Giovanna Riccardi

Antibiotic resistance of benthic bacteria in fish-farm and control sediments of the Western Mediterranean

The effects of fish farming on bacterial density, biomass, community structure and their possible link to antibiotic resistance have been investigated in coastal sediments of the Ligurian Sea (Western Mediterranean). The top 2 cm of the sediment under a fish farm and control areas were analysed during summer 2000. Bacterial density and biomass were three folds higher (up to 3 x 10(10) cells/g and 2602.7 muC/g) (ANOVA, p < 0,0 1) in sediments beneath the fish cages compared to the control sediments. The number of Colony Forming Units (CFUs) for culturable bacteria and microbiological investigations indicated a shift in the relative importance of the Gram-negative bacteria in impacted sediments. Gram-positive bacteria increased their relevance in the control site where they represented up to 90% of total isolates. Antibiotic sensitivity tests showed a high percentage of resistant strains in both control and impacted sediments, which indicates a widespread antibiotic resistance within bacterial populations in areas surrounding fish farms. A high frequency of antibiotic resistance was observed for ampicillin (AMP) in impacted sediments (ANOVA, p < 0.05). Gram-negative bacteria displayed the highest resistance to ampicillin, and streptomycin (STR) (ANOVA, p < 0.05) and the shift in the structure of microbial assemblage was apparently related to the presence of Gram-negative resistant strains in fish-farm sediments. The incidence of multiple resistance patterns in bacterial isolates was also greater in impacted sediments and the presence of Bacillus strains producing antimicrobial compounds may be related to the high level of drug resistance. This study highlighted a major change occurring in the structure of the benthic bacterial community most probably due to fish farming and its close association with antibiotic resistance patterns

Bacterial community structure and activity in fish farm sediments of the Ligurian sea (Western Mediterranean)

The environmental impact of a well-established fish farm has beeninvestigated in surface sediments of the Ligurian Sea in order to assess thebiodeposition, bacterial community structure and dynamics at a mature stage oforganic enrichment.The Biopolymeric carbon (BPC) fraction of organic matter and phytopigmentconcentrations displayed very high values beneath the fish cages. In particularlipid, carbohydrate and chlorophyll-a concentrations werehigher in farm sediment while protein concentrations did not show significantchange between farm sediment and control.Benthic bacteria were closely related to organic enrichment and their densitywas three times higher (up to 3 × 1010 cellsg−1) in stations beneath the cages being positivelycorrelated with BPC (n = 10, p < 0.05) and lipid (n = 10, p < 0.05)concentrations. Colony forming units (CFU) counts of heterotrophic bacteriaindicate a shift in the relative importance of the gram negative bacterialfraction, displaying the predominance of theCytophaga/Flexibacter-like bacteria (CBF), as well as theoccurrence of pathogenic bacteria (such as Vibrio) insediments beneath the farm. In contrast, Gram positive bacteria were moreprevalent in control site where they represented up to 90% of total isolates.Aminopeptidase activity displayed higher values in sediment beneath the cages,whereas the enzymatic activity per bacterial cell was lower. These data suggesta functional stress of bacterial degradation rates and represent a potentialvaluable environmental index of imbalance between supply and removal of organicmatter in eutrophicated environments.Data presented in this study also suggest that either the biochemicalcomposition of sedimentary organic matter as well as the selected microbialvariables may represent useful tools for evaluating the effects of organicenrichment due to fish farming and could be proposed as new environmentalindices of aquaculture impact on marine sediment.

Decaprenylphosphoryl-β-D-Ribose 2-Epimerase from Mycobacterium tuberculosis is a Magic Drug Target

Tuberculosis is still a leading cause of death in developing countries and a resurgent disease in developed countries. The selection and soaring spread of Mycobacterium tuberculosis multidrug-resistant (MDR-TB) and extensively drug-resistant strains (XDR-TB) is a severe public health problem. Currently, there is an urgent need of new drugs for tuberculosis treatment, with novel mechanisms of action and, moreover, the necessity to identify new drug targets. Several enzymes involved in various metabolic processes have been described as potential targets for the development of new drugs. Recently, two different classes of most promising drugs, the benzothiazinones (BTZ) and the dinitrobenzamide derivatives (DNB), have been found to be highly active against M. tuberculosis, including XDR-TB strains. Interestingly, both drugs have the same target: the heteromeric decaprenylphosphoryl-β-D-ribose 2-epimerase encoded by dprE1 (Rv3790) and dprE2 (Rv3791) genes, respectively. DprE1 and DprE2 are involved in the biosynthesis of D-arabinose and, in particular, they are essential to perform the transformation of decaprenylphosphoryl-D-ribose to decaprenylphosphoryl-D-arabinose, which is a substrate for arabinosyltransferases in the synthesis of the cell-envelope arabinogalactan and liporabinomannan polysaccharides of mycobacteria. Arabinogalactan is a fundamental component of the mycobacterial cell wall, which covalently binds the outer layer of mycolic acids to peptidoglycan. The heteromeric decaprenylphosphoryl-β-D-ribose 2-epimerase thus represents a valid vulnerable antimycobacterial drug target which could result in magic for tuberculosis treatment.

Gene arrangement and organization in a ∼ 76 kb fragment encompassing the oriC region of the chromosome of Mycobacterium leprae

A continuous 75627 bp segment of the Mycobacterium leprae chromosome spanning the oriC region was sequenced. The gene order at this locus was similar to that found in the replication origin region of many other prokaryotes, particularly Mycobacterium tuberculosis and Streptomyces coelicolor. As in the case of several Gram-positive bacteria, essential genes involved in basic cellular functions, such as DNA or RNA metabolism (dnaA, dnaB, dnaN, gyrB, gyrA, pcnB, recF, rnpA, ssb), cell wall synthesis (ponA, pbpA) and probably cell division (gidB, rodA) were found. Strikingly, the gidA gene was absent from this part of the genome and there was no rRNA operon near oriC. The gyrA gene harbours an intein coding sequence indicating that protein splicing is required to produce the mature A subunit of DNA gyrase. Among the many other noteworthy features were ORFs encoding putative serine/threonine protein kinases and a protein phosphatase, three tRNA genes, one M. leprae-specific repetitive element and a glnQ pseudogene.