Streptococcus pyogenes serotype-dependent and independent changes in infected HEp-2 epithelial cells

Abstract

The adherence, internalization and persistence of the human pathogen Streptococcus pyogenes (group A streptococci, GAS) to and within host cells were studied, and the induced responses of the infected epithelial cells were investigated. Next to common cellular responses on GAS infection, many responses of the infected HEp-2 epithelial cells are GAS serotype-specific. Moreover, several cellular responses do not correlate with the actual bacterial numbers adherent, internalized and persistent within the cells or the production of major cytolysins, as demonstrated for cytoskeletal pathways, cytokine release and apoptosis induction in infected cells. Measurement of activated caspases and caspase inhibition experiments uncovered activation of multiple caspase pathways by all GAS serotypes tested (M1, M3, M6 and M18). However, caspase 9 played a central role for M6 infections. During the persistence phase of the interaction, a differential and dynamic behavior of the infecting GAS serotype strains was found. After 14 h of host cell contact, all serotype strains caused host cell damage by virtually equal portions of apoptosis induction and necrosis mechanisms, as revealed by measurements of CK18Asp396/CK18 ratios. Between 14 and 24 h, persisting serotype M1 bacteria pertained this effect, whereas the serotype M6 GAS strain induced a major shift to necrotic mechanisms, and the serotype M3 and M18 GAS strains stimulated less necrosis, but shifted their host cells to apoptosis induction. Together, our study revealed that many cellular responses do not belong to general and uniform pathways, which are exploited by all GAS serotypes, explaining many of the already published discordant results.

SpyA, a C3-Like ADP-Ribosyltransferase, Contributes to Virulence in a Mouse Subcutaneous Model of Streptococcus pyogenes Infection

“…5). The overall rate of internalization was low but was consistent with previously published reports for M1 serotype strains (30). As with PMNs, cytotoxicity was monitored by assessing the amount of lactate dehydrogenase released from infected cells.…”

“…It has been demonstrated that GAS can enter epithelial cells (24,30,34,38,42,54), so we investigated whether or not SpyA affects bacterial entry into epithelial monolayers in vitro. HeLa cells were infected with wild-type or spyA mutant bacteria at a multiplicity of infection (MOI) of ϳ10:1, and association and internalization into these cells was measured.…”

“…An increase in the incidence of invasive infections beginning in the latter part of the 20th century has resulted in increased research into and identification of the organism's numerous virulence determinants. Though typically considered an extracellular pathogen, GAS have been shown to enter and survive intracellularly in macrophages (60), neutrophils (40,41), and epithelial cells (24,30,34,38,42,54).…”

Streptolysin S Contributes to Group A Streptococcal Translocation across an Epithelial Barrier

“…Over the past several decades, the molecular mechanisms underlying the adherence and internalization of GAS to epithelial cells as well as their intricate interactions have been extensively studied (8 -12). Although it was considered that most internalized GAS organisms are eliminated by intracellular killing, massive internalization or adherence of GAS preferentially induces programmed cell death of epithelial cells (13)(14)(15). These processes may lead to exposure of underlying tissues or cause damage to epithelium, providing GAS with a route to deeper tissues (intracellular route).…”

Group A Streptococcus translocates across an epithelial barrier via degradation of intercellular junctions

“…Whereas intracellular killing eliminates most internalized GAS pathogens, apoptosis of epithelial cells is preferentially induced by massive internalization or bacterial adherence of GAS [18][19][20]. In response to bacterial infections, apoptotic cell death can remove infected and damaged cells, thereby protecting the underlying tissues from bacterial replication and dissemination.…”