WEEK 5

BMY3101-1 MICROBIOLOGY I

WHAT HAVE I LEARN?

We start the class with the mind map of prokaryotes. We have to come out one by one to draw and add on to the mind map. But first, we didn't manage to do a good mind map since everyone is just rush and trying to throw whatever knowledge about this chapter and don't want to repeat other's point. But Dr stop us and then call us to organize and start all over again. We get a well organized and clear mind map at the second time with the help of whole class. Dr continue to discuss on the Taxonomy last week. She advise us to be more proactive and be more curious about what we are studying right now to gain more knowledge for our own good. After that we sit into our own group to discuss and choose one "adopt a microbe" among ourselves and to relate to what we have learn before. We have to find out all the information about the microbe and then share it online. Before the class end, my friend and I able to get some related information for Propionibacterium acnes and now we are more familiar and know more about this microbe.

Propionibacterium acnes

Kingdom:	Bacteria
Phylum:	Actinobacteria
Order:	Actinomycetales
Family:	Propionibacteriaceae
Genus:	Propionibacterium
Species:	P. acnes

Cutibacterium (Propionibacterium) acnes is the relatively slow-growing, typically aerotolerant anaerobic, Gram-positive bacterium (rod) linked to the skin condition of acne. P. acnes bacteria live deep within follicles and pores, away from the surface of the skin. In these follicles, P. acnes bacteria use sebum, cellular debris and metabolic byproducts from the surrounding skin tissue as their primary sources of energy and nutrients. Elevated production of sebum by hyperactive sebaceous glands (sebaceous hyperplasia) or blockage of the follicle can cause P. acnes bacteria to grow and multiply.

source: Wikipedia- Propionibacterium acnes https://en.wikipedia.org/wiki/Propionibacterium_acnes

P. acnes is an anaerobic-aerotolerant diphtheroid-like Gram-positive bacillus that resides in pilosebaceous follicles of the skin (Figure 2) [1], and is also found in the conjunctiva [2], oral cavity [2], intestinal tract [16], and external ear canal [1]. The P. acnes genome encodes all key components of oxidative phosphorylation (NADH dehydrogenase/complex I, cytochrome c reductase, cytochrome c oxidase, and FOF1-type ATP synthase). In addition, it also possesses the genes for the cytochrome d oxidase, which ensures growth in different conditions [3, 17, 18]. Therefore, P. acnes can tolerate exposure to oxygen for several hours and is capable in vitro to survive under anaerobic conditions for up to 8 months [19]. The latter observation suggests that P. acnes can also survive for a prolonged period in human tissues with low oxidation potential [18, 19].

Despite its oxygen-tolerant characteristics, P. acnes is not reliably detected by aerobic culture due its slow growth [20]. The optimal temperature for growth is 37°C. To increase the detection, prolonged aerobic and anaerobic agar cultures to 14 days and inoculation into thioglycollate broth should be routinely performed [20–22]. In particular, the low redox potential of enriched thioglycollate broth supports growth of P. acnes. Importantly, thioglycollate broth should be routinely subcultured on agar plates despite the absence of visible turbidity of the broth medium [23]. However, a positive culture with P. acnes should be interpreted with caution. For example, in case of recovery in broth cultures only or from only one of several tissue samples, additional criteria of infection (such as clinical signs, positive histopathology, or molecular tests) are required [23, 24]. In addition, P. acnes should be considered as pathogen in chronic or persistent low-grade implant-associated infections without positive cultures, in which this pathogen is probably underrecognized and underestimated [25, 26].

- Review Article Propionibacterium acnes: An Underestimated Pathogen in Implant-Associated Infections https://www.hindawi.com/journals/bmri/2013/804391/

We have our presentation for "adopt a microbes" today. Our group divided our part to talk about Propionibacterium acnes. I am giving some explanation on the metabolism of Propionibacterium acnes. Other groups perform some interesting bacteria and archaea in this two hours class. Everyone will have to jot down the points while classmate are explaining their bacteria and archaea. We pass up the notes after the class. Below are some bacteria which i am interested to. 

Metabolism of Propionibacterium acnes
Metabolic analysis shows that the P. acnes has the ability to live in anaerobic as well as " microaerobic" conditions. It has an optimal growing temperature of 37°C. It has the key metabolic requirements to carry out oxidative phosphorylation, Krebs cycle, Emdben- Meyerhof pathway and the pentose phosphate pathway. Under in vitro anaerobic conditions (in th lab using agar), P. acnes can grow permissively on media such as glucose, glycerol, ribose, fructose, mannose and N-acethylglucosamine. In vivo, the bacteria producevaarious lipases to digest excess skin oil and sebum in the pilosebaceous units ( region that contains the hair follicle and sebaceous gland) of adolescent and adult human skin.

Magnetotactic bacteria
Magnetotactic bacteria (or MTB) are a polyphyletic group of bacteria discovered by Richard P. Blakemore in 1975. Blakemore realised that these microorganisms were following the direction of Earth's magnetic field, from south to north, and thus coined the term "magnetotactic". 

• Morphology

all MTB studied so far are motile by means of flagella and are Gram-negativebacteria of various phyla: Despite the majority of known species' being proteobacteria, e.g. Magnetospirillum magneticum an alphaproteobacterium, members of various phyla possess the magnetosome gene cluster, such as Candidatus Magnetobacterium bavaricum a Nitrospira.^[13] The arrangement of flagella differs and can be polar, bipolar, or in tufts. 

• Metabolism

Magnetite-producing magnetotactic bacteria are usually found in an oxic-anoxic transition zone (OATZ), the transition zone between oxygen-rich and oxygen-starved water or sediment. Many MTB are able to survive only in environments with very limited oxygen, and some can exist only in completely anaerobic environments. It has been postulated that the evolutionary advantage of possessing a system of magnetosomes is linked to the ability of efficiently navigating within this zone of sharp chemical gradients by simplifying a potential three-dimensional search for more favourable conditions to a single dimension (see the "Magnetism" subsection below for a description of this mechanism). Some types of magnetotactic bacteria can produce magnetite even in anaerobic conditions, using nitric oxide, nitrate, or sulfate as a final acceptor for electrons. The greigite mineralising MTBs are usually strictly anaerobic.^[10]

• Magnotosomes

The biomineralisation of the magnetite requires regulating mechanisms to control the concentration of iron, the crystal nucleation, the redox potential and the pH. This is achieved by means of compartmentalisation in structures known as magnetosomes that allow the biochemical control of the above-mentioned processes. After the genome of several MTB species had been sequenced, a comparative analysis of the proteins involved in the formation of the BMP became possible. Sequence homology with proteins belonging to the ubiquitous cation diffusion facilitator (CDF) family and the "Htr-like" serine proteases has been found: While the first group is exclusively dedicated to the transport of heavy metals, the second group consists of heat shock proteins (HSPs) involved in the degradation of badly folded proteins. Other than the serine protease domain, some proteins found in the magnetosomial membrane (MM) also contain PDZ domains, while several other MM proteins contain tetratrico peptide repeat (TPR) domains.^[9]

Mycobacterium tuberculosis

Mycobacterium tuberculosis is an obligate^[1] pathogenic bacterial species in the family Mycobacteriaceae and the causative agent of tuberculosis.^[2] First discovered in 1882 by Robert Koch.

• Characteristics

 M. tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of mycolic acid. This coating makes the cells impervious to Gram staining, and as a result, M. tuberculosis can appear either Gram-negative or Gram-positive.^[3] Acid-fast stains such as Ziehl-Neelsen, or fluorescent stains such as auramine are used instead to identify M. tuberculosis with a microscope. The physiology of M. tuberculosis is highly aerobic and requires high levels of oxygen. Primarily a pathogen of the mammalian respiratory system, it infects the lungs. The most frequently used diagnostic methods for tuberculosis are the tuberculin skin test, acid-fast stain, culture, and polymerase chain reaction.

• Microscopy

Other bacteria are commonly identified with a microscope by staining them with Gram stain. However, the mycolic acid in the cell wall of M. tuberculosis does not absorb the stain. Instead, acid-fast stains such as Ziehl-Neelsen stain, or fluorescent stains such as auramine are used.^[4] Cells are curved rod-shaped and are often seen wrapped together, due to the presence of fatty acids in the cell wall that stick together.^[11] This appearance is referred to as cording, like strands of cord that make up a rope.^[9] M. tuberculosis is characterized in tissue by caseating granulomas containing Langhans giant cells, which have a "horseshoe" pattern of nuclei.

* Some sources taken from wikipedia.