Diseases Associated With Bacteremia By Dr. Emad AbdElhameed Morad Lecturer of Medical Microbiology and Immunology
Bacteremia means presence of bacteria circulating in blood. • Bacteremia is a characteristic feature of some diseases like: • Enteric fever (typhoid fever + paratyphoid fever) • Brucellosis (undulant fever) • Endocarditis • Meningitis • Puerperal sepsis • Note that blood culture is the main corner in laboratory diagnosis of bacteremia.
Species Members of this genus are pathogenic to animals from which they are transmitted to man causing brucellosis (Malta or undulant fever). Species are: Brucella abortus causing abortion in the cattle. Brucella melitensis causing infection in goats and sheep. Brucella susis causing infection in the pigs. Brucella canis causing infection in dogs.
Morphology Gram negative short cocco-bacilli, non motile, non spore forming and non capsulated.
Cultural characters Aerobe. Require enriched media for growth such as brucella agar, trypticase soy agar, chocolate agar, brain heart infusion agar, serum dextrose agar. Colonies are small, convex and translucent. 10% CO2 is required for isolation of Brucella abortus.
Biochemical reactions All are oxidase positive. All are catalase positive. All are urease positive.
Virulence factors Lipopolysaccharide (LPS) is the major virulence factor because it has endotoxic activity. It can survive intracellular, so immunity is mainly cell mediated immunity.
Brucellosis = Undulant fever Brucellosis is a zoonotic disease. Man is infected by: consumption of infected cow or goat milk or milk products. Farmers and butchers are infected by contact with diseased animals. Incubation period:1-6 weeks.
The disease is characterized by acute bacteremic phase followed by a chronic stage during which the bacteria localize in reticuloendothelial tissues (LNs, liver, spleen, bone marrow). Manifestations of the disease include: Fever for 3-4 weeks followed by afebrile period of similar duration, so it is called undulant fever. Weakness, bone pain, profuse sweating + enlarged LNs, liver and spleen. Brucella melitensis is the most severe form.
Laboratory diagnosis Specimen: blood, bone marrow, lymph node biopsy. Blood culture: Isolation requires repeated blood cultures. Blood culture is considered negative after 4 weeks incubation. Subculture is done on enriched media. Small convex translucent colonies are identified by biochemical reactions, serologically or PCR.
Standard tube agglutination test (STAT) Serological diagnosis: We use a wide range of dilutions of the patient’s serum (1/20 to 1/5120) to avoid prozone phenomenon. A titer of 1/160 or more is diagnostic. However, interpretation of the titer is done in light of endemicity of the disease and occupation of the patient. Used to detect non agglutinating IgA antibodies which interfere with agglutination by IgG or IgM in STAT. Coomb’s antiglobulin test
Rapid slide agglutination test -Ve +Ve Direct detection of brucella in the specimen by PCR. Brucellin skin test. ELISA
Treatment Due to chronicity and intracellular survival of the bacteria, combined prolonged antibiotic therapy with tetracycline and either streptomycin, rifampicin or gentamycin is recommended.
Prophylaxis Live attenuated vaccine is used for the cattle. No vaccine is available for humans. The disease could be prevented by pasteurization of milk which kill the bacteria.