Diagnostic testing and antibiotic utilization among inpatients evaluated for coronavirus disease 2019 (COVID-19) pneumonia

We evaluated diagnostic test and antibiotic utilization among 252 patients from 11 US hospitals who were evaluated for coronavirus disease 2019 (COVID-19) pneumonia during the severe acute respiratory coronavirus virus 2 (SARS-CoV-2) omicron variant pandemic wave. In our cohort, antibiotic use remained high (62%) among SARS-CoV-2-positive patients and even higher among those who underwent procalcitonin testing (68%).

Performance of ePlex® blood culture identification panels in clinical isolates and characterization of antimicrobial stewardship opportunities

We assessed the performance of GenMark's ePlex® Blood Culture Identification (BCID) Panels for overall agreement of organism identification and resistance mechanism detection with standard microbiologic methods. This study included patients with a positive blood culture from May 2020 to January 2021. The primary outcomes were to assess concordance of ePlex® organism identification with standard identification methods and concordance of ePlex® genotypic resistance mechanism detection with standard phenotypic susceptibility testing. Secondary outcomes included panel specific performance and characterization of antimicrobial stewardship opportunities. The overall identification concordance rate in 1276 positive blood cultures was 98.1%. The overall concordance for the presence of resistance markers was 98.2% and concordance for the absence of resistance markers was 100%. A majority of ePlex® results (69.5%) represented opportunities for potential antimicrobial stewardship intervention. High concordance rates between the ePlex® BCID panels and standard identification and susceptibility methods enable utilization of results to guide rapid antimicrobial optimization.

Association of vancomycin-induced acute kidney injury with trough versus AUC monitoring in patients receiving extended durations of therapy

Objective

Vancomycin therapy is associated with an increased risk of acute kidney injury (AKI). Previous studies suggest that area under the curve (AUC) monitoring reduces the risk of AKI, but literature is lacking to support this in patients receiving longer durations of vancomycin therapy.

Design

Retrospective cohort study.

Method

Patients ≥18 years old, admitted between August 2015 and July 2017 or October 2017 and September 2019, and received at least 14 days of intravenous (IV) vancomycin therapy were included in the study. Our primary outcome was the incidence of AKI between trough monitoring and AUC monitoring groups using Kidney Disease Improving Global Outcomes criteria. Secondary outcomes included inpatient mortality, median inpatient length of stay, and median intensive care unit length of stay.

Results

Overall, 582 patients were included in the study, with 318 patients included in the trough monitoring group and 264 included in the AUC monitoring group. The median duration of vancomycin therapy was 23 days (interquartile range, 16-39). Patients within the trough monitoring group had a higher incidence of AKI compared to the AUC monitoring group (45.6% vs 28.4%, p < 0.001). Furthermore, logistic regression analysis showed that AUC monitoring was associated with a 54% lower incidence of AKI (OR 0.46, 95% CI [0.31-0.69]). All-cause inpatient mortality was numerically higher in the trough monitoring group (12.9% vs 8.3%, p = 0.078).

Conclusions

In patients who received at least 14 days of IV vancomycin therapy, AUC monitoring was associated with a lower incidence of AKI.

Changing times: The impact of gram-negative breakpoint changes over the previous decade

We assessed breakpoint changes of 13,101 Enterobacterales and Pseudomonas aeruginosa isolates from the past decade. All β-lactams and fluoroquinolones demonstrated decreased susceptibilities following breakpoint changes. Enterobacter cloacae experienced the largest average decrease in susceptibility amongst the Enterobacterales at 5.3% and P. aeruginosa experienced an average decrease in susceptibility of 9.3%.

The impact of coronavirus disease 2019 (COVID-19) on the antimicrobial stewardship pharmacist workforce: A multicenter survey

OBJECTIVE

The coronavirus disease 2019 (COVID-19) pandemic has required healthcare systems and hospitals to rapidly modify standard practice, including antimicrobial stewardship services. Our study examines the impact of COVID-19 on the antimicrobial stewardship pharmacist.

DESIGN

A survey was distributed nationally to all healthcare improvement company members.

PARTICIPANTS

Pharmacist participants were mostly leaders of antimicrobial stewardship programs distributed evenly across the United States and representing urban, suburban, and rural health-system practice sites.

RESULTS

Participants reported relative increases in time spent completing tasks related to medication access and preauthorization (300%; P = .018) and administrative meeting time (34%; P = .067) during the COVID-19 pandemic compared to before the pandemic. Time spent rounding, making interventions, performing pharmacokinetic services, and medication reconciliation decreased.

CONCLUSION

A shift away from clinical activities may negatively affect the utilization of antimicrobials.

695. Infective endocarditis in people who inject drugs (PWID) at UK Medical Center

Background

The Intravenous Drug Use (IVDU) epidemic has been developing into a public health crisis in the last twenty years. As a result, the incidence of severe bacterial infections such as infective endocarditis (IE) has been rising dramatically.

Methods

Cross-sectional study, we reviewed records of all admissions to University of Kentucky hospitals with IVDU associated ICD9/10 codes who received an Infectious Diseases consult during 2018 and focused on the cases with a diagnosis of IE. We describe associated epidemiologic, clinical, and microbiological features

Results

We include 391 patients in this cohort, among those 157 patients were for IE. Patients had a median age of 34 years old (range: 20 - 62); 81 (51.5%) were female, and five (6.1%) were pregnant and 153 (97.4%) identified as white. A previous episode of infective endocarditis was reported in 55 (35%) cases. The most common illicit substances used were heroin 68 (43.3%) and methamphetamine 65 (41.45%). Tobacco abuse was reported in 134 (86.4%) cases. Fever reported in 93 (59.8%) cases, shortness of air in 43 (28.0%) cases, and chest pain in 44 (28.6%) cases were the most common symptoms. Hepatitis C antibody was positive in 115/149 (73.2%) and 3/143 (1.9%) were HIV positive. Right-sided IE was more frequent, the tricuspid valve was involved in 94 (59.8%) patients. Gram-positive pathogens were isolated in 139 (88.5%) patients, Staphylococcus aureus was isolated in 102 (64.9%) patients, of which 67 (65.7%) were methicillin resistant. Gram-negative pathogens were isolated in 18 (11.2%) patients. Eighty-eight (56.4%) patients had an addiction medicine consult during their admission, (22.9%) patients left against medical advice and 20 (12.7%) patients needed to be readmitted within 30 days after discharge. Overall mortality was 12.7% and was significantly associated with infection by gram-negative pathogens (RR: 2.5; CI 95% 1.05 – 6.25, p=0.037).

Conclusion

Infectious endocarditis is a frequent complication in PWID which carries a high risk of mortality and often involves the tricuspid valve. The most common pathogen isolated was S. aureus, isolation of gram-negative pathogens was associated with increased mortality.

Disclosures

All Authors: No reported disclosures

58. Evaluation of a Disease State Stewardship Intervention for Urinary Tract Infections at an Academic Medical Center

Background

Urinary tract infections (UTIs) are often misdiagnosed and mismanaged. Disease state stewardship initiatives targeting UTIs may have a significant impact on the overuse of antimicrobials (ABX). The purpose of our study is to evaluate the effectiveness of a UTI focused disease state stewardship intervention.

Methods

This retrospective study was conducted at a tertiary care academic medical center. Patients > 18 years of age with a collected urinalysis (UA) and receiving ABX for a UTI were included. Retrospective review of UTI management from 9–11/2017 was performed and used as the baseline. In the post-intervention period, 9–11/2018, the UTI management guideline had been published and service lines educated. A prospective audit and feedback (PAAF) initiative was started 6/2019, whereby the antimicrobial stewardship team performed daily reviews of patients on ABX for UTIs. Patients reviewed 9–11/2019 were included in the PAAF cohort. Exclusion criteria included: pregnancy, undergoing a urologic procedure, treatment of a concomitant infection, receiving therapy based on outside recommendations, or left AMA/expired during treatment. The primary outcome of this study was to evaluate overall guideline adherence.

Results

600 patients (200 in each group) were included, with 419 (69.8%) female and an overall median age of 61.4 years. Altered mental status (24.8%) and dysuria (21.5%) were the two main diagnostic testing indications. Treatment of asymptomatic presentations decreased between the three periods, 74.0% vs 48.5% vs 36.0%. Appropriate ordering of UA (33.5% vs 55.0% vs 68.5%, p< 0.001) and urine cultures (29.0% vs 57.1% vs 64.8%, p< 0.001) improved following guideline implementation and PAAF. Interventions by the stewardship team were made in 21% of patients during PAAF, namely therapy discontinuation (78.6%). Overall guideline adherence significantly improved over time, 13.0% vs 27.0% vs 36.5%, p< 0.001.

Conclusion

UTI disease state intervention was associated with a reduction in the treatment of asymptomatic presentations, increase in appropriate diagnostic ordering, and improvement in overall guideline adherence. PAAF can be a powerful stewardship strategy for promoting consistency in UTI treatment and decreasing unnecessary ABX use.

Disclosures

All Authors: No reported disclosures

1982. A Diagnostic Stewardship Intervention for Clostridioides difficile: Impact of Stool Toxin Testing on Treatment of Adult Inpatients

Background

Testing for Clostridioides difficile infection has been the subject of recent debate. Guidelines from the Infectious Diseases Society of America now support the addition of a stool toxin test to a positive nucleic acid amplification test (NAAT) as part of a multi-step testing algorithm. In November 2017, the University of Kentucky HealthCare system added stool toxin testing to any specimen positive for C. difficile by NAAT. This change was accompanied by face to face education with provider groups and clinical decision support in the form of interpretive verbiage added to the results that are reported into the electronic record. The objective of this study was to assess whether this diagnostic stewardship intervention made an impact on C. difficile treatment

Methods

We performed a retrospective review of adult patients admitted to UK HealthCare from November 1, 2017 through October 31, 2018 who tested positive by NAAT but negative by stool toxin test to determine whether or not they were treated. We also assessed treatment by service line to see whether there were treatment differences among these groups. A cost analysis was also performed.

Results

A total of 300 adult inpatients were positive for C. difficile by NAAT during the study period with 71% (213 patients) having a negative stool toxin test. Of those, 58% (123) were never started on C. difficile therapy and an additional 14% (30) had their therapy stopped after 48 hours. Only 28% (60) of these patients received a full course of therapy. Hospital medicine had the highest rate of non-treatment at 82%. Conversely, our solid-organ and bone marrow transplant services had the lowest rate of non-treatment at 31%. Overall, this approach was associated with an estimated 1470 oral vancomycin days avoided (5,880 doses) and a cost savings of $6,278.

Conclusion

The addition of stool toxin testing to NAAT combined with education and clinical decision support lead to a dramatic reduction of treatment for NAAT positive but toxin-negative patients. This form of diagnostic stewardship had a significant impact on therapy decisions and can be a powerful antimicrobial stewardship approach to decrease unnecessary treatment of C. difficile colonization.

Disclosures

All authors: No reported disclosures.

149. Short vs. Long Course of Antibiotics for Uncomplicated Gram-Negative Bacteremia

Background

Bloodstream infections (BSI) continue to be a major cause of morbidity and mortality in the United States; thus, the correct choice of antibiotics for an appropriate duration is imperative. However, there are limited recommendations on adequate duration of treatment of bacteremia caused by Gram-negative organisms. Therefore, treating an infection for an adequate duration to prevent complications while preventing adverse effects from unnecessary antibiotic exposure remains a balancing act. This study aims to compare clinical outcomes between patients treated with a short (7–10 days) vs. long (11–20 days) course of antibiotics for uncomplicated gram-negative bacteremia.

Methods

This single-center retrospective cohort study evaluated adult patients admitted between January 2007 to October 2018 with a blood culture positive for gram-negative bacteria. Data came from the University of Kentucky Microbiological Laboratory and Center for Clinical and Translational Science (CCTS) Data Bank. Patients included must have received appropriate antibiotics for at least 7 days. Appropriate antibiotics were defined as those to which the organism is susceptible with day one of therapy as the first day of appropriate antibiotic therapy. Patients were excluded if they were treated with aminoglycoside monotherapy, had polymicrobial bacteremia, or if treated for longer than 20 days of therapy.

Results

A total of 466 patients were identified (208 in the short-course group and 258 in the long course group). Gender and ethnicity were similar across both groups. The patients in the long course group had more ICU admissions compared with the short-course group (52.7% vs. 43.3%, P = 0.0426), tended to be older (57 ± 16.7 vs. 53 ± 15.9 years, P = 0.0119), had a higher Charlson Comorbidity Index (5.7 ± 3.6 vs. 4.6 ± 3.6, P = 0.0009) and remained admitted to the hospital longer (23.2 ± 25.6 vs. 15.8 ± 17.5 days, P = 0.0002). However, patients treated with a long course had no difference in 30-day mortality compared with the short-course group (3.9% vs. 3.4%, P = 0.7701).

Conclusion

Patients with an uncomplicated gram-negative BSI treated with a short course (7–10 days) of antibiotics do not appear to have a significant difference in 30-day mortality compared with those patients treated with a long course (11–20 days).

Disclosures

All authors: No reported disclosures.

Pharmacist Survey: Pharmacist Perception of Vancomycin Area Under the Curve Therapeutic Drug Monitoring

BACKGROUND

Evidence suggests the standard vancomycin trough goal of 15 to 20 mg/L for serious Staphylococcus aureus infections is associated with acute kidney injury, whereas appropriate monitoring of 24-hour area under the curve (AUC) may decrease nephrotoxicity. As a result, institutions have transitioned to AUC monitoring, the predictive pharmacokinetic/pharmacodynamic parameter of vancomycin to improve safety outcomes. However, this method may require increased pharmacist time and effort. Pharmacist perception of the practice change is largely unknown and warrants investigation.

METHODS

An electronic survey was disseminated via e-mail to pharmacists 5 months post-AUC implementation. Items of interest were focused on pharmacist perception, including quantity of patients monitored using AUC, justification of the practice change, differences in efficacy and safety, and changes in monitoring time requirements.

RESULTS

The pharmacist survey was distributed to 196 pharmacists and 84 responded (43% response rate). Eighty-one pharmacists had monitored patients using AUC methods. Sixty-nine percent of these respondents perceived the change to result in increased or slightly increased patient safety, 27% described no difference, and 4% stated safety was decreased or slightly decreased. Forty-two percent perceived the transition to result in increased or slightly increased efficacy, while 48% noted no difference and 10% responded that efficacy was decreased or slightly decreased. Pharmacists stated the creation of an institutional calculator decreased the time required to calculate AUC.

CONCLUSION

After the change to AUC monitoring, pharmacists perceived improvements in safety outcomes while efficacy was at least similar if not increased.

Vancomycin Area Under the Curve Dosing and Monitoring at an Academic Medical Center: Transition Strategies and Lessons Learned

Due to the inconsistent correlation of vancomycin trough concentrations with 24-hour area under the curve (AUC) and a desire to reduce rates of vancomycin-associated acute kidney injury, an institutional guideline was implemented by the Antimicrobial Stewardship Team in September 2017 to monitor vancomycin using AUC. Three stages were utilized to organize the process: preparation, implementation, and evaluation. The preparation stage was used to present literature to key stakeholders, and pharmacy meetings focused on the development of a dosing and monitoring guideline. Along with institution-wide education, the implementation stage included information technology development and support. The evaluation stage was comprised of quality improvement and clinical research. Future plans include dissemination of the results and analyses. Numerous lessons were learned due to barriers experienced during the process, but the transition was successful.

Amikacin target achievement in adult cystic fibrosis patients utilizing Monte Carlo simulation

AIM

Pseudomonas aeruginosa (PsA) is a common pathogen in cystic fibrosis (CF). Management of an acute pulmonary exacerbation (APE) caused by PsA is dual anti-pseudomonal antibiotics, a beta-lactam plus aminoglycoside. Aminoglycoside dosing in CF differs from the general population due to altered pharmacokinetics. The primary objective of this study was to utilize pharmacokinetic data from adult CF patients that received amikacin to determine the probability of target attainment for APEs caused by PsA.

METHODS

This was a single-center, non-randomized, retrospective cohort study of patients >18 years with CF that received intravenous amikacin between January 2010 and July 2016. Amikacin dose, frequency, and serum concentrations were used to calculate pharmacokinetic parameters assuming a one-compartment model. Monte Carlo simulation was conducted with MIC values from CF patients with a PsA positive sputum culture between January 2014 and September 2016 to predict concentration-time profiles for different doses of amikacin.

RESULTS

This study included pharmacokinetic parameters for 14 amikacin courses administered to six unique patients. The average empiric dose of amikacin was 24.3 ± 14.6 mg/kg, achieving a peak:MIC ratio ≥8 at a rate of 37% (median 5.87; IQR 3.05-10.96). A dose of 45 mg/kg/day was needed to achieve target peak:MIC ratios 90% of the time for a PsA MIC of 8 mg/L.

CONCLUSION

Our data suggests it may not be clinically feasible to utilize amikacin for PsA isolates with a MIC of 16 mg/L. Current guideline dosing recommendations of amikacin 30-35 mg/kg/day are only adequate for PsA with a MIC ≤4 mg/L.

1804. Impact of Susceptibility Testing Method on Antibiotic Selection for Methicillin-Resistant Staphylococcus Aureus (MRSA) Bacteremia

Background

The selection of intravenous (IV) antibiotics for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia can be influenced by the vancomycin minimum inhibitory concentration (MIC). This study explores the changes in antibiotic use and inpatient mortality for patients with MRSA bacteremia after switching the MIC testing methods.

Methods

At University of Kentucky Medical Center, Etest™ was implemented in November 2013 for all Staphylococcus aureus blood isolates. In April 2016, this was changed to Phoenix™ automated system. Data regarding antibiotic usage for patients with MRSA bacteremia were collected from July 2014 to December 2015 (Etest™) and September 2016 to March 2017 (Phoenix™). Only patients started on IV vancomycin were included. Daptomycin and ceftaroline use was monitored by the antimicrobial stewardship team with focus on guideline adherence.

Results

A total of 119 and 62 patients were identified before and after switching to Phoenix™. MICs of 2 μg/mL were significantly decreased (P < 0.001) after changing to Phoenix™ (Table 1). Daptomycin use (alone or in combination) decreased from 37% (44/119) to 21% (13/62) (P = 0.013). Ceftaroline use (alone or in combination) decreased from 32% (38/119) to 19% (12/62) (P = 0.036). The reason for escalation in 13 of 44 (30%) patients with daptomycin and 6 of 38 (16%) patients with ceftaroline was an MIC of 2 μg/mL. Overall, IV vancomycin use (alone or in combination) increased from 50% (60/119) to 69% (43/62) (P = 0.007). All-cause inpatient mortality was 16% (19/119) before and 10% (6/62) (P = 0.24) after switching to Phoenix.

Conclusion

A switch in vancomycin susceptibility testing from Etest™ to Phoenix™ automated system was associated with a significant decrease in daptomycin and ceftaroline use and an increase in IV vancomycin use without any change in all-cause inpatient mortality.

Disclosures

All authors: No reported disclosures.

2436. Use of Piperacillin/Tazobactam vs. Cefepime or Carbapenem for Infections Due to Serratia, Citrobacter, or Enterobacter

Background

Methods

Results

Conclusion

Disclosures

1026. Trends in Infective Endocarditis During the Substance Use Disorder Epidemic at an Academic Medical Center

Background

In many areas of the United States, substance use disorders (SUD) have increased dramatically over the past decade. Overdose deaths have increased as well, and Kentucky ranks among the nation’s leaders in deaths per 100,000 population. Infective endocarditis (IE) is a well-known complication of intravenous drug use, contributing to significant morbidity and mortality, but few studies have evaluated the effect of the current SUD epidemic on rates and demographics of IE. We sought to examine the trends in IE and IE with SUD at our institution.

Methods

We collected data from patients admitted to a large academic medical center in Kentucky between January 1, 2013 and December 31, 2016. Patients were classified according to the International Classification of Diseases, Tenth Revision. Patients were considered to have IE if they received codes I33 or I38. Patients were considered to have an SUD if they received codes F11.10, F15.10, F14.10, F19.10, or Z86.59. Data were collected through the TriNetX database (TriNetX, Cambridge, MA).

Results

There were 2,100 cases of IE during the study period. The mean (SD) age was 53 years (21). Of those, 440 also had an SUD. The mean (SD) age of these patients was 41 years (11). Patients in both the IE and IE/SUD categories were primarily male (54% and 55%) and white (94% and 94%). The number of cases of IE increased from 190 in 2013 to 430 in 2016 (R² = 0.9877). The number of IE cases diagnosed as having an SUD increased from 30 (16% of all IE cases) in 2013 to 130 (30% of all IE cases) in 2016 (R² = 0.7352 for the trend). This increase in cases corresponds to a 333% increase in the number of cases of IE with SUD.

Conclusion

Between 2014 and 2016, opioid overdose deaths in Kentucky rose from 24.7 to 33.5 per 100,000 population, a 35.6% increase. During a similar timeframe, the number of IE cases associated with SUD at our institution rose 333%. While it is possible that increased coding of substance use disorders factored into this dramatic increase, it appears that the number of IE cases associated with SUD is rising at a disproportionately rapid rate.

Disclosures

All authors: No reported disclosures.

1878. Expanding Kentucky’s “One and Done” Tradition: Lipoglycopeptide Administration in the Emergency Department at a Tertiary, Academic Medical Center

Background

Acute bacterial skin and skin structure infection (ABSSSI) incidence continues to rise, accounting for around 3.5 million emergency department (ED) visits per year in the United States. Dalbavancin and oritavancin are lipoglycopeptides with long half-lives allowing for single dose treatment options for eligible patients presenting with ABSSSIs in the ED, avoiding an inpatient admission. The objective of this study was to investigate the financial outcomes of utilizing these agents in the ED.

Methods

This was a single-center, retrospective study in adult patients with ABSSSIs that received a lipoglycopeptide in the ED at an academic medical center from April 2016 to February 2018. A multidisciplinary institutional guideline was developed and implemented in April 2016. Data were documented in the electronic medical record and/or REDCap™ database. A comparator group was identified by utilizing similar ICD-10 codes for patients that were admitted for ABSSSI. Variable direct cost-avoidance was examined to explore the financial implication of lipoglycopeptide treatment in this population.

Results

The average length of stay in the comparator group who were admitted for ABSSSIs during the predefined time period was 4.3 days. Because patients receiving a lipoglycopeptide did not require admission for intravenous antibiotics, 94.6 patient-days were avoided increasing the capacity by 14.1 patients. Overall, 22 patients received either dalbavancin (n = 18) or oritavancin (n = 4). The age was 40.8 ± 13.2 years for the study group with 55% male. The age of the comparator group was 40.5 ± 19.7 years. All patients were discharged home from the ED without being admitted. Two patients were readmitted for treatment failure requiring IV antibiotics. Despite 2 of 22 patients receiving a lipoglycopeptide without insurance, the variable direct cost avoidance was $4,560 per case, or $1,060 per day.

Conclusion

The use of lipoglycopeptides offers patient convenience and financial benefits, warranting its consideration for use in the ED at tertiary academic medical centers.

Disclosures

All authors: No reported disclosures.

529. Overdiagnosis of Clostridioides difficile with a Multiplex PCR Panel

Background

While advantageous by casting a wider diagnostic net, multiplex panels can be problematic if the pretest probability is low. A significant increase in reported Clostridioides difficile infections (CDI) was noted at our institution following introduction of a multiplex comprehensive GI (CGI) panel which includes an analyte for C. difficile. Owing to these concerns, the C. difficile analyte result was suppressed when reporting and providers were advised to order a standalone C. difficile PCR (CDPCR) test if CDI was a concern. The objective of this study was to investigate concerns of false positive C. difficile results from the CGI panel.

Methods

C. difficile diagnostic practices were prospectively evaluated from April to August 2017. Patient charts were reviewed in response to a positive C. difficile analyte on the CGI panel. CDPCR results were reviewed if ordered. If not ordered, chart review and discussion with the provider was conducted to investigate clinical suspicion for CDI. The results were analyzed to examine the performance of the C. difficile analyte on the CGI panel.

Results

Overall, a total of 1,611 CGI panels were performed with C. difficile being detected in 156 specimens. Of these positive results, a subanalysis was performed on 123 positive specimens for whom complete data was available. A CDPCR was performed in 80 (65%) of these specimens. Among those, only 44 (55%) were CDPCR positive and 22 (28%) were CDPCR negative (likely a false-positive CGI result), and 14 (17%) were rejected because of specimen consistency. For the remaining 43 C. difficile-positive CGI panel specimens that did not have an accompanying CDPCR, seven were in children below 2 years of age. Direct provider discussion occurred in the remaining 36 cases. Providers declined CDPCR testing in 24 of those cases due to a lack of clinical concern.

Conclusion

The use of the CGI panel for C. difficile led to over diagnosis of CDI. This could have significant consequences for clinical care and the reporting of hospital acquired infections.

Disclosures

All authors: No reported disclosures.

Acute kidney injury in patients treated with vancomycin and piperacillin-tazobactam: A retrospective cohort analysis

BACKGROUND

Empiric antimicrobial therapy often consists of the combination of gram-positive coverage with vancomycin (VAN) and gram-negative coverage, specifically an antipseudomonal beta-lactam such as piperacillin-tazobactam (PTZ). Nephrotoxicity is commonly associated with VAN therapy; however, recent reports show higher nephrotoxicity rates among patients treated with the combination of VAN and PTZ.

OBJECTIVE

This study evaluated the effect of the VAN/PTZ combination on acute kidney injury (AKI) compared to VAN and PTZ monotherapies.

DESIGN, SETTING, AND PATIENTS

This is a retrospective cohort analysis of adult patients without renal disease receiving VAN, PTZ, or the combination from September 1, 2010 through August 31, 2014 at an academic medical center.

MEASUREMENTS

The primary outcome was AKI incidence as defined by the Risk, Injury, Failure, Loss, End-stage (RIFLE) criteria.

METHODS

Continuous and categorical variables were assessed with appropriate tests. Univariate and multivariate logistic regressions were performed to assess for associations between variables and AKI incidence. Subanalyses based on severity of illness were performed.

RESULTS

Overall, 11,650 patients were analyzed, with 1647 (14.1%) developing AKI. AKI was significantly more frequent in the VAN/PTZ group (21%) compared to either monotherapy group (VAN 8.3%, PTZ 7.8%, P ⟨ 0.001 for both). Combination therapy was independently associated with higher AKI odds compared to monotherapy with either agent (adjusted odds ratio [aOR], 2.03; 95% confidence interval [CI], 1.74-2.39; aOR, 2.31; 95% CI, 1.97-2.71, for VAN and PTZ, respectively). Receipt of concomitant nephrotoxic drugs was independently associated with increased AKI rates, as were increased duration of therapy, hospital length of stay, increasing severity of illness, and increasing baseline renal function.

CONCLUSIONS

In this study of more than 10,000 patients, VAN combined with PTZ was associated with twice the odds of AKI development compared to either agent as monotherapy. This demonstrates the need for judicious use of combination empiric therapy. Journal of Hospital Medicine 2017;12:77-82.

Optimizing beta-lactam pharmacodynamics against Pseudomonas aeruginosa in adult cystic fibrosis patients

BACKGROUND

Patients with cystic fibrosis (CF) exhibit increased clearance of beta-lactams. The purpose of this study was to predict the probability of beta-lactam target attainment (PTA) against Pseudomonas aeruginosa in adult CF patients based on local microbiological data.

METHODS

CF-specific pharmacokinetic parameters were obtained from published data for aztreonam, cefepime, ceftazidime, meropenem and piperacillin-tazobactam. Pharmacodynamic modeling was used to determine the PTA for bolus, prolonged infusion, and continuous infusion regimens.

RESULTS

Prolonged infusion of meropenem 2g every 8h performed the best among all regimens tested, with a PTA of 83%. The PTA was increased with both prolonged and continuous infusion; however, no regimen reached the target PTA of >90% against P. aeruginosa in CF patients at our institution.

CONCLUSIONS

Prolonged and continuous infusion provided higher PTA than bolus for all regimens. Further investigation of novel regimens in CF patients is needed.

Respiratory Muscle Paralysis Associated With Colistin, Polymyxin B, and Muscle Relaxants Drugs: A Case Report

Polymyxins B and E (colistin) exert a bactericidal effect on the gram-negative bacterial cell wall, causing permeability changes in the cytoplasmic membrane, leading to cell death. Their use was substantially decreased in clinical practice from the 1970s to 2000s due to their significant nephrotoxicity and neurotoxicity compared to the newly introduced antibiotics. The increasing prevalence of multidrug-resistant gram-negative bacteria infections in this century has led to an upsurge in the use of these "older" drugs. Respiratory paralysis caused by neuromuscular blockage associated with the use of polymyxin B and E was reported mostly in literature published in the 1960s to 1970s with a few reports after 2000. In addition, such a reaction might be enhanced by the presence of other classes of drugs. We report a case of polymyxin B and E-induced apnea in a patient receiving "muscle relaxants."

Pharmacokinetic and Pharmacodynamic Analyses of Ceftaroline in Adults with Cystic Fibrosis

STUDY OBJECTIVE

To evaluate the pharmacokinetics and pharmacodynamics of ceftaroline in adults with cystic fibrosis (CF).

DESIGN

Open-label, single-center, prospective study.

SETTING

University-affiliated teaching institution.

PATIENTS

Eight patients with a diagnosis of CF and a history of methicillin-resistant Staphylococcus aureus who were treated with ceftaroline between November 2013 and September 2014.

INTERVENTION

All patients received at least three doses of intravenous ceftaroline 600 mg every 12 hours, administered as a 60-minute infusion, to achieve steady-state concentrations before blood sample collection. After an interim analysis of the first four patients' pharmacokinetic data, the remaining four patients received a change in dosage of ceftaroline to 600 mg every 8 hours.

MEASUREMENTS AND MAIN RESULTS

Patients' blood samples were collected at two time points, 2 and 6 hours after infusion initiation, after administration of at least three doses of ceftaroline. Serum ceftaroline concentrations were determined by using a validated mass spectrometry, with a lower limit of detection of 20 ng/ml. These ceftaroline concentrations were used to estimate patient-specific pharmacokinetic parameters, and 10,000-patient Monte Carlo simulations were performed to determine the pharmacodynamic probability of target attainment (PTA) for ceftaroline in adults with CF. A PTA of 90% or higher for the desired pharmacodynamic target was considered adequate. The PTA for 60% or higher of the dosing interval during which free (unbound) drug concentrations exceed the minimum inhibitory concentration (%fT > MIC) was simulated for various MICs. Compared with values previously reported in other populations, the volume of distribution was increased in the study patients, and the estimated half-life was shorter. Monte Carlo simulations revealed that a dose of ceftaroline 600 mg every 8 hours, infused over 60 minutes, maintained a higher than 90% PTA for %fT > MIC of 60% or higher for an MIC at the susceptibility breakpoint of 1 mg/L.

CONCLUSION

The pharmacokinetics of ceftaroline is altered in adults with CF, which suggests the need for modified dosing in this patient population to achieve adequate %fT > MIC. A dosage of intravenous ceftaroline 600 mg every 8 hours administered as a 60-minute infusion should be considered to achieve 60% fT > MIC.

Utilizing Monte Carlo Simulations to Optimize Institutional Empiric Antipseudomonal Therapy

Pseudomonas aeruginosa is a common pathogen implicated in nosocomial infections with increasing resistance to a limited arsenal of antibiotics. Monte Carlo simulation provides antimicrobial stewardship teams with an additional tool to guide empiric therapy. We modeled empiric therapies with antipseudomonal β-lactam antibiotic regimens to determine which were most likely to achieve probability of target attainment (PTA) of ≥90%. Microbiological data for P. aeruginosa was reviewed for 2012. Antibiotics modeled for intermittent and prolonged infusion were aztreonam, cefepime, meropenem, and piperacillin/tazobactam. Using minimum inhibitory concentrations (MICs) from institution-specific isolates, and pharmacokinetic and pharmacodynamic parameters from previously published studies, a 10,000-subject Monte Carlo simulation was performed for each regimen to determine PTA. MICs from 272 isolates were included in this analysis. No intermittent infusion regimens achieved PTA ≥90%. Prolonged infusions of cefepime 2000 mg Q8 h, meropenem 1000 mg Q8 h, and meropenem 2000 mg Q8 h demonstrated PTA of 93%, 92%, and 100%, respectively. Prolonged infusions of piperacillin/tazobactam 4.5 g Q6 h and aztreonam 2 g Q8 h failed to achieved PTA ≥90% but demonstrated PTA of 81% and 73%, respectively. Standard doses of β-lactam antibiotics as intermittent infusion did not achieve 90% PTA against P. aeruginosa isolated at our institution; however, some prolonged infusions were able to achieve these targets.

Effect of retinoids on rheumatoid arthritis, a proliferative and invasive non-malignant disease

In rheumatoid arthritis synovial tissue proliferates and destroys articular cartilage, bone and tendons. Collagenase is a major mediator of the connective tissue degradation. This enzyme is produced in large quantities by rheumatoid tissue and its synthesis can be inhibited by retinoids. However, knowledge of mechanisms controlling retinoid inhibition of collagenase production and of factors possibly controlling synovial cell proliferation is limited. We found that transforming growth factor beta in combination with epidermal growth factor, epidermal growth factor alone and immune interferon increased proliferation of cultured human and rabbit synovial fibroblasts. Only transforming growth factor beta caused a piling up of cells into foci resembling those seen in primary cultures of human rheumatoid tissue. All the factors were antagonized by retinoids but not by glucocorticoids or indomethacin. Adding retinoids or glucocorticoids to collagenase-producing cells decreased hybridizable collagenase mRNA by 50% within 24 h. Oral administration of retinoids to rats with experimental arthritis decreased clinical disease without toxicity, and inhibited collagenase synthesis by synovial cells taken from treated animals. Retinoids are both antiproliferative and anti-invasive, and therefore may be potential therapeutic agents in the treatment of rheumatoid arthritis.

Analysis of cytoskeletal and motility proteins in the sea urchin genome assembly

The sea urchin embryo is a classical model system for studying the role of the cytoskeleton in such events as fertilization, mitosis, cleavage, cell migration and gastrulation. We have conducted an analysis of gene models derived from the Strongylocentrotus purpuratus genome assembly and have gathered strong evidence for the existence of multiple gene families encoding cytoskeletal proteins and their regulators in sea urchin. While many cytoskeletal genes have been cloned from sea urchin with sequences already existing in public databases, genome analysis reveals a significantly higher degree of diversity within certain gene families. Furthermore, genes are described corresponding to homologs of cytoskeletal proteins not previously documented in sea urchins. To illustrate the varying degree of sequence diversity that exists within cytoskeletal gene families, we conducted an analysis of genes encoding actins, specific actin-binding proteins, myosins, tubulins, kinesins, dyneins, specific microtubule-associated proteins, and intermediate filaments. We conducted ontological analysis of select genes to better understand the relatedness of urchin cytoskeletal genes to those of other deuterostomes. We analyzed developmental expression (EST) data to confirm the existence of select gene models and to understand their differential expression during various stages of early development.

Interaction between EB1 and p150glued is required for anaphase astral microtubule elongation and stimulation of cytokinesis

In animal cells, microtubules (MTs) of the mitotic apparatus (MA) communicate with the cell cortex to stimulate cytokinesis; however, the molecular nature of this stimulus remains elusive . A signal for cytokinesis likely involves the MT plus end binding family of proteins, which includes EB1, p150glued, APC, LIS1, and CLIP-170. These proteins modulate MT dynamics and facilitate interactions between growing MTs and their intracellular targets, including kinetochores, organelles, and the cell cortex . The dynein-dynactin complex mediates many of these microtubule capture events . We report that EB1 and p150glued interactions are required for stimulation of cytokinesis in dividing sea urchin eggs. Injected antibodies against EB1 or p150glued suppressed furrow ingression but did not prevent elongation of anaphase astral MTs toward the cortex, suggesting that EB1 and dynactin are both required for communication between the MA and the cortex. Targeted disruption of the interaction between EB1 and p150glued suppressed anaphase astral MT elongation and resulted in a delay of cytokinesis that could not be overcome by manipulation of the asters toward the cortex. We conclude that EB1 and dynactin participate in stimulation of the cleavage furrow, and their interaction promotes elongation of astral MTs at anaphase onset.

Targeted new membrane addition in the cleavage furrow is a late, separate event in cytokinesis

Cytokinesis in animal cells is accomplished in part by an actomyosin contractile ring. Recent work on amphibian, Drosophila, and Caenorhabditis elegans embryos implicates membrane trafficking and delivery as essential for cytokinesis. However, the relative contributions of contractile ring constriction versus membrane insertion to cytokinesis and the temporal relationship between these processes are largely unexplored. Here we monitor secretion of the extracellular matrix protein, hyalin, as a marker for new plasma membrane addition in dividing sea urchin zygotes. We find that new membrane addition occurs specifically in the cleavage furrow late in telophase independent of contractile ring constriction. The directed equatorial deposition of new furrow membrane requires astral microtubules and release of internal stores of Ca(2+), but not the presence of a central spindle. Further, cells arrested in M phase do not secrete hyalin, suggesting that mitotic exit is required for new membrane addition. These results demonstrate that astral overlap in equilaterally dividing cells not only serves to specify positioning and contraction of the contractile ring, but also to direct the delivery of new membrane to the furrow as a late, independent event during cytokinesis.

Myosin-I nomenclature

We suggest that the vertebrate myosin-I field adopt a common nomenclature system based on the names adopted by the Human Genome Organization (HUGO). At present, the myosin-I nomenclature is very confusing; not only are several systems in use, but several different genes have been given the same name. Despite their faults, we believe that the names adopted by the HUGO nomenclature group for genome annotation are the best compromise, and we recommend universal adoption.

Budding roles for myosin II on the Golgi

Myosin II--conventional myosin--has been typecast in muscle-man roles. While members of the Schwarzenegger clan from skeletal muscle have grabbed the limelight, myosin II motors in nonmuscle cells labour away in many varied and subtle roles. Recent findings show that nonmuscle myosin II, along with other myosins and cytoskeletal proteins, assembles on Golgi membranes. Nonmuscle myosin II associates transiently with membranes of the trans-Golgi network during the budding of a subpopulation of transport vesicles. The exact role of myosin II in vesicular trafficking is not yet understood, but its participation heralds a novel role for actin-based motors in vesicle budding.

Molecular motors and a spectrin matrix associate with Golgi membranes in vitro

Cytoplasmic dynein is a microtubule minus-end-directed motor that is thought to power the transport of vesicles from the TGN to the apical cortex in polarized epithelial cells. Trans-Golgi enriched membranes, which were isolated from primary polarized intestinal epithelial cells, contain both the actin-based motor myosin-I and dynein, whereas isolated Golgi stacks lack dynein but contain myosin-I (Fath, K.R., G.M. Trimbur, and D.R. Burgess. 1994. J. Cell Biol. 126:661-675). We show now that Golgi stacks in vitro bind dynein supplied from cytosol in the absence of ATP, and bud small membranes when incubated with cytosol and ATP. Cytosolic dynein binds to regions of stacks that are destined to bud because dynein is present in budded membranes, but absent from stacks after budding. Budded membranes move exclusively towards microtubule minus-ends in in vitro motility assays. Extraction studies suggest that dynein binds to a Golgi peripheral membrane protein(s) that resists extraction by ice-cold Triton X-100. In the presence of cytosol, these membrane ghosts can move towards the minus-ends of microtubules. Detergent-extracted Golgi stacks and TGN-containing membranes are closely associated with an amorphous matrix composed in part of spectrin and ankyrin. Although spectrin has been proposed to help link dynein to organellar membranes, we found that functional dynein may bind to extracted membranes independently of spectrin and ankyrin.

Myosin II is associated with Golgi membranes: identification of p200 as nonmuscle myosin II on Golgi-derived vesicles

A variety of peripheral membrane proteins associate dynamically with Golgi membranes during the budding and trafficking of transport vesicles in eukaryotic cells. A monoclonal antibody (AD7) raised against Golgi membranes recognizes a peripheral membrane protein, p200, which associates with vesicles budding off the trans-Golgi network (TGN). Based on preliminary findings, a potential association between p200 and myosin on Golgi membranes was investigated. Immunofluorescence staining of cultured cells under a variety of fixation conditions was carried out using an antibody raised against chick brush border nonmuscle myosin II. We show that, in addition to being found in the cytoplasm or associated with stress fibres, nonmuscle myosin II is also specifically localized on Golgi membranes. Myosin II was also detected on Golgi membranes by immunoblotting and by immunogold labeling at the electron microscopy level where it was found to be concentrated on Golgi-derived vesicles. The association of myosin II with Golgi membranes is dynamic and was found to be enhanced following activation of G proteins. Myosin II staining of Golgi membranes was also disrupted by brefeldin A (BFA). Colocalization of the AD7 and myosin II antibodies at the light and electron microscopy levels led us to investigate the nature of the 200 kDa protein recognized by both antibodies. The 200 kDa protein immunoprecipiated by the AD7 antibody was isolated from MDCK cells and used for microsequencing. Amino acid sequence data enabled us to identify p200 as the heavy chain of nonmuscle myosin IIA. In addition, an extra protein (240 kDa) recognized by the AD7 antibody specifically in extracts of HeLa cells, was sequenced and identified as another actin-binding protein, filamin. These results show that nonmuscle myosin II is associated with Golgi membranes and that the vesicle-associated protein p200, is itself a heavy chain of myosin II.

Microtubule-entrained kinase activities associated with the cortical cytoskeleton during cytokinesis

Research over the past few years has demonstrated the central role of protein phosphorylation in regulating mitosis and the cell cycle. However, little is known about how the mechanisms regulating the entry into mitosis contribute to the positional and temporal regulation of the actomyosin-based contractile ring formed during cytokinesis. Recent studies implicate p34cdc2 as a negative regulator of myosin II activity, suggesting a link between the mitotic cycle and cytokinesis. In an effort to study the relationship between protein phosphorylation and cytokinesis, we examined the in vivo and in vitro phosphorylation of actin-associated cortical cytoskeletal (CSK) proteins in an isolated model of the sea urchin egg cortex. Examination of cortices derived from eggs or zygotes labeled with 32P-orthophosphate reveals a number of cortex-associated phosphorylated proteins, including polypeptides of 20, 43 and 66 kDa. These three major phosphoproteins are also detected when isolated cortices are incubated with [32P]ATP in vitro, suggesting that the kinases that phosphorylate these substrates are also specifically associated with the cortex. The kinase activities in vivo and in vitro are stimulated by fertilization and display cell cycle-dependent activities. Gel autophosphorylation assays, kinase assays and immunoblot analysis reveal the presence of p34cdc2 as well as members of the mitogen-activated protein kinase family, whose activities in the CSK peak at cell division. Nocodazole, which inhibits microtubule formation and thus blocks cytokinesis, significantly delays the time of peak cortical protein phosphorylation as well as the peak in whole-cell histone H1 kinase activity. These results suggest that a key element regulating cortical contraction during cytokinesis is the timing of protein kinase activities associated with the cortical cytoskeleton that is in turn regulated by the mitotic apparatus.

Differential regulation of the activity of the 42 kD mitogen activated protein kinase (p42mapk) during enterocyte differentiation in vivo

The family of mitogen activated protein (MAP) kinases appear to play a central role in relaying signals generated by receptor protein tyrosine kinases (RPTK) from the cell surface to the nucleus. We previously demonstrated that undifferentiated and mitotically active crypt cells have high levels of tyrosine phosphorylated proteins (DR Burgess, W Jiang, S Mamajiwalla and W Kinsey. 1989. J. Cell Biol., 109: 2139) possibly due to the activation of RPTKs and also have high pp60c-src protein tyrosine kinase activity (CA Cartwright, SN Mamajiwalla, SA Skolnik, W Eckhart and DR Burgess. 1993. Oncogene. 8: 1033) when compared to differentiated, non-mitotic villus cells. Since activation of RPTKs leading to cell proliferation or differentiation involves activation of the Ras-MAP kinase pathway, we chose to determine in this study if the activity of the MAP kinases were also regulated during differentiation of normal adult enterocytes. Our data show that although the 42 kD MAP kinase (p42mapk) was expressed in both crypt and villus cells, it was phosphorylated on tyrosine and active only in the crypt cells. Our data further suggest that p42mapk is inactivated during differentiation, possibly by a protein tyrosine phosphatase. Immunofluorescence studies revealed that p42mapk localized to the nuclei in both undifferentiated and differentiated enterocytes and colocalized with phosphotyrosine containing proteins at the region of the junctional complex. These results suggest that p42mapk and its regulators are tightly controlled during enterocyte differentiation in vivo and implicate p42mapk as a key regulatory molecule in the normal development of the adult intestinal epithelium.

Microvillus assembly. Not actin alone

Transfection studies provide supporting evidence for the proposed role of villin and fimbrin in bundling the core actin filaments of microvilli.

Molecular motors are differentially distributed on Golgi membranes from polarized epithelial cells

Microtubules (MT) are required for the efficient transport of membranes from the trans-Golgi and for transcytosis of vesicles from the basolateral membrane to the apical cytoplasm in polarized epithelia. MTs in these cells are primarily oriented with their plus ends basally near the Golgi and their minus-ends in the apical cytoplasm. Here we report that isolated Golgi and Golgi-enriched membranes from intestinal epithelial cells possess the actin based motor myosin-I, the MT minus-end-directed motor cytoplasmic dynein and its in vitro motility activator dynactin (p150/Glued). The Golgi can be separated into stacks, possessing features of the Golgi cisternae, and small membranes enriched in the trans-Golgi network marker TGN 38/41. Whereas myosin-I is present on all membranes in the Golgi fraction, dynein is present only on the small membrane fraction. Dynein, like myosin-I, is associated with membranes as a cytoplasmic peripheral membrane protein. Dynein and myosin-I coassociate with membranes that bind to MTs and cross-link actin filaments and MTs in a nucleotide-dependent manner. We propose that cytoplasmic dynein moves Golgi membranes along MTs to the cell cortex where myosin-I provides local delivery through the actin-rich cytoskeleton to the apical membrane.

Isolation and characterization of a sea urchin zygote cortex that supports in vitro contraction and reactivation of furrowing

The isolation of the cortex of the sea urchin blastomere by detergent lysis was explored with the aim of analyzing components important in the structure and function of the cortical cytoskeleton, and their relationship to such phenomena as contraction. Buffered EGTA medium supplemented with isotonic glycerol and with magnesium, at a level close to the reported internal cellular concentration, yields stable cytoskeletal cortices that retain their spherical shape. Cortices prepared this way contain actin, myosin, fascin and spectrin, components normally associated with the cortical cytoskeleton in a similar distribution to that in intact zygotes. They retain the organized cortical filamentous structure, including the actin-fascin bundles that form cores of microvilli. ATP and NaCl caused changes in cortical shape, described as either contraction or expansion, respectively. Spectrin, but not myosin, was partially extracted by NaCl, resulting in expansion of the cortex that suggests a role for spectrin in maintenance of cortical structure. ATP (but not ADP nor ATP gamma S), which caused the partial removal of myosin and spectrin, led to the contraction of the cortex, consistent with a role for myosin in cortical tension. In cortices isolated from dividing eggs, the zygotes retained their cleavage furrows and ATP induced continuation of furrow progression. This preparation appears to be a useful in vitro model for cytokinesis.

Membrane motility mediated by unconventional myosin

Largely on the basis of their physical properties and their localization to cell membranes, it has been proposed that the unconventional myosins are membrane motors. In the past year, a combination of immunological, biochemical and genetic approaches has begun to provide direct evidence that unconventional myosins have important roles in movements of the plasma membrane and cytoplasmic organelles.

The cytoskeleton in development of epithelial cell polarity

The polarization of intestinal epithelial cells and the stereotypic arrangement of their actin-based cytoskeleton have made these epithelia an excellent system to explore the organization and formation of a cortical actin-based cytoskeleton. Through a combined morphological and biochemical analysis, the molecular arrangement of many of the components of the brush border has been elucidated. Study of brush border assembly in the Crypts of Lieberkühn suggests that cytoskeletal mRNA and protein expression, as well as morphological development, occur rapidly following cell differentiation. Protein kinases appear to be important regulators of intestinal cell growth, for differentiating cells in the crypts possess 15-fold higher levels of tyrosine phosphorylated proteins than differentiated cells of the villus. One of these kinases, pp60c-src, has a 4- to 7-fold higher activity in crypts and increased association with the cytoskeleton than it has in villus cells. The development and maintenance of polarization in epithelial cells require the targeting and transport of specific proteins to the apical and basolateral plasma membrane. It has been proposed that a dynein-like, microtubule-based motor is involved in the transport of apically directed materials from the trans-Golgi to the apical plasma membrane. However, microtubules do not reach the plasma membrane, but terminate below the actin-rich network of filaments comprising the terminal web. We propose that vesicles translocate from the Golgi to the apical cytoplasm along microtubules using dynein, and then move through the terminal web to reach the apical plasma membrane using the actin-based motor myosin-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal crypt cells contain higher levels of cytoskeletal-associated pp60c-src protein tyrosine kinase activity than do differentiated enterocytes

Undifferentiated crypt cells from chicken small intestine contain 15-fold higher levels of tyrosine-phosphorylated proteins than do differentiated enterocytes located at the villus apex. The tyrosine kinase activity and the tyrosine-phosphorylated proteins are associated with the Triton-insoluble cytoskeleton. To determine whether: (1) pp60c-src is an active tyrosine kinase in crypt cell cytoskeletons and (2) cytoskeletal-associated pp60c-src activity decreases as crypt cells differentiate, we isolated pp60c-src from subcellular fractions of cells along the crypt-villus axis of chicken small intestine and measured its protein kinase activity. We observed that pp60c-src activity in crypt cytoskeleton was higher (on average, fourfold as measured by enolase phosphorylation or sevenfold as measured by autophosphorylation) than that in cytoskeletons from differentiated enterocytes. Moreover, nearly 70% of pp60c-src activity in crypt cells, like that of pp60v-src, pp60c-src mutants with elevated kinase, activity or pp60v-src from activated platelets, localized to the cellular cytoskeleton. In contrast, less than 20% of pp60c-src activity in differentiated enterocytes, like that of kinase-inactive pp60v-src or pp60c-src from fibroblasts or resting platelets, associated with the cytoskeleton. Furthermore, in crypt cells, unlike differentiated enterocytes, cytoskeletal-associated pp60c-src appeared to have higher specific protein tyrosine kinase activity than did soluble pp60c-src. The data suggest that a kinase-active form of pp60c-src located in the cytoskeleton of crypt cells may be responsible for phosphorylating proteins on tyrosine and regulating growth and differentiation of the cells.