Influence of the association between platelet-rich fibrin and bovine bone on bone regeneration. A histomorphometric study in the calvaria of rats

This study aimed to investigate the effects of platelet-rich fibrin (PRF) associated or not with Bio-Oss on bone defects in the calvaria of rats. A critical-size defect of 5-mm diameter was performed in the calvaria of 48 rats. These animals were divided into six groups of eight animals each, according to the treatment received: homogeneous clot, autogenous clot, autogenous PRF, homogeneous PRF, Bio-Oss, or Bio-Oss associated with PRF. The animals were euthanized after 30 or 60 days. Bone regeneration was evaluated by histomorphometric analysis. The highest mean percentages of new bone formation at 30 days (54.05% ± 5.78) and 60 days (63.58% ± 5.78) were observed in the Bio-Oss associated with PRF group; in particular, the percentage of new bone at 30 days was significantly higher than that of all of the other groups (P<0.01). At 60 days, the Bio-Oss associated with PRF (63.58% ± 5.78) and Bio-Oss (57.34% ± 5.78) groups had similar results, and both showed a statistical difference compared to the other groups. PRF had a positive effect on bone regeneration only when associated with Bio-Oss.

Penicillin tolerance among beta-hemolytic streptococci and production of the group carbohydrates, hemolysins, hyaluronidases and deoxyribonucleases

Penicillin tolerance among 67 strains of beta-hemolytic streptococci was examined by determining the ratio of the minimal bactericidal concentration to the minimal inhibitory concentration as 32 or greater. Tolerance was demonstrated in 15 group A strains and in 11.7, and 4 of groups B, C and G, respectively. Thereafter the effects of a subminimal inhibitory concentration (1/2 MIC) of penicillin on the bacterial products of four tolerant and four nontolerant strains (two of each Lancefield group) were analyzed and compared. The antibiotic caused a marked increase in the expression of the group carbohydrates for strains of group B. Penicillin was found to reduce the cell-bound hemolysin activities of the four tolerant strains and to increase the activity of the other (free) form of nontolerant groups A, C and G hemolysins. Penicillin caused an increase in the extracellular hyaluronidase activities of one group A and groups B, C and G streptococci. With added antibiotic the production of deoxyribonuclease by tolerant groups A, C and G was greatly enhanced and that of the group B streptococcus was arrested.

Hyaluronidase production by groups A, B, C, and G streptococci: a statistical analysis

Production of hyaluronidase by 147 strains of beta hemolytic streptococci was studied employing a sensitive dye-binding assay and levels of enzyme activity were evaluated statistically. The analysis of variance showed that group A strains isolated in Rio de Janeiro produced significantly smaller amounts of enzyme than group A strains from a Minneapolis (USA) collection or than groups B and G brazilian isolates. The t test revealed that M not typable nose/throat group A strains produced more hyaluronidase than skin isolates. The analysis of variance did not show a significant difference in the enzyme production between M typable and not typable brazilian strains of group A streptococci. High enzyme--producing strains were not restricted to a few serotypes of group B streptococci.

Effect of subminimal inhibitory concentrations of penicillin on hyaluronidase production by group A streptococci

A sensitive dye-binding assay was employed to study the extracellular hyaluronidase produced by three penicillin-sensitive strains of group A streptococci belonging to M types 4, 24 and 28. Enzyme was produced by all strains at appreciable levels. Subminimal inhibitory concentrations of penicillin in growing cultures increased enzyme production by M types 4 and 24 strains. Growth of the M type 28 R strain with added antibiotic was accompanied by a reduced production of hyaluronidase.