Bacterial morphology Flashcards
How can bacteria carbon usage be used as an indicator?
Bacteria with lactogene can ferment lactose
use of lactose alters the pH of the medium
precipitates bile salts and turns pH indicator red
What is the significance of Systemic classification?
- shows how much is present & cultures show variability
- significant in normally sterile samples e,g, blood and
CSF - quanitification - can give a measure risk
- significant in normally sterile samples e,g, blood and
- Pathogen confirmation
- could be commensals
- commensals in one host can cause disease in another
- Treatment options
- clinico-pathological manifestations are often species
specific - antibiotic selectivity for bacterial targets
- clinico-pathological manifestations are often species
- enables epidemiological study
What factors affect bacterial growth?
- Division rate
- Lag phase time
- O2 availability
- pH
- inhibitors
- growth factors
- Temperature
What are the pH requirements of bacteria?
Acidophiles: 1 to 5.5
Neutrophiles: 5.5 to 9
Alkaliphile: 7.5 to 11.5
Give examples of bacteria with different growth rates
Rapid growers - vibrio cholera divides every 20-40 minutes
Slow growers - Treponema pallidum (syphillis) divides every 30 hours
Dormancy - mycobacterium tuberculosis
Why do obligate aerobe bacteria require O2 for growth?
To form ATP for energy/growth
most is to tolerate 21% O2 in atm
some microaerophiles only tolerate 5% O2
some capnophiles require O2 higher than air - gonorrheae
What are the structural components of bacteria?
- Haploid (single chromosomes)
- circular DNA
- DNA in nucleoid region (not nucleus)
- ribosomes in cytoplasm
- peptidoglycan membrane
- no mitochondria
- no membrane bound organelles
- can include - capsid, flagella / pilli and spores
Why do non acid fasts have no colour when gram stained?
Non acid fasts don’t retain carbol fuschin on cell surface when acid washed
How can the different bacteria be visualised using gram staining?
Gram -ve
- extra outer membrane with integral lipopolysaccharides
have a periplasmic space e.g. e.Coli
Gram +ve
- thick peptidoglycan layer intergal with lipo/teichoic acid
e. g streptococcus pyogenes
Acid Fast
- thick outer layer of mycolic acids linked by arabino-
galactans integral with lipoarabinomannnan e,g,
myobacterium tuberculosis
What is the size of bacteria?
Bacteria size ranges from 0.3 - 3um
except for thiomarginita namibiensis - 300um
Describe the different temperature requirements of different bacteria
Psydorophile -20℃ to 20 ℃
e.g. campylobacter jejuni (food poisoning)
mesophiles 2℃ to 45℃
e.g. most animal pathogens
Thermophiles 42℃ to 80℃
e.g. bacillus stearothermophilus used for sterilisation tips
Extreme thermophiles 60℃ to 250℃
e.g. thermus aquaticus (source of Taq for PCR)
What colour does the acid fast membrane give when gram stained?
Fluorescent/red if acid fast
no colour if non acid fast
Which type of bacteria find O2 toxic?
Obligate anaerobes find O2 toxic e.g. clostiridium tetani
How do facultative anaerobes use O2?
For fermentation but can also undergo anaerobic respiration e,g, e.Coli
What are the methods of classifying bacteria?
- size
- gross structure
- cell wall structure
- differential strains
- morphology
- growth requirements
