Staphylococcus haemolyticus

From MicrobeWiki, the student-edited microbiology resource

A Microbial Biorealm page on the genus Staphylococcus haemolyticus

Classification

Higher order taxa

Bacteria; Firmicutes; Bacilli; Bacillales; Staphylococcaceae; Staphylococcus

Species

NCBI: Taxonomy

Staphylococcus haemolyticus

Description and significance

Staphylococus haemolyticus is a coagulase-negative member of the genus Staphylococcus. The bacteria can be found on normal human skin flora and can be isolated from axillae, perineum, and ingunial areas of humans. S.haemolyticus is also the second most common coagulase-negative staphylocci presenting in human blood.(1)

Coagulase-negative staphylococci are usually considered low-virulent pathogens comparing to the well-known pathogenic coagulase-positive Staphylococcus aureus. However, recent studies indicate that coagulase-negative staphylococci have emerged as a major cause of infection (2). Staphylococcus haemolyticus itself is also a remarkable opportunistic baterial pathogen that is well-known for its highly antibiotic-resistant phenotype (3). The bacteria can cause meningitis, skin or soft tissue infections, prosthetic join infections, or bacteremia (2). The ability of the bacteria to simultaneously resist against multiple types of antibiotic has been observed and studied for a long time.(2,4) Common antibiotics that are subject to resistance in S haemolyticus include methicillin, gentamycin, erythormycin, and uniquely among staphylococci, glycopeptide antibiotics.(2) The resistance genes for each type of anitbiotic can be located on the chromosome (methicillin), on the plasmids (erythromycin) or on both chromosome and plasmids (gentamycin)(4).

In order to study the multi-drug resistant ability of Staphylococcus haemolyticus and its pathogenic characters, researchers sequenced the whole genome of one strain, JCSC1435 (3). Beside the bacteria’s antibiotic resistance genes, the study of the sequence also revealed a surprising number of homologous insertion sequences (ISs). These sequences might be responsible for the frequent genomic arrangement observed in this organism.(4)

Genome structure

The genome of Staphylococcus haemolyticus (strain JCSC1435) includes a circular chromosome of 2,685,015 bp and 3 plasmids of 2,300 bp, 2,366 bp and 8,180 bp.

Comparative genomic analysis has revealed significant similarities between the genomes of S.haemolyticus and those of the other two well-known staphylococci, S.aureus and S.epidermis. Beside the comparable genome sizes, a large proportion of open reading frames (orfs) are conserved both in the sequences and in their order on the chromosome. However, the study also found a region on the chromosome that is unique for each of the 3 organisms. This region, which locate near the chromosome origin of replication (oriC), is called “oriC environ”. As most of the region could be deleted without affecting growth, it can be concluded that the oriC environ region does not contain genes essential for bacterial viability. On the other hand, the region is most likely responsible for the diversification of staphylococci species which enables them to successfully colonize and infect the human host.

Besides having the oriC environ region where rearrangements of the genome can take place frequently, S.haemolyticus also possess a surprisingly large number of insertion sequences (ISs). The ISs can either inactivate a gene by direct integration into the open reading frame or activate a gene by providing the gene with a potent promoter. By changing the content of the genome, the IS elements might contribute to the innate ability of the bacteria to acquire drug resistance.

While 6% of the orfs found in the more virulent S.aureus are pathogenic factors, only 2% of those found in S.haemolyticus are pathogenic factors. However, it is the ability of S.haemolyticus to alter its genome content and to acquire resistance to antibotics that makes the species a remarkable and hard-to-control opportunity pathogen.(3)

Cell structure and metabolism

Cell Wall

As a gram-positive species like other staphylococci, S.haemolyticus has a thick peptidoglycan wall outside of its membrane and therefore can be targeted by antibiotics interfering with the peptidoglycan biosynthesis process. However, some strains of S.haemolyticus have developed resistance to glycopeptide antibiotics such as teicoplanin and vancomycin. This is an ability that is unique among staphylococci. The structure of S.haemolyticus cell wall has been studied to find out the factors responsible to this special resistance.

Like that of other staphylococci, the peptidoglycan of S.haemolyticus is highly cross-linked. The predominant cross bridges are COOH-Gly-Gly-Ser-Gly-Gly-NH2 and COOH-Ala-Gly-Ser-Gly-Gly-NH2. Studies have found in resistant strains cross bridges that contain an additional serine in place of glycine (so the probable cross bridges structures are COOH-Gly-Ser-Ser-Gly-Gly-NH2 and COOH-Ala-Gly-Ser-Ser-Gly-NH2). Furthermore, the presence of a novel cystoplasmic peptidoglycan precursor, UDP-muramyl-tetrapeptide-D-lactate, has been detected in strains of S.haemolyticus. This precursor and the alterations of cross bridges are believed to interfere with the cooperative binding of glycopeptide antibiotics like vancomycin and teicoplanin to their targets in S.haemolyticus.(5)

Metabolism

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

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References

1. Brooks, G., Butel, J. & Morse, S. in Medical Microbiology 197-202 (McGraw-Hill, New York, 2001).

2. Falcone, M. et al. Staphylococcus haemolyticus endocarditis: clinical and microbiologic analysis of 4 cases. Diagn. Microbiol. Infect. Dis. 57, 325-331 (2007).

3. Takeuchi, F. et al. Whole-genome sequencing of staphylococcus haemolyticus uncovers the extreme plasticity of its genome and the evolution of human-colonizing staphylococcal species. J. Bacteriol. 187, 7292-7308 (2005).

4. Froggatt, J. W., Johnston, J. L., Galetto, D. W. & Archer, G. L. Antimicrobial resistance in nosocomial isolates of Staphylococcus haemolyticus. Antimicrob. Agents Chemother. 33, 460-466 (1989).

5. Billot-Klein, D. et al. Peptidoglycan synthesis and structure in Staphylococcus haemolyticus expressing increasing levels of resistance to glycopeptide antibiotics. J. Bacteriol. 178, 4696-4703 (1996).


Edited by Bao D. Truong, student of Rachel Larsen