Classification Of Pathogenic Bacteria Flashcards
What is the difference in structure of the wall in gram negative and positive bacteria?
Gram positive have a thick layer of peptidoglycan.
Gram negative have a much thinner layer and also have a lipoprotein layer and LPS antigen.
Describe the two major sections of the gram positive bacteria and the shapes of the bacteria
Aerobic bacteria come in chains (strep and entero) and clusters (staph) it cocci and small or large of bacilli.
Anaerobic have cocci or bacilli
What test can you do on staphylococcus to further differentiate them?
The coagulase Test to see if staphylococci are coagulase positive or negative.
Is staphylococcus aureus coagulase negative or positive, where is it found, what does it cause and what is it resistant to?
It is a coagulase positive and is a commensal organism found in the nose, axilla and perineum.
It causes a wide range of diseases such as septicaemia, soft tissue infections, boils/abscesses and osteomyelitis.
It is commonly resistant to penicillin due to penicillinase but some strains are also now resistant to methicillin resistant.
Name some coagulase negative bacteria and what they do
Staphylococcus epidemidis, haemolyticus and saprophyticus.
Staphylococcus lugdunensis has similar properties to staphylococcus aureus.
They are mainly skin commensals and they form biofilms and may be significant pathogens in the presence of foreign bodies (prosthetics etc).
What are the three classes of Gram positive streptococci?
Alpha haemolytic is partial haemolytic and turns the blood agar green.
Beta haemolytic is complete haemolytic and turns it clear.
Non haemolytic.
Name two alpha haemolytic streptococci and what they cause
Streptococcus pneumoniae can cause pneumonia, meningitis and septicaemia.
Viridans streptococci have many different species and are normal oral flora but can cause infective endocarditis (heart valve infection).
How are beta haemolytic streptococci further classified?
In groups A-G.
A,B,F and D clinically most important.
Name a Group A streptococci and what diseases it causes
Streptococcus pyogenes causes pharyngitis, cellulitis and necrotising fasciitis.
Name a Group B streptococci and what diseases it causes
Streptococcus agalactiae causes neonatal sepsis such as meningitis and bacteraemia. Around 25% of women carry it in their genital tract.
Also responsible for invasive infections in adults usually associated with another morbidity.
Name a Group D streptococci and what it causes
Enterococci such as faecalis and faecium. They’re often non-haemolytic and found in the gut as a normal commensal.
They cause UTIs and infective endocarditis.
Name an anaerobic type of gram positive bacteria
Clostridium difficile, perfringens and tetani.
Where is clostridium difficile found and what does it cause?
It is asymptomatically carried in the gut in healthy people-3% of adults and 66% of babies.
Toxins of it cause diarrhoea and pseudomembranous colitis. It is increased with antibiotic use that affects other flora.
Where is clostridium perfringens found and what can it cause?
It is found in the soil and is a normal commensal in human and animal faeces.
Can contaminate food and cause gastroenteritis from enterotoxin producing strains. It can also infect wounds and cause gas gangrene.
What does clostridium tetani cause?
Toxin production causes tetanus which causes muscle spasm due to loss of inhibition at neuromuscular junction.
