Characterization of clinical strains of Staphylococcus aureus associated with pneumonia

A total of 5 Staphylococcus aureus strains from patients with postinfluenzal staphylococcal pneumonia, 7 from burn patients with staphylococcal pneumonia, and 21 from the nasopharynx of carriers were phenotypically characterized. All or most strains produced coagulase, clumping factor, DNase, thermostable DNase, protease, gelatinase, lipase, and pigment; the strains were low to moderate producers of extracellular protein A, fibrinolysin, and alpha-hemolysin. All strains were sensitive to mercury, half were sensitive to arsenate and cadmium, and 67 to 92% were resistant to penicillin. Differences between strains were not statistically significant. Cell surface hydrophobicity was determined by measuring percent adsorption to hexadecane. Hydrophobicity of postinfluenzal staphylococcal pneumonia strains was significantly lower than that of pneumonia strains from burn patients and carriers (P less than 0.005). Immunoblot experiments with sera immune to one clinical test strain allowed the separation of all strains into three groups based on probe-positive reactions with primarily four staphylococcal polypeptides (154,200, 130,000, 77,100, and 64,400 molecular weight). The difference in distribution of clinical and carrier strains was highly significant (P = 0.007).