A Microbial Biorealm page on the genus Staphylococcus haemolyticus
Higher order taxa
Bacteria; Firmicutes; Bacilli; Bacillales; Staphylococcaceae; Staphylococcus
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).
Lacking coagulase, an enzyme-like protein that was traditionally associated with virulent potential of staphylococci, 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 opportunistic 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). 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 antibiotic 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), which might be responsible for the frequent genomic arrangements observed in this organism (4)
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 (3).
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 (3). However, the study also found a region on the chromosome that is unique for each of the 3 organisms. This region, located near the chromosome origin of replication (oriC), is therefore 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 (3). On the other hand, the region is most likely responsible for the diversification of staphylococci species and enables the bacteria to successfully colonize and infect the human host (3).
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) (3). These 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 (3).
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 (3). However, it is the ability of S.haemolyticus to alter its genome content and to acquire resistance to antibiotics that makes the species a remarkable and hard-to-control opportunistic pathogen.
Cell structure and metabolism
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 that interfere with the peptidoglycan biosynthesis process. However, some strains S.haemolyticus have developed resistance to glycopeptide antibiotics such as teicoplanin and vancomycin (5, 13). This is an ability that is unique among staphylococci (5). The peptidoglycan structure of S.haemolyticus has been studied (5) to find out the factors responsible to this special resistance.
Like those 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. In the resistant strains, studies have found cross bridges that contain an additional serine in place of glycine (so the cross bridge structures are COOH-Gly-Ser-Ser-Gly-Gly-NH2 and COOH-Ala-Gly-Ser-Ser-Gly-NH2) (5). Furthermore, the presence of a novel cytoplasmic peptidoglycan precursor, UDP-muramyl-tetrapeptide-D-lactate, has been detected in strains of S.haemolyticus (5). 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).
Whole-genome sequencing of S.haemolyticus (strain JCSC1435) revealed some orfs encoding metabolic genes unique to the species, such as those involved in transport of ribose and ribitol or biosynthesis of essential components of nucleic acids and cell wall techoic acids (3). Thanks to these unique orfs, S.haemolyticus has a relative great biosynthetic capacity. Strain JCSC1435 only requires arginine for growth, while the S.aureus strain N315 requires the availability of many different amino acids: alanine, glycine, isoleucine, arginine, valine and proline (3).
S.haemolyticus (strain JCSC1435) also possesses the ability to ferment mannitol, a metabolic characteristic also found in some other “non-aureus” staphylococci (3). However, genetic analysis suggested that certain strains of S.haemolyticus might have gained this ability through horizontal gene transfer of the mannitol PTS locus from other bacterial species (3). This is another example demonstrating the flexibility of S.haemolyticus genome.
Staphylococcus haemolyticus can be found on the skin and in the bodies of a wide range of mammals, including prosimians, monkeys, domestic animals, and human (1). The most common natural habitats of the bacteria on human are in the axillae (underarm area), in the perineum (pubic area), and in the inguinal area (1). S.haemolyticus survive successfully on the drier regions of the body (1), while it can also be found frequently in human blood cultures (3).
It has been known that S.haemolyticus produces gonococcal growth inhibitor, GGI (1). The substance was first discovered to cause cytoplasmic leakage in gonococcal cells and eventually lead to cell death (1,6). Remarkably, this substance can also lyse erythrocytes, especially those of horse and human (6).
Staphylococci in general cause disease through their ability to spread widely in tissues and their production of extracellular substances (7). One example of such substances is coagulase, an enzyme-like protein produced by S.aureus that may deposit fibrin on the surface of the bacteria, altering their ingestion and destruction by phagocytic cells (7).
Traditionally, production of coagulase is considered to represent the invasive pathogenic potential among staphylococci (7). S.haemolyticus, however, is a coagulase-negative species. Therefore, like other non-aureus staphylococci, its pathogenic characters were not well-studied until recently, when S.haemolyticus started emerging as a major cause of nosocomial infections (infections acquired during treatment at a hospital for another disease). Reported cases of infections caused by S.haemolyticus include septicemia (dysfunction of organ systems resulting from immune response to a severe infection), peritonitis (inflammation of the serous membrane lining abdominal cavity), and infections of urinary tract, wound, bone and joints (1). In rare cases, S.haemolyticus has also been reported to cause infective endocarditis, inflammation of the heart (the endocardium), which might lead to severe complications such as heart failure or death (2). Common clinical symptoms of a S.haemolyticus infection are fever and an increase in white blood cell population (leukocytosis) (2).
Being the most common pathogen among staphylococci, virulent factors of S.aureus have been well-known. Important among them are different classes of enterotoxin (toxins released in lower-intestine, causing food poisoning), toxic shock syndrome toxin, and hemolysin (substances that allow the bacteria to break down red-blood cells) (8). Some of these substances used to be considered to belong exclusively to S.aureus, but have been recently discovered in the other non-aureus coagulase-negative staphylococci as well (1). In one study published in 1994, for example, all strains of S.haemolyticus under investigation produced hemolysins in vitro (9). Investigators therefore suggested that hemolysins might be the important factor responsible for the high virulence of this staphylococcus species (9).
S.haemolyticus’ GGI are related in function and characteristics to other relative staphylococci virulent factors, such as delta-lysin in S.aureus and SLUSH (Staphylococcus lugdunensis synergistic hemolysin) in S.lugdunensis, the latter of which shows significant similarities in structure with GGI (1). These findings suggest a connection between pathogenesis pathways and virulent factors of common staphylococcal pathogens.
Application to Biotechnology
Staphylococcus haemolyticus, together with its related staphylococci like S.aureus and S.epidermis, possesses a class of lipase enzymes, that are involved in the hydrolysis process of long chain triacylglycerons (10). Thanks to the enzymes’ uniquely useful properties such as chain length selectivity and chiral selectivity, they are widely used in the industrial production and synthesis of fatty acids, fats, oils, esters and peptides (10).
A close relative of S.haemolyticus, the coagulase-negative Staphylococcus xylosus, has been used to construct a host-vector system that can express recombinant proteins on the surface of the bacterial cell (11). It was the first time such a system could be constructed in a Gram-positive species. This technique greatly facilitates the study of receptors, substrate-binding proteins and other antigenic determinants expressed on the surface of bacteria (11).
Although Staphylococcus haemolyticus is relatively less virulent than some other staphylococci such as S.aureus, the ability of the species to acquire multi-antibiotic resistance has made it a serious threat to worldwide health care facilities. Whole-genome sequencing of S.haemolyticus, carried out by a research group at Jutendo University in Tokyo, Japan and led by Dr. Keiichi Hiramatsu (3), is a very important and significant step in tackling this problem. The information provided by the genome sequence will not only allow further examinations of the species’ characteristic bacterial lifestyle, but also facilitates the “development of novel immunotherapeutic and chemotherapeutic approaches to control them” (3).
After discovering the presence of abundant IS copies in the chromosome as mentioned above (3), Dr. Hiramatsu’s group continues to examine the other types of genetic rearrangement that are also responsible for the frequent structural alteration of S.haemolyticus genome. Recent results have shed light on a new genetic shuffling mechanism of S.haemolyticus, in which “precise excision and self-integration of a composite transposon” (ISSha1) lead to a large-scale chromosome inversion/deletion found in the clinical strain JCSC1435 (12).
Beside genomic and genetic approaches, clinical investigations combined with molecular approaches are being carried out to find more effective strategies against the development of S.haemolyticus antibiotic-resistant strains. Studies are aiming at a promising strategy in which different types of antibiotics are used synergistically to fight against specific antibiotic-resistant strains. Some examples are the combination of glycopeptide and beta-lactams antibiotics against methicillin- and teicoplanin-resistant staphylococci strains, or the combination of vancomycin and beta-lactams antitbiotics (13).
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10. Oh, B., Kim, H., Lee, J., Kang, S. & Oh, T. Staphylococcus haemolyticus lipase: biochemical properties, substrate specificity and gene cloning. FEMS Microbiol. Lett. 179, 385-392 (1999).
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12. Watanabe, S., Ito, T., Morimoto, Y., Takeuchi, F. & Hiramatsu, K. Precise excision and self-integration of a composite transposon as a model for spontaneous large-scale chromosome inversion/deletion of the Staphylococcus haemolyticus clinical strain JCSC1435. J. Bacteriol. 189, 2921-2925 (2007).
13. Vignaroli, C., Biavasco, F. & Varaldo, P. E. Interactions between glycopeptides and beta-lactams against isogenic pairs of teicoplanin-susceptible and -resistant strains of Staphylococcus haemolyticus. Antimicrob. Agents Chemother. 50, 2577-2582 (2006).