Bacterial Pathogens Flashcards
How are bacteria classified?
By the gram stain
What are the 3 main Gram +ve cocci?
- Staphylococcus aureus
- Streptococcus pyogenes
- Streptococcus agalactiae
What are the 2 main Gram -ve cocci?
- Neisseria meningitidis
2. Neisseria gonorrhoeae
How do cocci differ from bacilli?
Cocci are round cells.
Bacilli are rod-shaped bacteria.
What classification does ‘Bacillus anthracis’ belong to?
Grame +ve bacilli
What classification does ‘Clostridium difficile’ belong to?
Gram +ve bacilli
What classification does ‘Salmonella typhi’ belong to?
Gram -ve bacilli
What classification does Escherichia coli (E. coli) belong to?
Gram -ve bacilli
What are coccobacilli?
A type of bacterium with a shape between cocci (spherical) and bacilli (rod-shaped).
Coccobacilli, then, are very short rods which may be mistaken for cocci.
What are the 3 basic shapes of bacteria?
- coccus
- bacillus
- spiral
What classification does Helicobacter belong to?
Spiral bacteria
What classification does Haemophilus belong to?
Gram -ve coccobacilli
How does the cell wall of a Gram + bacteria compare to a Gram -?
Gram positive bacteria have thicker cell walls composed of peptidoglycan.
What are the cell walls of bacteria composed of?
Peptidoglycan
How does a thicker cell wall (Gram +) affect the stain? What colour is given?
Thicker cell walls of Gram + bacteria can hold dye better –> stain is blue
How does a thinner cell wall (Gram -) affect the stain? What colour is given?
Thinner cell walls unable to hold dye –> stain is pinky-red
What colour do Gram + bacteria appear?
Dark blue
What colour do Gram - bacteria appear?
Pink/red
What are the 3 factors behind bacteria causing particular infections?
- Host factors
- Opportunity
- Bacterial factors
What does ‘host factors’ involve?
- Immune system
2. Devices (e.g. urinary catheter)
How may a catheter lead to infection?
Bypass normal structural integrity –> catheter may become colonised
What does ‘bacterial factors’ involve?
Virulence, resistance, environmental survival
Define virulence
The ability of a microorganism to cause disease in the host.
E.g. avoiding host immune responses
What does ‘opportunity’ involve?
- Exposure to pathogens
2. Normal flora
Where is Staphylococcus aureus found?
Skin, nose, vagina
What normal flora is E. coli part of?
Bowel flora (in most humans)
Due to the location of E. coli in human, what does this cause a risk of?
Why is this risk greater in females?
Colonisation of urethral meatus and surrounding area –> can cause UTI by travelling up urethra to bladder (or bypassing via catheter)
Short urethra in females
What abilities does E. coli bacteria have that enable them to cause UTIs?
- Able to adhere to uroepithelial cells/urinary catheter materials
- Triggers host inflammatory response in bladder
- Able to develop resistance to antibiotics
What bacteria is the most common cause of UTI?
E. coli (80%)
What is S. aureus able to adhere to? How can it cause infection?
Able to adhere to damaged skin
Produces exoenzymes and toxins that can damage tissues and provoke host response (e.g. pus formation)
Describe shape/arrangement of S. aureus?
cocci-shaped and tend to be arranged in clusters that are described as “bunches of grapes”
What bacteria is the commonest cause of skin/soft tissue infections (including of surgical site infections)?
Staphylococcus aureus
S. aureus can be invasive. What diseases can this lead to?
Bacteraemia / septicaemia
What is bacteraemia?
Bacteraemia occurs when bacteria get into the blood stream
What is septicaemia?
Blood stream infection, implies greater severity and clinical significance.
What bacteria is the most common cause of bacteraemia?
S. aureus
What other conditions can S. aureus cause?
Osteomyelitis/septic arthritis
Endocarditis
Pneumonia
UTI (less common)
Meningitis (rare)
Where is Staphylococcus epidermidis found?
Skin (normal flora), nostrils
What is an opportunistic pathogen?
A group of microorganisms that do not usually infect healthy hosts but produce infections in hospitals (to immunodepressed persons or those presenting underlying diseases such as as cystic fibrosis, which favors infection)
What makes S. epidermis less able to cause infections?
Doesn’t have the same exoenzymes or toxin capabilities
What gives S. epidermis the ability to cause infection?
Where does S. epidermis cause infections?
Can adhere to plastics/metals using glycocalyx (‘slime’), forming biofilms.
Therefore…
Causes infection in association with ‘foreign bodies’ e.g. intravascular catheters, prosthetic joints, prosthetic cardiac valves, etc
What can Streptococcus pyogenes also be referred to as?
Group A Strep
Which bacteria is the commonest cause of bacterial sore throat?
Streptococcus pyogenes
What classification is Streptococcus pyogenes?
Gram-positive cocci
What classification is Staphylococcus epidermidis?
Gram-positive cocci
What classification is S. aureus?
Gram-positive cocci
What other diseases does Streptococcus pyogenes cause?
Scarlet Fever (strawberry pink tongue)
Necrotising fasciitis
Other SSTIs
Invasive infections (such as pneumonia)
Puerperal sepsis
What is Necrotising fasciitis?
Flesh-eating disease –> infection that results in the death of parts of the body’s soft tissue.
What bacteria causes scarlet fever?
Streptococcus pyogenes
What is SSTI?
Skin and soft tissue infection
What is puerperal sepsis?
The infection of the genital tract occurring at labour or within 42 days of the postpartum period
What is the commonest cause of bacterial pneumonia?
Streptococcus pneumoniae
What classification is Streptococcus pneumoniae?
Gram-positive cocci
What is the commonest cause of bacterial meningitis? (except in neonates)
Streptococcus pneumoniae
What is the commonest cause of bacterial meningitis and sepsis in neonates?
Streptococcus agalactiae
What can Streptococcus agalactiae also be referred to as?
Group B Strep
What classification is Streptococcus agalactiae?
Gram-positive coccus
What is the Streptococcus milleri complex?
3 closely related species of pus-forming streptococci
What is the Streptococcus milleri complex associated with?
Abscesses: dental, lung, liver, brain and others
E.g. damage to gum/teeth can cause oropharyngeal abscesses
Where is the Streptococcus milleri complex normally found?
on the mucous membrane of the oral cavity, oral pharynx, gastrointestinal tract, and genitourinary tract
What are Viridans streptococci?
a large group of commensal streptococcal Gram-positive bacteria species that are α-hemolytic
Where do Viridans streptococci inhabit?
URT (e.g. S. oralis, S. mitis)
What classification are Viridans streptococci?
Gram-positive coccus
What is subacute bacterial endocarditis typically caused by?
Viridans streptococci
Where is Streptococcus gallolyticus found?
Part of bowel flora
What can bacteraemia with Streptococcus gallolyticus be associated with?
Colonic malignancies (e.g. cancer)
What classification is Streptococcus gallolyticus?
Gram-positive coccus
What classification is Listeria monocytogenes?
Gram-positive bacillus
Listeria monocytogenes is a rare but significant cause of sepsis and meningitis in who?
Pregnant women, neonates and immunosuppressed patients
Listeria monocytogenes is a zoonosis.
What is zoonosis?
diseases that can be passed from animals to humans
e.g. farmers
What is Listeria monocytogenes associated with?
Consuming cheese made from unpasteurised milk and other foodstuffs
Why shouldn’t pregnant women consume unpasteurised dairy?
Due to bacteria Listeria (monocytogenes)
What classification is Corynebacterium species?
Gram-positive bacteria
Where are Corynebacterium species found?
Commensals of skin and URT
What are opportunistic infections with Corynebacterium species associated with?
Devices and trauma
What bacteria is the classic cause of diptheria?
corynebacterium diphtheriae
Why is corynebacterium diphtheriae rarely seen in UK?
Immunisation
What classification is Propionibacterium acnes / Cutibacterium acnes?
Gram-positive baccilus
What bacteria is acne associated with?
Cutibacterium acnes
What else can Cutibacterium acnes cause?
Device-associated and post-procedural infections
What classification is Enterobacteriaceae (‘coliforms’)?
Gram-negative bacilli
What is Enterobacteriaceae (‘coliforms’)? Where is it found?
A collective term for a number of species of gram negative bacilli found in bowel flora
What are 3 common species of Enterobacteriaceae?
- Escherichia coli (E. coli)
- Klebsiella pneumoniae
- Enterobacter cloacae
What bacteria is the commonest cause of UTIs?
E. coli
What bacteria is the commonest cause of bacteraemia?
E. coli
What are nosocomial infections?
Infections originating in hospitals
What nosocomial infections can E. coli cause?
Line infections, pneumonia, wound infections
What are toxigenic strains of E. coli (e.g. O157) associated with?
severe diarrhoea and haemolytic uraemic syndrome (HUS)
What classification is Pseudomonas aeruginosa?
Gram-negative bacillus
What is important to note clinically about Pseudomonas aeruginosa?
Multi-resistant to antibiotics and opportunistic pathogen
What diseases can Pseudomonas aeruginosa cause?
respiratory infections, UTIs, soft-tissue and other infections in vulnerable patients
In the labs, what colour pigment does Pseudomonas aeruginosa produce?
Green
What classification is Neisseria meningitidis?
Gram-negative diplococcus
What diseases can Neisseria meningitidis cause?
meningococcal sepsis and/or meningitis
What is an important presentation of meningococcal infection?
A purpuric non-blanching rash
What is a purpuric non-blanching rash?
Purpuric - skin rash in which small spots of blood appear on the skin
Non blanching - rash that does not fade under pressure. The “glass test” - When a clear glass is pressed firmly against the skin the rash is still visible.
What classification is Neisseria gonorrhoeae?
Gram-negative diplococcus
What bacteria causes gonorrhoea?
Neisseria gonorrhoeae
What is ophthalmia neonatorum? What is it caused by?
An eye infection that occurs within the first 30 days of life.
It is caught during birth by contact with the mother’s birth canal that is infected with a sexually-transmitted disease.
Neisseria gonorrhoeae can occasionally cause invasive infections (e.g. septic arthritis) secondary to what?
Primary sexually transmitted infections
What classifications is Haemophilus influenzae?
Gram-negative bacillus
Where is Haemophilus influenzae normally found?
Part of normal respiratory tract flora
What infections can Haemophilus influenzae cause?
Respiratory tract infections (e.g. pneumonia, infective exacerbations of COPD)
Are most strains of Haemophilus influenzae capsulated or non capsulated?
Non capsulated
A few strains of Haemophilus influenzae are capsulated.
What does this mean?
The bacterial capsule is a polysaccharide layer that lies outside the cell envelope and is part of the outer envelope of a bacterial cell.
It is a well-organised layer, not easily washed off, and it can be the cause of various diseases.
What diseases can CAPSULATED types (e.g. type b) of Haemophilus influenzae cause?
Meningitis and epiglottitis
What is the HIb vaccine?
Vaccine prevents Haemophilus influenzae type b (Hib) infection
What are anaerobes?
Organisms that grow in the absence of oxygen
What 4 bacteria make up the Clostridium species?
- C. difficile
- C. perfringens
- C. tetani
- C. botulinum
What classification is the Clostridium species?
Gram-positive bacillus (spore forming)
What disease can C. difficile cause?
Bacteria that can infect the bowel and cause diarrhoea.
The infection most commonly affects people who have recently been treated with antibiotics.
What bacteria is the classic cause of gas gangrene?
C. perfringens
What is ‘gas gangrene’?
Bacterium C. perfringens develops in an injury or surgical wound that’s depleted of blood supply.
The bacterial infection produces toxins that release gas and cause tissue death.
What bacteria is the classic cause of tetanus?
C. tetani
What bacteria is the classic cause of botulism?
C. botulinum
What is botulism?
Bacteria attack the nervous system and cause paralysis
What is the Mycobacterium species often referred to as?
Acid Fast Bacilli (AFBs)
Are Mycobacterium species stained using the conventional gram staining?
No
What is the most important species in the Mycobacterium species?
Mycobacterium tuberculosis
What bacteria causes tuberculosis?
Mycobacterium tuberculosis
What are ‘Atypical Mycobacteria’?
infections caused by a species of mycobacterium other than Mycobacterium tuberculosis
What can atypical Mycobacteria cause?
respiratory infections in those with chronic lung disease or opportunistic infections in immuno-compromised patients e.g. AIDS, transplant patients, etc
Which bacteria lack a conventional cell wall?
- Chlamydia species
- Mycoplasma species (e.g. M. pneumoniae)
What bacteria is the commonest cause of STI? What does it cause?
Chlamydia trachomatis - causes chlamydia
What does Mycoplasma pneumoniae cause?
Common cause of respiratory tract infections
Why can gram stains not be used for Chlamydia species and Mycoplasma species?
They lack a cell wall
What are Spirochaetes?
any of a group of spiral-shaped bacteria
What diseases do Spirochaetes cause?
- Syphilis
- Leptospirosis
- Lyme disease
What bacteria causes syphilis?
Treponema pallidum
Which of the following are ‘Gram Negative’ bacteria?
A] Streptococcus pneumoniae B] Mycobacterium tuberculosis C] Escherichia coli D] Listeria monocytogenes E] Neisseria gonorrhoeae F] Mycoplasma pneumoniae
C] Escherichia coli
E] Neisseria gonorrhoeae
Do mycobacteria stain the gram stain?
No
Which of these bacteria is a common cause of skin infection?
A] Klebsiella pneumoniae B] Streptococcus pneumoniae C] Haemophilus influenzae D] Neisseria meningitidis E] Staphylococcus aureus F] Clostridium difficile
E] Staphylococcus aureus
Which of the following is the most common sexually transmitted infection?
A] Chlamydia trachomatis B] Treponema pallidum C] Corynebacterium diphtheriae D] Staphylococcus aureus E] Neisseria gonorrhoeae F] Viridans streptococci
A] Chlamydia trachomatis
Which of the following can cause meningitis?
A] Neisseria meningitidis B] Streptococcus pneumoniae C] Listeria monocytogenes D] Streptococcus agalactiae E] Haemophilus influenzae F] Staphylococcus aureus
ALL OF THEM
Which bacteria is responsible for puerperal sepsis?
Streptococcus pyogenes (Group A Strep)
