Important Bacteria Flashcards
What are some gram positive cocci?
Staph aureus / MRSA Staph epidermidis Streptococcus pneumoniae Viridans streptococci Streptococcus pyogenes
What are some gram negative cocci?
Neisseria meningitidis
What are some gram positive bacilli?
Clostridium difficile
What are some gram negative bacilli?
Escherichia coli
Haemophilus influenza
Salmonella typhi
Legionella pneumophila
How would clostridium difficile infection present? How would you treat? Also, discuss the virulence factors for this organism
common healthcare infection, often presents with diarrhoea, dehydration, fever
Spore forming- spores survive unfavourable conditions and are therefore a means of reproduction; they can tolerate dryness, cold and give off poisonous
chemicals
Minor component of normal flora of large intestine but use of antibiotics kills normal gut flora. C. Difficile can then thrive as there is fewer microbiota to compete and it is easier to proliferate.
It produces toxins:
Toxin A- Enterotoxin ‣ Causes excessive fluid secretion ‣ Stimulates inflammatory response ‣ Cytopathic effects on tissue
Toxin B- Cytotoxin ‣ Disorganisation of cytoskeleton ‣ Disrupts protein synthesis
Rx- metronidazole, vancomycin, fidoxamicin
How would neisseria meningitides infection present? How would you treat? Also, discuss the virulence factors for this organism
most people are harmlessly colonised as it is part of nasopharynx flora but some can deteriorate rapidly and can be fatal
spread by nasopharyngeal secretions and aerosols
numerous serogroups (A,B, C, W-135)
fatality rate around 10%
gram negative, polysaccharide capsular antigen (produces endotoxins), evade immune response by preventing phagocytosis
causes non blanching purpuric rash due to small blood vessel bleeding.
causes systemic vasodilation which can cause shock, endotoxins bind macrophages which release cytokines (TNF, IL1). Cytokines initiate production of thrombin
and thus promote coagulation. Cytokines also inhibit fibrinolysis. Coagulation cascade leads to
microvascular thrombosis and hence organ ischaemia, dysfunction and failure.
rx-ceftraxione
How would salmonella typhi infection present? How would you treat? Also, discuss the virulence factors for this organism
Prevalent in Asia, Africa, South America where there is poor sanitation.
Caused by Salmonella type faecal-oral spread through food or water usually. 7-14 day incubation period.
gram negative rods, enterobacteria
enteric fever, Headache, Abdominal discomfort, Constipation, Dry cough
Investigations:
Would present with raised LFTs, present in blood and faeces, with anaemia also
Treatment:
Could use ciprofloxacin but resistance is common, so can use ceftriaxone instead
virulence factors= Gram-negative endotoxin, VI antigen. Invasin - allows intracellular growth. Fimbriae adhere to epithelium over ileal lymphoid tissue (Peyer’s patches) → RE system
How would staphylococcus aureus infection present? How would you treat? Also, discuss the virulence factors for this organism
Virulence properties of Staphylococcus aureus in pus and abscess formation. S. aureus infections causes a rapid and extensive influx of white blood cells (e.g., neutrophils). S. aureus lyse neutrophils and red blood cells that have entered the infection area (lysins). The lysed neutrophils pour out large amounts of lysosomal enzymes, which damage surrounding tissue.
causes skin infections such as boils and abscesses.
rx= flucloxacillin
mrsa= methicillin resistant staph aureus.
presents in healthcare due to transmission from healthcare workers to patients via hands.
The recommended in-patient treatment for invasive MRSA is Vancomycin, a glycopeptide given intravenously. Infection prevention is all to do with cleanliness.
How would staphylococcus epidermis infection present? How would you treat? Also, discuss the virulence factors for this organism
- found on the skin
- causes disease when penetrates skin e.g. due to catheter so commonly linked to UTIs
- causes biofilm formation
S. epidermidis is a particular concern for people with catheters or other surgical implants because it is known to form biofilms that grow on these devices.
it can cause endocarditis.
antibiotics generally ineffective for surface infections due to poor penetration but can give vancomyosin potentially.
How would streptococcus pyogenes infection present? How would you treat? Also, discuss the virulence factors for this organism
- can cause streptococcal pharyngitis which can lead to suppurative complications such as abscess as well as further complications such as acute rheumatic fever, glomerulononephritis
- streptococcal toxic shock syndrome
- skin diseases- impetigo, necrotising fascitis, cellulitis, erysipelas
(see lecture for individual mechanisms)
numerous virulence factors:
Hyaluronic acid capsule. M protein Adhesins Streptolysins O and S Hyaluronidase Streptokinase Streptococcal pyrogenic exotoxins: DNAases A, B, C, D:
treat with flucloxacillin.
How would streptococcus pneumoniae infection present? How would you treat? Also, discuss the virulence factors for this organism
S. pneumoniae resides asymptomatically in healthy carriers typically colonizing the respiratory tract, sinuses, and nasal cavity. However, in susceptible individuals with weaker immune systems, such as the elderly and young children, the bacterium may become pathogenic and spread to other locations to cause disease.
S. pneumoniae is the main cause of community acquired pneumonia and meningitis in children and the elderly, and of septicemia in those infected with HIV.
Invasins, such as pneumolysin, an anti-phagocytic capsule, various adhesins, and immunogenic cell wall components are all major virulence factors. Once it colonizes the alveoli the body responds by stimulating the inflammatory response causing plasma, blood, and white blood cells to fill the alveoli. This condition is called pneumonia.
It is susceptible to clindamycin.
How would viridians streptococci infection present? How would you treat? Also, discuss the virulence factors for this organism
- found in the mouth
- cause valve endocarditis
Viridans streptococci have the unique ability to synthesize dextrans from glucose, which allows them to adhere to fibrin-platelet aggregates at damaged heart valves. This mechanism underlies their ability to cause subacute valvular heart disease following their introduction into the bloodstream (e.g., following dental extraction).
treatment via removal of heart valve and replacement, improved oral hygiene.
How would e coli infection present? How would you treat? Also, discuss the virulence factors for this organism
Escherichia coli is part of the normal flora of the colon in humans and other animals but can be pathogenic both within and outside of the GI tract.
Urinary tract infection
Neonatal meningitis
Transmission of intestinal disease is commonly by the fecal–oral route, with contaminated food and water serving as vehicles for transmission. At least five types of intestinal infections that differ in pathogenic mechanisms have been identified. EHEC E. coli infection should be suspected in all patients with acute bloody diarrhea, particularly if associated with abdominal tenderness and absence of fever.
E. coli has fimbriae or pili that are important for adherence to host mucosal surfaces.
treatment of uti caused by e coli via trimethoprim
How would haemophilus influenza infection present? How would you treat? Also, discuss the virulence factors for this organism
Most strains of H. influenzae are opportunistic pathogens; that is, they usually live in their host without causing disease, but cause problems only when other factors (such as a viral infection, reduced immune function or chronically inflamed tissues, e.g. from allergies) create an opportunity. They infect the host by sticking to the host cell using trimeric autotransporter adhesins.
In infants and young children, H. influenzae type b (Hib) causes bacteremia, pneumonia, epiglottitis and acute bacterial meningitis.
Clinical features may include initial symptoms of an upper respiratory tract infection mimicking a viral infection, usually associated with fevers, often low-grade. This may progress to the lower respiratory tract in a few days, with features often resembling those of a wheezy bronchitis. Sputum may be difficult to expectorate and is often grey or creamy in color. The cough may persist for weeks without appropriate treatment. Many cases are diagnosed after presenting chest infections do not respond to penicillins or first-generation cephalosporins.
rx= ceftriaxone
How would legionella pneumophila infection present? How would you treat? Also, discuss the virulence factors for this organism
In humans, L. pneumophila invades and replicates inside macrophages. The internalization of the bacteria can be enhanced by the presence of antibody and complement, but is not absolutely required.
causes legionnaires disease:
Legionnaires’ disease is a form of atypical pneumonia caused by any type of Legionella bacteria. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. Nausea, vomiting, and diarrhea may also occur. This often begins two to ten days after being exposed.
rx= respiratory tract quinolone e.g levofloxacin or macrolide e.g azithryomyocin
