The effect of sub-inhibitory concentrations of rifaximin on urease production and on other virulence factors expressed by Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa and Staphylococcus aureus.

Rifaximin, a topical derivative of rifampin, inhibited urease production and other virulence factors at sub-MIC concentrations in strains involved in hepatic encephalopathy and the expression of methicillin resistance in Staphylococcus aureus. In particular, urease production was affected in all Proteus mirabilis and Klebsiella pneumoniae strains as well as in all tested Pseudomonas aeruginosa isolates. Other exotoxins, synthesized by P. aeruginosa, such as protease, gelatinase, lipase, lecithinase and DNAse were also not metabolized in the presence of rifaximin. This antibiotic inhibited pigment production in both P. aeruginosa and Chromobacterium violaceum, a biosensor control strain. Lastly, rifaximin affected haemolysin production in S. aureus and was able to restore cefoxitin susceptibility when the strain was cultured in the presence of sub-MICs of the drug. The present findings confirm and extend previous observations about the beneficial effects of rifaximin for the treatment of gastrointestinal diseases, since in this anatomic site, it reaches a large array of concentrations which prevents enterobacteria from thriving and/or producing their major virulence factors.

Antimicrobial effect of MTAD, Tetraclean, Cloreximid, and sodium hypochlorite on three common endodontic pathogens.

OBJECTIVES: The aim of this in vitro study was to evaluate the antimicrobial action of BioPure MTAD (Dentsply Tulsa Dental, Johnson City, TN), Tetraclean, Cloreximid (a mixture of Chlorhexidine (CHX) digluconate and Cetrimide), and 5.25% NaOCl (Ogna Laboratori Farmaceutici, Milano, Italy) against selected endodontic pathogens (Enterococcus faecalis, Porphyromonas gingivalis, and Prevotella intermedia). MATERIALS AND METHODS: The agar plate diffusion procedure was used to observe the antimibrobial activity of irrigants. RESULTS: Statistical analysis revealed significant effects of the different irrigants on the bacteria colonies. Treatment with 5.25% NaOCl induced a larger zone of microbial inhibition in Prevotella intermedia and Porphyromonas gingivalis (Tukey HSD post-test, P = 0.0001) when compare to MTAD, Tetraclean and CHX. Anyway, MTAD and Tetraclean were more effective to inhibit bacterial growth compared to CHX (P < 0.0001, Tukey HSD post-test). Furthermore, post hoc analysis revealed that MTAD and Tetraclean induced the largest zone of microbial inhibition of Enterococcus faecalis cultured under both aerobic and anaerobic conditions, when compared with 2% CHX and NaOCl (P < 0.0001, Tukey HSD post-test). The control group showed no microbial inhibition. CONCLUSION: 5.25% NaOCl showed a high antimicrobial activity against anaerobic bacteria. MTAD and Tetraclean showed a high action against both, strictly anaerobic and facultative anaerobic bacteria. Chlorexidine + Cetrimide (Cloreximid) showed the lowest antibacterial activity against both, facultative and strictly anaerobic bacteria tested.

In vitro interaction between mecillinam and piperacillin-tazobactam in the presence of azithromycin against members of the Enterobacteriaceae family and Pseudomonas aeruginosa.

Mecillinam was tested in vitro alone or in combination with piperacillin-tazobactam and azithromycin against representative species of the Enterobacteriaceae family and Pseudomonas aeruginosa to extend its antibacterial spectrum, and to protect mecillinam from inactivating enzymes taking advantage of the presence of tazobactam. Drug interactions were studied by microdilution method, by selection of spontaneous resistant mutants on agar plates containing the drugs in combination and by time kill experiments. Against Enterobacteriaceae mecillinam and piperacillin-tazobactam showed synergistic interaction in 24/60 tests carried out by microdilution technology, in 4/16 by selecting resistant mutants and in 5/9 by time-kill experiments. P. aeruginosa reacted indifferently to the drug combinations, with few exceptions, when azithromycin was present a reduction of the MICs were recorded. Mecillinam reacted favourably in vitro in combination with piperacillin-tazobactam against not only strains included in its antibacterial spectrum but also against resistant Morganella morganii, Proteus spp and P. aeruginosa. The addition of azithromycin (8 mg/L) was beneficial for the drug combination increasing the bactericidal effect in the great majority of the cases. Only systematic in vivo studies may establish the clinical significance and benefits of the present observations.

Periodontal disease and coronary heart disease: an epidemiological and microbiological study.

AIMS: This is an investigation on the association between periodontal disease and an increased risk of coronary heart disease; the main hypothesis is that periodontal infections may increase the systemic inflammatory burden of the host above a threshold that may favour the atherogenic processes. MATERIALS AND METHODS: Case-control study with 27 cases, cardiologically affected, and 15 healthy controls. Patients underwent a complete periodontal probing. Periodontal conditions were compared between cases and controls to assess the mentioned association and to search for periodontal conditions related to the increased coronary risk. The presence and prevalence of periodontal pathogens was assessed in crevicular fluid samples. RESULTS: The overall periodontal conditions resulted worse in the test group. In particular periodontal conditions such as the presence of deep pockets (probing depth >6 mm) and the loss of more than 12 teeth might represent indicators of a strongly increased risk of cardiological disease and microbiological investigations confirmed these findings; Prevotella gingivalis was the most common bacteria. CONCLUSION: This study supports the existence of an epidemiologic association between periodontal disease and coronary heart disease and confirms previous data present in the literature. Two periodontal parameters, deep pockets and number of missing teeth, seem to be important risk factors for cardiovascular diseases.

Comparative evaluation of antimicrobial efficacy of sodium hypochlorite, MTAD, and Tetraclean against Enterococcus faecalis biofilm.

The aim of this study was to compare the antimicrobial efficacy of 5.25% NaOCl, BioPure MTAD (Dentsply Tulsa Dental, Johnson City, TN), and Tetraclean (Ogna Laboratori Farmaceutici, Milano, Italy) against Enterococcus faecalis biofilm generated on cellulose nitrate membrane filters. After incubation, the membrane filters were transferred into tubes containing 5 mL of the selected antimicrobial solution test agent or NaCl 0.9% (positive control) and incubated for 5, 30, and 60 minutes at 20 degrees C. After each period of time, the test agents were vortexed for 60 seconds to resuspend the microorganisms. Ten-fold serial dilutions were generated in reduced transport fluid. Each dilution was plated onto a brain heart infusion plates. The plates were then incubated for 48 hours in an aerobic atmosphere at 37 degrees C and colony-forming units per membrane was calculated. Statistical analysis showed that only 5.25% NaOCl can disgregate and remove the biofilm at every time; however, treatment with Tetraclean caused a high degree of biofilm disgregation in every considered time intervals as compared with MTAD (T5 p < 0.05, T30 p < 0.01, and T60 p < 0.001).

Records matching model for data survey on applied and experimental microbiology.

Experimental microbiology yields a huge quantity of raw data which needs to be evaluated and classified in a wide variety of situation from marine research, environmental pollution and pharmacokinetics of antimicrobial agents to epidemiological clinical trials on infectious diseases. It is indispensable in all kinds of disciplines to validate, transform and correlate data clusters to demonstrate the statistical significance of results. Whether academic or biotechnological, the scientific credibility of a work is strongly affected by the statistical methods and their adequacy. For a simple univariate analysis, many commercial or open source software products are available to perform sophisticated statistics for discriminant and multi-factorial analysis, but the majority of scientists use statistics partially. This is due to the high competence level required by a multivariate approach. It is known that the choice of a test, correct distribution assumption, valid experimental design and preliminary raw data validation are prejudicial to good science. All kinds of experimentation need analytical interpretation of descriptive evidence so that a classical numerical approach is not enough when raw data are not validated or incomplete. Microbiologists always wish to quickly discriminate, or correlate, group and data clusters concerning clinical patient profiles, auditing multi-sensor derived numbers, monitoring biosphere indicators on either chemical and physical parameters or dynamics of microbe populations. Mathematical and statistical analysis is essential to distinguish phenotypes or constraints. Data are in general stored in spreadsheet and database files which change continuously depending on the data collection and scope. We here propose a Records Matching Method (RMM) suitable for any kind of cluster analysis and pattern identification which can be used for either parametric or non parametric analysis without necessarily stating the pre-process statistical assumption on variable distribution. The RMM is an application of a theoretical approach based on the Unique Factorisation Domain and is explained with an ideal generalisation model and then applied to a real-world microbiological study. We used an easy mathematical formalism and discuss the possible application of the method as widely applicable to a plethora of taxonomic and phenetic investigations as well as for clinical trials and epidemiology. Prototyping of the model for a computational automated process are also described in order to devise simple software which can infer on data using a heuristic rules file.

Pleiotropic effect of sodium arsenite on Escherichia coli.

The effects of sodium arsenite at a sub-MIC concentration (25 mg/l) upon different bacterial functions were studied. This compound reduced the killing activity of nalidixic acid, amikacin, and meropenem. It also promoted the loss of F'lac from bacterial hosts and increased the number of recombinants in conjugation and transduction experiments. Transposition of Tn9 was also enhanced by the salt. In addition, sodium arsenite abolished the lethal effect of temperature on thermosusceptible DNA synthesis mutants in a similar manner to that seen in an anaerobic environment. Finally at a low dose, it induced the SOS response, and the related production of recA-dependent enzymes was reduced as the sodium arsenite concentration increased. It has been suggested that arsenite primarily affects the uvrA gene product, influencing the other bacterial functions studied. The energetic depletion caused by this compound appears to play a role in the activity of autolytic enzymes.

In vitro activity of ABT773, a new ketolide derivative exhibiting innovative microbiological properties against well-characterised antibiotic resistant pathogens in Italy.

The in vitro activity of ABT773, a new ketolide, was assessed against a collection (518) of well-characterised Gram-positive and Gram-negative pathogens and compared with that of other appropriate drugs. ABT773 was active (MIC-90=0.03 mg/l) against the staphylococci tested which included macrolide-resistant but clindamycin susceptible organisms. Streptococcus pneumoniae, S. pyogenes and S. agalactiae were also inhibited (MIC-90 range: <0.0075-0.5mg/l) irrespective of their antibiotic resistance phenotype. Enterococcus faecalis was sensitive to ABT773 with the exception of VanA mutants. E. faecium showed poor susceptibility to ABT773. The activity of the new ketolide against Haemophilus influenzae and Moraxella catarrhalis was comparable with that of the most potent drugs tested. ABT773 displays the characteristics of a promising agent that deserves to be introduced as the empirical therapy of infections caused by the bacterial species tested here, even if they are multiply resistant.

In vitro activity of fosfomycin against gram-negative urinary pathogens and the biological cost of fosfomycin resistance.

The aim of this study was to reassess the activity of fosfomycin against recently isolated uropathogens circulating in Italy and to evaluate the effect of fosfomycin resistance on the expression of several virulence traits using the rare mutant strains. In vitro activity of fosfomycin was evaluated using 441 Gram-negative organisms isolated from patients with uncomplicated urinary tract infections (UTIs). Fosfomycin was the most active antibiotic against Escherichia coli (99% susceptibility). The activity against Proteus mirabilis was more potent than that of co-trimoxazole and nitrofurantoin (87.5, 67 and 0% susceptibility, respectively). The other microorganisms, accounting for about 7% of all pathogens tested, showed variable susceptibilities to fosfomycin. Compared with susceptible strains, fosfomycin-resistant mutants showed a reduced rate of growth and were impaired in their ability to adhere to uroepithelial cells and to urinary catheters. They were also more resistant to UV irradiation and to phage T7 and showed diminished rates of colicin synthesis and transfer of plasmids.

Effect of fosfomycin alone and in combination with N-acetylcysteine on E. coli biofilms.

Four slime-producing uropathogenic Escherichia coli strains were used to investigate the activity of fosfomycin and N-acetylcysteine (NAC) against biofilms developed on 96-well polystyrene tissue culture plates. Biofilms aged, respectively, 5 (initial) and 48 h (mature) and two fosfomycin concentrations (128 and 2000 mg/l) were used. The effect of various levels (0.007-8 mg/ml) of NAC alone and in combination with fosfomycin on the formation or disruption of biofilms was assessed. Following exposure to the drugs, the percentage of residual slime relative to the control, ranged from 62.5-100 to 26.2-64.1% in the presence of 0.007 and 8 mg/ml of NAC. After treatment of pre-formed biofilms with NAC at the highest concentrations used, the remaining exopolysaccharide matrix was reduced to 25-68% of the amount found with the untreated control. Exposure to fosfomycin at 2000 mg/l reduced biofilms 40-57 and 41-49% for the initial and mature forms, respectively. Fosfomycin was more active at 2000 mg/l combined with NAC 2 mg/ml. Under these conditions initial and mature biofilms were reduced 66-80 and 60-73%, respectively. NAC, when used in combination, enhanced fosfomycin bactericidal activity producing a 99-99.9% reduction in viable cells. Fosfomycin and NAC at concentrations achievable in urine displayed a synergistic effect promoting both the formation of biofilms and reduction of sessile cell viability.

Postantibiotic effect and delay of regrowth in strains carrying mutations that save proteins or RNA.

The postantibiotic effect (PAE) values found for proteinase-defective (Lon(-)) Escherichia coli and RNase-defective E. coli exposed to antibiotics were reduced (31 to 60% and 35 to 50%, respectively) in comparison with the control (AB1157), and in the recA13 mutant these values were about 0.4 h with all drugs. Nalidixic acid, under anaerobic conditions, induced no PAE (0 to 0.1 h) in AB1157. A delay in regrowth (0.2 to 0.26 h) was noted with dnaA46(Ts), gyrA43(Ts), and gyrB41(Ts) mutants cultured for 2 h at 43 degrees C. These findings suggest that when proteins and RNA are saved, the cell rapidly resumes the original growth rate.

In vitro activity of quinupristin/dalfopristin against selected bacterial pathogens isolated in Italy.

OBJECTIVE: To evaluate the activity of quinupristin/dalfopristin, a new injectable streptogramin, against 732 clinical strains recently isolated in Italy. METHODS: Susceptibility tests were performed according to NCCLS-guided MIC methodology. Pathogens included in the evaluation included 108 Staphylococcus aureus isolates, 124 coagulase-negative staphylococcal isolates, 158 Streptococcus pyogenes isolates, 30 Streptococcus agalactiae isolates, 30 b-hemolytic streptococcal isolates, 18 Streptococcus sanguis isolates, 80 Streptococcus pneumoniae isolates, 69 Enterococcal isolates, 40 Haemophilus influenzae isolates, 30 Moraxella catarrhalis isolates and, finally, 30 Gram-positive and 25 Gram-negative anaerobes. RESULTS: Quinupristin/dalfopristin inhibited Staphylococcus aureus and other Staphylococcus spp., irrespective of their oxacillin or erythromycin resistance phenotypes. Similarly, streptococci were fully inhibited by quinupristin/dalfopristin. Enterococcus faecalis was not included in the spectrum of this streptogramin, while isolates of Enterococcus faecium were inhibited by the new compound. Respiratory pathogens such as H. influenzae and M. catarrhalis were inhibited by quinupristin/dalfopristin as well as all Gram-negative anaerobes tested. CONCLUSIONS: These findings suggest a putative role for quinupristin/dalfopristin in the empirical treatment of severe nosocomial and community-acquired infections caused by pathogens often displaying resistance to multiple antibiotics. This drug may provide an alternative to glycopeptide compounds.