How can one check if the food does not have excess levels of pesticides?  The need of the hour is to have some machine/tool that checks what is the composition of the food that we are eating and advices us to stop or go ahead with it. I am not sure if there is anything created like that? To take the examples of the news: Salmonella in eggs   How can we ensure that the food that we eat is not unhealthy? 
http://www.psfk.com/wp-content/uploads/2010/04/heidi_kenney_organic_food_chart_1.jpg  This picture is a quick and dirty cheat sheet that shows which foods generally have the most pesticides used.  As far as meat goes, most of the illnesses are byproducts of factory farming methods. Beef should ideally be grass-fed and pastured. Cows don't naturally eat grains so the corn-fed varieties have a skewed omega-3/omega-6 fat balance. Corn-fed cows also have weakened immune systems which necessitates the antibiotics that many people try to avoid.  www.eatwild.com has a list of farms in your area that support pastured livestock. It will generally be more expensive than store bought products,  but if you are looking for higher quality food, it is the way to go. 