bacterial pathogens Flashcards
what bacteria is MRSA?
staphylococcus aureus
what is responsible for rheumatic fever and what is a symptom?
streptococcus pyogenes and can give a fever
what does streptococcus agalactiae result in?
neonatal meningitis and pneumonia and sepsis - group B strep
what causes gonorrhoea and what is another name for gonorrhoea?
urethritis and is from steptococcus gonorrhoeae
what causes UTIs?
proteus
what is clostridium difficile?
it is antibiotic related diarrhoea, PMC
what does barrielia and leptospira result in?
barrielia - relapsing fever
leptospira - meninigitis
what do S and R in a blood culture report mean?
S means sensitive and R means resistant
what will happen to gram stain with a thick cell wall?
the cell wall will retain the gram stain - gram positive
what are the characteristics of a cell wall in a gram negative bacteria?
thin cell wall - they will contain lipopolysaccharides - fatty outer cell membrane layer
which one is more common on skin?
positive - they are more resistant to drying, negative will only survive in places with more moisture
what shape are bacilli and cocci?
bacilli are rods and cocci are circular
what are examples of virulence factors?
resistance factors or enzymes to break tissue down - they are designed to help the bacteria invade the host tissue
what does invasion depends on?
host factors, bacterial factors and opportunity (distance, exposure)
why are females more prone to UTIs?
they have a shorter urethra
why is E coli the commonest cause of UTIs?
E coli is normal flora in the bowel. It can ascend in the perineum by colonising the urethral meatus and then adheres to the urinary cells or urethral catheter equipment causing an inflammatory response and can develop resistance to antibiotics
what is the commonest form of skin and soft tissue infections and how does this occur?
S. Aureus - it adheres to damaged skin and secretes exoenzymes and toxins which can damage cells or promote the host inflammatory response such as pus. it can colonise the nasal carriages of up to 50% of people
what are some examples of diseases Staphylococcus aureus can cause?
UTIs, meningitis, pneumonia, endocarditis, osteomyelitis, septic arthritis, bacteriaemia or septicaemia
what does S aureus look like with a gram stain?
a bunch of grapes - clusters formed
what is staphylococcus epidermidis?
it is an opportunistic bacteria, commensal on skin - most people have it. It is described as a coagulase negative staphylococci
when can eidermidis strike?
associated with foreign bodies such as lines and prosthetic cardiac valves - needs an opportunity to infect
why does it infect with lines etc?
it can adhere to plastics or metals using glycocalyx and form biofilms - loosen bones and joints resulting in pain and instability
what are the differences between aureus and epidermidis?
epidermidis is more internal and has different pathogenicity factors
what bacteria is included in group A strep?
streptococcus pyogenes - commonest cause of bacterial sore throat
what can strep pyogenes cause?
puerperal sepsis, SSTIs, necrotisin fasciitis, scarlet fever and invasive infections such as pneumonia and is also associated with secondary immunological presentation - glomerulonephritis (autoimmune as have antibodies to strep A group)
what is the presentation of pyogenes with gram stain?
purple chains - gram positive
what is a common cause of childhood infections such as otitis media, bacterial meningitis and bacterial pneumonia?
streptococcus pneumoniae
what strep causes abscesses (dental, liver, lung, brain?)
streptococcus milleri complex
what are viridans streptococci?
collective name for a number of species of a-haemolytic streptococci that inhabit the upper respiratory tract - classic cause of sub-acute bacterial endocarditis
how do viridans streptococci work?
they adhere to areas of damage and alter blood flow around the heart valves giving aortic stenosis and disease of the heart valves
what strep forms part of the bowel flora, is a-haemolytic and was formerly known as streptoccocus bovis?
streptococcus gallolyticus - casues bacteriaemia and can be associated with colonic malignancies
what is listeria monocytogenes?
it is a gram positive bacillus - it is rare but is a significant cause of meningitis and sepsis in pregnancy, neonates and immunosupressed patient
what is an adaptive feature of listeria monocytogenes?
ti is zoophilic - animal origin so can grow at low temperatures
what is the corynebacterium species?
it is a rarely seen bacteria (unless in some parts of the world) that is a gram positive bacilli and is a commensal (some species)on the skin or URT.
why is diptheria not seen in the UK?
due to the vaccination - targets corynebacterium diptheriae
what is enterobacteriacae?
it is a collective term for a group of species that are gram negative bacilli and are commensal in the bowel
what are the commonest sources of bacteriaemia from E coli?
urinary, biliary or intra-abdominal
what are toxigenic strains of E coli associated with?
severe diarrhoea, and haemolytic uraemia syndrome
what is psuedomoas aeruginosa?
it is a multi-resistant gram negative bacillus that is an opportunistic pathogen. It often colonises leg ulcers but this can be wiped off but more commonly causes respiratory, UT, soft tissue and other infections in vulnerable patients and produces a characteristic green pigment
what is neisseria meningitidis?
it is a bacteria that can cause mengiococcal sepsis and or meningitis. It is a gram negative diplococcus and the infection is not as serious as that of strep. the classical presentation is a purpuric non blanching rash - reduction in cases since vaccination - B and C
what is a complication and a rare complication of neisseria gonorrhoeae?
rare - other secondary invasive infection such as septic arthritis
complication - baby born to mother with active illness can get form of conjunctivitis
what type of haemophilius influenzae (gram negative bacilli) causes epiglottis damage or meningitis?
capsulated types
type b is capsulated and is the only one that is in the Hib vaccine
what are the four infections caused by the main types of clostridium and what type of bacteria are these?
clostridium are anaerobes of which many are spore forming. C difficile causes antibiotic related diarrhoea or colitis, C tetani tetanus, C botulinum it botulism and C. perfringens classically causes gas gangrene
what are some types of anaerobe species?
prevatella, fusobacterium, and bacteroides - often part of polybacterial infections
what is often referred to as acid fast bacilli?
mycobacterium species as they use acid fast stain
why do mycobacterium not use the classic gram stain?
their cell wall does not allow for staining
what are atypical mycobacteria and what do they cause?
they are another species of mycobacterium and they cause respiratory infections in chronic lung disease and opportunistic infection in the immuncompromised
what are the species without a cell wall and what are examples?
these are the chlamydia and mycoplasma species
C. trachomatis - commonest cause of STI in uk
mycoplasma pneumoniae - comments cause of respiratory tract infection
what do spirochaetes not do?
they do not stain with gram stain such as treponema pallidum (syphilis)
what causes lyme disease and leptospirosis?
spirochaetes
lyme - chronic fatigue syndrome
leptospirosis - renal failure and meningitis
