OLDWICK, N.J.--(BUSINESS WIRE)--A.M. Best has assigned a financial strength rating of A+ (Superior) and an issuer credit rating of “aa-” to ProAssurance American Mutual, a Risk Retention Group (ProAssurance RRG) (District of Columbia). The outlook assigned to both ratings is stable. These ratings recognize the implementation of a quota share reinsurance agreement between ProAssurance RRG and ProAssurance Indemnity Company, Inc. (ProAssurance Indemnity), one of the lead companies of ProAssurance