The epidemiology of Pseudomonas aeruginosa in oncology patients in a general hospital

The impact of an intervention to reduce dispersal from wastewater drain sites on carbapenem-resistant Pseudomonas aeruginosa colonization and bloodstream infection on a hematopoietic cell transplant and hematologic malignancy unit

OBJECTIVE

To evaluate the impact of an intervention to limit dispersal from wastewater drain (WWD) sites on meropenem-nonsusceptible Pseudomonas aeruginosa patient and environmental colonization and bloodstream infection (BSI) on a hematopoietic cell transplant (HCT) and hematologic malignancy (HM) unit.

DESIGN

This quasi-experimental study included pre/postintervention point-prevalence surveys in July 2019 and June 2020, respectively. The retrospective cohort included HCT/HM patients with P. aeruginosa BSI between 2012 and 2022.

SETTING

Adult HCT/HM unit at an academic center.

PARTICIPANTS

This study included consenting HCT/HM patients on the unit at the time of the point-prevalence surveys. HCT/HM patients with P. aeruginosa BSI between 2012 and 2022.

METHODS

A quality improvement intervention targeting WWD sites was conceived and implemented on a HCT/HM unit. Pre and postintervention colonization samples were obtained from patients and environmental sites, cultivated on selective media, then characterized by susceptibility testing. Whole-genome sequencing and phylogenetic analysis were performed on select isolates. The impact of the intervention on colonization and BSI was evaluated, as was relatedness among isolates.

RESULTS

Although colonization of WWD sites with meropenem-nonsusceptible P. aeruginosa was widespread before and after this intervention, we observed a substantial decline in patient colonization (prevalence rate ratio, 0.35; 95% confidence interval [CI], 0.04-3.12) and BSI (incidence rate ratio, 0.67; 95% CI, 0.31-1.42) after the intervention. Among 3 predominant sequence types (ST-111, ST-446, and ST-308), there was striking genetic conservation within groups and among environmental colonization, patient colonization, and BSI isolates.

CONCLUSIONS

An intervention targeting WWD sites on a HCT/HM unit had a meaningful impact on meropenem-nonsusceptible P. aeruginosa patient colonization and BSI.

Collagenase-producing bacteria are common in anastomotic leakage after colorectal surgery: a systematic review

PURPOSE

Some gut bacteria can produce enzymes (collagenases) that can break down collagen in the intestinal wall. This could be a part of the pathophysiology of anastomotic leakage (AL). This systematic review aimed to investigate if such bacteria were present more frequently in AL patients versus non-AL patients following colorectal surgery.

METHODS

This systematic review was reported according to the PRISMA and AMSTAR guidelines. Before the literature search, a study protocol was registered at PROSPERO (CRD42022363454). We searched PubMed, EMBASE, Google Scholar, and Cochrane CENTRAL on April 9th, 2023, for randomized and observational human studies of AL following colorectal surgery with information on gastrointestinal bacteria. The primary outcome was bacteria with the potential to produce collagenase. The risk of bias was assessed with the Newcastle-Ottawa Scale, as all studies were observational.

RESULTS

We included 15 studies, with a total of 52,945 patients, of which 1,747 had AL, and bacteriological information from feces, mucosa, the resected specimen, or drain fluid was presented. In 10 of the 15 studies, one or more collagenase-producing bacteria were identified in the patients with AL. Neither the bacteria nor the collagenase production were quantified in any of the studies. The studies varied greatly in terms of sample material, analytical method, and time of collection. Studies using DNA sequencing methods did not report findings of collagenase-producing bacteria.

CONCLUSION

Collagenase-producing bacteria are more common in patients with AL following colorectal surgery than in patients without AL, but the significance is unclear. From the current studies, it is not possible to determine the pathogenicity of the individual gut bacteria.

Bacterial Wars-a tool for the prediction of bacterial predominance based on network analysis measures

Bacterial Wars (BW) is a network-based tool that applies a two-step pipeline to display information on the competition of bacterial species found in the same microbiome. It utilizes antimicrobial peptide (AMP) sequence similarities to obtain a relationship between species. The working hypothesis (putative AMP defense) is that friendly species share sequence similarity among the putative AMPs of their proteomes and are therefore immune to their AMPs. This may not happen in competing bacterial species with dissimilar putative AMPs. Similarities in the putative AMPs of bacterial proteomes may be thus used to predict predominance. The tool provides insights as to which bacterial species are more likely to 'die' in a competing environmental niche.

Mechanisms of Antibiotic and Biocide Resistance That Contribute to Pseudomonas aeruginosa Persistence in the Hospital Environment

Pseudomonas aeruginosa is an opportunistic bacterial pathogen responsible for multiple hospital- and community-acquired infections, both in human and veterinary medicine. P. aeruginosa persistence in clinical settings is worrisome and is a result of its remarkable flexibility and adaptability. This species exhibits several characteristics that allow it to thrive under different environmental conditions, including the ability to colonize inert materials such as medical equipment and hospital surfaces. P. aeruginosa presents several intrinsic mechanisms of defense that allow it to survive external aggressions, but it is also able to develop strategies and evolve into multiple phenotypes to persevere, which include antimicrobial-tolerant strains, persister cells, and biofilms. Currently, these emergent pathogenic strains are a worldwide problem and a major concern. Biocides are frequently used as a complementary/combination strategy to control the dissemination of P. aeruginosa-resistant strains; however, tolerance to commonly used biocides has also already been reported, representing an impediment to the effective elimination of this important pathogen from clinical settings. This review focuses on the characteristics of P. aeruginosa responsible for its persistence in hospital environments, including those associated with its antibiotic and biocide resistance ability.

Transmission routes of antibiotic resistant bacteria: a systematic review

Background

Quantification of acquisition routes of antibiotic resistant bacteria (ARB) is pivotal for understanding transmission dynamics and designing cost-effective interventions. Different methods have been used to quantify the importance of transmission routes, such as relative risks, odds ratios (OR), genomic comparisons and basic reproduction numbers. We systematically reviewed reported estimates on acquisition routes’ contributions of ARB in humans, animals, water and the environment and assessed the methods used to quantify the importance of transmission routes.

Methods

PubMed and EMBASE were searched, resulting in 6054 articles published up until January 1st, 2019. Full text screening was performed on 525 articles and 277 are included.

Results

We extracted 718 estimates with S. aureus (n = 273), E. coli (n = 157) and Enterobacteriaceae (n = 99) being studied most frequently. Most estimates were derived from statistical methods (n = 560), mainly expressed as risks (n = 246) and ORs (n = 239), followed by genetic comparisons (n = 85), modelling (n = 62) and dosage of ARB ingested (n = 17). Transmission routes analysed most frequently were occupational exposure (n = 157), travelling (n = 110) and contacts with carriers (n = 83). Studies were mostly performed in the United States (n = 142), the Netherlands (n = 87) and Germany (n = 60). Comparison of methods was not possible as studies using different methods to estimate the same route were lacking. Due to study heterogeneity not all estimates by the same method could be pooled.

Conclusion

Despite an abundance of published data the relative importance of transmission routes of ARB has not been accurately quantified. Links between exposure and acquisition are often present, but the frequency of exposure is missing, which disables estimation of transmission routes’ importance. To create effective policies reducing ARB, estimates of transmission should be weighed by the frequency of exposure occurrence.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07360-z.

Genome sequencing of Pseudomonas aeruginosa strain M2 illuminates traits of an opportunistic pathogen of burn wounds

Pseudomonas aeruginosa is a Gram-negative nosocomial pathogen and one of the most prevalent organisms isolated from burn wounds worldwide. Pseudomonas aeruginosa strain M2 (O5 serotype, type B flagella) is utilized for examining the murine model associated with burns. Pseudomonas aeruginosa M2 is similar in lethality to common laboratory P. aeruginosa strains when infecting CD-1 mice. Conversely, we recently showed that, relative to these strains, P. aeruginosa M2-infected mice are more susceptible to sepsis and demonstrate a 6-log reduction in LD50 from subcutaneous infection at the infection site directly after 10% total body surface area burn. To better understand this striking phenotypic difference from other P. aeruginosa strains employed in burn models, we sequenced the P. aeruginosa M2 genome. A total of 4,136,641 read pairs were obtained, providing an average genome coverage of 97.5X; subsequent assembly yielded a draft genome with 187 contigs comprising 6,360,304 bp with a G + C content of 66.45%. Genome-based phylogeny estimation of 92 P. aeruginosa strains placed P. aeruginosa M2 with P. aeruginosa-12-4-4(59), a nonairway clinical strain isolated from the blood culture of a burn patient. Phylogenomic analyses identified genes shared between P. aeruginosa M2 and P. aeruginosa 14, another strain exhibiting increased lethality in thermal tissues, as well as P. aeruginosa M2 unique genes with diverse functions like degradation of toxic aromatic compounds, iron scavenging, swarming motility and biofilm formation, defense against invasive DNA, and host assault. Predicted lateral gene transfers illuminate proteins heretofore uncharacterized for roles in P. aeruginosa biology. Our work yields a rich resource for assessing P. aeruginosa genes required for increased lethality in burn tissue seroma.

A Nonlethal Murine Flame Burn Model Leads to a Transient Reduction in Host Defenses and Enhanced Susceptibility to Lethal Pseudomonas aeruginosa Infection

Of the 486,000 burn injuries that required medical treatment in the United States in 2016, 40,000 people were hospitalized, with >3,000 fatalities. After burn injury, humans are at increased risk of sepsis and mortality from infections caused by Pseudomonas aeruginosa, an opportunistic pathogen. We hypothesize that systemic events were initiated from the burn that increased the host's susceptibility to P. aeruginosa. A nonlethal 10% total body surface area (TBSA), full-thickness flame burn was performed in CD-1 mice without and with subsequent P. aeruginosa (strain M2) infection. The 50% lethal dose for subcutaneous infection with P. aeruginosa M2 at the burn site immediately after the burn decreased by 6 log, with mortality occurring between 18 and 26 h, compared with P. aeruginosa-infected mice without burn injury. Bacteria in distal organs were detected by 18 h, concurrent with the onset of clinical symptoms. Serum proinflammatory cytokines (interleukin-6 [IL-6], IL-1β, gamma interferon, and tumor necrosis factor alpha) and the anti-inflammatory cytokine IL-10 were first detected at 12 h postburn with infection and continued to increase until death. Directly after burn alone, serum levels of HMGB1, a danger-associated molecular pattern and TLR4 agonist, transiently increased to 50 ng/ml before returning to 20 ng/ml. Burn with P. aeruginosa infection increased serum HMGB1 concentrations >10-fold (250 ng/ml) at the time of death. This HMGB1-rich serum stimulated TLR4-mediated NF-κB activation in a TLR4 reporter cell line. Treatment of infected burned mice with P5779, a peptide inhibitor of HMGB1, increased the mean survival from 23 to 42 h (P < 0.0001). We conclude that the high level of serum HMGB1, which preceded the increase in proinflammatory cytokines, is associated with postburn mortality.

A systematic review and meta-analyses show that carbapenem use and medical devices are the leading risk factors for carbapenem-resistant Pseudomonas aeruginosa

A systematic review and meta-analyses were performed to identify the risk factors associated with carbapenem-resistant Pseudomonas aeruginosa and to identify sources and reservoirs for the pathogen. A systematic search of PubMed and Embase databases from 1 January 1987 until 27 January 2012 identified 1,662 articles, 53 of which were included in a systematic review and 38 in a random-effects meta-analysis study. The use of carbapenem, use of fluoroquinolones, use of vancomycin, use of other antibiotics, having medical devices, intensive care unit (ICU) admission, having underlying diseases, patient characteristics, and length of hospital stay were significant risk factors in multivariate analyses. The meta-analyses showed that carbapenem use (odds ratio [OR] = 7.09; 95% confidence interval [CI] = 5.43 to 9.25) and medical devices (OR = 5.11; 95% CI = 3.55 to 7.37) generated the highest pooled estimates. Cumulative meta-analyses showed that the pooled estimate of carbapenem use was stable and that the pooled estimate of the risk factor "having medical devices" increased with time. We conclude that our results highlight the importance of antibiotic stewardship and the thoughtful use of medical devices in helping prevent outbreaks of carbapenem-resistant P. aeruginosa.

Genetic and phenotypic characterization of a Pseudomonas aeruginosa population with high frequency of genomic islands

Various genomic islands, PAPI-1, PAPI-2, PAGI-1, PAGI-2, PAGI-3, and PAGI-4, and the element pKLC102 have been characterized in different P. aeruginosa strains from diverse habitats and geographical locations. Chromosomal DNA macroarray of 100 P. aeruginosa strains isolated from 85 unrelated patients hospitalized in an intensive care unit was created to assess the occurrence of these genomic islands (GEIs). The macroarray was then hybridized with labeled probes derived from each genomic island. In addition, PFGE patterns with SpeI, frequency of virulence genes, and antimicrobial resistance patterns of the strains were studied. Our results showed that almost all P. aeruginosa strains presented up to eight virulence genes. By SpeI macrorestriction fragment analysis we were able to identify 49 restriction patterns; 35 patterns correspond to single strains and the remaining 14 to strains subgroup (a-n). Most of the strains showed variation in number or composition of GEIs and a specific antimicrobial pattern indicating that each strain was an unrelated isolate. In terms of the number of genomic islands per strain, 7 GEIs were found in 34% of the strains, 6 in 18%, 5 in 12%, 4 in 14%, 3 in 10%, 2 in 7%, and 1 in 4%; only one isolate did not present any GEI. The genomic islands PAPI-1 and PAPI-2 and the element pKLC102 were the most frequently detected. The analysis of the location of each GEI in the chromosome of two strains show that the islands PAGI-3, PAPI-1, PAPI-2 and pKLC102 are present in the insertion site previously reported, but that PAGI-2 and PAGI-4 are inserted in another chromosome place in a site not characterized yet. In conclusion our data show that P. aeruginosa strains exhibited an epidemic population structure with horizontal transfer of DNA resulting in a high frequency of GEIs.

Components of intestinal epithelial hypoxia activate the virulence circuitry of Pseudomonas

We have previously shown that a lethal virulence trait in Pseudomonas aeruginosa, the PA-I lectin, is expressed by bacteria within the intestinal lumen of surgically stressed mice. The aim of this study was to determine whether intestinal epithelial hypoxia, a common response to surgical stress, could activate PA-I expression. A fusion construct was generated to express green fluorescent protein downstream of the PA-I gene, serving as a stable reporter strain for PA-I expression in P. aeruginosa. Polarized Caco-2 monolayers were exposed to ambient hypoxia (0.1-0.3% O2) for 1 h, with or without a recovery period of normoxia (21% O2) for 2 h, and then inoculated with P. aeruginosa containing the PA-I reporter construct. Hypoxic Caco-2 monolayers caused a significant increase in PA-I promoter activity relative to normoxic monolayers (165% at 1 h; P < 0.001). Similar activation of PA-I was also induced by cell-free apical, but not basal, media from hypoxic Caco-2 monolayers. PA-I promoter activation was preferentially enhanced in bacterial cells that physically interacted with hypoxic epithelia. We conclude that the virulence circuitry of P. aeruginosa is activated by both soluble and contact-mediated elements of the intestinal epithelium during hypoxia and normoxic recovery.

Preventive and therapeutic effects of sugar cane extract on cyclophosphamide-induced immunosuppression in chickens

Effects of oral administration of sugar cane extract (SCE) on immunosuppression in chickens treated with cyclophosphamide (CPA) were evaluated. Three-week-old inbred chickens were inoculated into the crop with SCE (500 mg/kg/day) for three consecutive days before or after injection of CPA 12 or 20 mg/chicken. At the last day of SCE or CPA treatment, all chickens were immunized intravenously with sheep red blood cells (SRBC) and Brucella abortus (BA). Chickens administered SCE showed a significant increase in body weight, gain in body weight/day, relative weight of the bursa of Fabricius and antibody responses to SRBC and BA than untreated control chickens. Chickens injected with CPA alone showed significantly decreased body weight, gain in body weight/day, relative weight of the bursa and antibody responses to SRBC and BA, showing immunosuppression in the bursa-dependent immune system. All chickens administered SCE before or after the treatment with CPA showed significantly higher values in body weight, gain in body weight/day, relative bursal weight and antibody responses to both antigens, when compared to chickens treated with CPA alone. In histological examination, chickens administered SCE showed a typical bursa with well constituted follicles, although chickens treated with CPA alone showed a severely atrophied bursa with rudimentary follicles and enormous proliferation of interfollicular connective tissue. Chickens treated with SCE and CPA showed a well-reconstituted bursa with almost normal structure. These results suggest that SCE has functionally and morphologically reconstituting effects on the bursa-dependent immune system in immunosuppressed chickens induced by injection of CPA.

Recombinant OprF-OprI as a vaccine against Pseudomonas aeruginosa infections

A vaccine against Pseudomonas aeruginosa based on recombinant outer membranes has been developed. After intramuscularly injecting into patients with severe burns, antibodies against P. aeruginosa were induced. Vaccination was well tolerated. Intranasal application of the vaccine into volunteers, induced specific s-IgA antibodies. We conclude that the newly developed vaccine may be suitable for protection of the main risk groups of P. aeruginosa infections. In particular, for the protection of burn patients and patients with cystic fibrosis.

Typing of Pseudomonas aeruginosa from hospitalized patients: a comparison of susceptibility and biochemical profiles with genotype

Typing techniques are essential for understanding hospital epidemiology, permitting the elucidation of the source of infection and routes of bacterial transmission. Although DNA-based techniques are the "gold standard" for the epidemiological study of Pseudomonas aeruginosa, antibiotic profiles and biochemical results are used because they are easy to perform and to interpret and relatively inexpensive. Antibiotypes (susceptibility profiles) and biotypes (biochemical profiles) were compared to genotypes established by DNA restriction enzyme analysis in 81 clinical isolates of P. aeruginosa from three hospitals in Porto Alegre, Brazil. The epidemiological relationship among patients was also evaluated. Susceptibility and restriction profiles were discrepant in more than 50% of the cases, and many antibiotypes were observed among isolates from the same genotype. Furthermore, susceptibility profiles did not allow the distinction of isolates from unrelated genotypes. Since a large number of isolates (63%) yielded the same biochemical results, only 10 biotypes were detected, showing that this typing method has a low discriminatory power. On the other hand, DNA restriction enzyme typing allowed us to establish 71 distinct types. Epidemiological data about the relation among P. aeruginosa isolates were not conclusive. The results of the present study indicate that the only method that can establish a clonal relation is DNA restriction enzyme typing, whereas the other methods may cause misleading interpretations and are inadequate to guide proper infection control measures.

Gram-negative bacteraemia (GNB) after 428 unrelated donor bone marrow transplants (UD-BMT): risk factors, prophylaxis, therapy and outcome

Gram-negative infection is an important cause of morbidity and mortality after unrelated donor-bone marrow transplantation (UD-BMT). We performed a retrospective case-control study to examine the risk factors, prophylaxis, therapy and outcome of Gram-negative bacteraemia (GNB) in 428 patients undergoing UD-BMT. The incidence of GNB was 3.6% in children and 19% in adults. Of the adults, 11% developed GNB >60 days post UD-BMT. Predisposing risk factors for GNB included 'high-risk' disease status, chronic graft-versus-host disease and use of systemic steroids. Fever, a raised C-reactive protein (CRP) and hypotension were common findings at presentation. Patients were routinely given prophylactic ciprofloxacin: resistance to this antibiotic was seen in 33% of isolates. We identified an age-matched control group undergoing UD-BMT over the same time period as the study group. Gram-positive bacteraemia was significantly more common in cases than controls. Mortality from GNB was 17% in children and 24% in adults. We conclude that GNB is a common complication of UD-BMT with a high associated mortality. Patients should be educated further to present rapidly with symptoms suggestive of infection.

[Outbreak of nosocomial urinary tract infections due to a multidrug resistant Pseudomonas aeruginosa]

An outbreak of a multidrug resistant Pseudomonas aeruginosa including imipenem resistance occurred in the urology intensive care unit at Charles Nicolle Hospital (Tunis). All isolates presented the same antibiotic resistance pattern and were only susceptible to colistin. The epidemic strain was detected in different sites of this unit. Pulsed-field gel electrophoresis after enzymatic restriction using XbaI was performed in order to establish an epidemiologic link between these infections. Genotypic analysis showed two different patterns and the environmental source was identified in both cases. Although the same antibiotype was harbored by all the isolates, two outbreaks occurring in the same period were identified. The strengthening of hygiene measures allowed to stop the outbreak spreading. Since the hospital environment is the major source of Pseudomonas aeruginosa contamination, a continuous surveillance of the patients and the environmental sources is required for the implementation efficient control measures.

Pseudomonas aeruginosa infections in a neonatal intensive care unit

This report describes a cluster of nosocomial infections with Pseudomonas aeruginosa in a neonatal intensive care nursery. All 5 cases of P aeruginosa infection were clustered in September 1999. Aggressive infection control measures were instituted, including installation of a user-friendly handwashing soap and environmental cleaning. On the basis of the finding of persistent dirty equipment, a new full-time position was created that was dedicated to equipment cleaning. These measures were effective in eliminating the cluster. The nursery has remained free of P aeruginosa infection for more than 2 years, attesting to the success of our program.

An outbreak of multidrug-resistant Pseudomonas aeruginosa associated with increased risk of patient death in an intensive care unit

OBJECTIVE

To investigate an outbreak of multidrug-resistant Pseudomonas aeruginosa in an intensive care unit (ICU).

DESIGN

Epidemiologic investigation, environmental assessment, and ambidirectional cohort study.

SETTING

A secondary-care university hospital with a 10-bed ICU.

PATIENTS

All patients admitted to the ICU receiving ventilator treatment from December 1, 1999, to September 1, 2000.

RESULTS

An outbreak in an ICU with multidrug-resistant isolates of P aeruginosa belonging to one amplified fragment-length polymorphism (AFLP)-defined genetic cluster was identified, characterized, and cleared. Molecular typing of bacterial isolates with AFLP made it possible to identify the outbreak and make rational decisions during the outbreak period. The outbreak included 19 patients during the study period. Infection with bacterial isolates belonging to the AFLP cluster was associated with reduced survival (odds ratio, 5.26; 95% confidence interval, 1.14 to 24.26). Enhanced barrier and hygiene precautions, cohorting of patients, and altered antibiotic policy were not sufficient to eliminate the outbreak. At the end of the study period (in July), there was a change in the outbreak pattern from long (December to June) to short (July) incubation times before colonization and from primarily tracheal colonization (December to June) to primarily gastric or enteral July) colonization. In this period, the bacterium was also isolated from water taps.

CONCLUSION

Complete elimination of the outbreak was achieved after weekly pasteurization of the water taps of the ICU and use of sterile water as a solvent in the gastric tubes.

Reduced tissue macrophage population in the lung by anticancer agent cyclophosphamide: restoration by local granulocyte macrophage-colony-stimulating factor gene transfer

Granulocytopenia is thought to be the sole mechanism underlying the increased susceptibility to bacterial infection in hosts with anticancer chemotherapy. Little is known about the functional state of tissue macrophage populations in such hosts. Using a model of chemotherapy-induced leukopenia, the number and function of alveolar macrophages (AMS) were examined during and after multiple injections of an anticancer agent, cyclophosphamide (CP). Although CP quickly reduced peripheral blood leukocytes, the number of these cells rebounded quickly 3 to 4 days after the withdrawal of CP. Accompanying blood leukopenia was a profound reduction in the number of AMs. Contrary to the rapid onset of blood leukopenia, tissue macrophage deficiency was a more chronic process that worsened gradually as the CP regimen continued. Of importance, in contrast to blood leukopenia, which restored itself shortly after CP withdrawal, tissue macrophage deficiency was not immediately self-recoverable in spite of a restored number of circulating leukocytes. Although AMS had a decreased ability to proliferate during, but not after, the CP regimen, these cells retained a normal ability to release tumor necrosis factor-alpha and nitric oxide. To identify the potential therapeutics for recovering macrophages, a gene vector expressing granulocyte macrophage-colony-stimulating factor (GM-CSF) was delivered either systemically or locally. GM-CSF transgene was able to expand macrophage populations only when delivered to the lung after, but not during, the CP regimen. This study thus identifies tissue macrophage deficiency as a mechanism of weakened innate immunity by chemotherapy and suggests the usefulness of topical GM-CSF transgene expression for restoring innate immunity in the lung.

Epidemic population structure of Pseudomonas aeruginosa: evidence for a clone that is pathogenic to the eye and that has a distinct combination of virulence factors

The genetic structure of a population of Pseudomonas aeruginosa, isolated from patients with keratitis, endophthalmitis, and contact lens-associated red eye, contact lens storage cases, urine, ear, blood, lungs, wounds, feces, and the environment was determined by multilocus enzyme electrophoresis. The presence and characteristics of virulence factors were determined by restriction fragment length polymorphism analysis with DNA probes for lasA, lasB, aprA, exoS, exoT, exoU, and ctx and by zymography of staphylolysin, elastase, and alkaline protease. These analyses revealed an epidemic population structure of P. aeruginosa, characterized by frequent recombination in which a particular successful clone may increase, predominate for a time, and then disappear as a result of recombination. Epidemic clones were found among isolates from patients with keratitis. They were characterized by high activity of a hitherto-unrecognized size variant of elastase, high alkaline protease activity, and possession of the exoU gene encoding the cytotoxic exoenzyme U. These virulence determinants are not exclusive traits in strains causing keratitis, as strains with other properties may cause keratitis in the presence of predisposing conditions. There were no uniform patterns of characteristics of isolates from other types of infection; however, all strains from urinary tract infections possessed the exoS gene, all strains from environment and feces and the major part of keratitis and wound isolates exhibited high elastase and alkaline protease activity, and all strains from feces showed high staphylolysin activity, indicating that these virulence factors may be important in the pathogenesis of these infectious diseases.

Longitudinal study of bacterial, viral, and fungal infections in adult recipients of bone marrow transplants

The epidemiology of infections was studied in a retrospective cohort of 446 recipients of bone marrow transplants (BMTs; 92 of which were allogeneic and 354 of which were autologous) during 1993--1996. Infections that were microbiologically documented in 274 recipients included bacteremia, urinary tract infections, cytomegalovirus viremia, fungemia, invasive aspergillosis, and catheter-related infections. During the period of neutropenia, no differences were found between recipients of allogeneic BMTs and recipients of autologous BMTs with regard to the incidence and the nature of infection. After patients underwent engraftment, bacteremia, cytomegalovirus viremia, and invasive aspergillosis were significantly more common in recipients of allogeneic BMTs than in recipients of autologous BMTs. Deaths caused by infection were uncommon and were mainly the result of invasive aspergillosis. Therefore, empirical antimicrobial therapy should be the same for recipients of both allogeneic and autologous BMTs during the period of neutropenia; after engraftment, more attention should be paid to the risk of infection in allogeneic BMT recipients, particularly with regard to detection and prevention of invasive aspergillosis.

Safety and immunogenicity of an intranasal Pseudomonas aeruginosa hybrid outer membrane protein F-I vaccine in human volunteers

A hybrid protein [Met-Ala-(His)(6) OprF(190-342)-OprI(21-83)] consisting of the mature outer membrane protein I (OprI) and amino acids 190-342 of OprF of Pseudomonas aeruginosa was expressed in Escherichia coli and purified by Ni(2+) chelate-affinity chromatography. After several studies in healthy volunteers, as well as in patients, had proven the tolerability and immunogenicity of the the OprF-OprI vaccine, after intra-muscular application, we developed an emulgel for intranasal immunization. For this purpose we combined a highly concentrated OprF-I with sodium dodecylsulfate as vehicle and the gel matrix natriumlauryl sulfate. After safety and pyrogenicity evaluations in animals, eight healthy adult human volunteers received the OprF-I gel intranasally three times at 2-week intervals. The vaccination was well tolerated and no side effects were observed. An antibody induction (IgG and IgA) could be detected in the sera. These data support continued clinical investigation of the protection against infections in cystic fibrosis patients and patients prone to P. aeruginosa infections.

Enhanced phagocytic activity of neutrophils caused by administration of egg white derivatives (EWD) in cats injected with cyclophosphamide (CPA)

To examine in vivo effects of egg white derivatives (EWD), the numbers of peripheral blood cells and neutrophil phagocytosis were evaluated in cats injected intramuscularly with cyclophosphamide (CPA). There were no changes in the number of red blood cells (RBC) or packed cell volume (PCV) values regardless of oral administration of EWD or injection of CPA, but the numbers of platelets, white blood cells (WBC) and neutrophils in cats administered EWD significantly increased (p<0.05 to 0.01) when compared with those in control cats which received saline solution. In addition, the administration of EWD resulted in a significant enhancement in the phagocytic activity of neutrophils (p<0.01) when compared to control cats, suggesting that EWD has a stimulating effect on leukocyte progenitors. The numbers of platelets, WBC and neutrophils, and the phagocytic activity of neutrophils in cats injected with CPA alone were significantly lower (p<0.05 to 0.01) than those in control cats. However, co-administration of EWD to cats injected with CPA resulted in a significant increase in the numbers of platelets, WBC and neutrophils (p<0.05 to 0.01), and in the phagocytic response of neutrophils (p<0.01) when compared to cats injected with CPA alone. Therefore, these results suggest that co-administration of EWD may be effective in reducing some possible side effects in animals treated with immunosuppressive or antitumor agents.

Outbreak of severe Pseudomonas aeruginosa infections caused by a contaminated drain in a whirlpool bathtub

During a 14-month period, 7 patients with hematological malignancies acquired serious infections caused by a single strain of multiply resistant Pseudomonas aeruginosa. A case-control study, culture surveys, and pulsed-field gel electrophoresis implicated a whirlpool bathtub on the unit as the reservoir. All case patients and 32% of control patients used this bathtub (P=.003). The epidemic strain was found only in cultures of samples taken from the bathtub. The drain of the whirlpool bathtub, which was contaminated with the epidemic strain, closed approximately 2.54 cm below the drain's strainer. Water from the faucet, which was not contaminated, became contaminated with P. aeruginosa from the drain when the tub was filled. The design of the drain allowed the epidemic strain to be transmitted to immunocompromised patients who used the whirlpool bathtub. Such tubs are used in many hospitals, and they may be an unrecognized source of nosocomial infections. This potential source of infection could be eliminated by using whirlpool bathtubs with drains that seal at the top.

Gut-derived sepsis occurs when the right pathogen with the right virulence genes meets the right host: evidence for in vivo virulence expression in Pseudomonas aeruginosa

OBJECTIVE

To define the putative role of the PA-I lectin/adhesin, a binding protein of Pseudomonas aeruginosa, on lethal gut-derived sepsis after surgical stress, and to determine if this protein is expressed in vivo in response to physical and chemical changes in the local microenvironment of the intestinal tract after surgical stress.

SUMMARY BACKGROUND DATA

Previous work from the authors' laboratory has established that lethal gut-derived sepsis can be induced after the introduction of P. aeruginosa into the cecum of mice after a 30% hepatectomy. This effect does not occur when P. aeruginosa is introduced into the cecum of sham operated control mice. Previous experiments further established that the mechanism of this effect is due to the presence of the PA-I lectin/adhesin of P. aeruginosa, which induces a permeability defect to a lethal cytotoxin of P. aeruginosa, exotoxin A.

METHODS

Three strains of P. aeruginosa, one lacking functional PA-I, were tested in two complementary systems to assess virulence. Strains were tested for their ability to adhere to and alter the permeability of cultured human colon epithelial cells, and for their ability to induce mortality when injected into the cecum of mice after a 30% hepatectomy. To determine if PA-I is "in vivo expressed" when present in the cecal environment after hepatectomy, strains were retrieved from the cecum of sham-operated and hepatectomy-treated mice 24 and 48 hours after their introduction into the cecum and their PA-I expression was assessed.

RESULTS

Results indicated that PA-I plays a putative role in lethal gut-derived sepsis in the mouse, because strains lacking functional PA-I had an attenuated effect on cultured human epithelial cells, and were nonlethal when injected into the cecum of mice after 30% surgical hepatectomy. Furthermore, surgical stress in the form of hepatectomy significantly altered the intestinal microenvironment, resulting in an increase in luminal norepinephrine associated with an increase in PA-I expression in retrieved strains of P. aeruginosa. Co-incubation of P. aeruginosa with norepinephrine increased PA-I expression in vitro, suggesting that norepinephrine plays a role in the observed response in vivo.

CONCLUSIONS

Lethal gut-derived sepsis may occur when intestinal pathogens express virulence determinants in response to environmental signals indicating host stress. In this regard, the PA-I lectin/adhesin of P. aeruginosa appears to be a specific example of in vivo virulence expression in colonizing pathogens in the intestinal tract in response to surgical stress.

Pseudomonas aeruginosa bacteremia in children: analysis of trends in prevalence, antibiotic resistance and prognostic factors

OBJECTIVE

To determine the factors predisposing to Pseudomonas aeruginosa bacteremia as well as the prevalence, source of infection, outcome and prognostic factors in pediatric patients.

METHODS

Retrospective review of pediatric patients with P. aeruginosa bacteremia, at a large tertiary care hospital during a 6.5-year period.

RESULTS

Seventy patients with P. aeruginosa bacteremia were identified. The annual rate of P. aeruginosa bacteremia remained unchanged during the study period. Antibiotic susceptibility remained unchanged except for two patients with extensive burns who developed resistant strains. Underlying diseases were malignancy (50%), prematurity (6%), burns (7%) and others (37%). The overall mortality associated with P. aeruginosa bacteremia was 20%. The fatality rate was higher among the young infants (compared with older children) and those who received previous antibiotic therapy (P = 0.02). Mortality rate was higher in nosocomial than in community-acquired infections (25% compared with 11.5%). The mortality rate of low birth weight and burns patients was significantly higher when compared with oncology patients or other patients, 75 and 40% compared with 11 and 19%, P = 0.01. Multiple regression analysis revealed a correlation only between the underlying disease and mortality (P = 0.02). In the oncology patients the only significant risk factor for mortality was absolute neutrophil count < or =0.1 x 10(9)/l (P = 0.06).

CONCLUSION

P. aeruginosa bacteremia, although apparently not increasing in incidence and antibiotic resistance, is still a common serious complication in immunocompromised children with a high mortality rate. We conclude that the underlying disease is the main determinant of the clinical outcome.

Immunogenic efficacy of differently produced recombinant vaccines candidates against Pseudomonas aeruginosa infections

Three different variants of the recombinant hybrid outer membrane protein OprF (aa 190-342)-OprI (aa 21-83) could be obtained in high yield after expression in Escherichia coli. The hybrid protein was modified N terminally, either with a minimal histidine tag or with a homologous sequence of OprF. Both recombinant proteins were purified by nickel chelate affinity chromatography under native and denaturing conditions, and this produced three suitable candidates for a vaccination trial, protein His-F-I, which was purified in its native as well as in its refolded form; and the native purified N terminally extended protein, ex-F-I. In mice, significantly higher antibody titers and survival rates after challenge with Pseudomonas aeruginosa were observed following immunization with protein His-F-I, purified under native conditions.

The key role of Pseudomonas aeruginosa PA-I lectin on experimental gut-derived sepsis

OBJECTIVE

To examine the effect of Pseudomonas aeruginosa on intestinal barrier function and its lethal potential when introduced into the intestinal tract of mice.

SUMMARY BACKGROUND DATA

The mere presence of P. aeruginosa in the intestinal tract of critically ill patients is associated with a threefold increase in death compared with matched cohorts without this pathogen. Whether this effect is a cause or a consequence of the critically ill state has not been previously addressed.

METHODS

Transepithelial electrical resistance, a measure of tight junction permeability, was evaluated in Caco-2 intestinal epithelial cells cells apically inoculated with live P. aeruginosa, exotoxin A, or purified PA-I lectin, an adhesin of P. aeruginosa. Lethality studies to P. aeruginosa were carried out in mice undergoing 30% surgical hepatectomy by injecting the bacteria or its various components directly into the cecum.

RESULTS

Only cells exposed to P. aeruginosa or its PA-I lectin developed alterations in barrier function. P. aeruginosa or the combination of PA-I and exotoxin A was lethal to mice when injected into the cecum after partial hepatectomy. Alterations in epithelial barrier function and death in mice were prevented when Pseudomonas was pretreated with N-acetyl D-galactosamine (GalNAc), a binder of PA-I.

CONCLUSIONS

P. aeruginosa may act as a pathogen in the gastrointestinal tract, resulting in altered epithelial barrier function and death in a susceptible host. The PA-I lectin of P. aeruginosa may play a key role in its pathogenicity to the intestinal epithelium by inducing a permeability defect to its cytotoxic exoproducts such as exotoxin A.

Sequence diversity of Pseudomonas aeruginosa: impact on population structure and genome evolution

Comparative sequencing of Pseudomonas aeruginosa genes oriC, citS, ampC, oprI, fliC, and pilA in 19 environmental and clinical isolates revealed the sequence diversity to be about 1 order of magnitude lower than in comparable housekeeping genes of Salmonella. In contrast to the low nucleotide substitution rate, the frequency of recombination among different P. aeruginosa genotypes was high, leading to the random association of alleles. The P. aeruginosa population consists of equivalent genotypes that form a net-like population structure. However, each genotype represents a cluster of closely related strains which retain their sequence signature in the conserved gene pool and carry a set of genotype-specific DNA blocks. The codon adaptation index, a quantitative measure of synonymous codon bias of genes, was found to be consistently high in the P. aeruginosa genome irrespective of the metabolic category and the abundance of the encoded gene product. Such uniformly high codon adaptation indices of 0.55 to 0.85 fit the ubiquitous lifestyle of P. aeruginosa.

Protection of mice against P. aeruginosa infections by large-scale affinity-purified human IgG specific to P. aeruginosa outer membrane proteins

In order to develop an effective means to treat Pseudomonas aeruginosa infections, we designed a large-scale process for purification of human IgG specific to P. aeruginosa outer membrane proteins (Oprs) from normal human sera. The process we developed includes affinity column chromatography using P. aeruginosa Oprs as ligands, protein A column chromatography and ultrafiltration, which enriched P. aeruginosa Oprs-specific IgG antibody by 500-fold. The purified anti-Oprs IgG was specific to the Oprs as confirmed by an ELISA competition assay and retained opsonophagocytic-killing capacity. In vivo protective efficacy of anti-Oprs IgG was evaluated by passive protection assays in mice where the 50% protective dose of anti-Oprs IgG against P. aeruginosa infections was 41 microg/kg, which was 20 times lower than that of normal serum IgG. When administered to mice 3 h after bacterial challenge, only anti-Oprs IgG afforded protection. These data demonstrate the feasibility of use of the purification process in producing functionally active target-specific human antibodies for clinical use and provide a rationale for use of anti-Oprs IgG as a valuable adjunct to treat P. aeruginosa infections.

Characteristics of polyclonal endemicity of Pseudomonas aeruginosa colonization in intensive care units. Implications for infection control

We investigated the endemicity of Pseudomonas aeruginosa in intensive care units (ICUs) through analyses of surveillance cultures (from the rectum, stomach, oropharynx, and trachea; n = 1,089), and clinical cultures (n = 2,393) from 297 consecutive patients. Multiple isolates of P. aeruginosa (n = 353) were genotyped. Variables associated with acquisition of respiratory tract colonization (RTC) were tested in a risk factor analysis. The mean daily prevalence of colonization was 34%. On admission, 22 patients had intestinal colonization and 13 had RTC. Twenty patients acquired colonization in the intestinal and 24 in the respiratory tract. Forty-four different genotypes were found; 38 (86%) were isolated from individual patients only. In all, 37 patients had RTC with a total of 38 genotypes: 13 (34%) were colonized on admission, 9 (24%) acquired RTC with a novel genotype during a stay in the ICU, five (13%) acquired colonization from their intestinal tract and three (8%) were colonized via cross-acquisition. In eight patients (21%), no route could be demonstrated for colonization. Antibiotics providing P. aeruginosa with a selective growth advantage were associated with acquired RTC. Endemicity of colonization with P. aeruginosa is characterized by polyclonality, and seems to be maintained by continuous admittance of colonized patients and selection pressure from antibiotics rather than by cross-acquisition.

Human anti-Pseudomonas aeruginosa outer membrane proteins IgG cross-protective against infection with heterologous immunotype strains of P. aeruginosa

In order to develop an effective means to treat and prevent Pseudomonas aeruginosa infections, we have purified P. aeruginosa outer membrane protein (Oprs)-specific human IgG antibody using a large-scale affinity column. In this study, we investigated the cross-protective activity of the purified anti-Oprs IgG against various immunotype strains of P. aeruginosa. The anti-Oprs IgG reacted with Oprs isolated from seven Fisher-Devlin immunotype strains of P. aeruginosa and was able to promote opsonophagocytic killing of all seven immunotype strains by human phagocytic cells. Administration of 500 microg anti-Oprs IgG to mice raised the LD50 of the P. aeruginosa strains by 8-250-fold, indicating the protective capacity against heterologous P. aeruginosa strains as well as homologous strains. In contrast, despite high titers against P. (aeruginosa Oprs, total serum IgG isolated from burn patient sera was no better than normal serum IgG in protecting mice from infection with P. aeruginosa. These data demonstrate that the affinity-purified human anti-Oprs IgG could afford protection against heterologous immunotype P. aeruginosa strains and provide a rationale to use anti-Oprs IgG as an adjunct for treatment of P. aeruginosa infections in humans.

Enzyme polymorphism in Pseudomonas aeruginosa strains recovered from cystic fibrosis patients in France

Each of 314 strains of Pseudomonas aeruginosa recovered from 87 French cystic fibrosis (CF) patients was typed by multilocus enzyme electrophoresis to investigate the genetic diversity, the relatedness and the molecular epidemiology of strains isolated from cases of chronic pulmonary colonization. Comparison of allele profiles at 18 enzyme loci identified 17 electrophoretic types (ETs). Of the 314 isolates, 290 (92%) were either ET1 (n = 127) or ET2 (n = 163), which differed only at the shikimate dehydrogenase (SKD) locus. The mean genetic diversity (H) was 0.138. These results suggest that there is cross-colonization between patients and/or that two predominant groups of strains are able to colonize French CF patients. Sequential isolates collected from 18 patients during a period of 12-28 months were analysed to assess genomic variability and its relationship to clinical outcome. Six patients were colonized by a stable strain. For the others, double infections or changes in colonization over time were observed. No relationships were detected between the clinical outcome and the persistence of stable isolates, the emergence of transient superinfecting variants, the presence of multiple ETs or the shift of ET during the monitoring.

Safety and immunogenicity of a Pseudomonas aeruginosa hybrid outer membrane protein F-I vaccine in human volunteers

A hybrid protein [Met-Ala-(His)6OprF190-342-OprI21-83] consisting of the mature outer membrane protein I (OprI) and amino acids 190 to 342 of OprF of Pseudomonas aeruginosa was expressed in Escherichia coli and purified by Ni2+ chelate-affinity chromatography. After safety and pyrogenicity evaluations in animals, four groups of eight adult human volunteers were vaccinated intramuscularly three times at 4-week intervals and revaccinated 6 months later with either 500, 100, 50, or 20 microg of OprF-OprI adsorbed onto A1(OH)3. All vaccinations were well tolerated. After the first vaccination, a significant rise of antibody titers against P. aeruginosa OprF and OprI was measured in volunteers receiving the 100- or the 500-microg dose. After the second vaccination, significant antibody titers were measured for all groups. Elevated antibody titers against OprF and OprI could still be measured 6 months after the third vaccination. The capacity of the elicited antibodies to promote complement binding and opsonization could be demonstrated by a C1q-binding assay and by the in vitro opsonophagocytic uptake of P. aeruginosa bacteria. These data support the continued development of an OprF-OprI vaccine for use in humans.

Human immune response to a Pseudomonas aeruginosa outer membrane protein vaccine

In order to evaluate in humans the safety and immunogenicity of a Pseudomonas aeruginosa vaccine composed of outer membrane proteins (OMPs), CFC-101, we carried out a phase I/IIa clinical trial in healthy male volunteers. Groups of six volunteers were immunized either subcutaneously (s.c.) or intramuscularly (i.m.) with three dosages of the vaccine three times at 7-day intervals. The vaccine was well tolerated by volunteers. Local reactions in the injection sites were generally mild and transient. Significant increases in OMP-specific antibody were observed in both route groups after vaccinations but was higher in the i.m.-immunized group, where vaccination with 0.5 or 1.0 mg doses yielded 100% seroconversion. The specificity of the induced antibodies to P. aeruginosa OMP was demonstrated by western blot analysis and immunoprecipitation assay. An increase in Clq-binding capacity and ability to confer mice protection from lethal challenges with P. aeruginosa indicated the protective efficacy of the elicited antibodies. Based on these data, we concluded that the P. aeruginosa OMP vaccine is safe and effective in humans with an optimal dose of 0.5 and 1.0 mg and that i.m. is the better route than s.c. for this vaccine.

Neonatal infections with Pseudomonas aeruginosa associated with a water-bath used to thaw fresh frozen plasma

In our 15-bed neonatal intensive care unit (NICU), four new-borns were found to be colonized or infected with Pseudomonas aeruginosa within a period of one week. To identify the outbreak source, three independent studies were performed: epidemiological investigation, environmental surveillance and genotypic typing of isolates. Although epidemiological investigation by a case-control study revealed no conclusive results, the transfusion of fresh frozen plasma (FFP) and human albumin (HA) appeared to be the factor with highest risk. Environmental surveillance and random amplification of polymorphic DNA (RAPD) of isolates identified a water-bath used to warm FFP and HA as the likely reservoir for the outbreak. Further spread of the organism did not occur after elimination of this water-bath from the NICU. RAPD identified in addition an isolate from an infant hospitalized in the NICU five months before the outbreak with a pattern matching the one of the outbreak cluster.

Frequency and molecular diversity of Pseudomonas aeruginosa upon admission and during hospitalization: a prospective epidemiologic study

OBJECTIVE: To assess the molecular epidemiology and risk factors for Pseudomonas aeruginosa colonization and infection in hospitalized patients. METHODS: In a 1000-bed university hospital, newly admitted patients were assessed prospectively for colonization and infection with P. aeruginosa. Anal swabs were obtained upon admission and at discharge. Ribotyping was used for the typing of isolates. Epidemiologic and clinical data were recorded prospectively. Independent risk factors were assessed using multivariate analysis. RESULTS: The recovery rate of patients with P. aeruginosa from anal specimens on admission was 6.7% (42/628). Infection due to P. aeruginosa was observed in 20 of 628 (3.2%) patients, of whom 10 (1.6%) were already infected on admission. Independent risk factors for colonization/infection on admission were age, indwelling urinary catheter, the presence of wound and seropositivity for HIV. Independent risk factors for nosocomial infection were anal colonization on admission, alcoholism, indwelling urinary catheter and antibiotic treatment during hospitalization. Ribotyping revealed that 27 patients were colonized or infected with a unique ribotype, whereas 24 shared one or more ribotypes with other patients. Analysis of epidemiologic and molecular typing data revealed that transmission from patients to patients or from patients to environment was documented on only three occasions. CONCLUSIONS: A great many P. aeruginosa strains were isolated from patients and the environment, and most environmental strains were different from those recovered in patients, suggesting a low rate of hospital acquisition of P. aeruginosa from the environment. The main risk factors for hospital-acquired infection were detectable colonization on admission, antibiotic treatment and urinary catheter.

Epidemiologically related and unrelated strains of Pseudomonas aeruginosa serotype O12 cannot be distinguished by phenotypic and genotypic typing

A clonal origin for European isolates of antibiotic multi-resistant Pseudomonas aeruginosa serotype O12 has been suggested. This study was designed to assess the value and limitations of several typing methods for the investigation of outbreaks due to this serotype. In Hôpital de Rodez, France, this organism is endemic, and a prospective clinical epidemiological study was undertaken over a 15 month period, encompassing all patients at the hospital from whom P. aeruginosa O12 was isolated. All isolates were examined by auxanogram, antibiogram, phage-typing, electrophoresis of esterases and pulsed-field gel electrophoresis of DNA. The results suggest that (1) the methods used did not clearly differentiate between clinically-related and epidemiologically-unrelated European isolates, (2) in Hôpital de Rodez, while some isolates were likely to have been transmitted from patient-to-patient, most infections or colonizations with this organism were sporadic and their origin is unknown. The limits of typing methods for the investigation of outbreaks of nosocomial infection with multi-resistant P. aeruginosa O12 are emphasized.

Genetic diversity of Pseudomonas aeruginosa strains isolated from patients with cystic fibrosis revealed by restriction fragment length polymorphism of the rRNA gene region

The restriction fragment length polymorphism patterns of rDNAs from Pseudomonas aeruginosa strains isolated from the respiratory tracts of patients suffering from cystic fibrosis were obtained to evaluate the genetic polymorphism of this population of strains. Eighty-seven P. aeruginosa strains isolated from 87 patients from diverse areas of France and the ATCC 10145 strain were examined. Four restriction enzymes were used: BamHI, ClaI, EcoRI, and PstI. Forty-nine strains (56%) were in the three most frequent ribotypes (ribotypes R1 to R3). In addition, hierarchical clustering analysis of the data showed that 71 of the 88 strains (81%) clustered at a distance of less than one-third of the greatest distance observed in the total population. This indicates that clinical isolates implicated in the pathology of cystic fibrosis present a low degree of heterogeneity of rRNA operons, in contrast to the heterogeneity of strains of P. aeruginosa isolated from patients with various other pathologies. This relative homogeneity of rRNA genes was observed independently of the clinical status of the patient and the colony morphology.

Protection of immunocompromised mice against lethal infection with Pseudomonas aeruginosa by active or passive immunization with recombinant P. aeruginosa outer membrane protein F and outer membrane protein I fusion proteins

Recombinant outer membrane proteins (Oprs) of Pseudomonas aeruginosa were expressed in Escherichia coli as glutathione S-transferase (GST)-linked fusion proteins. GST-linked Oprs F and I (GST-OprF190-350 [GST linked to OprF spanning amino acids 190 to 350] and GST-OprI21-83, respectively) and recombinant hybrid Oprs (GST-OprF190-342-OprI21-83 and GST-OprI21-83-OprF190-350) were isolated and tested for their efficacy as vaccines in immunodeficient mice. GST-OprF-OprI protected the mice against a 975-fold 50% lethal dose of P. aeruginosa. Expression of GST-unfused OprF-OprI failed in E. coli, although this hybrid protein has been expressed without a fusion part in Saccharomyces cerevisiae and used for immunizing rabbits. The immune rabbit sera protected severe combined deficient (SCID) mice against a 1,000-fold 50% lethal dose of P. aeruginosa. Evidence is provided to show that the most C-terminal part of OprF (i.e., amino acids 332 to 350) carries an important protective epitope. Opr-based hybrid proteins may have implications for a clinical vaccine against P. aeruginosa.

TH1 cells trigger tumor necrosis factor alpha-mediated hypersensitivity to Pseudomonas aeruginosa after adoptive transfer into SCID mice

Recent experiments have shown that gamma interferon (IFN-gamma), either administered or induced in vivo, e.g., by certain bacteria, is a key mediator in inducing hypersensitivity to bacterial lipopolysaccharides. The source of endogenous IFN-gamma in this context (natural killer versus TH1 cells) has not been investigated yet. In order to investigate the role of antigen-specific, IFN-gamma-producing TH1 cells in murine Pseudomonas aeruginosa infection, a murine TH1 cell line was propagated in vitro by using recombinant P. aeruginosa outer membrane protein I. Adoptive transfer experiments were performed by intravenous injection of various amounts of TH1 cells into P. aeruginosa-challenged SCID mice. Adoptive transfer of 5 x 10(6) T cells into SCID mice followed by an intraperitoneal challenge with 1.4 x 10(6) CFU of live P. aeruginosa resulted in the rapid death of the animals within 12 h postchallenge, whereas transfer of lower T-cell doses and saline as a control did not cause any detrimental effects. After challenge with 2.8 x 10(6) CFU of P. aeruginosa, similar results were obtained 18 h postchallenge; however, at the end of the 72-h observation period, no significant differences in survival rates were obtained between the groups treated with different amounts of T cells. The rapid death of mice treated with 5 x 10(6) T cells was reflected by 860-fold-elevated levels of tumor necrosis factor alpha (TNF-alpha) present in serum 2 h postchallenge, whereas no significant differences in TNF-alpha serum levels were detectable in mice treated with lower doses of T cells or with saline. Pretreatment of T-cell-reconstituted SCID mice with neutralizing anti-IFN-gamma monoclonal antibodies completely protected mice from bacterial challenge and reduced TNF-alpha levels in serum. We conclude that under the experimental conditions described here, IFN-gamma- and interleukin-2-producing TH1 cells represent an important trigger mechanism inducing TNF-alpha-mediated hypersensitivity to bacterial endotoxin.

Risk factors and a clinical index for diagnosis of Pseudomonas aeruginosa bacteremia

OBJECTIVE: To define risk factors significantly and independently associated with Pseudomonas aeruginosa bacteremia and to combine them in a diagnostic index which will define groups of septic patients at low or high risk of bloodstream infection caused by P. aeruginosa. METHODS: Logistic regression analysis was used to identify risk factors associated with pseudomonal bacteremia among all patients with bacteremia at St Thomas' Hospital, London, from 1969 to 1989. The coefficients of the final logistic model were used to compile a linear model for the diagnosis of pseudomonal bacteremia. The index was validated in another set of patients with bacteremia detected at Beilinson Medical Center, Petah Tiqva, Israel, from 1988 to 1991. RESULTS: Seven factors were significantly and independently predictive of pseudomonal bacteremia: 1) neutropenia; 2) previous or current treatment with antibiotics; 3) cytotoxic or corticosteroid treatment; 4) hospital acquisition of infection; 5) detection in the intensive care unit; 6) male gender; and 7) focus of infection. High-risk foci were the urinary tract with catheter or post-instrumentation, or unknown source. Low-risk foci were bone, joint, meninges, female genital tract and upper respiratory tract. The index score divided patients into three groups with increasing likelihood of P. aeruginosa bacteremia: 1%, 7% and 19%, respectively (p=0.0001). In the validation set, the percentage of P. aeruginosa bacteremia in the three respective groups defined by the index were 5%, 18% and 22% (p=0.0001). CONCLUSIONS: The use of simple clinical and laboratory data known within hours of detection of an infectious episode can define patients at high and low risk for P. aeruginosa bacteremia.

Lack of association between clinical and environmental isolates of Pseudomonas aeruginosa in hospital wards

Seventy-three environmental and clinical isolates of Pseudomonas aeruginosa recovered from a single hospital over a 6-month period were compared for epidemiological type characteristics. Environmental isolates were obtained from sinks, taps and water, in rooms where patients were treated. The strains represented only six O-antigenic types and 8.2% of them were not typable. Serotype 011 was most frequent in the environment, whereas serotypes 06, 012 and 02,5 predominated among clinical isolates. More than 60% of all isolates belonged to four pyocin types (1, 10, 33 and 45), and approximately 80% were phage typable. Environmental isolates were more sensitive to antibiotics than clinical isolates. There was little correspondence between the types of strains of P. aeruginosa isolated from patients and those isolated from the environment. However, isolates of identical type were frequently recovered from different patients within the same clinic and were found to be related in time and location. We conclude that the environment was not an important source of P. aeruginosa infection and that transfer of organisms was mainly from patient-to-patient.

An overview of nosocomial infections, including the role of the microbiology laboratory

An estimated 2 million patients develop nosocomial infections in the United States annually. The increasing number of antimicrobial agent-resistant pathogens and high-risk patients in hospitals are challenges to progress in preventing and controlling these infections. While Escherichia coli and Staphylococcus aureus remain the most common pathogens isolated overall from nosocomial infections, coagulase-negative staphylococci (CoNS), organisms previously considered contaminants in most cultures, are now the predominant pathogens in bloodstream infections. The growing number of antimicrobial agent-resistant organisms is troublesome, particularly vancomycin-resistant CoNS and Enterococcus spp. and Pseudomonas aeruginosa resistant to imipenem. The active involvement and cooperation of the microbiology laboratory are important to the infection control program, particularly in surveillance and the use of laboratory services for epidemiologic purposes. Surveillance is used to identify possible infection problems, monitor infection trends, and assess the quality of care in the hospital. It requires high-quality laboratory data that are timely and easily accessible.

Molecular epidemiology of Pseudomonas aeruginosa in an intensive care unit

Genotyping was used to analyse Pseudomonas aeruginosa isolates from sink drains and 15 intubated patients as part of a 3-month prospective study of strain transmission in a medical-surgical intensive care unit. Ninety percent of all washbasin drains were persistently contaminated with several P. aeruginosa genotypes. In 60% (9/15) of the patients, P. aeruginosa colonization or infection was hospital-acquired: P. aeruginosa strains isolated from these patients were present in hospital sinks or in other patients before their admission. Since all patients were immobile, personnel were the probable route of transmission of P. aeruginosa in the hospital. The mechanism of strain transmission from sinks to hands during hand washing was investigated in a children's hospital. When P. aeruginosa was present at densities of > 10(5)/c.f.u. per ml in sink drains, hand washing resulted in hand contamination with P. aeruginosa via aerosol generation in the majority of experiments or P. aeruginosa was detected using an air sampler above the washing basin. High P. aeruginosa cfu were present at 4.30 h in the eight sinks (5.4 x 10(5)-7.0 x 10(10) c.f.u./ml), whereas at 13.00 h P. aeruginosa c.f.u. were significantly lower (3.1 x 10(2)-8.0 x 10(5) c.f.u./ml). These data reveal that the danger of bacterial contamination of hands during hand washing is highest in the morning. The identified transmission routes demand more effective hygienic measures in hospital settings particularly concerning personnel hands and sink drains.

Exogenous or endogenous reservoirs of nosocomial Pseudomonas aeruginosa and Staphylococcus aureus infections in a surgical intensive care unit

OBJECTIVE

A 4 month prospective study was performed to assess the incidence and routes of endogenous or exogenous colonization and nosocomial infection caused by Staphylococcus aureus and Pseudomonas aeruginosa in surgical critically ill patients.

DESIGN

A total of 4634 specimens were obtained. Patient's nasal, scalp, and rectal swabs as well as tracheal secretion (TS) were cultured every second day beginning on the day of admission. Nasal swabs and hand cultures of the personnel as well as cultures from gowns were also taken. All isolates of S. aureus were phage typed and 116 of these isolates were also plasmid typed. P. aeruginosa isolates were sero- and pyocin typed. Resistance patterns were determined in all isolates.

SETTING

The study was carried out in the surgical intensive care unit (SICU) of an teaching hospital.

PATIENTS

During the study period each patient (a total of 153 patients) admitted to the SICU entered the study.

RESULTS

P. aeruginosa and S. aureus colonisation rate on admission were 5% and 36.5% respectively. Only 10 patients (6.5%) were colonized with P. aeruginosa during hospitalization, and only 7 patients (4.5%) acquired S. aureus in the surgical intensive care unit (SICU). The most common primary colonisation site of P. aeruginosa was the rectum, whereas S. aureus was predominantly found in nasal cultures. Horizontal transmission of S. aureus occurred in only 2 patients.

CONCLUSION

The study suggests that colonisation with P. aeruginosa and S. aureus occurs from endogenous rather than from exogenous sources and that the endogenous acquisition of both bacteria play a more important role in development of nosocomial infections than the exogenous route of transmission.