Use of pharmacodynamic parameters to predict efficacy of combination therapy by using fractional inhibitory concentration kinetics

Combination therapy with antimicrobial agents can be used against bacteria that have reduced susceptibilities to single agents. We studied various tobramycin and ceftazidime dosing regimens against four resistant Pseudomonas aeruginosa strains in an in vitro pharmacokinetic model to determine the usability of combination therapy for the treatment of infections due to resistant bacterial strains. For the selection of an optimal dosing regimen it is necessary to determine which pharmacodynamic parameter best predicts efficacy during combination therapy and to find a simple method for susceptibility testing. An easy-to-use, previously described E-test method was evaluated as a test for susceptibility to combination therapy. That test resulted in a MICcombi, which is the MIC of, for example, tobramycin in the presence of ceftazidime. By dividing the tobramycin and ceftazidime concentration by the MICcombi at each time point during the dosing interval, fractional inhibitory concentration (FIC) curves were constructed, and from these curves new pharmacodynamic parameters for combination therapy were calculated (i.e., AUCcombi, Cmax-combi, T>MIC-combi, and T>FICi, where AUCcombi, Cmax-combi, T>MIC-combi, and T>FICi are the area under the FICcombi curve, the peak concentration of FICcombi, the time that the concentration of the combination is above the MICcombi, and the time above the FIC index, respectively). By stepwise multilinear regression analysis, the pharmacodynamic parameter T>FICi proved to be the best predictor of therapeutic efficacy during combination therapy with tobramycin and ceftazidime (R2 = 0.6821; P < 0.01). We conclude that for combination therapy with tobramycin and ceftazidime the T>FICi is the parameter best predictive of efficacy and that the E-test for susceptibility testing of combination therapy gives promising results. These new pharmacodynamic parameters for combination therapy promise to provide better insight into the rationale behind combination therapy

Electronically assisted surveillance systems of healthcare-associated infections: a systematic review

BackgroundSurveillance of healthcare-associated infections (HAI) is the basis of each infection control programme and, in case of acute care hospitals, should ideally include all hospital wards, medical specialties as well as all types of HAI. Traditional surveillance is labour intensive and electronically assisted surveillance systems (EASS) hold the promise to increase efficiency.ObjectivesTo give insight in the performance characteristics of different approaches to EASS and the quality of the studies designed to evaluate them.MethodsIn this systematic review, online databases were searched and studies that compared an EASS with a traditional surveillance method were included. Two different indicators were extracted from each study, one regarding the quality of design (including reporting efficiency) and one based on the performance (e.g. specificity and sensitivity) of the EASS presented.ResultsA total of 78 studies were included. The majority of EASS (n = 72) consisted of an algorithm-based selection step followed by confirmatory assessment. The algorithms used different sets of variables. Only a minority (n = 7) of EASS were hospital-wide and designed to detect all types of HAI. Sensitivity of EASS was generally high (> 0.8), but specificity varied (0.37-1). Less than 20% (n = 14) of the studies presented data on the efficiency gains achieved.ConclusionsElectronically assisted surveillance of HAI has yet to reach a mature stage and to be used routinely in healthcare settings. We recommend that future studies on the development and implementation of EASS of HAI focus on thorough validation, reproducibility, standardised datasets and detailed information on efficiency

Serotyping, ribotyping, PCR-mediated ribosomal 16S-23S spacer analysis and arbitrarily primed PCR for epidemiological studies on Legionella pneumophila

Fifty clinical and environmental isolates of Legionella pneumophila were typed serologically and by DNA fingerprinting using arbitrarily primed polymerase chain reaction (AP-PCR). Furthermore, variability in and around ribosomal operons was assessed by conventional ribotyping and PCR-mediated amplification of the spacer region separating the 16S and 23S genes. It appears that serotyping suffers from low resolution capabilities, and ribotyping and spacer PCR display intermediate resolving capabilities, whereas AP-PCR is more discriminating. Results from AP-PCR and both forms of ribotyping analysis correlate with epidemiological and environmental data. It is suggested that AP-PCR typing may be the method of choice for rapidly determining clonality among L. pneumophila isolates

Patient-to-patient spread of a single strain of Corynebacterium striatum causing infections in a surgical intensive care unit

Over a 12-month period, Corynebacterium striatum strains were isolated from clinical specimens from 14 patients admitted to a surgical intensive care unit. These isolates were identical by morphology and biotype and displayed the same antibiogram. Ten isolates were found to be the sole possible pathogen. These 10 isolates were from six patients, three of whom had signs of infection at the time of positive culture. Further typing was performed by random amplification of polymorphic DNA analysis, by which all strains were identical and were found to differ to various degrees from reference strains and from isolates found in clinical samples from other wards. In a case-control study the only independent risk factor for acquiring the strain was intubation for longer than 24 h (odds ratio, 20.09; 95

Density and molecular epidemiology of Aspergillus in air and relationship to outbreaks of Aspergillus infection

After five patients were diagnosed with nosocomial invasive aspergillosis caused by Aspergillus fumigatus and A. flavus, a 14-month surveillance program for pathogenic and nonpathogenic fungal conidia in the air within and outside the University Hospital in Rotterdam (The Netherlands) was begun. A. fumigatus isolates obtained from the Department of Hematology were studied for genetic relatedness by randomly amplified polymorphic DNA (RAPD) analysis. This was repeated with A. fumigatus isolates contaminating culture media in the microbiology laboratory. The density of the conidia of nonpathogenic fungi in the outside air showed a seasonal variation: higher densities were measured during the summer, while lower densities were determined during the fall and winter. Hardly any variation was found in the numbers of Aspergillus conidia. We found decreasing numbers of conidia when comparing air from outside the hospital to that inside the hospital and when comparing open areas within the hospital to the closed department of hematology. The increase in the number of patients with invasive aspergillosis could not be explained by an increase in the number of Aspergillus conidia in the outside air. The short-term presence of A. flavus can only be explained by the presence of a point source, which was probably patient related. Genotyping A. fumigatus isolates from the department of hematology showed that clonally related isolates were persistently present for more than 1 year. Clinical isolates of A. fumigatus obtained during the outbreak period were different from these persistent clones. A. fumigatus isolates contaminating culture media were all genotypically identical, indicating a causative point source. Kn

Survival of Chlamydia pneumoniae following contact with various surfaces

Objective: In this study, the survival and recovery of Chlamydia pneumoniae (Cp) strains TW‐183, AR‐39, AR‐388 and CWL‐029 were measured after inoculation on glass, stainless steel, FormicaR laminate, paper, fabric and human skin. Methods: Inoculum in throat washes from healthy volunteers was applied to each surface. Samples were taken immediately after inoculum application and at specified intervals thereafter to determine infectivity. Results: Infectious Cp was recovered from glass for up to 4 h, from paper and fabric for up to 3 h, from FormicaR laminate for up to 2 h, from stainless steel for up to 60 min and from human skin for up to 30 min. Drying of the inoculated area had no significant effect on the recovery of infectious Cp. Further experiments demonstrated that infectious Cp could be transferred to hands by touching these contaminated surfaces and could be recovered from these hands for up to 3 min. Addition of albumin, surfactant or phosphatidylcholine had no significant effect on the survival of Cp. Conclusions: These results suggest that contact with contaminated surfaces may be a potential mode of transmission of Cp. 1995 European Society of Clinical Microbiology and Infectious Disease

Rapid detection of methicillin resistance in Staphylococcus aureus isolates by the MRSA-screen latex agglutination test

The slide agglutination test MRSA-Screen (Denka Seiken Co., Niigata, Japan) was compared with the mecA PCR ("gold standard") for the detection of methicillin resistance in Staphylococcus aureus. The MRSA-Screen test detected the penicillin-binding protein 2a (PBP2a) antigen in 87 of 90 genetically diverse methicillin-resistant S. aureus (MRSA) stock culture strains, leading to a sensitivity of 97%. The three discrepant MRSA strains displayed positive results only after induction of the mecA gene by exposure to methicillin. Both mecA PCR and MRSA-Screen displayed negative results among the methicillin-susceptible S. aureus strains (n = 106), as well as for Micrococcus spp. (n = 10), members of the family Enterobacteriaceae (n = 10), Streptococcus pneumoniae (n = 10), and Enterococcus spp. (n = 10) (specificity = 100%). Producing the same PBP2a antigen, all 10 methicillin-resistant Staphylococcus epidermidis strains score positived in both the latex test and the mecA PCR. Consequently, the MRSA-Screen test should be applied only after identification of the MRSA strain to the species level to rule out coagulase-negative staphylococci. In conclusion, due to excellent specificity and sensitivity the MRSA-Screen latex test has the potential to be successfully used for routine applications in the microbiology laboratory

Liposomal amphotericin B (AmBisome) reduces dissemination of infection as compared with amphotericin B deoxycholate (Fungizone) in a rate model of pulmonary aspergillosis

The efficacy of AmBisome, a liposomal formulation of amphotericin B, was compared with that of Fungizone (amphotericin B desoxycholate), in a rat model of unilateral, pulmonary aspergillosis. Repeated administration of cyclophosphamide resulted in persistent, severe granulocytopenia. The left lung was inoculated with a conidial suspension of Aspergillus fumigatus, thus establishing an unilateral infection. Antifungal treatment was started 40 h after fungal inoculation, at which time mycelial disease was confirmed by histological examination. Both Fungizone 1 mg/kg and AmBisome 10 mg/kg resulted in increased survival in terms of delayed as well as reduced mortality. Quantitative cultures of lung tissue showed that only AmBisome 10 mg/kg resulted in reduction of the number of fungal cfus in the inoculated left lung. Compared with Fungizone, both AmBisome 1 mg/kg/day and AmBisome 10 mg/kg/day significantly prevented dissemination from the infected left lung to the right lung. In addition, both AmBisome regimens reduced hepatosplenic dissemination, and the 10 m/kg dosage fully prevented this complication. In conclusion, when compared with Fungizone, in this model AmBisome is more effective in reducing dissemination of unilateral, pulmonary aspergillosis, even when given in relatively low dosage. Such low dosages may have a place in prophylactic settings

High-throughput typing of Staphylococcus aureus by amplified fragment length polymorphism (AFLP) or multi-locus variable number of tandem repeat analysis (MLVA) reveals consistent strain relatedness

This study investigates aspects of the general assumption that, in bacteria, genetic variation in functionally-constrained genomic regions accumulates at a lower rate than in regions of hypermutability such as DNA repeat loci. We compared whole genome polymorphism (using high-throughput amplified fragment length polymorphism [ht-AFLP]) as well as short sequence repeat length variation (using multi-locus variable number of tandem repeat analysis [MLVA]) for 994 Staphylococcus aureus strains isolated from both healthy carriers and invasive infections. MLVA and ht-AFLP minimum spanning trees (MSTs) were similar in their identification of totally different types of genetic variants. This suggests that, despite the enhanced inherent variability of repeats, clusters of strains remain traceable. Finally, no specific molecular marker of epidemicity or virulence was identified in this large strain collection by the MLVA approach. We demonstrate that there is a difference in the rates of cross-genome mutation versus regional repeat variability in the clonal bacterial pathogen S. aureus. Despite these dynamic differences, a conservation of type assignments as based upon these two inherently different typing techniques was observed