Institute for Microbiology, Medical Faculty of Masaryk University     and St. Anna Faculty Hospital
in Brno
Agents of bloodstream infections

Bloodstream infections
•less common than respiratory or urinary tract infections, but  severe and lifethreatening
•Types of bloodstream infections:
   1) Infection of the complete bloodstream = sepsis
    2) Infection of a part of bloodstream (endocarditis, tromboflebitis), leads to sepsis

Bacteremia = mere presence of bacteria in blood.
      Bacteria (at least in higher ammounts) = starting mechanism of sepsis

      Interaction of microbial products with macrophages releases a lot of cytokines
→  systemic inflammatory response syndrome (SIRS) characterized by:
–elevated temperature
–accelerated pulse and breathing
–leukocytosis

Sepsis
Sepsis = suspect or proved infection + systemic inflammatory response syndrome
Severe sepsis = sepsis + organ dysfunction (hypotension, hypoxemia, oliguria, metabolic acidosis,
thrombocytopenia, confusion, DIC)
Septic shock = severe sepsis + hypotension despite adequate supply of fluids




Features of sepsis
Clinical:
fever or hypothermia (often changing)           ↑↓ T
       tachycardia                         ↑   P
tachypnoe ↑   B
lowered blood pressure ↓   BP
confusion
Pathophysiological:
higher heart output
lower peripheral vascular resistance
Laboratory:
leucocytes      ↑↓  Leu
serum bicarbonate ↓   HCO3-
  bacteremia                  may not be already demonstrable







Types of bacteremia – I
Intermitent – in localized infections
pneumonia (for example pneumococci)
meningitis (for example meningococci)
pyelonephritis (Escherichia coli)
osteomyelitis (Staphylococcus aureus)
septic arthritis (S. aureus, gonococci)

Types of bacteremia – II
Continual  – in generalized infections
typhoid fever (Salmonella Typhi)
brucellosis (Brucella melitensis)
plague (Yersinia pestis)

Types of bacteremia – III
 Bacteremia in bloodstream infections
thrombophlebitis (S. aureus, S. pyogenes)
acute endocarditis (S. aureus, S. pyogenes, S. pneumoniae, Neisseria gonorrhoeae)
subacute bacterial endocarditis = sepsis lenta                  (viridans streptococci,
enterococci,                                                      HACEK group
=                                                   Haemophilus aphrophilus
       Actinobacillus actinomycetemcomitans
        Cardiobacterium hominis
      Eikenella corrodens
        Kingella kingae)
„culture-negative“ endocarditis (bartonellae, coxiellae, legionellae)

Types of bacteremia – IV
Special circumstanses
Bacteremia in some malignities (colonic Ca – Streptococcus bovis, leukemia - various bacteria)
Bacteremia in intravenous drug users ( skin flora – staphylococci, corynebacteria;  mouth flora and
bacteria from the environment)
!!Bacteremia in iatrogenic  infections          (e. g. mouth floora after tooth extraction,
pharyngeal flora after bronchoscopy etc.)

Types of bacteremia – V
Bacteremia related to artificial material
Vascular catheters, invasive devices and implants, endoprotheses etc. (biofilm)
 ICU, immunocompromised, febrile neutropenia
 Coagulase-neg. staphylococci, S.aureus, enterococci, corynebacteria, yeasts etc.
   True bacteremia vs contaminants!

Biofilm on a catheter (stafylococci and candidae):
 a) - canaliculus,  b) - porous structure
Photo: Dr. Veronika Holá, MÚ

Sepsis according to the origin
•Wound sepsis (Staphylococcus  aureus, Streptococcus pyogenes and other beta-hemolytic
streptococci, Pseudomonas aeruginosa in burns)
•Urosepsis (Escherichia coli, Proteus mirabilis and other enteric bacteria)
•Abdominal sepsis (often polymicrobial etiology, anaerobes (Bacteroides etc.) and facultative
anaerobes (Escherichia coli)

Fulminant sepsis
... a quick course; when it is not diagnosed in time, it often kills the patients
Clonal strains of Neisseria meningitidis (sepsis with or without meningitis)
Streptococcus pyogenes (often together with necrotizing fasciitis)
Yersinia pestis

Nosocomial sepsis
- Staphylococci, coagulase-negative (intravenous catheter-associated sepsis, infections of plastic
devices in situ,  febrile neutropenia)
- Staphylococcus aureus (infected surgical wounds)
- E. coli + other enterobacteria (catheter-associated infections of the urinary tract)
- Gram-negative non-fermenting rods (contaminated infusion fluids)
- yeasts (catheter-associated sepsis, febrile neutropenia)
- Enterococci and many other microbes

Staphylococci in blood culture
www.medmicro.info


Diagnostics of sepsis
•Blood cultures (not clotted blood;  blood for serological examintion!)
–special vessels, authomated culture
–two, but better 3 blood cultures

–At least one blood culture should be taken from  venepunction (i. e. not only central venous
cathether)
•parts of blood catethers

Contaminants
•Inproper sampling, insufficient disinfection
•Sampling from cathehers only and not venepunction (the bacterium colonizing the venous catether is
not necesarilly a real bloodstream pathogen)
•Coagulase-negative staphylococci

Examples of blood culture vessels
www.medmicro.info


Blood culture device
Foto: O. Z.


The same device open
Foto: O. Z.


Treatment of sepsis
 ICU
•antibiotics – empiric therapy in the beginning, targeted therapy later
•removal of all infected tissues or devices
•support of breathing and hemodynamics (artificial ventilation, oxygen, fluids, vasopressors etc.)


Michael Sweerts (1618-1664):      Plague in an Ancient City