Just over a month after Amazon.com Inc. ate Whole Foods, the shakeout in the American grocery aisle keeps getting uglier. The latest sign of trouble: Private-equity giant Apollo Global Management recently tossed a $50 million lifeline to Fresh Market, the struggling high-end chain it took private only 17 months ago. It will only get worse from here, analysts say. Under Amazon, Whole Foods has been cutting prices of marquee products including organic kale and avocados — a harbinger of the price wars to come. Among the most vulnerable are small regional chains that were facing fierce competition even before Amazon showed up.