The consecutive cell activation, including Ca 2+ -channel opening, and pore formation leading to human neutrophil lysis were the two functions of the staphylococcal PantonValentine leucocidin attempted to be discoupled by site-directed mutagenesis. In a first approach consisting in deletions of the cytoplasmic extremity of the transmembranous domain, we produced a LukF-PV v vSer125-Leu128 with a slightly reduced Ca 2+ induction but with a significantly lowered lytic activity when combined with its synergistic protein LukS-PV. The second approach consisted in the modification of charges and/or introduction of a steric hindrance inside the pore, which also led to interesting mutated proteins: LukF-PV G131D, G131W and G130D. The latter had an intact Ca 2+ induction ability while the lytic one was 20-fold diminished. Binding properties and intrinsic pore diameters of these discoupled toxins remained comparable to the wild-type protein. The mutated proteins promoted interleukin-8 secretion, but they were rather inactive in an experimental model. New insights are brought concerning the role of the two functions in the virulence of this bi-component leucotoxin.z 1999 Federation of European Biochemical Societies.

No abstract

Staphylococcal leucotoxins result from the association of class S components and class F component inducing the activation and the permeabilization of the target cells. Like α-toxin, the leucotoxins are pore-forming toxins with more than 70% β-sheet. This was confirmed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. In addition, threonine 28 of a predicted and conserved β-sheet at the N-terminal extremity of class S proteins composing leucotoxins aligns with histidine 35 of α-toxin, which has a key role in oligomerization of the final pore. Flow cytometry was used to study different aminoacid substitutions of the threonine 28 in order to evaluate its role in the biological activity of these class S proteins. Finally, results show that threonine 28 of the leucotoxin probably plays a role similar to that of histidine 35 of α-toxin. Mutations on this threonin largely influenced the secondary interaction of the class F component and led to inactive toxin.

Background: Infectious diseases are serious public health issue both in developing countries and industrialized nations. In developing countries, they are the main cause of high mortality rates. In the second group, existing resistance strains to antibiotics is developing and growing at an alarming rate. The purpose of this study was to produce data of national interest to implement sustainable control program against the spread of antimicrobial resistance strains in Benin. Methods: One hundred and ninety (190) urine samples were collected in selected hospitals in Benin from patients with urinary tract infection. After getting the informed consent from the patients, samples collections were performed under aseptic conditions and cultured for further analysis in the laboratory. The resistance profile of the bacterial strains was established. The search for beta-lactamase production by the isolates was performed using the synergy test for amoxicillin/clavulanic acid and cephalosporins. Mathematical modeling for predicting the development of resistance of the strains by the year 2024 was carried out employing the compartmental deterministic models. Results: Two hundred and thirty (230) strains were identified from the urine samples. Male individuals were the most affected by urinary tract infections. Individuals between the ages of 21-30 were predominantly infected. E. coli was the most isolated species (32.43%) in the urine samples, followed by K. pneumoniae (26.85%) and E. cloacae (25.92%). The susceptibility testing of isolates showed a high resistance to amoxicillin (91.82%). Whereas the lowest resistance was to imipenem (2%). The beta-lactamase was produced by 24.03% of the strains. Escherichia coli (32.43%) was the most productive of broad spectrum beta-lactamase, followed by K. pneumoniae (31.03%). The mathematical modeling revealed a rampant rise in resistance development of the strains to the tested antibiotics. Conclusions: These results provide important data for developing new preventive strategies against the evolution of bacterial resistance to antibiotics. It therefore, further deserves a constructive advocacy so that more actions are taken against the rampant spread of antimicrobial resistance strains in our health facilities as well as in the communities.