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Crew scheduling problem includes two separate subproblems, namely, crew pairing and crew rostering problems. Solving these two subproblems in a sequential order may not lead to an optimal solution. This study includes two main novelties. It combines these two subproblems and presents them in a single model. On the other hand, despite previous researches that considered a pairing continuously, the proposed model benefits from the capability of considering one or more days off in a pairing assigned to a crew member. This is extremely useful as it enables the crew to participate in required courses, doing medical checks, etc. Two solution approaches, namely, Genetic Algorithm (GA) and Particle Swarm Optimization (PSO), are used to solve the model. Eventually, the performance of the proposed algorithms is evaluated. Both ended to satisfactory results; however, PSO relatively outperformed GA in terms of solution optimality and computational time.

Background: Streptococcus agalactiae, also known as Group B Streptococcus (GBS) is a commensal organism in the urogenital tract and rectum in approximately 25% of the healthy adult female population. The bacterium is the leading cause of bacterial meningitis, pneumonia, and sepsis in human infants. Materials and Methods: Our study was performed over a three -month period from April to June 2014. Midstream specimens of urine were collected from outpatients suspected of having a bacterial urinary tract infection, which had not received any antibiotics. Group B Streptococci isolates were confirmed by typical colony morphology and identified by differential tests. Antibiotic susceptibility testing was carried out by disk diffusion method on Mueller Hinton agar (Merck, Germany) based on (CLSI) Guidelines 2012. Results: GBS strains were isolated from 264 (21.1%) cases (out of 1249 positive bacterial urine cultures). The higher prevalence was recorded in the 15-44 and 45-64 age groups. Antibiotic susceptibility tests revealed that vancomycin, penicillin, and linezolid had the lowest, and tetracycline had the highest resistance rate. Conclusion: In conclusion, the results of the present study confirm the universal susceptibility of GBS strains to the penicillin family and assert the use of penicillin or ampicillin as the first drug of choice for treatment and prophylaxis against GBS infections. However, it is important to perform antibiotic susceptibility testing whenever penicillin could not be prescribed.

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