Staphylococcus aureus persisters are associated with reduced clearance in a catheter-associated biofilm infection.

Background: Staphylococcus aureus causes a wide variety of infections, many of which are chronic or relapsing in nature. Antibiotic therapy is often ineffective against S. aureus biofilm-mediated infections. Biofilms are difficult to treat partly due to their tolerance to antibiotics, however the underlying mechanism responsible for this remains unknown. One possible explanation is the presence of persister cells-dormant-like cells that exhibit tolerance to antibiotics. Recent studies have shown a connection between a fumC (fumarase C, a gene in the tricarboxylic acid cycle) knockout strain and increased survival to antibiotics, antimicrobial peptides, and in a Drosophila melanogaster model. Objective: It remained unclear whether a S. aureus high persister strain would have a survival advantage in the presence of innate and adaptive immunity. To further investigate this, a fumC knockout and wild type strains were examined in a murine catheter-associated biofilm model. Results: Interestingly, mice struggled to clear both S. aureus wild type and the fumC knockout strains. We reasoned both biofilm-mediated infections predominantly consisted of persister cells. To determine the persister cell population within biofilms, expression of a persister cell marker (Pcap5A::dsRED) in a biofilm was examined. Cell sorting of biofilms challenged with antibiotics revealed cells with intermediate and high expression of cap5A had 5.9-and 4.5-fold higher percent survival compared to cells with low cap5A expression. Based on previous findings that persisters are associated with reduced membrane potential, flow cytometry analysis was used to examine the metabolic state of cells within a biofilm. We confirmed cells within biofilms had reduced membrane potential compared to both stationary phase cultures (2.5-fold) and exponential phase cultures (22.4-fold). Supporting these findings, cells within a biofilm still exhibited tolerance to antibiotic challenge following dispersal of the matrix through proteinase K. Conclusion: Collectively, these data show that biofilms are largely comprised of persister cells, and this may explain why biofilm infections are often chronic and/or relapsing in clinical settings.

Hardware Infection From Surgical Stabilization of Rib Fractures Is Lower Than Previously Reported.

Introduction Surgical stabilization of rib fractures (SSRF) is an emerging therapy for the treatment of patients with traumatic rib fractures. Despite the demonstrated benefits of SSRF, there remains a paucity of literature regarding the complications from SSRF, especially those related to hardware infection. Currently, literature quotes hardware infection rates as high as 4%. We hypothesize that the hardware infection rate is much lower than currently published. Methods This is an IRB-approved, four-year multicenter descriptive review of prospectively collected data from January 2016 to June 2022. All patients undergoing SSRF were included in the study. Exclusion criteria included those patients less that 18 years of age. Basic demographics were obtained: age, gender, Injury Severity Score (ISS), Abbreviate Injury Scale-chest (AIS-chest), flail chest (yes/no), delayed SSRF more than two weeks (yes/no), number of patients with a pre-SSRF chest tube, and number of ribs fixated. Primary outcome was hardware infection. Secondary outcomes included mortality rate and hospital length of stay (HLOS). Basic descriptive statistics were utilized for analysis. Results A total of 453 patients met criteria for inclusion in the study. Mean age was 63 ± 15.2 years and 71% were male. Mean ISS was 17.3 ± 8.5 with a mean AIS-chest of 3.2 ± 0.5. Flail chest (three consecutive ribs with two or more fractures on each rib) accounted for 32% of patients. Forty-two patients (9.3%) underwent delayed SSRF. The average number of ribs stabilized was 4.75 ± 0.71. When analyzing the primary outcome, only two patients (0.4%) developed a hardware infection requiring reoperation to remove the plates. Overall HLOS was 10.5 ± 6.8 days. Five patients suffered a mortality (1.1%), all five with ISS scores higher than 15 suggesting significant polytrauma. Conclusion This is the largest case series to date examining SSRF hardware infection. The incidence of SSRF hardware infection is very low (<0.5%), much less than quoted in current literature. Overall, SSRF is a safe procedure with low morbidity and mortality.

Polymicrobial Interactions Induce Multidrug Tolerance in Staphylococcus aureus Through Energy Depletion.

Staphylococcus aureus is responsible for a high number of relapsing infections, which are often mediated by the protective nature of biofilms. Polymicrobial biofilms appear to be more tolerant to antibiotic treatment, however, the underlying mechanisms for this remain unclear. Polymicrobial biofilm and planktonic cultures formed by S. aureus and Candida albicans are 10- to 100-fold more tolerant to oxacillin, vancomycin, ciprofloxacin, delafloxacin, and rifampicin compared to monocultures of S. aureus. The possibility of C. albicans matrix components physically blocking antibiotic molecules from reaching S. aureus was ruled out as oxacillin, ciprofloxacin, delafloxacin, and rifampicin were able to diffuse through polymicrobial biofilms. Based on previous findings that S. aureus forms drug tolerant persister cells through ATP depletion, we examined nutrient deprivation by determining glucose availability, which indirectly correlates to ATP production via the tricarboxylic acid (TCA) cycle. Using an extracellular glucose assay, we confirmed that S. aureus and C. albicans polymicrobial cultures depleted available glucose faster than the respective monocultures. Supporting this finding, S. aureus exhibited decreased TCA cycle activity, specifically fumarase expression, when grown in the presence of C. albicans. In addition, S. aureus grown in polymicrobial cultures displayed 2.2-fold more cells with low membrane potential and a 13% reduction in intracellular ATP concentrations than in monocultures. Collectively, these data demonstrate that decreased metabolic activity through nutrient deprivation is a mechanism for increased antibiotic tolerance within polymicrobial cultures.