a. Higher order taxa
Bacteria: Bacteria Phylum: Actinobacteria Order: Actinomycetales Suborder: Corynebacterineae Family: Mycobacteriaceae Genus: Mycobacterium Species: Mycobacterium mucogenicum
2. Description and significance
Mycobacterium mucogenicum was first discovered in a dialysis patient who developed septicemia via a catheter line that had been washed in infected water (1). It was characterized in 1982 as Mycobacterium chelonae-like organisms and in 1995 was delineated as a unique species, M. mucogenicum. This bacterium grows rapidly (colony formation in less than 7 days), is nonpigmented, and weakly Gram-positive (2). It is nonmotile, curved, and has a smooth colony morphology. Testing also reveals it is an aerobic, acid-fast rod; it has been found in both water and soil.
M. mucogenicum are associated with a wide range of clinical diseases and has been observed in complex infections of both immunocompromised and immunocompetent individuals. M. mucogenicum is able to tolerate various disinfectants including chlorination and extreme temperature (3). The bacteria’s unique structure is relevant to correctly identifying and treating the disease outbreaks because the susceptibility pattern and epidemiological links are distinct to this species (4). Recent outbreaks continue to occur, but the time before identification, number of infections, and mortality rate are all lower than when this bacteria was first being studied. Updating procedures as well as knowledge about this species can only continue to improve outcomes in vulnerable
3. Genome structure
The genome of Mycobacterium mucogenicum has been partially sequenced. The group was originally named in 1982 as Mycobacterium chelonae-like organism because of its similarity to Mycobacterium fortuitum and Mycobacterium chelonae. This similarity in 16S rRNA sequence impedes characterization and identification of this bacterium. Because of the similarities among 16S rRNA gene sequences of similar Mycobaterium species, differences must be determined using gene analysis (5). The analysis of multiple genes including hsp65, 16S rRNA genes, rpoB, sod, and recA were the most useful in differentiating between Mycobacterium species. Finally, in 1994 the new name, Mycobacterium mucogenicum, was proposed when it became established as its own species.
Closely Related Species: The Mycobacterium mucogenicum group includes M. mucogenicum, Mycobacterium aubagnese and Mycobacterium phocaicum (5). Together they are responsible for the outbreaks in both water and hospital sources.
4. Cell structure
Mycobacterium mucogenicum is a Gram-positive, acid-fast rod. A unique characteristic of these bacteria is the absence of an outer cell membrane that occasionally yields a false Gram-negative result during staining. M. mucogenicum and mycobacterium in general have a thick, hydrophobic, waxy cell wall with a cell envelope containing lipid components made of mycolic acid (6). The presence of mycolic acid in the cellular structure is unique to this genus of bacteria and confers resistance to many alcohols and antibiotics. Additional structures of long chain, saturated fatty acids found in M. mucogenicum contribute to chlorine resistance and the bacteria’s disinfectant resistance mechanism (7).
5. Metabolic processes
Mycobacterium mucogenicum are able to grow on simple substrates by using ammonium as a nitrogen source and manitol or citrate as carbon sources. Colony growth is inhibited by 5% NaCl. The bacteria test positive for 3-day arylsulfatase reaction and have no color on iron uptake testing. These bacteria are aerobic and have variable nitrate reduction (8). These results are from tests intended to discriminate M. mucogenicum from other strains that instead were only able to reveal more about the bacteria’s metabolic processes. To determine between M. mucogenicum and M. chelonae, a close species, either cell wall analysis by high performance liquid chromatography (HPLC) of cell wall mycolic acid esters or molecular characterization can be utilized. Gene determinations must often be used to characterize the bacteria found in patients (8)
In the environment, M. mucogenicum are most often detected ubiquitously in both water and soil, particularly in sewage and hospital water systems (5). This bacterium exists as biofilms in disinfected water sources (9).
There have been numerous incidents of M. mucogenicum outbreaks in various hospitals and water supplies. There are a variety of effects depending on the patient population that is infected. This bacterium and other nontuberculosis species of Mycobacteria were originally found in immunocompromised patients, particularly those diagnosed with AIDS. Recently, infection has occurred in those who are immunocompetent (10). M. mucogenicum is related to catheter-related infections, central nervous system disease, respiratory infection, skin and soft tissue infection, other miscellaneous disease (9).
In a study of 113 that compared tap water at various sites, M. mucogenicum was the most frequently occurring nontuberculous mycobacterium (11). M. mucogenicum can colonize a variety of locations both inert and alive. The respiratory tract is one such location where the bacteria can cause a cutaneous (skin) infection. Skin and soft tissue infections normally occur in immunocompromised patients or patients with posttraumatic injury through a break in the skin. Once inside the body, a granulomatous immune reaction within the infection site occurs. Although most nontuberculous Mycobateria infections are difficult to treat because of their antibiotic resistance, M. mucogenicum is susceptible to numerous antibiotics including fluoroquinolones, certain cephalosporins, macrolides, and aminoglycosides (12). Because of the difference in susceptibility to antibiotics, correct identification of this bacterium is crucial. Treatment periods vary from 1 to 6 months and patients are normally successful treated with 500mg of oral clarithromycin twice a day for 6 months (13). Overall mortality is 30%; symptoms of infection normally include fever, tunnel irritation, fever, cough, chills, shortness of breath, tender wound or central venous catheter site, or skin lesion. These symptoms result in hospitalization and antibiotic treatment (12). Frequently the M. mucogenicum infection is found in the blood.
7. Key microorganisms
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8. Current Research
This bacterium is researched because it was established as a new species of mycobacterium recently and is frequently linked to outbreaks in human populations. Because of its susceptibility to antibiotics, the biggest hindrance for correctly identifying this bacterium is when it manifests in patients, then localizing it to the source. Current research involves updating infection control measures to stop further cases by regularly assessing the water supply (4).
Several immunosuppressed patients are at a risk of mortality from this bacterium, which makes identification, continued characterization, and treatment significant. Studies focused on recent cases, such as in 2013 in a pediatric hematology-oncology unit, show promising results after an outbreak from a common water source (14).
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3. Reddy, Y., Reddy, Y., Balasubramaniam, L., Mathew, M., & Abraham, G. (2012). Mycobacterium mucogenicum Peritonitis in a Continuous Ambulatory Peritoneal Dialysis Patient. Peritoneal Dialysis International, 226-227.
4. Humphreys, H. (n.d.). Infection-Microbiology and Management, 3rd edn. Clinical Microbiology and Infection, 1038-1038.
5. Adekambi, T. (2004). Dissection of phylogenetic relationships among 19 rapidly growing Mycobacterium species by 16S rRNA, hsp65, sodA, recA and rpoB gene sequencing. International Journal of Systematic and Evolutionary Microbiology, 2095-2105.
6. Marrakchi, H., Lanéelle, M., & Daffé, M. (n.d.). Mycolic Acids: Structures, Biosynthesis, and Beyond. Chemistry & Biology, 67-85.
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8. Conville, P., & Witebsky, F. (2001). Lack of Usefulness of Carbon Utilization Tests for Identification of Mycobacterium mucogenicum. Journal of Clinical Microbiology, 2725-2728.
9. Simoes, L., Simoes, M., & Vieira, M. (2007). Biofilm Interactions between Distinct Bacterial Genera Isolated from Drinking Water. Applied and Environmental Microbiology, 6192-6200.
10. Adekambi, T., Foucault, C., Scola, B., & Drancourt, M. (2006). Report of Two Fatal Cases of Mycobacterium mucogenicum Central Nervous System Infection in Immunocompetent Patients. Journal of Clinical Microbiology, 837-840.
11. Banks, M. K., and J. D. Bryers. 1991. Bacterial species dominance within a binary culture biofilm. Appl. Environ. Microbiol. 57:1974–1979.
12. Hawkins, C., Qi, C., Warren, J., & Stosor, V. (n.d.). Catheter-related bloodstream infections caused by rapidly growing nontuberculous mycobacteria: A case series including rare species. Diagnostic Microbiology and Infectious Disease, 187-191.
13. Brown-Elliott, B., & Wallace, R. (n.d.). Clinical And Taxonomic Status Of Pathogenic Nonpigmented Or Late-Pigmenting Rapidly Growing Mycobacteria. Clinical Microbiology Reviews, 716-746.
14. Zolg, J. W., and S. P. Schulz. 2013. The superoxide dismutase gene, a target for detection and identification of mycobacteria by PCR. J. Clin. Microbiol. 32:2801-2812.
15. Mycobacterium mucogenicum: Report of a skin infection associated with etanercept. (2008). EScholarship, University of California.