properties of bacteria Flashcards
Staphylococcus aureus
Gram Positive
- main coagulase positive species
- stains golden on a blood agar plate
- produces pus-forming soft tissue infections that are carried in the bloodstream
- eg. MRSA
where does Staph aureus invade?
axilla anterior nares throat perineum GI tract
virulence factors of Staph aureus
- protein A on cell wall helps it to evade phagocytosis by immune cells
- coagulase enzyme produces a fibrin capsule to protect against phagocytosis
- hyalurorindase enzyme breaks down host tissue
- haemolysins (exotoxin) produces pores in RBCs
- toxins cause toxic shock, boils, pneumonia
conditions caused by Staph aureus
Skin and soft tissue infections Pneumonia Bone and joint infections Endocardits - Discitis Toxin mediated diseases: - Scalded skin syndrome - Toxic shock syndrome - Gastroenteritis
Gram positive
coagulase negative
S. epidermis
S. capitis
S. saphrophyticus
action of…
S. epidermis
S. capitis
S. saphrophyticus
- normal commensal flora of the skin
- can cause infection in the presence of prosthetic material
alpha haemolytic streptococci
S. pneumoniae
S. oralis
S. salivaris
diseases of S. pneumoniae
- most common cause of community acquired pneumonia linked to... - meningitis - sinusitis - otitis media - infective endocarditis
virulence of S. pneumoniae
- Produces pneumolysin which causes – α-haemolysis
- Peptidoglycan and theicoic acid are the main components of cell wall
- Has ability to form a capsule which stops phagocytosis by PMN
- Colonises the nasopharynx of 5 to 10% healthy adults and 20-40% of healthy children
S. oralis, S. salivarius
normal mucosal flora, can cause endocarditis if they infect heart valves
gram positive, beta haemolytic Group A
S. pyogenes
gram positive, beta haemolytic Group B
S. agalactiae
Streptococcus pyogenes causes…
- pharyngitis
- scarlet fever
- rheumatic fever
- post-streptococcal glomerulonephritis
- bacteraemia
- necrotising faciitis
virulence factor of S. pyogenes
protein M
S. agalactiae
- normal vaginal/rectal flora
- can cause neonatal meningitis, bacteraemia, pneumonia, fever in labour
enterococci
invade the gut to produce UTIs and intra-abdonimal sepsis
gram positive bacilli
Bacillus anthracis
Listeria monocytogenes
Corynebacterium diphtheriae
Bacillus anthracis
- found in soil
- disease of herbivores
- multiple toxins and virulence factors - high mortality
- humans infected by cutaneous inoculation or inhalation
L. monocytogenes
Gram positive, aerobic, bacillus
- from soft cheese
- causes intrauterine/neonatal septicaemia or meningitis in pregnany
C. diphtheriae
Gram positive, aerobic, bacillus
- Corynebacterium
- most pathogenic of normal skin commenals
- transmitted via respiratory droplets
- inflammation of the throat pseudomembrane - suffocation and bull neck
- exotoxins inhibit protein synthesis - cell death in host
gram positive anaerobes
C. tetani
C. botulinum
C. difficile
C. perfringens
clostridium
- gram positive rods
- large, pleomorphic
- obligate anaerobes
- highly toxigenic
C. tetani
- causes tetanus
- ubiquitous in soil
- neurotoxin - blocks GABA
- causes spastic paralysis, hyper-sympathetic state, death
C. difficile
- caused by ingestion of spores in (hospital) environment
- enterotoxin causes diarrhoea and cell death of colonic epithelium
- causes severe watery diarrhoea
C. perfringens
- found in soil and human gut
- a-toxin lecithinase - damages cell membranes and causes haemolysis
- causes gas gangrene and soft tissue infections
- food poisoning
gram negative cocci
Neisseria meningitidis
Neisseria gonorrhoeae
Moraxella catarrhalis
Neisseria meningitidis
- some people carry it in their nasopharynx without any symptoms (commensal)
- transmitted ny inhalation, direct contact
- causes meningitis, bacteraemia, pneumonia
- 6 groups: A, B, C, W, X, Y
- characterised by polysaccharide capsule
- effective vaccine available for most groups
Neisseria gonorrhoeae
- causal agent of gonorrhoea
- transmitted sexually or perinatally (mother to child)
- causes…
- urithritis, cervicitis, pharyngitis, conjunctivitis
- rectal infection
- pelvic inflammatory disease
- perihepatitis
- disseminated infection
- concerns about drug resistance means prevention is more realistic / a better option than cure
Moraxella catarrhalis
- common commensal of the human upper respiratory tract
- opportunistic pathogen - altered flora causes commensal to become pathogen
- in children, causes otitis media
- in adults with COPD, causes lower respiratory tract infection
gram negative fastidious bacilli
Haemophilus influenzae
Helicobacter pylori
Legionella pneumophilia
Haemophilus influenzae
- uncapsulated - pneumonia
- capsulated - meningitis
- otitis media
Helicobacter pylori
- produces buffers to allow it to survive stomach acid
- causes gastritis, ulceration
- linked to stomach cancer
Legionella pneumophilia
- carried by amoebae in water
- causes severe pneumonia
non-fastitious sugar fermenters
(aka enterobacteriae) Escherichia coli Klebisella Shigella Salmonella
features of enterobacteriae
- non-fastitious sugar fermenters
- motile by polar flagella
- have fimbriae for adhesion
Escherichia coli
- commonly found in human/animal guts
causes. ..
- diarrhoea
- UTIs
- bacteraemia
- intra-abdominal and biliary tract infection
- neonatal meningitis
- hospital acquired infections
pathotypes of E. coli
enteropathogenic EPEC
enterotoxigenic ETEC
shiga-toxin producing STEC (aka. enterohaemorrhagic EHEC / verocytotoxin producing VTEC)
- most common
- causes bloody diarrhoea
- comes from cattle
enteroinvasive EIEC
enteroaggregative EAEC
diffusively aggregative DAEC
Klebisella
- causes UTI, bacteraemia, pneumonia, liver abscesses
- important in hospitals due to antibiotic resistance and the need for infection control
Shigella
- found in unclean water and contaminated food
- causes dynentery (bloody, low volume diarrhoea), abdominal pain, fever
- can survive transit through stomach (acid resistant)
types of Shigella
- Shigella flexneri
- Shigella sonnei
from travelling: - Shigella dysenteriae
- Shigella boydii
Salmonella
Salmonella typhi:
- traveller’s diarrhoea
- typhoid fever
non typhoidal
- gastroenteritis
there are carriers of salmonella (typhoid carriers)
- salmonella excreted in stool and persists in the gall bladder
gram negative non fastidious non fermenters
Campylobacter
Pseudomonas aeruginosa
Burholderia cepacian
Vibrido cholerae
Campylobacter
- microaerophilic - grows at sub atmospheric levels of oxygen
- causes food poisoning
- usually self limiting
- from raw meat, unpasteurised milk, untreated water
- C. fetus - causes severe infection in neonates
Pseudomonas aeruginosa
- huge range of virulence factors and AB resistance mechanisms
- found widely in soil and water, has few nutritional requirements
- opportunistic pathogens
- Leads to cystic fibrosis complications and ventilator penumonia and bacteraemia in immunocompromised
- resistant to many antibiotics
- produces extracellular pigments eg. pyocyanin
Burholderia cepacia
poor prognosis for CF patients
Vibrido cholerae
causes bacterial gastroenteritis, self limiting diarrhoea
gram negative anaerobes
Bacteroides fragilis
Fusobacterium necrophorum
Bacteroides fragilis
associated with intra-abdominal and skin/soft tissue infections below the waist. highly penicillin resistant.
Fusobacterium necrophorum
long filamentous rods which cause sore throat, peritonsillar abscess, Lemierre’s syndrome (infectious thrombophlebitis of the internal jugular vein)
small, virus-like bacteria
Mycoplasma pneumoniae Chlamydia trachomatis C. penumonia and C. psittaci Rickettsia Mycobacterium tuberculosis
acid fast bacteria
Mycobacterium tuberculosis
features of acid fast bacteria
These bacteria are strict aerobic bacilli. Their cell wall is composed of a very thick layer of wax and lipid called mycolic acid. It is a very slow growing bacterium.
acid fast test
Ziehl-Neelsen staining
- carbol-fuchsin and heat
- then decolorized with an acid alcohol
- counter stained with methylene blue
acid fast = red
non acid fast = blue
Mycoplasma pneumoniae
- walking pneumonia
- haemolytic anaemia
- rash, erythema
- cervical lymphadenopathy
- diagnosed by PCR, serology
- causes penicillin resistant pneumonia
- treated with clarithromycin
Chlamydia trachomatis
- intracellular
- causes trachoma
- STI
- lyphogranuloma vereum
- diagnosed by PCR
- treated with macrolides
Rickettsia
transmitted by parasites, present as spotted fever or typhus
Mycobacterium tuberculosis
causes pneumonia with latency, requires intense combination treatment
features of non culturable bacteria
- no cell wall
- limited metabolic activity
- replicate intracellularly
- resistance to many antibiotics
- cannot be cultured by standard methods
atypical pneumonia is caused by…
- Mycoplasma pneumonia
- Legionella pneumophillia
- Chlamydophila pneumoniae
- Chlamydophila psittaci
- Coxiella burnetii
how are anaerobes treated?
metronidazole
C. botulinum
- causes botulism
- usually food-bourne, from improper storage
- neurotoxin - prevents release of ACh
- causes symmetrical flaccid descending paralysis
- oculomotor muscles - dysphagia, respiratory depression
- clinical use in BOTOX
