Maria del Mar Lleò

University of Verona, Verona, Veneto, Italy

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Publications (13)41.28 Total impact

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    ABSTRACT: Bacterial translocation seems to precede the occurrence of overt bacterial infection in patients with cirrhosis. The presence of bacterial DNA in blood and ascites correlates with bacterial translocation and is frequent in patients with advanced cirrhosis without overt infection. Our aim was to search for bacterial DNA in patients with cirrhosis both with and without ascites, and to study its correlation with abnormal intestinal motility or permeability and the presence of bacterial overgrowth. Blood and ascites samples were obtained on day 1, and blood samples were taken twice a day for the following 3 days. Bacterial DNA was assayed by polymerase chain reaction using universal primers for rRNA 16 s. Oro-caecal transit time and bacterial overgrowth were assessed with Lactulose H(2) breath testing. Intestinal permeability was assessed by determining urinary lactulose and mannitol excretion with high performance liquid chromatography. We studied seven patients (six were male, age range was 42-78 years). Aetiology was alcohol in four, HCV in two, HBV in one; ascites was present in four and Child-Pugh grade was A in four and B in three. All patients had increased intestinal permeability, six had decreased transit time and one had bacterial overgrowth. In only one patient (with ascites), polymerase chain reaction was positive for bacterial DNA both in ascites and serum for all 4 days on which samples were taken. Increased intestinal permeability and abnormal motility were frequent without evidence of bacterial translocation in cirrhosis even without ascites. They are likely to be facilitators for bacterial translocation and thus precede it.
    European journal of gastroenterology & hepatology 10/2010; 22(10):1228-34. DOI:10.1097/MEG.0b013e32833b4b03 · 2.15 Impact Factor
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    ABSTRACT: The viable but non-culturable (VBNC) state is a survival strategy adopted by bacteria when exposed to environmental stresses capable of inducing cell growth inhibition and cell death. This state can be summarized as a quiescent form of life waiting for suitable conditions. This strategy has been shown to be activated by medically important bacteria either when present in natural environments or in the human body during the infection process. In this study we have evaluated the effects of antibiotics acting on peptidoglycan or protein synthesis of Enterococcus faecalis in the VBNC state. The activity of the antibiotics was determined by their ability both to inhibit resuscitation (i.e. recovery of cell division) and to bind the molecular target of action. Benzylpenicillin, piperacillin and gentamicin block cell resuscitation at the minimal inhibitory concentrations (MICs) of growing cells, while vancomycin acts only at doses 500 times higher than the MIC. This different behaviour is discussed taking into consideration the mode of action of the antibiotics.
    Environmental Microbiology 10/2007; 9(9):2313-20. DOI:10.1111/j.1462-2920.2007.01345.x · 6.24 Impact Factor
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    ABSTRACT: Enterococci may survive in adverse environments including the human body where bacteriocins, antibiotics, iron-limitation and immune response represent stressing conditions for bacteria that cause division block. In those conditions, bacteria present in the human body would hardly be in an exponentially growing phase but would mostly be in physiological states such as starvation or the viable but nonculturable (VBNC) state. The possibility that the starved and VBNC bacteria can maintain their ability to adhere to living and inanimate substrates is the first mandatory step for them potentially to cause an infection process. In this study it is shown that starved and stationary enterococcal cells are able to form biofilms on plastic material albeit with reduced efficiency as compared to growing cells. Moreover, although VBNC enterococcal forms are not capable of forming biofilms, Enterococcus faecalis and other enterococcal species of medical interest maintain their ability to synthesize the polymeric matrix for a limited period of time under adverse environmental conditions. The data presented, together with those regarding the maintenance of the division recovery potential already proved in nonculturable bacteria, further support the possibility for the VBNC and other nondividing bacterial forms to have a role as infectious agents and to constitute a risk to human health.
    FEMS Microbiology Letters 10/2007; 274(2):232-7. DOI:10.1111/j.1574-6968.2007.00836.x · 2.72 Impact Factor
  • Maria del Mar Lleò · Caterina Signoretto · Pietro Canepari
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    ABSTRACT: The classic Gram-positive bacteria used as fecal contamination indicators are enterococci (fecal streptococci) and clostridia. However, many other Gram-positive bacteria of human origin or potentially human pathogens, such as staphylococci, listeriae, mycobacteria, bifidobacteria, may be present in seawater. The route for human infection by these microorganisms may be either by contact with water (Mycobacterium marinum, Mycobacterium balnei, Staphylococcus aureus) or byingestion of contaminatedwater or seafood (classicwater-borne diseases). Thus, a correct evaluation of the microbiological quality of marine water is fundamental for preventing human infection. The methods currently used to assess the microbiological quality of seawater are based only on culture, thus implying that nongrowing bacteria (unable to form colonies) are non-viable, i.e. dead. As is the case with many Gram-negative bacteria, certain survival strategies (e.g. the viable but nonculturable (VBNC) state) activated also by Gram-positive bacteria are at present under investigation. Such strategies allow the bacteria to survive and persist in a viable state even in oligotrophic stress-inducing conditions such as those present in the marine environment. In these conditions, many bacteria are shown to maintain their pathogenic potential (i.e. infectivity and transmissibility), and resuscitation (i.e. recovery of cell division) has been described upon restoration of suitable environmental conditions that coincides, for example, with ingestion by humans. As these bacterial forms may no longer be recoverable by culture, one could argue that culture methods alone would not be considered enough to protect human health. Thus, it could be postulated that culture-independent methods would be preferable.
    12/2006: pages 307-330;
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    Maria del Mar Lleò · Barbara Bonato · Dennis Benedetti · Pietro Canepari
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    ABSTRACT: Analysis of the survival ability of faecal streptococci/enterococci in the environment has almost invariably been conducted using the standard culture method (CFU counts) despite the demonstration that these microorganisms are capable of entering a viable but nonculturable (VBNC) state. In this study we evaluated the fate, in terms of culturability and viability, of different enterococcal species under laboratory stress conditions mimicking those of the aquatic environment. The results indicate that enterococcal species may activate two different survival strategies, namely starvation and the VBNC state, depending on the specific environmental condition. Moreover, the different enterococcal species can be divided into three groups on the basis of the time needed to activate the VBNC state and the resuscitation capability. The differences in activation of the two survival strategies and the different kinetics observed among the enterococcal species reaching the VBNC state should be taken into consideration when the microbiological quality of waters has to be evaluated and because of their role as faecal contamination indicators.
    FEMS Microbiology Ecology 11/2005; 54(2):189-96. DOI:10.1016/j.femsec.2005.03.016 · 3.88 Impact Factor
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    ABSTRACT: The presence of enterococci in lake and seawater in an 18-month survey comparing molecular (PCR and quantitative PCR) and culture methods was evaluated, as well as the possibility that zooplankton could act as reservoirs for enterococci. Samples of both water and zooplankton were collected monthly from a Lake Garda site and an Adriatic Sea site. In lake water, the positive samples numbered 13 of 54 (24%) by culture and 32 of 54 (59%) when PCR was applied. In seawater, they numbered 0 of 51 by culture and 18 of 51 (35%) by PCR. Enterococci were found either totally bound to plankton or totally in water, depending on the presence or absence of plankton, respectively. These results clearly indicate that the PCR assay is a powerful tool for detecting fecal indicators and pathogens in the environment, thus providing a much more sensitive method than culture.
    Applied and Environmental Microbiology 12/2004; 70(11):6892-6. DOI:10.1128/AEM.70.11.6892-6896.2004 · 3.95 Impact Factor
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    ABSTRACT: The effect of exposure to artificial sea water (ASW) on the ability of classical Vibrio cholerae O1 cells to interact with chitin-containing substrates and human intestinal cells was studied. Incubation of vibrios in ASW at 5 degrees C and 18 degrees C resulted in two kinds of cell responses: the viable but non-culturable (VBNC) state (i.e. <0.1 colony forming unit ml-1) at 5 degrees C, and starvation (i.e. maintenance of culturability of the population) at 18 degrees C. The latter remained rod shaped and, after 40 days' incubation, presented a 47-58% reduction in the number of cells attached to chitin, a 48-53% reduction in the number of bacteria adhering to copepods, and a 48-54% reduction in the number of bacteria adhering to human cultured intestinal cells, compared to control cells not suspended in ASW. Bacteria suspended in ASW at 5 degrees C became coccoid and, after 40 days, showed 34-42% fewer cells attached to chitin, 52-55% fewer adhering to copep-ods, and 45-48% fewer cells adhering to intestinal cell monolayers, compared to controls. Sarkosyl-insoluble membrane proteins that bind chitin particles were isolated and analysed by SDS-PAGE. After 40 days incubation in ASW at both 5 degrees C and 18 degrees C vibrios expressed chitin-binding ligands similar to bacteria harvested in the stationary growth phase. It is concluded that as vibrios do not lose adhesive properties after long-term exposure to ASW, it is important to include methods for VBNC bacteria when testing environmental and clinical samples for purposes of public health safety.
    Environmental Microbiology 10/2003; 5(10):850-8. DOI:10.1046/j.1462-2920.2003.00498.x · 6.24 Impact Factor
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    ABSTRACT: When exposed to stress-provoking environmental conditions such as those of ground waters, many medically important bacteria have been shown to be capable of activating a survival strategy known as the viable but non-culturable (VBNC) state. In this state bacteria are no longer culturable on conventional growth media, but the cells maintain their viability and pathogenicity genes/factors and can start dividing again, in a part of the cell population, upon restoration of favourable environmental conditions. Little is known about the genetic mechanisms underlying the VBNC state. In this study we show evidence of involvement of the rpoS gene in persistence of Escherichia coli in the VBNC state. The kinetics of entry into the non-culturable state and duration of cell viability were measured in two E. coli mutants carrying an inactivated rpoS gene and compared with those of the parents. For these experiments, laboratory microcosms consisting of an artificial oligotrophic medium incubated at 4 degrees C were used. The E. coli parental strains reached the non-culturable state in 33 days when the plate counts were evaluated on Luria-Bertani agar containing sodium pyruvate, whereas cells of the rpoS mutants lost their culturability in only 21 days. Upon reaching unculturability the parents yielded respiring cells and cells with intact membranes for at least the next three weeks and resuscitation was allowed during this time. In contrast, the RpoS- mutant cells demonstrated intact membranes for only two weeks and a very restricted (<7 days) resuscitation capability. Guanosine 3',5'-bispyrophosphate (ppGpp) acts as a positive regulator during the production and functioning of RpoS. A mutant deficient in ppGpp production behaved like the rpoS mutants, while overproducers of ppGpp displayed a vitality at least comparable to that of RpoS+ strains. These results suggest that the E. coli parental strains enter the VBNC state which lasts for, at least, three weeks, after which apparently all the cells die. The rpoS mutants do not activate this survival strategy and early die. This implies involvement of the rpoS gene in E. coli persistence in the VBNC state.
    Environmental Microbiology 10/2003; 5(10):986-96. DOI:10.1046/j.1462-2920.2003.00497.x · 6.24 Impact Factor
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    ABSTRACT: Stressed vancomycin-resistant enterococci (VRE) can activate a survival strategy known as the viable but nonculturable (VBNC) state and are able to maintain vancomycin resistance. During restoration of division they continue to express the vancomycin resistance trait. We suggest that VBNC enterococci may constitute further reservoirs of VRE and therefore represent an additional risk for human health.
    Antimicrobial Agents and Chemotherapy 04/2003; 47(3):1154-6. DOI:10.1128/AAC.47.3.1154-1156.2003 · 4.45 Impact Factor
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    ABSTRACT: The protein expression patterns of exponentially growing, starved, and viable but nonculturable (VBNC) Enterococcus faecalis cells were analyzed to establish whether differences exist between the VBNC state and other stress responses. The results indicate that the protein profile of VBNC cells differs from that of either starved or exponentially growing bacteria. This demonstrates that the VBNC state is a distinct physiological phase within the life cycle of E. faecalis, which is activated in response to multiple environmental stresses.
    Journal of Bacteriology 01/2003; 184(23):6739-45. DOI:10.1128/JB.184.23.6739-6745.2002 · 2.69 Impact Factor
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    ABSTRACT: The ability of viable but nonculturable (VBNC) Enterococcus faecalis to adhere to Caco-2 and Girardi heart cultured cells and to urinary tract epithelial cells (ECs) was studied. Enterococci were harvested during the vegetative growth phase (early exponential and stationary), in the VBNC state, and after recovery of the ability to divide. VBNC bacteria maintained their adherence capability but the efficiency of attachment was reduced by about 50 to 70%, depending on the target cell employed. The decrease was transient, since enterococci that regained their culturability showed adherence values similar to those observed for actively growing cells. Analysis of the invasive properties of E. faecalis revealed that the VBNC state caused a decrease in the number of bacteria that entered the cultured HEK cells as a result of the reduction in the number of adhering bacteria. These results highlight the importance of studies of the VBNC phenomenon, with respect to both microbial survival in the environment and the impact on human health.
    Current Microbiology 09/2002; 45(2):105-10. DOI:10.1007/s00284-001-0089-2 · 1.36 Impact Factor
  • Caterina Signoretto · Maria Mar Lleò · Pietro Canepari
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    ABSTRACT: The aim of this study was to analyse the chemical composition of peptidoglycan and the state of some of the enzymes involved in its metabolism in Escherichia coli KN126 in the viable but nonculturable (VBNC) state which is a survival strategy adopted by bacteria (including those of medical interest) when exposed to environmental stresses. When entering the VBNC state, E. coli cells miniaturised and became coccus-shaped. Analysis of peptidoglycan chemical composition, by separation in HPLC of muropeptides released by muramidase digestion of purified peptidoglycan, indicated a high degree of cross-linking, a threefold increase in unusual DAP-DAP cross-linking, an increase in muropeptides bearing covalently bound lipoprotein, and a shortening of the average length of glycan strands in comparison with dividing cells. Analysis of penicillin-binding proteins (PBPs), enzymes involved in the terminal stage of peptidoglycan assembly showed the disappearance of high-molecular-weight PBPs 1A, 1B, 2, and 3 in VBNC cells. Finally, VBNC cells displayed an autolytic capability which was far higher than that of exponentially growing cells. It is suggested that part of these alterations of peptidoglycan may be connected with the VBNC state.
    Current Microbiology 03/2002; 44(2):125-31. DOI:10.1007/s00284-001-0062-0 · 1.36 Impact Factor
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    ABSTRACT: ~ ~~~ A series of thermosensitive cell growth mutants of Enterococcus hirae have been isolated. Most of these mutants elongate and some show reduced autolytic activity when incubated at the non-permissive temperature (42 "C) in comparison to the wild-type incubated at the same temperature. When mutants were incubated for longer than 15 min at 42 "C and were then shifted to 30 "C, a lag proportional to the time of preincubation at 42 "C was observed before division, indicating that a certain time is necessary to restore normal levels of an active molecule(s) needed for septum formation and division. The addition of wild-type muramidase-1 permitted the immediate formation of septa and a single cell division; further addition of the enzyme stimulated the cells to divide once again. The other E. hivae autolytic enzyme, peptidoglycan-hydrolase-2, which is found in the culture medium, seemed to be involved in separation of daughter cells but may also take over the function of muramidase-1. A key role of both enzymes in septum formation and division is postulated.
    Journal of general microbiology 12/1993; 139(12):3099-3107. DOI:10.1099/00221287-139-12-3099

Publication Stats

452 Citations
41.28 Total Impact Points


  • 1993–2010
    • University of Verona
      • • Section of Microbiology
      • • Department of Philology, Literature and Linguistics
      Verona, Veneto, Italy
  • 2004
    • Università Politecnica delle Marche
      Ancona, The Marches, Italy