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Staphylococcus aureus Alpha-Toxin Is Conserved among Diverse Hospital Respiratory Isolates Collected from a Global Surveillance Study and Is Neutralized by Monoclonal Antibody MEDI4893

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ABSTRACT

Staphylococcus aureus infections lead to an array of illnesses ranging from mild skin infections to serious diseases, such endocarditis, osteomyelitis, and pneumonia. Alpha-toxin (Hla) is a pore-forming toxin, encoded by the hla gene, that is thought to play a key role in S. aureus pathogenesis. A monoclonal antibody targeting Hla, MEDI4893, is in clinical development for the prevention of S. aureus ventilator-associated pneumonia (VAP). The presence of the hla gene and Hla protein in 994 respiratory isolates collected from patients in 34 countries in Asia, Europe, the United States, Latin America, the Middle East, Africa, and Australia was determined. Hla levels were correlated with the geographic location, age of the subject, and length of stay in the hospital. hla gene sequence analysis was performed, and mutations were mapped to the Hla crystal structure. S. aureus supernatants containing Hla variants were tested for susceptibility or resistance to MEDI4893. The hla gene was present and Hla was expressed in 99.0% and 83.2% of the isolates, respectively, regardless of geographic region, hospital locale, or age of the subject. More methicillin-susceptible than methicillin-resistant isolates expressed Hla (86.9% versus 78.8%; P = 0.0007), and S. aureus isolates from pediatric patients expressed the largest amounts of Hla. Fifty-seven different Hla subtypes were identified, and 91% of the isolates encoded an Hla subtype that was neutralized by MED4893. This study demonstrates that Hla is conserved in diverse S. aureus isolates from around the world and is an attractive target for prophylactic monoclonal antibody (MAb) or vaccine development.

No MeSH data available.


Phylogenetic tree of alpha-toxin subtypes. The evolutionary distances of the different hla types were computed using the maximum composite likelihood method and are shown as the number of base substitutions per site. The analysis was performed on 984 full-length nucleotide sequences, as sequences that contained gaps or missing sequence were not included. There were a total of 941 positions in the final data set. Evolutionary analyses were conducted in MEGA5. The 3 major clades (C1, C2, and C3) are indicated at their respective branch points. Multilocus sequence typing analysis was performed using whole-genome sequence data from 10 hla gene-negative isolates, MLST assignment and allele usage are listed in the table, and the seven genes in the MLST schema are shown in the table headers. Concatenated MLST alleles from the 10 hla gene-negative isolates were used to construct a phylogenetic tree using the neighbor-joining method in MEGA5, and branch length values are indicated. SA ST, S. aureus sequence type.
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Figure 5: Phylogenetic tree of alpha-toxin subtypes. The evolutionary distances of the different hla types were computed using the maximum composite likelihood method and are shown as the number of base substitutions per site. The analysis was performed on 984 full-length nucleotide sequences, as sequences that contained gaps or missing sequence were not included. There were a total of 941 positions in the final data set. Evolutionary analyses were conducted in MEGA5. The 3 major clades (C1, C2, and C3) are indicated at their respective branch points. Multilocus sequence typing analysis was performed using whole-genome sequence data from 10 hla gene-negative isolates, MLST assignment and allele usage are listed in the table, and the seven genes in the MLST schema are shown in the table headers. Concatenated MLST alleles from the 10 hla gene-negative isolates were used to construct a phylogenetic tree using the neighbor-joining method in MEGA5, and branch length values are indicated. SA ST, S. aureus sequence type.

Mentions: Sequence analysis revealed 82 different amino acid substitutions compared to the USA300 reference strain, which corresponded to 57 distinct Hla subtypes (Table 2) that grouped into three distinct clades (Fig. 5). Forty-seven MSSA and 27 MRSA subtypes were identified (P < 0.0133), with 17 subtypes in common between MSSA and MRSA strains (Table 2). In addition to amino acid changes, 50 isolates had a stop codon and 13 had a frameshift mutation in the hla gene. The majority (42 of 47) of the isolates with the previously described Q113 stop codon (34, 35) were MSSA strains (Table 2). The 6 most abundant MRSA subtypes comprised 90% of the MRSA isolates, and the 6 most abundant MSSA subtypes comprised 79% of the MSSA isolates. For MRSA, 18 of 29 (62%) subtypes had less than 3 members, and for MSSA, 33 of 47 (70%) subtypes had less than 3 members. These data show that not only the presence of Hla, but also the protein sequence is highly conserved.


Staphylococcus aureus Alpha-Toxin Is Conserved among Diverse Hospital Respiratory Isolates Collected from a Global Surveillance Study and Is Neutralized by Monoclonal Antibody MEDI4893
Phylogenetic tree of alpha-toxin subtypes. The evolutionary distances of the different hla types were computed using the maximum composite likelihood method and are shown as the number of base substitutions per site. The analysis was performed on 984 full-length nucleotide sequences, as sequences that contained gaps or missing sequence were not included. There were a total of 941 positions in the final data set. Evolutionary analyses were conducted in MEGA5. The 3 major clades (C1, C2, and C3) are indicated at their respective branch points. Multilocus sequence typing analysis was performed using whole-genome sequence data from 10 hla gene-negative isolates, MLST assignment and allele usage are listed in the table, and the seven genes in the MLST schema are shown in the table headers. Concatenated MLST alleles from the 10 hla gene-negative isolates were used to construct a phylogenetic tree using the neighbor-joining method in MEGA5, and branch length values are indicated. SA ST, S. aureus sequence type.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 5: Phylogenetic tree of alpha-toxin subtypes. The evolutionary distances of the different hla types were computed using the maximum composite likelihood method and are shown as the number of base substitutions per site. The analysis was performed on 984 full-length nucleotide sequences, as sequences that contained gaps or missing sequence were not included. There were a total of 941 positions in the final data set. Evolutionary analyses were conducted in MEGA5. The 3 major clades (C1, C2, and C3) are indicated at their respective branch points. Multilocus sequence typing analysis was performed using whole-genome sequence data from 10 hla gene-negative isolates, MLST assignment and allele usage are listed in the table, and the seven genes in the MLST schema are shown in the table headers. Concatenated MLST alleles from the 10 hla gene-negative isolates were used to construct a phylogenetic tree using the neighbor-joining method in MEGA5, and branch length values are indicated. SA ST, S. aureus sequence type.
Mentions: Sequence analysis revealed 82 different amino acid substitutions compared to the USA300 reference strain, which corresponded to 57 distinct Hla subtypes (Table 2) that grouped into three distinct clades (Fig. 5). Forty-seven MSSA and 27 MRSA subtypes were identified (P < 0.0133), with 17 subtypes in common between MSSA and MRSA strains (Table 2). In addition to amino acid changes, 50 isolates had a stop codon and 13 had a frameshift mutation in the hla gene. The majority (42 of 47) of the isolates with the previously described Q113 stop codon (34, 35) were MSSA strains (Table 2). The 6 most abundant MRSA subtypes comprised 90% of the MRSA isolates, and the 6 most abundant MSSA subtypes comprised 79% of the MSSA isolates. For MRSA, 18 of 29 (62%) subtypes had less than 3 members, and for MSSA, 33 of 47 (70%) subtypes had less than 3 members. These data show that not only the presence of Hla, but also the protein sequence is highly conserved.

View Article: PubMed Central - PubMed

ABSTRACT

Staphylococcus aureus infections lead to an array of illnesses ranging from mild skin infections to serious diseases, such endocarditis, osteomyelitis, and pneumonia. Alpha-toxin (Hla) is a pore-forming toxin, encoded by the hla gene, that is thought to play a key role in S. aureus pathogenesis. A monoclonal antibody targeting Hla, MEDI4893, is in clinical development for the prevention of S. aureus ventilator-associated pneumonia (VAP). The presence of the hla gene and Hla protein in 994 respiratory isolates collected from patients in 34 countries in Asia, Europe, the United States, Latin America, the Middle East, Africa, and Australia was determined. Hla levels were correlated with the geographic location, age of the subject, and length of stay in the hospital. hla gene sequence analysis was performed, and mutations were mapped to the Hla crystal structure. S. aureus supernatants containing Hla variants were tested for susceptibility or resistance to MEDI4893. The hla gene was present and Hla was expressed in 99.0% and 83.2% of the isolates, respectively, regardless of geographic region, hospital locale, or age of the subject. More methicillin-susceptible than methicillin-resistant isolates expressed Hla (86.9% versus 78.8%; P = 0.0007), and S. aureus isolates from pediatric patients expressed the largest amounts of Hla. Fifty-seven different Hla subtypes were identified, and 91% of the isolates encoded an Hla subtype that was neutralized by MED4893. This study demonstrates that Hla is conserved in diverse S. aureus isolates from around the world and is an attractive target for prophylactic monoclonal antibody (MAb) or vaccine development.

No MeSH data available.