Bacterial Infections Flashcards
What signs suggest pharyngitis has a bacterial cause?
- Fever in past 24 hrs
- rapid attendance (within 3 days or less of 1st symptoms)
- muscle aches
- absence of cough
- severely inflamed tonsils (with visible pus, not just red)
- Enlarged anterior cervical glands
(more than 4 of these means probably bacterial
What viruses can cause pharyngitis and how is it managed?
- adenovirus, influenza virus, EBV, Rhinovirus (common cold)
- usually let limiting so manage supportivly
What bacteria most commonly cause pharyngitis ?
Streptococcus pyogenes
What organisms commonly cause meningitis?
strep pneumonia
neisseria meningitidis
haemophilus influenzae type b
some viruses- less severe
What are the features of neisseria meningitidis on a gram stain?
- gram negative (red)
- diplococcus
How is neisseria meningitidis spread?
by respiratory secretions- coughing ect
Is neisseria meningitidis encapsulated?
yes
What are the key virulence factors of neisseria meningitidis?
- pilus- enhances attachment
- polysaccharide capsule- promotes adherence and evades phagocytes
- lipopolysaccharide endotoxin- triggers inflammation
What antibiotic is used to treat meninigitis and why?
ceftriaxone
- active against pathogens that usually causes menigitis in late teens
- penetrates into CSF well
- can be administered IV
What tests would be conducted when meningitis is suspected ?
- lumbar puncture and PCR to find causative organism (if appropriate)
- FBCs- are WBC higher
- U&E- check renal function
- CRP- marker of severity of inflammation
- coagulation studies- checks liver function
- blood gases - lactic acidosis?
- liver function- AST, ALT ect
- blood sugar- ensure its high enough
Which strain of neisseria meningitidis is most common in UK?
- group B
What are the key features of a septic strep. pneumoniae infection?
- yellow sputum
- short of breath
- cough
- chest crackles
- fluid on chest x ray
What are the key features of a septic E. coli infection?
- peritonitis
- abdo pain
- bowl gas seen on xray under diaphragm
In what population are UTIs most common?
sexually active females
What are the common causative organisms of UTIs?
- 70- 95% caused by e. coli
- rest usually staph. Saprophyticus (gram +)
How are UTIs treated?
- trimethoprim
What organism commmonly causes infective endocarditis, what are its key features on a gram stain and how does it enter the blood?
- viridans steptococcus (also staph aureus)
- gram + coccus in chains
- usually through cuts in gums
How does infective endocarditis occur?
- bacteria get into blood
- heart valve faulty causing stagnant blood
- bacteria stay there longer so able to infect valve and endocardium
What is the common presentation of someone with infective endocarditis?
- high fever
- weight loss
- generally unwell
- cardiac symptoms (murmer ect)
- history of heart valve problems
- high WBC, low Hb (haemolytic anaemia), high CRP
What are the key features of all streptococci on a gram stain?
gram + cocci in chains
What are the 3 main groups of streptococci? Describe each group and give an example
alpha haemolysis
- partially break down RBCs and produce a green colour on red agar
- known as viridans streptococcus
- most common example is strep. pneumoniae
beta haemolysis
- fully breakdown RBCs and clear a zone around them on red agar
- strep pyogenes
Non- haemolytic
- enterococcus faecalis
How can beta haemolytic streptococci be classified?
- by cell wall antigens (lancefield)- A,B,C ect
- by sherman group (pyogenic, viridans, enterococcal, lactic)
what is another name for strep. pyogenes?
- group A, beta hamolytic streptococci
What disease is the most common result of a strep. pyogenes infection?
- strep throat (streptococcal pharyngitis)
How do strep. pyogenes spread and what are the different possible outcomes of infection?
- spread by droplets (short range) or break through skin
- colonisation with no harm
- just secrete toxins (pharyngitis)
- invade blood stream (septicaemia)
- spread to subcutaneous tissue (cellulitis), fasica (fascaeitis) and muscle (myonecrosis)
Describe 3 endotoxins that act as virulence factors for strep. pyogenes?
- hyaluronic capsule: inhibits phagocytosis
- M protein: resists phagocytosis, complement and aids adhesion
- Adhesins: helps colonise
describe 2 key exotoxins and state 2 others that are released by strep. pyogenes
- DNAases
- hyaluronidase
- streptakinas (dissolves clots)
- streptacoccal pyrogenic exotoxin-causes toxic shock syndrome
In what age group is strep throat most common?
5-15 yrs old
Describe the key features of strep throat
- abrupt onset of mild sore throat (severe sore throats more likely to be viral)
- fever
- headache
- enlarged lymphoid tissue with tonsil exudate and pus
How is strep throat treated?
supportively
no antibiotics because its self limiting - could use flucoxacillin
Why are overcrowded living conditions associated with spread of strep throat?
as it is spread by droplets
How does scarlet fever develop from strep throat?
if ppl dont have an antibody to the exotoxin and the strain must release a pyogenic exotoxin
What is scarlet fever?
When strep throat is accompanied by a characteristic rash on the neck and trunk and a ‘strawberry’ tongue
- often leads to high fever, sepsis, arthiritis and jaundice
Name some suppurative complications of strep throat?
- peritonsillar cellulitis/ abcesses
- retropharyngeal abcess
- mastoiditis, sinusitis, otis media
- meningitis, brain abcesses
What is acute rheumatic fever?
- inflammation of heart, joints and CNS 10-14 days after step throat
- due to rheumatic M proteins causing antibody production against own tissues
- rarely seen in UK
What is acute post- strep glomerulnophritis?
- inflammation of glomerulus leading to renal failure as a result of specific M proteins
What is impetigo? What causes it and what is it the most common cause of?
A superficial infection of the skin by strep pyogenes that causes blisters and sores. It occurs when the skin is innoculated and then breaks.
It is highly contageous and generally occurs in 2-5 yr olds.
It is the most common cause of glomerulonephritis
What is erysipelas?
Deep strep. pyogenes infection of skin involving dermis and lymphatics. Commonly in face after strep. throat and lower limbs after trauma, skin disease or fungal infection
What is cellulitis? what are risk factors for it?
skin and subcutaneous tissue infected by strep. pyogenes or staph (or other) following break in skin.
risk factors inc impaired lymphatic drainage, IV drug use ect
What is necrotising fascitis and presentation
- infection to deep cutaneous tissue and fascia.
- very rapid deterioration and extensive necorsis
- secondary to skin break
- severe pain at first w/ high fever
- high mortality rate, need to remove necrotic tissue
what is streptococcal toxic shock syndrome? How does it occur?
- entry of s. pyogenes into blood and deeper tissue
- leads to vascular collapse and organ failure, death within hrs of onset
How does streptococcal toxic shock syndrome occur?
- M proteins being released and binding with fibrinogen
- This complex stimulated some WBCs to release hydrolytic enzymes, respiratory burst ect into endothelium and damage it
- this leads to hypercoaglation (leads to DIS), organ damage and vascular leakage- hypotension
What does strep pneumoniae look like on gram stain?
gram + diplococcus
Where can strep. pneumonia be carried harmlessly?
nasopharynx
When can infection of strep. pneumonia occur?
- when a carries has less ressistance
- when a non infected individual looses inhales infected droplets
What disease is most commonly caused by strep. pneumoniae infection?
pneumonia
meningitis also
What are the virulence factors for strep. pneumoniae?
- capsule
- cell associated enzymes
How does pneumonia present?
- often preceeded by upper/ mid respiratory tract infection (coughing, fever, purelent red/ yellow sputum, breathlessness, malaise anorexia)
- fluid accumulated in lungs can be heard and seen on CXR
- high breathing and heart rate
- low blood pressure and O2
What does staph. aureus look like on a gram stain?
gram + cocci in clusters
Where does staph. areus normally reside?
skin, mucous membranes
What diseases does staph areus most commonly cause?
- most common is skin and soft tissue infections in breaks of skin (cuts, needle stick ect)
- also endocarditis, septicemia, food poisioning, toxic shock, necrotising pneumonia, osteomyelitis
Name some virulence factors for staph areus
- protein A in cell wall inactivated IgG
- capsule
- many exotoxins
- enterotoxins (cause sickness when ingested on food)
- toxic shock sydrome toxin ( activates T cells to produce massive release to cytokines like TNF, IL-2 ect
How does staph. areus infections lead to abcesses?
- infects skin break
- bacteria clump together
- causes inflammation, necrosis of nearby tissue and pus
- fibroblasts from fibrous wall around bacteria due to clotting induced by coagulase release from the bacteria
- this means abcess present
What is the difference between coagulase negative and positive bacteria? out of staph epididermis and staph areus which is coagulase positive?
- coagulase positive bacteria produce coagulase and so induce more clotting and create abcesses
- epididermis is coagulase negative, areus is coagulase positive
Where do staph epididermis normally reside?
skin and eyes
What infections does staph epididermis often cause?
- infections of prosthetics and catheters (it produces adhesion molecules to help it stick to prosthetics)
- infections of wounds
- infections of heart valves
What are the gram stain features of clostridium difficile?
gram + rods
How do c. diff infections usually occur? name 2 virulence factors and how they cause diarrhoea and bowel ulcers
- normal in small numbers
- some antibiotics change normal flora of gut
- c. diff able to reproduce as less competition
- produces toxin A which causes excessive fluid secretion (diarhoea) and inflammation
- and toxin B which disrupts protein synthesis and disorganises cytoskeletons (necrosis of epithilium leads to ulcers)
What antibiotics carry high risk of c. diff infection?
- clindamycin
- ampicillin
- cephalosporins
- amoxicillin
How can c. diff infections be detected?
- in stool sample
What symptoms come with c. diff infections
- diarrhoea
- exudate in bowel
- ulcers of bowel (blood in stool)
- vomiting
- fever
How does c. diff infection be managed?
- fluids, antibitoics (metronidazole or might have to be IV vancomysin if severe)
- isolate Pt and PPE to prevent spread
What are the gram stain features of escherichia coli?
- gram - rods
Is E. coli found naturally in body?
yes in colon
What infections does E. coli commonly cause?
- UTIs
- Meningitis in infants
- travellers diarrhoea (if its a strain producing enterotoxin)
What is route of transmission of e coli?
- faecal- oral (contaminated food/ water)
- spread for anus to urethra via peritoneum
What are key virulence factors to e. coli?
- pilli facilitate adhesion
- exotoxins to enable attachment and invasion of host cells
- enterotoxins
Are haemophilus influenzae normally found in the body?
yes in upper resp tract
What are gram stain features of haemophilus influenzae?
gram - rods
How is H. influenzae transmitted?
- resp droplets from coughing, sneezing ect
What is common presentation of H. influenzae infection?
- upper resp tract infections in children
- pneumonia in elderly and immunosurpressed
- also meningitis (rare cause)
How can H. influenzae be treated and prevented?
- vaccine can be given
- amoxycillin
What are general signs and symptoms of sepsis?
- look unwell
- fever
- headache
- unresponsive
- weakness
- chills and rigour
- photophobia
- high HR
- low BP
- nausia
- abdopain and muscle aches
What type of bacteria is legionella pneumonia?
a gram neg rod with a capsule
how does legionella spread?
swimming in contaminated water, resp droplets person to person
What infection does legionella cause?
respiratory tract infections (pneumonia)
- lobar pneumonia
