Common Cause of Bacteremia and Sepsis

By Acharya Tankeshwar •  Updated: 05/03/22 •  3 min read

Pathogens of all four major groups of microbes- bacteria, fungi, viruses and parasites may be found circulating in blood during the course of many diseases.

Presence of bacteria in the blood is called bacteremia. Bacteria may reach to bloodstream

On the basis of duration of presence of bacteria in the blood, bacteremia  is classified as;

  1. Transient (incidental) bacteremia,
  2. Continuous bacteremia and
  3. Intermittent bacteremia

Transient bacteremia may occur spontaneously or with such minor events as brushing teeth or chewing food. Bacteria may transiently appear while the manipulation of infected tissues, instrumentation of contaminated surfaces, and surgery of non-sterile sites. These bacteria are often cleared from the blood within minutes by immune cells but if the immune system is overwhelmed or evaded these organisms may persist in the blood, resulting in the symptoms and signs of septicemia.

Bacteria are released into the bloodstream at a fairly constant rate during septic shock, bacterial endocarditis, and other endovascular infections. Continuous bacteremia is also seen during the early stages of infections such as typhoid fever, brucellosis, and leptospirosis.

Bacteria can be found intermittently in the bloodstream of patient’s with undrained abscesses. Causative agents of pneumonia, meningitis, pyogenic arthritis, and osteomyelitis are often recovered from blood during the early course of these diseases.

Although septicemia (literally sepsis of the blood) implies a more serious clinical condition than bacteremia in practice many clinicians and microbiologists used the term interchangeably.

Difference between “Bacteremia” and “Septicemia”

Traditionally the term bacteremia referred to the transitory presence of bacteria in the blood of a patient in the absence of symptoms; the origin of bacteria was usually from a site of commensal colonization. The term septicemia meant the presence of bacteria in the blood with clinical signs and symptoms of infection. Their origin was from a focus of infection from which they entered the circulation.

The difference is largely ignored in new medical literature and publications. The presence of fungi in blood is termed as fungemia.

Lists of most common cause of bacteremia and fungemia are:

Gram-negative organisms associated with bacteremia

  1. Escherichia coli  (most common cause)
  2. Klebsiella spp.
  3. Enterobacter spp.
  4. Proteus spp.
  5. Salmonella typhi
  6. Salmonella spp. other than S. typhi
  7. Pseudomonas aeruginosa
  8. Neisseria meningitidis
  9. Haemophilus influenzae
  10. Bacteroides fragilis (anaerobe)
  11. Brucella spp.
  12. Burkholderia pseudomallei  (in certain areas)

Gram-Positive organisms associated with bacteremia

  1. Staphylococcus aureus (most common cause)
  2. Staphylococcus epidermidis
  3. α-Haemolytic (viridans) Streptococci
  4. Streptococcus pneumoniae
  5. Enterococcus faecalis (group D)
  6. S. pyogenes (group A)
  7. S. agalactiae (group B)
  8. Listeria monocytogenes
  9. Clostridium perfringens
  10. Peptostreptococcus spp. (anaerobes)


  1. Candida albicans
  2. Cryptococcus neoformans etc.

Native valve Endocarditis

  1. Viridans streptococci (Streptococcus sanguinis, Streptococcus salivarius, Streptococcus mutans, Streptococcus mitis, etc.)
  2. Enterococcus faecalis
  3. Enterococcus faecium
  4. Streptococcus pyogenes
  5. Streptococcus agalactiae
  6. Staphylococcus aureus
  7. Staphylococcus lugdunensis
  8. Coagulase-negative staphylococci
  9. Streptococcus pneumoniae
  10. Neisseria gonorrhoeae
  11. Haemophilus spp.
  12. Pseudomonas spp.
  13.  Listeria spp.
  14. Corynebacterium spp.

Endocarditis in Intravenous drug abuser

  1. Staphylococcus aureus
  2. Streptococcus spp.
  3. Enterococcus spp.
  4. Gram-negative rod-shaped bacteria (mostly Pseudomonas spp. and Serratia spp.)
  5. Candida spp.
  6. Haemophilus spp.
  7. Neisseria spp.
  8. Anaerobic oral bacteria.

Prosthetic valve Endocarditis

  1. Staphylococcus epidermidis
  2. Staphylococcus aureus
  3. Aerobic Gram-negative rods
  4. Fungi (usually Candida spp. and/or Aspergillus spp.)
  5. Streptococcus spp.
  6. Enterococcus spp.
  7. Corynebacterium spp.

References and further readings

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please email at

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