According to this link, which is similar to the Reuter's article, the FDA basically sat on their hands when the Abbot plant shut down and whatever investigation happened was slowed by inertia in both- while the bacteria wasn't found in the areas where the formula was made, it was found in the plant.
From the article,
"The company halted production while Food and Drug Administration inspectors conducted a six-week investigation
of the plant."
"Rep. Rosa DeLauro, D-Conn., reported last month that a whistleblower had contacted the FDA in October with allegations about unsafe conditions and practices at the plant, including falsifying plant records and failing to properly test formula for contamination. She said the FDA did not interview the whistleblower until late December. Califf is scheduled to answer questions from DeLauro and other lawmakers on Thursday."
Many questions remain about the shuttered Abbott baby formula plant at the center of a nationwide shortage