Foodborne Pathogens: Bacteria

March 2nd, 2010

Bacterial pathogens in food• Foodborne disease is likely

underreported• Not all foodborne outbreaks are

recognized• Causes can be difficult to pinpoint• Occur in all types of foods

Categories of foodborne disease

• Diseases caused by ingestion of the organism and subsequent infection– E. coli O157:H7– Salmonella spp– Listeria monocytogenes– Campylobacter jejuni

• Diseases caused by ingestion of toxins produced by bacteria in foods– Clostridium botulinum– Staphylococcus aureus

Escherichia coli• Example: O157:H7• Belongs to the enterohemorrhagic

group• Cattle are the major reservoir

– Found in their intestinal tracts– Contamination during slaughter process

• Major risk group is children: hemolytic uremic syndrome

Escherichia coli• Food risks• Beef• Ground beef is higher risk

(contamination during processing)• Vegetables that become

contaminated by fecal matter (spinach!)

Salmonella

• Diarrheal disease• Fecal-oral route• Species enterica• Many serogroups that cause

foodborne disease• Distinct from typhoid fever

– Typhoid fever can spread via food, but is rare in countries with advanced sanitation

Salmonella

• Food risks• Eggs• Chicken• Unpasteurized milk• Has been linked to processed foods

as well

Listeria• Listeria monocytogenes• Often a mild disease, but can

progress to meningitis and septicemia• High risk for pregnant women; can

cause miscarriage• Bacteria has environmental reservoirs

(soil, grains used as livestock feed)• Can survive and grow at refrigeration

temperatures

Listeria• Gram positive rod

Listeria• Food risks• Unpasteurized milk• Raw milk soft cheeses• Deli meats

Staphylococcus aureus

• Disease is caused by the toxin produced by the bacteria

• Foodborne intoxication• Bacteria produce the toxin while in

the food• Onset is usually short time after

eating• Toxin is fairly heat stable

Staphylococcus aureus

• Gram positive cocci• Distinguishing feature is a positive

coagulase (plasma coagulation) reaction

Staphylococcus aureus

• Food risks• Custards• Sliced meats• Meat products

Botulism• Clostridium botulinum• Get into food, grow and produce toxin• Neurotoxin: causes descending paralysis

– Can be fatal– Treated with antitoxin

• Bacteria occur naturally in soil as spores• No person-to-person transmission

Botulism• Gram positive anaerobic rod• Toxin can be detected using

antibody assays• Bacteria may not be culturable in

suspect food

Botulism• Food risks• Improperly processed low-acid canned

foods• Low oxygen content• Toxin can be destroyed by heating, but

improperly heated foods are at risk• Outbreaks associated with home

canning

Control of foodborne bacteria

• Food sanitation• Prevention of spread from ill food handlers• Handwashing• Sanitizing production environments• Prevention of cross-contamination from

raw foods• Process control during food production• Adequate cooking and refrigeration• Pasteurization