Epidemiology of infections due to Pseudomonas aeruginosa

Detection of a highly prevalent and potentially virulent strain of Pseudomonas aeruginosa from nosocomial infections in a medical center

BACKGROUND

We correlated genotypes, virulence factors and antimicrobial susceptibility patterns of nosocomially identified Pseudomonas aeruginosa isolates from clinical specimens to those of environmental isolates encountered in the same units of a medical center. Antibiotic susceptibility testing, RAPD analysis and detection of enzymatic activities of extracellular virulence factors, were done on these isolates.

RESULTS

Data showed that most of the clinical and environmental isolates were susceptible to tested antimicrobial agents. RAPD analysis determined the presence of 31 genotypes, with genotype 1 detected in 42% of the clinical isolates and 43% of the environmental isolates. Enzymatic activity testing showed that genotype 1 produced all virulence factors tested for.

CONCLUSION

In conclusion, our data demonstrated the predominant prevalence of a potentially virulent P. aeruginosa genotype, circulating in a number of units of the medical center and emphasize the need to reinforce infection control measures.

Antimicrobial activity of chlorhexidine diacetate and benzalkonium chloride against Pseudomonas aeruginosa and its response to biocide residues

AIMS

The aims of this study were to evaluate the antimicrobial activity of chlorhexidine diacetate (CHX) and benzalkonium chloride (BZK) for strains of Pseudomonas aeruginosa exhibiting increased minimum inhibitory concentrations (MIC) for CHX, and to determine whether residues of chlorhexidine digluconate (CHG) and Hibiscrub (Hib, a formulation containing CHG) affect the susceptibility of P. aeruginosa to these biocides and a number of antibiotics.

METHODS AND RESULTS

The bactericidal activity of CHX and BZK was evaluated for strains of P. aeruginosa exhibiting increased MIC for CHX with established suspension and surface disinfection tests. None of the strains of P. aeruginosa exhibiting raised MIC for CHX was less sensitive than the parent strain to CHX or BZK in either method. A test was designed to investigate the effects of dried CHG and Hib residues on P. aeruginosa cells. Exposure of P. aeruginosa to dried residues of CHG or Hib did not result in the organism becoming less sensitive to either biocide or a number of antibiotics.

CONCLUSIONS

Pseudomonas aeruginosa strains with raised MIC to CHX were no less sensitive than the parent strain to CHX and BZK in bactericidal investigations. Exposure to dried residues of CHG and Hib did not render P. aeruginosa less sensitive to either of these agents or a number of antibiotics.

SIGNIFICANCE AND IMPACT OF THE STUDY

An increase in the MIC for a biocide in a micro-organism does not necessarily result in a failure of the biocide to effectively kill the organism. The residue that remains after the use of an antimicrobial agent can be at a far lower concentration than that initially applied and this study highlights the necessity for further investigations into the effect of residues, at low concentration, on bacterial populations and their role, if any, in the continued problem of antibiotic resistance.

Faucets as a reservoir of endemic Pseudomonas aeruginosa colonization/infections in intensive care units

OBJECTIVE

To evaluate the role of faucets as a reservoir for Pseudomonas aeruginosa colonization/infection of patients hospitalized in intensive care units (ICUs).

DESIGN

Prospective epidemiological investigation performed during a nonepidemic period of 1 year. The inner part of the ICU faucets were swabbed for P. aeruginosa. Data were recorded on all patients with at least one culture of a clinical specimens positive for P. aeruginosa. Pulsed-field gel electrophoresis was used to characterize the strains.

SETTING

Five ICUs of a university hospital which are supplied by two separate water distribution networks.

PATIENTS

During a 1-year period 132 cases were investigated.

RESULTS

In 42% of cases (56/132) there were isolates identical to those found in the faucets, with a total of nine different genotypes. Among the nine genotypes isolated from both patients and faucets one of them, the most prevalent, was isolated in the two networks and in 30 cases. The other eight genotypes were recovered almost exclusively from either one (three genotypes in 12 cases) or the other (five genotypes in 12 cases) network and from the patients in the corresponding ICUs.

CONCLUSIONS

These results suggest that the water system of the ICUs was the primary reservoir of patient's colonization/infection with P. aeruginosa in a substantial proportion of patients, although the exact mode of acquisition could not be determined.

Rare occurrence of heterotrophic bacteria with pathogenic potential in potable water

Since the discovery of Legionella pneumophila, an opportunistic pathogen that is indigenous to water, microbiologists have speculated that there may be other opportunistic pathogens among the numerous heterotrophic bacteria found in potable water. The US Environmental Protection Agency (USEPA) developed a series of rapid in vitro assays to assess the virulence potential of large numbers of bacteria from potable water to possibly identify currently unknown pathogens. Results of surveys of potable water from several distribution systems using these tests showed that only 50 of the approximately 10,000 bacterial colonies expressed one or more virulence characteristics. In another study, 45 potable water isolates that expressed multiple virulence factors were tested for pathogenicity in immunocompromised mice. None of the isolates infected mice that were compromised either by treatment with carrageenan (CG), to induce susceptibility to facultative intracellular pathogens, or by cyclophosphamide (CY), to induce susceptibility to extracellular pathogens. These results indicate that there are very few potential pathogens in potable water and that the currently developed in vitro virulence screening tests give an overestimation of the numbers of heterotrophic bacteria that may be pathogens. Current efforts are focused on using the animal models to screen concentrated samples of waters known to contain large numbers of heterotrophic bacteria and newly discovered Legionella-like organisms that parasitize amoebae.

Defective Phagocytosis and Clearance ofPseudomonas aeruginosain the Lung Following Bone Marrow Transplantation

Bone marrow transplantation (BMT) is an important therapeutic option for a variety of malignant and nonmalignant disorders. Unfortunately, BMT recipients are at increased risk of infection, and in particular, pulmonary complications occur frequently. Although the risk of infection is greatest during the neutropenic period immediately following transplant, patients are still vulnerable to pulmonary infections even after neutrophil engraftment. We evaluated the risk of infection in this postengraftment period by using a well-established mouse BMT model. Seven days after syngeneic BMT, B6D2F(1) mice are no longer neutropenic, and by 3 wk, they demonstrate complete reconstitution of the peripheral blood. However, these mice remain more susceptible throughout 8 wk to infection after intratracheal administration of Pseudomonas aeruginosa; increased mortality in the P. aeruginosa-infected BMT mice correlates with increased bacterial burden in the lungs as well as increased systemic dissemination. This heightened susceptibility to infection was not secondary to a defect in inflammatory cell recruitment to the lung. The inability to clear P. aeruginosa in the lung correlated with reduced phagocytosis of the bacteria by alveolar macrophages (AMs), but not neutrophils, decreased production of TNF-alpha by AMs, and decreased levels of TNF-alpha and IFN-gamma in the bronchoalveolar lavage fluid following infection. Expression of the beta(2) integrins CD11a and CD11c was reduced on AMs from BMT mice compared with wild-type mice. Thus, despite restoration of peripheral blood count, phagocytic defects in the AMs of BMT mice persist and may contribute to the increased risk of infection seen in the postengraftment period.

Epidemiology of burn unit infections in children

OBJECTIVE

The aim of this study was to determine the epidemiology of burn unit infections, the effect of these infections on the mortality rate, and antibiotic resistance pattern of the predominant bacteria isolated from children. Patients and method Epidemiologic data for 610 children, aged 0 to 15 years, admitted to the burn unit at Dicle University Hospital during a 5-year period were collected and analyzed.

RESULTS

In 207 patients (33.9%), 279 nosocomial infections were identified. The most common types of infections were burn wound infections (72.4%), urinary tract infections (10.8%), pneumonia (9.3%), and septicemia (7.5%). Pseudomonas aeruginosa (181 isolates) was the most common microorganism. Thirty-six patients (5.9%) died at the hospital. Sepsis was associated with mortality in 18 (50%) cases, pneumonia in 6 (17%), and varied noninfectious reasons in 12 patients (33%). P aeruginosa isolates showed high resistance to commonly used antimicrobials. Antibiotic susceptibility test results suggested that imipenem was the most effective agent for P aeruginosa and Escherichia coli strains.

CONCLUSION

The major type of nosocomial infections in the burn unit was burn wound infections, and the majority of nosocomial infections resulted from multiple drug-resistant, gram-negative bacteria.

Epidemiological risk factors for isolation of ceftriaxone-resistant versus -susceptible citrobacter freundii in hospitalized patients

Antimicrobial resistance is an emerging problem among nosocomial bacteria. Risk factors for the recovery of ceftriaxone-resistant (CRCF) or -susceptible (CSCF) Citrobacter freundii in clinical cultures from hospitalized patients were determined by using a case-case-control study design. CRCF was isolated from 43 patients (case group 1) and CSCF was isolated from 87 patients (case group 2) over a 3-year period. Risk factors for CRCF were exposure to imipenem (odds ratio [OR], 7.5; 95% confidence interval [CI], 1.2 to 45.4), broad-spectrum cephalosporins (OR, 6.9; 95% CI, 1.8 to 26.7), vancomycin (OR, 3.0; 95% CI, 1.2 to 7.4), or piperacillin-tazobactam (OR, 2.6; 95% CI, 1.1 to 6.2), as well as hospital length of stay >or=1 week (OR, 3.6; 95% CI, 1.3 to 10.2) and intensive care unit (ICU) stay (OR, 2.6; 95% CI, 1.1 to 6.2). Risk factors for CSCF were peripheral vascular disease (OR, 23.2; 95% CI, 4.3 to 124.6), AIDS (OR, 9.5; 95% CI, 1.6 to 55.5), cerebrovascular disease (OR, 4.2; 95% CI, 1.6 to 10.8), and ICU stay (OR, 3.1; 95% CI, 1.8 to 5.4).

[Pseudomonas aeruginosa epidemiology in intensive care units: importance of cross-transmission]

OBJECTIVES

To update the local epidemiological data of Pseudomonas aeruginosa in intensive care units (ICU) by assessing the colonisation incidence rate and the level of cross-transmission.

METHODS

Study carried out in both adult ICUs of the university-hospital of Besançon during a 2 years period. Clinical and surveillance specimens were screened for P. aeruginosa. Pulsed-field-gel-electrophoresis was used as genotyping method to evaluate the rate of cross-transmission.

RESULTS

During the study, 314 patients were positive for P. aeruginosa (incidence rate of 19.1 patients per 100 admitted patients). One hundred sixty-six of these patients were detected with a clinical specimen and 148 with a screening specimen. Seventy-seven patients were colonised upon admission in the intensive care unit and 237, negative on admission, became positive during their stay. Of the ICU-acquired cases, the mean length of stay before P. aeruginosa colonisation was acquired was 15.7 days. Genotyping revealed that 53.5% of P. aeruginosa colonisation was acquired via cross-transmission (respectively 48.1% in the medical ICU and 59.2% in the surgical ICU); the other cases probably originated from endogenous sources.

CONCLUSION

The incidences of P. aeruginosa colonisation upon admission and during hospitalisation are consistent with other french and european studies. Although we probably over-estimated the rate of cross-transmission, our results demonstrate that cross-transmission may be a major cause of P. aeruginosa dissemination in ICUs.

Myeloid progenitors protect against invasive aspergillosis and Pseudomonas aeruginosa infection following hematopoietic stem cell transplantation

Myelotoxic treatments for oncologic diseases are often complicated by neutropenia, which renders patients susceptible to potentially lethal infections. In these studies of murine hematopoietic stem cell transplantation (HSCT), cotransplantation of lineage-restricted progenitors known as common myeloid progenitors (CMP) and granulocyte-monocyte progenitors (GMP) protects against death following otherwise lethal challenge with either of 2 pathogens associated with neutropenia: Aspergillus fumigatus and Pseudomonas aeruginosa. Cotransplantation of CMP/GMP resulted in a significant and rapid increase in the absolute number of myeloid cells in the spleen, most of which were derived from the donor CMP/GMP. Despite persistent peripheral neutropenia, improved survival correlated with the measurable appearance of progenitor-derived myeloid cells in the spleen. A marked reduction or elimination of tissue pathogen load was confirmed by culture and correlated with survival. Localization of infection by P aeruginosa and extent of disease was also assessed by in vivo bioluminescent imaging using a strain of P aeruginosa engineered to constitutively express a bacterial luciferase. Imaging confirmed that transplantation with a graft containing hematopoietic stem cells and CMP/GMP reduced the bacterial load as early as 18 hours after infection. These results demonstrate that enhanced reconstitution of a tissue myeloid pool offers protection against lethal challenge with serious fungal and bacterial pathogens.

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.

Modification of dienes mutual inhibition test for epidemiological characterization of Pseudomonas aeruginosa isolates

Pseudomonas aeruginosa is an important cause of community-associated and nosocomial infections related to exposure to aqueous environments. Such infections often occur in the setting of a common-source outbreak, in which case epidemiological characterization of isolates may be necessary. In this preliminary study, a modification of the Dienes mutual inhibition test, ordinarily used to assess the relatedness of swarming Proteus mirabilis strains, was used to study 15 P. aeruginosa isolates, with the results compared to those obtained by ribotype analysis. Complete concordance was noted between the results of the Dienes test and those of ribotyping. These observations suggest that further studies are warranted to assess the utility of the modified Dienes test as a simple, inexpensive, and reliable means for epidemiological typing of P. aeruginosa.

The Pseudomonas autoinducer N-(3-oxododecanoyl) homoserine lactone induces cyclooxygenase-2 and prostaglandin E2 production in human lung fibroblasts: implications for inflammation

Pseudomonas aeruginosa causes lethal lung infections in immunocompromised individuals such as those with cystic fibrosis. The lethality of these infections is directly associated with inflammation and lung tissue destruction. P. aeruginosa produces several acylated homoserine lactones (AHL) that are important in the regulation of bacterial virulence factors. Little is known about the effects of AHLs on human cells. In this work we report that the AHL N-(3-oxododecanoyl) homoserine lactone (3O-C(12)-HSL) from P. aeruginosa induces cyclooxygenase (Cox)-2, a seminal proinflammatory enzyme. When primary normal human lung fibroblasts were exposed to 3O-C(12)-HSL, an 8-fold induction in mRNA and a 35-fold increase in protein for Cox-2 were observed. In contrast, there was no substantial change in the expression of Cox-1. We also demonstrated that the induction of Cox-2 was regulated by 3O-C(12)-HSL activation of the transcription factor NF-kappaB. 3O-C(12)-HSL also stimulated an increase in the newly discovered inducible membrane-associated PGE synthase but had no effect on the expression of the cytosolic PGE synthase. We also demonstrate that 3O-C(12)-HSL stimulated the production of PGE(2). PGE(2) is known to induce mucus secretion, vasodilation, and edema, and acts as an immunomodulatory lipid mediator. We propose that 3O-C(12)-HSL induction of Cox-2, membrane-associated PGE synthase, and PGE(2) likely contributes to the inflammation and lung pathology induced by P. aeruginosa infections in the lung. These studies further reinforce the concept that bacterial AHLs not only regulate bacterial virulence but also stimulate the activities of eukaryotic cells important for inflammation and immune defenses.

Risk factors for piperacillin-tazobactam-resistant Pseudomonas aeruginosa among hospitalized patients

Antimicrobial resistance is an emerging problem with Pseudomonas aeruginosa. This study determined risk factors for the recovery of piperacillin-tazobactam-resistant P. aeruginosa from clinical cultures from hospitalized patients. A case-control study design was used to compare two groups of case patients with control patients. The first group of case patients was defined by nosocomial isolation of piperacillin-tazobactam-resistant P. aeruginosa, and the second group of cases yielded piperacillin-tazobactam-susceptible P. aeruginosa. Controls were selected in a 6:1 ratio from the same medical or surgical services among which piperacillin-tazobactam-resistant P. aeruginosa arose in patients. Risk factors analyzed included antimicrobial drug exposure, comorbid conditions, and demographics. Bivariate and multivariable analyses were performed. Piperacillin-tazobactam-resistant P. aeruginosa was isolated from 179 patients, and piperacillin-tazobactam-susceptible P. aeruginosa was isolated from 624 patients over a 2.5-year period. Piperacillin-tazobactam (odds ratio [OR] = 6.82; 95% confidence interval [CI], 4.56 to 10.21), imipenem (OR = 2.42; 95% CI, 1.19 to 4.94), aminoglycosides (OR = 2.18; 95% CI, 1.44 to 3.28), vancomycin (OR = 1.87; 95% CI, 1.21 to 2.89), and broad-spectrum cephalosporins (OR = 2.38; 95% CI, 1.45 to 3.88) were the antibiotics associated with the isolation of piperacillin-tazobactam-resistant P. aeruginosa. Exposure to vancomycin (OR = 1.53; 95% CI, 1.13 to 2.06) or ampicillin-sulbactam (OR = 2.28; 95% CI, 1.62 to 3.21) was associated with recovery of piperacillin-tazobactam-susceptible P. aeruginosa. In this study, antibiotics associated with piperacillin-tazobactam-susceptible P. aeruginosa were different from antibiotics associated with piperacillin-tazobactam-resistant P. aeruginosa. Piperacillin-tazobactam was a strong risk factor for piperacillin-tazobactam-resistant P. aeruginosa. Our results suggest that the nosocomial isolation of piperacillin-tazobactam-resistant P. aeruginosa may be affected by multiple antibiotics.

Risk factors for imipenem-resistant Pseudomonas aeruginosa among hospitalized patients

Risk factors for the nosocomial recovery of imipenem-resistant Pseudomonas aeruginosa (IRPA) were determined. A case-control study design was used for the comparison of 2 groups of case patients with control patients. The first group of case patients had nosocomial isolation of IRPA, and the second group had imipenem-susceptible P. aeruginosa (ISPA). Control patients were selected from the same medical or surgical services from which case patients were receiving care when isolation of IRPA occurred. Risk factors analyzed included antimicrobials used, comorbid conditions, and demographic variables. IRPA was recovered from 120 patients, and ISPA from 662 patients. Imipenem (odds ratio [OR], 4.96), piperacillin-tazobactam (OR, 2.39), vancomycin (OR, 1.80), and aminoglycosides (OR, 2.19) were associated with isolation of IRPA. Vancomycin (OR, 1.64), ampicillin-sulbactam (OR, 2.00), and second-generation cephalosporins (OR, 2.00) were associated with isolation of ISPA. Antibiotics associated with ISPA are different from antibiotics associated with IRPA. The OR for imipenem as a risk factor for IRPA is less than that reported from studies in which control group selection was suboptimal.

IL-8 production in human lung fibroblasts and epithelial cells activated by the Pseudomonas autoinducer N-3-oxododecanoyl homoserine lactone is transcriptionally regulated by NF-kappa B and activator protein-2

The destructive pulmonary inflammation associated with Pseudomonas aeruginosa colonization is caused, in part, by the production of the chemokine IL-8, which recruits neutrophils into the lung. The Pseudomonas autoinducer, N-3-oxododecanoyl homoserine lactone (3-O-C12-HSL), is a small lipid-soluble molecule that is essential in the regulation of many P. aeruginosa virulence factors, but little is known about how it affects eukaryotic cells. In this report we demonstrate that 3-O-C12-HSL is a potent stimulator of both IL-8 mRNA and protein from human fibroblasts and epithelial cells in vitro. The IL-8 produced from these 3-O-C12-HSL-stimulated cells was found to be functionally active by inducing the chemotaxis of neutrophils. To determine a mechanism for this IL-8 induction, deletion constructs of the IL-8 promoter were examined. It was found that the DNA region between nucleotides -1481 and -546 and the transcription factor NF-kappaB were essential for the maximal induction of IL-8 by 3-O-C12-HSL. This was confirmed by EMSAs, where 3-O-C12-HSL induced a shift with both AP-2 and NF-kappaB consensus DNA. The activation of NF-kappaB and subsequent production of IL-8 were found to be regulated by a mitogen-activated protein kinase pathway. These findings support the concept that the severe lung damage that accompanies P. aeruginosa infections is caused by an exuberant neutrophil response stimulated by 3-O-C12-HSL-induced IL-8. Understanding the mechanisms of 3-O-C12-HSL activation of lung structural cells may provide a means to help control lung damage during infections with P. aeruginosa.

Incidence and determinants of Pseudomonas aeruginosa infection among persons with HIV: association with hospital exposure

BACKGROUND

Little information exists on risk factors for Pseudomonas aeruginosa infection in persons with HIV. We assessed the incidence and factors associated with P aeruginosa among persons with HIV enrolled in a large observational cohort study in Los Angeles.

METHODS

Data were analyzed from 4825 persons aged > or =13 years with HIV infection enrolled from 4 outpatient facilities from 1990 to 1998. The association between P aeruginosa infection and demographic, risk behavior, and clinical factors was assessed.

RESULTS

P aeruginosa was diagnosed in 72 (1.5%) patients representing a crude incidence rate of 0.74 per 100 person-years. The most frequent site of infection was pulmonary (47%). In multivariate analysis, prior hospitalization (adjusted rate ratio = 7.9, 95% CI, 3.8-16.2), and both dapsone (adjusted rate ratio = 4.0, 95% CI, 2.2-7.4) and trimethoprim-sulfamethoxazole (adjusted rate ratio = 2.5, 95% CI, 1.2-5.3) use were independently associated with higher rates of infection. Increasing days of inpatient stay (P <.01) and decreasing CD4(+) counts (P <.01) were strongly associated with P aeruginosa. Azithromycin use decreased the risk of infection by nearly 70%.

CONCLUSION

Although the overall observed incidence of P aeruginosa was low, hospital exposure, declining CD4(+) levels, and the use of dapsone or trimethoprim-sulfamethoxazole increased the risk of P aeruginosa disease, and azithromycin use was protective in this population. These findings may assist in the early recognition and diagnosis of persons likely to be at increased risk of P aeruginosa infection.

Nosocomial pneumonia. Diagnostic and therapeutic considerations

Many patients with presumed nosocomial pneumonia probably have infiltrates on the chest radiograph, fever, and leukocytosis resulting from noninfectious causes. Because of the high mortality and morbidity associated with nosocomial pneumonias, however, most clinicians treat such patients with a 2-week empiric trial of antibiotics. Before therapy is initiated, the clinician should rule out other causes of pulmonary infiltrates, fever, and leukocytosis that mimic a nosocomial pneumonia (e.g., pre-existing interstitial lung disease, primary or metastatic lung carcinomas, pulmonary emboli, pulmonary drug reactions, pulmonary hemorrhage, collagen vascular disease affecting the lungs, or congestive heart failure). If these disorders can be eliminated from diagnostic consideration, a 2-week trial of empiric monotherapy is indicated. The clinician should treat cases of presumed nosocomial pneumonia as if P. aeruginosa were the pathogen. Although P. aeruginosa is not the most common cause of nosocomial pneumonia, it is the most virulent pulmonary pathogen associated with nosocomial pneumonia. Coverage directed against P. aeruginosa is effective against all other aerobic gram-negative bacillary pathogens causing hospital-acquired pneumonia. The clinician should select an antibiotic for empiric monotherapy that is highly effective against P. aeruginosa, has a good side-effect profile, has a low resistance potential, and is relatively inexpensive in terms of its cost to the institution. The preferred agents for empiric monotherapy for nosocomial pneumonia are cefepime, meropenem, and piperacillin. Single organisms are responsible for nosocomial pneumonia, not multiple pathogens. S. aureus rarely, if ever, causes nosocomial pneumonia but is mentioned frequently in studies based on cultures of respiratory tract secretions. S. aureus, unless accompanied by a necrotizing pneumonia with rapid cavitation within 72 hours, in the sputum indicates colonization rather than infection and should not be addressed therapeutically. Antibiotics associated with a high resistance potential should not be used as monotherapy or included in combination therapy regimens (i.e., ceftazidime, ciprofloxacin, imipenem, or gentamicin). Combination therapy is more expensive than monotherapy and is indicated only when P. aeruginosa is extremely likely, based on its characteristic clinical presentation, or is proved by tissue biopsy. Therapy should not be based on respiratory secretion cultures regardless of technique. Optimal combination regimens include cefepime or meropenem plus levofloxacin or piperacillin or aztreonam or amikacin. Nosocomial pneumonias usually are treated for 14 days. Lack of radiographic or clinical response to appropriate empiric nosocomial pneumonia monotherapy after 14 days suggests an alternate diagnosis. In these patients, a tissue biopsy specimen should be obtained to determine the cause of the persistence of pulmonary infiltrates unresponsive to appropriate antimicrobial therapy.

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.

RecombinantPseudomonasexoenzyme S and exoenzyme S fromPseudomonas aeruginosaDG1 share the ability to stimulate T lymphocyte proliferation

Exoenzyme S from P. aeruginosa DG1 and recombinant exoenzyme S derived from strain 388 have distinct characteristics, which has led to a controversy about their homology and their pathophysiologic consequences. We have been investigating the ability of exoenzyme S to activate T lymphocytes, and therefore performed studies to determine whether exoenzyme S from P. aeruginosa DG1 and recombinant exoenzyme S derived from strain 388 and expressed in Pseudomonas aeruginosa PA103 or in E. coli BL21(DE3), could induce T lymphocyte activation and proliferation. Both preparations were able to activate T cells and induce lymphocyte proliferation at similar levels as measured by flow cytometry of surface-activation markers and DNA synthesis, respectively. Further, a monoclonal antibody raised against exoenzyme S from strain DG1 partially neutralized T cell activation induced by recombinant exoenzyme S and bound to it in an immunoblot suggesting that the epitope responsible for T cell activation is shared by exoenzyme S from strain DG1 and recombinant exoenzyme S. These data suggest that the two different preparations of exoenzyme S, despite biochemical differences, share the characteristic that is responsible for T lymphocyte activation.Key words: exoenzyme S, Pseudomonas aeruginosa, T lymphocyte, cystic fibrosis.

Community acquired fulminant Pseudomonas infection of the gastrointestinal tract in previously healthy infants

Three previously healthy infants presented with diarrhoea and pyrexia and deteriorated rapidly. Two patients had necrotizing bowel disease requiring aggressive surgical intervention. All survived. P. aeruginosa gastrointestinal infection in previously healthy children is an extremely rare condition with a high mortality. Ecthyma gangrenosum was present in over 60% of reported cases although often not recognized initially. A high index of clinical suspicion, including prompt recognition of ecthyma gangrenosum, is mandatory for an early diagnosis of P. aeruginosa gastrointestinal infection. Early diagnosis and treatment may improve the prognosis.

[The good use of antibiotics in intensive care: results of a program for rationalization of prescriptions]

OBJECTIVE

To assess the impact of an antibiotic prescribing programme in a intensive therapy unit.

TYPE OF STUDY

Prospective comparative study.

METHODS

We compared antibiotic prescriptions and bacterial susceptibility to antimicrobial agents before and after introduction of a programme focusing on injection control and therapeutic indications.

RESULTS

The introduction of the programme resulted in a major decrease in antibiotic administration. Moreover, the susceptibility of Pseudomonas aeruginosa to ticarcillin increased from 40 to 68%, and susceptibility of Staphylococcus aureus to methicillin increased from 55 to 73%.

CONCLUSIONS

Antibiotic control policies must be considered integral to any effort to decrease resistance and cost of therapy with antibiotics.

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.

Detection of persistent vegetative bacteria and amplified viral nucleic acid from in-use testing of gastrointestinal endoscopes

Hospital-acquired infection attributed to inadequate decontamination of gastrointestinal endoscopes prompted an in use evaluation of recommended procedures. Specimens were obtained from the internal channels of 123 endoscopes before, during and after decontamination by flushing with saline and brushing with a sterile brush, and examined for vegetative bacteria by broth and plate culture. Four endoscopy units were tested; the chemical disinfectants used were: 2% glutaraldehyde in Centres 1 and 2 (automated) and Centre 3 (manual); peracetic acid in Centre 4 (automated). Samples from patients in Centre 1 with known chronic hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV-1) infection were also examined for viral nucleic acid by ultracentrifugation, nucleic acid extraction, reverse transcription (for RNA) and polymerase chain reaction (PCR). No persistent vegetative bacteria were found following standard manual cleaning and disinfection for 20 min in 2% glutaraldehyde in Centres 2 and 3 (N = 37). At Centre 1, while plate culture yielded no growth, 34% of samples (10/29) grew vegetative bacteria in broth culture after cleaning and disinfection for 20 min in 2% glutaraldehyde. Investigation revealed an error in manual cleaning; no bacteria were detected in 37 samples taken after this was corrected. At Centre 4, despite the use of peracetic acid as a sterilant, three out of 20 (15%) of post decontamination samples grew bacteria; one contained persistent bacteria. HBV and HCV PCR analysis detected viral nucleic acid in three out of four and four out of six samples from viraemic patients undergoing endoscopy in Centre 1 during the period of improper manual washing. After proper cleaning was instituted, samples from nine out of nine HCV viraemic patients were negative. HIV RNA was detected in five of 14 samples taken from endoscopes after use on HIV positive patients but all post decontamination samples were negative. Detection of bacteria in washes from endoscope channels is a useful warning of a breakdown in decontamination practice. Inadequate brushing of internal channels may result in persistent HCV and HBV viral nucleic acid, the significance of which is not clear. These results reinforce the importance of adequate manual cleaning of endoscopes before chemical disinfection.

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.

Isolation, purification, and characterization of the major autolysin from Pseudomonas aeruginosa

The major (26 kDa) autolysin from Pseudomonas aeruginosa was purified to apparent homogeneity by a combination of preparative electrophoresis, ion-exchange, and dye-ligand chromatographies. This purification was facilitated by the development of a spot-assay that involved the spotting and subsequent incubation of autolysin samples on polyacrylamide gels containing peptidoglycan. The pl of the 26-kDa autolysin was determined to be between 3.5 and 4 and disulfide bonds within the enzyme were essential for activity. The autolysin catalyzed the release of reducing sugars from the peptidoglycans of Pseudomonas aeruginosa and Escherichia coli indicating it to be a beta-glycosidase. It was ineffective at hydrolysing the peptidoglycan from Gram-positive bacteria and the O-acetylated peptidoglycans from either Proteus mirabilis or Staphylococcus aureus. The N-terminal sequence of the purified autolysin was determined to be His-Glu-Pro-Pro-Gly. The 26-kDa autolysin together with a 29-kDa autolysin was determined to be secreted into the medium by a mechanism that involves the production and release of surface membrane vesicles during normal growth, but the enzymes were not found free and active in culture broth supernatants.

Pseudomonas aeruginosa: assessment of risk from drinking water

Pseudomonas aeruginosa is an ubiquitous environmental bacterium. It can be recovered, often in high numbers, in common food, especially vegetables. Moreover, it can be recovered in low numbers in drinking water. A small percentage of clones of P. aeruginosa possesses the required number of virulence factors to cause infection. However, P. aeruginosa will not proliferate on normal tissue but requires previously organs. Further narrowing the risk to human health is that only certain specific hosts are at risk, including patients with profound neutropenia, cystic fibrosis, severe burns, and those subject to foreign device installation. Other than these very well-defined groups, the general population is refractory to infection with P. aeruginosa. Because of its ubiquitous nature, it is not only not practical to eliminate P. aeruginosa from our food and drinking water, but attempts to do so would produce disinfection byproducts more hazardous than the species itself. Moreover, because there is no readily available sensitive and specific means to detect and identify P. aeruginosa available in the field, any potential regulation governing its control would not have a defined laboratory test measure of outcome. Accordingly, attempts to regulate P. aeruginosa in drinking water would not yield public health protection benefits and could, in fact, be counterproductive in this regard.

Infectious pseudomonas subglottic stenosis occurring in a patient with acquired immunodeficiency syndrome

Pseudomonas aeruginosa is emerging as an increasingly common opportunistic infective agent in the immunocompromised human immunodeficiency virus (HIV) positive patient (Kielhofner et al., 1992). Improvements in the prevention and treatment of opportunistic infections in HIV and acquired immunodeficiency syndrome (AIDS) has led to longer life expectancy (Graham et al., 1992), and this has changed the incidence of Pseudomonas aeruginosa infection in this population (Baron and Hollander, 1993). We present a case of a patient with AIDS who developed a fulminant Pseudomonas aeruginosa stenosing subglottic infection. We are unaware of any previous reports of this particular manifestation of Pseudomonas aeruginosa infection.

Ribotyping of Pseudomonas aeruginosa isolates from patients and water springs and genome fingerprinting of variants concerning mucoidy

Thirty-one strains of Pseudomonas aeruginosa, isolated from water springs, clinical isolates (some of which were from cystic fibrosis (CF) patients), and two type cultures, were characterized by ribotyping. After restriction of chromosomal DNA of the different isolates with EcoRI and hybridization of Southern transfer blots with 2-acetylaminofluorene labelled Escherichia coli 16S + 23S rRNA probe, eleven different ribopatterns were obtained, representing variations of a dominant profile. This largely predominant pattern included both type cultures, all six isolates from water springs, 33% of the nine CF isolates and 43% of fourteen other clinical isolates most of them from nosocomial infections. When the genomic macrorestriction fingerprints of three mucoid CF isolates, with Asel, Drai or BfrI were compared with those of their spontaneous variants, concerning mucoidy, no differences were detected.

Pharmacodynamic parameters of aminoglycosides and their effect on exoenzymes of Pseudomonas aeruginosa

Aminoglycosides at 2x or 4x minimum inhibitory concentration induced postantibiotic effects against Pseudomonas aeruginosa lasting 3.5-4.9 h (gentamicin) and 0.5-3.7 h (selemycin). Postantibiotic effects of subinhibitory concentrations of the aminoglycosides tested were substantially longer. Some combinations of supra- and subinhibitory concentrations of antibiotics did not even allow any regrowth of the bacterial strain. The postantibiotic effects and postantibiotic effects of subinhibitory concentrations of gentamicin and selemycin were associated with changes of P. aeruginosa elastase and proteinase. Combinations of supra- and subinhibitory concentrations more pronouncedly suppressed enzymic activities than did suprainhibitory concentrations alone.

Use of pulsed-field gel electrophoresis as an epidemiologic tool during an outbreak of Pseudomonas aeruginosa lung infections in an intensive care unit

OBJECTIVE

A retrospective study was performed to evaluate the use of DNA polymorphism analysis by pulsed-field gel electrophoresis (PFGE) in assessing the rate of exogenous contamination during an outbreak of Pseudomonas aeruginosa lung infections in an intensive care unit ICU. Another goal was to determine the risk factors, involved in the outbreak.

DESIGN

Rectal swabs and tracheal secretions were cultured from all patients upon admission and thereafter once a week throughout their stay in the ICU. Resistance patterns were determined in all P. aeruginosa isolates. We determined the serotypes, pyocin types, plasmid profiles and total DNA macrorestriction patterns for isolates. The restriction fragment length polymorphism (RFLP) of Dra I total DNA digest was studied by PFGE. A retrospective case-control study was performed to determine the risk factors for P. aeruginosa bronchopulmonary colonization.

SETTING

The study was carried out in the medical ICU of Besancon University Hospital (France).

RESULTS

The typability, stability and reproducibility of phenotypic markers were not completely satisfactory. Only the RFLP profile satisfied all the criteria for a good typing technique. In four of the 17 patients, P. aeruginosa strains with the same DNA pattern were found. Among the previously reported risk factors for hospital-acquired bronchopulmonary infections, only invasive procedures were determined by multivariate analysis to be significant in our study group. The oropharynx and the bronchial tract are the most likely endogenous sources.

CONCLUSION

PFGE-RFLP is a valuable tool for the epidemiologic study of P. aeruginosa. This typing method revealed that exogenous contamination is not always the major source of P. aeruginosa lung infections in mechanically ventilated patients in ICUs.

Inhibition of the human platelet cyclooxygenase response by the naturally occurring phenazine derivative, 1-hydroxyphenazine

The phenazine derivative, 1-hydroxyphenazine (OHP), is produced in vivo by Pseudomonas aeruginosa, an organism that colonises the airways of patients with cystic fibrosis. While known to inhibit leukotriene production by human neutrophils, the effects of OHP on cyclooxygenase pathways have not previously been reported. We used [3H] arachidonic acid (AA) under conditions of concurrent labelling-stimulation or pre-labelling for one hour followed by stimulation to determine the effects of OHP on the production of cyclooxygenase metabolites by human platelets stimulated with the calcium ionophore, A23187. Thromboxane B2 (TxB2) and 12-hydroxyheptadecatrienoic acid (HHT) production was inhibited in a dose-dependent manner by OHP using either pre-labelled or concurrently labelled platelets. However, production of 12-hydroxyeicosatetraenoic acid (12-HETE) was not diminished. Determination of the amount of total free label (AA+non-esterified AA metabolites) after stimulation of pre-labelled platelets indicated a dose-dependent inhibition of the release of AA from phospholipid by OHP. This was reflected in a corresponding increase in phospholipid AA content. These data indicate that phenazine derivatives of bacterial origin exhibit complex interactions with pathways of arachidonic acid metabolism in host cells. These effects may prove to be of pharmacological importance.

In vitro activity of commercially manufactured disinfectants against Pseudomonas aeruginosa

The in vitro activity of 17 commercially manufactured disinfectants routinely used in a large teaching hospital was tested against 128 strains of Pseudomonas aeruginosa isolated from hospitalized patients and the hospital environment. Except for quaternary ammonium salts, all the disinfectants at dilutions higher or equalling those recommended by the manufacturer were adequate to suppress P. aeruginosa. Chlorhexidine-, povidone-iodine- and glutaraldehyde-based disinfectants at dilutions 4 to 8-fold lower than the normal use dilution had a marked bactericidal effect ( > 3 log10 reduction of viable cells) within a short time (10 to 120 min). Similar formulations produced by different manufacturers exhibited comparable activity against P. aeruginosa.

Epidemiological characteristics of Pseudomonas aeruginosa strains causing infection in an Italian general hospital. A one-year surveillance

During the 1989 calendar year, P. aeruginosa caused clinical infections in 0.46% of patients admitted to Ospedali Riuniti (a general hospital), Bergamo, Italy. Strains (n = 267) of P. aeruginosa were collected during this period, and epidemiological characteristics were studied. The mean prevalence of P. aeruginosa infection in inpatients was 1.1% (range 0.06-7.3), whereas outpatients showed a significantly lower prevalence of infection (0.05%). Strains were recovered from inpatients of surgical wards (n = 126; 47.2%), and outpatients (n = 15; 5.6%). Males were more often affected than females (2.7:1). Infection of the urinary tract was the most common (34.1%). Pseudomonas aeruginosa was also involved in lower respiratory tract infections (18.7%) and septicaemia (17.6%). Four typing methods were performed, i.e. serotyping, antibiotyping, pyocin typing, and restriction endonuclease analysis (REA). Serotypes O:11 and O:6 were endemic in the hospital. Some serotypes correlated with specific clinical wards. Pyocin typing was an unreliable epidemiological tool. However, antibiotyping showed the presence of some epidemic clusters, probably related to the antibiotic consumption of the patients. REA suggested the circulation of edemic P. aeruginosa strains in both the obstetrics and neurosurgery wards.

Malignant Otitis Externa in AIDS Patients: Case Report and Review of the Literature

Malignant otitis externa is a necrotizing infection of the external ear canal and surrounding soft tissue and bone, usually caused by Pseudomonas aeruginosa. The infection classically occurs in diabetic patients, however recently, several patients with the acquired immunodeficiency syndrome (AIDS) have been reported to have malignant otitis externa. A patient with AIDS who had malignant otitis externa with skull base osteomyelitis is presented and reported cases in patients with AIDS are reviewed. Predisposing factors include immunologic abnormalities (notably neutropenia), dermatitis, medications, neoplasm, and iatrogenic procedures, e.g., ear lavage. Treatment of malignant otitis externa has traditionally included anti-pseudomonal cephalosporins/penicillins and aminoglycosides for prolonged durations. Recently, ciprofloxacin has been shown to be effective as an oral regimen.

With the increasing number of patients with AIDS being seen in the outpatient clinics, the diagnosis of malignant otitis externa should be considered in any patient with persistent ear pain or otorrhea who does not respond to conventional treatment for external otitis.

Investigation of a pseudo-outbreak of orthopedic infections caused by Pseudomonas aeruginosa

OBJECTIVE

To report a pseudoepidemic of Pseudomonas aeruginosa infections discovered during an investigation of postoperative joint infections.

DESIGN

A retrospective review of case patients' hospital charts, operative reports, and laboratory data, as well as environmental culturing, polymerase chain reaction (PCR) ribotyping of outbreak isolates, and in vitro analysis of P aeruginosa growth characteristics.

SETTING

A 510-bed, university-affiliated adult tertiary care hospital.

RESULTS

Between October 1 and December 1, 1992, seven postsurgical joint infections were diagnosed, including four caused by P aeruginosa. A bottle of "sterile" saline used to process tissue specimens was found to be contaminated with P aeruginosa. Further investigation revealed that P aeruginosa had grown from seven additional tissue cultures, all of which had been processed with the contaminated saline. PCR ribotypes of the contaminant matched those of the clinical isolates. In vitro, P aeruginosa strains were viable in commercial nonbacteriostatic saline, but never caused visible turbidity. Six patients received antibiotics for their presumed infections; four patients had peripherally inserted central catheters placed, and one experienced severe anaphylactic reactions to several antibiotics.

CONCLUSIONS

Pseudoepidemics due to common organisms are often difficult to detect, and delayed recognition can result in substantial morbidity. This outbreak investigation illustrates the potential for contamination of diluents in the microbiology laboratory and emphasizes the need for meticulous quality control.

Initial characterization of two extracellular autolysins from Pseudomonas aeruginosa PAO1

Two extracellular autolysins have been detected in the spent culture supernatants of Pseudomonas aeruginosa PAO1 by using renaturing polyacrylamide gel electrophoresis. The two autolysins were isolated from the culture supernatant by trichloroacetic acid precipitation and were shown to have apparent molecular masses of 26 and 29 kDa. The 26-kDa autolysin first appears during the early exponential phase of growth and then declines sharply, while the 29-kDa autolysin first appears in the late exponential phase of growth and continues well into the stationary phase. Fractionation of whole cells indicated that the 26-kDa enzyme was also localized within the periplasm, with a lesser amount of activity associated with the cytoplasmic membrane. The 29-kDa autolytic activity was distributed within the cell equally between the periplasm and the cytoplasmic membrane. The pH optima of the isolated 26- and 29-kDa autolysins are 6.0 and 5.0, respectively. Further evidence from both protease susceptibility and inhibition studies confirms that these two extracellular autolysins isolated from P. aeruginosa PAO1 are separate and distinct.

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.

Serious Infections Caused by Pseudomonas Aeruginosa

Over the last 3 decades, Pseudomonas aeruginosa has become a leading cause of infectious morbidity and mortality in certain predisposed patient populations. It primarily affects those with impaired host defenses, and its prevalence in the hospital environment makes it an important nosocomial pathogen. Infection with this organism may result in a broad spectrum of clinical manifestations, many of which may be seen in the intensive care setting. This review focuses on epidemiology, clinical presentations, nad treatment of serious Pseudomonas infections.

Pseudomonas aeruginosa bronchopulmonary infection in late human immunodeficiency virus disease

Pseudomonas aeruginosa infection is unusual in individuals with human immunodeficiency virus infection, and it most often occurs in the setting of other risk factors, such as neutropenia or cytotoxic drug use. We noted an increasing number of pulmonary isolates of this organism in our clinic population and sought to describe the clinical correlates of this finding. Our study consisted of a retrospective review of the microbiology, radiology, and clinical records of 1,852 HIV-seropositive adults seen at a university-based outpatient AIDS clinic. We identified 16 individuals with Pseudomonas bronchopulmonary infection. All subjects had advanced HIV disease with prior AIDS diagnoses, and mean CD4 counts of 25/mm3 (0.025 x 10(9)/L). Pseudomonas was the sole pulmonary pathogen in 14 of 16 patients and was associated with new chest X-ray abnormalities in 14 cases. Four individuals had acute pseudomonal pneumonia with sepsis; this presentation was associated with hospitalization and other known risk factors for Pseudomonas infection. In contrast, 12 patients had more indolent, community-acquired infection, which had a low mortality rate and occurred in the absence of other risk factors. Survivors of the initial bout of Pseudomonas infection had an 86% relapse rate despite a median survival of only 4.5 months. This pattern of pseudomonal disease is reminiscent of cystic fibrosis and suggests a role for maintenance therapy.

Susceptibility to antimicrobial agents of Pseudomonas aeruginosa attached to siliconized latex urinary catheters

The effect of siliconized latex urinary catheters on the in vitro activity of amikacin, ceftazidime, ciprofloxacin, norfloxacin and meropenem against Pseudomonas aeruginosa was determined by a microdilution assay. MICs of amikacin and meropenem increased at least 4-fold and 16-fold respectively in the presence of catheter material. The effect of catheter material on meropenem activity was not strain dependent and was similar for different brands of catheters. The susceptibility to antimicrobial agents of Pseudomonas aeruginosa attached to catheters for 6 and 24 hours was also evaluated. When bacteria attached for 6 hours were used as inoculum, MBCs increased at least 8-fold for amikacin, 64-fold for ceftazidime, 64-fold for ciprofloxacin, 32-fold for norfloxacin and 2048-fold for meropenem. Similar results were observed when bacteria attached to catheters for 24 hours were used as inoculum. It is concluded that catheter material itself affected the in vitro activity of meropenem, and that the bactericidal activity of all antimicrobial agents against Pseudomonas aeruginosa present in biofilms on the surface of siliconized latex urinary catheters decreased dramatically, this effect being more pronounced with meropenem.

Epidemiologic typing of multiply drug-resistant Pseudomonas aeruginosa isolated from an outbreak in an intensive care unit

From June to August 1991, there was an outbreak of Pseudomonas aeruginosa infections in an intensive care unit in a general hospital in Sao Paulo, Brazil. We obtained 14 isolates from 14 patients, 11 from tracheal aspirate, and 3 from surgical wound exudates. These strains were typed by serotyping, pyocin typing, and pulsed-field electrophoresis (CHEF) of chromosomal DNA (chrDNA), and the different typing methods were analyzed. These three methods demonstrated seven identical strains. We also performed an extensive antibiogram (33 drugs) in all 14 isolates. The incidence of resistance to aminoglycosides, extended-spectrum beta-lactams, and quinolones was very high among the seven identical isolates; however, the antibiogram profile differed significantly among the isolates. Our results suggest that a unique strain caused several cross-transmitted infections during this period of time, and the emergence of antimicrobial resistance has been occurring before and after the establishment of the epidemic strain by selective drug use. The chrDNA fingerprinting proved to be versatile and precise for epidemiologic investigations of P. aeruginosa infections.

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.