MIAMI — Losing is a disease. The Mets are living proof of that.

They have perfected the art of losing with a 5-21 month of June, their worst June swoon ever, and their second straight loss to the Marlins on Saturday at Marlins Park. Even Jacob deGrom is not immune from the losing.

There needs to be a complete cultural shift and a lot of different players, because these Mets have become an embarrassment. They own the key to unlock a different way to lose nearly every game.

Bad defense. Check.

Bad selection of pitches. Check.

Bad instincts. Check.

Bad clutch hitting. Check.

With Saturday’s 5-2 loss to the Marlins, the 32-48 Mets have dropped to bottom of the NL with a .400 winning percentage. The tear-it-down-brick-by-brick Marlins are at 34-50.

Mets manager Mickey Callaway said it would do no good to blow up in the media regarding the Mets’ losing ways. He said he addresses those issues with the players. With so much losing, there certainly is disharmony in the clubhouse. Some players who thought Terry Collins was the Mets’ problem are now not happy with Callaway’s first-year managing style.

Too bad. Get a bigger mirror and look into it.

Callaway has made his mistakes, but this goes way beyond managerial decisions.

Losing is a disease. Losing is a culture.

This time a 2-0 lead thanks to Jose Bautista and Todd Frazier solo home runs (are there any other kind in Metland?) was lost as the Marlins scored three times in the sixth. The first two runs came on a Brian Anderson home run on a do-nothing changeup from deGrom — the third straight changeup deGrom delivered and the fourth in five pitches to Anderson.

The go-ahead run came with runners on first and third and two out on a little roller up the first base line. No, that ball did not get under Wilmer Flores’ glove. But Flores never instinctively charged the baseball and JT Riddle beat Flores to first base on the play.

Flores insisted he really had no play and Callaway said, “You just got to come and get it, you gotta sell out. He still had a chance to come get it hard and put the tag on way before the runner would have gotten past him.’’

The Mets just don’t get it, and a lot of this goes back to their construction and not valuing defense.

Two more insurance runs came in the seventh after a two-out error by learning-on-the-job shortstop Amed Rosario led to a J.T. Realmuto two-run double to left off Robert Gsellman, who has lost his reliever’s touch.

And so it goes. There also was a weird pull-up at first base when pinch-hitter Jose Reyes grounded out batting for deGrom in the seventh. Callaway inquired about the play and said Reyes told him he “felt something coming out of the box and he was scared he was going to pull something, he didn’t say what it was,’’ Callaway explained.

For his part, Reyes moved quickly out of the clubhouse and was not available for comment.

Losing is a disease.

The Mets have now somehow gone 12 straight series without a series win. They are the complete opposite of the Yankees.

They have lifted losing to an art form.

The talent is not there for the Mets. The defense is abysmal which leads to so many problems. Every day is spring training with a new tutorial being taught to players like Flores, who simply does not have the foot speed to cover up for his defensive shortcomings.

The Mets lost to a pair of 22-year-old starters the past two days as the Marlins rebuild is going full blast. Pedro Lopez made his major league debut Saturday to get his first win. DeGrom is 5-4, despite a 1.84 ERA.

“It’s difficult right now,’’ Callaway said. “I know the players are feeling it, the fans are feeling it, we are going to continue to try to do everything we can as a staff, organization and the players to try and get in a better spot than we are because this isn’t acceptable to anybody.’’

Losing is a disease.