Aetiologic Agents in Respiratory Illness

Factors influencing adherence of Staphylococcus aureus to influenza A virus-infected cell cultures

A quantitative radioassay was used to study the factors affecting the adherence of (3)H-labeled Staphylococcus aureus 1071 to Madin-Darby canine kidney cells, either uninfected or infected with the human FM1 strain of influenza A virus. Enhanced adherence to virus-infected cell cultures was independent of nonspecific factors-hydrophobicity, surface charge, and monolayer cell density. Viral hemagglutinin and neuraminidase did not act as the cell receptors for S. aureus because the growth of virus-inoculated monolayers in tunicamycin (an inhibitor of glycosylation) and the pretreatment of virus-infected cells with trypsin or virus-specific antiserum, which inhibit hemadsorption, had no effect on staphylococcal adherence. In contrast, adherence to uninfected and virus-infected cells was significantly reduced by protease treatment of either monolayers or staphylococci and by heat treatment of staphylococci. UV irradiation and treatment of bacteria with 0.1 M EDTA enhanced adherence. Pretreatment of monolayers with a thermal extract of S. aureus decreased adherence by 89 to 97%. The staphylococcal adhesin, which blocks adherence to virus-infected cells, appears to be a remarkably heat-stable, protease- and trypsin-sensitive macromolecule which is distinct from protein A, clumping factor, and teichoic acid. Lastly, pretreatment of S. aureus with human fibrinogen significantly enhanced adherence to virus-infected cells (P < 0.005) compared with binding with untreated S. aureus. The treated bacteria also adsorbed virus out of suspension. These results suggest that fibrinogen forms a bridge between S. aureus and receptors present on virus-infected cells and free virus.

Colonization and clinical superinfection with gram-negative bacilli in influenza

Among 197 influenza A patients admitted to Roslagstull Hospital, abundant growth of gram-negative bacilli was found in 74 cases (38%). When assays for antibodies with the patients own strains as antigen were performed on paired sera with the indirect immunofluorescence technique, titre increases were obtained in 21 out of 55 patients (38%). In this last group signs of secondary infection, as secondary pneumonia, prolonged or recurring fever or late occurrence of leukocytosis and granulocytosis, were significantly more common than in patients without gram-negative findings. An analysis of possible interference by other bacteria did not invalidate the observations. Findings of gram-negative bacilli occurred most often in patients more than 50 years of age. The bacteria were probably hospital acquired in 32 out of 55 patients. Antibody responses took place both in the IgM and the IgG fraction.

The influence of bacterial superinfection on the clinical course of influenza. Studies from the influenza epidemics in Stockholm during the winters 1969-70 and 1971-72

During two epidemics of influenza A infection in Stockholm 1969-72, 249 cases were selected for a study on the effect of bacterial superinfection. Bacterial involvement was demonstrated through cultures and serologic reactions. The occurrence of C-reactive protein in increased amount in serum was significantly more common in the group which had the strongest indication of bacterial infection. An increased duration of fever, and a higher incidence of pneumonia, leukocytosis and erythrocyte sedimentation rate over 50 mm/l h was also the rule in cases with bacterial involvement. During both epidemics the bacteria most often involved were pneumococci.