Propionibacterium acnes

Propionibacterium acnes

Propionibacterium acnes is a slow-growing gram-positive, anaerobic bacterium. The bacterium is a member of the commensal flora and skin, but also participates as a secondary factor in the pathogenesis of acne. It was formerly known as Bacillus acnes and Corynebacterium acnes. From the way Propionibacterium acnes about 100 tribes are known, the genome of numerous tribes has already been completely sequenced. The research, which strains are pathogenic and are involved eg in the disease acne vulgaris, (as of 2013) is not yet complete.

Features

Appearance

Propionibacterium acnes is a Gram-positive short rod-shaped bacterium, also ellipsoidal cell lines before coming. A single cell is 0.4-0.5 microns ( microns) wide and 0.8-0.9 microns long. In light microscopic image would generally be paired cells that are not in consecutive order, but at an angle. This results in further cell division to form the V- or Y-shaped chain. The bacterium does not possess flagella for active movement and can not form Überdauerungsformen as endospores.

On solid media, which are incubated under anaerobic conditions to form after four to five days round colonies. Viewed from the side, the colonies are raised, while they appear smooth and shiny, their diameter is 1.5-4.0 mm. The colonies are white, show, however, after several days of incubation, the culture medium a slight coloration towards pink.

Growth and metabolism

Propionibacterium acnes is an anaerobic bacterium. Like lactic acid bacteria, it is considered aero tolerant, this means that while it is growing in the presence of oxygen, but this is not required for its metabolism. Studies for the cultivation of the bacteria, however, show that the presence of oxygen has an inhibiting effect on the growth. It has the enzyme catalase and cytochrome can form. The optimum temperature for culturing is about 37 ° C. At 45 ° C no growth takes place at room temperature (approx. 20 ° C), the growth is very slow. The optimum pH of the nutrient medium is in the neutral range, ie at about pH 7.0. Growth even under optimal conditions proceeds rather slowly, only after 4-5 days, colonies are observed.

Propionibacterium acnes operates a chemoorganotrophic and heterotrophic metabolism, he uses organic compounds as an energy source as well as for the construction of cellular materials. It can be used in a fermentation utilize various substrates for energy. Since a main product of this fermentation is propionic acid, this pathway is referred to as propionic acid. More products of this fermentation are acetic acid and carbon dioxide ( CO2). Can be used as substrates of Propionibacterium acnes various carbohydrates such as glucose, fructose, mannose and galactose. Some sugar alcohols, e.g., Glycerin ( glycerol) can be recycled. Propionibacterium species may also usually lactate - used as a substrate for the propionic acid - is the anion of lactic acid. This does not apply to Propionibacterium acnes.

Some enzymes used in the metabolism, in order to reduce certain substrates are detected in a "Bunte number " to identify a bacterium. Propionibacterium acnes has also catalase and on proteolytic enzymes which may degrade gelatin, also referred to as the gelatin liquefaction. A nitrate reduction is carried out by the enzyme nitrate reductase (NADH ) (EC 1.7.1.1 ). The formation of indole from tryptophan do not perform all the tribes, so the result in the indole test can be positive or negative results. On nutrient media containing an addition of blood (so-called blood agar ), a beta- hemolysis is observed. However, this behavior is typical of all strains. Investigations of 2010 show that especially strains which are assigned to Group I, the ability to show hemolysis, other strains are not.

Genetics

The genome of numerous strains of the bacterium has been completely sequenced. The first sequencing was carried out in 2004 to Propionibacterium acnes KPA171202. The genome has a size of 2560 kilobase pairs (kb ), which is about 55% of the genome size of Escherichia coli. The investigated strain ( DSM 16379 ) was isolated as a commensal of the human skin and classified as pathogenic, since he was involved in the disease acne vulgaris. In the following years further strains were genetically analyzed, with similar results with respect to the genome size. The investigated bacterial strains originated also from the human skin. These strains were also examined, which came from subjects who were not suffering from acne, these strains were therefore classified as non- pathogenic.

The results of sequencing show a GC content ( the fraction of nucleic bases guanine and cytosine) in the bacterial DNA of about 60 mole percent. This is within the range of 53-68 mole percent, which is typical for the genus Propionibacterium, the representatives are therefore counted in the phylogenetic group of Gram-positive bacteria with high GC content.

Pathogenicity

Propionibacterium acnes (Technical Rules for Biological Agents ) is assigned 466 in risk group 2 by the Biological Agents in connection with the TRBA. Microorganisms in this risk group are defined in the Biostoffverordnung as " biological substances that can cause human disease and might be a hazard to workers [ ... ] ." However, it is counted as a commensal of the normal skin flora. On the skin, it is not just a harmless residents but is a causative agent of acne and can contribute to this disease. The research, which strains are considered to be pathogenic and virulence factors to which it can be detected in the genome is still (as of 2013) and is further described in section systematics.

Evidence

A medium must have many nutrients, so Propionibacterium acnes can be cultivated it. Commonly used ingredients include meat extract, peptone from casein, yeast extract, dipotassium hydrogen phosphate ( KH2PO4 ), cysteine, hemins and some vitamins. In the preparation of the medium, inoculation and incubation, care must be taken to comply with the strict Anaerobentechnik. Is incubated at a temperature of 37 ° C. More recommended additives in the medium are glucose and thioglycolate.

Occurrence

The bacterium is a part of the skin flora and commensal. Propionibacterium acnes lives primarily in the sebum of the hair follicle, but was found already in the digestive tract. From one cm2 of human skin can be up to 100,000 bacteria of this type isolate.

System

Propionibacterium acnes is one of a plurality of species in the genus Propionibacterium. From the way about 100 bacterial strains are known. Of these numerous tribes on the human skin detectable without them trigger the disease acne vulgaris. On the other hand is found in patients with acne vulgaris, an increased number of these bacteria. Studies on these pathogenic strains show that they induce in the cells of the sebaceous gland ( sebocytes ), the production of cytokines and chemokines and thus contribute to an inflammatory process.

Serological studies on the different tribes led to these into groups, depending on whether and what factors were detectable. So the groups I to III have been identified, and two sub-groups IA ( I-1) and IB (I -2). These phenotypic features based on classification is based on the distinction existing in the bacterial cell wall polysaccharide chains and was supplemented by studies in which host-specific bacteriophages to cells attach ( Type differentiation ). This division into phenotypic groups followed later genetic studies. Since 2010, the genetic study carried out as part of a multi-locus sequence analysis ( MLSA ), in this case only certain genes are examined. This sequence analysis was restricted to the detection of nine housekeeping genes (english housekeeping gene, non- regulated genes that are expressed regardless of cell type, cell stage and external factors) and two genes ( tly and camp5 ), which presumably encode virulence factors. The study includes 210 isolates of Propionibacterium acnes in patients with acne, patients with other infections, to denes it is involved, and of healthy people, where it is part of the normal skin flora. As a result, the MLSA can the 210 isolates, 57 sequence types assigned, ie 57 different populations, each type of sequence has the same result in the multi-locus sequence analysis.

Using this data, the MLSA, a phylogenetic tree can be created, which confirmed the division into these groups (see figure). Within a group of the family tree, the sequence types in a similar composition of the investigated genes. Comparing the affiliation of the isolates with the medical history of the patient, we find the majority of isolates from patients with severe acne (shown with a black dot marks ) in the subgroup I-1. Only a few isolates found in subgroup I- 2 or Group II and not one in the group III. On the other hand include the isolates that are involved in other infections (marked in the figure with a red circle ) were more likely to subgroup 1-2 or to groups II and II as to the accommodated with acne in conjunction subgroup I-1. These isolates among others originate from blood, cerebrospinal fluid (CSF, cerebrospinal fluid ) and post- operative infections in hip joints. In these cases, it is assumed that an opportunistic infection with Propionibacterium acnes present.

Therefore, it is likely that only a limited number of types of sequences - and hence a limited number of bacterial strains - Propionibacterium acnes are classified as pathogenic in relation to the disease Acne vulgaris and these strains are very closely related to each other. For more MLSA studies, a database was set up, in which the results of all studies conducted so far can be compared. The 2012 study concluded on 285 isolates confirm the assumption that there is a " lineage " of the pathogenic strains.

Etymology

The genus name refers to the production of propionic acid in the same fermentation, the species name on the participation of the disease acne. Propionibacterium acnes was as Bacillus acnes 1900 by John Dow Fisher Gilchrist first described. By David Hendricks Bergey, inter alia, it was in 1923 assigned to the genus Corynebacterium. The investigations of Howard C. Douglas and Shirley E. Günter 1946 led to the fact that it is provided to the genus Propionibacterium, in particular based on detection of the propionic acid fermentation and anaerobic growth.

Medical importance

Propionibacterium acnes is involved as a secondary factor in the pathogenesis of acne and is particularly associated with acne vulgaris. In the comedones can be propagated, since there prevail rather anaerobic conditions. It is in the sebum of the hair follicle to find especially the sebaceous follicle. Since it has the enzyme lipase, it can degrade components of the sebum of the sebaceous glands to produce energy and multiply so. The resulting inflammatory substances cause chemotaxis by the accumulation of leukocytes into the tissue occur in the death of pus-filled blisters, a symptom of acne.

In addition, P. acnes has been associated with cases of keratitis, and sarcoidosis. In the context of medical treatment it may postoperatively or after use of equipment to infection. Are documented cases of discitis, spondylodiscitis, infections of the central nervous system, endocarditis, osteomyelitis, endophthalmitis and joint infection. Circulating immune complexes, which were formed against Propionibacterium acnes antigen deposit on bones or joints and cause an immune response there are suspected as the cause of rheumatic symptoms in the context of SAPHO syndrome.