Yes it is possible... Please read the following
The concern of buying a used pump is something many breastfeeding moms encounter. Although a used pump may be more affordable than a new one, there are real health implications involved.
The practice of re-using single user pumps may be dangerous because some disease organisms are know to be present in the breast milk of infected women. Additionally, if a woman has used the breast pump during an episode of cracked bleeding nipples, blood contamination may have also occurred. Home sterilization methods are not always reliable to ensure the safe destruction of all pathogens especially in the rubber parts such as washers and diaphragms.
Some pumps have internal diaphragms that cannot be removed and cleaned or replaced. In addition, even if you get a new collection kit (the part the touches your breast and collects the milk) it may be possible for air-born pathogens or droplets of milk that are not visible to the naked eye to get into a pump motor and cause contamination to the next user. Most single user pumps are "open system" pumps and do not have any protective barrier to prevent cross contamination to multiple users.
Many of the diseases that can be found in the milk of infected women are very serious or life threatening. Pathogens like Human immunodeficiency virus (HIV), hepatitis, cytomegalovirus (CMV) and others can be found in the breastmilk of infected women.
These diseases frequently go undetected for long periods of time, so even if the former user of the pump is trustworthy and willing to share this personal health information with you, she may not be aware she or her partner are carriers.
Though there have not been any documented cases of mothers or babies being infected through the use of a second-hand pump, I dont't believe sharing single user pumps is worth even a very small or theoretical risk.
taken from Used Breast Pumps - Breastfeeding Online