Risk factors for Pseudomonas aeruginosa acquisition in intensive care units: a prospective multicentre study

BACKGROUND

Pseudomonas aeruginosa is a major nosocomial pathogen in intensive care units (ICUs); however, endogenous versus exogenous origin of contamination remains unclear.

AIM

To identify individual and environmental ICU risk factors for P. aeruginosa acquisition.

METHODS

A five-month prospective multicentric study was performed in ten French ICUs. Adult patients hospitalized in ICU for ≥ 24 h were included and screened for P. aeruginosa colonization on admission, weekly and before discharge. P. aeruginosa acquisition was defined by a subsequent colonization or infection if screening swabs on admission were negative. Water samples were obtained weekly on water taps of the ICUs. Data on patient characteristics, invasive devices exposure, antimicrobial therapy, P. aeruginosa water and patient colonization pressures, and ICU characteristics were collected. Hazard ratios (HRs) were estimated using multivariate Cox model.

FINDINGS

Among the 1314 patients without P. aeruginosa on admission, 201 (15%) acquired P. aeruginosa during their ICU stay. Individual characteristics significantly associated with P. aeruginosa acquisition were history of previous P. aeruginosa infection or colonization, cumulative duration of mechanical ventilation and cumulative days of antibiotics not active against P. aeruginosa. Environmental risk factors for P. aeruginosa acquisition were cumulative daily ward 'nine equivalents of nursing manpower use score' (NEMS) [hazard ratio (HR): 1.47 for ≥ 30 points; 95% confidence interval (CI): 1.06-2.03] and contaminated tap water in patient's room (HR: 1.76; CI: 1.09-2.84).

CONCLUSION

Individual risk factors and environmental factors for which intervention is possible were identified for P. aeruginosa acquisition.

[Contribution of direct bacteriologic examinations to the diagnosis of early materno-fetal bacterial infection: the Lille experience]

A prospective study was conducted in 3056 live-born infants delivered at the Jeanneade-Flandre maternity hospital of the Lille Teaching Hospital between January and August 1997. Clinical, laboratory test, and microbiological test findings were compared. A cohort of 1003 infants who remained in the maternity ward but were considered at increased risk of maternofetal infection (MFI) based on history and/or obstetrical criteria and/or neonatal criteria underwent routine collection of specimens including gastric fluid, auricular and anal swabs, amniotic fluid, and placental fragments. Microscopic examination of gastric fluid smears, the first result available to the clinician, was found to have 27.5% sensitivity (983 samples). Positive predictive value (PPV) was only 17.8% because of a high rate of colonization (16.8%), defined as absence of clinical symptoms and three peripheral specimens positive for the same organism. However, negative predictive value (NPV) was as high as 99.8% as a result of high sensitivity (97.8%) in the infected neonates. The gastric fluid smear was positive in 30% and 35% of neonates born to mothers with hyperpyrexia during early and late labor, respectively, and in 42% of neonates born to mothers with a history of group B streptococcus carriage during the pregnancy. Forty-two per cent of neonates with a history of fetal tachycardia had a positive gastric fluid smear. Diagnostic criteria for infection were three peripheral specimens positive for the same organism, C-reactive protein elevation, and/or one or more clinical signs suggestive of infection, and/or a positive central specimen (blood, CSF). The infection rate in infants who remained in the maternity ward was 1.6%. The most common causative organisms were group B streptococci. These findings illustrate the useful contribution of gastric fluid smears to the early diagnosis of MFI and confirm the predominant role of group B streptococci.

[Determination of the nosocomial origin of vancomycin-resistance strains of Enterococcus isolated from stool of patients in a hematology department]

Patients severely neutropenic, when hospitalized, occasionally receive selective digestive decontamination, and the risk of vancomycin-resistant strain selection is a drawback since glycopeptide resistance is often associated with betalactam and aminoglycosid resistance. Bacterial translocation can lead to multiresistant bacterial sepsis. Eighteen Enterococcus faecium strains were collected from patients hospitalized in the leukemia unit of the Universitary Hospital of Lille (CHRU, Pr Bauters) between October 1992 and July 1997 and were studied. Nosocomial acquisition or endogenous origin were investigated to choose well-adapted prevention. All the vancomycin-resistant strains were shown by Polymerase Chain Reaction having the van A gene. The clonality of these strains was investigated by Pulsed-Field-Gel-Electrophoresis after Sma I restriction. Pulsotype analysis showed variable homology (52%-100%). Our results do not show evidence of patient-to-patient E. faecium transmission and suggest vancomycin-resistant strains were independently selected by antibiotic therapy from individual fecal flora. Except when epidemic events or happen, this strain isolation is more related to antibiotic prescription than misuse of isolation techniques.

[Comparison of the pharmacokinetics of tobramycin administered in a single daily dose or in 3 doses in cystic fibrosis]

An aminoglycoside in association with beta-lactam antibiotic are usually the most efficient treatment for Pseudomonas aeruginosa infections in cystic fibrosis patients. Tobramycin has the lower MICs than the other aminoglycosides to Pseudomonas aeruginosa. The aim of the work was to compare pharmacokinetics of tobramycin after once daily (15 mg/kg/day; 11 patients) or thrice daily dose (5 mg/kg/day; 9 patients) in combination ceftazidime (CAZ 200 mg/day in 3 inj. IVD) in sputum and sera for two weeks. No statistical difference in the serum concentration obtained in each group of patients was observed between the first and the 14th day. Serum concentrations were three fold higher when tobramycin was administered in once daily dose. Low through concentrations were quickly obtained, but they were slightly higher after thrice daily doses. Bronchial concentrations were 2 to 2.5 superior and near the critical concentration of tobramycin. The clinical efficacy were comparable in the two regimens.

Siderophore production by Staphylococcus aureus and identification of iron-regulated proteins

Siderophore activity of Staphylococcus aureus was detected in an iron-restricted chemically defined medium. The molecular mass of this siderophore, called aureochelin, was 577 Da. Surface-associated proteins of 120, 88, 57, 35, and 33 kDa were mainly expressed under iron restriction conditions. Results showed a relationship between siderophore production and the existence of the 120- and 88-kDa proteins. Western blotting of surface-associated proteins revealed that these proteins were recognized both by patients sera and polyclonal rabbit serum.

The binding of surface proteins from Staphylococcus aureus to human bronchial mucins

Colonization by Staphylococcus aureus is frequently observed in obstructive lung diseases, particularly in cystic fibrosis. It has been shown that the bacteria bind to mucins, the main constituent of bronchial secretions. The binding mechanism, however, remains unclear. We have investigated the interactions of two strains of S. aureus, one mucoid and one nonmucoid, with human bronchial mucins. Using a solution phase assay, the binding capacity of the two strains to radiolabelled bronchial mucins was assessed. The bacterial constituents were released by lysostaphin lysis and the surface components of the nonmucoid strain were extracted with the use of a detergent (3-([3-cholamidopropyl] dimethylammonio)-1-propane sulphonate (CHAPS)). All were analysed for mucin-binding using an overlay assay. The amount of mucins bound to the nonmucoid strain was threefold greater than that of the mucoid strain. In the lysostaphin extract from the mucoid strain, only a 57 kDa protein faintly bound 125I-labelled mucins, whereas three mucin-binding proteins (52, 57 and 71 kDa) were identified from the nonmucoid strain. Two surface proteins, one major at 60 kDa and one minor at 71 kDa, bound radiolabelled bronchial mucins and their binding was almost completely inhibited by ovine submaxillary mucin. These results indicate: 1) differences in the mucin-binding capacity from one strain of S. aureus to another; and 2) the presence of external and internal adhesins binding to human respiratory mucins in the nonmucoid strain.

The binding of surface proteins from Staphylococcus aureus to human bronchial mucins

Colonization by Staphylococcus aureus is frequently observed in obstructive lung diseases, particularly in cystic fibrosis. It has been shown that the bacteria bind to mucins, the main constituent of bronchial secretions. The binding mechanism, however, remains unclear. We have investigated the interactions of two strains of S. aureus, one mucoid and one nonmucoid, with human bronchial mucins. Using a solution phase assay, the binding capacity of the two strains to radiolabelled bronchial mucins was assessed. The bacterial constituents were released by lysostaphin lysis and the surface components of the nonmucoid strain were extracted with the use of a detergent (3-([3-cholamidopropyl] dimethylammonio)-1-propane sulphonate (CHAPS)). All were analysed for mucin-binding using an overlay assay. The amount of mucins bound to the nonmucoid strain was threefold greater than that of the mucoid strain. In the lysostaphin extract from the mucoid strain, only a 57 kDa protein faintly bound 125I-labelled mucins, whereas three mucin-binding proteins (52, 57 and 71 kDa) were identified from the nonmucoid strain. Two surface proteins, one major at 60 kDa and one minor at 71 kDa, bound radiolabelled bronchial mucins and their binding was almost completely inhibited by ovine submaxillary mucin. These results indicate: 1) differences in the mucin-binding capacity from one strain of S. aureus to another; and 2) the presence of external and internal adhesins binding to human respiratory mucins in the nonmucoid strain.

Iron depletion and virulence in Staphylococcus aureus

Staphylococcus aureus is able to grow in the presence of extremely low iron concentrations (0.04 microM). In iron-limiting conditions, this species develops alternative metabolic strategies such as highly efficient iron-uptake mechanisms which are only partially shared with S. epidermidis. Here we summarize the mechanisms induced by iron starvation in S. aureus in order to elucidate the virulence characteristics of this bacterium.

Influence of iron depletion on growth kinetics, siderophore production, and protein expression of Staphylococcus aureus

Growth rates, siderophore secretion, and bacterial proteins of two clinical isolates of Staphylococcus aureus were studied over 72 h of growth in iron-supplemented and iron-restricted chemically defined media. Under iron restriction the growth rates were decreased to different extents depending on the strain. Production of siderophore was detected in the mid-exponential and stationary phases of growth. The expression of iron-regulated proteins of 81, 23, and 17 kDa was time-dependent, associated with the same stage of growth, and might be involved in siderophore efficiency.