High-resolution imaging of C60 molecules using tuning-fork-based non-contact atomic force microscopy.

Recent advances in non-contact atomic force microscopy (nc-AFM) have led to the possibility of achieving unprecedented resolution within molecular structures, accomplished by probing short-range repulsive interaction forces. Here we investigate C(60) molecules adsorbed on KBr(111) and Cu(111) by tuning-fork-based nc-AFM. First, measurements of C(60) deposited on KBr(001) were conducted in cryogenic conditions revealing highly resolved nc-AFM images of the self-assembly. Using constant-frequency shift mode as well as three-dimensional spectroscopic measurements, we observe that the relatively weak molecule-substrate interaction generally leads to the disruption of molecular assembled structures when the tip is probing the short-range force regime. This particular issue hindered us in resolving the chemical structure of this molecule on the KBr surface. To obtain a better anchoring of C(60) molecules, nc-AFM measurements were performed on Cu(111). Sub-molecular resolutions within the molecules was achieved which allowed a direct and unambiguous visualization of their orientations on the supporting substrate. Furthermore, three-dimensional spectroscopic measurements of simultaneous force and current have been performed above the single molecules giving information of the C(60) molecular orientation as well as its local conductivity. We further discuss the different imaging modes in nc-AFM such as constant-frequency shift nc-AFM, constant-height nc-AFM and constant-current nc-AFM as well as three-dimensional spectroscopic measurement (3D-DFS) employed to achieve such resolution at the sub-molecular scale.

Three-dimensional dynamic force spectroscopy measurements on KBr(001): atomic deformations at small tip-sample separations.

Three-dimensional dynamic force spectroscopy measurements were carried out above KBr(001) at low temperature in order to investigate the distance dependence of the tip-sample interactions. In particular, the recorded 3D frequency shift data as well as the extracted interaction force and potential energy fields were analysed with respect to influences of tip and/or sample deformations. We found that a postprocessing correction of the observed deformations significantly modifies the magnitude of the extracted interaction forces and also the image contrast.

The monomer-to-dimer transition and bimodal growth of Co-salen on NaCl(001): a high resolution atomic force microscopy study.

Molecules of Co-salen, a paramagnetic metal-organic Schiff base complex, self-assemble into two different well ordered morphologies on a NaCl(001) substrate: nanowires, which form networks, and compact nanocrystallites. Their growth can be controlled by adjusting the deposition parameters. It turns out that the nanowires are metastable. Molecular resolution images suggest that the packing in both morphologies is the same as in bulk Co-salen single crystals. Only the orientation of the c-axis with respect to the substrate is different. The origin of this intriguing bimodal growth is associated with a monomer-to-dimer transition, which probably takes place during initial nucleation at step edges.

Characteristics of Salmonella contamination of broilers and slaughterhouses in the region of Constantine (Algeria).

The present study provides the first data about the prevalence of Salmonella contamination of broilers and slaughterhouses in the region of Constantine, Algeria. The serotypes and anti-microbial resistance phenotypes of the isolates were determined, and risk factors contributing to the contamination were evaluated. A total of 2490 samples, 1800 originating from 30 broiler farms and 690 from 15 slaughterhouses, were taken during two periods: March 2005-June 2006 and September 2006-March 2007. Salmonella contamination concerned 37% of the broiler farms and 53% of the slaughterhouses. Among the 55 isolates recovered, 10 different serotypes were identified. The most frequently recovered serotypes in both slaughterhouses and breeder farms were S. Hadar (36%, n = 20), S. Virchow (16%, n = 9), S. Infantis (10.9%, n = 6), S. Albany (11%, n = 6) and S. Carnac (7%, n = 4). Isolates belonging to S. Heidelberg (2%, n = 1) and S. Rissen (2%, n = 1) were found only in farms, while those belonging to S. Typhimurium (9%, n = 5), S. Enteritidis (4%, n = 2) and S. Montevideo (2%, n = 1) were recovered only from slaughterhouses. Thirty-nine isolates (80%) were resistant to at least one anti-microbial and 51% were multi-resistant, i.e. resistant to two or more anti-microbial molecules. About 58% (n = 32) were resistant to streptomycin, 36% (n = 20) to tetracyclines, 27% (n = 15) to nalidixic acid, 13% (n = 7) to ofloxacin and one isolate to enrofloxacin. Finally, seven distinct anti-microbial resistance profiles were identified. In parallel, four risk factors were found to be significantly associated with Salmonella contamination. Together with the huge spread of Salmonella in the broiler production chain in Constantine, Algeria, these risk factors highlight the hazards of the broiler channels, particularly linked to poor technical and hygiene practices.

Antibiotic resistance in salmonellae isolated from humans and animals in France: comparative data from 1994 and 1997.

Among 25526 recorded isolates of salmonellae, 5086 isolated from humans and 20440 from animals in 1994 and 1997 in France, the antibiotic resistance phenotype was determined for all human and 5336 animal isolates. In Salmonella enterica serovar typhimurium, one of the two most frequently isolated serovars from humans as well as animals, resistance to ampicillin was observed in 61% of both human and animal isolates in 1994 and in 73% of human and 53% of animal isolates in 1997. During these periods, resistance to co-amoxiclav was between 45% and 66% for both types of isolate. Resistance to ampicillin was associated with resistance to streptomycin, spectinomycin, sulphonamide, tetracycline and chloramphenicol in over 70% of isolates. Resistance to ampicillin as well as co-amoxiclav never exceeded 7% in Salmonella enteritidis. While Salmonella hadar was practically absent among the human isolates in 1994, this serovar was the third most frequent in 1997, and at that time 92% were resistant to nalidixic acid. Among the animal S. hadar isolates, the prevalence of resistance to nalidixic acid increased from 3% in 1994 to 72% in 1997. None of these isolates manifested high-level resistance to ofloxacin. The levels of resistance to aminoglycosides (< or =3%) and trimethoprim-suphamethoxazole (< or =14%) remained practically unchanged in all three serovars. The resistance markers of 463 ampicillin-resistant S. typhimurium isolated in 1997 were determined. Among the 24 phenotypes observed, six multiresistance phenotypes, representing 82% of these isolates (as compared with 80% in 1994), were associated with the PSE-1 gene typically found in the lysotype DT104 of this serovar.