to form a biofilm. Analysis of biofilm formation in different growth conditions showed that changing of temeperature and pH had the stronggest effect on biofilm formation almost equally in group of cystic fibrosis (CF) and non-CF strains. TMP/SMX in concentration of 50 μg/ml reduced completely 24 h old biofilms while concentration of 25 μg/ml effects formed biofilms in a strain dependent manner. Among strains able to form strong biofilm CF isolates formed biofilm slower than non-CF isolates, while shaking conditions did not affect biofilm formation. Swimming motility was detected in both CF and non-CF isolates, however more motile strain formed stronger biofilms. This study suggests that temperature, pH and TMP/SMX had the strongest influence on biofilm formation in analyzed collection of S. maltophilia. A positive correlation between motility and strength of formed biofilm was demonstrated.

Genotypic and Phenotypic Characterization of Stenotrophomonas maltophilia Strains from a Pediatric Tertiary Care Hospital in Serbia.

BackgroundStenotrophomonas maltophilia is an environmental bacterium and an opportunistic pathogen usually associated with healthcare-associated infections, which has recently been recognized as a globally multi-drug resistant organism. The aim of this study was genotyping and physiological characterization of Stenotrophomonas maltophilia isolated in a large, tertiary care pediatric hospital in Belgrade, Serbia, hosting the national reference cystic fibrosis (CF) center for pediatric and adult patients.MethodsWe characterized 42 strains of cystic fibrosis (CF) and 46 strains of non-cystic fibrosis (non-CF) origin isolated from 2013 to 2015 in order to investigate their genetic relatedness and phenotypic traits. Genotyping was performed using sequencing of 16S rRNA gene, Pulse Field Gel Electrophoresis (PFGE) and Multi locus sequencing typing (MLST) analysis. Sensitivity to five relevant antimicrobial agents was determined, namely trimethoprim/sulfamethoxazole (TMP/SMX), chloramphenicol, ciprofloxacin, levofloxacin and tetracycline. Surface characteristics, motility, biofilm formation and adhesion to mucin were tested in all strains. Statistical approach was used to determine correlations between obtained results.ResultsMost of the isolates were not genetically related. Six new sequence types were determined. Strains were uniformly sensitive to all tested antimicrobial agents. The majority of isolates (89.8%) were able to form biofilm with almost equal representation in both CF and non-CF strains. Swimming motility was observed in all strains, while none of them exhibited swarming motility. Among strains able to adhere to mucin, no differences between CF and non-CF isolates were observed.ConclusionsHigh genetic diversity among isolates implies the absence of clonal spread within the hospital. Positive correlation between motility, biofilm formation and adhesion to mucin was demonstrated. Biofilm formation and motility were more pronounced among non-CF than CF isolates.

75 A single clone of Achromobacter xylosoxidans colonizes Belgian cystic fibrosis patients from different centres

Objective Several major infection problems with Achromobacter xylosoxidans were observed for CF patients in Belgium. We tried to assess the epidemiology. Methods We typed 50 strains from 24 CF patients – from Ghent University Hospital (UZG, n=17) and from the University of Antwerp Hospital (UZA, n=7), most of which (14 from Ghent and 5 from Antwerp) had stayed at the rehabilitation centre. CF-related strains had been collected over a period of 10 years. We also included 8 unrelated strains: 7 clinical strains from non-CF patients and the type strain. McRAPD (arbitrarily primed PCR in combination with melting curve analysis)(Deschaght et al. 2011. Res Microbiol 162: 386–392), nrdA gene sequencing (Spilker et al. 2013. J Cystic Fibrosis 12: 298–301) and MALDI-TOF typing (newly developed) were used for typing. Results Typing revealed that most isolates from CF patients were indistinguishable by any of the three approaches. Only 6 CF patients had invididual types of A. xylosoxidans . Non-CF strains, including the one isolated from a non-CF patient at the rehabilitation centre, belonged to separate genotypes. The major clone observed in this study had previously been recognized as a major cluster (10 patients) in the rehabilitation centre of De Haan and its distinctness from a previously established minor cluster in De Haan (4 patients, Van Daele et al. 2005. J Clin Microbiol 43: 2998–3002) was confirmed in this study. Conclusion These data indicate that most CF patients from different CF centres in Belgium are colonized by a single clone of genuine A. xylosoxidans , that is spreading since at least 10 years. We thank the MucoVereniging Belgium

Antibodies against outer membrane proteins of Moraxella catarrhalis and nontypeable Haemophilus influenzae cross-react with various pathogens of human respiratory tract

Event Abstract Back to Event Antibodies against outer membrane proteins of Moraxella catarrhalis and nontypeable Haemophilus influenzae cross-react with various pathogens of human respiratory tract Daria Augustyniak1*, Joanna Bonarowska1, Paweł Mackiewicz2 and Zuzanna Drulis-Kawa1 1 University of Wroclaw, Department of Pathogen Biology and Immunology, Institute of Genetics and Microbiology, Poland 2 University of Wroclaw, Department of Genomics, Faculty of Biotechnology, , Poland Introduction: Moraxella catarrhalis and nontypaeble Haemophilus influenzae are important, human-restricted respiratory tract pathogens [1,2]. Outer membrane proteins (OMPs) of these bacteria are their most immunogenic antigens and targets for the host immune response [3,4]. The goal of the study was to quantitatively and qualitatively assess the reactivity of anti-OMPs antibodies against cross-reactive and surface-exposed epitopes of other important pathogens of human respiratory tract. Materials and Methods: Antisera were obtained from six groups of mice, each immunized with OMPs isolated from different Moraxella catarrhalis strains (anti-OMPMc sera) or nontypeable Haemophilus influenzae strains (anti-OMPNTHi sera). OMPs were isolated using Zwittergent 3-14 procedure [4]. The titers of cross-reactive antibodies were measured by whole-cell ELISA whereas their specificities with bacterial OMPs was confirmed by Western-blot according to described methods [4]. The studied pathogens were: Pseudomonas aeruginosa including cystic fibrosis (CF) and non-cystic fibrosis (non-CF) strains, Burkholderia cepacia (CF), Acinetobacter baumanii, Haemophilus parainfluenzae and additionally Candida albicans. To find potential cross-reactive antigens and epitopes in these pathogens, we performed BLAST searches of their protein databases using as a query M. catarrhalis and H. influenzae OMPs for which immune reaction was proved. Results: We found statistically significant homologues especially to Moraxella OMP CopB, E and CD as well as to Haemophilus OMP P1, P4, D15 and Tbp1. Majority of the found homologues are peripheral or outer membrane proteins and could be involved in the cross immune reactions. In whole-cell ELISA we found cross-reactive epitopes in all studied pathogens of respiratory tract. We found that among analyzed anti-OMPMc and anti-OMPNTHi sera, the several were medium or highly cross-reactive. The cross-reactive titers in anti-OMPMc sera were in the range 1:200 – 1:1500 that was 500 – 1000-fold lower than titers for homologous strains. The cross-reactivity of anti-OMPNTHi sera were in the range 1:2000 – 1:11000 that was 4 – 20-fold lower than for homologous counterparts. The reactivity of some cross-reactive antibodies was confirmed with OMPs of tested strains. The differences in recognition of cross-reactive surface epitope between CF and non-CF strains were dependent on used antisera rather than particular strain. Within anti-OMPMc sera the weakest reactivity was usually detected for A. baumanii whereas the highest for C. albicans. In the case of anti-OMPNTHi sera the weakest reactivity was observed for C. albicans and the highest for H. parainfluenzae. The sera with greater cross-reactive potency were found within anti-OMPNTHi ones. Conclusion: The results indicate that IgG antibodies induced against OMPs of particular M.catarrhalis and H.influenzae recognize cross-reactive surface-exposed epitopes in multiple strains of respiratory pathogens. The biological role of this phenomenom is supposed to be confirm in antibody-dependent functional assays. The presence of cross-reactivity should be take under consideration in immunodiagnostic tests for respiratory pathogens.

Multilocus Sequence Analysis of Isolates of Achromobacter from Patients with Cystic Fibrosis Reveals Infecting Species Other than Achromobacter xylosoxidans

A multilocus sequence analysis (MLSA) scheme was developed for characterization of strains and species from the genus Achromobacter, which are increasingly recovered from patients with cystic fibrosis (CF). Five conserved housekeeping genes were selected for the MLSA, which was applied to a diverse collection of 77 strains originating from Europe, Asia, and South America and including type strains of the seven recognized Achromobacter species, six environmental strains, eight non-CF clinical strains, and 56 CF clinical strains. The discriminatory power of MLSA, based on 2,098 nucleotides (nt), was much superior to a 16S rRNA gene comparison based on 1,309 nt. Congruence was observed between single-gene trees and a concatenated gene tree. MLSA differentiated all seven current Achromobacter species and also demonstrated the presence of at least four novel potential species within the genus. CF isolates were predominantly Achromobacter xylosoxidans (64%), an undescribed Achromobacter species (18%), and Achromobacter ruhlandii (7%). A clone of Achromobacter, which has spread among patients from Danish CF centers in Aarhus and Copenhagen, was identified as Achromobacter ruhlandii. MLSA facilitates the specific identification of isolates of Achromobacter necessary for describing their role in clinical infections.

Parallel evolution and local differentiation in quinolone resistance in Pseudomonas aeruginosa

The emergence and spread of antibiotic resistance in pathogens is a major impediment to the control of microbial disease. Here, we review mechanisms of quinolone resistance in Pseudomonas aeruginosa, an important nosocomial pathogen and a major cause of morbidity in cystic fibrosis (CF) patients. In this quantitative literature review, we find that mutations in DNA gyrase A, the primary target of quinolones in Gram-negative bacteria, are the most common resistance mutations identified in clinical samples of all origins, in keeping with previous observations. However, the identities of non-gyrase resistance mutations vary systematically between samples isolated from CF patients and those isolated from acute infections. CF-derived strains tend to harbour mutations in the efflux pump regulator nfxB, while non-CF strains tend to bear mutations in the efflux regulator mexR or in parC, which encodes one of two subunits of DNA topoisomerase IV. We suggest that differences in resistance mechanisms between CF and non-CF strains result either from local adaptation to different sites of infection or from differences in mutational processes between different environments. We further discuss the therapeutic implications of local differentiation in resistance mechanisms to a common antibiotic.

IL-8 released from human lung epithelial cells induced by cystic fibrosis pathogens Burkholderia cepacia complex affects the growth and intracellular survival of bacteria

Burkholderia cepacia complex (Bcc) is a group of Gram-negative pulmonary pathogens associated with life-threatening infections in patients with cystic fibrosis (CF). The airway epithelium plays a crucial role in the initiation and modulation of inflammatory responses to these pathogens. Interleukin (IL)-8 released from epithelial cells is a potent chemoattractant for neutrophils. The aims of this study were to compare the IL-8 response to Bcc infection in different epithelial cell types and to investigate the impact of IL-8 on Bcc growth and intracellular survival. To compare epithelial cell IL-8 responses, 4 human epithelial cell lines were used in the study; A549 cells, an alveolar epithelial cell line, Calu-3 cells, a sub-bronchial epithelial cell line, 16HBE14o− cells, and CFBE41o− cells, which are CFTR-positive and CFTR-negative bronchial epithelial cell lines, respectively. Two B. multivorans and 2 B. cenocepacia strains all induced a significant IL-8 response by 12 h and further increased in all cell lines at 24 h. Furthermore, the levels of IL-8 from Calu-3 and A549 cells were approximately 3 times that of 16HBE14o− or CFBE41o− cells. In 2 of the cell lines examined (16HBE14o− and CFBE41o−), B. cenocepacia LMG 16656 (J2315), an epidemic strain, induced greater levels of IL-8 ( P < 0.01) compared to other Bcc strains tested. The CFTR-positive and -negative cell lines secreted similar levels of IL-8 indicating a CFTR-independent induction of IL-8. However, the CFTR-negative cells did secrete constitutive levels of IL-8 greater than that of CFTR-positive cells. An investigation of the effect of IL-8 on Bcc extracellular and intracellular growth found that at low concentrations (<10 ng/ml) of recombinant human (rh) IL-8, the growth of B. cenocepacia LMG 16656 and B. multivorans LMG 13010 was enhanced, whereas at higher concentrations (10 ng/ml), growth of both strains was significantly reduced. Growth of both non-CF Bcc strains remained unchanged in the presence of rhIL-8. In contrast to extracellular growth, higher concentrations (10 ng/ml) of rhIL-8 enhance the intracellular growth and survival of both LMG 16656 and LMG 13010 in 16HBE14o− and CFBE41o− cell lines. Although LMG 13010 uptake by epithelial cells was higher than LMG 16656 ( P < 0.01), the intracellular growth of LMG 16656 is greater than LMG 13010 ( P < 0.05). These studies demonstrated that the type of epithelial cells encountered by Bcc strains determines the extent of the IL-8 responses triggered and that this cytokine in addition to its well-established proinflammatory properties can enhance both the extracellular and intracellular growth of Bcc strains.

Role of the multidrug efflux system MexXY in the emergence of moderate resistance to aminoglycosides among Pseudomonas aeruginosa isolates from patients with cystic fibrosis.

This study investigates the role of active efflux system MexXY in the emergence of aminoglycoside (AG) resistance among cystic fibrosis (CF) isolates of Pseudomonas aeruginosa. Three genotypically related susceptible and resistant (S/R) bacterial pairs and three other AG-resistant CF strains were compared to four non-CF strains moderately resistant to AGs. As demonstrated by immunoblot experiments, pump MexY was strongly overproduced in all of the resistant bacteria. This MexXY upregulation was associated with a 2- to 16-fold increase in the MICs of AGs in the S/R pairs and lower intracellular accumulation of dihydrostreptomycin. Alterations in mexZ, the repressor gene of operon mexXY, were found in all of the AG-resistant CF isolates and in one non-CF strain. Complementation of these bacteria with a plasmid-borne mexZ gene dramatically reduced the MICs of AGs, thus highlighting the role played by MexXY in the development of moderate resistance in CF patients. In contrast, complementation of the three non-CF strains showing wild-type mexZ genes left residual levels of resistance to AGs. These data indicate that a locus different from mexZ may be involved in overproduction of MexXY and that other nonenzymatic mechanisms contribute to AG resistance in P. aeruginosa.

Antimicrobial susceptibility profile of molecular typed cystic fibrosis Stenotrophomonas maltophilia isolates and differences with noncystic fibrosis isolates

Multiresistance in Stenotrophomonas maltophilia limits the effectiveness of antimicrobial therapy for infections due to this organism. It can be of special concern in cystic fibrosis (CF) patients due to frequent antimicrobial administration. The in vitro activity of 41 antimicrobial agents against 76 epidemiologically defined CF S. maltophilia isolates by pulsed-field-gel electrophoresis (PFGE) technique under XbaI and SpeI restriction was compared with that obtained with 51 non-CF strains recovered from respiratory sources. Minimal inhibitory concentrations (MICs) were determined with the standard National Committee for Clinical Laboratory Standards agar dilution technique, but with 24-hr incubation. Forty-seven different PFGE profiles were observed within 76 S. maltophilia CF isolates. Minocycline (resistance rate, 0%; MIC(90), 1 microg/ml), doxycycline (6.4%; 8 microg/ml), trovafloxacin (4.2%; 2 microg/ml), moxifloxacin (6.3%; 2 microg/ml), clinafloxacin (6.3%; 2 g/ml), and moxalactam (17.0%; 64 g/ml) displayed low resistance rates. On the contrary, resistance rates were higher with ceftazidime (70.0%; 256 microg/ml), cefepime (83.0%; 128 microg/ml), piperacillin (87.2%; >1,024 microg/ml), ticarcillin (87.2%; >512 microg/ml), and aztreonam (95.7%; >1,024 microg/ml). Clavulanate reverted resistance to ticarcillin and aztreonam in 40.4% and 31.7% of strains, respectively. Aminoglycosides displayed reduced activities with susceptibility rates lower than 20% and MIC(90) higher than 128 microg/ml. With the exception of trimethoprim-sulfamethoxazole (25.4 vs. 31.3%), CF isolates were more resistant than non-CF isolates. Remarkably, resistance was enhanced in S. maltophilia isolates persistently recovered in chronically colonized patients. Susceptibility analysis demonstrated higher resistance rates among CF S. maltophilia isolates when compared with respiratory isolates from non-CF patients. Moreover, persistently recovered CF S. maltophilia isolates were more resistant than sporadic non-CF isolates.

Evaluation of reference dilution test methods for antimicrobial susceptibility testing of Pseudomonas aeruginosa strains isolated from patients with cystic fibrosis.

The development of multidrug-resistant Pseudomonas aeruginosa in patients with cystic fibrosis (CF) is most likely a consequence of increasing life expectancy and more prolonged exposure to antibiotics. The optimal method for antibiotic susceptibility testing of CF strains, particularly mucoid P. aeruginosa strains, is unknown. Antimicrobial susceptibilities of 48 CF strains (25 mucoid) and 50 non-CF strains to 12 anti-Pseudomonas agents were tested by both agar dilution and commercially custom-prepared broth microdilution plates (PML Microbiologicals, Portland, Oreg.) in three laboratories simultaneously to determine if broth microdilution could substitute for agar dilution as the reference method in subsequent studies. Comparison of MICs generated by agar dilution and broth microdilution demonstrated correlation coefficients (r) exceeding 0.85 for all agents tested; correlation was excellent for aminoglycosides (r >/= 0.92) and very good for beta-lactam agents including agents paired with a beta-lactamase inhibitor (r >/= 0.87) and for ciprofloxacin (r = 0.86). Correlation was not improved by 48-h readings, but correlation between 24- and 48-h readings ranged between 0.91 and 0.98 for both methods. Interlaboratory variations were minimal, as the percentage of acceptable variations was 94% for both methods, and serious discords were infrequent (<2% of comparisons). However, CF strains were more likely to have serious discords than were non-CF strains (P < 0. 0001), although mucoid strains were not more likely to have serious discords than were nonmucoid strains. In this study, MICs determined by custom-prepared broth microdilution compared favorably with MICs determined by agar dilution. Thus, this broth microdilution assay can serve as a reference method and facilitate future studies to determine the optimal method for antibiotic susceptibility testing of CF strains.

Pyocin typing of Pseudomonas aeruginosa isolates from children with cystic fibrosis

Pyocin typing and serotyping of 433 strains of Pseudomonas aeruginosa from children with cystic fibrosis (CF) showed that pyocin type 9 was predominant, particularly in association with polyagglutinating serotype. The common pyocin groups, 1, 5 and 10, made up only 20% of these isolates in contrast to reported rates of up to 89% in other studies using non-CF strains. No strains of pyocin type 3 were found. Polyagglutinating strains made up 72% of strains from patients colonized with P. aeruginosa for more than 12 mths. Pyocin type 9 was associated with 93% of polyagglutinating strains. The parallel between pyocin type 9 and polyagglutinating serotype suggests that these may both be characteristics acquired by P. aeruginosa colonizing patients with CF. Because of confounding between duration of colonization and exposure to cross-infection, this study does not allow definition of the role of cross-infection in determining the characteristics of these strains in most patients. In siblings, however, evidence supports a role for cross-infection either between siblings or from a common source. In 6 pairs of siblings studied, each pair had at least 1 pyocin group in common concurrently, either at entry to the study or after an interval of several months. Identical and unusual pyocin groups were recognized in samples obtained on the same day from pairs of siblings. More studies are needed to compare results of pyocin typing with methods such as genome fingerprinting to characterize these strains and determine whether the observed distribution of pyocin groups in CF isolates is related to cross-infection or whether the combination of pyocin type 9 with polyagglutinating serotype is a characteristic of CF strains.

The role of complement in the opsonization of mucoid and non-mucoid strains of Pseudomonas aeruginosa.

Requirements for complement and/or antibody for opsonization were assessed for 34 strains of Pseudomonas aeruginosa. Included were mucoid strains from patients with cystic fibrosis (CF), non-mucoid derivatives of these strains, and non-CF strains with classical morphology. Non-CF strains are known to vary as to opsonic requirements, but this study shows that mucoid strains are also diverse. Among the 14 mucoid strains, five could not be opsonized and completely resisted phagocytosis. All non-mucoid strains can be opsonized. When the bacteria were incubated in fresh human serum and stained with fluorescein, conjugated anti-C3 non-opsonizable strains did not bind C3 on the surface whereas five of six mucoid strains, which could be opsonized by complement alone, stained with anti-C3. In mucoid strains, surface characteristics correlate with differences in functional requirements for opsonization. In non-CF strains this specificity was not seen. Most mucoid strains required an intact classical complement pathway for opsonization. A number of mucoid strains could not be opsonized in the absence of a functional alternative complement pathway whereas in contrast, non-CF strains were not greatly affected by inactivation of the alternative pathway.