Bone, Joint and Soft Tissue Infections

MICR2220 18/02/21 Bone, joint and soft tissue infections: Learning Outcomes: At the end of this lecture & after further reading you should be able to… – Provide an overview of virulence factors found in S. aureus and S. pyogenes – Name and describe (symptoms/causative organisms) skin and skin structure infections provided in this lecture. – Name and describe (symptoms/causative organisms) bone and joint infections provided in this lecture. – Describe the sources and causes of periodontal disease Skin/skin structure infections (SSSIs): • 2 Gram-postive organisms • Staphylococcus aureus • Gram-positve coccus (clusters) • Catalase positive • Virulence factors: o Coagulase o Hyaluronidase o Protein A o Heamolysins o Staphylokinase o Lipase o Protease • • • • • • • Can distinguish them with a catalase test Streptococcus pyogenes Gram-positive coccus (chains) Catalase negative Lancefield Group A strep Virulence factors o Capsule o Adhesins o Anti-opsonic factors o Streptolysin O/S o Hyaluronidase MICR2220 18/02/21 o Streptokinase • • • • • • • • Skin is an inhospitable environment for microorganisms o Dry o Constant shedding o Low pH o Sebaceous secretions o Competition with resident microbiota If skin is intact, very unlikely you’ll get a skin or skin structure infection Skin infection typically results from trauma o Accidental (e.g. scrapes, cuts) o Deliberate (e.g. surgery) Can allow organisms to get in lower levels where some of the listed things above are not present Can result from ‘haematogenous’ colonisation Varying severity of skin infections, can range from relatively minor to major and systemic MICR2220 • • • • Folliculitis o Superficial infection of the hair follicle o Staphylococcus aureus o Pseudomonas aeruginosa (hot tub folliculitis) o “Itis” inflammation o Prevalent in hot tubs and can cause rash if enters your follicles Furuncle (boil) o ‘Deep folliculitis’ o Involves a single follicle o Occur in areas of hairy skin, face neck armpits o Can get spread of these individuals o Rugby players, get outbreaks o Sports o Large outbreaks in indivduals who have poor vascularisation o Can progress Carbuncle o Collection of furuncles –connected subcutaneously o Lesion extends into subcutaneous fat o Multiple follicles involved o Collection of ducts underneath that have joined together o Causes people to become very unwell, systmemic type of infection, temperature and generall tiredness 18/02/21 MICR2220 • • • • Impetigo: o Superficial skin infection o Highly infectious o Group A streptococci/ S. aureus o Disruption of corneal layer > access to subcorneal keratinocytes o Contact sports o Incredibly infectious, spreads very easily o Lesions can be itchy o Mild, easily treated with oral antibiotics Staphylococcal scalded skin syndrome (SSSS) o Children <6 y.o. most susceptible o S. aureus elaborating exfoliative exotoxin o Widespread exfoliation o Risk of secondary infection & severe fluid/electrolyte imbalance o Mortality rate <3% (can be up to 60% in adults) o Exotoxin disrupts junction 18/02/21 MICR2220 • • • • • • 18/02/21 o o If you lose too much skin, lose a lot of fluid with it, become dehydrated and can die o Restoring electrolyte is most important treatment to begin with Erysipelas: o Superficial form of cellulitis (particular type of skin infection) o Bright red lesion –face or lower extremities o Group A streptococci o Demarkation, draw a line dividing normal skin and infecteed skin o Desquamation – layers of skin coming off Cellulitis o Rapidly spreading infection of skin and underlying tissues (dermis and subcutaneous fats) o Group A streptococci ▪ S. aureus ▪ P. aeruginosa ▪ anaerobes (Fournier’s gangrene) o Can lead to sepsis o Not as demarkated o If don’t treat can very easilt get into blood system, systemic infection, lose limbs Surgial wound infetion: o “Every surgical operation is an experiment in bacteriology” - Berkeley Moynihan o S. aureus (particularly MRSA) o Antibiotic prophylaxis frequently employed ▪ Bowel surgery ▪ Orthopaedic surgery o If open skin barrier, allow organisms from top of skin and elsewhere into lower layers of skin where there is fewer lines of defence Necrotising fascilitis: (i.e. ‘Flesh-eating bug ate my face!’) Uncommon, yet severe infection o Soft tissues –the superficial and deep fascia o Can affect any part of the body o Starts with group A strep MICR2220 18/02/21 ▪ ▪ ▪ Cellulitis Fluid accumulation Impaired blood flow, losing a lot of oxygen in the tissue area, allows anaerobes to start to come in ▪ Anaerobe involvement ▪ Tissue destruction ▪ Rapid o Treatment: Surgical intervention o Spreads incredibly fast Gangrene: • Infection of deep tissues, muscle • Caused by Clostridium spp. • Infection arises in areas of poor blood flow o Used to be v. common in war wounds o If got shot/stabbed, they would just stitch you back up, cuases localised area where you get massive loss of blood oxygenation o Now leave wound open, put some packing material in there, but then ship you off to hospital as quickly as possible, did not want individual to get gangrene • C perfringens (gas gangrene) • Alpha toxin – phospholipase • Rapid metabolism = gas • Extremely rapid spread • Surgical intervention required Anthrax: • Anthrax • Caused by Bacillus anthracis o Gram-positive sporing bacillus o endospores found in a variety of nsimal products, if not treated properly will cause an infection o Spores found in: ▪ Soil ▪ Animal hides ▪ Bone meal ▪ Fleeces • Cutaneous anthrax o V. rare o Occurs predominantly in workers exposed to animal products o Ulcerative skin lesion o Central necrosis – black “eschar” • Edema factor and lethal factory both binary toxins • Lethal factor – compolex of lethal factor subunit with protective antigen again Rickettsial infection: • Organisms transferred by ticks or fleas MICR2220 • • • • • • 18/02/21 Rickettsia spp. o Obligate intracellular pathogens o Transmitted by fleas/ticks/mites/lice Epidemic typhus o Rickettsia prowazekii o Skin rash resembling that of typhoid o Transmitted by Pediculus corporis (body louse) Endemic typhus o Rickettsia typhi Scrub typhus o Orientia tsutsugamushi Rocky mountain spotted fever o Rickettsia rickettsii Don’t really find these within the UK, more the states and central and southern americas Bite infections: • Can go systemic • Cat/dog bites o Pasturella multocida infection o Capnocytophaga canimorus • Rat bites o Spirillum minus o Streptobacillus moniliformis • Human bites • Oral commensal microbiota • Eikenella corrodens – can cause pitting in nutrient agar, not many bacteria that can do this • Deoth of wound that’s important an dhow many organisms incoulated • Get organisms that stick to our teeth and form a biofilm Lyme disease (Lyme borelliosis): • Borellia burgdorferi o Spirochete • Transmitted to humans by the Ixodes tick • Fever • Muscle pain • Headache • ‘Target shaped’ rash • Not as thin as treponema pallidum • Bullseye legion • Difficult to spot if on head (covered with hair) or different skin tones • Can progress past this to systemic infection Bone/joint infections: • Caused by 2 organisms we were talking about with skin infections MICR2220 18/02/21 Osteomyelitis: • Infection of bone o Haematogenous seeding o Direct inoculation (trauma/surgery) • Clinical manifestations: o Pain/swelling/redness/warmth around affected area • Causative organisms: o S. aureus o S. pyogenes o M. tuberculosis o Actinomyces israelii – find in jaw o Kingella kingae – pelvis of younge children o T. pallidum • Looking at circular region, almost like a halo, how osteomyelitis can appear in imaging • How do we get bone infection in the first place • Don’t believe we have microorganisms on our bone Arthritis: • Arthritis • Swollen/painful/red joints – warm to the touch o Immunological reaction (reactive, rheumatoid arthritis) o Infection (septic arthritis) o Causative agents ▪ Staphylococcus aureus ▪ Coagulase-negative staphylococi ▪ Salmonella enterica ▪ Haemophilus influenzae ▪ N. gonorrhoeae ▪ S. pyogenes (rheumatic fever) Infections of the oral cavity: • Opportunistic infection from commensal oral microbiotia o Dental caries – tooth decay o Abcesses o Periodontal infections o Gingivitis • Infection from primary pathogens o HSV o Oral thrush o Syphilitic lesions o AIDS-associated lesions MICR2220 • Dental caries – toothe decay: • Breakdown of teeth due to bacterial activity o Polymicrobial o Central role of Streptococcus mutans (biofilm formation) o Enamel>dentine>tooth pulp ▪ Apical abscess ▪ Osteomyelitis ▪ Sinusitis ▪ Brain abscess o Treatment ▪ Removal of affected tissue & replacement with inert filling o Prevention ▪ Brushing teeth w/fluoride toothpaste ▪ Fluoride addition to mains water o 18/02/21