bClonal complex 30 (CC30), one of the major Staphylococcus aureus lineages, has caused extensive hospital-acquired and community-acquired infections worldwide. Recent comparative genomics studies have demonstrated that three CC30 clones-phage type 80/81, Southwest Pacific (SWP), and contemporary EMRSA-16 associated (Con) strains-shared a recent common ancestor more than 100 years ago. Panton-Valentine leukocidin (PVL), a bacteriophage encoded toxin that has been epidemiologically linked with community-associated methicillin-resistant S. aureus (CA-MRSA), has frequently been identified in CC30 clones, although the pvl gene variation and distribution of PVL-encoding phages are poorly understood. We determined here the distribution of PVL phages, PVL gene sequences, and chromosomal phage insertion sites in 52 S. aureus CC30 PVL-harboring isolates, collected from four continents over a 75-year period. Our results indicate that PVL phages with icosahedral heads, including ⌽108PVL and ⌽PVL, were mainly associated with phage 80/81 strains, whereas phages with elongated heads were predominantly found in SWP (⌽Sa2958 and ⌽TCH60) and Con (⌽Sa2USA) strains. Nine single-nucleotide polymorphisms were identified in the lukSF-PV gene, with six isolates harboring the R variant that has been previously associated with CA-MRSA strains. Interestingly, all six R variant strains belonged to the same Con CC30 clone and carried a ⌽Sa2USA-like phage. Similar chromosomal phage insertion sites were also identified in all 52 PVL-harboring CC30 strains. These analyses provide important insights into the microepidemiology of PVL-harboring CC30 strains, while the discovery of ⌽Sa2USA-associated R variant strains sheds further light on the evolution of PVL-positive CA-MRSA.
Purpose
The purpose of this paper is to illustrate how Six Sigma methodology has been applied in a small-scale foundry industry to improve the overall first-pass material yield and quality, with a view to the product and the process.
Design/methodology/approach
The researchers have reported this paper based on a case study carried out in industry using the Six Sigma Define, Measure, Analyze, Improve and Control (DMAIC) and its application in improving the manufacturing process of a foundry shop.
Findings
Identified root causes are validated and countermeasures are implemented for improvement. As a result of this case study, the overall first-pass yield of the sand casting process is improved to 78.88% from the previous yield of 67%. For product-specific case, yield is improved by 18% through the improved gating system design. Sigma level of the process is improved to 3.08 from baseline 2.21. Key lessons learned from this case study are mentioned in the current study.
Research limitations/implications
This case study provides a standard road map and motivates small-scale foundry industries to implement Six Sigma methodology for productivity improvement, especially in jobbing foundry. The presented paper is based on a single case study, and the results are limited to the company only. Also, one of the reasons for low process yield is slag creation, which is not covered here, as it is a concern of the material quality supplied by the vendor. However, the approach of this paper is generic for learning perspective.
Practical implications
This case study provides a standard road map and motivates small-scale foundry industries to implement Six Sigma methodology for productivity improvement, especially in jobbing foundry. Through the effective application of Six Sigma quality initiative, how a quantum jump in financial aspect could be gain, has been demonstrated.
Originality/value
This research study showcases step-by-step implementation of Six Sigma-DMAIC methodology at a small-scale foundry industry. This paper could serve as a unique roadmap for practitioners and academicians to improve the material productivity of the foundry industry both ways, product and process.
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