Infectious Diseases Flashcards
Gram positive bacteria
- Stain purple
- Thicker cell wal
- Capsule and then thick peptidoglycan layer beneath this
- Produce exotoxins
Gram negative bacteria
- Stain pink
- Thinner cell envelope
- Have an additional outer membrane containing endotoxin
Endotoxin
LPS that is released upon cell wall lysis of gram negative bacteria. Major contributor to SIRS and ARDS in gram negative bacteraemia
Cocci
Spherical
Bacilli
Rod-like
Sphirocaete
Helical
Staph aureus morphology
“Bunch of grapes” clusters of gram positive cocci
Streptococci morphology
Chains of gram positive cocci
Neisseria meningitidis, neisseria gonnorhoea morphology
Gram negative diplococci
Staphylococcus aureus
- Most often colonizes nose and perineum
- Colonizes skin in patients with inflammatory derm conditions
- Pus forming organism
- Most common infective agent in many MSK infections incl. OM, septic arthritis, discitis
Staph epidermidis
- Skin commensal, usually non-virulent
- Most common prosthetic infective agent
- V difficult to eradicate- often requires removal of foreign body
- Coagulase negative staph- antibiotic susceptibility is unpredictable
- Growing fluclox resistance
Cellulitis- common causative organisms
Usually anaerobic organisms, clostridial and non-clostridial
Bursitis- common causative organisms
Gram-negative organisms
Necrotising fasciitis- common causative organisms
Most common is pyogenic strep (strep pyogenes), can also be clostridium perfringens, staph aureus, vibrio vulnificus, aeromonas hydrophilia
Progressive bacterial synergistic gangrene- common causative organisms
A mixture of organisms and usually strep pyogenes and gram-negative bacillus e.g coliform
Myonecrosis- common causative organisms
Clostridium species
Infected vascular gangrene- common causative organisms
Any organism
Necrotising fasciitis- skin changes
Pain deceptively out of proportion to skin findings that then changes to exquisitely tender, swollen area of extensive soft tissue erythema. The disease progresses at an alarming rate changing from a shiny red-purple to a pathognomonic grey-blue with ill-defined patches within 36 hours of onset
Necrotising fasciitis- signs
Skin changes, extreme pain that can progress to no pain in effected area as cutaneous nerves are destroyed, hard wooden feeling subcut tissues, crepitance in 30% of cases, can become extremely toxic with high fever, anxiety, altered GCS, leukcytosis, shock and tachycardia
Fournier’s gangrene- causes
Spread from perianal, retroperitoneal or urinary tract infection or following genital trauma (e.g. postpartum)
Fournier’s gangrene- definitions
Perianal and anal gangrene, spreads from scrotum and rapidly progresses to perineum and anterior abdominal wall. The testes are spared due to separate blood supplyy. Urethral obstruction can occur from excessive penile oedema
Most common cause of diarrhoea in hospitalised patients
Clostridium difficile infection. Occurs due to disturbance of normal anaerobic gut flora leading to overgrowth of c. diff. Usually secondary to borad-spectrum antibiotics e.g. cephalosporins/ clindamycin. Can occur spontaneously in underlying malignancy
Clostridium tetani
Gram-positive with terminal spores giving the appearance of drumsticks on gram staining. Lives in soil, manure and rust. Low numbers of cases due to immunisations
Clostridium tetani infection
Clostridium tetani exotoxin blocks inhibitory nerve impulses by preventing GABA release. This leads to tetanic muscle spasm. Patients present with either generalised spasms (lockjaw spreading to extensor muscles) or localised- characteristic risus sardonicus smile
Treatment of clostridium tetani
ICU management esp for airway and ventilation, wound debridement, IV metro/benpen, tetanus immunisation, anti-tetanus immunoglobulin, muscle relaxants
Tetanus prone wounds
Punctures wounds if contaminated with soil or manure, extensive tissue devitalisation, containing foreign bodies, development of sepsis, compound fractures, more than 6 hours between injury and surgery
Clostridium perfringens
Gram positive, obligate anaerobe, normally part of bowel flora. Produces exotoxin that can cause soft tissue necrosis and produces gas- “gas-gangrene”
Most common causes of infection following abdominal surgery or injury
Coliforms (facultative anaerobes), bacteroides fragilis. These are often minor gut flora demonstrating the disease causing abilities of these organisms
Bacteroides fragilis
The most important strict anaerobic non-spore former causing clinical disease. It has a prominent capsule that inhibits phagocytosis and is involved in abscess formation. Also produces low toxicity endotoxin
Polymicrobic anaerobe infection
When tissue injury occurs, there is limited blood and therefore oxygen supply- this leads to opportunity for infection with anaerobic and facultative anaerobic organisms. Often a mixed infection e.g with strep milleri (often present in abscesses)
Infected pancreatic necrosis- causative organisms
Often coliforms
H. Pylori
Spiral shaped gram-negative bacterium that lives in the mucous layer of stomach lining. It is microaerophilic, surviives by making urease that breaks down urea into CO2 and ammonia. The ammonia increases the local pH and enables the bacteria to survive the acidic stomach environment.
H. Pylori treatment
Triple therapy: PPI, amoxicillin and clarithromycin
Mycobacterium tuberculosis
Acid-fast bacillus, obilgate aerobe (hence why normally occurs in the lungs). Grows very slowly on agar, faster in liquid (2 weeks)
Mycobacterium tuberculosis extra-pulmonary manifestations
Pott’s disease- spinal TB, may require surgery if spinal instability or nerve root compression. Psoas abscess “cold abscess”. Scrofula- cervical lymph node TB, can occasionally produce abscess that can sinus to skin
Mycobacterium treatment
“RIPE” Rifampicin, isoniazid, pyrazinamide, ethambutol. Usually 6 month course
Infectious causes of psoas abscess
Staph aureus, coliforms in secondary psoas abscess, rarely mycobacterium tuberculosis
Neisseria Gonorrhoea- aetiology
Gram-negative diplococcus, sexually transmitted, most common cause of septic monoarthritis in the USA. Can also present with asymetric septic polyarthritis- knee, ankle, elbow and wrist joints. If joint aspirate and blood cultures negative- reactive arthritis
Gonococcal septic arthritis epidemiology
Most common cause of monoarthritis in the USA. Young people, 3 to 4 times higher in women common during menstruation/ pregnancy.
Reiters syndrome
Can occur due to gonococcal infection or GI infection e.g salmonella/ shigella. Pathophysiology is poorly understood. Triad of conjunctivitis, reactive arthritis and urethritis
Treatment of neisseria gonorrhoea septic arthritis
Joint washout and cephalosporins
Chlamydia Trachomatis
Most common, treatable sexually transmitted disease. Incubation period of 13 weeks, is asymptomatic in ~80% of women and ~50% of men. Can cause PID
Fitz-Hugh-Curtis syndrome
Perihepatitis secondary to inflammation of liver capsule in PID causing adhesions. Often mimics ectopic pregnancy, pyelo/renal colic, cholecystitis, viral hepatitis, PE, appendicitis
Actinomyces
branching, filamentous, gram-positive bacilli that are anaerobic to micro-aerophilic. May colonise the oral cavity, lower GI tract and female genital tract
Actinomycosis
Subacute to chronic bacterial infection that is often polymicrobial. It is characterized by contiguous spread, suppurative and granulomatous inflammation, and formation of multiple abscesses, sinus tracts and fistulae that may discharge ‘sulphur granules’ within the pus. Commonly affects cervicofacial, thoracic and abdomino-pelvic areas
Treatment of actinomycosis
Ben pen, or penicillin V. Surgical excision may be required for abscesses/ sinus tracts/ fistulae
What type of bacteria is pseudomonas aeruginosa?
Pseudomonas aeruginosa is an encapsulated, gram-negative rod and a highly pathogenic, opportunistic microorganism.
What are some virulence factors of pseudomonas aeruginosa?
Pseudomonas aeruginosa has several virulence factors, including phospholipase C, endotoxin, exotoxin A, pyoverdine, and pyocyanin.
What type of endocarditis are IV drug users most at risk of?
Tricuspid valve/ right sided endocarditis
Are primary or secondary lung abscesses more common?
Primary- 80%
What are the characteristics of primary lung abscesses?
Usually as a result of aspiration and polymicrobial
What are characteristics of secondary lung abscesses?
P. aeurginosa and gram negative rods are common causes
Which organisms can cause necrotising pneumonia and lung abscesses?
Necrotising lung infections and abscesses are common with aggressive infections by organisms such as Staphylococcus aureus, Klebsiella pneumonia, Streptococcus pyogenes, anaerobic bacteria, and, uncommonly, type 3 pneumococci.
What is silver nitrate stain used for?
Fungi e.g. pneumocystis jiroveci
What is sudan black stain used for?
Identifying fat deposits in tissues
What is Prussian blue stain used for?
Identifying iron deposits in tissues
What is gram stain/ giemsa stain used for?
Identifying bacteria and parasites
What are live attenuated vaccines?
MMR, rotavirus, nasal flu, shingle, chickenpox, BCG vaccine, Yellow fever, oral typhoid
What are inactivated vaccines?
Inactivated polio vaccine, some flu vaccines, hepatitis A vaccine, rabies vaccine, japanese encephalitis vaccine
What are toxoid vaccines
diphtheria, tetanus, pertussis,
What are recombinant vaccines?
Heb B, Pfizer, Moderna, Astrazeneca
What are conjugate vaccines?
Hib, MenC, PCV, MenACWY
