Can a nursing mother eat unpasteurized soft cheeses?
Yes, nursing mothers can eat soft cheeses. Unpasteurized soft cheeses (and other unpasteurized dairy products) can carry a bacteria called listeria monocytogenes. Cheese made in the United States must be made from pasteurized milk (pasteurization kills the listeria organism), but imported cheeses may be a problem. Listeriosis is usually a minor flu-like illness in healthy adults, but can cause serious problems for pregnant women and may be linked to stillbirth and miscarriage (as it can be passed to baby via the placenta). Although eating unpasteurized dairy products is not recommended during pregnancy, it is not considered a problem for nursing moms.
Per Lawrence (Breastfeeding: A guide for the medical profession 1999, p 569), "No evidence in the literature suggests transmission of Listeria through breastmilk." This reference indicates that the only thing that might interfere with breastfeeding is a mother's inability to nurse due to severe illness.
Other foods that can carry listeria that are considered safe for nursing moms (but not during pregnancy):
cold hot dogs, luncheon meats, or deli meats
soft cheeses such as feta, Brie, Camembert, blue-veined cheeses; and Mexican-style cheeses such as "queso blanco fresco"
refrigerated pâté or meat spreads
refrigerated smoked seafood (not part of a cooked dish)
unpasteurized milk
Source: Listeriosis and Pregnancy: What is Your Risk?
The rules for pregnancy and the rules for breastfeeding are quite different