Microbiology Flashcards
What is the difference I cell biology of gram +ve be gram -ve bacteria.
Gram +ve bacteria have thicker peptidoglycan layer and lack outer lipopolysaccharide layer.
How does gram staining differentiate between gram +ve and gram -ve bateria
After staining with Crystal violet and fixation with iodine, a third decolouriser is added, this remove the stain from gram -ve bacteria but not gram +ve (remains purple).
A final stain is added (pink safranin) which is taken up by gram -ve
What other characteristic are used to classify bacteria?
Shape:
Cocci vs bacilli
Oxygen requirement:
Aerobes:
- oblique arobes
- faculatative aerobes
Anaerobes
List differences between exotoxins and endotoxins
Exotoxins: Gram +ve organisms Proteins Heat labile and denatures by formaldehyde Neutralised by specific antibodies
Endotoxins
Gram -ve organisms
Lipopolysaccaride
Heat stable and not denatured by formaldehyde
Poorly antigenic (partially denaturalised by antibodies)
What group of bacteria is streptococcaeae?
What is the 2 main pathogens in this genera?
Gram +ve, facultative anaerobes that grow in pairs or chains, negative catalase test.
Streptococcus
Enterococcus
If diagnosed with skin infection cause by streptococcus pyogenes what should happen?
Highly infectious and virulent.
Isolated until 48 hours of IV Abx
Explains the causative agents of the types of necrotising fasciitis
NF type 1: poly microbial: anaerobes, gram negative, strep, staph
NF type 2: group A strep (+/- concomitant staph)
NB: group A: streptococcus pyogenes (Lancefield group A)
What complication can arise by invasive streptococcal disease if exotoxins are release?
Streptococcal pyogenic exotoxins A and C can result in toxic shock syndrome - systemic inflammation response + shock - few superficial signs
Group B strep is what bacteria!
Where is it’s normal habitat?
Streptococcus agalactiae (lancefield group B)
Normal flora of lower GI, throat and female genital tract.
What % of woman have GBS in pregnancy
What % of babies born to mothers colonised with GBS will become colonised through the passage of the vagina?
30% but may be intermittent
60%
What are the risk factors for the baby accruing GBS
Preterm <37/40 PROM (more than 18 hours) Intrapartun fever >38 Precious infant GBS Heavy maternal carriage of GBS
How can GBS present in the infant?
Early (hours to days): bacteraemia, meningitis, pneumonia
Significant morbidity neurological sequela (blindness, mental retardation)
Late (not a quite during del): meningitis with bacreraemia
Incidence of neonatal GBS disease in UK
0.5/1000
Which mother receive prophylactic Abx intrapartun?
Previous GBS disease in baby or pregnancy
GBS found in vagina or urine during pregnancy
PROM (18 hours)
Preterm rupture of membrane in labour (<37/40)
Preterm rupture of membrane with known GBS (whether in labour or not)
Intrapartun temp
What is the Abx regime to prevent GBS in labour + if pen allergic
IV benpen 3g at onset of labour, 1.5G every 4 hours until delivary
IV clinda 900mg every 8 hours
Despite the gram stain and morphology of staphylococceae .
Result of catalase test
Gram +ve, facultative anaerobes in clusters (like grapes)
Catalase test +ve (note streptococci is negative)
How is the presence of extra cellular enzyme coagulate used to classify staph
The prsescence of coagulase allows the ability to clot plasma
S.aureus: coagulse +ve
Coag negative: S.epidermidis, s.haemolyticus
How to decolonisw those identified with MRSA
Chlorexidine gluconate: shampoo, body wash and mouthwash
Nasal mupirocin
Do coagulase negative staphylococci cause serious infections
Mostly low pathogenicity,
Often contaminants of microbiological specimens
What gram stain and morphology is listeria monocytogenes (most significant form of listeria)
Gram +ve, rod, facultative anaerobes
Beta haemolytic on blood agar
Where is Listeria monocytogenes often found in the environment, how can it be contracted by humans?
Soil, water, faeces of many animals,
Can multiply in foods that have been refrigerated for long periods of time,
Food borne outbreaks: contaminated milk, soft cheese, undercooked meat, unwashed or uncooked vegetables
What is the effect of listeria monocytogenes in pregnancy on the mother + baby
Mother: asymptotic or mild febrile illness with conjunctive, headache sore throat
Fetal infection can occur at any gestation
Early: spont abortion
Late: Preterm, stillbirth
Infant: neonatal listeriosis (less than 2 days), mortality 60%
How if it Dx in mothers?
HVS, MSU, stool sample
AF may be discoloured or contain meconium
If late neonatal listeriosis - where has the baby likely contracted the infection
Either during labour/passage through the birth canal or hospital cross infection
Mortality 10%
