Blood stream infections- clinical microbiology

Blood stream infections (BSI) refers to the presence of organisms in blood which are threat to every organ in the body.
It causes shock, multiple organ failure and DIC (Disseminated Intravascular Coagulation).
The presence of bacteria in blood is called Bacteremia.
The bacteria circulate and actively multiply in the blood stream is called Septicemia.
The presence of virus in blood is called Viremia.
The presence of parasite in blood is called Parasitemia.
The presence of fungi in blood is called Fungemia.

1. BLOOD STREAM INFECTIONS Sijo.A M.Sc. Microbiology St. Berchmans College, Changanacherry, Kottayam

2. Reference Bailey & Scotts; Diagnostic Microbiology Anandanarayan & Paniker ; Textbook of Microbiology Apoorba S Sastry & Sandya Bhatt; Essentials of medical microbiology

3. Blood stream infections (BSI) refers to the presence of organisms in blood which are threat to every organ in the body. It causes shock, multiple organ failure and DIC (Disseminated Intravascular Coagulation). The presence of bacteria in blood is called Bacteremia . The bacteria circulate and actively multiply in the blood stream is called Septicemia. The presence of virus in blood is called Viremia . The presence of parasite in blood is called Parasitemia . The presence of fungi in blood is called Fungemia . BLOOD STREAM INFECTIONS

4. Etiological agents Bacteria – S. aureus, S. pneumoniae , E. coli Fungi – C. albicans , H. capsulatum Parasites – T. gondii , P. malaria Virus – Epstein Barr Virus, Cytomegalovirus, SARS, SARS CoV 2(Novel corona virus), HSV, HIV. Hepatitis etc.

5. Types of bacteremia 1. Transient Bacteremia It is the sudden destruction of the tissue. It occur during brushing teeth, chewing food, manipulation of infected tissues, devices inserted through contaminated mucosal surface, surgery in non- sterile sites. 2. Continous Bacteremia Here the organism released into the bloodstream at fairly constant rate. It occurs in the early stages of certain infections such as typhoid fever, brucellosis & leptospirosis .

6. Types of bacteremia 3. Intermittent bacteremia Here the organism released into the blood stream at various time intervals. It is found in patients with undrained abscess. It occurs in the early stages of meningitis, pneumoniae , pyrogenic arthritis and osteomyelitis .

7. Types of blood stream infections They are 2 types: Intravascular and extravascular . The factors that contribute bloodstream infections are Use of immunosuppressive agents’ Widespread use of broadspectrum antibiotics. Invasive surgical procedures. Prolonged survival of prolonged ill patients.

8. Intravascular infection It originates within cardiovascular system which include Infective endocarditis Mycotic aneurysm Suppurative thrombophlebitis Intravascular catheter associated bacteremia

9. 1. Infective endocarditis It is the infection of the endocardium . It is characterised by the presence of vegetation which is composed of platelets, fibrin, inflammatory cells and entrapped organism. It is mainly caused by viridans streptococci. It is a normal inhabitant of oral cavity. It enter into the bloodstream through gingivitis, predontitis or dental manipulation.

10. 2. Mycotic aneurysm It is the inflammation of arterial wall. It is characterised by the bulging of arterial wall and its rupture. The etiological agent is similar to that of endocarditis .

11. 3. Suppurative thrombophlebitis It is the inflammation of vein wall. It is characterised by alteration in the vein endothelial lining followed by clot formation. It is found in hospitalized patients using IV catheters.

12. 4. Intravenous catheter associated bacteremia Central venous catheter is a triple lumen used to provide fluid, blood products, medications, antibiotics and nutrition. Bacteremia occurs in two routes: Movement of organism from patient skin to catheter. Movement of organism from catheter to catheter tip within the blood stream. It is mainly caused by Staphylococcus aureus and it causes biofilm formation on catheter surface.

13. Intravenous catheter associated bacteremia

14. extravascular infection It is the infection of lymphatic system . It includes liver, spleen and bone marrow. Portal of entry: genitourinary tract (25%), respiratory tract (20%), abscess (10%), surgical wound infections (5%), miscellaneous sites (10%). Clinical manifestations Septecemia / Sepsis It is the presence of bacteria and its toxic products in blood. Symptoms include fever, hyperventillation , respiratory alkalosis, diarrhoea .

15. 2. Septic shock it occurs due to the production of cytokines from tumor necrosis factor and interleukins. Symptoms include fever, renal failure, change in mental status. 3. DIC (Disseminated Intravascular Coagulation) It is characterised by Formation of blood clots within blood vessels. Bleeding due to the depletion of coagulation factors.

16. LABORATORY DIAGNOSIS (exam point of view) Specimen collection The blood should be collected before antimicrobial therapy. The skin is wiped with 70% isopropyl alcohol. Using sterile disposable syringe the blood is collected aseptically by venipuncture . The blood volume is around 10-20 ml for adults and 1-5 ml for infants. The collected blood transported to the laboratory in anticoagulant containg tube. Heparin, EDTA are not used, because it inhibits the growth of organisms. Hence, Sodium polyanethol sulphonate (SPS) is a coagulant for blood culture.

17. 2. Blood culture media It consists of nutrient broth and anticoagulant. It includes Trypticase soy broth, Brainheart infusion broth, Columbia or Brucella broth. Biphasic medium is used as a conventional culture medium. 3. Instrument based system i. BACTEC System BACTEC is a fully automated machine which consists of incubator, shaker and incubator. It consists of a glass permeable flourescene to measure Co2 produced by microorganisms. ii. BacT Alert It is based on the colorimetric detection of Co2. iii. Versa TREK System It is unique agitation system during blood culture inoculation

18. 4. Identification The isolated organism is identified by colony morphology, gram staining, biochemical reactions and serological tests. HACEK refers to group of fastidiuos slow growing bacteria. It is a gram negative bacilli. It is found in mouth. It include Hemophilus species, Cardiobacterium hominis etc. Blood cultures from HACEK patients take 7-30 days to become positive. Antibiotic sensitivity test is essential for effective therapy. The drug resistance is very common.