Characterization of Staphylococcus aureus from Pasteur Institute in Côte d'Ivoire: Methicillin Resistance, Reduced Sensitivity to Vancomycin, Panton-Valentine Leucotoxin and Exfoliatins.

Staphylococcus aureus, which causes various infections, particularly suppurations, expresses many virulence factors. The resistance of S. aureus to methicillin (MRSA) which can spread to vancomycin constitutes a major challenge in infectiology. The search for virulence and resistance factors is therefore of interest to better understand the mechanisms of this pathogenicity. The objectives of this study were to determine the frequency of phenotypic and genotypic (mecA, vanB) resistances, the frequency of virulence genes (eta, etb, and lukS) and to investigate the resistant strains for the presence of virulence genes. On thirty-one strains isolated from infections at the Pasteur Institute of Côte d'Ivoire, the study of susceptibility to methicillin and vancomycin was carried out by phenotypic and molecular methods. We observed phenotypic and genotypic resistance to methicillin of 41.9% and 32.3% respectively. Despite a suspicion of very high vancomycin susceptibility reduced, 25.8% by phenotypic method, the vanB gene was only found in 3.2% of strains. The prevalence of virulence genes was high with the eta gene, 96.8%, and the lukS gene 45.2%. The mecA gene was present with an eta gene in 32.3% of strains and in 9.7% with the lukS gene, however the vanB gene was not present in any strain carrying virulence factors. These results should lead to the screening of other van genes for resistance to vancomycin.

[Production lead time of coagulase in 180 Staphylococcus aureus strains collected at Abidjan]. / Delai de production de la coagulase chez 180 souches de Staphylococcus aureus isolees a Abidjan.

INTRODUCTION: The pathogenic capacity of S. aureus is related.to the production of many virulence factors of which the coagulase. Several genotypes of coagulase were described and are associated to various populations of S. aureus. According the susceptibility to methicillin, methicillin-resistant strains of S. aureus, are described. The aim of this subject was to study the coagulase expression of Staphylococcus aureus according to the site of infection, patient origin and the resistance against methicillin. MATERIAL AND METHODS: The study is related about 180 strains of S. aureus collected in the three University Teaching Hospital of Abidjan. S. aureus are identified with laboratory classical methods. Coagulase delay was determined by the test of the coagulase on citrated rabbit plasma at 2, 4 and 18 hours. The resistance against methicillin was researched by disc diffusion agar technique. RESULTS: In 60% of cases, the bacterial strains gave a coagulum at the end of four hours, fast coagulase, against 40% of strains whose coagulating activity appeared at 18 h, slow coagulase. Fast coagulase strains are isolated from the majority of infections (55% to 71%), in hospital patients (66%) and in paediatrics (58%). Fast coagulase strains are methicillin-resistant in 65% of cases against 48.5% of methicillin-susceptible and low coagulase strains (p < 0.0001). CONCLUSION: According to the production lead time of the coagulase, fast coagulase and slow coagulase variants of S. aureus coexisted. The expression of the coagulase is not related to the site of infection and the origin of the patients. On the other hand, the type of coagulase is associated to resistance of methicillin. However, the time of formation of the coagulum typed by the test of the coagulase, didn't constitute a sufficient discriminating factor in the medical following and the treatment of infections caused by S. aureus.

Comparison of clarithromycin-sensitive and clarithromycin-resistant Mycobacterium avium strains isolated from AIDS patients during therapy regimens including clarithromycin.

OBJECTIVES: Sixteen Mycobacterium avium strains were isolated from the blood of eight AIDS patients over a period of months. All the patients were on combination therapies including clarithromycin, and all had treatment failure and relapses of M.avium bacteremia. Paired clarithromycin-sensitive and resistant M.avium strains isolated at the beginning of treatment and at the first relapse of bacteremia were compared. METHODS: The M.avium isolates were identified after hybridization with DNA probes specific for M.avium rRNA and typed epidemiologically with random amplified polymorphic DNA analyses using three arbitrary primers. The rate of intracellular cell entry or the tumour necrosis factor alpha induction by the M.avium isolates were studied in human monocytes and J774 cells. RESULTS: When the M.avium isolates were hybridized with the rRNA probes, we obtained lower hybridization values with clarithromycin-resistant isolates than with clarithromycin-sensitive isolates. This appeared to be due to smaller amounts of rRNA available for hybridization than to mutation of the 23S rRNA sequences in clarithromycin-resistant strains. The RAPD analyses showed that the clarithromycin-resistant isolates were clonally related to the clarithromycin-sensitive strains in six of the eight patients. The other two patients had a RAPD profile, suggesting a re-infection and/or polyclonal infection. The M.avium isolates obtained on day 0 and after the emergence of resistance to clarithromycin did not differ in terms of their intracellular entry rate, or in terms of tumour necrosis factor alpha induction. CONCLUSIONS: We infer that M.avium strains isolated during bacteraemic relapses on combination therapies including clarithromycin are epidemiologically related to the initial strain and do not show changes in the rate of intracellular cell entry and in terms of tumour necrosis factor alpha induction. Re-infections and/or polyclonal infections however, although less frequent, can also occur.

Interaction of virulent and non-virulent Rhodococcus equi human isolates with phagocytes, fibroblast- and epithelial-derived cells.

Rhodococcus equi is a facultative, intracellular, Gram-positive coccobacillus, increasingly reported in pneumonia of AIDS-infected patients. We investigated killing resistance properties of human R. equi virulent and avirulent human strains. Avirulent beta-lactam-susceptible strains had lower intracellular colony forming units after 45 min incubation in murine macrophages J774 and human monocyte-macrophage TPH-1 than those of virulent strains. Only virulent beta-lactam-resistant strains persisted within macrophages for at least 18 min only. A beta-lactam-resistant mutant was obtained from a beta-lactam-susceptible strain after selection in a penicillin G-containing culture medium. This mutant strain, like the natural virulent strains, persisted within macrophages, harboured cell-associated appendages, produced phage-like particles and induced, after its intravenous inoculation, a chronic infection in BALB/c nude mice. Supernatant culture of virulent strains transferred partial macrophage-killing resistance properties to avirulent strains. The same supernatant was toxic for L-929, HeLa and Vero cell cultures. These supernatant effects were heat-inactivated, trypsin-inactivated and did not seem to be linked to phage-like particle presence. These data argue that virulence, beta-lactam-resistance, and macrophage-killing resistance are associated in human R. equi isolates. Moreover, only virulent strains produced uncharacterized toxic factors.