[Persistent and recurrent skin infection with small-colony variant methicillin-resistant Staphylococcus aureus]

S. aureus is one of the problematic bacteria, capable to develop resistance mechanisms to all antibiotics that the bacteria are naturally susceptible. A particular phenotypic mechanism, especially against the antibiotics that repressed the synthesis of the cellular wall and aminoglycosides, was evidenced in subpopulations that grows in small-colonies and represents auxotrophic mutants for hemin, menadione or thymidine. This type of strains has been isolated most frequently from patients with osteomyelitis, septic arthritis or pulmonary infections after a long period of antibiotic treatment. The authors present the case of a patient with persistent and recurrent staphylococcal infection of the peritoneal dialysis exit site, treated with different antibiotics (ciprofloxacin, vancomycin, amoxicillin and clavulanic acid, cephalexin) from witch has been isolated a small-colony strain of methicillin-resistant S. aureus. Therapeutic failure can be explain by the slow multiplication of this strain in vivo, persistence into phagocytes and the protection offered by biofilm from the surface of the catheter. Bacteriologic diagnosis in these cases is difficult because of the culture, biochemical and susceptibility testing particularities of these strains. All these may lead failure to identification small colony variants of S. aureus and mis-evaluation of the frequency of infection with these strains in patients with long-term antibiotherapy.