Classification of pathogenic bacteria Flashcards
Bacteria- what are they?
major group of micro-organisms causing disease
mainly single-celled prokaryotes
most reproduce by binary fission
What is a major threat to public health currently?
drug resistance
Why are gram positive and negative bacteria important clinically?
Different classes of antibiotics are effective against Gram positive and Gram negative bacteria -> targeted treatment.
Staphylococci
aerobic gram-positive cocci that cause pus formation. Group together in grape-like clusters
Streptococci
a genus of gram-positive coccus- group together in chains
Enterococci
a Gram-positive bacterium inhabiting the GI tracts of humans and other mammals. Group together in chains
Define coccus
any spherical or roughly spherical bacterium
What is the coagulase test?
used to distinguish between staphylococci species
What does it mean to be coagulase positive?
Staphylococcus aureus present- MSSA or MRSA skin infections.
Commensal organism carried in nose, axilla, perineum. A major human pathogen!
Wide range of disease from boils/abscesses and soft tissue infections to septicaemia and osteomyelitis.
Commensal bacteria?
are part of the normal flora in the mouth.
Why is Staphylococcus commonly resistant to penicillin?
strands of staphylococcus can produce penicillinase that resists use of penicillin to fight infection.
Aerobic gram positive cocci
staphylococci
streptococci
and enterococci
What is a blood agar test for?
used to determine types of streptococci (a type of gram positive cocci)
Which organism turns blood agar green?
α-haemolytic streptococci
partial haemolysis- splitting of red blood cells
which organism turns blood agar clear?
β- haemolytic streptococci (complete haemolysis)
organism has no effect on blood agar colour?
non-haemolytic streptococci
disease caused by streptococci pneumoniae (pneumococcus)
pneumonia, meningitis, septicemia
Infection caused by viridans streptococci (oral commensal bacteria)
cause infective endocarditis (infection of heart valves)
Two types of α-haemolytic streptococci
Streptococcus pneumoniae (pneumococcus) and Viridans streptococci
What can β- haemolytic streptococci be divided into?
divided into groups A-G
How are β- haemolytic streptococci further identified?
by carbohydrate surface antigens
Lancefield Group
Which groups of β- haemolytic streptococci are most clinically important?
A, B, F and D
Group A streptococci
Streptococcus pyogenes- a major ‘flesh eating’ pathogen
Group B streptococci
Streptococcus agalactiae
Neonatal sepsis:- Meningitis, Bacteraemia (in the blood)
Also responsible for invasive infections in adults (often older and underlying factors e.g. diabetes, liver disease / alcohol abuse etc
Group D streptococci
Now re-classified as Enterococcus spp. e.f Enterococcus faecalis.
often non-haemolytic i.e no effect on colour of blood agar. Found in the gut as normal commensal bacteria. Cause UTI’s and endocarditis
Gram positive bacilli can be…
aerobic or anaerobic
Clostridium difficile
- ‘difficult’ to culture.
- Important cause of diarrhoea, associated with toxin production and potentially fatal.
- Increased risk with antibiotic use and anything else that disrupts the normal gut flora.
- Spread / transmitted via spores.
- Detect antigen & toxin in stool sample by ELISA
Four common and clinically important Gram Positive bacteria?
Staphylococcus aureus
Streptococcus pyogenes
Streptococcus pneumoniae
Clostridium difficile
Bacteria are also broadly classified according
to what morphology (shape) under the microscope
Cocci = round. Bacilli = rod-shaped.
Clinically significant Gram Negative bacteria?
Coliforms Neisseria spp Moraxella spp Haemophilus influenzae Campylobacter spp. and Helicobacter spp. Bacteroides and other anaerobes
Neisseria spp types
Neisseria meningitidis
Clinically significant bacteria which are not readily identified by Gram staining?
Mycobacteria
Spirochaetes
Chlamydia
Neisseria meningitidis
Meningitis – inflammation of the meninges and septicaemia. Often life threatening
Neisseria gonorrhoeae
Causes urethritis in men and pelvic inflammatory disease in women. Sexually transmitted.
Moraxella catarrhalis
Causative agent of respiratory tract infections.
Especially in those with underlying lung pathology
What is a coliform?
organisms which are in the family Enterobacteriaceae
Gram negative bacteria are usually found where?
Mainly commensals of the human large intestine.
What is a useful preliminary test in classifying Gram negative bacilli?
Lactose fermentation as these bacteria can ferment the sugar lactose
E.coli
Gram negative bacilli
Human and animal reservoirs.
Ferments lactose.
Strains vary considerably in disease potential.
Important cause of urinary tract infection (UTI).
Enterotoxogenic E.coli
commonest cause of traveller’s diarrhoea
Enterohaemorrhagic E.coli
bloody diarrhoea
Campylobacter spp.
strain of gram negative bacteria
Spread via faecal-oral route.
Foul smelling -> bloody diarrhoea
Commonest cause of bacterial diarrhoea in UK
Helicobacter pylori
Curved rods
Natural habitat is human stomach.
Damages mucosa and causes ulcers.
Strong risk factor for gastric adenocarcinoma (malignant tumour)
oral anaerobes
Important in aetiology of periodontal disease and
may be part of polymicrobial dental abscesses
Salmonella spp
salmonella enterica
salmonella typhi
doesn’t ferment lactose
salmonella enterica:- Self-limiting enterocolitis with or without bloody diarrhoea. Second commonest cause of bacterial diarrhoea in UK. Can be invasive (enter bloodstream)
Salmonella typhi:- cause of typhoid fever
Miscellaneous bacteria
this bacteria cannot be:-
stained with Gram’s method.
cultured by standard methods
mycobacteria:- Mycobacterium tuberculosis
Tb caused by this bacteria
also has a link with HIV
way of diagnosing Tb?
rapid diagnostic nucleic acid amplification tests
Mycobacterium leprae
Causes leprosy
This bacterium cannot be cultured
Mainly India, Nepal, Brazil
Attacks peripheral nerves
Spirochaetes
Long, spiral-shaped bacteria.
Not easily visualised by light microscopy.
Very difficult to culture
Often diagnosed by serology
Common spirochaete diseases
Treponema pallidum= Syphilis
Borrelia burgdorferi= Lyme disease
Leptospira interrogans= Leptospirosis- kidney infection
Syphilis stages
primary- skin lesion
secondary- generalised systemic illness and rash
tertiary- years after primary symptoms CNS
latent
congenital- stillbirth, neonatal death or disease
diagnosis and management of syphilis
serology, nucleic acid amplification tests
(NAAT)
Management – antibiotics, contact tracing and
screening
Chlamydia
Culture only in cell lines (do not grow on agar).
Can be diagnosed by serology.
respiratory chlamydia infection
Chlamydophila pneumoniae Chlamydophila psittaci (psittacosis) - contact with birds
Ophthalmic and genital tract chlamydia infection
Chlamydia trachomatis
– Trachoma (tropical eye infections)
– Genital and neonatal infection
Neonatal infections
Diagnosis of Chlamydia trachomatis
nucleic acid amplification tests (NAAT) on first void urine (first urine excreted in the morning)
vulval/vaginal swabs
What causes syphilis?
Treponema pallidum
bio film
a mucous layer with colony of bacteria that lies on a solid surface
e.g on a catheter
frimbriae
short hair like fibres enabling adhesion of bacterial cell onto surfaces
capsule
has H20- prevents dessication
enhances ability to cause disease- virulence factor
