Does pseudomonas cross-infection occur between cystic-fibrosis patients

Resistance Is Not Futile: The Role of Quorum Sensing Plasticity in Pseudomonas aeruginosa Infections and Its Link to Intrinsic Mechanisms of Antibiotic Resistance

Bacteria use a cell-cell communication process called quorum sensing (QS) to orchestrate collective behaviors. QS relies on the group-wide detection of extracellular signal molecules called autoinducers (AI). Quorum sensing is required for virulence and biofilm formation in the human pathogen Pseudomonas aeruginosa. In P. aeruginosa, LasR and RhlR are homologous LuxR-type soluble transcription factor receptors that bind their cognate AIs and activate the expression of genes encoding functions required for virulence and biofilm formation. While some bacterial signal transduction pathways follow a linear circuit, as phosphoryl groups are passed from one carrier protein to another ultimately resulting in up- or down-regulation of target genes, the QS system in P. aeruginosa is a dense network of receptors and regulators with interconnecting regulatory systems and outputs. Once activated, it is not understood how LasR and RhlR establish their signaling hierarchy, nor is it clear how these pathway connections are regulated, resulting in chronic infection. Here, we reviewed the mechanisms of QS progression as it relates to bacterial pathogenesis and antimicrobial resistance and tolerance.

Pseudomonas aeruginosa Volatilome Characteristics and Adaptations in Chronic Cystic Fibrosis Lung Infections

Pseudomonas aeruginosa is a leading cause of chronic lung infections in cystic fibrosis (CF), which are correlated with lung function decline. Significant clinical efforts are therefore aimed at detecting infections and tracking them for phenotypic changes, such as mucoidy and antibiotic resistance. Both the detection and tracking of lung infections rely on sputum cultures, but due to improvements in CF therapies, sputum production is declining, although risks for lung infections persist. Therefore, we are working toward the development of breath-based diagnostics for CF lung infections. In this study, we characterized of the volatile metabolomes of 81 P. aeruginosa clinical isolates collected from 17 CF patients over a duration of at least 5 years of a chronic lung infection. We found that the volatilome of P. aeruginosa adapts over time and is correlated with infection phenotype changes, suggesting that it may be possible to track chronic CF lung infections with a breath test.

Pseudomonas aeruginosa chronic lung infections in individuals with cystic fibrosis (CF) significantly reduce quality of life and increase morbidity and mortality. Tracking these infections is critical for monitoring patient health and informing treatments. We are working toward the development of novel breath-based biomarkers to track chronic P. aeruginosa lung infections in situ. Using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC–TOF-MS), we characterized the in vitro volatile metabolomes (“volatilomes”) of 81 P. aeruginosa isolates collected from 17 CF patients over at least a 5-year period of their chronic lung infections. We detected 539 volatiles produced by the P. aeruginosa isolates, 69 of which were core volatiles that were highly conserved. We found that each early infection isolate has a unique volatilome, and as infection progresses, the volatilomes of isolates from the same patient become increasingly dissimilar, to the point that these intrapatient isolates are no more similar to one another than to isolates from other patients. We observed that the size and chemical diversity of P. aeruginosa volatilomes do not change over the course of chronic infections; however, the relative abundances of core hydrocarbons, alcohols, and aldehydes do change and are correlated with changes in phenotypes associated with chronic infections. This study indicates that it may be feasible to track P. aeruginosa chronic lung infections by measuring changes to the infection volatilome and lays the groundwork for exploring the translatability of this approach to direct measurement using patient breath.

IMPORTANCEPseudomonas aeruginosa is a leading cause of chronic lung infections in cystic fibrosis (CF), which are correlated with lung function decline. Significant clinical efforts are therefore aimed at detecting infections and tracking them for phenotypic changes, such as mucoidy and antibiotic resistance. Both the detection and tracking of lung infections rely on sputum cultures, but due to improvements in CF therapies, sputum production is declining, although risks for lung infections persist. Therefore, we are working toward the development of breath-based diagnostics for CF lung infections. In this study, we characterized of the volatile metabolomes of 81 P. aeruginosa clinical isolates collected from 17 CF patients over a duration of at least 5 years of a chronic lung infection. We found that the volatilome of P. aeruginosa adapts over time and is correlated with infection phenotype changes, suggesting that it may be possible to track chronic CF lung infections with a breath test.

Epidemiology, Biology, and Impact of Clonal Pseudomonas aeruginosa Infections in Cystic Fibrosis

Chronic lower airway infection with Pseudomonas aeruginosa is a major contributor to morbidity and mortality in individuals suffering from the genetic disease cystic fibrosis (CF). Whereas it was long presumed that each patient independently acquired unique strains of P. aeruginosa present in their living environment, multiple studies have since demonstrated that shared strains of P. aeruginosa exist among individuals with CF. Many of these shared strains, often referred to as clonal or epidemic strains, can be transmitted from one CF individual to another, potentially reaching epidemic status. Numerous epidemic P. aeruginosa strains have been described from different parts of the world and are often associated with an antibiotic-resistant phenotype. Importantly, infection with these strains often portends a worse prognosis than for infection with nonclonal strains, including an increased pulmonary exacerbation rate, exaggerated lung function decline, and progression to end-stage lung disease. This review describes the global epidemiology of clonal P. aeruginosa strains in CF and summarizes the current literature regarding the underlying biology and clinical impact of globally important CF clones. Mechanisms associated with patient-to-patient transmission are discussed, and best-evidence practices to prevent infections are highlighted. Preventing new infections with epidemic P. aeruginosa strains is of paramount importance in mitigating CF disease progression.

Long-term clinical outcomes of 'Prairie Epidemic Strain' Pseudomonas aeruginosa infection in adults with cystic fibrosis

RATIONALE

Epidemic Pseudomonas aeruginosa (PA) plays an important role in cystic fibrosis (CF) lung disease. A novel strain, the 'Prairie Epidemic Strain' (PES), has been identified in up to 30% of patients in Prairie-based Canadian CF centres.

OBJECTIVE

To determine the incidence, prevalence and long-term clinical impact of PES infection.

METHODS

A cohort of adults with CF was followed from 1980 to 2014 where bacteria isolated from clinical encounters were prospectively collected. Strain typing was performed using pulse-field gel electrophoresis and multilocus sequence typing. Patients were divided into one of four cohorts: no PA, transient PA, chronic PA with unique strains and chronic PES. Proportional Cox hazard and linear mixed models were used to assess for CF-associated respiratory death or transplantation, and rates of %FEV₁ and body mass index (BMI) decline.

RESULTS

274 patients (51.7% male) were analysed: 44--no PA, 29--transient PA, 137--unique PA, 64--PES. A total of 92 patients (33.6%) died or underwent lung transplantation (2423.0 patient-years). PES infection was associated with greater risk of respiratory death or lung transplant compared with the no PA group (aHR, 3.94 (95% CI 1.18 to 13.1); p=0.03) and unique PA group (aHR, 1.75 (95% CI 1.05 to 2.92) p=0.03). Rate of lung function decline (%FEV₁ predicted) was greatest in the PES group (1.73%/year (95% CI 1.63% to 1.82%); p<0.001). BMI improved over time but at an attenuated rate in the PES group (p=0.001).

CONCLUSIONS

Infection with PES was associated with increased patient morbidity through three decades and manifested in an increased risk of respiratory death and/or lung transplantation.

Several siblings with Cystic Fibrosis as a risk factor for poor outcome

BACKGROUND

Occurrence of Cystic Fibrosis (CF) in more than one member in a family is not uncommon. The aim of our study was to assess the influence of multiple siblings with CF on disease expression and outcome.

METHODS

Study group consisted of 2-siblings (2-sibs, n = 42) or 3/4 siblings (3/4-sibs, n = 22) with CF in one family. Each sibling was matched by age, mutation, and gender to a single CF patient.

RESULTS

3/4-sibs subgroup compared to singles showed a lower mean FEV1 with a faster decline rate (58.4 ± 27.5 vs. 72.7 ± 25.4 and -5 ± 6.4 vs. -1.7 ± 2.8 %predicted decline/year respectively, p < .05), more airway colonization by Pseudomonas aeruginosa and Mycobacterium abscessus (15 (68%) vs. 8 (36%) and 7 (32%) vs. 4 (18%), respectively, p < .05) and more lung transplants (5 (23%) vs. 2 (9%), respectively, p < .02). Last mean FEV1 within 3/4-sibs was significantly lower for the youngest sib (p < .05).

CONCLUSIONS

Three or more CF patients in one family may be a risk factor for more severe disease and poor prognosis. In our view this reflects the burden of disease on the patients and families.

Twenty-five-year outbreak of Pseudomonas aeruginosa infecting individuals with cystic fibrosis: identification of the prairie epidemic strain

Transmissible strains of Pseudomonas aeruginosa have been described for cystic fibrosis (CF) and may be associated with a worse prognosis. Using a comprehensive strain biobank spanning 3 decades, we sought to determine the prevalence and stability of chronic P. aeruginosa infection in an adult population. P. aeruginosa isolates from sputum samples collected at initial enrollment in our adult clinic and at the most recent clinic visit were examined by a combination of pulsed-field gel electrophoresis and multilocus sequence typing and compared against a collection of established transmissible and local non-CF bronchiectasis (nCFB) isolates. A total of 372 isolates from 107 patients, spanning 674 patient-years, including 66 patients with matched isolates from initial and final encounters, were screened. A novel clone with increased antibacterial resistance, termed the prairie epidemic strain (PES), was found in 29% (31/107 patients) of chronically infected patients referred from multiple prairie-based CF centers. This isolate was not found in those diagnosed with CF as adults or in a control population with nCFB. While 90% (60/66 patients) of patients had stable infection over a mean of 10.8 years, five patients experienced strain displacement of unique isolates, with PES occurring within 2 years of transitioning to adult care. PES has been present in our cohort since at least 1987, is unique to CF, generally establishes chronic infection during childhood, and has been found in patients at the time of transition of patients from multiple prairie-based CF clinics, suggesting broad endemicity. Studies are under way to evaluate the clinical implications of PES infection.

Pseudomonas aeruginosa genotype prevalence in Dutch cystic fibrosis patients and age dependency of colonization by various P. aeruginosa sequence types

The patient-to-patient transmission of highly prevalent Pseudomonas aeruginosa clones which are associated with enhanced disease progression has led to strict segregation policies for cystic fibrosis (CF) patients in many countries. However, little is known about the population structure of P. aeruginosa among CF patients. The aim of the present cross-sectional study was to determine the prevalence and genetic relatedness of P. aeruginosa isolates from CF patients who visited two major CF centers in The Netherlands in 2007 and 2008. These patients represented 45% of the Dutch CF population. P. aeruginosa carriage in the respiratory tract was determined by standard microbiological culture techniques, and all phenotypically different isolates in the first specimens recovered in 2007 and 2008 were genotyped by multilocus sequence typing. A total of 313 (57%) of 551 patients whose samples were cultured carried P. aeruginosa. Two sequence types (STs), ST406 and ST497, were found in 15% and 5% of the patients, respectively, and 60% of the patients harbored a strain that was also found in at least two other patients. The risk ratios for carrying ST406 and ST497 were 17.8 (95% confidence interval [CI], 7.2 to 43.6) for those aged between 15 and 24 years and 6 (95% CI, 1.4 to 26.1) for those aged >25 years. ST406 and ST497 were not genetically linked to previously described epidemic clones, which were also not found in this CF population. The population structure of P. aeruginosa in Dutch CF patients is characterized by the presence of two prevalent STs that are associated with certain age groups and that are not genetically linked to previously described epidemic clones.

Bacterial contamination in the environment of hospitalised children with cystic fibrosis

Pathogenic bacterial colonisation in Cystic Fibrosis patients is associated with a poor prognosis; thus, protective measures need to be taken to prevent their transmission. We studied the extent of contamination in the environment of hospitalised children with cystic fibrosis (CF) associated with specific activities. We assessed the levels of bacterial contamination in 432 air and surface samples collected from various locations in our CF centre over a three-month period: the bedrooms, corridor, communal showers, school, leisure centre and the respiratory functional explorations (RFE) unit. Staphylococcus aureus and Pseudomonas aeruginosa strains found in bedrooms and the RFE were compared with those found in patient expectorations using pulsed field gel electrophoresis. In all sampling locations, there were high levels of airborne contamination just after the presence of patients or nursing staff. In the bedrooms, the amount of S. aureus or P. aeruginosa in the air, at wake-up and after physiotherapy, were significantly higher than that after the bedroom had been cleaned. For P. aeruginosa, 33% of isolates were multiresistant to antibiotics; 50% of the colonised patients had the same P. aeruginosa strain in their sputum as in air taken from their bedroom. P. aeruginosa was detected in 23% of samples taken from the surfaces in the showers after patient washing. Very low levels of pathogenic bacteria were found in samples from the other locations. Overall, activities with the highest risk of contamination in the CF ward are physiotherapy and washing in the communal shower room. We therefore recommend to open windows after physiotherapy and to implement a strong decontamination after showers.

[Various typing methods of Pseudomonas aeruginosa strains isolated from cystic fibrosis patients]

Typing methods are essential to understand the epidemiology of bacterial infections. Strain typing is important for the detection of sources or routes of infections, identification between endemic and epidemic strains and prevention of transmission between patients. Some Pseudomonas aeruginosa cystic-fibrosis strains could not be typed with conventional typing methods. Due to the diverse phenotypic nature of P. aeruginosa, phenotyping methods are not discriminatory enough to identify strains belonging to the same genotype. Thus, molecular typing methods are required. These methods should be applied when data from phenotypic typing analysis becomes ambiguous, such as in cystic fibrosis. Molecular typing methods, developed over the past decade, are highly discriminatory in capacity and reproducibility. However, they are more likely applied in specialized laboratories since they are expensive and increase the workload. A reliable and low-cost typing system is required for better defining the epidemiology of this pathogen and designing more rational policies of infection control. Comparison between typing methods will pinpoint the limits and effectiveness of each method and will improve in turn the choice of a nonspecialized laboratory in terms of simplicity, time and cost.

Disease severity in siblings with cystic fibrosis

Since cross-infection occurs between cystic fibrosis (CF) siblings, we hypothesized that subsequent siblings may acquire respiratory pathogens at an earlier age and have a more severe course of pulmonary disease. We studied a retrospective cohort of 31 sibling pairs from the CF database at the Hospital for Sick Children. Kaplan-Meier curves and modified log-rank tests were used to test sibling differences in age of acquisition of Pseudomonas aeruginosa (PA), Staphylococcus aureus (SA), or any positive culture. Differences in disease severity outcomes were explored. Older siblings were more likely to have both SA and any CF pathogen first isolated from respiratory culture at an older age than younger siblings (P = 0.0050 and P = 0.0008, respectively, by modified log-rank tests). However, more of the older siblings were positive on first culture at time of diagnosis, introducing an age-of-diagnosis bias. Hospitalization rates, courses of oral antibiotics, FEV(1) % predicted, and weight and height measurements were not better in the older children. No differences in clinical parameters were found between older and younger siblings. The apparent finding of younger age at first isolation of pathogens from respiratory cultures in younger siblings is likely because many older siblings were already infected with these organisms at time of diagnosis.

Epidemiology of Pseudomonas aeruginosa in cystic fibrosis in British Columbia, Canada

Pseudomonas aeruginosa is the most common respiratory pathogen in patients with cystic fibrosis (CF), but the predominant mechanism by which it is acquired is controversial. To determine the frequency of patient-to-patient spread, we evaluated P. aeruginosa isolates from 174 patients treated at the CF clinics in Vancouver, BC, Canada, since 1981. Multiple isolates were obtained from each patient and genetically typed by random amplified polymorphic DNA and pulsed field gel electrophoresis analyses. A total of 157 genetic types of P. aeruginosa was identified, 123 of which were unique to individual patients. A total of 34 types was shared by more than one patient; epidemiologic evidence linked these individuals only in the cases of 10 sibships and 1 pair of unrelated patients. We conclude that there is an extremely low risk in Vancouver for patients with CF to acquire P. aeruginosa from other patients. It appears that prolonged close contact, such as occurs between siblings, is necessary for patient-to-patient spread. The major source of acquisition of P. aeruginosa in CF appears to be from the environment. Considering these observations, we do not recommend segregation of patients with CF on the basis of their colonization status with P. aeruginosa.

Dynamics of bacterial colonisation in the respiratory tract of patients with cystic fibrosis

Mutations in the human genome may result in altered phenotypes. The cystic fibrosis (CF) patient, for instance, suffers from an aberrant composition of the epithelial lining of the gastrointestinal and respiratory tract. In this particular case, a single point mutation in the cystic fibrosis conductance regulator (CFTR) gene results in major physiological changes resulting in ecological changes that generate a niche particularly attractive to a selected set of microbial pathogens. We here present a review on the dynamics of the bacterial populations inhabiting the CF lung. Studies focusing on Staphylococcus aureus, Haemophilus influenzae and Pseudomonas aeruginosa will be summarised and discussed, whereas the technology used for microbial characterisation will be shortly highlighted. Emphasis, however, will be on those studies that assessed the genetic diversity among clinical isolates that were obtained over prolonged periods of time, enabling the distinction between persistent colonisation versus frequent re-infection by the selected pathogens. Evolutionary adaptation of pathogens to the CF lung is a common theme in many of these studies.

Evaluation of random amplified polymorphic DNA typing of Pseudomonas aeruginosa

A method for distinguishing among Pseudomonas aeruginosa strains using random amplified polymorphic DNA (RAPD) typing was evaluated for reproducibility and discriminatory power. A total of 200 isolates, blinded in triplicate, were evaluated by RAPD. All 600 samples were typeable; 197 of 200 isolates gave identical results on all three occasions, and 131 distinct RAPD types were identified.

Changing epidemiology of Pseudomonas aeruginosa infection in Danish cystic fibrosis patients (1974-1995)

Recurrent and chronic lower airway infection with Pseudomonas aeruginosa (PA) is an important component of cystic fibrosis (CF) pulmonary disease. Different modes of treatment and control of CF patients have been introduced at the Copenhagen CF Centre over the past 20 years and have been associated with improved survival. Treatment consisted of: 1) elective antibiotics for 14 days every 3 months to patients with chronic PA infection (started in 1976), 2) cohort isolation to prevent cross-infection (patients with PA were separated from patients without PA, starting in 1981); and 3) early intensive treatment with inhaled colistin and oral ciprofloxacin from time of initial PA colonization (started in 1989). The aim of the present study was to evaluate the impact of each of these interventions on the changes in the epidemiology of PA. Based on monthly cultures of lower airway secretions in each CF patient seen during 1974-1995, significant changes in the incidence and prevalence of the PA infection were found. The monthly prevalence of chronic PA increased significantly (P < 0.0001) from below 40% before 1976 to above 60% in 1980, which was found to be due to cross-infection among the CF patients after introduction of elective antibiotic courses in 1976. To deal with this problem, cohort isolation was introduced in 1981, and since then the monthly point prevalence of chronic PA decreased slowly until 1989 (P < 0.0001), when early intensive treatment from initial PA colonization was introduced; this was associated with a further decrease in point prevalence to 45% in 1995 (P < 0.005). The annual incidence of chronic PA infection also decreased significantly (P < 0.01) from 16% to below 2% after introduction of cohort isolation and early intensive treatment from initial PA isolation. Furthermore, the time from acquisition of first PA to development of chronic PA infection increased significantly, from approximately 1 year to almost 4 years after introduction of cohort isolation (P < 0.0001). After introduction of early intensive treatment, the probability of still not having developed chronic PA infection 7 years after the first isolation of PA was above 80% (P < 0.0001). In conclusion, the introduction of cohort isolation and early intensive treatment following the initial isolation of PA resulted in a reduced incidence and prevalence of chronic PA infection. We are not aware of other studies showing a decreasing prevalence of chronic PA infection, as survival of CF patients has increased.

Acquisition of Pseudomonas aeruginosa in children with cystic fibrosis

OBJECTIVE

This study was pursued as an extension of a randomized clinical investigation of neonatal screening for cystic fibrosis (CF). The project included assessment of respiratory secretion cultures for pathogens associated with CF. The objective was to determine whether patients diagnosed through neonatal screening and treated in early infancy were more likely to become colonized with Pseudomonas aeruginosa compared with those identified by standard diagnostic methods.

METHODOLOGY

The design involved prospective cultures of respiratory secretions obtained generally by oropharyngeal swabs at least every 6 months and more often if clinically indicated. Patients were managed with a standardized evaluation and treatment protocol at the two Wisconsin certified CF centers; however, there were community and environmental variations associated with the follow-up period as described below.

RESULTS

Overall, there were no differences in acquisition of respiratory pathogens between the screened and the control (standard diagnosis) groups. Evaluation of the data between and within the two centers, however, revealed significant differences with earlier acquisition of P aeruginosa in the center with the following distinguishing characteristics: urban location; following patients with the standard US approach in which newly diagnosed, young children were interspersed with older CF patients; and where there were more opportunities for social interactions with other CF patients. The differences were confined to the screened group followed in the urban center in which the median pseudomonas-free survival period was 52 weeks contrasted with 289 weeks in the other center. In addition, assessment of data for the entire CF populations followed at the two centers revealed that the urban center showed a significantly higher prevalence of P aeruginosa colonization in patients between the ages of 3 and 9 years.

CONCLUSIONS

These results present questions and generate hypotheses on risk factors for acquisition of P aeruginosa in CF and suggest that clinic exposures and/or social interactions may predispose such patients to pseudomonas infections.

Exchange of Pseudomonas aeruginosa strains among cystic fibrosis siblings

The molecular epidemiology of Pseudomonas aeruginosa infection in cystic fibrosis (CF) siblings was analysed by DNA fingerprinting using arbitrary primed polymerase chain reaction. A total of 306 strains collected from six pairs of siblings over a period of 20-126 months (median 64) was studied. Fifty-four different P. aeruginosa genotypes were recognized. Two out of six pairs of siblings were ultimately colonized by identical strains, and it was shown that a single P. aeruginosa clone can persist in an individual patient for over ten years. No overlap in P. aeruginosa genotypes was encountered between families, whereas in all families at least transient cross-colonization with the same genotype was observed. This finding demonstrates that P. aeruginosa cross-infection or acquisition of the same strain from an identical environmental source exists within the family situation, but does not always result in a long-term colonization by identical genotypes in all family members suffering from CF.

Genome macrorestriction analysis of diversity and variability of Pseudomonas aeruginosa strains infecting cystic fibrosis patients

Genome macrorestriction fingerprinting with XbaI and DraI was used to analyze the relatedness of 166 Pseudomonas aeruginosa isolates collected from 31 cystic fibrosis patients over a 1- to 20-month period and to correlate their genotype with patterns of resistance to 14 antimicrobial agents. Quantitative comparison of intra- and interpatient similarities of P. aeruginosa macrorestriction patterns disclosed two discrete ranges that clearly discriminated subclonal variation (> 80% relatedness) and clonal diversity (10 to 70% relatedness). Cloning-derived mutants exhibited up to 20% divergence of genomic macrorestriction patterns during the course of chronic colonization of individual patients. Change of susceptibility to multiple antimicrobial agents developed in 50% of sequential pairs of isolates from individual patients. Only 19% of these susceptibility changes were attributable to strain substitution, while the majority (56%) of resistance changes were associated with minor genomic variations of a persistent strain. Sixty-six percent of patients harbored one strain, and 33% carried two strains. Three common strains colonized 5 (28%) of 18 patients attending a cystic fibrosis clinic, and another two strains colonized two patient pairs (31%) of 13 patients staying at a rehabilitation center, suggesting potential cross-infection in these settings. By indexing regional polymorphisms throughout the chromosome structure, macrorestriction analysis can monitor subclonal evolution of P. aeruginosa and identify isogenic resistance mutants. Quantitative macrorestriction fingerprinting enables discrimination between clonal variants and clones of distinct origins and should therefore provide a reliable tool for investigating the mode of acquisition of P. aeruginosa in cystic fibrosis patients.

Pseudomonas cepacia in lung transplant recipients with cystic fibrosis

Twenty-four isolated double lung transplants (LTXs) have been performed in 22 patients with cystic fibrosis, with a follow-up of 4 to 47 months. Prior to LTX, all patients were colonized with Pseudomonas aeruginosa, and ten patients were also colonized with Pseudomonas cepacia. Both organisms were specifically sought before LTX. All patients who grew P cepacia before LTX did so after LTX. Five additional patients only grew this bacterium after LTX. There was no difference between those who grew P cepacia and those who did not in terms of data before LTX for age, weight, pulmonary function, and 6-min walk. After LTX, 7 of the 15 patients who had ever grown P cepacia died. No patient who grew only P aeruginosa died. The median survival in the subgroup with P cepacia was 28 days. Five of the seven died as a direct result of P cepacia pneumonia and sepsis. One died of cyclosporin A (cyclosporine) neurotoxicity with concurrent P cepacia pneumonia, and one died at the time of a retransplant for graft failure (associated with three bouts of P cepacia pneumonia and cytomegalovirus). Four of seven had not grown this bacterium before LTX. There were no perioperative factors, including antibiotic choices, that distinguished survivors and nonsurvivors. Overall 1-year survival is about 70 percent (15/22). Fourteen bouts of P cepacia pneumonia occurred in 12 patients. Four empyemas, one lung abscess, one suppurative pericarditis, and five cases of sinusitis were also due to this bacterium. In conclusion, P cepacia is responsible for excess morbidity and mortality after LTX. This organism is particularly lethal if isolated for the first time after LTX. Factors predicting its acquisition in this setting are unknown. While it is possible that the facial sinuses may act as an unrecognized reservoir or that patients or equipment provide a source, further study into the epidemiology of this organism is necessary to improve the survival of colonized patients undergoing LTX.

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.

Nosocomial acquisition of Pseudomonas aeruginosa by cystic fibrosis patients

During a 4-year period, at least 12 of 40 patients with cystic fibrosis (CF) who were newly colonized with Pseudomonas aeruginosa had acquired it at CF recreation camps, clinics, or rehabilitation centers. After introduction of hygienic precautions at the CF clinic, only a single episode of nosocomial transmission of P. aeruginosa was detected at the CF ward during the subsequent 2 years.

Microbiology of airway disease in patients with cystic fibrosis

Individuals with cystic fibrosis have abbreviated life spans primarily due to chronic airway infection. A limited number of types of organisms are responsible for these infections, with Staphylococcus aureus and Pseudomonas aeruginosa being of primary importance. In the pre-antibiotic era, greater than 90% of deaths due to infection were caused by S. aureus and death usually occurred in the first 2 years of life. With the advent of effective antistaphylococcal therapy, life spans increased and P. aeruginosa became the pathogen of primary importance. P. aeruginosa isolates recovered from patients with cystic fibrosis have a unique phenotypic characteristic referred to as "mucoid." The mucoid phenotype is due to the production of a mucoid exopolysaccharide. A mucoid exopolysaccharide is believed to play a central role in the establishment of chronic pseudomonal lung infection in these patients. A third organism, Pseudomonas cepacia, has recently been detected in the airways of older patients with cystic fibrosis and is associated with increased mortality. The virulence of P. cepacia is not understood, but the organism is extremely refractory to antimicrobial therapy. Other bacteria, including Haemophilus influenzae and members of the family Enterobacteriaceae, appear to play a secondary role in airway infection. Aspergillus fumigatus is the most important fungal agent causing allergic bronchopulmonary disease. The role of viruses has only recently been examined. At least in some patients with cystic fibrosis, respiratory syncytial virus may be important in predisposing to subsequent bacterial infections.

Serotype and serum sensitivity of Pseudomonas aeruginosa from children with cystic fibrosis: longitudinal studies and typing with monoclonal antibodies

Pseudomonas aeruginosa isolated from the respiratory tract of children with cystic fibrosis from Perth, Sydney or Brisbane, were serotyped with polyclonal antisera using the International Antigenic Serotyping System. Predominant strains were untypable among isolates from Brisbane (86% of 50 strains) and Sydney (60% of 50 strains) but 64% of the 408 isolates from Perth were polyagglutinating. The frequency distributions of typable strains showed differences from those reported in clinics in the northern hemisphere, but it appears that these local differences do not affect the emergence of strains with defective lipopolysaccharide antigens. Isolates from patients studied longitudinally showed correlation between duration of colonization, appearance of untypable or polyagglutinating strains and sensitivity to normal serum. Mucoid colonies were found more commonly from patients colonized for at least 12 months but, overall, there was no significant association between serotype and mucoid colonial morphology. Commercial monoclonal antibodies did not react with polyagglutinating or untypable strains and gave identical results to the polyvalent typing system with strains classified as typable.

Nosocomial infections in the pediatric patient: an update

Substantial progress has been made in measuring the burden of nosocomial infection in pediatric patients, particularly in certain populations (e.g., critical care, immunocompromised, chronic care, and patients with acquired immunodeficiency syndrome) and after certain procedures (e.g., central catheter lines and open-sternum cardiovascular surgery). Preventive measures, such as the use of goggles, gowns, and gloves, have been subjected to new and additional study. The following report is a summary of recent progress. A review of factors responsible for infection in various patient care populations and settings and recommendations for control are presented.

Use of a pilin gene probe to study molecular epidemiology of Pseudomonas aeruginosa

Strains of Pseudomonas aeruginosa from patients with cystic fibrosis (CF) are unusual. The majority have a rough lipopolysaccharide (LPS) which renders them nontypeable by conventional typing systems based on a serological reaction with the O polysaccharide of smooth LPS. We developed a new typing scheme using a pilin gene probe as a marker for hybridization with endonuclease-digested genomic DNA from P. aeruginosa. Twenty-one different restriction fragment length polymorphism (RFLP) types were found among 249 isolates. RFLP type 7 was recovered only from patients with thermal burns (9 of 14 isolates) in both Vancouver, British Columbia, and Edmonton, Alberta, Canada. None of the other RFLP types showed a clear predilection for disease state or environmental niche. Multiple morphologically different isolates from individual patients with CF were studied; each isolate in 33 of 40 sputum samples had an identical RFLP type, despite considerable LPS serotype heterogeneity. Sequential isolates from 23 patients were studied; in 10 isolates there was a clear change in both the RFLP and the LPS serotype. We conclude that patients with CF usually harbor a single P. aeruginosa RFLP type in their sputa, but that one strain can replace another as the predominant colonizing type.

Estimated risk of cross-infection with Pseudomonas aeruginosa in Danish cystic fibrosis patients

During the period 1970-1987 the number of cystic fibrosis (CF) patients treated at the Danish CF Center increased from 54 to 226. The prevalence of patients with chronic P. aeruginosa infection (CF + P) increased from 35% to 59%, whereafter it decreased to 54%. The yearly incidence of new CF + P patients averaged 8.4% in 1970-1975, 17% in 1976-80, 6.5% in 1981-85, and 3% in 1986-87. These changes correlated to the increased "contact density" between CF + P and non-infected CF patients (CF-P) due to intensified treatment starting in 1976, and the reduced "contact density" due to separation of the two groups starting in 1981. The same trends were observed during an epidemic spread of a multiply resistant P. aeruginosa in the CF + P group, which was also interrupted by separation of two groups of patients, with and without the multiply resistant strain. The observed prevalences of CF + P in different age groups of patients are in accordance with a 20% incidence/year in patients older than three years. The highest probability of acquiring chronic P. aeruginosa infection was calculated to be 2%/day and the lowest 0.09%/day spent in the Centre. By employing a simple mathematical model of the spread of infectious diseases it can be shown, that the highest incidence of CF + P is present when the prevalence of CF + P is 20-80%, and that an increase in the total number of patients also increases the incidence of CF + P unless the patients are divided into smaller groups. The observations in the Danish CF Centre are in accordance with this model.

Pseudomonas aeruginosa cross-colonization and persistence in patients with cystic fibrosis. Use of a DNA probe

To investigate cross-colonization with and persistence of Pseudomonas aeruginosa in cystic fibrosis (CF), 181 isolates from 76 CF patients were typed using a P. aeruginosa-specific DNA probe. Whereas sibling pairs predominantly harboured genotypically identical P. aeruginosa strains, all of the other patients harboured different strains. Seventy-nine per cent (22/31) of the infected CF patients harboured the same strains at the beginning and the end of a summer camp. A change of strains was seen in 10% (3/31) of the patients at the end of the camp. Forty-six per cent (6/13) of the patients who were apparently initially uninfected, acquired P. aeruginosa by the end of the period. Genotyping proved that strain change or acquisition was due to cross-colonization in four of nine cases. Very little P. aeruginosa was isolated from the inanimate environment. Persistence of P. aeruginosa after a temporary loss due to antibiotic therapy was seen in 12/16 paired patient strains before and after antibiotic therapy. Thus, suppression followed a flare-up seemed to occur in these patients rather than eradication and a new infection. When 35 patients were followed over a period of 6 months, 7 (20%) changed the strain in their sputum. Only one of 43 patients harboured two different P. aeruginosa strains simultaneously over a long period.

Genome fingerprinting of Pseudomonas aeruginosa indicates colonization of cystic fibrosis siblings with closely related strains

The epidemiology of Pseudomonas aeruginosa infection at a cystic fibrosis (CF) center was monitored over a 3-year period. A total of 835 isolates from 72 unrelated patients and 22 siblings with CF were analyzed by genome fingerprinting and serotyping, bacteriophage typing, and pyocin typing. For genome fingerprinting, bacterial chromosomes were digested with one of the restriction endonucleases SpeI, DraI, XbaI, SspI, and NheI, which cut only rarely, and subsequently separated by field inversion gel electrophoresis. The physical genome analysis allowed us to classify P. aeruginosa strains in terms of DNA relatedness. Related strains differed by fewer than six DraI bands in the fingerprint, whereas unrelated strains differed by more than 20 DraI bands. All unrelated CF patients were colonized with different strains. The absence of a nosocomial spread of organisms at the CF center was attributed to the strict hygiene measures observed at the hospital. CF siblings were harboring either identical or closely related strains; transmission within the family is thought to be the most likely cause.

Hospital epidemiology of Pseudomonas aeruginosa from patients with cystic fibrosis

Pseudomonas aeruginosa colonizes the respiratory tract of most older patients with cystic fibrosis. The means by which these bacteria are acquired and the risk for patient-to-patient spread among subjects with cystic fibrosis are poorly understood. We studied the spread of Ps. aeruginosa within a hospital environment. Pseudomonas was rarely recovered from the inanimate environment surrounding patients with cystic fibrosis or from hand or rectal cultures of patients who were colonized in the oropharynx. There was transient cross-colonization with Ps. aeruginosa between patients with cystic fibrosis sharing a hospital room in three of seven pairs studied. In all cases the "new" isolate was recoverable only once and was not found during a 2-year follow-up. Three of four sibling pairs with cystic fibrosis shared the same Ps. aeruginosa serotype(s). The risk of sustained cross-colonization by Ps. aeruginosa between patients with cystic fibrosis appears to be minimal, except under conditions of prolonged close contact.

Does centralized treatment of cystic fibrosis increase the risk of Pseudomonas aeruginosa infection?

Two hundred and forty Danish patients with cystic fibrosis (97% of the total CF population in Denmark) participated in a point-prevalence study of Pseudomonas aeruginosa infection. One hundred and ninety-two patients were treated at the Danish CF centre and 48 patients were treated in other places. The age distribution was significantly different as no patients older than 19 years were found in the non-centre group. Pathogenic bacteria were isolated from the sputum of 96% of the patients. P. aeruginosa was more prevalent in patients from the centre, whereas Staphylococcus aureus was more prevalent in the non-centre group. No difference in serogroup and phage pattern of P. aeruginosa was found. There was a tendency that non-centre treated patients acquired chronic broncho-pulmonary P. aeruginosa infection later, but at the age of 16 years 90% of all patients will be chronically infected. Chronic P. aeruginosa infection was significantly more common in the age group 10-14 years at the centre than outside the centre. It is not possible to prevent chronic P. aeruginosa infection in CF patients treated in small groups and because of the better prognosis of centralized treatment the latter must be recommended.