Classification of Pathogenic Bacteria Flashcards
How do bacteria reproduce
Mainly by binary fission
Is cocci rod shaped or circular
Circular
Is bacilli rod shaped or circular
Rod shaped
Is staphylococci in clusters or chains
Clusters
Is streptococci in clusters or chains
Chains
What does a positive coagulase test mean
Staphylococcus aureus is present which may indidicate MSSA or MRSA
What is Staphylococcus aureus
A major human pathogen carried in the nose, axilla and perineum
What can Staphlyococcus aureus cause
Wide range of diseases Boils/abscesses Soft tissue infections Septicaemia Osteomyelitis
What is Staphylococcus aureus commonly resistant to and why
Penicillin
Due to the production of penicillinase however using a different mechanism can produce strains which are methicillin resistant
What does a negative coagulase test indicate
Many different species such as: S. epidemidis S. haemolyticus S. saprophyticus S. lugdunenis
What are the categories of Streptococcus
α-haemolytic (partial haemolysis) which turns blood agar green
β-haemolytic (complete haemolysis) which turns blood agar clear
non haemolytic
Give an example of an α-haemolytic streptococci and what it can cause
Streptococcus pneumoniae which causes pneumonia, meningitis and septicaemia
How can β-haemolytic streptococci be further identified
Through carbohydrate surface antigens which are split into groups A-G
The clinically most important groups are A, B, F and D
How are gram positive bacilli able to grow
Aerobically
Anaerobically
Give an example of a group A streptococci
Streptococcus pyogenes which is a major pathogen causing pharyngitis, cellulitis and necrotising fasciitis (‘flesh eating bug’)
What is an important cause of diarrhoea that is which is associated with toxin production and can be potentially fatal
Clostridium difficile which is difficult to culture and asymptomatic when carried in the gut of healthly people
What increases the risk of obtaining Clostridium difficile
Antibiotics
Anything which disrupts the normal gut flora
How can Clostridium difficile spread
Spores
How is Clostridium difficile detected
Using its antigens and toxins in stool samples by ELISA.
Name 2 Gram negative cocci
Neisseriac spp.
Moraxella spp.
What is meningitis
Inflammation of the meninges and septicaemia
What does Neisseria meningitidis cause and how can it be identified
Meningitis which is the inflammation of the meninges and septicaemia.
PCR can be used on EDTA blood
What does Neisseria gonorrhoeae cause and how is it spread
Urethritis in men
Pelvic inflammation disease in women
Sexual contact
What does Moraxella catarrhalis act as the causative agent for
Respiratory tract infections especially in those with underlying lung pathology.
What are coliforms
Organisms which are in the Enterobacteriaceae family
Where are coliforms mainly found
Human large intestine
What is a useful test to identify Gram negative bacteria
Lactose fermentation is useful as a preliminary test
What are the virulance factors for E. coli
Pili
Capsule
Endotoxin
Exotoxins
Where can E. coli be found
Human and animal reservoirs
What does E. coli ferment
Lactose
How many serotypes of E. coli are there and what are they based on
Over 160
Based on O antigen (LPS)
What can E. coli cause
UTI’s
Name two types of E. coli
Enterotoxogenic
Enterohaemorrhagic
What can enterohaemorrhagic cause
Bloody diarrhoea
Haemolytic uraemic syndrome (HUS) which is associated with E. coli O157
What can enterotoxogenic cause
A common cause of traveller’s diarrhoea
Can the Salmonella spp. ferment lactose
No
What can the Salmonella spp. cause
Self-limiting enterocolitis with or without bloody diarrhoea
It has an incubation period of 12-48 hours
Can Salmonella enter the bloodstream
Yes
What can Salmonella typhi cause and what are its symptoms
Typhoid fever
Symtoms include:
Fever
Constipation in the early stages
Where can Salmonella typhi be isolated from
Blood cultures
Faeces
Name 3 coliforms
Shigella spp
Klebsiella spp
Proteus spp
Is E. coli a coliform
Yes
How does the Campylobacter spp grow
In the presence of low oxygen
What is the source of Campylobacter
Domestic animals e.g. Chickens
How can Campylobacter be transmitted
Faecal-oral route (incubation period of 2-5 days)
What can Campylobacter cause
Foul smelling then bloody diarrhoea
What type of bacteria is Campylobacter
Curved Gram negative bacilli
What type of bacteria is Helicobacter pylori
Curved Gram negative bacilli
What is Helicobacter pylori’s natural habitat
Human stomach
What can Helicobacter do
Damage mucosa
Cause ulcers
A strong risk factor for gastric adenocarcinoma
What does the Haemohilus influenzae virus appear as
Cocco-bacilli
What can the Haemohilus influenzae virus cause
Respiratory tract infections
What can the capsulate form (type b) of Haemohilus influenzae cause
Meningitis in children
Where can Pseudomonas colonise
Water and soil
e.g. drains, sinks, mops
What type of nosocomial infection can Pseudomonas cause
Sepsis (e.g. UTI, bacteramia, pneumonia)
How can the Pseudomonas spp be treated
Has limited treatment options as it has multi-drug resistance mechanisms
What are anaerobes normally a part off
Polymicrobial infection
Name some anaerobes
Bacteriodes spp.
Prevotella
Porphyromonas
Describe Bacteroides fragilis
Part of normal colonic flora
Can cause intra-abdominal abscess
May spread to other sites
What do oral anaerobes have a role in
Aspiration pneumonia
Human and animal bite infections
Can all bacteria be Gram stained
No
Give examples of bacteria which cannot be Gram stained
Mycobacterium spp.
Spirochaetes.
Chlamydia
What is acid and alcohol fast bacilli (AAFB)
This type of bacilli are resistant to decolourisation by acid or alcohol once it has been stained with carbol fuchsin
How can Mycobacterium be visualised
Using Ziehl-Neelsen staining
Auramine staining
This does do help identify the species
How can a Mycobacterium species be identified
Culture
The new automated liquid culture allows growth to occur within 2-4 weeks.
What causes TB
Mycobacterium tuberculosis
When is rapid diagnostic nucleic acid amplification tests recommended for pulmonary TB diagnosis
When TB is suspected in a HIV positive patient
When rapid information about the mycobacterial species would alter a persons care
When a large contact tracing initiative is being explored
What can Mycobacterium leprae cause
Leprosy
Can Mycobacterium leprae be cultured
No
What are spirochaetes
Long, spiral shaped bacteria
How can spirochaetes be visualised
Not very well with light microscopy but can be seen with immunofluorescence
Name some spirochaete diseases
Syphilis caused by Treponema pallidum
Lyme disease caused by Borrelia burgdorferi
Leptospirosis caused by Leptospira interrogans
What is primary syphilis
Non-painful skin lesions (chancre) at the site of infection, usually the skin or mucous membranes
What is secondary syphilis
Occurs 6-8 weeks after the primary symptoms causing generalised systemic illness and rash
What is tertiary syphilis
Can occur years after the primary symptoms and affects the CNS
How can syphilis be diagnosed
Serology
Nucleic acid amplification tests
What is Chlamydia
An obligate intracellular bacteria that can only be cultured in cell lines
What type of chlamydia causes genital tract infections
Chlamydia trachomatis
How can Chlamydia trachomatis be diagnosed
Using NAAT on the first void urine or vulval/vaginal swabs
