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.

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. MethodsThis 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. ResultsA 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. ConclusionThis 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.

S. aureus accounts for approximately 80,000 infections every year, resulting in 11,000 deaths. While antibiotic resistance has been researched heavily, antibiotic tolerance has not. Persister cells are dormant like cells that are tolerant to antibiotic treatment. Persister cells could be the cause of many chronic and relapsing infections. Recent experiments have shown central metabolism is a critical component of persister cell formation. Results suggest that interruptions in the tricarboxylic acid (TCA) cycle increase persister cell formation. While many studies have been performed concerning the mechanism of formation of persister cells, few have been done to analyze how persister cells react in in vivo models or against aspects of the innate immune system. Antimicrobial peptides (AMPs) are a key component of the innate immune system. Challenging wild type S. aureus with AMPs, LL-37 and hBD-3, showed several logs of killing. Interruption of the TCA cycle (fumC) resulted in 100-fold more surviving cells compared to wild type. Following infection in Drosophila melanogaster, the fumC knockout exhibited increased survival. Furthermore, D. melanogaster that were infected with fumC had reduced survival. Interruption of the TCA cycle also led to increased survival within a macrophage suggesting persister cells represent a multifaceted problem for the immune system. These data suggest that persisters not only present a challenge during antimicrobial therapy but also for the innate immune system.

Staphylococcus aureus is known for its ability to cause chronic reoccurring infections in clinical settings. The organism’s ability to thrive despite antibiotic treatment has led to the severity of disease that is often exhibited with these infections. It has been hypothesized that energy-dependent persister formation leads to antibiotic tolerance in S. aureus. Persister cells are a dormant-like phenotypic variant of S. aureus that resemble cells growing in stationary phase. Previously, it was shown that a knockout in the tricarboxylic acid (TCA) cycle gene, fumC, which reduced intracellular ATP, led to an increase in the number of persisters. While persisters have been examined in relationship to antibiotic tolerance, it is currently unknown how persisters interact with the innate immune system. Considering a vast amount of chronic reoccurring infections in a clinical environment involve a biofilm, persisters were examined in a biofilm-associated catheter infection within a mouse. Following a 9 day infection, the fumC knockout exhibited increased survival within the tissue surrounding the catheter and within the heart compared to wild type S. aureus. Fluorescent activated cell sorting (FACS) analysis revealed similar recruitment of M1 and M2 macrophages, as well as neutrophils, suggesting there was not a difference in immunogenicity between the two strains. The fumC knockout exhibited increased survival compared to wild type S. aureus within a macrophage demonstrating persisters are better equipped to tolerate the innate immune system. These results indicate persisters are not only a problem with antibiotic treatment but are also better suited to survive the host’s immune system leading to increased survival within a host.