Gram Positive Bacteria Flashcards
What are the clinically important varieties of staphylococcus?
S.aureus, s. Epidermidis, s.saprophyticus.
How are staphylococci grown?
They grow easily under aerobic conditions on blood and other non selective agars.
What is the catalase status of staphylococci?
Catalase positive
What is the coagulase status of staphylococci?
S.aureus- coagulase positive.
Others are coagulase negative.
Where are staphylococci found?
On skin and mucosal surfaces of humans and other animals.
What are the virulence factors of Staphylococci?
Polysaccharide capsule allows them to resist phagocytosis.
What does catalase (found in staphylococci) do?
Inactivates hydrogen peroxide
What invasive diseases does S.aureus cause?
Superficial pustules or boils Surgical wound infections Abcesses of deep soft tissue Osteomyelitis Septicaemia
What toxin mediated diseases does S.aureus cause?
Toxic shock syndrome
Scalded skin syndrome
Food poisoning
In what clinical situations is S.epidermidis commonly found?
Found in invasive medical devices such as intravascular cannulas.
What is a virulence factor of S.epidermidis that allows it to be resistant to a lot of antibiotics and adhere to surfaces?
Biofilm production
Which infections does S. Saprophyticus cause?
UTIs in adult women (10%)
Which antibiotics are used to treat staphylococci infections?
Most commonly-
B lactamase resistant : flucloxacillin
If MRSA
Then- vancomycin.
What shape are streptococci?
Chain forming cocci
What are B haemolytic streptococci?
They produce haemolysins which cause a zone of clearing around bacterial colonies growing on blood agar. This group is further subdivided according to the polysaccharide present in bacterial cell wall. These are classified A-G
What classification is strep pyogenes?
Group A beta haemolytic strep.
What invasive conditions are caused by strep pyogenes?
Invasive- impetigo, pharyngitis, lymphangitis, necrotising fasciitis, septicaemia
What toxin mediated conditions are caused by strep pyogenes?
Streptococcal toxic shock syndrome, scarlet fever
What are the post infective conditions caused by strep pyogenes?
Rheumatic fever, glomerulonephritis, syndehams chorea
Which abx are group A strep sensitive to?
Penicillin.
What are the virulence factors of streptococci?
M protein- resists phagocytosis
DNAses
Hyaluronidase
Which classification are the viridans streptococci?
Alpha haemolytic- causes green discoloration on blood agar.
Where are strep viridans found?
In the oropharyngeal flora
What diseases can viridans strep cause?
Infective endocarditis
What is the morphology of strep pneumoniae?
Gram positive diplococcus
What classification is strep pneumoniae?
Alpha haemolytic
What is the major virulence factor of strep pneumoniae?
Polysaccharide capsule- resists phagocytosis.
Where is strep pneumoniae commonly found?
In oro and nasopharyngeal flora of healthy individuals.
How is strep pneumoniae transmitted?
Respiratory route in droplet form
What diseases can strep pneumoniae cause?
Pneumonia and meningitis
Which group of patients are particularly at risk from strep pneumoniae infection?
Asplenic patients
What is the first line treatment for strep pneumoniae infection?
Penicillin
Erythromycin is used as an alternative in penicillin allergy.
What are enterococci?
Closely related to group D strep.
Group D polysaccharide allows them to be bile tolerant and to grow in GI tract where they present as minority members of flora.
How are enterococci grown?
On macConkey agar.
What is the most common member of the enterococci?
Enterococcus faecalis- is a cause of UTIs and other hospital acquired infections.
Which abx can be used for enterococcal UTI?
Nitrofurantoin
What is the morphology of c.perfringens?
Bacillus
What conditions does c.perfringens live in?
Anaerobic conditions
What toxins do clostridium perfringens bacteria produce?
Enterotoxin- causes food poisoning
Exotoxins
What diseases does C.perfringens cause?
Gas gangrene
Food poisoning
What abx are clostridia sensitive to?
Penicillin and metronidazole
What is c.difficile?
An anaerobic spore forming G+ bacillus found in the enteric flora. Responsible for abx associated diarrhoea and pseudomembranous colitis.
Which abx is c.difficile sensitive to?
Vancomycin, metronidazole.
