Small-colony variants (SCVs) of Staphylococcus aureus were cultured from five patients with persistent and relapsing infections. All five SCV strains were nonhemolytic and nonpigmented and grew very slowly on routine culture media in an ambient atmosphere. In several instances, these phenotypic characteristics led to the initial misidentification of the organisms in the clinical microbiology laboratory. All four strains available for further analysis were shown to be auxotrophs that reverted to normal growth and morphology in the presence of menadione, hemin, and/or a CO2 supplement. Similarly, these isolates were resistant to aminoglycosides under routine conditions but susceptible in the presence of the metabolic supplements. For two patients, the large and small colony forms isolated concurrently were indistinguishable when analyzed by pulsed field gel electrophoresis and thus represented phenotypic variants within individual clones. We propose a model relating the phenotypic characteristics of S. aureus SCVs with the clinical pattern of persistent and relapsing infection.

Staphylococcus aureus menadione and hemin auxotrophs, generated by in vitro gentamicin selection, demonstrated reduced hemolytic activity and enhanced intracellular survival within cultured bovine aortic endothelial cells relative to their hemolytic parent. Supplementation of the auxotrophs with exogenous menadione or hemin resulted in rapid growth, increased hemolytic activity, and reduced intracellular persistence to the level found for the hemolytic clinical parent. Aminoglycoside selection of staphylococcal menadione and hemin auxotrophs and subsequent persistence of these variants in the intracellular milieu may adapt S. aureus for evasion of host defenses and resistance to antimicrobial therapy.

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Antibiotics with different mechanisms of action may vary with respect to their effects on the release and immunostimulatory activities of cell wall fragments from gram-positive bacteria. Therefore, after Staphylococcus aureus was cultured for 4 h in the absence of antibiotics (control) and in the presence of β-lactam antibiotics (imipenem, flucloxacillin, or cefamandole) and protein synthesis-inhibiting antibiotics (erythromycin, clindamycin, or gentamicin), the lipoteichoic acid (LTA) and peptidoglycan (PG) levels in the bacterial supernatants were measured. β-Lactam antibiotics greatly enhanced the release of LTA and PG (4- to 9-fold and 60- to 85-fold, respectively), whereas protein synthesis inhibitors did not affect PG release and even inhibited the release of LTA compared to the amount of LTA released in control cultures. The capacity of β-lactam supernatants to stimulate the production of tumor necrosis factor alpha and interleukin-10 in human whole blood was significantly higher than that of protein synthesis inhibitor or control supernatants; the amounts of these cytokines released were directly proportional to the concentrations of PG and LTA in the supernatants. Enzymatic degradation of PG in the supernatants indicated that PG was mainly responsible for the observed biological reactivity.

We prospectively examined 464 febrile patients (median age, 61 years) for predictors of in-hospital death, by use of univariate and multivariate logistic regression using clinical data (age, underlying disease, duration of fever, chills, and shock on admission) and plasma endotoxin, TNF-alpha, IL-6, IL-10, and procalcitonin levels. The mortality rate was 4.6-fold higher (95% confidence interval [CI], 1.8-12) in 31 patients with shock on admission, 7 of whom died; the strongest association with mortality was the endotoxin concentration (relative risk, 13.7; 95% CI, 1. 4-136), which predicted 5 of the deaths with a 5% false-positive rate. For 433 patients without shock on admission, mortality (26 deaths) was associated with age and underlying disease: clinical data predicted 30% of the deaths, whereas IL-6 and procalcitonin levels identified an extra 10% with a 5% false-positive rate. When febrile patients are screened on hospital admission to identify those with a high risk for mortality, clinical judgment on the basis of age, underlying disease, and recent history outweighs the predictive value of endotoxin, cytokine, and procalcitonin levels. Only in patients who present with shock will measurement of endotoxin levels help predict those who will likely die at the cost of few false-positive results.