The Opp (AmiACDEF) Oligopeptide Transporter Mediates Resistance of Serotype 2 Streptococcus pneumoniae D39 to Killing by Chemokine CXCL10 and Other Antimicrobial Peptides

Abstract

Antimicrobial peptides (AMPs), including chemokines, are produced during infections to kill pathogenic bacteria. To fill in gaps in knowledge about the sensitivities of and related species to chemokines and AMPs, we performed a systematic, quantitative study of inhibition by chemokine CXCL10 and the AMPs LL-37 and nisin. In a standard Tris-glucose buffer (TGS), all strains assayed lacked metabolic activity, as determined by resazurin (alamarBlue) reduction, and were extremely sensitive to CXCL10 and AMPs (50% inhibitory concentration [IC], ∼0.04 μM). In TGS, changes in sensitivities caused by mutations were undetectable. In contrast, strains that retained reductive metabolic activity in a different assay buffer (NPB [10 mM sodium phosphate {pH 7.4}, 1% {vol/vol} brain heart infusion {BHI} broth]) were less sensitive to CXCL10 and AMPs than in TGS. In NPB, mutants known to respond to AMPs, such as Δ mutants lacking d-alanylation of teichoic acids, exhibited the expected increased sensitivity. serotype 2 strain D39 was much (∼10-fold) less sensitive to CXCL10 killing in NPB than serotype 4 strain TIGR4, and the sensitivity of TIGR4 was unaffected by the absence of capsule. Candidate screening of strain D39 revealed that mutants lacking Opp (Δ) oligopeptide permease were significantly more resistant to CXCL10 than the wild-type strain. This increased resistance could indicate that Opp is a target for CXCL10 binding or that it transports CXCL10 into cells. Finally, Δ or Δ mutants of or amino acid changes that interfere with FtsX function in did not impart resistance to CXCL10, in contrast to previous results for , indicating that FtsX is not a general target for CXCL10 binding. (pneumococcus) is a human commensal bacterium and major opportunistic respiratory pathogen that causes serious invasive diseases, killing millions of people worldwide annually. Because of its increasing antibiotic resistance, is now listed as a "superbug" for which new antibiotics are urgently needed. This report fills in knowledge gaps and resolves inconsistencies in the scientific literature about the sensitivity of and related pathogens to chemokines and AMPs. It also reveals a new mechanism by which can acquire resistance to chemokine CXCL10. This mechanism involves the Opp (AmiACDEF) oligopeptide transporter, which plays additional pleiotropic roles in pneumococcal physiology, quorum sensing, and virulence. Taking the results together, this work provides new information about the way chemokines kill pneumococcal cells.

An in vivo atlas of host–pathogen transcriptomes during Streptococcus pneumoniae colonization and disease

“…These genes encode ZmpB, endopeptidase PepO, manganese transporter PsaB, and AmiA. Our results with these mutants agree with studies that have previously linked these proteins to Spn pathogenicity ( 24 , 33 – 35 ). Importantly, experiments performed with this panel of mutants in vitro found that only PsaB and AmiA were essential for growth in media, thus the requirement for the remainder of proteins was specific to the in vivo condition ( Fig.…”

“…Our results with these mutants agree with studies that have previously linked these proteins to Spn pathogenicity (24,(33)(34)(35).…”

“…5 B and C ). While many of these shared genes were housekeeping genes (cell division, translation, and so forth), two were previously studied potential vaccine candidates—lactoferricin-resistance associated PspA and zinc metalloprotease ZmpB ( 22 , 23 )—and another was an oligopeptide transporter operon ( amiACDEF ) shown to have relevance to nasopharyngeal colonization ( 24 ). The two vaccine candidates and genes amiA , amiC , and amiD were also shown to be essential for TIGR4 lung survival in vivo in the signature tagged mutagenesis study ( 10 ).…”

Molecular Identification and Dual Functions of Two Different CXC Chemokines in Nile Tilapia (Oreochromis niloticus) against Streptococcus agalactiae and Flavobacterium columnare

“…However, the differences in mechanism of action on Gram-positive and -negative bacteria of these Nile tilapia CXC chemokines are still not clear. Based on current information, the defense mechanism of Gram-positive bacteria may protect against AMPs by increasing the positive charge of the bacterial cell surface through the addition of D-alanine to wall teichoic and lipoteichoic acids [ 66 , 67 , 68 ], while the extracellular membranes of Gram-negative bacteria contain a layer of lipopolysaccharide (LPS), which imparts a strongly negative charge. In addition, cationic AMPs can bind to LPS, causing cell membrane damage, lysis and death [ 69 ].…”

The Potential of Human Peptide LL-37 as an Antimicrobial and Anti-Biofilm Agent

“…Upon binding, the introduction of transmembrane pores causes a disruption of cell integrity that leads to cell lysis and death. In addition, LL-37 is able to permeate the cell membrane in order to interact with intracellular targets, such as acyl carrier proteins [12,13]. LL-37 has additional immunomodulatory properties, including both pro-inflammatory and anti-inflammatory responses, that are important for the indirect killing of bacteria.…”