Effect of influenza A on phagocytic cell function.

The effect of various strains of influenza virus on polymorphonuclear leucocyte (PMNL) function were studied by chemiluminescence (CL) and bacterial killing assays. All virus strains induced PMNL CL and peak CL correlated with haemagglutination (HA) but not neuraminidase (NA) activity of virus pools. Heat-treatment of virus pools generally had little effect on HA activity or ability to generate a PMN CL response but almost completely destroyed NA activity. Exposure of PMNL to each of the six virus strains resulted in loss of surface-associated sialic acid and a marked depression in both zymosan-induced PMNL CL and PMNL bactericidal capacity. However, there was no correlation between the degree of PMNL functional impairment and virus NA activity and, furthermore, heat treatment of virus pools removed NA activity but generally had little effect on their ability to reduce PMNL function. NA does not appear to play a primary role in impairment of PMNL function by influenza virus.

Measurement of phagocyte chemiluminescence in a microtitre plate format.

Previously described assays of phagocyte chemiluminescence have required large numbers of cells and have not been able to follow responses from a large number of samples in single experiments. Recently, sensitive luminometers which employ a 96 well microtitre plate format have become available. We describe the application of this equipment to the measurement of phagocyte chemiluminescence using lucigenin to enhance the response and the estimation of the opsonic activity of serum. It was found that as few as 5 X 10(4) cells (polymorphonuclear leukocytes or monocytes) per well and a ratio of 10:1 zymosan particles to cells gave good results when opsonised with 10% whole serum. This method allows assays of opsonic activity to be performed in triplicate on large numbers of sera with a relatively small number of phagocytes and should aid the investigation of the role of opsonisation in infectious disease.

Group B streptococcal colonisation and the outcome of pregnancy.

Vaginal colonisation of pregnant women with group B streptococci (GBS) was not related to age, parity or blood group. There were marked differences between racial groups, Asians having a low colonisation rate and Negroes a high rate. Vaginal GBS colonisation was associated with intrapartum pyrexia, but not with preterm labour, premature rupture of membranes or other complications in labour. Group B streptococci may be an important cause of bacteriuria in pregnancy and their effect on the outcome of pregnancy as urinary pathogens needs further evaluation.

Opsonization of group B Streptococcus type III: studies using clinical strains and maternal sera.

Luminol-dependent phagocytic chemiluminescence was used to measure opsonins to group B Streptococcus type III in serum samples from pregnant women. Mean levels were similar amongst patients colonized with this organism and those who were not. Values remained fairly constant for individual women during pregnancy apart from a small, but consistant fall in cord blood samples. Again using luminol-dependent chemiluminescence, 54 clinical isolates of group B Streptococcus type III were evaluated for susceptibility to serum opsonization. Six were found to be resistant and these originated from both colonized babies and babies with systemic GBS infections. Further studies demonstrated strain-to-strain variation in the degree of dependence on both heat-labile and heat-stable opsonins.

Is group B streptococcal screening during pregnancy justified?

Twenty-eight per cent of women investigated during pregnancy were carriers of group B streptococci (GBS). The use of broth enrichment was the most significant factor in determining GBS carriage rates. GBS carriage decreased during pregnancy. Transmission of GBS from mother to baby was related to vaginal carriage but rectal carriage in pregnancy was the best predictor of maternal carriage at term. Rectal and vaginal swabs taken at 28 and 36 weeks correctly predicted 92% of intrapartum GBS carriage. Although accurate prediction of intrapartum GBS carriage is possible, mass screening for GBS in pregnancy is unlikely to be cost-effective in those countries with a low incidence of neonatal GBS sepsis.

The effect of intrapartum chemoprophylaxis on the vertical transmission of group B streptococci.

Intrapartum chemoprophylaxis with benzylpenicillin or erythromycin significantly reduced the rate of transmission of group B streptococci (GBS) from mothers colonized during pregnancy to their babies from 45% to 3% (P less than 0.001). None of the babies born to women who were given prophylaxis was colonized with GBS in the first 24 h of life. Six weeks after leaving hospital, however, 23% of the babies in the antibiotic group had become colonized with GBS compared with 44% in the control group. GBS strains resistant and tolerant to both benzyl-penicillin and erythromycin were found in this study. Intrapartum chemoprophylaxis breaks the cycle of GBS transmission at birth and may be useful in preventing early onset GBS disease, but is unlikely to affect late onset infections.

Epidemiology of group B streptococci: one year's experience in an obstetric and special care baby unit.

The epidemiology of group B streptococci (GBS) was studied in an obstetric unit and the related special care baby unit (SCBU). In 1 year 53 (77%) of 69 babies who acquired GBS from their mothers were colonized within 24 h of birth, compared with only 9 (35%) of 38 who acquired GBS from non-maternal sources. While 38 (36%) of 107 GBS colonized babies in the obstetric unit derived the organism from a non-maternal source, the value for the SCBU was only 2 (9%) of 23. In babies rectal and umbilical swabs gave the highest GBS isolation rates. Phage-typing and serotyping suggested that colonized mother baby pairs, rather than staff, were the primary source of hospital acquired GBS. This mode of GBS acquisition did not result in long-term carriage once babies had left hospital. Nosocomial transmission can play an important part in GBS epidemiology, but can be minimized by attention to infection control procedures.

The effect of culture media on the production and measurement of luminol-dependent chemiluminescence.

The effect of various media constituents on the production and measurement of luminol-dependent chemiluminescence by neutrophils stimulated by opsonized zymosan was studied. Glucose, calcium ions and magnesium ions were found to be necessary for optimal chemiluminescence although high concentrations of glucose had a detrimental effect. For our luminol-dependent system, a pH of 8.5 give maximal readings. The use of simple balanced salt solutions gave higher chemiluminescence responses than did more complex media with added protein, amino acids, and vitamins. However, the latter were important in the maintenance of optimal cell function.

Variations in the opsonic requirements of group B streptococcus type III.

The opsonic requirements of strains of Type III Group B streptococci (GBS) were studied using Luminol-dependent chemiluminescence and microscopy. Growth and storage conditions, particularly any reduction in the pH of the medium, affected GBS resistance to opsonization. Opsonization was complement-dependent but there was considerable variation in the requirements of individual strains for the classical and alternative pathways. Antibody was also necessary for opsonization. A few type III GBS strains were resistant to opsonization by pooled serum known to contain type-specific antibody, raising the possibility that protective antibody might in certain circumstances be strain- rather than type-specific. Treatment of these strains with neuraminidase, however, rendered them sensitive to opsonization by the same pool of serum. The resistance of GBS to opsonization in the neonate, where complement activity can be reduced and antibody levels are low, may be a major determinant of virulence.

Nosocomial transmission of group B streptococci.

The acquisition of group B streptococci by babies in a special-care baby unit and two postnatal wards was investigated over a six-month period using serology and phage typing. Sixty-three culture-positive babies were identified in the postnatal wards, one-third of whom had been born to mothers who were not carrying the organism in the genital tract or anorectal area during labour. A non-maternal source was identified for 14 of these 21 infants: either colonised mothers and babies in the same ward or, on one occasion, a member of the hospital staff. In the special-care baby unit, however, only one instance of nosocomial acquisition of group B streptococci was recorded despite a high prevalence of colonisation in the staff on the unit and the presence of heavily colonised babies. The results of this survey suggest that although sepsis caused by group B streptococci may be the result of nosocomial transmission, this may be prevented by careful attention to hygiene.

Factor affecting the in vitro assessment of opsonization: a study of the kinetics of opsonization using the technique of phagocytic chemiluminescence.

The importance of several factors involved in the investigation of opsonic defects was studied using phagocytic Luminol-dependent chemiluminescence. The range for the opsonization of zymosan and bakers' yeast by serum from healthy individuals was wide and kinetic studies showed comparative differences for different periods of incubation, serum concentrations and particles. Decay in the opsonic activity of serum stored at different temperatures was demonstrated and its clinical implications emphasized. By using techniques to ablate independently the classical and alternative pathways of complement activation, the contribution of these to the opsonization of zymosan, Staphylococcus aureus (NCTC 6571), Pseudomonas aeruginosa and group B streptococcus (NCTC 11080) by normal and hypogammaglobulinaemic serum at a concentration of 7% was assessed. By comparison of the results obtained for different periods of incubation between particle and serum, the need for consideration of this parameter when assessing opsonic activity was shown. The results using the chemiluminescence assay were compared with those using other methods and were found to correlate well.