Persistent septic arthritis with recurrent bacteremia as a result of a tolerant strain of Staphylococcus aureus

The general stress response of Staphylococcus aureus promotes tolerance of antibiotics and survival in whole human blood

Staphylococcus aureus is a frequent cause of invasive human infections such as bacteraemia and infective endocarditis. These infections frequently relapse or become chronic, suggesting that the pathogen has mechanisms to tolerate the twin threats of therapeutic antibiotics and host immunity. The general stress response of S. aureus is regulated by the alternative sigma factor B (σB) and provides protection from multiple stresses including oxidative, acidic and heat. σB also contributes to virulence, intracellular persistence and chronic infection. However, the protective effect of σB on bacterial survival during exposure to antibiotics or host immune defences is poorly characterized. We found that σB promotes the survival of S. aureus exposed to the antibiotics gentamicin, ciprofloxacin, vancomycin and daptomycin, but not oxacillin or clindamycin. We also found that σB promoted staphylococcal survival in whole human blood, most likely via its contribution to oxidative stress resistance. Therefore, we conclude that the general stress response of S. aureus may contribute to the development of chronic infection by conferring tolerance to both antibiotics and host immune defences.

Persistence in Staphylococcus aureus bacteremia: incidence, characteristics of patients and outcome

Staphylococcus aureus bacteremia often persists. The reasons for persistence and its outcome are poorly defined. We conducted a prospective-observational study among 245 consecutive S. aureus (MRSA: n=125; MSSA: n=120) bacteremias (>or=1 positive blood cultures (BC)) among 234 adults (18-103-y-old; median=59 y) hospitalized during 1 January 2002-31 December 2002 at a 600-bed teaching hospital. Measurements included bacteremia duration, complication-rate (metastatic infection, relapse or attributable mortality) and outcome. Bacteremia duration was measured based on follow-up BC among 193 patients and estimated based on symptoms resolution in the rest. Measured (1-59 d; median=2) and estimated (median=1 d) duration correlated (r=0.885) though positive follow-up BC was often detected without fever (57/105 patients, 54.3%). Persistence (defined as bacteremia for >or=3 d) was noted in 84 cases (38.4%). Complication-rate increased steadily with bacteremia duration (6.6%, 24.0% and 37.7% in bacteremia for 1-2, 3 and >or=4 d, respectively; p=0.05). Cox regression analysis revealed that bacteremia duration correlated positively with endovascular sources (p=0.006), vancomycin treatment (p=0.016), cardiovascular prosthesis (p=0.025), metastatic infections (p=0.025) and diabetes (p=0.038). It is concluded that persistent bacteremia is a feature of S. aureus infection, irrespective of oxacillin susceptibility, associated with worse outcome. Risk factors include endovascular sources, cardiovascular prosthesis, metastatic infections, vancomycin treatment and diabetes. Patients at risk may benefit from novel treatment strategies.