lecture 7- Gram+ 1 Mycoplasmas, lactic acid bacteria and Streptococci Flashcards
Gram positive vs gram negative bacteria test difference
the purple colour comes from the complex of crystal violet and iodine which gets stuck in the cell wall of gram positive bacteria
difference in the membrane of gram positive and gram negative bacteria
the gram positive has a thick layer of peptidoglycan which keeps hold of the iodine stain
gram negative has a inner and outer mmebrane which contains a periplasmic space that contains the smaller amount of peptidoglycan
the peptidglycan is what allows for the possibility to do a gram stain
The Firmicutes- Low GC gram-positive bacteria
-Non Spore forming bacteria
-The lactic acid bacteria
Streptococcus
Lactobacillus
Staphylococcus
Listeria
Mycoplasma
-The spore forming bacteria
Clostridium
Bacillus
Actinobacteria –
the high GC gram positive bacteria
Streptomyces
Corynebacteria
Mycobacteria
Mycoplasmas-
The Mollicutes
Latin mollis, soft; cutis, skin
Completely lack cell wall - only plasma
membrane.
Therefore they stain gram negative but
sequencing of their genes reveals that they are clearly phylogenetically related to the low GC gram positives( Lactobacillus-Clostridium branch)
Sensitive to osmotic lysis.
Plasma membrane is strengthened by
inclusion of sterols.
Plasma membrane also includes lipoglycans (heteropolysaccharide linked to the membrane lipids) and lipoproteins – involved
in avoiding the immune response.
Pleomorphic – big, small, long, branched (they come in many shapes)…… the coccoid cells 0.12µm -0.25µm in diameter are probably the smallest living cells.
Easily deformable cells that can squeeze into different shapes
Most mycoplasmas are non-motile, except some human and animal pathogens (eg. M. pneumoniae, M. genitalium)
Growth of Mycoplasmas
All mycoplasmas are parasites of eukaryotes
-some if not most of them live on the outside of eukaryotic cells
Many can be grown outside of cells in lab media
Mycoplasma can have complex growth factor requirements due to their
Limited biosynthetic capabilities
All require sterols except Acholeplasma, Asteroleplasma and Mesoplasma
Many require a variety of vitamins, fatty acids, amino acids, purines and pyrimidines
Mycoplasma Genomics
GC content approx 25-35 % depending on the species. so low amount
Mycoplasma genitalium has the smallest known genome of any self-replicating
Organism measuring only 580 kbp and encoding 472 genes. it was possibly the first living organism to have its genome sequenced
Close to the smallest amount of DNA capable of encoding a living cell
The genome of Mycoplasma pneumoniae is larger at 816 kbp, containing 679 putative genes.
For comparison: Escherichia coli genome = 5440 kbp Human genome = 3,300,000
During the evolution of mycoplasma, multiple reductions in genome size have occurred
and the overall rate of evolution uncharacteristically high.
During the evolution of mycoplasma, multiple reductions in genome size have occurred
and the overall rate of evolution uncharacteristically high. but why?
they are parasites so do not need the other capabilities provided to them by a larger genome, they can give up the other genes as they are able to rely on host cells
The evolution of Mycoplasma species is characterized by significant genome reduction and a high rate of genetic change. This phenomenon can be attributed to several factors linked to their lifestyle, adaptation, and evolutionary pressures:
- Parasitic or Symbiotic Lifestyle
Obligate Parasitism: Mycoplasma species are often obligate parasites, meaning they rely on a host organism for survival. As a result, they can lose genes that are not essential for their life cycle within the host. This process, known as genome streamlining, reduces the genome to only the genes necessary for parasitism.
Dependence on Host: Many metabolic functions that free-living bacteria require are not necessary for Mycoplasma because they obtain nutrients and other essential molecules directly from their host. This allows them to lose genes responsible for biosynthetic pathways. - Genetic Drift and Relaxed Selection
Genetic Drift: In small populations or populations with reduced genetic diversity, genetic drift can play a significant role. Genetic changes that would normally be selected against might persist because of random fluctuations rather than natural selection.
Relaxed Selective Pressure: Because Mycoplasma species live in stable environments (like the host organism), the selective pressures that typically maintain the integrity of complex metabolic pathways are relaxed. This makes it easier for non-essential genes to be lost over time. - High Mutation Rates
Lack of DNA Repair Mechanisms: Mycoplasma has a reduced repertoire of DNA repair enzymes compared to other bacteria, leading to an increased mutation rate. Mutations can accumulate more rapidly, which accelerates the rate of evolution.
Evolutionary Adaptability: High mutation rates can be advantageous for organisms that need to quickly adapt to changing environments or host immune responses. This allows Mycoplasma to evolve rapidly in response to host defenses or antibiotic treatments. - Horizontal Gene Transfer (HGT)
Gene Exchange: Mycoplasma species have been shown to engage in horizontal gene transfer, which can bring in new genes or regulatory elements from other organisms. This process can introduce variability and contribute to the high rate of evolutionary change.
Loss of Non-Essential Genes: Over time, genes that are not useful or beneficial in their specific host environment may be lost, resulting in a smaller genome. - Specialization to a Specific Niche
Niche Specialization: Mycoplasma species have adapted to live in very specific environments, such as the respiratory or urogenital tracts of their hosts. This specialization reduces the need for genes that are not directly involved in exploiting their niche, leading to genome reduction.
Metabolic Minimization: As Mycoplasma becomes more specialized, it relies more heavily on its host for nutrients and energy, eliminating the need for genes related to independent metabolism. - Genome Reduction as an Evolutionary Strategy
Energy Efficiency: A smaller genome can be advantageous because it requires less energy and resources to replicate. This energy-efficient strategy can be beneficial in nutrient-limited environments like the host organism.
Increased Replication Speed: Smaller genomes can be replicated faster, which may give Mycoplasma a competitive advantage in rapidly dividing populations.
Conclusion
The genome reduction and high rate of evolution in Mycoplasma are mainly driven by their parasitic lifestyle, genetic drift, relaxed selection pressures, high mutation rates, horizontal gene transfer, and adaptation to specific ecological niches. These factors combined allow Mycoplasma to evolve quickly and adapt to the host environment, but at the cost of losing many genes that are no longer necessary for survival. This evolutionary strategy is what enables them to thrive as efficient and specialized parasites
Overview of the Mollicutes
(Mycoplasma-like organisms)
- different genera
Mycoplasmas - require cholesterol. Parasites of animal mucous membranes.
Facultative anaerobes. Over 60 species recognised.
Ureaplasma (T-Strain Mycoplasmas) - microaerophilic. Require cholesterol and
urea for growth as they have Urease which breaks down urea -> ammonia and CO2. Tiny colonies that are not
visible with naked eye. May be associated with nongonococcal urethritis but can
be isolated from genital tract of 15% asympomatic people. Maybe disease only
on initial exposure?
if you have urethritis and it is not gonorrhea then there is a good chance it is ureaplasma
However transmitted by sexual contact. Also been associated with arthritis
animal models - but not isolated from tissue.
Acholeplasma - widely distributed animal parasites. Facultative aerobes. Able to
grow in absence of sterols. Common contaminants of cell lines in tissue culture.
Anaeroplasma - strict anaerobes. Inhabit bovine or ovine rumen.
Spiroplasma - helical, motile. parasites on arthropods and plants, but a few
cause disease in animals
Mycoplasma pneumoniae
*Causes primary atypical pneumonia in humans, PAP, sometimes called
“walking pneumonia“ as it is a respiratory lung infection that gives a patchy diffuse pneumonia that people walk around with for up to a month until it hopefully resolves
*Usually in individuals 5-20 years old
*Symptoms: Range from mild flu-like disease headache, sore throat, cough
to severe pneumonia characterised by fever, chills and malaise
Protracted course with gradual resolution (month)
Mycoplasma pneumoniae: respiratory pathogen
Mycoplasma pneumoniae is communicated through close personal contact via
respiratory droplets. May be a prevalence of infections occurring in autumn. it is epidemic
The bacterium settles on a respiratory epithelial cell and binds to it.
Polar tip organelles - specific adhesion P1 protein, interactive proteins, and adherenceaccessory proteins.
Result – colonization of mucous membranes and eukaryotic cell surfaces
The bacterium produces hydrogen peroxide
which is thought to be responsible for much of the initial cell disruption in the respiratory
Mycoplasma interacting
with an epithelial cell
M. pneumoniae:
Diagnosis and treatment
-Diagnosis is generally hard to give
Clinical symptoms
including a patchy diffuse bronchopneumonia by X-Ray
Serological tests (Serum cold agglutination, Complement fixation test, ELISAs) “Old
fashioned, not used commonly”
DNA test (PCR) is used for definitive diagnosis
Microbiological detection: Not that useful because culture is slow. Take sputum, or throat
swab.
M. pneumoniae can be grown in media containing serum with penicillin to inhibit growth of
other bacteria. Beta-hemolytic
Fluorescent antibody
N.B. Accurate diagnosis is important since organism is resistant to antibiotics that act on the
cell wall (such as amoxicillin, penicillins, cephalosporins).
Treatment
Erythromycin, doxycycline (not children), azithromycin,
levofoxacin. Erythromycin is often used as it is also effective
against legionella.
GENITAL MYCOPLASMAS
Mycoplasma genitalium
M. hominis and Ureaplasma urealyticum
important as any inflammation in the GU tract (urinary system) can result in infertility in men and women and this can cause this
50% of normal adults have antibodies
Causes of non-gonnococcal (non-chlamydial)
urethritis NGU
May also be associated with infertility in men
Woman – associated with cervicitis and endometritis
and serologically with tubal factor infertility
Transmitted by direct venereal contact.
Also vertically transmitted from mother to offspring at
delivery or directly to the fetus – pneumonia,
bacteremia and meningitis.
Detection relies on molecular techniques (PCR) due to difficulty in culturing
UK recommended Treatment with doxycycline pretreatment then azithromycin (or moxifloxacin)
Antibiotic resistance is high!
(azithromycin is a macrolide, moxifloxacin is a fluoroquinolone)
there is lots of resistance to macrolide antibiotics
The lactic acid bacteria
contain very important human pathogens from the genus streptococcus
The lactic acid bacteria produce lactic acid as a product of fermentation- a product of their metabolism that helps them make energy andf this
can be useful if trying to form selective media that allows for the production of certain bacteria; we can possibly lower pH and allow lactic acid to grow and produce lactic acid bacteria
Non spore forming non motile.
They lack cytochromes and obtain energy by substrate level phosphorylation and not by
Electron transport and oxidative phosphorylation
Normally obtain energy only from sugars
Only limited biosynthetic capability and require many vitamins, amino acids
purines and pyrimidines
Aerotolerant anaerobes. Growth not affected by presence of air.
Usually grown on media containing yeast, peptone, supplemented by a fermentable
carbohydrate. Even when grown on rich media, the colonies are usually small, rarely
pigmented.
They are also tolerant of acid - many other bacteria cannot grow at pH 6.
The ability to produce and tolerate high concentrations of lactic acid is of great selective
value. - eliminates competition - also used in selective media
Lactic Acid Bacteria can be grouped by their fermentation patterns
important to know that they can be split into homo and heterofermenters
Homofermentative – produces a single fermentation product – lactic acid
Embden- Meyerhof (glycolytic) pathway
Heterofermentative – produces lactic acid and other products, mainly CO2 and
ethanol, uses pentose phosphate pathway
Lactic acid bacteria and dairy products
useful in food and probiotics
Streptococcus
*Spherical cells divide only in one plain and so form chains important to know
*Require complex media for growth
*Unable to make haem group of cytochromes or catalase
*Grown on blood agar (good source of catalase)
lancefield Group A Strep. = Streptococcus pyogenes
Beta hemolytic
It causes many of the streptococcal diseases of humans.
can be further grouped by the Antigenicity of M-proteins in the cell wall which provides sub-classification of group A into over 100 sub-serotypes.
Habitat: 5 - 30% of healthy people may be carriers of group A, beta hemolytic
Streps in their throat and nasopharynx; however numbers usually low.
Bacitracin sensitivity test
Strep Throat
About 20% of sore throats are caused by streptoccocus pyogenes and its not given antibiotics as symptoms usually pass unless they are very severe,
common charachteristics are
Acute tonsillitis
swollen uvula
your tonsils have little holes in them which means that if you have white follicles (exudate) on tonsils in the holes on them then it is an indicator that you likely have a strep throat caused by a group A strep)
Other Streptococci
Group B Streptocci: S. agalactiae is the predominant species in this Lancefield group
Present in vaginal flora of 25% of woman.
May cause serious infections in newborn - septicaemia, pneumonia, meningitis
with high fatality rates. if mothers tested positive for it they were often given antibiotics before birth
infection of neonates can be split into early onset and late onset- early onset is when the strep agalacitiae is passed to the neonate before or during birth, late onset is a nosocomial infection that is acquired after birth maybe in the hospital by workers or equipment
Group D Streptococci - faecal flora - enterococci.
these are carried in our guts and are problems for wound infections and infections after surgery
Urinary and wound infections.
Major problem of vancomycin-resistance. this is a common antibiotic strain in gram positive bacteria
In just ten years resistance has increased from virtually zero to
nearly 50% in some communities.
Hippurate test can be used to identify strep agalacitiae
Some streps can Hydrolyse sodium hippurate to produce the purple colour
Streptococcus pneumoniae
Lancet shaped organism - usually arranged in pairs. not in a chain but on a plane still with the pair
Virulent organisms are encapsulated. -resist phagocytosis. the capsule makes them virulent, the capsule makes them slippery as it is a method used by the bacteria to stop phagocytes from grabbing a hold of the bacteria as the polysaccaride capsule makes it slippery
Subdivided into 90 types on the basis of antigenicity of capsular polysaccaride.
Habitat: normal commensal of the upper respiratory tract.
How does a bacterial capsule protect streptococcus pneumoniae
