Bacterial Infections Flashcards
Staphylococcus aureus - morphology and gram stain
Gram positive (purple) bunches of cocci
Streptoccus pneumoniae - morphology, gram stain
Gram positive (purple) diplococci
Staphylococcus epidermidis - morphology and gram stain
Gram positive (purple) bunches of cocci
Neisseria meningitidis - morphology and gram stain
Gram negative (pink) diplococci
Neisseria gonorrhoea - morphology and gram stain
Gram negative (pink) diplococci
Clostridium difficile - morphology and gram stain
Gram postive (purple) rods
Clostridium perfringens - morphology and gram stain
Gram positive (purple) rods
Streptococcus pyogenes - morphology, gram stain and group
Gram positive (purple) chains of cocci, referred to as Group A Streptococci or GAS
Escherichia coli - morphology and gram stain
Gram negative (pink) rods
Salmonella - morphology and gram stain
Gram negative (pink) rods
Bordetella - morphology and gram stain
Gram negative (pink) cocci
Non typhoidal salmonella (NTS) - morphology and gram stain
Gram negative (pink) rods
Typhoidal salmonella (enteric fever) - morphology and gram staining
Gram negative (pink) rods
Haemophilus influenzae - morphology and gram stain
Gram negative (pink) cocci
What is the test for gram staining?
1 - Stain slide with crystal violet for 1-2 minutes
2 - Flood slide with Gram’s iodine for 1-2 minutes
3 - Decolourize slide by briefly washing with acetone for 2-3 seconds
4 - Stain with safranin counterstain for 2 minutes
5 - View under microscope
What are the main differences between Gram positive and negative bacteria?
Gram negative bacteria have an outer membrane.
Gram positive have 90% peptidoglycan and negative have 10%.
What are the implications of differences between gram positive and gram negative bacteria?
Susceptible to different antibiotics, different ability to survive infection control procedures and cause different diseases.
Cocci can be arranged…
Singularly, in pairs, in bunches, in chains.
Rods can be arranged…
Singularly or in chains.
Rods can be shaped…
Fat or thin, long or short.
Streptococcus pyogenes is (?)-haemolytic and which colour does this show on blood agar?
Beta-haemolytic and this shows as yellow with zone of clearing around colonies. (Beta-better at degrading)
Streptococcus pneumonia is (?)-haemolytic and which colour does this show on blood agar?
Alpha-haemolytic and this shows as green and is partially degrading.
Clostridium difficile and perfringens form what?
Anaerobic (air hating) spores.
Neisseria meningitidis is capsulated/non-capsulated?
Capsulated.
Neisseria gonorrhoea capsulated/non-capsulated?
Non-capsulated.
Haemophilus influenzae capsulated/non-capsulated?
Capsulated.
Neisseria meningitidis is motile/non-motile?
Non-motile.
Neisseria gonorrhoea is motile/non-motile?
Motile.
Neisseria meningitidis is referred to as what?
The meningococci.
Non-haemolytic bacteria is called what?
The enterococci.
Which of these is more important medically? Alpha and beta haemolytic or non-haemolytic.
Alpha and beta haemolytic.
Which bacteria are classified by putting on blood agar (haemolytic)?
Streptococcus (e.g. this method is used to determine streptococcus pneumoniae from streptococcus pyogenes).
What percentage of infections caused by Haemophilus influenzae are invasive?
80%.
Haemophilus influenzae causes what mainly?
Meningitis - however not most common cause of meningitis due to vaccine.
Bordetella pertussis causes what?
Whooping cough.
The only reservoir for bordetella pertussis is what?
Humans.
Whooping cough most commonly affects who, and what are the important death rates for this group?
Under 1’s, with 90% of deaths from this in babies under 3 months old.
Recent cases of whooping cough has been observed in which age range?
15-40 year olds.
Whooping cough is more severe in whom: adults or babies?
Babies, cases in adults are more mild.
Neisseria gonorrhoea is commonly called what?
The gonococci.
Neisseria gonorrhoea is ranked where in STD’s in the UK?
2nd.
What type of infections does Neisseria gonorrhoea cause?
Urethral, rectal, throat - men and women. Endocervical - women. Eye infections in newborns - contracted during passage through birth canal - conjunctivitis - yellow, crusty eyes.
Neisseria gonorrhoea is symptomatic/asymptomatic?
Asymptomatic - causes increase in cases in new sexual partners as not showing signs of infection.
Neisseria gonorrhoea can lead to what?
Pelvic inflammatory disease and ectopic pregnancy.
What is the leading cause of meningitis?
Neisseria meningitidis.
What type of meningitis is caused by Neisseria meningitidis?
Typically Group B due to lack of vaccine.
Meningitis caused by Neisseria meningitidis can be associated with what and what does this mean must happen?
Septicaemia - prompt antibiotics are needed.
Non-typhoidal salmonella is abbreviated to what?
NTS.
Typhoidal salmonella is sometimes called what?
Enteric fever.
Non-typhoidal salmonella causes what?
Gastrointestinal disease previously associated with eggs. Associated with gastroenteritis and diarrhoea.
How is non-typhoidal salmonella transmitted?
Faecal-oral route or contaminated foods.
Typhoidal salmonella causes what?
Typhoid fever.
What are the symptoms of typhoid fever?
Systemic symptoms - fever. Symptoms to look out for are diarrhoea in the returning traveller.
Typhoidal salmonella is maintained by carriers how?
Passing it on through poor hygiene- e.g. Typhoid Mary.
The enterobacteriaceae includes what?
Escherichia coli and salmonella.
Escherichia coli typically colonises/infects the GI tract.
Typically colonises but virulent (disease-causing) strains can cause infections.
What type of infections does Escherichia coli commonly cause?
UTI’s - simple - resolve without treatment, complicated - can lead to kidney infections such as pyelonephritis. Bacteraemia, GI infections (travellers diarrhoea).
Predisposing factors for developing UTI’s include what?
Being female (shorter urethra), sexual intercourse, pregnancy and catheterisation.
Escherichia coli also causes what?
Severe infection is caused by EHEC (enterohaemorrhagic e.coli) e.g. E.coli 0157 - can lead to haemorrhagic colitis and haemolytic uremic syndrome. Rarely causes neonatal meningitis.
Clostridium perfringens flourishes in what?
Necrotic (dead) tissue.
Clostridium perfringens can cause what?
Gas gangrene.
Treatment for clostridium perfringens is what?
Surgical debridement or amputation.
Streptococcus pyogenes can cause what?
Tonsillitis, skin and soft tissue infections such as impetigo and cellulitis and necrotising infections such as necrotising fasciitis.
Necrotising fasciitis is also referred to as what?
Flesh eating disease.
Streptococcus pneumoniae is capsulated/non-capsulated?
Capsulated.
The presence of a capsule around streptoccus pneumoniae is linked to what?
Invasive infections.
Invasive infections are linked to what?
Capsules around the bacterium.
Streptococcus pneumoniae can cause what?
Pneumonia, meningitis, septicaemia, otitis media, ear infections, septic arthritis and sinusitis.
Urgent antibiotics are needed for meningitis - true/false?
True.
Symptoms of pneumococccal meningitis in adults include?
Blotchy, non-blanching, red rash; headache; fever; nausea and vomiting.
Streptococcus pneumonia colonises the nasopharynx in..
5-10% healthy adults, 40% healthy children.
Symptoms of pneumococcal meningitis in under 2 year olds include?
Floppy; unresponsive; pale, blotchy skin; staring expression; loss of appetite and vomiting.
How is streptococcus pneumonia treated?
Depends on sensitivity - if sensitive - penicillin. Vancomycin can be used. Sensitivity takes time to determine due to needing to grow culture.
How streptococcus pneumonia be prevented?
Vaccination: Pneumococcal conjugate vaccine in under two’s, pneumococcal polysaccharide vaccines in over 65’s.
Invasive pneumococcal diseases mainly affect?
Under two’s: 20% cases, over 65’s.
Symptoms of pneumonia (Streptococcus pneumoniae)?
Productive cough, rusty sputum, fever.
Streptococcus pneumoniae accounts for what percentage of pneumonias?
25-60%.
What percentage of sore throats are viral?
90%.
GAS infections in the throat can cause what complications?
Scarlet fever, Quinsy, Sinusitis.
How are GAS throat infections treated?
Oral antibiotics - amoxicillin.
Impetigo is most commonly seen in who and when?
Children: 2-5 year old, more commonly in summer than winter.
Symptoms of impetigo are?
Bullae/blisters which burst releasing a yellow discharge which crusts.
How is impetigo treated?
With oral antibiotics - flucloxacillin.
Impetigo is contagious - true or false?
True.
How is cellulitis contracted?
Enters skin through trauma or previous lesion/boyle?
What are the symptoms of cellulitis?
Hot red skin that rapidly spreads.
Treatment for cellulitis is what?
Anti staph/strep antibiotics such as flucloxacillin or penicillin.
How is cellulitis monitored?
Draw around redness to monitor progress from treatment.
Necrotising fasciitis is a medical emergency - true/false?
True.
What is necrotising fasciitis?
Acute infection of deeper layer of skin (fascia).
What are the symptoms of necrotising fasciitis?
Red, hot, painful, swollen skin.
What can necrotising fasciitis progress to?
Cutaneous gangrene (death of tissue) or if severely unwell - septic shock.
What are the predisposing factors for necrotising fasciitis?
Trauma/surgical wounds, diabetes, intravenous drug use.
What is the mortality for necrotising fasciitis?
20-30%
Treatment for necrotising fasciitis?
Aggressive treatment with intravenous antibiotics and debridement of dead tissue.
How does c.perfringens cause gas gangrene?
Spore makes its way into wound.
Germinates and produces toxins.
Foul discharge and pain.
How can c.perfringens be prevented?
Clean and debride wounds.
How does c.diff cause diarrhoea?
Antibiotic use kills normal flora allowing c.diff to flourish. Releases toxins which at a certain level cause diarrhoea.
Gut commensal for c.diff?
3% adults, 75% children.
Main risk factors for c.diff?
Over 65 (80% cases), using a broad spectrum antibiotic.
Treatment for c.diff?
Metronidazole, Vancomycin, Fidaxomicin.
Outcomes of c.diff?
Can cause pseudomembranous colitis - inflammation of the colon causing diarrhoea (offensive smelling), abdominal pain and fever.
What can pseudomembranous colitis as a result of c.diff lead to?
Toxic mega colon - extreme dilation of the colon.
Fatality of toxic mega colon?
40-50% of cases.
Treatment for toxic mega colon?
Possible removal of bowel and vancomycin.
Treatment for pseudomembranous colitis?
Vancomycin.
American treatment for c.diff?
Homogenise relatives faeces and feed to patient to replace natural flora.
What is SIGHT prevention?
Suspect that a case is infective Isolation Gloves and aprons Hand washing Test stool for toxin
Prevention is better than cure - true or false?
True.
Why has incidence of c.diff declined?
Better prescribing of antibiotics
More isolation
Better environmental disinfection
Better hand hygiene
Many gram positive bacteria are members of the normal flora - asymptomatic carriage - true or false?
True.
Bacteria can cause a range of diseases from minor to medical emergencies - true or false?
True.
The prevention of spore contamination is essential in preventing clostridial infections - true or false?
True.
Staphylococcus aureus causes what?
Skin and soft tissue infections such as cellulitis and impetigo (leading cause), food poisoning, bone infections, endocarditis and bacteraemia (bugs in blood).
Staphylococcus aureus is present in what percentage of the population and where?
Nose of 30-40% of population.
How does s.aureus cause scalded skin syndrome?
Caused by 6-10% of s.aureus strains. Strain grows locally and then moves to blood but only affects the skin causing top layers to shed (exfoliation).
Who is affected by scalded skin syndrome?
Children under 6.
What is the mortality of scaled skin syndrome?
Less than 3% of cases.
How is scalded skin syndrome treated?
With oral antibiotics
Side effects of scalded skin syndrome?
Fluid loss through impaired sweating and blistering.
Strep toxic shock has a mortality of what?
40%.
Toxic shock syndrome related to s.aureus has a mortality of what?
<3%.
Why are adults not affected by scalded skin syndrome?
The adult immune system can deal with the toxin.
Fluid found in scalded skin syndrome blisters are sterile - true/false?
True.
Mortality of scalded skin syndrome?
<3%.
Toxic shock syndrome is caused by what?
S.aureus.
Scalded skin syndrome is caused by what?
S.aureus.
What percentage of T-Cells are activated in TSS?
30% - massive immune response effecting multiple organs. Normal infections activate 0.1%
Effects of TSS?
Fever, hypotension, rash, desquamation of skin on soles and palms.
TSS is associated with what?
Tampons - breeding ground for S.aureus causing toxin secretion and mass immune response.
MRSA stands for?
Methicillin resistant staphylococcus aureus.
What is MRSA resistant to?
Penicillin and other antibiotics
MRSA is common in…
Elderly
Lines and catheters
Surgical wounds
Intensive Care Units
Treatments for MRSA?
Vancomycin
Staphylococcus epidermidis causes infection where?
Catheters
Long lines
Cannulae
Indwelling medical devices (pacemakers etc.)
How often should cannulae be changed?
Every 72 hours.
How are bacteria classified?
First by gram stain and what they look like under a microscope, then by properties often based on biochemical reactions - e.g. one may be able to metabolise a sugar that another can’t.
Gram stain differentiates most bacteria but not all - true/false?
True.
What is the gram stain based on?
Cell wall type.
Bacteria are what size?
<15 micrometres length
Bacteria are capable of independent replication - True/false?
True.
Bacteria are the cause of most infections seen in hospital - true/false?
True.
There are many different species on bacteria - true/false?
True.
Bacteria is treated using antibiotics?
True.
Humans are super organisms comprising of what ration bacterial to human cells?
10:1
10^14 bacterial cells
10^13 human cells
How are complications from GAS infections treated?
With oral antibiotics - amoxicillin.
Medically important gram negative bacteria include?
Escherichia, salmonella, shigella, proteus, klebsiella, enterobacter, citrobacter, yersinia.
Which bacteria is notorious for encrustation of catheters and how long does it take to do so?
Proteus mirabilis (gram negative) - withing 10 days.
What does shigella cause?
Watery diarrhoea.
Salmonella are not commensal - true or false?
True.
All strains of salmonella cause disease in humans - true or false?
True.
How many eggs are now contaminated with salmonella due to chicken vaccination?
0.1%
What is the source of salmonella?
Poultry, cattle, reptiles, arthropods and humans (enteric fever).
What type of infection can salmonella cause?
Self-limiting (diarrhoea) or enteric fever (typhoid).
What is the pathway for gastroenteritis caused by salmonella?
Ingestion of viable bacteria (10^4-7 cells)
Non typhoidal salmonella - 12-72 hours
Gastroenteritis - often localised to GI, diarrhoea, short clinical course (<10 days).
What is the pathway for enteric fever caused by salmonella?
Ingestion of viable bacteria (10^4-7 cells)
Typhoidal salmonella - 7-14 days
Enteric fever - system infection, diarrhoea/constipation
Longer symptom duration than gastroenteritis (3 weeks)
Can lead to either acute or chronic carriage
Shigella is also called?
Bacillary dysentery.
Shigella causes what?
Shigellosis - dysentery.
Enteric fever is caused by what?
Salmonella paratyphi or typhi
How many people are infected annually with enteric fever?
17 million.
How many deaths annually from enteric fever.
600,000.
What percentage of people infected with enteric fever become chronic carriers?
5%.
The infectious does of shigella is very low - true or false?
True.
Symptoms of shigellosis are?
Abdominal cramps, tenesmus (intense desire to use the toilet), frequent passage of mucoid - bloody diarrhoea.
How is shigella spread?
Person to person via faecal-oral route.
Outbreaks of shigella are typically seen where?
Primary schools.
E.coli is commensal in the human gut - true or false?
True.
Source and transmission of E.coli?
Natural habitats - GI tracts of human, pigs, amphibians, fish and cattle. Transmission: undercooked contaminated meat, unpasteurised dairy products, contaminated fruit and vegetables, environmental contamination.
Which is the first type of clincal syndrome for E.coli and which version of this is most relevant to us? Is it commensal?
Diarrhoeagenic
EHEC - enterohaemorrhagic - Most important - non-commensal.
Most relevant strain of EHEC?
E.coli 0157.
How common is e.coli 0157?
Relatively rare
What does e.coli 0157 cause?
Mild gastroenteritis to severe bloody diarrhoea.
Can result in:
Haemorrhagic colitis: Abdominal pain, watery diarrhoea.
Haemolytic uremic syndrome (HUS): Renal failure, bloody diarrhoea.
For positive ID of UTI there must be:
High bacterial cell numbers, symptoms and raised white blood cell count in urine.
What is used to treat e.coli UTI’s?
Trimethoprim.
Types of UTI and where are they found:
Kidney: Pyelonephritis
Bladder: Cystitis
Urethra: Urethritis
How do UTI’s get to the kidney?
Through the cysto-ureteric valve and bacterial ascension to the kidney.
Cystitis is most common in?
Young females who have been sexually active recently.
What percentage of women report 1 or more than 1 case of cystitis?
50%
Treatment for cystitis?
Can be treated empirically (before diagnosis) by GP with antibiotics or may be uncomplicated and resolve alone.
Symptoms of cystitis?
Burning sensation when urinating.
Symptoms of pyelonephritis?
Same as cystitis but also severe lower back pain, fever, chills and nausea and vomiting. Bacteraemia may be present. Costovertebral (CVA) tenderness. Elevated red blood cell count in urine and white blood cell casts may be seen.
Pyelonephritis can lead to what?
Urosepsis.
Which two bacteria are the most responsible for UTI’s?
E.coli and staphylococcus prophyticus.
Less common causes of UTI’s include?
Klebsiella spp., Enterobacter spp., Proteus spp., Citrobacter spp., Pseudomonas spp., Group B Strep, Group D Strep, Enterococci, Corynebacterium urealyticum and Yeasts.
How does proteus mirabilis act on culture plates?
Swarming.
Besides catheter encrustation what does proteus cause?
UTI, bacteraemia and pneumonia.
What does proteus form?
A biofilm.
What does bacteria in catheter urine indicate?
Not definitely indicative of infection, often indicates colonisation but catheter should be removed.
Bacteraemia can lead to what?
Sepsis.
Increase of bacteraemia between 2004-2008 and 2009-2010? What happened in June 2011?
2004-2008: 33%
2009-2010: 5%.
June 2011: Mandatory surveillance
What are 50% cases of sepsis attributed to?
Pneumonia.
Diagnosis of sepsis?
Symptoms: Fever - over 38 or hypothermia under 36.
Raised heart rate - over 90 bpm.
Fast breathing.
Nausea.
Confusion.
Evidence of an infection. (50% attributed to pneumonia)
Types of sepsis?
Uncomplicated: no need for hospital admission.
Severe: Interference with vital organs - heart, kidneys and lungs.
Septic shock: Severe, organ failure, 20-30% mortality, over 60% cases yield gram negative bacteria.
