MEET OUR TEAM

Karen-Whitley Bishop, PA-C – Board certified as a Physician Assistant Karen has been a part of the team since opening in 2013. She joined us after working for more than 20 years in the emergency department at HealthAlliance Leominster and Burbank Hospitals. She previously was a research assistance at Massachusetts Eye and Ear Infirmary in Boston.

Karen received her Master’s in Physician Assistant Studies from Mount Holyoke College in South Hadley. She is a resident of Rutland.

Michael Cobill, PA-C – Board Certified as a Physician Assistant, Mike joined our team in 2021.

Before joining our team Mike worked primarily in the Emergency Department at Mount Auburn Hospital in Cambridge, where he became the Chief PA for the department. His prior experience also includes working per diem at the North Shore Medical Center Emergency Department in Salem, the Brigham and Women’s Faulkner Emergency Department in Boston, as well as in the urgent care setting in both the Boston and Springfield areas.

A graduate of the University of Connecticut, he received his Master’s in Physician Assistant Studies at Northeastern University in 2013. He has undergone training in Basic Life Support, Advanced Cardiac Life Support, Advanced Trauma Life Support, and Pediatric Advanced Life Support. Mike is a resident of Longmeadow.

Bob Cooke, PA-C – Board Certified as a Physician Assistant, Bob has been a member of the team since 2019.

In joining our team Bob brings with him 25+ years of experience. A graduate of the Northeastern University PA Program in 1996, he has worked in the fields of cardiology, primary care medicine, as well as emergency and urgent care medicine. Bob has over 10 years of experience working in the ER having worked primarily in Leominster with the Wachusett Emergency Physicians. He also spent time working in the emergency room at Nantucket Cottage Hospital, Sturdy Memorial Hospital in Attleboro, and Saint Vincent Hospital in Worcester.

Karl Hirschegger, PA-C – Karl is a board-certified physician assistant that joined our team in 2023.

He brings with him a breadth of knowledge in critical care and emergency medicine. After graduating from the PA program at Bay Path University in 2015 Karl began working at Berkshire Medical Center in the emergency room. After four years in the ER Karl transitioned to working at Cooley Dickinson Hospital as a Critical Care PA in the ICU, where he continues to work full time. In the ICU he cares for the sickest patients in the hospital and performs a wide range of complex procedures. Since joining our team, he has enjoyed contributing to the continuum of patient care by applying his broad knowledge to the urgent care setting.

Karl received his undergraduate degree from Assumption University where he majored in Biology and Philosophy with a minor in Psychology. He currently resides in Chester with his wife and two children.

Karl is also one of only about sixty licensed falconers in the state of Massachusetts.

Donald P. Jackel, DO. FACEP – Board Certified in Emergency Medicine and a doctor of Osteopathic Medicine, Don joined our team in 2013 from Wachusett Emergency Physicians, PC (WEP), UMASS Memorial Health Alliance Hospitals.

He has served as Department Chair and Clinical Director of Wachusett Emergency Physicians in Leominster and is affiliated with the emergency department at Saint Vincent Hospital in Worcester.

A Magna Cum Laude graduate of the University of Southern Maine, Don received his doctorate from the University of New England’s College of Osteopathic Medicine. He then conducted his internship at UMASS Medical Center, where he also completed his residency in Coordinated Emergency Medicine.

He is resident of Worcester.

Donald P. Jackel, DO. FACEP – Board Certified in Emergency Medicine and a doctor of Osteopathic Medicine, Don joined our team in 2013 from Wachusett Emergency Physicians, PC (WEP), UMASS Memorial Health Alliance Hospitals.

He has served as Department Chair and Clinical Director of Wachusett Emergency Physicians in Leominster and is affiliated with the emergency department at Saint Vincent Hospital in Worcester.

A Magna Cum Laude graduate of the University of Southern Maine, Don received his doctorate from the University of New England’s College of Osteopathic Medicine. He then conducted his internship at UMASS Medical Center, where he also completed his residency in Coordinated Emergency Medicine.

He is resident of Worcester.

Mary Beth (Reidy) Laliberte, PA-C – Board Certified as a Physician Assistant, Mary Beth joined our team in 2013 from Wing Emergency Physicians.

Prior to becoming an integral member of our team Marybeth worked as a Physician Assistant at Wachusett Emergency Physicians in Leominster as well as in the Baystate Emergency Department. Before her time working in the ER she worked in the Department of Cardiology at the University of Massachusetts-Wing Memorial Hospital; Hampden County Sheriff’s Department, Springfield; and Department of Cardiothoracic Surgery, Veterans Administration Hospital, West Roxbury.

Mary Beth has received a Physician Assistant Certificate and Master of Health Professions degree from Northeastern University in Boston. A Frances Perkins Fellow at Mount Holyoke in South Hadley, she also received a bachelor of science nursing degree, magna cum laude, from Elms College in Chicopee.

William O’Callahan Jr., M.D. – Board Certified in Emergency Medicine, Bill joined our team in 2022 from Newton-Wellsley Hospital ER.

After attending Harvard University during his undergraduate years, Bill then attended the University of Massachusetts Medical School where he proceeded to do his Emergency Medicine residency and became the Chief Resident in his final year.

Following his residency Dr. O’Callahan went on to practice as a Flight Physician for two years, spent a year practicing Emergency Medicine at Kaiser Permanente Hospital in Honolulu, and then went on to act as an emergency medicine clinical instructor at Boston University School of Medicine as well as at the former Boston City Hospital.

Dr. O’Callahan continues to work clinically in the ER but has joined our team and brings with him 30+ years of emergency medicine experience.

When Bill is not working in the clinic or the emergency room you are likely to find him on his boat, deep sea fishing.

Sara McGowan, PA-C – Board Certified as a Physician Assistant, Sara joined our team in 2025.

Sara began her career in the field of Emergency Medicine, working at Mercy Medical Center in Springfield, MA. While working in the ER she also worked per diem for Noble Express Urgent Care in Westfield.

In 2019 Sara left Mercy Medical Center and transitioned to a full-time role at the former Baystate Health Urgent Care until its closure in 2023.

Sara received her Master’s Degree in Physician Assistant Studies at Springfield College and has now returned to her alma mater to work as an Assistant Professor for the PA program, acting as Director of Clinical Education.

With her many years of ER and Urgent Care experience Sara brings with her a breadth of knowledge and expertise to our group.

Charity Pressey, PA-C – Board certified as a Physician Assistant, Charity joined our group in 2025.

With a strong scientific and medical foundation, Charity holds an Associates in Radiologic Technology, a Bachelors in Science (Biology, Chemistry, and Movement Science), and a Masters in Physician Assistant Studies. This diverse academic background enables her to approach patient care holistically, with a focus on inclusivity and evidence-based medicine.

Her clinical experience spans Urgent Care, Emergency Medicine, and Occupational Medicine, equipping her to manage a wide spectrum of medical conditions with confidence. As a provider certified in BLS, ACLS, and PALS, Charity prioritizes patient safety and quality of care in every encounter.

Charity’s dedication to excellence has earned her recognition as a Top Massachusetts Provider (2024) and Advanced Practice Practitioner of the Year (2023). Passionate about medical education and practice improvement, she actively mentors future healthcare providers and contributes to initiatives aimed at enhancing patient outcomes.

Beyond her professional commitments, Charity finds joy in outdoor adventures like biking, snowboarding, kayaking, and tennis, as well as reading and board games. Whether exploring nature or creating memories with loved ones, she values balance, adventure, and meaningful connections.

Laura Mitrowski, PA-C– Board certified as a Physician Assistant, Laura joined our team in 2025.

Laura brings over 12 years of experience in Emergency Medicine from Mercy Medical Center in Springfield, MA, where she became Senior Physician Assistant. She also brings 6 years of prior Urgent Care experience to the team.

Laura holds the NCCPA Certificate of Added Qualifications in Emergency Medicine. She is certified in Basic Life Support, Advanced Cardiac Life Support, and Pediatric Advanced Life Support. She is also trained in Advanced Trauma Life Support, Emergency Ultrasound and Medication Assisted Treatment.

She received her Bachelor of Science in Microbiology from the University of Massachusetts, Amherst in 2009 and a Master of Science in Physician Assistant Studies from Springfield College, Springfield, MA in 2012.

Leila Ketterman, PA-C– Board certified as a Physician Assistant, Leila joined our group in 2025.

Since graduating from Springfield College in 2014, where she received her Master’s in Physician Assistant Studies, Leila has worked primarily in Emergency Medicine and Urgent Care.

Leila began her career at Connecticut Children’s Emergency Department, where she learned invaluable lessons on managing acutely ill or injured neonates, toddlers, and children.

Wanting to broaden her knowledge and experience outside of the pediatric realm, Leila went on to work at several urgent care centers before accepting a full-time position in the Mercy Medical Center Emergency Department in Springfield where she continues to work per diem.

Leila has undergone training in Basic Life Support, Advanced Cardiac Life Support, Pediatric Advanced Life Support, and Moderate Sedation.

Rebecca Gregor, PA-C– Board Certified as a Physician Assistant, Rebecca joined our team in 2025.

Rebecca graduated with her Master’s in Physician Assistant Studies from Springfield College in 2015. After graduating she went on to work in the Emergency Department at Mercy Medical Center, where she worked for over 6 years, gaining experience managing acutely ill or injured patients of all ages.

After leaving the ER Rebecca went on to work in urgent care medicine, both in Connecticut and Massachusetts, where her valuable ER experience allowed her to provide prompt, evidence-based care to those seeking her help.

Rebecca holds certificates in Basic Life Support, Advanced Cardiac Life Support, and Pediatric Advanced Life Support.

Natalee Georgantas, PA-C–Board Certified as a Physician Assistant, Natalee joined our team in 2025.

Natalee attended MCPHS Boston and graduated with her master’s degree in Physician Assistant Studies in 2012. After graduation Natalee began her career in Emergency Medicine working full time at Cambridge Health Alliance.

In 2014 Natalee moved back to her hometown of East Longmeadow and began working full time in the Emergency Department at Mercy Medical Center. In 2020 she then transitioned to a per diem role in the ED and became a part time provider for Baystate Health Urgent Care in Longmeadow until its closure in 2023. Natalee continues to work per diem in the ED but is excited to bring her many years of experience in both emergency and urgent care medicine to our group.