Metal phytostabilization by mastic shrub (Pistacia lentiscus L.) and its root-associated bacteria in different habitats of Sardinian abandoned mining areas (Italy).

Pistacia lentiscus L. is an excluder metallophyte proposed for the revegetation and phytostabilization of metal-contaminated sites in the Mediterranean area. The present study aims at evaluating the linking between bacterial communities and plants spontaneously growing in ecosystems chronically impacted by mining activities. Environmental properties and metal accumulation into hypogeal and epigeal tissues were analyzed in wild plants of two contrasting habitats with extreme metal contamination (> 2300 mg/kg for Zn, > 1100 mg/kg for Pb, > 10 mg/kg for Cd). The community structures of rhizospheric and root endophytic bacteria were fingerprinted by terminal restriction fragment length polymorphism of the 16S rRNA gene. The wild shrubs efficiently restrict the accumulation of the three major contaminants to the epigeal tissues in the two habitats under study (249 ± 68 mg/kg dw for Zn, 43 ± 21 mg/kg dw for Pb, and 1.4 ± 0.5 mg/kg dw for Cd). Evidence was provided that the combined but not individual effect of environmental conditions (moisture, inorganic carbon, pH) and proportion between Zn and Cd in the mine substrate play a role in structuring rhizosphere bacterial communities. The observed changes in community structures of root endophytes were found to be strongly associated with Pb level in roots and substrate properties (inorganic carbon and Zn/Cd ratio). Overall, our study highlights the importance of the analysis of multifactorial interactions among mine substrate, plant, and microbes for understanding how the environmental context affects phytoremediation under real conditions.

Molecular characterization of acinetobacter isolates collected in intensive care units of six hospitals in Florence, Italy, during a 3-year surveillance program: a population structure analysis.

The strain diversity and the population structure of nosocomial Acinetobacter isolated from patients admitted to different hospitals in Florence, Italy, during a 3-year surveillance program, were investigated by amplified fragment length polymorphism (AFLP). The majority of isolates (84.5%) were identified as A. baumannii, confirming this species as the most common hospital Acinetobacter. Three very distinct A. baumannii clonal groups (A1, A2, and A3) were defined. The A1 isolates appeared to be genetically related to the well-characterized European EU II clone. A2 was responsible for three outbreaks which occurred in two intensive care units. Space/time population dynamic analysis showed that A1 and A2 were successful nosocomial clones. Most of the A. baumannnii isolates were imipenem resistant. The genetic determinants of carbapenem resistance were investigated by multiplex PCR, showing that resistance, independently of hospital origin, period of isolation, or clonal group, was associated with the presence of a bla (OXA-58-like) gene and with ISAba2 and ISAba3 elements flanking this gene. bla (OXA-58) appeared to be horizontally transferred. This study showed that the high discriminatory power of AFLP is useful for identification and typing of nosocomial Acinetobacter isolates. Moreover the use of AFLP in a real-time surveillance program allowed us the recognition of clinically relevant and widespread clones and their monitoring in hospital settings. The correlation between clone diffusion, imipenem resistance, and the presence of the bla(OXA-58-like) gene is discussed.

Molecular surveillance and population structure analysis of methicillin-susceptible and methicillin-resistant Staphylococcus aureus in high-risk wards.

In this study we report the results of analysis of 253 isolates of Staphylococcus aureus (132 methicillin [meticillin]-resistant S. aureus [MRSA] isolates and 121 methicillin-susceptible S. aureus [MSSA] isolates) from 209 patients admitted to 18 high-risk wards of six hospitals located in Florence, Italy, over an 8-month period during which a program of epidemiological surveillance of hospital-acquired infections was conducted. The majority (69%) of the 87 reported S. aureus infections were caused by MRSA. No outbreak events have been reported. All the isolates were typed by amplified fragment length polymorphism (AFLP), and AFLP profiles were analyzed in order to define similarity groups. The discriminatory power of AFLP is very high with MSSA (Simpson index of diversity [D], 95.9%), whereas its resolution capability with MRSA (D, 44.7%) is hampered by the well-known high clonality of these populations (the main MRSA group accounted for 74% of the MRSA isolates). Combining AFLP, improved by visual inspection of polymorphisms, with multiplex PCR greatly increases MRSA resolution (D, 85.5%), resolving the MRSA population to a level that is one of the highest reported in the literature. Widespread and sporadic clones of MSSA and MRSA were identified, and their diffusion in the different hospitals and wards over the surveillance period was studied. The understanding of MSSA and MRSA population structures should be the starting point for the design of a more rational surveillance program for S. aureus species, maximizing benefits and reducing the cost of infection control strategies.