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
Describe the appearance, habitat, etc. of the organism, and why you think it is important.
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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 . 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 . 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 . 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) . Genomic analysis of S. hominis subsp. Hudgins has revealed absence of flagellar encoding genes .
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 . 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 . 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 . The teichoic acid was further isolated and was found to be composed of a glycerol and glucosamine .
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) .
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 . 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 . 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 . 3M3SH is then presumed to be exported through the bacterial membrane . 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 .
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 . These compounds contribute to the vinegar-like smell of sweat. This biochemistry is particularly noticeable in the neck region of adolescents . 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.
The Staphylococcus genus is consistently found colonizing moist areas of higher humidity . While S. hominis is found almost entirely across the body, it is identified as the most abundant bacterial species in the human underarm region . S. hominis has also been preferentially isolated from axillae and pubic areas concentrated with apocrine glands . Inside the human body, S. hominis exhibits acid tolerance, bile resistance, and adherence to the epithelial cell line, thus showing potential as a probiotic . Studies show that certain strains of S. hominis can provide protection against S. aureus through the production of an antimicrobial peptide (AMP) called hominicin , . 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 . Homincin acts by preventing S. aureus colonization and has been effective against antibiotic resistant bacteria such as MRSA and VISA .
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 . 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 . 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 .
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 . 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 .
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 . 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 .
8. Current Research
Microbial enzymes can be used for purposes beyond the microbe itself. They are advantageous over plant or animal enzymes because there is such a wide range of catalytic activities with higher yield that does not fluctuate with seasonal changes . Identified in oil contaminated soil from India in 2013, S. hominis showed great potential for lipase production with essential nutrients present . Through optimizing conditions such as pH, temperature, and agitation speed, S. hominis has been used as a reservoir to generate large amounts of enzyme. Treated with basal mineral media where olive oil was added as a source of carbon, cultures were left overnight to generate lipase .
The probiotic capabilities of S. hominis against S. aureus are currently being studied. A strain of S. hominis, MBBL 2-9, in the female vaginal microbiota shows qualities of an effective probiotic. It expresses S. aureus inhibition, adherence to the epithelial cell line and shows a greater tolerance to gastric juices compared to a known probiotic, Lactobacillus rhamnosus KCTC 5033 . Purified bacteriocin from this particular strain of S. hominis shows similar molecular and antimicrobial activity with typical antibiotics used against S. aureus .
There is current research studying the potential of S. hominis as a reducing agent to synthesize gold nanoparticles (AuNPs) to antitubercular and anticancer therapies. The conventional synthesis of AuNPs requires high energy expenditure, and utilizes synthetic chemicals that are both expensive and toxic to human health and the environment. Using bacteria as reducing agents in this process is a promising environmentally friendly alternative to the conventional method of AuNP production . S. hominis strain MANF2 was isolated from fermented foods, and used to synthesize AuNPs via microwave irradiation and reduced Au3+ to Au+. Analysis using scanning electron microscopy (SEM) and dynamic light scattering (DLS) demonstrated the synthesis of gold nanoplates of 100 nm by S. hominis, suggesting AuNPs can deliver anti-tubercular and anticancer agents .
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.
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