Antimicrobial and anti-pathogenic activity of some thioureides derivatives against Erwinia amylovora phytopathogenic strains

A series of N-(1-methyl-1 Hpyrazole-4-carbonyl)-thiourea derivatives were assessed for their in vitro antimicrobial and anti-pathogenic activity against twenty-two strains of Erwinia amylovora isolated from different regions in Romania. The compounds were solubilised in dimethylsulfoxide and screened for their in vitro antimicrobial activity. The qualitative screening of the susceptibility spectra of various strains to the compounds was performed by adapted diffusion techniques (distribution of the tested compound solution directly on the solid medium previously seeded with the bacterial inoculums). The quantitative assay of the minimal inhibitory concentration (MIC, microg/mL) was based on liquid medium two-fold microdilutions. The subinhibitory concentrations of the tested substances were investigated for their influence on biofilm development on inert substrata. The present study showed that six new thiourea compounds exhibited a low antibacterial activity (MIC values > 500 microg/ml), but the subinhibitory concentrations inhibited the biofilm development on inert substrata. Thus, these results could suggest the usefulness of the tested compounds as control agents for preventing the first stage (colonization) of the infection with the fire blight pathogen.

Genetic characterization of Erwinia amylovora strains by random amplified polymorphic DNA fragments (RAPD)

Erwinia amylovora is the causative agent of fire blight, a destructive disease of rosaceous plants subjected to strict quarantine regulations worldwide. Previous studies showed that the population of E. amylovora in Romania is homogenous in its biochemical and serological characteristics, despite the different strains' geographical and host origin. The aim of the present study was to establish and test a typing method to quantify genetic diversity among the Romanian strains of this plant pathogen. Fourteen strains isolated from different hosts and geographical locations in Romania were examined by random amplified polymorphism DNA (RAPD) fragment analysis with two ten-base primers. This molecular method has not revealed any polymorphism, producing the same amplification patterns for all tested strains. Clustering of strains in the resulting dendrogram was not correlated with host, or region of isolation. The RAPD technique did not allow the detection of genetic markers in E. amylovora strains isolated in Romania and proved not to be discriminating among strains of this pathogen. The results presented in this study suggest that the population of E. amylovora in Romania is homogenous.

Molds and mycotoxin content of cereals in southeastern Romania

Fungal species and toxin contamination were determined in 110 cereal samples (54 maize, 35 wheat, and 21 barley) collected in the southeastern part of Romania from 2002 to 2004. The most frequent fungal contaminants belonged to Aspergillus and Fusarium, and maize was the most contaminated cereal. The main toxigenic species identified were Aspergillus flavus, Aspergillus fumigatus, Fusarium graminearum, and Fusarium culmorum in all cereals and Fusarium verticillioides in maize. The presence of aflatoxin B1 (AFB1), deoxynivalenol (DON), zearalenone (ZEA), fumonisins, and ochratoxin A was determined by enzyme-linked immunosorbent assay. More than 90% of the samples were contaminated with at least one toxin. Around 30% of maize samples were contaminated with AFB1, and in 20% of these samples the level of toxin exceeded that allowed by European Union regulations. In 48 and 42% of samples, levels of DON and ZEA, respectively, exceeded those allowed by the European Union. Neither fumonisins nor ochratoxin A were found in samples from any year or cereal. These results indicate that cereals produced in Romania have a particular pattern of mycoflora and mycotoxin contamination because DON and ZEA in addition to AFB1 were found.

Novel antipathogenic strategies against adherent enterobacterial strains isolated from the hospital environment

The emergence of the bacterial antibiotic multi-resistance made more and more stringent the developing of new anti-microbial strategies. The purpose of the present study was to investigate the antimicrobial potential of six (6) newly synthesized chemical compounds (derivating from phenantroline and dimethylguanin-copper complex combinations) versus 97 enterobacterial strains isolated from the hospital environment. The qualitative screening of the antimicrobial activity of the chemical compounds was performed by an adapted diffusion method. The minimal inhibitory concentrations (MIC) of the active chemical compounds were established by Mueller Hinton broth microdillution method. The tested chemical compounds were also tested for their ability to inhibit microbial adherence and biofilm development on inert substrata by a simple microtiter method. All six chemical compounds proved to have antimicrobial activity versus the most of the tested strains, the phenantroline derivatives exhibiting higher antimicrobial activity than the dimethylguanidine-copper complex combinations. The subinhibitory concentrations of the tested chemical products slightly inhibited the adherence ability of the bacterial strains to the inert substratum. Our results demonstrated that phenantroline derivatives may represent a new strategy of antimicrobial treatment, simultaneously with the bactericidal effect, the subinhibitory concentrations of these newly synthesized chemical compounds decreasing the adherence ability of bacteria to the inert substratum.