Clostridioides difficile infection is associated with differences in transcriptionally active microbial communities

Clostridioides difficile infection (CDI) is responsible for around 300,000 hospitalizations yearly in the United States, with the associated monetary cost being billions of dollars. Gut microbiome dysbiosis is known to be important to CDI. To the best of our knowledge, metatranscriptomics (MT) has only been used to characterize gut microbiome composition and function in one prior study involving CDI patients. Therefore, we utilized MT to investigate differences in active community diversity and composition between CDI+ (n = 20) and CDI- (n = 19) samples with respect to microbial taxa and expressed genes. No significant (Kruskal-Wallis, p > 0.05) differences were detected for richness or evenness based on CDI status. However, clustering based on CDI status was significant for both active microbial taxa and expressed genes datasets (PERMANOVA, p ≤ 0.05). Furthermore, differential feature analysis revealed greater expression of the opportunistic pathogens Enterocloster bolteae and Ruminococcus gnavus in CDI+ compared to CDI- samples. When only fungal sequences were considered, the family Saccharomycetaceae expressed more genes in CDI-, while 31 other fungal taxa were identified as significantly (Kruskal-Wallis p ≤ 0.05, log(LDA) ≥ 2) associated with CDI+. We also detected a variety of genes and pathways that differed significantly (Kruskal-Wallis p ≤ 0.05, log(LDA) ≥ 2) based on CDI status. Notably, differential genes associated with biofilm formation were expressed by C. difficile. This provides evidence of another possible contributor to C. difficile's resistance to antibiotics and frequent recurrence in vivo. Furthermore, the greater number of CDI+ associated fungal taxa constitute additional evidence that the mycobiome is important to CDI pathogenesis. Future work will focus on establishing if C. difficile is actively producing biofilms during infection and if any specific fungal taxa are particularly influential in CDI.

The impact of existing total anti-toxin B IgG immunity in outcomes of recurrent Clostridioides difficile infection

Late anti-toxin-B humoral immunity acquired after treatment is important for preventing recurrent Clostridioides difficile infection. We prospectively-measured anti-toxin-B IgG and neutralization titers at diagnosis as potential early predictors of recurrence. High anti-toxin-B-IgG/neutralizing antibodies were associated with short-lasting protection within 6-weeks, however, no difference in recurrence risk was observed by 90-days post-infection.

Systemic neutrophil degranulation and emergency granulopoiesis in patients with Clostridioides difficile infection

OBJECTIVES

Clostridioides difficile infection (CDI) is characterized by neutrophilia in blood, with a high leukocyte count accompanying severe infection. In this study, we characterized peripheral blood neutrophil activation and maturity in CDI by (i) developing a method to phenotype stored neutrophils for disease-related developmental alterations and (ii) assessing neutrophil-associated biomarkers.

METHODS

We stored fixed leukocytes from blood collected within 24 h of diagnosis from a cohort of hospitalized patients with acute CDI. Additional study cohorts included recurrent CDI patients at time of and two months after FMT therapy and a control healthy cohort. We assessed levels of neutrophil surface markers CD66b, CD11b, CD16 and CD10 by flow cytometry. Plasma neutrophil elastase and lipocalin-2 were measured using ELISA, while G-CSF, GM-CSF and cytokines were measured using O-link Proteomic technology.

RESULTS

CD66b+ neutrophil abundance assessed by flow cytometry correlated well with complete blood counts, establishing that neutrophils in stored blood are sufficiently well-preserved for phenotyping by flow cytometry. Neutrophil abundance was significantly increased in CDI patients compared to healthy controls. Emergency granulopoiesis in acute CDI patients was evidenced by lower neutrophil surface expression of CD10, CD11b and CD16. CD10+ staining of neutrophils started to recover within 3-7 days of CDI treatment. Neutrophil activation and degranulation were higher in acute CDI as assessed by plasma neutrophil elastase and lipocalin-2. Biomarker levels in immunocompetent subjects were associated with recurrence and fatal outcomes.

CONCLUSIONS

Neutrophil activation and emergency granulopoiesis characterize the early immune response in acute CDI, with plasma degranulation biomarkers predictive of disease severity.

Early Initiation of Ceftaroline-Based Combination Therapy for Methicillin-resistant Staphylococcus aureus Bacteremia

Purpose

Monotherapy with vancomycin or daptomycin remains guideline-based care for methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B) despite concerns regarding efficacy. Limited data support potential benefit of combination therapy with ceftaroline as initial therapy. We present an assessment of outcomes of patients initiated on early combination therapy for MRSA-B.

Methods

This was a single-center, retrospective study of adult patients admitted with MRSA-B between July 1, 2017 and April 31, 2023. During this period, there was a change in institutional practice from routine administration of monotherapy to initial combination therapy for most patients with MRSA-B. Combination therapy included vancomycin or daptomycin plus ceftaroline within 72 hours of index blood culture and monotherapy was vancomycin or daptomycin alone. The primary outcome was a composite of persistent bacteremia, 30-day all-cause mortality, and 30-day bacteremia recurrence. Time to microbiological cure and safety outcomes were assessed. All outcomes were assessed using propensity score-weighted logistic regression.

Results

Of 213 patients included, 118 received monotherapy (115 vancomycin, 3 daptomycin) and 95 received combination therapy with ceftaroline (76 vancomycin, 19 daptomycin). The mean time from MRSA-positive molecular diagnostic blood culture result to combination therapy was 12.1 hours. There was no difference between groups for the primary composite outcome (OR 1.58, 95% CI 0.60, 4.18). Time to microbiological cure was longer with combination therapy (mean difference 1.50 days, 95% CI 0.60, 2.41). Adverse event rates were similar in both groups.

Conclusions

Early initiation of ceftaroline-based combination therapy did not improve outcomes for patients with MRSA-B in comparison to monotherapy therapy.

Modeling relaxed policies for discontinuation of methicillin-resistant Staphylococcus aureus contact precautions

OBJECTIVE

To evaluate the economic costs of reducing the University of Virginia Hospital's present "3-negative" policy, which continues methicillin-resistant Staphylococcus aureus (MRSA) contact precautions until patients receive 3 consecutive negative test results, to either 2 or 1 negative.

DESIGN

Cost-effective analysis.

SETTINGS

The University of Virginia Hospital.

PATIENTS

The study included data from 41,216 patients from 2015 to 2019.

METHODS

We developed a model for MRSA transmission in the University of Virginia Hospital, accounting for both environmental contamination and interactions between patients and providers, which were derived from electronic health record (EHR) data. The model was fit to MRSA incidence over the study period under the current 3-negative clearance policy. A counterfactual simulation was used to estimate outcomes and costs for 2- and 1-negative policies compared with the current 3-negative policy.

RESULTS

Our findings suggest that 2-negative and 1-negative policies would have led to 6 (95% CI, -30 to 44; P < .001) and 17 (95% CI, -23 to 59; -10.1% to 25.8%; P < .001) more MRSA cases, respectively, at the hospital over the study period. Overall, the 1-negative policy has statistically significantly lower costs ($628,452; 95% CI, $513,592-$752,148) annually (P < .001) in US dollars, inflation-adjusted for 2023) than the 2-negative policy ($687,946; 95% CI, $562,522-$812,662) and 3-negative ($702,823; 95% CI, $577,277-$846,605).

CONCLUSIONS

A single negative MRSA nares PCR test may provide sufficient evidence to discontinue MRSA contact precautions, and it may be the most cost-effective option.

Novel Biomarkers, Including tcdB PCR Cycle Threshold, for Predicting Recurrent Clostridioides difficile Infection

Traditional clinical models for predicting recurrent Clostridioides difficile infection do not perform well, likely owing to the complex host-pathogen interactions involved. Accurate risk stratification using novel biomarkers could help prevent recurrence by improving underutilization of effective therapies (i.e., fecal transplant, fidaxomicin, bezlotoxumab). We used a biorepository of 257 hospitalized patients with 24 features collected at diagnosis, including 17 plasma cytokines, total/neutralizing anti-toxin B IgG, stool toxins, and PCR cycle threshold (CT) (a proxy for stool organism burden). The best set of predictors for recurrent infection was selected by Bayesian model averaging for inclusion in a final Bayesian logistic regression model. We then used a large PCR-only data set to confirm the finding that PCR CT predicts recurrence-free survival using Cox proportional hazards regression. The top model-averaged features were (probabilities of >0.05, greatest to least): interleukin 6 (IL-6), PCR CT, endothelial growth factor, IL-8, eotaxin, IL-10, hepatocyte growth factor, and IL-4. The accuracy of the final model was 0.88. Among 1,660 cases with PCR-only data, cycle threshold was significantly associated with recurrence-free survival (hazard ratio, 0.95; P < 0.005). Certain biomarkers associated with C. difficile infection severity were especially important for predicting recurrence; PCR CT and markers of type 2 immunity (endothelial growth factor [EGF], eotaxin) emerged as positive predictors of recurrence, while type 17 immune markers (IL-6, IL-8) were negative predictors. In addition to novel serum biomarkers (particularly, IL-6, EGF, and IL-8), the readily available PCR CT may be critical to augment underperforming clinical models for C. difficile recurrence.

Convalescent Plasma for Preventing Critical Illness in COVID-19: a Phase 2 Trial and Immune Profile

The COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an unprecedented event requiring frequent adaptation to changing clinical circumstances. Convalescent immune plasma (CIP) is a promising treatment that can be mobilized rapidly in a pandemic setting. We tested whether administration of SARS-CoV-2 CIP at hospital admission could reduce the rate of ICU transfer or 28-day mortality or alter levels of specific antibody responses before and after CIP infusion. In a single-arm phase II study, patients >18 years-old with respiratory symptoms with confirmed COVID-19 infection who were admitted to a non-ICU bed were administered two units of CIP within 72 h of admission. Levels of SARS-CoV-2 detected by PCR in the respiratory tract and circulating anti-SARS-CoV-2 antibody titers were sequentially measured before and after CIP transfusion. Twenty-nine patients were transfused high titer CIP and 48 contemporaneous comparable controls were identified. All classes of antibodies to the three SARS-CoV-2 target proteins were significantly increased at days 7 and 14 post-transfusion compared with baseline (P < 0.01). Anti-nucleocapsid IgA levels were reduced at day 28, suggesting that the initial rise may have been due to the contribution of CIP. The groups were well-balanced, without statistically significant differences in demographics or co-morbidities or use of remdesivir or dexamethasone. In participants transfused with CIP, the rate of ICU transfer was 13.8% compared to 27.1% for controls with a hazard ratio 0.506 (95% CI 0.165-1.554), and 28-day mortality was 6.9% compared to 10.4% for controls, hazard ratio 0.640 (95% CI 0.124-3.298). IMPORTANCE Transfusion of high-titer CIP to non-critically ill patients early after admission with COVID-19 respiratory disease was associated with significantly increased anti-SARS-CoV-2 specific antibodies (compared to baseline) and a non-significant reduction in ICU transfer and death (compared to controls). This prospective phase II trial provides a suggestion that the antiviral effects of CIP from early in the COVID-19 pandemic may delay progression to critical illness and death in specific patient populations. This study informs the optimal timing and potential population of use for CIP in COVID-19, particularly in settings without access to other interventions, or in planning for future coronavirus pandemics.

Binary Toxin Expression by Clostridioides difficile Is Associated With Worse Disease

BACKGROUND

The incidence of Clostridioides difficile infection (CDI) has increased over the past 2 decades and is considered an urgent threat by the Centers for Disease Control and Prevention. Hypervirulent strains such as ribotype 027, which possess genes for the additional toxin C. difficile binary toxin (CDT), are contributing to increased morbidity and mortality.

METHODS

We retrospectively tested stool from 215 CDI patients for CDT by enzyme-linked immunosorbent assay (ELISA). Stratifying patients by CDT status, we assessed if disease severity and clinical outcomes correlated with CDT positivity. Additionally, we completed quantitative PCR (PCR) DNA extracted from patient stool to detect cdtB gene. Lastly, we performed 16 S rRNA gene sequencing to examine if CDT-positive samples had an altered fecal microbiota.

RESULTS

We found that patients with CdtB, the pore-forming component of CDT, detected in their stool by ELISA, were more likely to have severe disease with higher 90-day mortality. CDT-positive patients also had higher C. difficile bacterial burden and white blood cell counts. There was no significant difference in gut microbiome diversity between CDT-positive and -negative patients.

CONCLUSIONS

Patients with fecal samples that were positive for CDT had increased disease severity and worse clinical outcomes. Utilization of PCR and testing for C. difficile toxins A and B may not reveal the entire picture when diagnosing CDI; detection of CDT-expressing strains is valuable in identifying patients at risk of more severe disease.

Improving hand hygiene measures in low-resourced intensive care units: experience at the Kigali University Teaching Hospital in Rwanda

Background

Proper hand hygiene (HH) practices have been shown to reduce healthcare-acquired infections. Several potential challenges in low-income countries might limit the feasibility of effective HH, including preexisting knowledge gaps and staffing.

Aim

We sought to evaluate the feasibility of the implementation of effective HH practice at a teaching hospital in Rwanda.

Methods

We conducted a prospective quality improvement project in the intensive care unit (ICU) at the Kigali University Teaching Hospital. We collected data before and after an intervention focused on HH adherence as defined by the World Health Organization '5 Moments for Hand Hygiene' and assuring availability of HH supplies. Pre-intervention data were collected throughout July 2019, and HH measures were implemented in August 2019. Post-implementation data were collected following a 3-month wash-in.

Results

In total, 902 HH observations were performed to assess pre-intervention adherence and 903 observations post-intervention adherence. Overall, HH adherence increased from 25% (222 of 902 moments) before intervention to 75% (677 of 903 moments) after intervention (P < 0.001). Improvement was seen among all health professionals (nurses: 19-74%, residents: 23-74%, consultants: 29-76%).

Conclusions

Effective HH measures are feasible in an ICU in a low-income country. Ensuring availability of supplies and training appears key to effective HH practices.

Convalescent plasma for preventing critical illness in COVID-19: A phase 2 trial and immune profile

Rationale

The COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an unprecedented event requiring rapid adaptation to changing clinical circumstances. Convalescent immune plasma (CIP) is a promising treatment that can be mobilized rapidly in a pandemic setting.

Objectives

We tested whether administration of SARS-CoV-2 CIP at hospital admission could reduce the rate of ICU transfer or 28 day mortality.

Methods

In a single-arm phase II study, patients >18 years-old with respiratory symptoms documented with COVID-19 infection who were admitted to a non-ICU bed were administered two units of CIP within 72 hours of admission. Detection of respiratory tract SARS-CoV-2 by polymerase chain reaction and circulating anti-SARS-CoV-2 antibody titers were measured before and at time points after CIP transfusion.

Measurements and Main Results

Twenty-nine patients were transfused CIP and forty-eight contemporaneous controls were identified with comparable baseline characteristics. Levels of anti-SARS-CoV-2 IgG, IgM, and IgA anti-spike, anti-receptor-binding domain, and anti-nucleocapsid significantly increased from baseline to post-transfusion for all proteins tested. In patients transfused with CIP, the rate of ICU transfer was 13.8% compared to 27.1% for controls with a hazard ratio 0.506 (95% CI 0.165-1.554), and 28-day mortality was 6.9% compared to 10.4% for controls, hazard ratio 0.640 (95% CI 0.124-3.298).

Conclusions

Transfusion of high-titer CIP to patients early after admission with COVID-19 respiratory disease was associated with reduced ICU transfer and 28-day mortality but was not statistically significant. Follow up randomized trials may inform the use of CIP for COVID-19 or future coronavirus pandemics.

Propensity-Matched Cost of Clostridioides difficile Infection Overdiagnosis

Background

Clostridioides difficile is the leading health care–associated pathogen, but clinicians lack a test that can reliably differentiate colonization from infection. Health care costs attributed to C. difficile are substantial, but the economic burden associated with C. difficile false positives is poorly understood.

Methods

A propensity score matching model for cost per hospitalization was developed to estimate the costs of both true infection and false positives. Predictors of C. difficile positivity used to estimate the propensity score were age, Charlson comorbidity index, white cell count, and creatinine. We used polymerase chain reaction (PCR) cycle threshold to identify and compare 3 groups: (1) true infection, (2) C. difficile colonization, and (3) C. difficile negative.

Results

A positive test was associated with $3018 higher unadjusted hospital cost. Among the 3 comparisons made with propensity-matched negative controls (all positives [+$179; P = .934], true positives [–$1892; P = .100], and colonized positives), only colonization was associated with significantly increased (+$3418; P = .012) cost. Differences in lengths of stay (all positives 0 days, P = .126; true 0 days, P = .919; colonized 1 day, P = .019) appeared to underly cost differences.

Conclusions

In the first C. difficile cost analysis to utilize PCR cycle threshold to differentiate colonization, we found high propensity-matched hospital costs associated with colonized but not true positives. This unexpected finding may be due to misdiagnosis of non–C. difficile diarrhea or unadjusted factors associated with colonization.

Case Report: Lower Gastrointestinal Bleeding due to Entamoeba histolytica Detected Early by Multiplex PCR: Case Report and Review of the Laboratory Diagnosis of Amebiasis

We report a case of Entamoeba histolytica infection in a young man who presented with cerebral infarction and shortly after admission developed bloody diarrhea with fever. A rapid diagnosis of severe E. histolytica colitis was established through the use of a multiplex polymerase chain reaction enteropathogen stool panel. This result was unexpected in a patient native to the United States without known risk factors for amebiasis and negative stool microscopy examination for ova and parasites. Rapid diagnosis allowed prompt initiation of appropriate anti-amebic therapy and ultimately a good outcome in a condition that otherwise carries high morbidity and fatality.

Patient Outcomes With Prevented vs Negative Clostridioides difficile Tests Using a Computerized Clinical Decision Support Tool

Background

Overtesting and overdiagnosis of Clostridioides difficile infection are suspected to be common. Reducing inappropriate testing through interventions designed to promote evidence-based diagnostic testing (ie, diagnostic stewardship) may improve C. difficile test utilization. However, the safety of these interventions is not well understood despite the potential risk for missed or delayed diagnoses.

Methods

This retrospective case-control study examined the outcomes of patients admitted to the University of Virginia Medical Center following introduction of a computerized clinical decision support tool without hard-stops designed to reduce inappropriate tests. Outcomes were compared between patients with a prevented C. difficile nucleic acid amplification test and those with a negative result. Chart reviews were performed for patients with a subsequent positive within 7 days, as well as those patients who received C. difficile-active antibiotics after implementation of the computerized clinical decision support tool.

Results

Multivariate analysis of 637 cases (490 negative, 147 prevented) showed that a prevented test was not significantly associated with the primary composite outcome (inpatient mortality or intensive care unit transfer) compared with a negative test (adjusted odds ratio, 0.912; P = .747). Fifty-four of 147 (37%) prevented tests were followed by a completed test within 7 days; 11 of these results were positive, resulting in a potential delay in diagnosis. Individual case reviews found that either clinical changes warranted the delay in testing or no adverse events occurred attributable to C. difficile infection. C. difficile treatment without a positive test was not identified.

Conclusions

Diagnostic stewardship of C. difficile testing using computerized clinical decision support may be both safe and effective for reducing inappropriate inpatient testing.

HIV-Associated Vacuolar Encephalomyelopathy

We report a case of human immunodeficiency virus (HIV)-associated vacuolar encephalomyelopathy with progressive central nervous system dysfunction and corresponding vacuolar degeneration of the spinal cord, cranial nerves, and brain, the anatomic extent of which has not previously been described.

Case report: Anaerobiospirillum prosthetic joint infection in a heart transplant recipient

Background

We report a case of prosthetic hip joint infection in a heart transplant recipient due to Anaerobiospirillum succiniciproducens, a genus of spiral-shaped curved anaerobic gram-negative rod which colonizes the gastrointestinal tract of cats and dogs. Invasive infections in humans are rare and typically occur in immunocompromised hosts.

Case presentation

A 65-year-old male dog breeder with a history of rheumatoid arthritis, bilateral hip arthroplasties, and non-ischemic cardiomyopathy with a heart transplant 10 years ago presented with a three month history of progressive left hip pain and frank purulence on hip aspiration. He underwent irrigation and debridement of the left hip and one-stage revision with hardware exchange. Although gram stain and culture from synovial fluid and intraoperative cultures were initially negative, anaerobic cultures from tissue specimens later grew a spiral-shaped gram-negative rod, identified as Anaerobiospirillum spp. by 16S rRNA gene sequencing. The patient was treated with ceftriaxone 2 g daily for 6 weeks with a good response to treatment. A similar organism was unable to be isolated from culture of 2 of the patient’s dogs, however, they were thought to be the most likely source of his infection.

Conclusion

Anaerobiospirillum spp. should be considered in immunocompromised patients with exposure to dogs or cats who present with bacteremia, gastrointestinal infection, pyomyositis, or prosthetic joint infections, especially in cases of culture-negative or with anaerobic culture growth.

Reduced Clostridioides difficile Tests Among Solid Organ Transplant Recipients Through a Diagnostic Stewardship Bundled Intervention

BACKGROUND Clostridioides difficile infection (CDI) is a frequent complication of solid organ transplantation, especially in the early post-transplantation period. Overdiagnosis of CDI is likely common in hospitals using nucleic acid amplification testing (NAAT), potentially leading to unnecessary iatrogenesis and cost. Recently, multiple studies have shown that computerized clinical decision support (CCDS)-based interventions can significantly reduce inappropriate C. difficile testing and healthcare facility-onset CDI events across hospitals and health systems. We aimed to determine if a CCDS-based intervention could reduce C. difficile testing and surveillance infection events among recent solid organ transplant recipients, a population at high risk for CDI. We also sought to determine the safety of the CCDS intervention. MATERIAL AND METHODS Quasi-experimental census-adjusted interrupted time-series analyses were performed retrospectively to examine testing and CDI events pre- and post-intervention. Mortality and readmissions rates were also examined. RESULTS A significant 33% relative reduction in tests and a nonsignificant trend towards fewer CDI events were observed following the intervention, without significant differences in mortality or 30-day readmission. A review of patients with positive C. difficile NAATs after prevented tests revealed no specific adverse events attributable to a possible delay in CDI diagnosis. CONCLUSIONS CCDS may be a helpful and safe adjunctive strategy to reduce unnecessary testing in accordance with guideline recommendations among solid organ transplant recipients.

Diagnostic stewardship and the 2017 update of the IDSA-SHEA Clinical Practice Guidelines for Clostridium difficile Infection

Diagnostic stewardship is an increasingly recognized means to reduce unnecessary tests and diagnostic errors. As a leading cause of healthcare-associated infection for which accurate laboratory diagnosis remains a challenge, Clostridium difficile offers an ideal opportunity to apply the principles of diagnostic stewardship. The recently updated 2017 Infectious Diseases Society of America (IDSA)-Society for Healthcare Epidemiology of America (SHEA) Clinical Practice Guidelines for C. difficile infection now recommend separate diagnostic strategies depending on whether an institution has adopted diagnostic stewardship in test decision making. IDSA-SHEA endorsement of diagnostic stewardship for C. difficile highlights the increasing role of diagnostic stewardship in hospitals. In this opinion piece, we introduce the concept of diagnostic stewardship by discussing the new IDSA-SHEA diagnostic recommendations for laboratory diagnosis of C. difficile. We outline recent examples of diagnostic stewardship, challenges to implementation, potential downsides and propose future areas of study.

Pseudo-Atrial Flutter Secondary to a Chest Wall Percussion Device

Pseudo-atrial flutter is an EKG artifact that mimics a true atrial flutter. We report a case of pseudo-atrial flutter in a 67-year-old male with quadriplegia and ventilator dependence due to amyotrophic lateral sclerosis (ALS) who was hospitalized for respite care. Ihe pseudo-atrial flutterwas found to be due to percussions from a built-in chest wall percussion device in a hospital mattress used for chest physiotherapy.

P2Y2 receptors regulate osteoblast mechanosensitivity during fluid flow

Mechanical stimulation of osteoblasts activates many cellular mechanisms including the release of ATP. Binding of ATP to purinergic receptors is key to load-induced osteogenesis. Osteoblasts also respond to fluid shear stress (FSS) with increased actin stress fiber formation (ASFF) that we postulate is in response to activation of the P2Y2 receptor (P2Y2R). Furthermore, we predict that ASFF increases cell stiffness and reduces the sensitivity to further mechanical stimulation. We found that small interfering RNA (siRNA) suppression of P2Y2R attenuated ASFF in response to FSS and ATP treatment. In addition, RhoA GTPase was activated within 15 min after the onset of FSS or ATP treatment and mediated ASFF following P2Y2R activation via the Rho kinase (ROCK)1/LIM kinase 2/cofilin pathway. We also observed that ASFF in response to FSS or ATP treatment increased the cell stiffness and was prevented by knocking down P2Y2R. Finally, we confirmed that the enhanced cell stiffness and ASFF in response to RhoA GTPase activation during FSS drastically reduced the mechanosensitivity of the osteoblasts based on the intracellular Ca(2+) concentration ([Ca(2+)]i) response to consecutive bouts of FSS. These data suggest that osteoblasts can regulate their mechanosensitivity to continued load through P2Y2R activation of the RhoA GTPase signaling cascade, leading to ASFF and increased cell stiffness.