The man, identified as George Clarke, was pinched by a crab Saturday night in Florida's Nassau County and is the 27th case of suspected Vibrio vulnificus infection in Florida this year, the Orlando (Fla.) Sentinel reported.
"His arm turned completely black, and they have given him five antibiotics," Clarke's grandson, Bob Karstetter, said Wednesday.
State officials have not yet commented on the case.
Karstetter said he contacted the Sentinel in hopes of raising awareness of the bacteria.
"This bacteria is so fast moving that it is imperative people know to get to a hospital immediately," Karstetter said.
So far there have been 26 confirmed cases of Vibrio in Florida this year -- nine of which have been fatal, the Sentinel said.
Vibrio is a coastal bacteria that needs salt from seawater to survive. It is more prevalent in warmer months and is found in salt water and contaminated raw seafood.