Listeria monocytogenes is the only species that infect humans. Infection most common in: Pregnant women still birth Fetuses Newborns Immunocompromised individuals. Specimen received: CSF. Blood.
Gram Positive Bacilli Pleomorphic rods (coccobacilli = short bacilli) can form chains. Non-capsulated
Aerobic and facultative anaerobe. Grow on Nutrient Agar: very light growth & give bluish coloration reflect blue light. Nutrient Agar
On BA: small translucent drop-like colonies (moist) with small zone of slight beta-hemaolysis
Can grow at refrigeration temperature (4 ˚C) Temperature range for growth is 3 – 45 ˚C; with an optimum of 30 ˚C. 24 h.
Listeria. Catalase +ve. CAMP +ve. Group B Streptococcus. Catalase –ve. CAMP +ve (GBS)
Listeria. Catalase +ve. Esculin Hydrolysis +ve Group D Streptococcus Catalase -ve. Esculin hydrolysis +ve (GDS)
Listeria Short gram positive rods, can occur as diplobacilli or in short chain. Catalase +ve. Motile at room temperature 25 ºC Corynebacterium spp. Polymorphic gram positive rods. Catalase +ve. Non motile at any temperature
Semisolid medium showing the typical "umbrella" growth. Negative control non-motile Positive umbrella like motility at Room Temperature
Wet preparation examined under microscope X40. Slide + drop of saline examine under X40 Listeria monocytogenes Distinctive tumbling motility in a liquid medium @ 25 ºC
1. Gram stain (short gram positive rods) 2. Catalase +ve. 3. Slight beta-hemolysis on blood agar. 4. Umbrella like motility on semi-sold media (soft agar) at room temperature.
Keep your refrigerator clean and cold—below 40° F. Refrigerate or freeze food within two hours. Thoroughly cook meat and poultry. If you just can’t resist the idea of a pastrami and Swiss, be sure to heat the meat until steaming to kill bacteria. Separate uncooked meats from other foods. Eat only pasteurized dairy products. Avoid soft cheeses like feta. Don't eat refrigerated meat or seafood spreads, and smoked seafood For Pregnant women and others at higher risk for Listeriosis :
1. Perform Gram Stain. 2. Perform Catalase. 3. Inoculate organism in soft agar to see Umbrella like motility. F OR DEMONSTRATION : 1. See Listeria on blood agar. 2. See listeria on Nutrient agar. 3. See umbrella like motility in a soft agar. 4. See gram stain of Listeria.