Classification of pathogenic bacteria- gram negatives Flashcards
How are bacteria named?
genus and then species
What organism causes meningitis disease? (cocci)
Neisseria meningitidis (meningococcus)
What is meningitis?
inflammation of the meninges and septicaemia.
How could you diagnose meningitis?
CSF and Blood cultures
What bacteria causes urethritis in men and pelvic inflammatory disease in women? (cocci)
Neisseria gonorrhoeae
spread by sexual contact
What bacteria causes respiratory tract infections? (cocci)
moraxella catarrhalis
What are coliforms? (gram negative bacilli)
organisms which are in the family enterobacteriaceae
mainly commensals of large human intestine
What is used in preliminary identification?
Lactose fermentation is a useful preliminary test in classifying
Gram negative bacilli
CLED Agar gives colour change if lactose is fermented
What is Escherichia coli?
vast array of virulence mechanisms- pili, capsule, endotoxin and exotoxins
ferments lactose
over 160 serotypes based on O antigen (LPS)
Important cause of UTI but causes a wide spectrum
What is the E coli that is the commonest cause of traveller’s diarrrhoea?
Enterotoxogenic E.coli - produces toxins
What E coli gives rise to bloody diarrhoea?
Enterohaemorrhagic E.coli
What E coli is associated with haemolytic uraemic syndrome?
E coli O157
Describe salmonella spp?
Does not ferment lactose.
Second commonest cause of bacterial diarrhoea in UK.
Can be invasive i.e. enters bloodsteam
Describe salmonella typhi?
cause of typhoid fever
* Fever, constipation early stages.
* Organism can be isolated from blood cultures as well as faeces.
* Risk during foreign travel but vaccine available
What is Shigella spp?
cause of diarrhoea,dysentry
What is klebsiella spp?
cause of UTI and hospital acquired pneumonia
What is proteus spp?
Causes UTI – often associated with stones
What is campylobacter spp?
- Microaerophilic– likes low O2 .
- Source is domestic animals and chickens.
- Spread via faecal-oral route.
content - Foul smelling -> bloody diarrhoea (incubation period 2-5
days). - Commonest cause of bacterial diarrhoea in UK
What is helicobacter pylori?
- Curved rods.
- Natural habitat is human stomach.
- Damages mucosa and causes ulcers.
- Strong risk factor for gastric adenocarcinoma
What is haemophilus influenzae?
- Cocco-bacilli (mixed appearance).
- Causes respiratory tract infection (second to S. pneumoniae).
- Capsulate form (type “b”) was formerly an important cause of
meningitis in children (Hib conjugate vaccine)
What is pseudomonas spp?
- Water and soil coloniser – drains, sinks, mops.
- May contaminate medical equipment.
- Hospital acquired cause of sepsis: e.g. UTI,
bacteraemia, pneumonia (rare). - Feared respiratory pathogen in cystic fibrosis.
- Multi-drug resistance mechanisms.
- Limited treatment options.
What are anaerobes?
- Often part of a polymicrobial infection.
- Increasing importance and recognition.
- Bacteriodes spp.
- Prevotella
- Porphyromonas
What is bacteroides fragilis?
- Part of normal colonic flora.
- Causes intra-abdominal abscess.
- May spread to other sites
Give examples of oral anaerobes?
-Prevotella
* Porphyromonas e.g. P. gingivalis
* Pasteurella spp
* Capnocytophyga spp
Why would bacteria not stain by gram method?
not all bacteria have same cell wall and some don’t have cell wall.
Describe the acid and alcohol fast bacilli?
Resistant to decolourisation by acid or alcohol after staining with carbolfuchsin.
* Mycobacterium species are visualised with special
stains e.gZiehl-Neelsen(ZN) or Auramine
Why are we interested in AAFBs? (mycobacteria)
the aetiological agent of tuberculosis , Mycrobacterium tuberculosis is an important member of the AAFB
-if clinician suspicious of tuberculosis- stained using special stains
Laboratory identification of mycobacteria?
- ZN or Auramine phenol (screening).
- Does not identify species!!!
- Culture required for ID.
- New automated liquid culture.
- Growth in 2-4 weeks.
- Molecular detection and
identification of MTB possible
What is the disease that mycobacterium tuberculosis causes?
tuberculosis
What disease is caused by mycobacterium leprae and what is its features?
leprosy
mycobacterium leprae cannot be cultured
attacks peripheral nerves
Describe spirochaetes?
- Long, spiral-shaped bacteria.
- Not easily visualised by light microscopy.
- Very difficult to culture (never Treponema pallidum).
- Dark ground microscopy or immunofluorescence.
- Often diagnosed by serology
What diseases are caused by spirochaetes?
syphillis
lyme disease
leptospirosis
Describe the stages of syphillus?
- Primary syphilis: non-painful skin lesion (chancre) at the
site of infection (skin or mucous membranes) - Secondary syphilis (6-8 weeks after primary symptoms):
generalised systemic illness and rash - Latent phase: symptomatic episodes may occur
- Tertiary syphilis (years after primary symptoms): central nervous system
- Congenital syphilis: stillbirth, neonatal death or disease
Describe the stages of lyme disease?
- Transmitted by ticks.
- Stage 1: Skin rash (erythema chronicum migrans) appears at the site of
the tick bite. - Stage 2: Systemic illness occurs in some patients
weeks or months later when patients suffer cardiac
or neurological and musculoskeletal symptoms - Stage 3: Chronic disease, occurring years later when patients present with
chronic skin, nervous system or joint abnormalities - Diagnosed by clinical assessment and serology (antibody detection)
Describe leptospirosis?
- Infects animals and concentrates in the kidneys.
- Spread is via infected urine and other body fluids and
tissues (zoonosis). - At-risk groups– sewage workers– watersports.
- Range of clinical presentations– Weil’s disease – febrile illness with systemic upset, liver
and renal failure, aseptic meningitis, 10 % mortality.
Describe chlamydia?
- Obligate intracellular bacteria.
- Culture only in cell lines (do not grow on agar).
- Can be diagnosed by serology.
What are the chlamydia respiratory infections?
– Chlamydophila pneumoniae– Chlamydophila psittaci (psittacosis)- contact with birds.
What is chalmydia trachomatis?
can cause trachoma and genital and neonatal infections
What shape are bacilli bacteria?
rod shaped
