Staphylococcus hominis
1. Classification
Kloos and Schleifer first classified S. hominis in 1975 (10).
S. hominis is a Gram-positive, mesophilic aerobic coccoid bacterium (2, 4).
The genus Staphylococcus contains many virulent Gram-positive bacteria (5). Among this genus, S. hominis is known as the third most common Coagulase-negative staphylococci (CoNS) (6). CoNS are opportunistic pathogens that exist in the normal human microflora (5).
a. Higher order taxa
Domain Bacteria Phylum Firmicutes Class Bacili Order Bacialleaus Family Staphylococcaeceae Genus Staphylococcus
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2. Description and significance
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3. Genome structure
The S. hominis genome is 2.25 Mb, with a GC composition of 31.4%, and contains 2131 protein coding genes [7]. There are no proteins unique to S. hominis. The genome of S. hominis consists of multiple antibiotic resistant genomic elements that decrease the organism’s susceptibility to antibiotic treatments. These genes include mecA, which encodes for the resistance of methicillin or oxacillin, and is located on the Staphylococcal Cassette Chromosome mec (SCCmec), a mobile genetic element [2]. In biofilm formation, the gene atl1E is responsible for initial adherence of the S. hominis strain and the gene sea is responsible for toxin production [8]. The S. hominis genome also expresses the ermC gene, a ribosomal target for modification, and the lnuA gene which mediates enzymatic drug inactivation especially in macrolides, lincosamides and streptogramin B antibiotics (MLSB) [9]. Genomic analysis of S. hominis subsp. Hudgins has revealed absence of flagellar encoding genes [12].
4. Cell structure
S. hominis is a Gram-positive spherical, non-motile bacteria with a raised center measuring about 1.0 to 1.5 μm in diameter [10]. Colonies are small and often grow in tetrads with wide beveled edges that develop with age. Older colonies also exhibit concentric rings of light and dark color [10]. On the cell wall, the composition of teichoic acid and glutamic acid is relatively low and other subspecies, such as S. hominis subsp. Novobiosepticus (SHN) exhibits thickened walls [11]. The teichoic acid was further isolated and was found to be composed of a glycerol and glucosamine [10].
A study done in 2010 found that S. hominis secretes antimicrobial peptides, which have high antibacterial activities against Methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-Intermediate Staphylococcus aureus (VISA) [13].
5. Metabolic processes
S. hominis possesses unique metabolic processes that contribute to human body odor production. As a heterotroph, it hydrolyzes simple monosaccharides and amino acids through mostly aerobic respiration to obtain energy [14]. Interestingly, S. hominis ingests the peptide S-Cys-Gly-3M3SH through secondary active transport as the precursor to the thiolalcohol that is responsible for malodor. The cotransporter called the SH1446 transporter couples the proton movement with oligopeptides [14]. Once inside, peptidases and lyase-catalyzed reactions lead to the production of not only 3-methyl-3-sulfanylhexanol (3M3SH), the odor causing compound, but also pyruvate, glycine, and ammonia [14]. 3M3SH is then presumed to be exported through the bacterial membrane [14]. This process is thought to be nutritionally beneficial to S. hominis, as it releases nitrogen, amino acids, and a carbon source in pyruvate. Targeting the SH1446 cotransporter is now a potential solution for controlling body odor. To test the effect of overexpressing the proton-coupled oligonucleotide membrane transporter (POT), E. coli was transformed with a vector that encoded POT. The resulting E. coli was found to be capable of malodor production [14].
In addition to metabolizing sulfur compounds, S. hominis is also capable of utilizing biotic materials such as lactic acid, aliphatic amino acids, and glycerol present in sweat, even in sterile conditions, to produce acetic and isovaleric acid [1]. These compounds contribute to the vinegar-like smell of sweat. This biochemistry is particularly noticeable in the neck region of adolescents [1]. Similar to the pathway that produces 3M3SH, the production of acetic and isovaleric acids also seems to benefit S. hominis nutritionally through the release of pyruvate and acetyl CoA. Given S. hominis’ ability to complete the entire citric acid cycle and electron transport chain, acetic and isovaleric acid are likely the byproduct of energy acquisition.
6. Ecology
The Staphylococcus genus is consistently found colonizing moist areas of higher humidity [15]. While S. hominis is found almost entirely across the body, it is identified as the most abundant bacterial species in the human underarm region [1]. S. hominis has also been preferentially isolated from axillae and pubic areas concentrated with apocrine glands [16]. Inside the human body, S. hominis exhibits acid tolerance, bile resistance, and adherence to the epithelial cell line, thus showing potential as a probiotic [23]. Studies show that certain strains of S. hominis can provide protection against S. aureus through the production of an antimicrobial peptide (AMP) called hominicin [13], [17]. AMPs are known to control growth of microorganisms residing on the skin’s surface. Hominicin is heat-tolerant up 121˚C to and pH-tolerant (from pH 2.0 to 10.0) thus stable in harsh conditions [13]. Homincin acts by preventing S. aureus colonization and has been effective against antibiotic resistant bacteria such as MRSA and VISA [13].
7. Pathology
Multifactorial Mechanisms of Pathogenesis
Although S. hominis is a common commensal bacteria on human skin, its different mechanisms of pathogenesis are not fully understood. Some pathogenic mechanisms include adhesion and invasion of cells, antimicrobial peptides, extracellular toxins, and biofilm formation. To assess bacterial adherence and invasion, infected cells were lysed and plated on agar. Of the thirty total isolates, thirteen isolates invaded and four isolates adhered to HeLa cells [18]. S. hominis isolates studied in vitro show icaADBC genes coding for polysaccharide intercellular adhesins are central to biofilm formation. The biofilm matrix is susceptible to detachment by sodium metaperiodate (NaIO4), and proteinase K. Having similar biofilm degradation mechanisms can aid in developing clinical therapies that target the gene responsible for biofilm formation in order to treat bacterial pathogenesis in clinical strains of S. hominis [3]. S. hominis isolates were also found to have extracellular toxins, causing cytopathic effects. Using PCR, all strains were shown to carry the mecA gene, which confers methicillin resistance, and twenty-eight isolates had genes for resistance to aminoglycoside antibiotics [18].
Nosocomial Infections
CoNS bacteria are commonly present in bloodstream infections of immunocompromised patients, and S. hominis is one of the three most common strains recoverable from neonates and immunocompromised patients [19]. Isolates that have been studied demonstrate a wide range of biofilm production levels and a large majority of isolates are resistant to at least one beta-lactam antibiotic or possess the mecA gene that confers methicillin resistance. Isolates are also shown to have genetic diversity when evaluated using pulsed-field gel electrophoresis (PFGE), with at least three different bands between each isolate. Repetitive sequence-based PCR (BOX-PCR) were performed to differentiate the strains of S. hominis, and it revealed large genetic diversity among the strands [20].
There are also dangers of nosocomial infection via invasive medical devices; S. hominis biofilm formation peaks between 4-24 hours of weak adherence and decreases in adherence after 48 hours. The gene atl1E for an autolysin responsible for initial adhesion was found in all strains [8]. These findings can explain how nosocomial infections occur, since biofilms can adhere to medical equipment and resistance to different antibiotics increases the difficulty of treating the infection. The antimicrobial peptide hominicin derived from S. hominis acts against MRSA and VISA, the two most prominent nosocomial infectious agents [13].
8. Current Research
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9. References
It is required that you add at least five primary research articles (in same format as the sample reference below) that corresponds to the info that you added to this page. [Sample reference] Faller, A., and Schleifer, K. "Modified Oxidase and Benzidine Tests for Separation of Staphylococci from Micrococci". Journal of Clinical Microbiology. 1981. Volume 13. p. 1031-1035.
[1] Lam, T. H., Verzotto, D., Brahma, P., Ng, A. H. Q., Hu, P., Schnell, D., Tiesman, J., Kong, R., Ton, T. M. U., Li, J., Ong, M., Lu, Y., Swaile, D., Liu, P., Liu, J., & Nagarajan, N. (2018). Understanding the microbial basis of body odor in pre-pubescent children and teenagers. Microbiome. 6(1):213.
[2] Pereira, E.M., de Mattos, C.S., dos Santos, O.C. et al. (2019). Staphylococcus hominis subspecies can be identified by SDS-PAGE or MALDI-TOF MS profiles. Sci Rep 9: 11736
[3] Szczuka, E., Telega, K. & Kaznowski, A. (2015) . Biofilm formation by Staphylococcus hominis strains isolated from human clinical specimens. Folia Microbiology 60:1–5
[4] Reimer, L. C., Vetcininova, A., Carbasse, J. S., Söhngen, C., Gleim, D., Ebeling, C., & Overmann, J. (2019). Bac Dive in 2019: Bacterial phenotypic data for High-throughput biodiversity analysis. Nucleic Acids Research, 47(D1), D631–D636.
[5] Akiyama, H., Kanzaki, H., Tada, J., & Arata, J. (1998). Coagulase-Negative Staphylococci Isolated from Various Skin Lesions. The Journal of Dermatology, 25(9), 563–568.
[6] Nizet, V., & Bradley, J. S. (2011). CHAPTER 14—Staphylococcal Infections. In J. S. Remington, J. O. Klein, C. B. Wilson, V. Nizet, & Y. A. Maldonado (Eds.), Infectious Diseases of the Fetus and Newborn (Seventh Edition) (pp. 489–515). W.B. Saunders.
[7] Staphylococcus hominis [Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information; 2004 – [cited 2020 Nov 22]. Available from:https://www.ncbi.nlm.nih.gov/genome/?term=Staphylococcus%20hominis[Organism]&cmd=DetailsSearch
[8] Pedroso, S. H. S. P., Sandes, S. H. C., Luiz, K. C. M., Dias, R. S., Serufo, J. C., Farias, L. M., & Santos, S. G. (2016). Biofilm and toxin profile: A phenotypic and genotypic characterization of coagulase-negative staphylococci isolated from human bloodstream infections. Microbial pathogenesis, 100:312-318.
[9] Szczuka, E., Makowska, N., Bosacka, K., Słotwińska, A., & Kaznowski, A. (2016). Molecular basis of resistance to macrolides, lincosamides and streptogramins in Staphylococcus hominis strains isolated from clinical specimens. Folia microbiologica, 61(2), 143-147.
[10] Kloos, W. E., & Schleifer, K. H. (1975). Isolation and Characterization of Staphylococci from Human Skin II. Descriptions of Four New Species: Staphylococcus warneri, Staphylococcus capitis, Staphylococcus hominis, and Staphylococcus simulans. International Journal of Systematic Bacteriology, 25(1), 62-79. doi:10.1099/00207713-25-1-62
[11] Abdalla, N. M., Haimour, W. O., Osman, A. A., Sarhan, M. A., & Musaa, H. A. (2012). Antibiotics Sensitivity Profile Towards Staphylococcus hominis in Assir Region of Saudi Arabia. Journal of Scientific Research, 5(1), 171-183. doi:10.3329/jsr.v5i1.11704
[12] Calkins, S., Couger, M., Jackson, C., Zandler, J., Hudgins, G. C., Hanafy, R. A., . . . Youssef, N. (2016). Draft genome sequence of Staphylococcus hominis strain Hudgins isolated from human skin implicates metabolic versatility and several virulence determinants. Genomics Data, 10, 91-96. doi:10.1016/j.gdata.2016.10.003
[13] Kim, P. I., Sohng, J. K., Sung, C., Joo, H.-S., Kim, E.-M., Yamaguchi, T., Park, D., & Kim, B.-G. (2010). Characterization and structure identification of an antimicrobial peptide, hominicin, produced by Staphylococcus hominis MBBL 2–9. Biochemical and Biophysical Research Communications, 399(2), 133–138.
[14] Minhas, G. S., Bawdon, D., Herman, R., Rudden, M., Stone, A. P., James, A. G., Thomas, G. H., & Newstead, S. (2018). Structural basis of malodour precursor transport in the human axilla. eLife, 7, e34995.
[15] Grice, E. A., & Segre, J. A. (2011). The skin microbiome. Nature Reviews Microbiology, 9(4), 244–253.
[16] Becker, K., Heilmann, C., & Peters, G. (2014). Coagulase-Negative Staphylococci. Clinical Microbiology Reviews, 27(4), 870–926.
[17] Nakatsuji, T., Chen, T. H., Narala, S., Chun, K. A., Two, A. M., Yun, T., Shafiq, F., Kotol, P. F., Bouslimani, A., Melnik, A. V., Latif, H., Kim, J.-N., Lockhart, A., Artis, K., David, G., Taylor, P., Streib, J., Dorrestein, P. C., Grier, A., … Gallo, R. L. (2017). Antimicrobials from human skin commensal bacteria protect against Staphylococcus aureus and are deficient in atopic dermatitis. Science Translational Medicine, 9(378).
[18] Szczuka, E., Krzymińska, S., Bogucka, N., & Kaznowski, A. (2018). Multifactorial mechanisms of the pathogenesis of methicillin-resistant Staphylococcus hominis isolated from bloodstream infections. Antonie van Leeuwenhoek, 111(7), 1259-1265.
[19] Mendoza-Olazarán, S., Morfin-Otero, R., Rodríguez-Noriega, E., Llaca-Díaz, J., Flores-Treviño, S., González-González, G. M., ... & Garza-González, E. (2013). Microbiological and molecular characterization of Staphylococcus hominis isolates from blood. PLoS One, 8(4), e61161.
[20] Szczuka, E., Trawczyński, K., & Kaznowski, A. (2014). Clonal Analysis of Staphylococcus hominis Strains Isolated from Hospitalized Patients. Polish Journal of Microbiology, 63(3):349–354.
[21] Behera, A. R., Veluppal, A., & Dutta, K. (2019). Optimization of physical parameters for enhanced production of lipase from Staphylococcus hominis using response surface methodology. Environmental Science and Pollution Research, 26(33), 34277–34284.
[22] Marimuthu, K. (2013). Isolation and characterization of Staphylococcus hominis JX961712 from oil contaminated soil. Journal of Pharmacy Research, 7(3), 252–256.
[23] Sung, C., Kim, B.-G., Kim, S., Joo, H.-S., & Kim, P. I. (2010). Probiotic potential of Staphylococcus hominis MBBL 2–9 as anti-Staphylococcus aureus agent isolated from the vaginal microbiota of a healthy woman. Journal of Applied Microbiology, 108(3), 908–916.
[24] Calkins, S., Couger, M. B., Jackson, C., Zandler, J., Hudgins, G. C., Hanafy, R. A., Budd, C., French, D. P., Hoff, W. D., & Youssef, N. (2016). Draft genome sequence of Staphylococcus hominis strain Hudgins isolated from human skin implicates metabolic versatility and several virulence determinants. Genomics data, 10, 91–96.
[25] Khusro, A., Aarti, C., & Agastian, P. (2020). Microwave irradiation-based synthesis of anisotropic gold nanoplates using Staphylococcus hominis as reductant and its optimization for therapeutic applications. Journal of Environmental Chemical Engineering, 8(6), 104526.
Edited by JH, student of Jennifer Bhatnagar for BI 311 General Microbiology, 2020, Boston University.
