Livestock and food products of animal origin constitute important reservoirs of intestinal and extraintestinal pathogenic Escherichia coli including antibiotic-resistant E. coli isolates. To assess potential risks to public health related to E. coli strains of animal origin in Tunisia, 65 E. coli isolates recovered from healthy animals and food products of animal origin were studied. Antimicrobial susceptibility was determined according to CLSI guidelines and genes encoding antibiotic resistance as well as virulence factors were investigated by PCR. High rates of antibiotic resistance were observed to kanamycin (78.4%), gentamicin (75.3%) and streptomycin (75.3%, encoded by strA-strB (7 isolates)), amoxicillin (64.6%), amoxicillin/clavulanic acid (60%), tetracycline (44.6%; tetA (8 isolates) and tetB (7 isolates)), nalidixic acid (27.6%, qnrS (3 isolates), qnrB (2 isolates) and qnrA (one isolate)) and sulfonamides (36.9%; sul1 (1 isolate), sul2 (4 isolates), and sul3 (1 isolate)). Virulotypes classified some isolates as STEC (3%), MNEC (1.5%) and atypical EPEC (1.5%). This study demonstrated high rates of antimicrobial resistance and the presence of some pathogenic pathovars from animal origins that are a cause of concern for public health.

The present study deals with the isolation, the identification, and the characterization of heavy metal-resistant bacteria selected from several polluted sources with the aim of using them as bioremediation agents of contaminated sites by heavy metals. Four protocols were used in a different way to select the maximum of isolates resistant to heavy metals. Isolates obtained, according to the fourth selection protocol by using the free nutrients medium, showed the highest values of minimum inhibitory concentration (MIC), and it can be deduced from this last result that when the bacteria are subjected to stressful conditions they develop a system that will enable them to withstand high levels of heavy metals. The study of the MIC at all resistant isolates allowed determining that the order of toxicity of the different metals was as follows: Cu > Cr > Cd > Ni > Zn > Co. These metals might exert varying effects depending on their adsorption and their complexation capacities to the bacterial cell wall. In addition, we can assume from the results of different screening protocols that the mixture of heavy metals exerts a more significant stressful effect on the life of the bacterial cell than the metal used alone. Isolates are all bacilli and cocci of gram-negative and of gram-positive bacteria. Pseudomonas aeruginosa and Staphylococcus aureus appeared as the most dominant genera. Therefore, the presence of metals in the growth medium has as an effect to conserve and to keep the character of resistance in the bacteria, contrary to its or their absence allowed the direct loss of this resistance. The study on the morphology of resistant isolates showed that the contour and the size of colonies would change in the presence of heavy metals. The heavy metal tolerant isolates were as of two types, of gram-positive and of gram-negative bacteria, and isolates of gram-negative were generally more resistant to the mixture of metals than those of gram-positive, since they could tolerate a 30 mM of heavy metal mixture. In addition, the identification of isolates selected by the mixture of metals revealed the dominance of the P. aeruginosa. The study of the growth of P. aeruginosa in the presence of increasing concentrations of metals showed a significant toxic effect of the high concentrations. Low concentrations are essential as trace elements for the bacterial growth and metabolism. Considering P. aeruginosa metal resistant strains, the quantity of total proteins synthesized appeared variable and generally an increase of the metal concentration is accompanied with an inhibition of the protein synthesis. The study of the protein profile for heavy metals resistant isolates of P. aeruginosa is mainly shown by the decrease in the level of proteins. This decrease pointed out the toxic effect of metals on the bacterial metabolism.

The objective of this study was to quantify copper‐, bacteria‐ and bacteriophage‐binding capacities of natural day with the aim of predicting the adsorption of heavy metals, human pathogenic bacteria and viruses by a clayey landfill liner. X‐ray diffraction analysis of six natural clays showed that the dominant phase in all deposits consists of smectites together with illite, kaolin and, sometimes, palygorskite and sepiolite. The specific surface areas of different day substrates were very high ranging from 293 to 351 m² g^‐1, and indicating a high proportion of phyllosilicates, consisting especially of smectites. The physico‐chemical identification of separated smectites showed a high potential adsorbent character indicative of a large industrial use. The Kb 12 smectite substrate chosen arbitrarily among six separated substrates, appeared as an excellent copper adsorbent. Copper was adsorbed to day in a proportion ranging from 94.6 to 96.0% with an average of 95.1% and its adsorption occurred rapidly in less than 30 min. Organic contents of the day substrate, evaluated as 17% of dry mass, may contribute and enhance copper adsorption. Different elution protocols using distilled water, 2 and/ or 5% nitric add revealed that while nitric add resulted in the removal of more than 59% of the metal at the lower concentration and its complete depletion with a further elution at the higher concentration, distilled water alone was unable to remove more than 1% of adsorbed copper. This finding suggested that copper ions form high‐energy bonds with layer‐silicate surfaces. Interestingly, the use of a regenerated substrate as copper adsorbent subsequent to abundant washings of the used substrate consecutively, with 0.1N HNO3 and distilled water, reduced copper adsorption by approximately 14%, suggesting a slight disturbance of day initial structure. Batch adsorption experiments with phage T7 and raw day Kbl2 showed that the tested day substrate appeared as a relatively moderate phage adsorbent since the quantity of adsorbed phage averaged 98.2 ± 0.88% (2 log₁₀ retention) as measured by infectivity for Escherichia coli ATCC 11303. As shown by two types of separating procedures, natural sedimentation and a low speed centrifugation, bacteriophage partides were bound essentially to fine and not to relatively coarse partides of the clay suspension. The retention capadty of purified day Kbl2 appeared low, with average values lower than 60 and 50%, for Pseudomonas aeruginosa ATCC 15442 and Bacillus cereus ATCC 1135, respectively. A significant increase of retention, in the order of 30%, was found for both bacteria when the mixture day‐bacteria was incubated at laboratory temperature for 6 hours.