Staphylococcus aureus alpha-Toxin Effect on Acinetobacter baumannii Behavior

Simple Summary Polymicrobial infections, infections that are caused by more than one pathogen, are known to be responsible associated with high mortality rates. The bacterial organisms involved in these infections favor each other, resulting in pathogens' success. Our work examined the behavioral response of Acinetobacter baumannii after exposure to cell-free conditioned media of Staphylococcus aureus, two pathogens responsible for severe infections. We focus on the effect of alpha-toxin, the primary cytotoxic agent released by S. aureus, on A. baumannii's behavior. Results indicated that alpha-toxin contributes to the proliferation and survival of A. baumannii. One or more soluble molecules secreted by S. aureus can be sensed by A. baumannii and trigger diverse responses to adapt to environmental changes. The coexistence between bacteria can result in modifications in their general biology. Polymicrobial infections are more challenging to treat and are recognized as responsible for significant morbidity and mortality. It has been demonstrated that multiple Gram-negative organisms take advantage of the effects of Staphylococcus aureus alpha-toxin on mucosal host defense, resulting in proliferation and dissemination of the co-infecting pathogens. Through phenotypic approaches, we observed a decrease in the motility of A. baumannii A118 after exposure to cell-free conditioned media (CFCM) of S. aureus strains, USA300 and LS1. However, the motility of A. baumannii A118 was increased after exposure to the CFCM of S. aureus strains USA300 Delta hla and S. aureus LSI Delta agrA. Hemolytic activity was seen in A118, in the presence of CFCM of S. aureus LS1. Further, A. baumannii A118 showed an increase in biofilm formation and antibiotic resistance to tetracycline, in the presence of CFCM of S. aureus USA300. Transcriptomic analysis of A. baumannii A118, with the addition of CFCM from S. aureus USA300, was carried out to study A. baumannii response to S. aureus' released molecules. The RNA-seq data analysis showed a total of 463 differentially expressed genes, associated with a wide variety of functions, such as biofilm formation, virulence, and antibiotic susceptibility, among others. The present results showed that A. baumannii can sense and respond to molecules secreted by S. aureus. These findings demonstrate that A. baumannii may perceive and respond to changes in its environment; specifically, when in the presence of CFCM from S. aureus.