Identification, Cloning, and Characterization of Staphylococcus pseudintermedius Coagulase

Description of extraintestinal pathogenic Escherichia coli based on phylogenetic grouping, virulence factors, and antimicrobial susceptibility

Background and Objectives

Extraintestinal pathogenic Escherichia coli (ExPEC) is a recently recognized and highly diverse pathotype of E. coli. Its significance as a pathogen has increased due to the emergence of hypervirulent and multidrug-resistant (MDR) strains. The aim of this study was to characterize ExPEC isolates from humans based on their phylogenetic group, virulence factor profile, and antimicrobial susceptibility.

Materials and Methods

The isolates were collected from patients with extraintestinal infections caused by E. coli, including urinary tract infections, bacteremia, and surgical site infections. The E. coli phylogenetic groups were determined using multiplex PCR. Additionally, the isolates were evaluated for their biofilm-forming abilities, susceptibility to antimicrobial agents, and presence of virulence genes.

Results

In this study, the isolates were classified into four phylogenetic groups: A (48.3%), B2 (25.8%), D (19.35%), and B1 (6.45%). All isolates exhibited at least one of the ten analyzed virulence factors. However, there was no direct evidence linking a specific phylogenetic group to a particular virulence factor. Nevertheless, the presence of the fimH, fyuA, ompT, traT, and kpsMTII virulence genes was correlated with the production of strong biofilms, multidrug resistance (MDR), and the production of alpha hemolysin.

Conclusion

This study provides a description of the phylogenetic groups in ExPEC and their potential association with virulence factor profiles and antimicrobial susceptibility.

Pathogenic potential and antimicrobial resistance of Staphylococcus pseudintermedius isolated from human and animals

Crossing of interspecies barriers by microorganisms is observed. In recent years, Staphylococcus pseudintermedius-a species formerly thought to be animal-has also been isolated from human clinical materials. Many virulence factors are responsible for the colonization, which is the first step an infection, of the new host organism. We analyzed the factors influencing this colonization as well as susceptibility to antibiotics in fourteen S. pseudintermedius strains isolated from clinical cases from humans and animals. The occurrence of genes responsible for binding elastin, fibronectin, and fibrinogen and some phenotypic features, although different between strains, is comparable in both groups. However, the animal isolates had more genes coding for virulence factors. All isolates tested had the exfoliating toxin gene and the leukotoxin determining genes, but only the human strains had enterotoxin genes. The assessment of antibiotic resistance of strains of both groups indicates their broad resistance to antibiotics commonly used in veterinary medicine. Antibiotic resistance was more common among animal isolates. The multilocus sequence typing analysis of the studied strains was performed. The results indicated a large diversity of the S. pseudintermedius population in both studied groups of strains. Equipped with important virulence factors, they showed the ability to infect animals and humans. The clonal differentiation of the methicillin-susceptible strains and the multidrug resistance of the strains of both studied groups should be emphasized. The considerable genetic diversity of strains from a limited geographical area indicates the processes of change taking place within this species. Thus, careful observation of the ongoing process of variation is necessary, as they may lead to the selection of S. pseudintermedius, which will pose a significant threat to humans.

Evolutionary and Functional Analysis of Coagulase Positivity among the Staphylococci

The bacterial genus Staphylococcus comprises a large group of pathogenic and nonpathogenic species associated with an array of host species. Staphylococci are differentiated into coagulase-positive or coagulase-negative groups based on the capacity to promote clotting of plasma, a phenotype historically associated with the ability to cause disease. However, the genetic basis of this important diagnostic and pathogenic trait across the genus has not been examined to date. Here, we selected 54 representative staphylococcal species and subspecies to examine coagulation of plasma derived from six representative host species. In total, 13 staphylococcal species mediated coagulation of plasma from at least one host species including one previously identified as coagulase negative (Staphylococcus condimenti). Comparative genomic analysis revealed that coagulase activity correlated with the presence of a gene (vwb) encoding the von Willebrand binding protein (vWbp) whereas only the Staphylococcus aureus complex contained a gene encoding staphylocoagulase (Coa), the classical mediator of coagulation. Importantly, S. aureus retained vwb-dependent coagulase activity in an S. aureus strain deleted for coa whereas deletion of vwb in Staphylococcus pseudintermedius resulted in loss of coagulase activity. Whole-genome-based phylogenetic reconstruction of the Staphylococcus genus revealed that the vwb gene has been acquired on at least four different occasions during the evolution of the Staphylococcus genus followed by allelic diversification via mutation and recombination. Allelic variants of vWbp from selected coagulase-positive staphylococci mediated coagulation in a host-dependent manner indicative of host-adaptive evolution. Taken together, we have determined the genetic and evolutionary basis of staphylococcal coagulation, revealing vWbp to be its archetypal determinant. IMPORTANCE The ability of some species of staphylococci to promote coagulation of plasma is a key pathogenic and diagnostic trait. Here, we provide a comprehensive analysis of the coagulase positivity of the staphylococci and its evolutionary genetic basis. We demonstrate that the von Willebrand binding protein rather than staphylocoagulase is the archetypal coagulation factor of the staphylococci and that the vwb gene has been acquired several times independently during the evolution of the staphylococci. Subsequently, vwb has undergone adaptive diversification to facilitate host-specific functionality. Our findings provide important insights into the evolution of pathogenicity among the staphylococci and the genetic basis for a defining diagnostic phenotype.

Methicillin-resistant Staphylococcus pseudintermedius synthesizes deoxyadenosine to cause persistent infection

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) is an emerging zoonotic pathogen of canine origin that causes an array of fatal diseases, including bacteremia and endocarditis. Despite large-scale genome sequencing projects have gained substantial insights into the genomic landscape of MRSP, current knowledge on virulence determinants that contribute to S. pseudintermedius pathogenesis during human or canine infection is very limited. Using a panel of genetically engineered MRSP variants and a mouse abscess model, we here identified the major secreted nuclease of S. pseudintermedius designated NucB and adenosine synthase A (AdsA) as two synergistically acting enzymes required for MRSP pathogenesis. Similar to Staphylococcus aureus, S. pseudintermedius requires nuclease secretion along with the activity of AdsA to degrade mammalian DNA for subsequent biosynthesis of cytotoxic deoxyadenosine. In this manner, S. pseudintermedius selectively kills macrophages during abscess formation thereby antagonizing crucial host immune cell responses. Ultimately, bioinformatics analyses revealed that NucB and AdsA are widespread in the global S. pseudintermedius population. Together, these data suggest that S. pseudintermedius deploys the canonical Nuc/AdsA pathway to persist during invasive disease and may aid in the development of new therapeutic strategies to combat infections caused by MRSP.

Identification, cloning and characterization of SpEX exotoxin produced by Staphylococcus pseudintermedius

Staphylococci have evolved numerous strategies to evade their hosts’ immune systems. Some staphylococcal toxins target essential components of host innate immunity, one of the two main branches of the immune system. Analysis of the Staphylococcus pseudintermedius secretome using liquid chromatography mass spectrometry guided by genomic data, was used to identify an S. pseudintermedius exotoxin provisionally named SpEX. This exoprotein has low overall amino acid identity with the Staphylococcus aureus group of proteins named staphylococcal superantigen like proteins (SSLs) and staphylococcal enterotoxin- like toxin X (SEIX), but predictive modeling showed that it shares similar folds and domain architecture to these important virulence factors. In this study, we found SpEX binds to complement component C5, prevents complement mediated lysis of sensitized bovine red blood cells, kills polymorphonuclear leukocytes and monocytes and inhibits neutrophil migration at sub-lethal concentrations. A mutant version of SpEX, produced through amino acid substitution at selected positions, had diminished cytotoxicity. Anti-SpEX produced in dogs reduced the inhibitory effect of native SpEX on canine neutrophil migration and protected immune cells from the toxic effects of the native recombinant protein. These results suggest that SpEX likely plays an important role in S. pseudintermedius virulence and that attenuated SpEX may be an important candidate for inclusion in a vaccine against S. pseudintermedius infections.

Staphylococcus pseudintermedius Sbi paralogs inhibit complement and bind IgM, IgG Fc and Fab

The success of staphylococci as pathogens has been attributed, in part, to their ability to evade their hosts’ immune systems. Although the proteins involved in evasion have been extensively studied in staphylococci affecting humans little characterization has been done with Staphylococcus pseudintermedius, an important cause of pyoderma in dogs. Staphylococcus aureus binder of immunoglobulin (Sbi) interferes with innate immune recognition by interacting with multiple host proteins. In this study, a S. pseudintermedius gene that shares 38% similarity to S. aureus Sbi was cloned from S. pseudintermedius strains representative of major clonal lineages bearing two paralogs of the protein. Binding of immunoglobulins and Fab and Fc fragments as well as interaction with complement was measured. S. pseudintermedius Sbi protein bound IgG from multiple species and canine complement C3, neutralized complement activity and bound to canine IgM and B cells. Evidence from this work suggests Sbi may play an important role in S. pseudintermedius immune evasion.