Prevalence, determinants, and molecular epidemiology of Streptococcus pneumoniae isolates colonizing the nasopharynx of healthy children in Rome.

The aim of this study was to determine the factors favouring Streptococcus pneumoniae nasopharyngeal colonization of healthy children attending daycare centres and to describe the circulation of penicillin-nonsusceptible strains using molecular techniques. A single nasopharyngeal swab was obtained from 610 children attending daycare centres in the southeast area of Rome. Streptococcus pneumoniae isolates were serotyped, and antibiotic susceptibility was assayed by the E test. The genetic determinants of erythromycin resistance were detected by a duplex polymerase chain reaction, and the penicillin-nonsusceptible isolates were typed by pulsed-field gel electrophoresis. The overall carriage rate of Streptococcus pneumoniae was 14.9%. Living with more than three persons in the same household was the only risk factor statistically associated with carriage. Sixteen of 85 (18.8%) strains were nonsusceptible to penicillin, and 44 (52%) were resistant to erythromycin. Of the erythromycin-resistant strains, the vast majority showed a high level of resistance and carried the erm(B) gene. The penicillin-nonsusceptible strains belonged to six different serotypes; molecular typing showed that in only one case (2 strains) was there a circulation of the same clone in the same daycare centre. In view of the high rate of resistant Streptococcus pneumoniae strains, risk factors for carriage of resistant strains were evaluated. Children who received macrolides in the previous month had a higher risk of being colonized by macrolide-resistant strains as well as by strains resistant to both penicillin and erythromycin. Limiting the use of antibiotics in children seems the most appropriate measure to control the spread of antibiotic-resistant strains.

Labelling of blood platelets with stable tracers.

Half-time values of platelets labelled with stable rubidium are compared to those of platelets labelled with Cr51. Platelets labelled with stable rubidium are assayed by a very simple version of the X-Ray fluorescence equipment. The mean quantity of rubidium incorporated by the cells is of about some microgram Rb per ml blood. The in vitro half-time of human Rb labelled platelets stored at 22 degrees C is 41.2 +/- 3h compared with the value 44.8 +/- 3h for platelets labelled with Cr51, as deduced by six experiments. The in vivo half-time of rabbit platelets labelled with stable rubidium is 22 +/- 3h compared with the value 18 +/- 3h of platelets labelled with Cr51; ten experiments were carried out.

In vitro effect of levamisole on oxygen consumption and survival of platelets.

Levamisole at a concentration of 10(-3)M inhibits the oxygen consumption of resting platelets, the thrombin induced burst and the platelet aggregation induced by ADP. At the concentration of 10(-7)M it exerts still an inhibitory activity of the thrombin induced burst, but it does not inhibit neither the basal oxygen consumption nor the platelet aggregation. At every tested concentration platelet survival in the presence of levamisole is comparable to that of controls. Levamisole moreover, together with theophylline and glucagon, shows a synergistic inhibiting influence toward the burst of oxygen consumption. Our data suggest that levamisole may act by producing an enzymatic block of cyclo-oxygenase.

In vitro labeling of platelets with stable rubidium compounds.

It is a common practice in diagnostic hematology to mark blood cells with radioactive tracers, such as 51Cr, 55Fe, 75Fe, etc., to determine their life-span and study their metabolism. A program has been started to verify the possibility of marking blood cells with stable indicators, assayed by radioisotope-induced X-ray fluorescence analysis. All elements may be considered as indicators aggregating to blood cells, and for in vivo measurements, which are not toxic in the quantities injected, calculated on the basis of the limit of detection of the technique. In this study platelets were marked with a very small quantity of stable compounds of rubidium, a potassium analog. Measurements were carried out in vitro on platelets of normal subjects and in vivo on platelets of rats and rabbits. Several survival curves were deduced and life-span values obtained in accord with previously reported values.