5 _Isolation and Detection of Listeria monocytogenes and Yersinia enterocolitica in Food

• deep red center

• Surrounded by clear, colorless zone

• 1-2mmdiameter

Y. enterocolitica on YSA (CIN) agar should have:

• Lactose negative colonies

• flat, colorless, or pale pink

• 1-2mmdiameter

Y. enterocolitica on MacConkey agar(MAC) agar should have:

Listeria monocytogenes

• Causes the foodborne disease Listeriosis.

• Commonly found in nature; soil, groundwater, rotting vegetation and animal feces.

• Most people get listeriosis from eating contaminated foods.

Listeriosis

Listeria monocytogenes Causes the foodborne disease ____

Characteristic of Listeria monocytogenes

• Gram (+) bacilli

• Motile (multi-flagellated)

• Non-spore forming

• Facultative anaerobe 

• Catalase positive, oxidase negative

• Indole negative, Urease negative

Contaminated foods

are the most common cause of listeriosis infections.

• Hot dogs and Deli meats

• Fresh vegetables

• Fresh fruits, especially melons

• Unpasteurized dairy products

The most common foods that cause listeriosis include:

• Pregnant people 

• Developing fetuses

• People 65 or older

• People with a weakened immune system

Greatest risk of becoming very ill or dying include:

• Blood.

• Cerebrospinal fluid

• Meconium (baby’s first poop; it’s dark green and thicker and stickier than normal poop).

• Vomit.

• Food.

• Animal feed

Tests may include checking the following for the presence of L. monocytogenes:

Meconium

baby’s first poop; it’s dark green and thicker and stickier than normal poop

sulfamethoxazole and ampicillin

Antibiotics commonly used to treat listeriosis include

Yersinia enterocolitica

• Cause the foodborne disease Yersiniosis.

• People get this infection when they eat pork that’s raw or undercooked.

• Common in children than adult

chitlins

People who prepare ___(a food made from pig intestines) are more likely to get the infection.

Yersiniosis

Yersinia enterocolitica Cause the foodborne disease

• Gram (-) bacilli

• Non-spore forming

• Motile

• Aerobic, Facultative anaerobe or Microaerophile

• Catalase positive, oxidase negative

• Indole variable, Urease positive

Characteristic of Yersinia enterocolitica:

• Most commonly by eating contaminated food, especially raw or undercooked pork.

• Drinking contaminated water or unpasteurized milk 

• Touching contaminated feces

• Contact with an infected animal, such as a pig, dog, cattle

• Receiving a blood transfusion contaminated with Yersinia

Yersiniosis is a bacterial disease caused by:

blood, bile, cerebrospinal fluid, mesenteric lymph nodes, peritoneal fluid, throat swab, and wounds

Other specimens that may be tested for the detection of Yersiniosis include: 

Cefsulodin-irgasan-novobiocin (CIN) agar

as colonies with a bulls-eye appearance, a deep red center, and a translucent outer border.

Purple slant/purple butt (alkaline), the butt reaction may be masked by H2S production

Positive reaction of Lysine Decarboxylation (detected in butt)

Purple slant/yellow butt (acid), fermentation of glucose only

Negative reaction of Lysine Decarboxylation (detected in butt)

Red slant

Positive reaction of Lysine Deamination (detected in slant)

Slant remains purple

Negative reaction of Lysine Deamination (detected in slant)

Black precipitate

Positive H2S production:

No black color development

Negative H2S production:

demonstrated by the presence of bubbles or cracks in the medium

Gas production H2S production: