Common Pathogenic Bacteria Found in Blood


Bacteria are microscopic organisms that can be found in various environments and habitats. Some bacteria are beneficial for human health, such as those that live in the gut and help with digestion. However, some bacteria can cause infections and diseases when they enter the body through wounds, inhalation, ingestion, or contact with contaminated surfaces.

One of the most serious types of bacterial infections is when bacteria enter the bloodstream and cause bacteremia. Bacteremia is the presence of viable bacteria in the blood, which can trigger an inflammatory response throughout the body known as sepsis. Sepsis can lead to organ failure, shock, and death if not treated promptly and effectively.

Bacteria can enter the blood from different sources, such as:

  • Infections in other parts of the body, such as pneumonia, urinary tract infections, skin infections, or stomach infections
  • Medical procedures or devices that breach the skin barrier, such as surgery, catheters, intravenous lines, or injections
  • Exposure to contaminated food, water, or animals that carry zoonotic pathogens

Bacteria isolated from blood can be classified into different groups based on their morphology, staining properties, biochemical characteristics, and genetic features. One of the most common ways to categorize bacteria is by their Gram stain reaction, which depends on the structure of their cell wall. Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall that retains a purple dye, while Gram-negative bacteria have a thin layer of peptidoglycan and an outer membrane that loses the dye and appears pink.

Some of the most common pathogenic bacteria found in blood are:

  • Gram-positive bacteria: Staphylococcus spp., Streptococcus spp., Enterococcus spp., Clostridium spp., Mycobacterium spp.
  • Gram-negative bacteria: Escherichia coli, Klebsiella spp., Salmonella serovars, Haemophilus spp., Pseudomonas spp., Neisseria spp., Enterobacter spp., Brucella spp., Yersinia spp., Proteus spp., Leptospira spp., Citrobacter spp.

To isolate and identify these bacteria from blood samples, various methods are used, such as:

  • Blood culture: A technique that involves inoculating blood samples into sterile media and incubating them under optimal conditions to allow bacterial growth and detection
  • Immunological tests: Tests that use antibodies or antigens to detect specific bacterial components or markers in blood samples
  • Molecular tests: Tests that use nucleic acid amplification or hybridization to identify bacterial DNA or RNA sequences in blood samples

The identification of bacteria isolated from blood is crucial for diagnosing the cause and source of infection, determining the antibiotic susceptibility profile, and guiding the appropriate treatment and management of patients with bacteremia and sepsis. In this article, we will review some of the common pathogenic bacteria found in blood and their characteristics, clinical manifestations, and treatment options.