Gram negative bacterial pathogens L3 Flashcards
what are the three layers of gram negative cell wall
outer membrane
periplasmic space
cytoplasmic membrane
what colour are gram positive strains in dye
blue
what colour are gram negative strains in dye
pink/red
what shape is Neisseria meningitidis and Neisseria gonorrhoeae
Gram-negative diplococci
what does Neisseria meningitidis and Neisseria gonorrhoeae
require for growth
Fastidious – grow well on supplemented chocolate agar at 37°C in 5% CO2 in air
what are Neisseria meningitidis and Neisseria gonorrhoeae
colonies like
Colonies transparent, non-haemolytic, 1-5 mm in diameter
what oxidase is Neisseria meningitidis and Neisseria gonorrhoeae
oxidase positive
what does Neisseria meningitidis and Neisseria gonorrhoeae
do to glucose
Metabolize glucose (meningococcus also utilises maltose) to acid
what is Neisseria meningitidis
Obligate human pathogen
where is Neisseria meningitidis found
Asymptomatic nasopharyngeal carriage in c. 10% population
when does Neisseria meningitidis cause disease
bacterium enters the bloodstream and crosses the blood/brain barrier
how are meningococci segregated
13 serogroups – serogroups A, B, C, W135 and Y cause most infections
what causes bacterial meningitis in children & young adults – may cause epidemics
Neisseria meningitidis
what does Neisseria meningitidis cause
sepsis, septic arthritis, endophthalmitis, conjunctivitis etc.
what vaccines are available for Neisseria meningitidis
C and B
what are symptoms of Meningococcal meningitis
marked neck
stiffness
photophobia
purpuric non-blanching rash
what is CSF
Cerebrospinal fluid
what is gonorrhoea and an example of a bacteria that causes it
Gonorrhoea is a common bacterial infection transmitted by sexual contact or perinatally
Neisseria gonorrhoeae
what are gonococci like
do not tolerate drying, hence samples should be inoculated onto appropriate media immediately
what does Neisseria gonorrhoeae cause
acute urethritis in men and cervicitis (predominantly) in women
in neonates – causes eye infection (ophthalmia neonatorum)
what is Gram-stain of urethral discharge
made of
Numerous polymorphonuclear cells
Intra-cellular gram-negative diplococci
what can Ophthalmia neonatorum
cause
Purulent ocular discharge
May cause blindness if untreated
what is Moraxella catarrhalis
Gram-negative diplococcus indistinguishable from Neisseria by Gram staining
where does Moraxella catarrhalis colonise
Colonises upper respiratory tract in c. 5% of adults
what does Moraxella catarrhalis cause
Otitis media, Sinusitis, pneumonia in the elderly and in patients with Chronic Obstructive Pulmonary Disease (COPD)
what are examples of Enterobacteriaceae
Escherichia Klebsiella Proteus / Morganella Salmonella Serratia Shigella Yersinia
what is an increasing problem with Enterobacteriaceae
antibiotic resistance is an increasing problem in these organisms
many produce enzymes that degrade commonly used antibiotics
enzymes are called Extended Spectrum Beta lactamases – ESBLs)
what is Escherichia coli and where does it colonise
Commensal flora in human and other animals GI tract where they do not normally cause any problems
survive in soil and water
what is Escherichia coli like
Facultatively anaerobic
Bacilli
Motile
what does Escherichia coli do to lactose
Most strains ferment lactose and are indole positive
what can Escherichia coli cause
UTI
Neonatal meningitis
Wound infection Intra-abdominal abscess
Sepsis – bacteria enter the bloodstream
how does a UTI form due to Escherichia coli
persons own gut flora due to contamination of the urethra - ascends to the bladder and may reach the kidneys in some cases
what does Escherichia coli cause
Some strains of E.coli cause diarrhoea
how does Escherichia coli lead to disease
Disease follows ingestion of contaminated/uncooked food or contact with faeces - sources of contamination : animals or environmental contamination
how are Escherichia coli grouped
Based on biochemical/serological properties and the types of pathogenic mechanism used, strains are placed into different groups
what bacteria causes the commonest food poisoning
Campylobacter
then salmonella
what is Campylobacter associated with
Most cases sporadic, associated with poultry and raw milk
Contamination of chicken – where they naturally live
When slaughter they get contaminated with the faecal material
what is Campylobacter like
Spiral bacterium, micro-aerophilic, grows at 42°C
oxidase test on Campylobacter
oxidase positive
what does Campylobacter jejuni cause
Prodromal fever (fever before they see any symptoms), headache
Diarrhoea
vomiting
Abdominal pain
Rare systemic infections – fever & positive blood cultures
why can there be blood in diarrhoea if infected with Campylobacter jejuni
move from the gut and get into the blood – due to the damage of the mucus lining
what is Helicobacter pylori like
Pleomorphic rod – microaerophilic (doesn’t like too much oxygen)
many spiral shaped
what does Helicobacter pylori cause
infection in the stomach (gastric acid in stomach usually kills everything, but this organism has evolved to survive) and duodenum
Powerful urease enzyme, colonise gastric mucosa
what does Helicobacter pylori need for growth
Selective media for culture from tissue biopsies
what is the most common bacteria to cause infection
Helicobacter pylori
what can be used for diagnosis from biopsies
helicobacter pylori produces a powerful urease enzyme allowing colonisation of the gastric mucosa – used in diagnosis from biopsies
what is the effect of Helicobacter pylori
making urease
Urease breaks down urea produces ammonia, it neutralizes gastric acid around organism
what are Pseudomonads and non-fermenters associated with
Associated with moist environments
P. aeruginosa most associated with human disease
what are Pseudomonads and non-fermenters like
Non-sporing Non-capsulate (no capsule) Usually motile Strictly aerobic (under most conditions will only grow when there is oxygen around) Thin GNB (gram negative bacillus)
what do many strains ofPseudomonads and non-fermenters produce
produce pigments (thought to be part of virulence mechanism) e.g. pyocyanin
what is the Pseudomonads and non-fermenters metabolism
Oxidative metabolism (compared to the Enterobacteriaceae-fermentative)
where does Pseudomonas aeruginosa commonly colonise
colonises wounds
what can Pseudomonas aeruginosa cause
outer (otitis externa) and inner (malignant otitis) ear infections
eye infections
sepsis
what can Pseudomonas aeruginosa cause in cystic fibrosis patients
pneumonia
what are non-fermenters
Heterogeneous group including Acinetobacter it is biochemically inert and resistant to many antibiotics
what are vibrionaceae like
Short, comma-shaped bacilli
Actively motile
Fermentative
what oxidase are Vibrionaceae
oxidase positive
what is halophilic and and example
Halophilic live in salt water (eg. V. vulnificus)
what is non halophilic and an example
non-halophilic live in non salt water (eg. V. cholera)
how does Vibrionaceae cause infection
occurs through ingestion of contaminated food or water
what agar is Vibrionaceae grown on
thiosulphate, citrate, bile-salt, sucrose (TCBS) agar or in alkaline peptone-water
what does Vibrionaceae cholerae need for growth and what does it produce
grown on TCBS – ferments sucrose and produces yellow colonies
what is Vibrionaceae cholerae like
has a flagellum so is motile
Gram-negative bacilli
