Bacteremia Infections

Bacteremia and Sepsis

• Bacteremia can be caused by most bacteria, with features differing between gram-negative and gram-positive bacteria.
• Gram-negative bacteremia is mainly caused by Enterobacteriaceae (e.g., E. coli, Klebsiella, Proteus, Serratia) and P. aeruginosa, often entering the body through the gastrointestinal tract, urogenital tract, and skin.
• Gram-positive bacteremia is mainly caused by S. aureus and coagulase-negative staphylococci (e.g., S. epidermis, S. saprophyticus), often entering the body through the skin or any source of infection.

Septic Infections

• Bacteroides fragilis and Prevotella melaninogenica are common causes of septicemia, often found in association with other bacteria.
• P. melaninogenica enters the body through the oral cavity, while B. fragilis enters through the gastrointestinal tract.
• Clostridia-caused septicemia often involves C. perfringens, which enters the body through the intestinal tract, bile ducts, and sometimes the mucous membranes of the uterus after abortions.

Principles of Diagnosis of Septic Infections

• Microbiological diagnosis is based on bacteriological examination of blood, taken from the elbow vein in strict adherence to aseptic conditions before or after antibacterial treatment.
• Bacteriological examination involves acquiring the pathogen from blood and transferring it to a liquid nutrient medium or a sterile vial containing reagents to prevent blood clotting.
• The blood is inoculated into a nutrient medium 5-10 times its volume, and samples are incubated at 37°C for 10 days under daily observation.

Bacteriological Examination of Blood: Interpretation

• Obtaining any microorganism from blood is assessed as bacteremia and sepsis.
• A single blood test may not always provide a positive hemoculture, and at least three examinations should be performed if the result is negative.

Automated Blood Culture System

• Automatic cultivation systems, such as the Bactec system, are used to speed up the obtaining of hemoculture and facilitate multiple examinations.
• The system detects carbon dioxide formed as a result of microbial growth in nutrient media containing glucose, amino acids, and a labeled carbon isotope.

Characteristics of Nosocomial Infections

• Opportunistic microorganisms causing nosocomial infections are more resistant to antibacterial drugs, antiseptics, disinfectants, physical agents, bacteriophages, and bacteriocins.
• These microorganisms have higher virulence and do not have organ tropism, allowing them to cause diseases in any organ or tissue.
• The population of nosocomial infections has higher heterogeneity (antigen variability, etc.) than other microorganisms.

Principles of Microbiological Diagnosis of Nosocomial Infections

• Materials for investigation are selected depending on the location and nature of the disease.
• The microscopic method allows for approximate conclusions about the nature of the causative agents and determines the direction of cultural methods.
• The culture method is the main method of microbiological diagnosis, and determining the sensitivity of the culture to antibiotics and other antimicrobial chemical therapeutic drugs is important.