6. Infections On Surfaces Flashcards
What is a surface
—> Interface between a solid and either a liquid or gas
3 natural body surfaces
• Skin
• GI tract
• Urinary tract
We have innate mechanisms to prevent infections establishing there
4 artificial surfaces
- Use of intravenous lines,
- central venous line catheters,
- NG tubes,
- Prosthetic devices and implants provide ideal surfaces for organism to establish infection
Specific examples of natural surfaces
○ Skin – epithelieum, hair, nails
○ Mucosal surfaces = conjunctivial, gastrointestinal, respiratory, genitourinary
○ Secretion of enzymes to prevent infection of surfaces
What are skin microorganisms
e.g. commensals can casue infection udner certain circumstances
Skin microorganisms - viruses
– Papilloma
– Herpes simplex
Skin microorganisms - bacteria
Gram positive
– Staph aureus
– Coagulase negative staphylococci
– Corynebacterium
Gram negative
– Enterobacteriaceae
Skin microorganisms - fungi
– Yeasts
– Dermatophytes
Skin microorganisms - parasites
– mites
Microflora examples
- Nasopharynx- step pneumonia
- Nose armpits – staph aureus
- Mouth = streptococci can dislodge and enter blood system can cause endocarditis in heart
Natural infection sites – external surfacses
– Pharyngitis – sore throat = viruses and bacteria
– Conjunctivitis – infection of conjunctiva
– Gastroenteritis - inflammation of the gastrointestinal tract due to infection giving rise to diarrhoea - due to toxins
– Urinary tract infection - infection in any part of the urinary system including kidneys, bladder, ureter, and urethra
– Pneumonia – infection of one or both lungs causing inflammation of alveoli which fill with liquid or pus
Natural surface infections = internal surfaces
– Endocarditis - infection of the endocardium, which is the inner lining of the heart chambers and heart valves.
– Septic arthritis – joint infection where microorganism invades the joint and causes inflammation
– Osteomyelitis – infection of the bone difficult to treat need antibiotics than can penetret bone
– Empyema – pus in the pleural cavity due to infection (space between the outside of the lungs and the inside of the chest cavity)
Cystic fibrosis
Mucus build up in lungs and digestive system = gives ideal environemnts for infectiosn to grow
•Patients have persistent lung infections
– Pseudomonas aeruginosa
– Mycobacterium abscessus
– Aspergillus species
What are adhesins
- Ways bacteria attach to surface and establish infection
- Adhesins which help bacteria bind to host surfaces for example, skin, mucous membranes (oral cavity, nasopharynx, urogenital tract), and deeper tissues (lymphoid tissue, gastric and intestinal epithelia, alveolar lining, endothelial tissue).
Adhesins examples
•Adhesins can be proteins for example fimrae (pili) as in E.coli attach themselves to the bladder mucosa or non-fimbrae proteins which facilitate adherence
- Polysaccharide adhesins - usually components of the bacterial cell membrane, cell wall, or capsule.
- Teichoic acids in the cell envelopes of Gram-positive bacteria serve as adhesins for Staphylococcus and Streptococcus species
- Capsular polysaccharide (external) components (glucan and mannan) of Mycobacteria species promote adherence
Examples of Prosthetic surface infections
- Intravascular lines
- Central venous catheters including Hickman catheters
- Peritoneal dialysis catheters
- Prosthetic joints
- Breast prostheses
- Cardiac valves
- Pacing wires – wires put in during heart operations to maintain heart beat
- Endovascular grafts
- Ventriculoperitoneal shunts
Sources of infection – IV line
• IV line – hub, liquid, breaking skin
○ Device can be contaminated as needle enters skin
○ Contamination of catheter hub
○ Infections can establish at catheter
How to Prevent transfer of microorganism with n lines
- Wash hands
- Gloves on
Positive pressure of lines – liquid gushes out instead of limb to prevent infection
Hickman line
• Used for chemotherapy
• To take antibiotics
To take blood
Hip replacement
- Ususally metal
- Not compleletly able to prevent setlling of microorganism
- Infection tends to be at head of prosthetic device
Staph aureus on the surface of an indwelling catheter
• Microorganisms have a polysaccharide coating and matrix
• They produce slime = slime creates biofilm
○ Biofilm = difficult for antibiotics or immune cells to penetrate
Bacteria settle on surface
Wait for right environment to multiply
Build polysaccharide matrix and biofilm to protect themselves from immune system
Infections of join replacement
• Operation required to take out infected joint
Revision surgery = taking replacements out and adding in spacer with antibiotiv to clear area of infection, biut it is more likely for second joint to be infected
- Require antibiotic therapy for weeks or months
- Longer stay in hospital Incidence of infection:
Microorganisms causing infections
• Early post operative infections (1 month)
– S.aureus, Gram-negative organisms ( E.coli, Proteus, Klebsiella), Enterobacteraceae, Enterococci (E.faecalis)
Microorganisms causing infections
• Late post operative infection 2 to >12 months (takes longer for infection to establish):
• Coagulase negative Staphylococci (mainly Staphylococcus epidermidis) and Staphylococcus aureus, to a lesser extent other species for example: Staphylococcus haemolyticus, Staphylococcus simulans, Staphylococcus warneri Enterobacteraceae
Endocarditis
—> organisms going to heart valve and causes endocarditis
- Coagulase negative Staphylococci including S.epidermidis
- Staphylococcus aureus
- Viridans streptococci
- Enterococcus faecalis
- Staphylococcus aureus
- HACEK group (Haemophilus species, Aggregatibacter species,Cardiobacterium hominis, Eikenella corrodens, and Kingella species
- Candida
4 Process of pathogeneisis of infection at surfaces
- Adherence to host cells or prosthetic surface
- Biofilm formation
- Invasion and multiplication
- Host response
3 Stages of biofilm development
- Attachment
- Maturation
- Dispersion
Biofilm maturation
- Microorganism come to surface but become dormant due to not enough nutrients
- Microorganisms activate and multiply
- Microorganisms do quorum sensing – communicate and bring microorganism
- Form biofilm
- Biofilm sheers and floats of with microorganisms
- Spreads the infection
What is Quorum sensing
—> communication of bacteria with each other and formation of biofilm
Quorum sensing
Controls
– Sporulation
– Biofilm formation
– Virulence factor secretion
Quorum sensing
Three principles
– Signalling molecules – autoinducers (AI) secreted by microorganism
– Cell surface or cytoplasmic receptors detect signalling molecules
– Gene expression ->co-operative behaviours and more AI production., message causes change in infection
5 Symptoms of infection
- Fever (generally yes but not everyone gets fever)
- Inflammation at the site of insertion
- Purulence or erythema – pus at site of infection
- Pain
- Malaise
Investigations of infection
•Full Blood Count = blood cells and neutrophils •C reactive proteins •ESR •Blood culture (looking for organisms in patients blood) – Gram stain – Antibiotic sensitivity •Samples (fluid, biopsy) – Bacterial Growth – PCR •Scans
Infection Management
Diagnosis • Aim is to identify infecting organism and its antimicrobial susceptibilities.
• Challenges = trying to id organism takes time so first give broad spectrum antibiotics
– Adherent organisms - biofilm
– Low metabolic state/small colony variants (bacteria don’t go through the state or actions that antibiotics targets)
- Blood cultures
- Tissue/prosthetic material sonication and culture
Aim of treatments
– sterilise tissue
– reduce bioburden
Treatment examples
- Antibacterials
- Remove prosthetic material - remove thing causing infection like iv lines etc
- Surgery – resect infected material
Challenges of treatment to organisms with biofilm
– poor antibacterial penetration into biofilm
– low metabolic activity of biofilm micro-organisms
– dangers/difficulties of surgery
Prevention of infection on natural surfaces
- Maintain surface integrity
- Prevent bacterial surface colonisation
- Remove colonizing bacteria (clean patient)
Prevention of infection on prosthetic surfaces
- Prevent contamination
- Inhibit surface colonisation
- Removing colonising bacteria
Coagulase test
Test to see if organism produces coagulase or not
Add blood plasma
- if clumping is present = coagulative positive
- if clumping is not present = coagulativenegative
