Piero Micheletti

Repeated Epidemics Caused by Extended-Spectrum Beta-Lactamase-Producing Serratia marcescens Strains

An outbreak ofSerratia marcescens involving 42 patients admitted to the general intensive care unit of the Hospital of Varese, Italy, occurred from March 1994 to August 1995. The causative strains were resistant to oxyimino-cephalosporins and monobactams due to their production of an extended-spectrumβ-lactamase. Another outbreak caused bySerratia marcescens strains had occurred in the same unit a few months earlier, from February to October 1993, with the strains involved producing a novel TEM-derived extended-spectrumβ-lactamase. In order to verify whether there were any relationships between isolates from the two epidemics, the strains and their enzymes were characterized. Biochemical data and gene amplification experiments showed that the isolates of the second outbreak harbored a non-conjugative plasmid of approximately 48 kb, codifying for the production of an SHV-derived extended-spectrumβ-lactamase with pI 8.2. Restriction fragment length polymorphism analysis of total genomic DNA by pulsed-field gel electrophoresis ofSerratia marcescens isolates unambiguously identified two different bacterial clones responsible for the two epidemics. Epidemiological and microbiological investigations demonstrated the long persistence ofSerratia marcescens strains and their circulation in other hospital wards, thus suggesting their possible role as a long-term reservoir for further epidemic spread.

Comparative activity of piperacillin/tazobactam against clinical isolates of extended-spectrum β-lactamase-producing enterobacteriaceae

β-Lactam resistance on the part of the Enterobacteriaceae causes serious therapeutic problems in our institutions due to their production of extended-spectrum β-lactamases (ESβLs). We studied the in vitro activity of β-lactam/β-lactamase inhibitor combinations and third-generation cephalosporins and monobactams against 71 clinically relevant Enterobacteriaceae which produced TEM- and SHV-derivative ESβLs. Of the single drugs and combinations tested, piperacillin/tazobactam proved to be the most effective. Piperacillin/tazobactam was highly active against Proteus mirabilis, with minimum inhibitory concentrations (MICs) ranging from 0.125 to 16 µg/ml; Escherichia coli (MICs from 2 to 16 µg/ml) and Serratia marcescens (MICs from 4 to 8 µg/ml), while its activity against Klebsiella pneumoniae ESβL producers turned out to be closely related to the type and the amount of enzyme produced, the MIC ranging from 1 to 128 µg/ml. The antibacterial activity of piperacillin/tazobactam was stronger than that of ticarcillin/clavulanate, ceftriaxone, cefotaxime, ceftazidime and aztreonam, and the combination shared favorable in vitro activity properties against the ESβL producers with imipenem which, however, should be kept as reserve product.

Molecular characterisation of the nucleic acids recovered from aged forensic samples.

Abstract.The molecular composition of the genetic substrate recovered from seven aged forensic samples has been extensively investigated. A simple enzymatic test based on DNAseI incubation of the extracts showed that the UV-fluorescent material from the forensic specimens is composed of nucleic acids, with the DNA fraction representing at least 90% of the total amount. Since spectrophotometric determinations of the extracts showed unreliable results due to anomalous OD260/OD280 ratios, quantification of the nuclease-sensitive genetic material was performed by a slightly modified agarose plate method. The first quantitative data on exogenous contamination in aged forensic samples are provided by slot-blot hybridisation of the extracts to human, bacterial and fungal probes. Only limited amounts of human and contaminant DNA were detected in the samples. The molecular integrity of the primary structure of these aged DNA samples was analysed by reversed-phase HPLC/MS. The data show a good correlation between the degree of chemical damage and the ability to hybridise to molecular probes. The ability to achieve specific genetic profiles was assessed by multiplex PCR amplification of STR loci. Our data show that accurate determination of the molecular composition of the DNA recovered from forensic samples can be extremely useful for a reliable evaluation of the PCR typing results.

Are physicians aware enough of patient radiation protection? Results from a survey among physicians of Pavia District– Italy

BackgroundRadiological practices are the first anthropic sources of ionizing radiation exposure of the population. However, a review of recent publications underlines inadequate doctors’ knowledge about doses imparted in medical practices and about patient protection that might explain unnecessary radiological prescriptions. We investigated the knowledge of the physicians of Pavia District (Italy) on the risk of radiation exposure.MethodsA cross sectional study was performed involving the Medical Association of Pavia District. Data were collected with a self-administered questionnaire, available on-line with private login and password.ResultsFour hundred nineteen physicians fulfilled the questionnaire; 48% of participants reported training about radiation protection. The average percentage of correct answers on the knowledge on ionizing radiation was 62.29%, with a significantly higher result between radiologist. Around 5 and 13% of the responders do not know that, respectively, ultrasonography and magnetic resonance do not expose patients to ionizing radiations. Only 5% of the physicians properly identified the cancer risk rate associated to abdomen computed tomography.ConclusionsThe findings show a quite good level of the general knowledge about ionizing radiations, higher that reported in literature. Nevertheless, we believe the usefulness of training on the risk linked to radiation exposure in medicine for physicians employed in every area.