Staphylococcus hominis

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Staphylococcus hominis
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Bacteria
Phylum: Bacillota
Class: Bacilli
Order: Bacillales
Family: Staphylococcaceae
Genus: Staphylococcus
Species:
S. hominis
Binomial name
Staphylococcus hominis
Kloos & Schleifer 1975

Staphylococcus hominis is a coagulase-negative member of the bacterial genus Staphylococcus , consisting of Gram-positive, spherical cells in clusters. It occurs very commonly as a harmless commensal on human and animal skin and is known for producing thioalcohol compounds that contribute to body odour. [1] [2] Like many other coagulase-negative staphylococci, S. hominis may occasionally cause infection in patients whose immune systems are compromised, for example by chemotherapy or predisposing illness.

Contents

Description

Colonies of S. hominis are small, usually 1–2 mm in diameter after 24 hours' incubation at 35 °C, and white or tan in colour. Occasionally, strains are resistant to novobiocin and may be confused with other resistant species (e.g. S. saprophyticus ). [3]

It is one of only two species of Staphylococcus to display sensitivity to desferrioxamine, the other being S. epidermidis . Unlike S. epidermidis, S. hominis produces acid from trehalose, so the two tests together serve to identify the species.

Biology

Numerous coagulase-negative staphylococci appear commonly on human skin. Of these species, S. epidermidis and S. hominis are the most abundant. While S. epidermidis tends to colonize the upper part of the body, S. hominis tends to colonize in areas with numerous apocrine glands, such as axillae and the pubic region. In a certain study, S. hominis was calculated to account for 22% of the total staphylococcal species recovered from individuals, second to S. epidermidis at 46%. S. hominis is the predominant species on the head, axillae, arms, and legs.

S. hominis, as well as most other staphylococcal species common on the human skin, is able to produce acid aerobically from glucose, fructose, sucrose, trehalose, and glycerol. Some strains were also able to produce acid from turanose, lactose, galactose, melezitose, mannitol, and mannose. Most strains colonize on the skin for relatively short periods of time compared to other Staphylococcus species. They, on average, stay on the skin for only several weeks or months.

The cell wall contains low amounts of teichoic acid and glutamic acid. The cell wall teichoic acid contains glycerol and glucosamine.

S. hominis cells are Gram-positive cocci, usually 1.2 to 1.4 μm in diameter. They appear normally in tetrads and sometimes in pairs. [4]

Resistance

Based on a total of 240 strains, all were resistant to lysozyme, some were slightly resistant to lysostaphin, 77% were susceptible to penicillin G, 97% to streptomycin, 93% to erythromycin, 64% to tetracycline, and 99% to novobiocin. [4]

Multi drug resistant strains of s. hominis have been isolated from blood and wound cultures in humans.

Culturing

When grown in agar cultures, colonies are usually circular, 4.0 to 4.5 mm in diameter. Agar colonies usually have wide edges and an elevated center. They are commonly smooth with dull surfaces, and are yellow-orange pigmented in the center of the opaque colonies. They grow both in aerobic and anaerobic conditions, but tend to grow significantly less in the latter. Optimal NaCl concentrations of the agar culture for the growth of S. hominis seem to be around 7.5%, and a salt concentration of 15% yielded poor growth to no growth at all. The optimal growth temperature range was around 28 to 40 °C, but good growth is still observed at 45 °C, while no growth is observed at 15 °C.

S. hominis can be differentiated from staphylococci by its colony morphology and pigmentation patterns, predominant tetrad cell arrangement, poor growth in thioglycolate, low tolerance of NaCl, and carbohydrate reaction pattern. Each species is also significantly different in cell wall composition, lactic acid configuration, temperature extremes of growth, coagulase activity, hemolysis acetylmethylcarbinol production, nitrate reduction, and phosphatase, DNase, and bacteriolytic activities. Similarities in these properties between S. hominis and several other species suggest a close relationship between S. hominis and S. epidermidis, S. haemolyticus, and S. warneri. [4]

Antibiotic-resistant subspecies

Staphylococcus hominis is normally found on human skin and is usually harmless, but can sometimes cause infections in people with abnormally weak immune systems. Most, if not all, strains are susceptible to penicillin, erythromycin, and novobiocin, but a divergent strain, S. hominis subsp. novobiosepticus (SHN), was isolated between 1989 and 1996. [3]

This strain was named so because of its unique resistance to novobiocin and its failure to produce acid aerobically from trehalose and glucosamine. In addition, the 26 isolated strains of this new subspecies are resistant to nalidixic acid, penicillin G, oxacillin, kanamycin, and streptomycin. They were also somewhat resistant to methicillin and gentamicin, and most strains were resistant to erythromycin, clindamycin, chloramphenicol, trimethoprim/sulfamethoxazole, and ciprofloxacin, as well. In addition, S. hominis hominis is commonly found isolated from human skin, but as of 1998, no SHN isolate from human skin had been reported. [3]

The SHN is so similar to the original S. hominis, now called S. hominis subsp. hominis, that in 2010, a MicroScan system that clinical microbiology laboratories used, identified 7 of 31 S. hominis novobiosepticus cultures as S. hominis hominis. The relationship between the two was unknown, but antibiotic-resistant isolates of S. hominis belonged only to SHN. [5]

SHN strains seems to have thickened cell walls, which can be the result of a genetic background that also allows for vancomycin resistance. The thickened cell walls exist in subspecies with and without vancomycin resistance which suggests this subspecies did not originate from the acquiring of resistance genes. [6]

Origin

The combined resistance to novobiocin and oxacillin is hypothesized to have originated from a simultaneous introduction of genes controlling the resistance to the two. These genes were believed to have been acquired originally through heterologous DNA from a methicillin-resistant strain of one of the novobiocin-resistant species belonging to the S. sciuri or the S. saprophyticus groups. The larger genome size of the SHN compared to that of S. hominis hominis may be the result of the acquiring of heterologous DNA. This new, divergent strain was first described in 1998, and was first implicated in causing bacteremia in 2002.

Another hypothesis is the insertion of the mec A gene and its flanking sequence into the chromosome of SHN might have affected the expression of a closely linked gene, which converted the host to become novobiocin-resistant. [3]

Recent cases

In 2002 and 2003, 32 isolates of SHN were found in 21 patients. Twenty-three of these were from blood cultures, six from catheters, one from cerebrospinal fluid, one from a wound, and one from external ear fluid. Eighteen of the 21 patients from whom these isolates were recovered were neonates, one was a 13-year-old boy, and two were adults.

Thirteen of these cases were confirmed as sepsis in neonates resulting from SHN infection. These were the first clinical reports of SHN causing bacteremia in hospitalized patients. SHN infections were high in morbidity, but had a low rate of mortality. More undocumented instances of SHN infections may not have been reported because not all coagulase-negative staphylococcal infections are identified to the species level.

Molecular epidemiology was successful in tracing 13 cases of sepsis in neonates to a single clone of SHN during a two-year study period in neonatal ICUs. Formal investigation regarding the mode of transmission this microbe uses were not conducted, but infants are believed to serve as reservoirs for the microorganism, and transmission takes place with contact between health workers and the infants. In addition, staphylococcal isolates from the nasopharynges and hands of health care workers were shown to be genetically similar to those that colonize or cause disease in neonates. This supports the idea that health workers serve as a form of nosocomial transmission of coagulase-negative staphylococi.

If SHN indeed takes residence on human skin, it probably exists in small numbers and would require enrichment for detection. [7]

SHN has also been responsible for nosocomial outbreaks elsewhere. SHN strains have been causing bloodstream infections, but have still been classified as vancomycin-susceptible. [6]

In May 2015, two babies from Simojovel rural communities of Chiapas, Mexico, were killed and about 30 required medical attention after receiving vaccines for Hepatitis B, the Mexican Social Security Institute (IMSS) launched an investigation to identify the cause of such events, the preliminary results showed that the cause was external contamination with Staphylococcus hominis. [8]

Related Research Articles

<i>Staphylococcus aureus</i> Species of Gram-positive bacterium

Staphylococcus aureus is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive for catalase and nitrate reduction and is a facultative anaerobe that can grow without the need for oxygen. Although S. aureus usually acts as a commensal of the human microbiota, it can also become an opportunistic pathogen, being a common cause of skin infections including abscesses, respiratory infections such as sinusitis, and food poisoning. Pathogenic strains often promote infections by producing virulence factors such as potent protein toxins, and the expression of a cell-surface protein that binds and inactivates antibodies. S. aureus is one of the leading pathogens for deaths associated with antimicrobial resistance and the emergence of antibiotic-resistant strains, such as methicillin-resistant S. aureus (MRSA), is a worldwide problem in clinical medicine. Despite much research and development, no vaccine for S. aureus has been approved.

<span class="mw-page-title-main">Coagulase</span> Class of bacterial proteins

Coagulase is a protein enzyme produced by several microorganisms that enables the conversion of fibrinogen to fibrin. In the laboratory, it is used to distinguish between different types of Staphylococcus isolates. Importantly, S. aureus is generally coagulase-positive, meaning that a positive coagulase test would indicate the presence of S. aureus or any of the other 11 coagulase-positive Staphylococci. A negative coagulase test would instead show the presence of coagulase-negative organisms such as S. epidermidis or S. saprophyticus. However, it is now known that not all S. aureus are coagulase-positive. Whereas coagulase-positive Staphylococci are usually pathogenic, coagulase-negative Staphylococci are more often associated with opportunistic infection.

<i>Staphylococcus haemolyticus</i> Species of bacterium

Staphylococcus haemolyticus is a member of the coagulase-negative staphylococci (CoNS). It is part of the skin flora of humans, and its largest populations are usually found at the axillae, perineum, and inguinal areas. S. haemolyticus also colonizes primates and domestic animals. It is a well-known opportunistic pathogen, and is the second-most frequently isolated CoNS. Infections can be localized or systemic, and are often associated with the insertion of medical devices. The highly antibiotic-resistant phenotype and ability to form biofilms make S. haemolyticus a difficult pathogen to treat. Its most closely related species is Staphylococcus borealis.

<i>Staphylococcus saprophyticus</i> Species of bacterium

Staphylococcus saprophyticus is a Gram-positive coccus belonging to the genus Staphylococcus. S. saprophyticus is a common cause of community-acquired urinary tract infections.

Staphylococcus caprae is a Gram-positive, coccus bacteria and a member of the genus Staphylococcus. S. caprae is coagulase-negative. It was originally isolated from goats, but members of this species have also been isolated from human samples.

<i>Staphylococcus xylosus</i> Species of bacterium

Staphylococcus xylosus is a species of bacteria belonging to the genus Staphylococcus. It is a Gram-positive bacterium that forms clusters of cells. Like most staphylococcal species, it is coagulase-negative and exists as a commensal on the skin of humans and animals and in the environment.

Staphylococcus warneri is a member of the bacterial genus Staphylococcus, consisting of Gram-positive bacteria with spherical cells appearing in clusters. It is catalase-positive, oxidase-negative, and coagulase-negative, and is a common commensal organism found as part of the skin flora on humans and animals. Like other coagulase-negative staphylococci, S. warneri rarely causes disease, but may occasionally cause infection in patients whose immune system is compromised.

<i>Staphylococcus epidermidis</i> Species of bacterium

Staphylococcus epidermidis is a Gram-positive bacterium, and one of over 40 species belonging to the genus Staphylococcus. It is part of the normal human microbiota, typically the skin microbiota, and less commonly the mucosal microbiota and also found in marine sponges. It is a facultative anaerobic bacteria. Although S. epidermidis is not usually pathogenic, patients with compromised immune systems are at risk of developing infection. These infections are generally hospital-acquired. S. epidermidis is a particular concern for people with catheters or other surgical implants because it is known to form biofilms that grow on these devices. Being part of the normal skin microbiota, S. epidermidis is a frequent contaminant of specimens sent to the diagnostic laboratory.

Lysostaphin is a Staphylococcus simulans metalloendopeptidase. It can function as a bacteriocin (antimicrobial) against Staphylococcus aureus.

<span class="mw-page-title-main">Staphylococcal infection</span> Medical condition

A staphylococcal infection or staph infection is an infection caused by members of the Staphylococcus genus of bacteria.

mecA is a gene found in bacterial cells which allows them to be resistant to antibiotics such as methicillin, penicillin and other penicillin-like antibiotics.

<i>Staphylococcus capitis</i> Species of bacterium

Staphylococcus capitis is a coagulase-negative species (CoNS) of Staphylococcus. It is part of the normal flora of the skin of the human scalp, face, neck, scrotum, and ears and has been associated with prosthetic valve endocarditis, but is rarely associated with native valve infection.

<i>Staphylococcus</i> Genus of Gram-positive bacteria

Staphylococcus is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillales. Under the microscope, they appear spherical (cocci), and form in grape-like clusters. Staphylococcus species are facultative anaerobic organisms.

Staphylococcus stepanovicii is a Gram-positive, coagulase-negative member of the bacterial genus Staphylococcus consisting of single, paired, and clustered cocci. The species is novobiocin-resistant and oxidase-positive. It was named in honor of Serbian microbiologist Srdjan Stepanović.

Staphylococcus carnosus is a bacterium from the genus Staphylococcus that is both Gram-positive and coagulase-negative. It was originally identified in dry sausage and is an important starter culture for meat fermentation. Unlike other members of its genus, such as Staphylococcus aureus and Staphylococcus epidermidis, S. carnosus is nonpathogenic and safely used in the food industry.

Staphylococcus delphini is a Gram-positive, coagulase-positive member of the bacterial genus Staphylococcus consisting of single, paired, and clustered cocci. Strains of this species were originally isolated from aquarium-raised dolphins suffering from skin lesions.

<i>Staphylococcus hyicus</i> Species of bacterium

Staphylococcus hyicus is a Gram-positive, facultatively anaerobic bacterium in the genus Staphylococcus. It consists of clustered cocci and forms white circular colonies when grown on blood agar. S. hyicus is a known animal pathogen. It causes disease in poultry, cattle, horses, and pigs. Most notably, it is the agent that causes porcine exudative epidermitis, also known as greasy pig disease, in piglets. S. hyicus is generally considered to not be zoonotic, however it has been shown to be able to cause bacteremia and sepsis in humans.

Staphylococcus schleiferi is a Gram-positive, cocci-shaped bacterium of the family Staphylococcaceae. It is facultatively anaerobic, coagulase-variable, and can be readily cultured on blood agar where the bacterium tends to form opaque, non-pigmented colonies and beta (β) hemolysis. There exists two subspecies under the species S. schleiferi: Staphylococcus schleiferi subsp. schleiferi and Staphylococcus schleiferi subsp. coagulans.

Staphylococcus pseudintermedius is a gram positive coccus bacteria of the genus Staphylococcus found worldwide. It is primarily a pathogen for domestic animals, but has been known to affect humans as well. S. pseudintermedius is an opportunistic pathogen that secretes immune modulating virulence factors, has many adhesion factors, and the potential to create biofilms, all of which help to determine the pathogenicity of the bacterium. Diagnoses of Staphylococcus pseudintermedius have traditionally been made using cytology, plating, and biochemical tests. More recently, molecular technologies like MALDI-TOF, DNA hybridization and PCR have become preferred over biochemical tests for their more rapid and accurate identifications. This includes the identification and diagnosis of antibiotic resistant strains.

<span class="mw-page-title-main">Georg Peters</span> German physician

Georg Peters was a German physician, microbiologist and university professor. From 1992 until his fatal mountain accident he headed the Institute of Medical Microbiology at the University of Münster. He was an internationally recognised expert in the field of staphylococci and the infectious diseases caused by them, to which he had devoted himself since the beginning of his scientific career.

References

  1. ↑ Rudden, Michelle; Herman, Reyme; Rose, Matthew; Bawdon, Daniel; Cox, Diana S.; Dodson, Eleanor; Holden, Matthew T.G.; Wilkinson, Anthony J.; James, A. Gordon; Thomas, Gavin H. (2020). "The molecular basis of thioalcohol production in human body odour". Scientific Reports. 10 (1): 12500. Bibcode:2020NatSR..1012500R. doi: 10.1038/s41598-020-68860-z . PMC   7385124 . PMID   32719469.
  2. ↑ Society for General Microbiology (30 March 2015). "Bacterial genetic pathway involved in body odor production discovered". ScienceDaily (Press release).
  3. 1 2 3 4 Kloos, W. E.; George, C. G.; Olgiate, J. S.; Van Pelt, L.; McKinnon, M. L.; Zimmer, B. L.; Muller, E.; Weinstein, M. P.; Mirrett, S. (1 July 1998). "Staphylococcus hominis subsp. novobiosepticus subsp. nov., a novel trehalose- and N-acetyl-D-glucosamine-negative, novobiocin- and multiple-antibiotic-resistant subspecies isolated from human blood cultures". International Journal of Systematic Bacteriology. 48 (3): 799–812. doi: 10.1099/00207713-48-3-799 . PMID   9734034.
  4. 1 2 3 Kloos, W. E.; Schleifer, K. H. (1 January 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 .
  5. ↑ Fitzgibbon, Joseph E; Nahvi, Massoumeh D; Dubin, Donald T; John, Joseph F (November 2001). "A sequence variant of Staphylococcus hominis with a high prevalence of oxacillin and fluoroquinolone resistance". Research in Microbiology. 152 (9): 805–810. doi: 10.1016/s0923-2508(01)01264-5 . PMID   11763241.
  6. 1 2 Palazzo, I. C. V.; d'Azevedo, P. A.; Secchi, C.; Pignatari, A. C. C.; Darini, A. L. d. C. (10 September 2008). "Staphylococcus hominis subsp. novobiosepticus strains causing nosocomial bloodstream infection in Brazil". Journal of Antimicrobial Chemotherapy. 62 (6): 1222–1226. doi: 10.1093/jac/dkn375 . PMID   18775890.
  7. ↑ Chaves, Fernando; García-Álvarez, Mónica; Sanz, Francisca; Alba, Concepción; Otero, Joaquín R. (September 2005). "Nosocomial Spread of a Staphylococcus hominis subsp. novobiosepticus Strain Causing Sepsis in a Neonatal Intensive Care Unit". Journal of Clinical Microbiology. 43 (9): 4877–4879. doi:10.1128/JCM.43.9.4877-4879.2005. PMC   1234135 . PMID   16145165.
  8. ↑ Raab, Lauren (11 May 2015). "Mexico halts some vaccinations after 2 children die, 29 are hospitalized". Los Angeles Times.

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