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The depletion of natural aggregate sources which generally accounts for a huge percent of Hot Mixed Asphalts (HMAs) and the difficulty posed by disposal scrap tires are a major environmental concern for the future. The use of waste products like scrap tires in highway construction is considered a sustainable way of dealing with these issues. Crumb rubber is a material pulverized from waste polymer products like scrap tires which are then added to HMAs to improve their performance. This study focuses on the sensitivity of crumb rubber particle sizes (fine ≤1.18 mm), (coarse ≥1.18 mm and ≤3.35 mm) (and mix of 50% fine and 50% coarse) and partial replacement (1.5 and 2.5% of total weight) of aggregates on the Marshall test parameters of rubberized asphalt mixes. The Marshall test parameters: density, stability, VTM, VFB of both rubberized asphalt and conventional asphalt samples were compared and also the Asphalt Institute (AI) and National Asphalt Pavement Association (NAPA) methods were used to obtain the optimum bitumen content (OBC). From the results, it suggests that; the utilization of dry process methodology of adding crumb rubber additives in different sizes and percentages had a considerable effect on Marshal test parameters and also influences the optimum binder content estimates. The results of this study can be used as a reference point for the use of crumb rubber in HMAs.

Introduction: Antibiotics are lifesaving compounds that have been successful for decades. However, many pathogenic bacteria are becoming resistant to them. Cross-resistance of the macrolide-lincosamide-streptogramin B (MLSB) antibiotic classes is a major cause of increased morbidity. This study appraises the phenotypic and genotypic distribution of inducible clindamycin resistance among methicillin-resistant Staphylococcus aureus (MRSA) isolates. Materials and Methods: Erythromycin-induced resistance to clindamycin antibiotics among MRSA isolates was verified phenotypically using the Double-disk diffusion test (D-test) and genotypically by the polymerase chain reaction. Results: All MRSA isolates were resistant to erythromycin. The prevalence of iMLSB (iMLSB: inducible macrolide-lincosamide-streptogramin B) phenotype was 23.7% (9/38), macrolide streptogramin (MS) phenotype 47.4% (18/38), and cMLSB (cMLS: constitutive macrolide-lincosamide-streptogramin) phenotype 28.9% (11/38) of the isolates. The nine isolates with the iMLSB phenotype were tested for the presence of the erythromycin ribosomal methylase (erm) gene. The ermA gene was detected in five (55.6%) isolates, the ermB gene in two (22.2%) isolates, and the ermC gene in two (22.2%) isolates. Conclusion: The erm-positive isolates expressed the iMLSB phenotype, and the ermA gene was predominant. We showed that the cMLSB phenotype was prevalent among the MRSA isolates, signifying the possibility of achieving a good therapeutic outcome when clindamycin is used. The observed distribution of the erm gene explored here gives credence to the adequacy of the D-test in monitoring and testing for potential clindamycin treatment failures.