Biomedical subjects
F D Daschner
Publications and source records attributed to F D Daschner.
Microbiological contamination of drinking water in a commercial household water filter system.
The microbiological quality of filtered water in a commercial water filter system (Brita) was tested in households and in two laboratories. In 24 of 34 filters used in households, bacterial counts increased in the filtered water up to 6,000 cfu/ml. In 4 of 6 filters tested in the laboratory, bacterial counts in the fresh filtrate were higher than in tap water after approximately one week of use both at room temperature and at 4 degrees C, suggesting growth or biofilm formation in the filter material. In some cases colony counts in the filtered water were 10,000 times those in tap water. The filter material of 5 of 13 new commercial filters was contaminated with bacteria or moulds. National or international regulatory agencies should ensure that water filters marketed for domestic use do not allow deterioration in the microbiological quality of drinking water.
Killing activity of microwaves in milk.
The killing activity of microwaves of 2450 MHz frequency and 600 W power on Pseudomonas aeruginosa, Escherichia coli, Enterobacter sakazakii, Klebsiella pneumoniae, Staphylococcus aureus, Candida albicans, Mycobacterium terrae and poliomyelitis vaccine-virus suspended in five infant formula preparations was investigated. The samples were brought to the boil (85-100 s depending on milk type). They had reached average temperatures of 82-93 degrees C at this point. Most of the vegetative organisms were killed. In those samples where growth was still detectable after microwave treatment, a significant reduction in viable micro-organisms (at least 5000-fold) was noted. We conclude that microwave beating to the boil is a convenient and fast method to reduce microbial contamination of infant feeds. However, care should be taken to ensure that milk is adequately cooled to the required temperature before it is fed to an infant.
Acinetobacter species identification by using tRNA spacer fingerprinting.
Identification of Acinetobacter spp. to the DNA group level by phenotypic techniques is problematic, and there is a need for an alternative identification method for routine use. The present study validated the suitability of a rapid identification technique based on tRNA spacer (tDNA) fingerprinting in comparison with that of a commercially available assay involving carbon source utilization tests (Biolog MicroStation System) for identifying the 21 DNA-DNA hybridization groups belonging to the genus. For this purpose, 128 strains identified previously by DNA-DNA hybridization were analyzed by both techniques. tDNA fingerprinting was highly reproducible and classified all strains into 17 groups. Six DNA groups belonging to the A. calcoaceticus-A. baumannii complex were grouped into two distinct clusters, indicating the high degree of genetic similarity within this complex. Strains of the more recently described DNA groups BJ13 to BJ16 were ambiguously grouped and displayed three pattern types. The software used with the commercial carbon source utilization method grouped the 128 strains into 12 clusters, explaining the less discriminatory power of this system. We conclude that tDNA fingerprinting offers a quick and reliable method for the routine differentiation of most Acinetobacter spp. at the subgenus level.
Fluorescence-based DNA fingerprinting elucidates nosocomial transmission of phenotypically variable Pseudomonas aeruginosa in intensive care units.
DNA fingerprinting based on automated laser fluorescence analysis of randomly amplified polymorphic DNA (RAPD-ALFA) is a rapid and convenient technique for detecting clonal relatedness of bacterial isolates of nosocomial concern. During an outbreak of Pseudomonas aeruginosa among five patients in a medical intensive care unit, transmission was not suspected because of the phenotypic variability of the initial isolates. However, DNA fingerprinting by RAPD-ALFA and macrorestriction analysis identified a single genotype (strain A) for isolates from three patients and another genotype (strain B) for isolates from the remaining two patients. Strain A isolates displayed three phenotypes defined by different antibiotypes and distinct colony appearance. Retrospective analysis of DNA fingerprints demonstrated that strain A had been transmitted to the index patient one year previously in a different intensive care unit. The study demonstrates that genetic typing approaches are warranted should epidemiological relatedness be identified between phenotypically variant pathogens. Automated laser fluorescence analysis of PCR fingerprints may facilitate routine screening of bacterial isolates for in-house epidemiological surveillance. Antibiograms are an unsuitable approach for the typing of Pseudomonas aeruginosa.
Combined effect of human neutrophils, ceftazidime and granulocyte colony-stimulating factor on killing of Escherichia coli.
The combination effect of subinhibitory and inhibitory concentrations of ceftazidime, granulocyte colony-stimulating factor (G-CSF) and polymorphonuclear leukocytes (PMNL) against Escherichia coli was investigated. PMNL obtained from healthy volunteers were incubated with different concentrations of G-CSF and ceftazidime for 180 min. The addition of 0.25 x MIC of ceftazidime or 1 x MIC significantly enhanced the bactericidal activity of PMNL. G-CSF at a concentration of 6,000 units/ml led to only a slight improvement in the bactericidal activity of PMNL. The combination of 6,000 units/ml G-CSF and ceftazidime in inhibitory as well as subinhibitory concentrations, however, showed a significant synergistic effect (p < 0.01) on the antibacterial activity of PMNL during the entire incubation period. Combinations of G-CSF and antibiotics could therefore be beneficial for infected patients, especially those with impaired cellular host defence.
Low birth weight and nosocomial infection of neonates in a neonatal intensive care unit.
A one year prospective surveillance of nosocomial infections (NI) in a neonatal intensive care unit (NICU) was performed. Among 229 neonates the infection rate was 27.1%, the infection proportion 20.1%, and the incidence density 21.9 infections per 1000 patient days. Infants were stratified into four birth weight categories. Degrees of infection ranged from 44.4% in the < or = 1000 g group to 10.1% in the > 2500 g group. Differences between the groups were statistically significant (P < 0.01). The mean birth weight of infants with NI was significantly lower than that of infants without NI (1711 g, SD +/- 841 g vs. 2213 g, SD +/- 896 g; P < 0.01). Mortality of < or = 1000 g babies was 44.4 and 7.6% in > 2500 g neonates. Major sites of infection were pneumonia (32.3%), blood-stream infections (27.4%), infections of the skin, and surgical site infections (11.3% each). The predominant pathogen was Staphylococcus aureus (24.2%) whilst Gram-negative bacteria accounted for 22.7% of the total. Other major infective agents were Staphylococcus epidermidis, Escherichia coli, and Group B streptococci. It is concluded, that low birth weight was a major risk factor for the acquisition of NI in the observed NICU population.
Brita water filters contaminated.
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Serum bactericidal activity against Moraxella catarrhalis and Streptococcus pneumoniae after administration of four oral cephalosporins in healthy volunteers.
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Automated laser fluorescence analysis of randomly amplified polymorphic DNA: a rapid method for investigating nosocomial transmission of Acinetobacter baumannii.
A rapid method for genotyping Acinetobacter baumannii based on PCR-fingerprinting with fluorescent primers was evaluated. Automated laser fluorescence analysis (ALFA) enabled on-line generation of high resolution DNA-fingerprints during polyacrylamide gel electrophoresis of randomly amplified polymorphic DNA (RAPD) products. The results were in concordance with macro-restriction fragment patterns produced by pulse-field gel electrophoresis (PFGE) of ApaI digests of chromosomal DNA. RAPD-ALFA was able to identify homologous strains suggestive of horizontal transmission in < 8 h after colonies were obtained on solid media, whereas PFGE analysis took c. 90 h. Speed and digitised data format renders RAPD-ALFA attractive for routine in-house epidemiological screening of isolates from intensive care and other hospital units.
Discriminatory power of three DNA-based typing techniques for Pseudomonas aeruginosa.
We assessed the capacity of three DNA typing techniques to discriminate between 81 geographically, temporally, and epidemiologically unrelated strains of Pseudomonas aeruginosa. The methods, representing powerful tools for hospital molecular epidemiology, included hybridization of restricted chromosomal DNA with toxA and genes coding for rRNA (rDNA) used as probes and macrorestriction analysis of SpeI-digested DNA by pulsed-field gel electrophoresis. The probe typing techniques were able to classify all strains into a limited number of types, and the discriminatory powers were 97.7 and 95.6% for toxA and rDNA typing, respectively. Strains that were indistinguishable on the basis of both toxA and rDNA types defined 12 probe type homology groups. Of these, one contained five strains, three contained three strains each, and eight groups were represented by two strains each. Strains in 10 of the homology groups had the same O serotype. SpeI macrorestriction patterns discriminated between all strains with at least four band differences, which corresponded to a similarity level of 85%. Fifteen pairs of strains were similar at a level of > 75% and differed by only four to seven bands. Of these pairs, 11 belonged to the same probe type homology group, indicating their clonal relatedness. We conclude that macrorestriction analysis of P. aeruginosa with SpeI provides the best means of discrimination between epidemiologically unrelated strains. However, DNA probe typing with either toxA or rDNA reveals information on the strain population structure and evolutionary relationships.
Glycopeptides in the treatment of staphylococcal infections.
Gram-positive bacteria are rapidly becoming the most important pathogens in nosocomial infections. In recent years, attention and concern have been focused on the gram-positive bacteria, Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. These microorganisms are well equipped to exert their pathogenic effects and to display virulence. Treatment of severe infections caused by gram-positive bacteria remains difficult because of the increase in infections caused by methicillin-resistant staphylococci, and this has renewed interest in the glycopeptide antibiotics, vancomycin and teicoplanin. According to National Nosocomial Infection Surveillance Study data, in 1989, 60% of coagulase-negative staphylococci and 22% of Staphylococcus aureus strains showed methicillin resistance. Among other factors, successful antimicrobial therapy depends on rapid and reliable antibiotic delivery to the infection site at a concentration adequate to inhibit the majority of infecting organisms. Glycopeptides may be important in the therapy of catheter-related infections, which are mainly caused by coagulase-negative staphylococci and Staphylococcus aureus.
Bactericidal activity of clarithromycin and cefaclor against Streptococcus pneumoniae and Moraxella catarrhalis in healthy volunteers.
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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.
In vitro activity of vancomycin and teicoplanin against Staphylococcus aureus and Staphylococcus epidermidis colonizing catheters.
In a quantitative in vitro model the activity of vancomycin and teicoplanin in two concentrations (4 x MBC and 1 mg/l) against Staphylococcus aureus and a slime-producing Staphylococcus epidermidis strain colonizing the internal surface of polyurethane and silicone catheters was studied. In comparison with vancomycin, teicoplanin achieved a significantly greater reduction (p < 0.05) in the counts of Staphylococcus aureus and Staphylococcus epidermidis adhering to both polyurethane and silicone catheters.
Serum bactericidal activity after administration of four cephalosporins in healthy volunteers.
Serum bactericidal activity (SBA) was determined against ten strains each of Staphylococcus aureus, Klebsiella pneumoniae, Proteus vulgaris and Enterobacter cloacae in six volunteers 1 h and 4 h after intravenous infusion of 1 g and 2 g cefotaxime and cefmenoxime, and 2 g flomoxef, and against ten strains of Pseudomonas aeruginosa after infusion of 1 g and 2 g ceftazidime. Flomoxef showed the highest SBA against methicillin-susceptible Staphylococcus aureus. All cephalosporins had high SBA against gram-negative rods. Cefotaxime had the highest SBA against Klebsiella pneumoniae and Enterobacter cloacae. The SBA against Pseudomonas aeruginosa after 1 g and 2 g doses of ceftazidime was very similar.
Comparison of three typing methods in hospital outbreaks of Acinetobacter calcoaceticus infection.
During a period of 11 months Acinetobacter baumanii was isolated from 27 patients and 21 environmental samples in the Intensive Care Unit (ICU) and in one surgical unit of a University Hospital. The isolates were characterized by biotyping, antibiograms and plasmid profiles and compared with co-isolates. Plasmid fingerprinting distinguished three outbreaks, whereas other typing methods were less sensitive and discriminatory. Although plasmid profiles seem to be a simple and reproducible marker for epidemiological studies with acinetobacter strains, it might be useful to combine at least two typing methods since plasmids are unstable genetic structures, and not all strains possess plasmids.
Chemical disinfection of medical waste--a totally wrong approach.
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