Bacterial Infection Flashcards
What is gram negative bacteria
has LPS (O polysaccharide and lipid A). Peptidoglycan gives cell wall strength. Porin mutation allows antibiotic resistance.
What is gram positive bacteria
has teichoic acid in cell wall. Lipoteichoic acid is anchored in cell membrane (activated in immune system).
What are characteristics of gram +
survive well on drying, some produce spores (Clostridium, bacillus), produce exotoxins, have teichoic acids in their cell wall
What are characteristics of gram -
do not survive drying, no spores, have endotoxin in their cell wall
What is ZN stain used for
Mycobacterium
What is S. aureus
Skin, soft tissue and wound infection. Bloodstream infection which can lead to endocarditis. Infection of bone, causing osteomyelitis and joints, causing septic arthritis.
Pneumonia, especially following influenza
Produces numerous exotoxins - enterotoxins cause food poisoning; toxic shock toxin - staphylococcal toxic shock
Identified by golden colonies on blood agar. Positive coagulase reaction-plasma clot produced - convert fibrinogen to fibrin.
What is streptococci
Gram positive. Occurs in pairs and chains. Many different species - normal flora at various body sites - oral cavity, gut, genital tract
Several medically important species show beta haemolysis on blood agar.
What is Group A strep (beta)
Streptococcus pyogenes (sore throat, impetigo, cellulitis)
What is Group B strep (beta)
Streptococcus agalactiae (neonatal sepsis - carried in the vagina)
How is strep classified
Alpha-hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar. Beta-hemolytic species cause complete rupture of red blood cells.
What is oral strep
Oral streptococci often alpha haemolytic and may be referred to collectively as viridans streptococci.
What are clostridium species
Anaerboic spore forming gram positive rods
What are bacillus species
Aerobic spore former
What are corynebacterium diphtheria and listeria sp
Non spore forming gram positive rods
What is pseudomonas aeruginosa
Pseudomonas aeruginosa - aerobe; environmental organism; likes moist areas
Bloodstream and UTI; important cause of HCAI in immunocompromised patients
What is haemophilus influenzae
Commensal of throat but also causes OM, sinusitis, pneumonia
What are Neisseria species
Gram negative cocci
What are enterobacteriaceae species
facultative anaerobes - some are normal flora of the human colon
E coli, Kiebsiella, Proteus, Salmonella,
Gram negative rods
What is legionella
Gram negative - Environmental organism causing pneumonia. Lives inside fresh water amoebae.
What is the sepsis contiuum
Infection -> SIRS -> Sepsis syndrome (SIRS with a presumed or confirmed infectious process) -> Severe sepsis
What does sepsis cause
Sepsis causes endothelial injury. Increases inflammation. Increases coagulation. Decreases fibrinolysis.
What is SIRS
2 or more of
Temperature over 38 or less than 36. Heartrate over 90. Respiration over 20/min. WBC over 12,000/mm^3 or less than 4,000/mm^3
What is sepsis syndrome
Sepsis with >1 of organ failure:
- CV (leads to shock)
- Renal
- Respiratory
- Hepatic
- Hematologic
- CNS
- Unexplained metabolic acidosis
What is severe sepsis
Sepsis with acute organ dysfunction (including hypoperfusion and hypotension) caused by sepsis
What is septic shock
Sepsis with persistent or refractory hypotension (circulatory collapse in surgical patients thought to have normal blood volume but cannot maintain adequate circulation)
What microbacteria cause shock
Endotoxin (LPS) - Gram negative
Lipoteichoic Acid - Gram positive
Direct - vascular endothelium
Indirect: TLR, complement cascade, coagulation cascade, depletion of protein C
What are super antigens
Super antigens can bring T cells with MHC II without APCs. Much higher inflammatory response. Much quicker. E.g. Group A strep, Staph aureus TSST-1
What’s the management of sepsis
Fluids, dopamine, transfusion
Resolution of precipitating problems
Monitoring of: blood gases, Glasgow coma score, renal function, LFTs, CNS, myocardial function
Antimicrobial
What is the management of community acquired infection
Origin unknown or gut, renal or binary: Co-amoxiclav (Augmentin - covers gram positive) + gentamicin. Add vancomycin if MRSA.
Cefuroxime + metronidazole (covers anaerobes) + gentamicin
Ciprofloxacin (covers gram negative) + metronidazole + gentamicin (gram negative)
Covers a large group of bacteria
What is the management of skin/soft tissue infection
Flucloxacillin + penicillin. Add gentamicin (Add clindamycin if Group A strep or Staph aureus toxic shock)
What is the management of pneumonia
Co-amoxiclav + doxycycline OR Cefuroxime + erythromycin
What is the treatment of malaria
Quinine
What is the alternative if px has penicillin or cephalosporin allergy
ciprofloxacin, vancomycin, erythromycin
What is used to treat hospital acquired infection shock
use gentamicin + piperacillin-tazobactam
MRSA (Vancomycin)
ESBL positive GNR i.e. highly resistant GNR (Meropenem, Colistin), VRE - vancomycin resistant enterococci (Linezolid and others)
What are the examination findings of infection
High index of suspicion if recent tropical travel or immunodeficiency
Examination findings: fever (or hypothermia - especially in elderly), local evidence of inflammation e.g. red/swollen leg (cellulitis), red throat, enlarged lymph nodes (arms, inguinal, back of knees, neck), signs of sepsis (fast pulse, rapid breathing, low blood pressure, confusion)
Disease and travel
Africa - malaria common
Asia - typhoid common
SE Asia - dengue virus common
What is the incubation for falciparum malaria
Minimum 7 days from mosquito bite -> symptoms. Usually less than 1 month from return to onset of illness
What is the incubation period for dengue fever
less than 10 days
What is Pneumocystis jirovecii
The causative organism of Pneumocystis pneumonia, esp in immunocompromised px
What is meningitis
Inflammation of the meninges
What is acute bacterial meningitis
Purulent inflammation of the meninges surrounding the brain and spinal cord caused by bacterial infection
What is the pathogenesis of acute bacterial meningitis
Organisms usually enter via the bloodstream
Direct spread of contiguous parameniogeal focus e.g. sinusitis, otitis media (inflammatory diseases of the medial ear)
What are the likely causative meningitis agents in neonates
Early onset: S. agalactiae (group B Streptococcous) - acquired from maternal reproductive system. E Coli or other gram negative bacilli, L monocytogenes
What are the likely causative meningitis agents in infants and children
N. meningitidis (meningococcus), S. pneumoniae (pneumococcus)
What is the likely causative meningitis agent as the px gets get older
patients are more susceptible to pneumococcus
Viral meningitis common in 20-40 year olds
What are the symptoms of meningitis
fevers, altered mental state, neck stiffness, headache, nausea, vomiting, lethargy/irritability/reduced feeding, photophobia
Classic triad of fever, altered mental state and neck stiffness
Clinical features cannot distinguish between viral and bacterial meningitis.
Old people less likely to present with neck stiffness
What is the gold standard of meningitis diagnosis
: Examine CSF through lumbar puncture
What are CSF findings for meningitis
CSF opening: raised intracranial pressure
Turbid
Raised CSF WCC
CSF protein is raised
CSF/plasma glucose ratio is very low
Neutrophils differential count
WBC may be normal especially in early infection. CSF may be lymphocytic in early stages of bacterial meningitis, if antibiotics given prior to LP, in Listeria monocytogenes or Leptospiral infection.
Where does meningococcus often colonise
Meningococcus often colonises the throat. Can invade the bloodstream and enter CNS in some people
What is likely causative organism of meningitis when a rash is present
N. meningitides is causative in 92
What is meningococcal sepssi
Endotoxins ->Inflammatory response
Widespread vasodilation, myocardial damage, and intravascular coagulation causes CV shock
Vessel damage leads to haemorrhage into tissues (e.g. petechial rash)
What is pneumococcal vaccination
Prevenar
What are the red flag symptoms of meningitis
limb pain ,cold hands and feet or pale and motted skin. Sepsis
Limb pain - highly specific for meningococcal.
Younger: drowsy, fast/laboured breathing, diarrhoea
Older children: thirst
What is miliary TB
wide dissemination into the human body and has tiny lesions. Typically occurs in immunocompromised patients. Don’t have CD4 cells to cause cavitating TB. Arrest at multiple granuloma stage.
What is spinal TB
typically evolve in adjacent thoracic bodies. Leads to collapse of spin (Pott’s diseases of the spine)
What do M avium/intracellulare, M kansaii, M xenopi, M malmoense cause
Resp disease
What do M fortuitum/absecessus/chelonae cause
skin and soft tissue infection related to indwelling devices/respiratory
What does M marinum cause
SSTI (fish tank granuloma)
What are nosocomial infections
New symptoms and signs of infection appearing >48 hours after admission which had not been present on admission.
What are the commonest HCAI
Lower respiratory tract infection (usually pneumonia) - causes 34% of all HCAI and 57% of HCAI in patients in intensive care
UTI
Surgical site
GI infection: inc. C. dif and hospital acquired norovirus
Bloodstream infection
What is C.dif
Ubiquitous in nature
Gram positive spore forming bacilli; produce exotoxins with diverse effects
Spores are resistant to heat, drying, freezing, UVl light and many disinfectants
What does s. aureus cause
Cellulitis, infection of traumatic and surgical wounds, impetigo
Upper respiratory tract infections - sinusitis, ottis media
Lower respiratory tract infection - pneumonia secondary to influenza infection
Severe deep seated and systemic infection: osteomyelitis and septic arthritis; bloodstream infection and endocarditis
Toxin mediated diseases: staphylococcal toxic shock; food poisoning
What is the treatment of MRSA
MSSA can be treated with anti-staphylococcal penicillin such as flucoaxcillin
MRSA has mecA gene encoding altered penicillin binding protein ,pbp 2
Altered pbp has low affinity for all beta lactams - penicillin, cephalosporin, carbapenems, including beta lactamase inhibitor combinations such as co-amoxicalv
Frequently resistant to other abx classes - macrolides, tetracycline
Glycopeptides such as vancomycins
What is VRE
VRE: vancomycin resistant enterococci
Gram positive cocci, part of normal gut microflora
What does VRE cause
UTI (usually in structurally or functionally abnormal urinary tract), as part of polymicrobial infection in intraabdominal sepsis, bloodstream infection and increasingly important cause of endocarditis
How is VRE transmitted
Unwell patients acquire skin colonisation as well as gut and other sites and contaminate their local environment. HCW hands. VRE survives well in the environment - mode of transmission. Resistant to vancomycin and usually teicoplanin. May require oxazolidinone abx linezolid and strains resistant to linezolid are also reported
What is norovirus
ssRNA virus of the family Caliciviridae
Sudden onset of vomiting and diarrhoea
Recovery within 48-72 hours
Very common in the community, especially in winter
Small infective dose - may be as low as 100 virus particles and vomit contains many millions
