Lecture 6.1 - Infections on Surfaces PDF

What is a surface?: ◦Interface between a solid and either a liquid or gas ◦Natural body surfaces: ‣ Skin ‣ GI tract ‣ Urinary tract ◦Artificial surfaces: ‣ Use of intravenous lines, central venous line catheters, NG tubes, prosthetic...

What is a surface?: ◦Interface between a solid and either a liquid or gas ◦Natural body surfaces: ‣ Skin ‣ GI tract ‣ Urinary tract ◦Artificial surfaces: ‣ Use of intravenous lines, central venous line catheters, NG tubes, prosthetic devices and implants provide ideal surfaces for organism to establish infection Skin microorganisms: ◦Viruses: ‣ Papilloma ‣ Herpes simplex ◦Bacteria: ‣ Gram positive: Staphylococcus aureus Coagulase negative staphylococci Corynebacterium ‣ Gram negative: Enterobacteriaceae ◦Fungi: ‣ Yeasts ‣ Dermatophytes ◦Parasites: ‣ Mites Mucosal microflora: Examples of natural infection sites: ◦External surfaces: ‣ Pharyngitis - sore throat ‣ Conjunctivitis - infection of conjunctiva ‣ Gastroenteritis - inflammation of the gastrointestinal tract due to infection giving rise to diarrhoea ‣ 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  ◦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 ‣ 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 ◦Patients have persistent lung infections: ‣ Pseudomonas aeruginosa ‣ Mycobacterium abscessus ‣ Aspergillus species Adhesins: ◦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 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 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 ◦Endovascular grafts ◦Ventriculoperitoneal shunts Sources of infection in an IV line:  IV line: Examples of prosthetic surface infections: Prosthetic joint infections: ◦Prosthetic joint infections result in morbidity and are costly ◦Require antibiotic therapy for weeks/months ◦Longer stay in hospital ◦Incidence of infection: ‣ Hip replacement approximately 0.43% for primary and 1.58% for revision ‣ Knee replacement approximately 0.54% for primary and 2.1% for revision Microorganisms causing infections of joint replacements: ◦Microorganisms causing infection: ‣ Early post operative infections (1 month) - S.aureus, gram-negative organisms (E.coli, Proteus, Klebsiella), Enterobacteraceae, Enterocicci (E.faecalis) ‣ Late post operative infection 2 to > 12 months: Coagulase negative staphylococci (mainly staphylocccus epidermis) and staphylococcus aureus, to a lesser extent other species, for example: Staphylococcus haemolyticus, Staphylococcus simulans, Staphylococcus warneri, Enterobacteraceae Endocarditis (prosthetic and non-prosthetic valve): ◦Coagulase negative staphylococci including S.epidermis ◦Staphylococcus aureus ◦Viridans streptococci ◦Enterococcus faecalis ◦HACEK group ‣ Haemophilus species, Aggregatibacter species, Cardiobacterium hominis, Eikenella corrodens and Kingella species ◦Candida  Cardiac pacing wire endocarditis: Processes in the pathogenesis of infection at surfaces: ◦Adherence to host cells or prosthetic surface ◦Biofilm formation ◦Invasion and multiplication ◦Host response Biofilms: ◦Stages of biofilm formation: ‣ Attachment ‣ Maturation ‣ Dispersion Quorum sensing: ◦Controls: ‣ Sporulation ‣ Biofilm formation ‣ Virulence factor secretion ◦Three principles: ‣ Signalling molecules - autoinducers (AI) ‣ Cell surface or cytoplasmic receptors ‣ Gene expression -> co-operative behaviours and more AI production Symptoms of infection: ◦Fever ◦Inflammation at the site of insertion ◦Purulence or erythema ◦Pain ◦Malaise Investigations: ◦Full blood count (FBC) ◦C reactive proteins ◦ESR ◦Blood culture (gram stain, antibiotic sensitivity etc) ◦Samples (fluid, biopsy) - bacterial growth; PCR  ◦Scans Management: ◦Diagnosis: ‣ Aim is to identify infecting organism and its antimicrobial susceptibilities ‣ Challenges: Adherent organisms Low metabolic state/small colony variants ‣ Blood cultures ‣ Tissue/prosthetic material sonication and culture Treatments: ◦Treatment ◦Aim: ‣ Sterilise tissue ‣ Reduce bioburden ◦Antibacterials ◦Remove prosthetic material ◦Surgery - resect infected material ◦Challenges: ‣ Poor antibacterial penetration into biofilm ‣ Low metabolic activity of biofilm microorganisms ‣ Dangers/difficulties of surgery Prevention: