1. Microbiology Laboratory, University Hospital “St. Marina”—Varna, 9010 Varna, Bulgaria
2. Medical University of Varna, Varna 9002, Bulgaria
3. Pediatric Hematology and Oncology Clinic, University Hospital “St. Marina”—Varna, 9010 Varna, Bulgaria
4. Department of Ecology and Environmental Protection, Technical University of Varna, 9010 Varna, Bulgaria