The impact of a blood-culture diagnostic stewardship intervention on utilization rates and antimicrobial stewardship

Blood-culture overutilization is associated with increased cost and excessive antimicrobial use. We implemented an intervention in the adult intensive care unit (ICU), combining education based on the DISTRIBUTE algorithm and restriction to infectious diseases and ICU providers. Our intervention led to reduced blood-culture utilization without affecting safety metrics.

Detection of invasive Bartonella infections with next-generation sequencing of microbial cell-free DNA

We report 9 patients with invasive Bartonella infections, including 5 with endocarditis, who were diagnosed with microbial cell-free DNA next-generation sequencing and Bartonella serology studies. Diagnosis with plasma mcfDNA NGS enabled a faster clinical and laboratory diagnosis in 8 patients. Prompt diagnosis impacted antibiotic management in all 9 patients.

329. Bedside Inoculation of Blood Culture Bottles Does Not Improve Ascites Culture Positivity Rate in Spontaneous Bacterial Peritonitis

Background

Prior research demonstrates increased positivity rate for ascites cultures in spontaneous bacterial peritonitis (SBP) when directly inoculated into blood culture bottles at bedside, versus the “conventional method” - transportation of ascitic fluid in a sealed syringe to the laboratory, centrifuging, and plating on Chocolate, Blood, and MacConkey’s agars and in a Schaedler broth. We hypothesized that collection of ascites via direct inoculation into blood culture bottles would improve ascites culture positivity rate in SBP when compared to prior methods.

Methods

In November of 2021, our institution implemented a policy in which all ascites cultures were directly inoculated into blood culture bottles at bedside. We retrospectively reviewed all ascites cultures collected from May of 2021 through April of 2022, including all cultures with an absolute neutrophil count of greater than 250 cells/mm3. We excluded all samples from patients with secondary bacterial peritonitis and all samples collected in November. If a patient had multiple samples that met inclusion criteria, only the first was included for analysis. Our primary outcome was positivity rate of cultures pre- and post-implementation of this new policy.

Results

1375 ascites cultures were collected. Of these, 52 met our inclusion criteria. These patients were on average 58 years old (range 33-74), 50% female, with a median MELD of 25.5 (range 8-40). The conventional method was positive in 7/37 (18.9%) cultures, and direct inoculation of blood cultures in 1/15 (6.67%), p = .27.

Conclusion

As opposed to the previous literature, we detected no difference in positivity rate between the conventional method of ascites culture compared to direct inoculation of blood cultures at the bedside. This difference from prior literature may be due to differences in time to inoculation, our smaller sample size, or overfilling of the bottles during inoculation.

Disclosures

All Authors: No reported disclosures.

185. Implementation of Multiplex Polymerase Chain Reaction in Clinical Practice: Impact on Antimicrobial Management In Infectious Diarrhea

Background

Stool culture and stool polymerase chain reaction (PCR) panels are both used to evaluate patients with suspected infectious diarrhea. Stool PCR panels are especially advantageous because of their ability to detect a broad array of infectious pathogens in less than one hour. Our study assessed how the use of stool PCR panels instead of stool culture impacted antibiotic days of therapy (DOT) and length of therapy (LOT) in hospitalized patients with suspected infectious diarrhea.

Methods

In December 2021, an intervention was implemented in our hospital in which all electronic orders for stool cultures were automatically switched to stool PCR testing. The pre-intervention group was comprised of 75 hospitalized adult patients who had a stool culture obtained from September to November 2021. The post-intervention group was comprised of 81 adult patients who had a stool PCR obtained from December 2021 to February 2022. The DOT and LOT for antibiotics prescribed specifically for infectious diarrhea were determined for each patient; DOT and LOT were compared between the pre- and post- intervention groups.

Results

The median DOT in the pre- and post-intervention groups was 0 with a range of 0-10 and 0-8, respectively. The median LOT in the pre- and post-intervention groups was 0 (range 0-5 for both groups). No significant difference in the median DOT (Wilcoxon rank sum test, p-value = 0.967) or LOT (Wilcoxon rank sum test, p-value = 0.993) was found between the pre- and post-intervention groups (Figure 1). After adjusting for patient days present, no significant change in DOT or LOT incidence rate was found between the pre- and post-intervention groups. The DOT incidence rate ratio (RR) was 0.71 (95% CI 0.42, 1.22), and the LOT incidence RR was 0.67 (95% CI 0.36, 1.24). Figure 1.

149. Increasing Oxacillin Resistance of Staphylococcus lugdunensis Over Time, Utilizing Whole Genome Sequencing to Characterize Resistance

Background

Staphylococcus lugdunensis (SL) is a coagulase negative staphylococci (CoNS) demonstrating more virulent pathogenicity compared to other CoNS. With implementation of rapid diagnostics such as multiplex PCR on blood culture and use of MALDI-TOF (MALDI), CoNS can now be routinely specifically identified as SL. We sought to describe the antibiotic susceptibility of SL over time, and to utilize whole genome sequencing (WGS) to identify the characteristics of oxacillin (OXA) resistant SL.

Methods

Retrospective review of all culture isolates positive for SL from two major hospital systems, Memorial Hermann Hospital System (MHHS) and Baylor St. Lukes Medical Center (BSLMC) in Houston, TX. MALDI was implemented in 2016 at BSLMC and 2019 at MHHS. MHHS utilizes Microscan®, and BSLMC utilizes Vitek2® for susceptibility testing. For this study, all duplicated isolates within a 2-week period were excluded. Six patient isolates, three OXA resistant and three susceptible, were sent for WGS and analysis.

Results

Between 2014 and 2021, 744 culture isolates were identified as SL, 325 from MHHS and 419 from BSLMC (Fig 1). An increasing trend was observed at MHHS over time, however this trend was not observed at BSLMC. 83.6% (622/744) of isolates were susceptible to OXA. An overall trend towards increasing resistance was observed over time (Fig 2). Six isolates, three OXA susceptible (S) and three resistant (R), were sent for WGS. The R isolates were found to share the same sequence type (ST3), and while they were not clonal, were closely related and all harbored an SCCmec cassette most closely related to SCCmec type IVg.

Conclusion

In our study, an increasing number of isolates were identified at MHHS over time. This finding may be related to implementation of MALDI. Overall OXA susceptibility was lower than expected at 83.6%, when compared to a prior large-scale United States based study in 2017 demonstrating 95.3% susceptibility. This finding of developing resistance is concerning. While WGS analysis of R isolates did not demonstrate clonality, it did show close relation. This data may suggest expansion of an emerging lineage, however more isolates will need to be studied for conclusion given limited sample size.

Disclosures

All Authors: No reported disclosures.

An integrated approach to evaluate different tetracycline derivatives for formulary decisions

DISCLAIMER

In an effort to expedite the publication of articles, AJHP is posting manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

PURPOSE

Stenotrophomonas maltophilia has emerged as a critical opportunistic pathogen associated with significant morbidity and mortality. Tetracycline derivatives have been recognized as alternative treatment options, but they have varied pharmacokinetic properties. An integrated approach to different tetracycline derivatives for formulary decisions is reported.

METHODS

The minimum inhibitory concentration (MIC) data from clonally diverse bloodstream S. maltophilia isolates were examined, along with the pharmacokinetic profiles of 4 tetracycline derivatives, to predict achievable pharmacodynamic exposures with standard intravenous dosing regimens. Antimicrobial therapy was assessed using the ratio of daily drug acquisition cost relative to the ratio of the free-drug area under the time-concentration curve (fAUC) to the 90th percentile for minimum inhibitory concentration (MIC) values for isolates (fAUC/MIC90).

RESULTS

In our analysis, minocycline had the greatest fAUC/MIC90. Doxycycline was the most financially preferred agent, as calculated using 2020 average wholesale price for base-case estimates of drug acquisition cost.

CONCLUSION

An integrated evaluation for antimicrobial formulary decision-making addressed local susceptibility data, pharmacokinetics, pharmacodynamics, dosing regimens, and drug acquisition costs. This comprehensive method is more objective than the conventional approach and warrants validation.

Prevalence and predictors of spontaneous bacterial peritonitis due to ceftriaxone-resistant organisms at a large tertiary centre in the USA

OBJECTIVES

The epidemiology of spontaneous bacterial peritonitis (SBP) due to ceftriaxone-resistant organisms has not been well studied in the USA. The primary objective of this study was to assess the prevalence and predictors of ceftriaxone-resistant SBP at a large US tertiary-care centre.

METHODS

This 1:1:4 case-case-control study included 141 adults with liver cirrhosis admitted from November 2011 to March 2016. Case group 1 were patients with SBP with a ceftriaxone-resistant organism (n=21). Case group 2 were patients with SBP with a ceftriaxone-susceptible organism (n=26). The control group were patients without SBP (n=94). Multiple logistic regression analysis was used to identify predictors of ceftriaxone-resistant SBP.

RESULTS

Fifty isolates were identified from 47 patients with culture-positive SBP (case groups 1 and 2). Of these 50 isolates, 32 (64%) were Gram-negatives [mostly Enterobacteriaceae (91%)], 15 (30%) were Gram-positives and 3 (6%) were Candida spp. The prevalence of ceftriaxone resistance in patients with culture-positive SBP was 45% (21/47). The most common ceftriaxone-resistant organisms were ESBL-producing Enterobacteriaceae (45%). Independent predictors of ceftriaxone-resistant SBP included duration of β-lactam therapy in the past 90days (aOR=1.07, 95% CI 1.01-1.13) and recent invasive gastrointestinal procedure (aOR=12.47, 95% CI 2.74-56.67).

CONCLUSIONS

The prevalence of ceftriaxone-resistant SBP was significant at a US tertiary centre. Local epidemiological data and identification of risk factors associated with ceftriaxone-resistant SBP, e.g. increased usage of previous β-lactam therapy and invasive gastrointestinal procedure, may help clinicians identify patients requiring alternative empirical antibiotics.

Prevalence of extended-spectrum beta-lactamase and carbapenemase-producing bloodstream isolates of Klebsiella pneumoniae in a tertiary care hospital

To improve prescribing of empiric therapy, the local molecular epidemiology of extended-spectrum beta-lactamases (ESBLs) and Klebsiella pneumoniae carbapenemases (KPCs) in bloodstream isolates of K. pneumoniae were evaluated. Isolates resistant to third generation cephalosporins were screened phenotypically for ESBLs and carbapenemases, and subsequently confirmed by PCR for the presence of ESBL (bla_TEM, bla_SHV and bla_CTX-M) and carbapenemase (bla_KPC, bla_VIM, bla_NDM and bla_OXA-48) genes. Hydrolytic activity (functional gene expression) was quantified using a nitrocefin degradation assay and correlated to ceftazidime or meropenem MIC. Clonality was assessed by repetitive element-based PCR. Beta-lactamases were functionally expressed in 13 isolates (15.5%); 7 (53.8%) harboured bla_CTX-M-15 and 6 (46.2%) carried the bla_KPC-2 gene. Correlation of hydrolytic activity to MIC yielded a coefficient of 98% for isolates expressing ESBLs alone and 56% for carbapenemase producers. Four unique ESBL-expressing clones and five carbapenem-resistant clones were identified. All 13 resistant isolates were susceptible to ceftazidime/avibactam (MIC ≤ 8/4 mg/L).

Activity of minocycline against Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae clinical isolates, with comparison to doxycycline and tigecycline

We examined the in vitro activity of minocycline against 103 Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae isolates and found approximately half had susceptible (26%) or intermediate (26%) MICs. For a subset of 35 isolates, susceptibility was highest to tigecycline (71% FDA vs. 20% EUCAST) followed by minocycline (14%) and then doxycycline (6%).

Outcomes and Risk Factors for Mortality among Patients Treated with Carbapenems for Klebsiella spp. Bacteremia

Background

Extensive dissemination of carbapenemase-producing Enterobacteriaceae has led to increased resistance among Klebsiella species. Carbapenems are used as a last resort against resistant pathogens, but carbapenemase production can lead to therapy failure. Identification of risk factors for mortality and assessment of current susceptibility breakpoints are valuable for improving patient outcomes.

Aim

The objective of this study was to evaluate outcomes and risk factors for mortality among patients treated with carbapenems for Klebsiella spp. bacteremia.

Methods

Patients hospitalized between 2006 and 2012 with blood cultures positive for Klebsiella spp. who received ≥ 48 hours of carbapenem treatment within 72 hours of positive culture were included in this retrospective study. Patient data were retrieved from electronic medical records. Multivariate logistic regression was used to identify risk factors for 30-day hospital mortality.

Results

One hundred seven patients were included. The mean patient age was 61.5 years and the median APACHE II score was 13 ± 6.2. Overall, 30-day hospital mortality was 9.3%. After adjusting for confounding variables, 30-day mortality was associated with baseline APACHE II score (OR, 1.17; 95% CI, 1.01–1.35; P = 0.03), length of stay prior to index culture (OR, 1.03; 95% CI, 1.00–1.06; P = 0.04), and carbapenem non-susceptible (imipenem or meropenem MIC > 1 mg/L) infection (OR, 9.08; 95% CI, 1.17–70.51; P = 0.04).

Conclusions

Baseline severity of illness and length of stay prior to culture were associated with 30-day mortality and should be considered when treating patients with Klebsiella bacteremia. These data support the change in carbapenem breakpoints for Klebsiella species.

Multiplex Real-Time PCR Method for Simultaneous Identification and Toxigenic Type Characterization of Clostridium difficile From Stool Samples

Background

The aim of this study was to develop and validate a multiplex real-time PCR assay for simultaneous identification and toxigenic type characterization of Clostridium difficile.

Methods

The multiplex real-time PCR assay targeted and simultaneously detected triose phosphate isomerase (tpi) and binary toxin (cdtA) genes, and toxin A (tcdA) and B (tcdB) genes in the first and sec tubes, respectively. The results of multiplex real-time PCR were compared to those of the BD GeneOhm Cdiff assay, targeting the tcdB gene alone. The toxigenic culture was used as the reference, where toxin genes were detected by multiplex real-time PCR.

Results

A total of 351 stool samples from consecutive patients were included in the study. Fifty-five stool samples (15.6%) were determined to be positive for the presence of C. difficile by using multiplex real-time PCR. Of these, 48 (87.2%) were toxigenic (46 tcdA and tcdB-positive, two positive for only tcdB) and 11 (22.9%) were cdtA-positive. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of the multiplex real-time PCR compared with the toxigenic culture were 95.6%, 98.6%, 91.6%, and 99.3%, respectively. The analytical sensitivity of the multiplex real-time PCR assay was determined to be 103colonyforming unit (CFU)/g spiked stool sample and 0.0625 pg genomic DNA from culture. Analytical specificity determined by using 15 enteric and non-clostridial reference strains was 100%.

Conclusions

The multiplex real-time PCR assay accurately detected C. difficile isolates from diarrheal stool samples and characterized its toxin genes in a single PCR run.

Real-world performance of a microarray-based rapid diagnostic for Gram-positive bloodstream infections and potential utility for antimicrobial stewardship

The Verigene Gram-positive blood culture assay (BC-GP) is a microarray-based rapid diagnostic test, which includes targets for 12 bacterial species and 3 resistance determinants. We prospectively compared the diagnostic accuracy of the BC-GP to routine microbiologic methods and evaluated the potential of the BC-GP for antimicrobial stewardship programs. A total of 143 consecutive patients with Gram-positive bacteremia were included in the analysis. BC-GP correctly identified 127/128 (99.2%) of organisms from monomicrobial blood cultures and 9/14 (64.3%) from polymicrobial, including all methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. Stewardship interventions were possible in 51.0% of patients, most commonly stopping or preventing unnecessary vancomycin or starting a targeted therapy. In Monte Carlo simulations, unnecessary antibiotics could be stopped at least 24 hours earlier in 65.6% of cases, and targeted therapy could be started at least 24 hours earlier in 81.2%. BC-GP is a potentially useful test for antibiotic stewardship in patients with Gram-positive bacteremia.

Healthcare resource utilization for recurrent Clostridium difficile infection in a large university hospital in Houston, Texas

Background

There are limited data examining healthcare resource utilization in patients with recurrent Clostridium difficile infection (CDI).

Methods

Patients with CDI at a tertiary-care hospital in Houston, TX, were prospectively enrolled into an observational cohort study. Recurrence was assessed via follow-up phone calls. Patients with one or more recurrence were included in this study. The location at which healthcare was obtained by patients with recurrent CDI was identified along with hospital length of stay. CDI-attributable readmissions, defined as a positive toxin test within 48 hours of admission and a primary CDI diagnosis, were also assessed.

Results

372 primary cases of CDI were identified of whom 64 (17.2%) experienced at least one CDI recurrence. Twelve of 64 patients experienced 18 further episodes of CDI recurrence. Of these 64 patients, 33 (50.8%) patients with recurrent CDI were readmitted of which 6 (18.2%) required ICU care, 29 (45.3%) had outpatient care only, and 2 (3.1%) had an ED visit. Nineteen (55.9%) readmissions were defined as CDI-attributable. For patients with CDI-attributable readmission, the average length of stay was 6±6 days.

Conclusion

Recurrent CDI leads to significant healthcare resource utilization. Methods of reducing the burden of recurrent CDI should be further studied.

FKS mutant Candida glabrata: risk factors and outcomes in patients with candidemia

BACKGROUND

Echinocandins are recommended for Candia glabrata candidemia. Mutations in the FKS1 and FKS2 genes are associated with echinocandin resistance. Few studies have assessed risk factors for FKS mutant isolates and outcomes in patients receiving micafungin treatment.

METHODS

Patients with C. glabrata bloodstream infection admitted to a large, tertiary care hospital between 2009 and 2012 were included in this study. For each isolate, FKS1 and FKS2 genes were sequenced to identify mutations. Risk factors for FKS mutations and treatment outcomes in patients receiving an echinocandin were assessed using multivariate logistic regression.

RESULTS

Seventy-two patients were included in the study of which 13 (18%) had an FKS mutant isolate. The only significant predictor for FKS mutations was prior echinocandin exposure (odds ratio [OR], 19.9; 95% confidence interval [CI], 4.7-84.7; P ≤ .01). Treatment failure occurred in 17 (30%) of 57 patients who received an echinocandin and was more common in patients with FKS mutants (6 of 10; 60%) compared with non-FKS mutants (11 of 47; 23%). Underlying gastrointestinal disorder (OR, 4.7; 95% CI, 1.1-20.9; P = .04) and prior echinocandin exposure (OR, 8.3; 95% CI, 1.7-40.4; P ≤ .01) were independent predictors of echinocandin treatment failure. Treatment response and echinocandin minimum inhibitory concentrations varied among specific FKS mutations.

CONCLUSIONS

FKS mutations were identified in 18% of 72 patients with C. glabrata candidemia. Common risk factors for FKS mutant isolates included previous echinocandin exposure, which also influenced response rates.

Clinical Practice Patterns in Hospitalized Patients at Risk for Invasive Candidiasis

Background: Rapid diagnostic tests for Candida are becoming available that may supplement traditional microbiological identification. Objective: Assess clinical practice patterns in patients with or at risk of candidiasis who may benefit from the use of rapid diagnostic tests. Methods: This was a prospective cohort study of patients with candidemia or receiving systemic antifungals conducted at a university-affiliated tertiary care hospital. Time to initiation of therapy, Candida species, time to identification, and indications for antifungal use were assessed. Results: A total of 162 patients with candidemia aged 58 ± 17 years were identified. Average time to yeast identification yeast was 2.2 ± 1.3 days and varied by Candida species (range = 0.6-7.9 days). Average time for patient to start antifungal therapy was 3.5 ± 2.1 days. In Monte Carlo simulations, average time to initiation of antifungal therapy was 0.6 ± 0.2 days for T2Candida, 2.6 ± 1.3 days for PNA-FISH (fluorescence in situ hybridization using peptide nucleic acid probes), and 2.5 ± 1.4 days for MALDI-TOF (matrix-assisted laser desorption/ionization time of flight). Use of T2Candida on the day of the blood culture collection resulted in 3136 to 6078 fewer doses of echinocandins annually per 5000 patients. Conclusion: Many interventions are possible for antifungal stewardship programs to improve care of patients at risk for systemic candidiasis, including rapid identification of yeast species and limiting unnecessary antifungal agents. Technology enabling rapid diagnosis of Candida will be paramount to appropriate, cost-effective treatment of patients with or at risk for candidiasis.

An evaluation of multiple phenotypic screening methods for Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae

Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae may display MICs to carbapenems within susceptible or intermediate ranges, prompting confirmatory testing. Four phenotypic methods to detect KPC producers were evaluated against a collection of clinical Enterobacteriaceae isolates. Meropenem-phenylboronic acid double disk synergy testing demonstrated the best performance with 100% sensitivity and specificity.

Evaluation of antifungal therapy in patients with candidaemia based on susceptibility testing results: implications for antimicrobial stewardship programmes

BACKGROUND

Definitive antifungal therapy is typically based on Candida species and clinical status, rather than susceptibility reports. Antifungal susceptibility testing is available, but the impact on treatment decisions is unknown. The purpose of this study was to assess antifungal therapy in hospitalized patients with candidaemia during the time period between the start of empirical therapy and after antifungal susceptibility testing reports are available.

METHODS

A retrospective study of 161 hospitalized patients with candidaemia was conducted. Patients who received fluconazole or an echinocandin were evaluated for changes in empirical antifungal therapy prior to and after susceptibility reporting.

RESULTS

One hundred and sixty-one patients aged 59 ± 16 years (male, 54%; Caucasian, 52%; APACHE II score ≥ 15, 48%; and intensive care unit, 50%) were identified, of whom 130 (81%) had fluconazole-susceptible candidaemia. Fifty-eight patients (36%) were initiated on fluconazole and 103 (64%) on an echinocandin. The mean time from culture to the susceptibility report was 5 ± 2 days. Prior to availability of the susceptibility report, 20 fluconazole-initiated patients (34%) were switched to an echinocandin, while 14 echinocandin-initiated patients (14%) were switched to fluconazole. Once a susceptibility report was available, 35 of 89 (39%) patients with fluconazole-susceptible candidaemia on an echinocandin were de-escalated to fluconazole. Eleven patients on fluconazole just prior to a susceptibility report were identified with a fluconazole-resistant Candida species.

CONCLUSIONS

Using antifungal susceptibility testing, patients given fluconazole with fluconazole-resistant Candida species were identified. Less than 40% of echinocandin-treated patients with fluconazole-susceptible organisms were de-escalated to fluconazole. Antifungal susceptibility testing may help to identify patients in need of clinical intervention.

Cross-reaction of anti-human CD monoclonal antibodies on guinea pig cells: A summary of the guinea pig section of the HLDA8 animal homologues data

A panel of 377 commercially available monoclonal antibodies (mAbs) specific for a total of 144 CD antigens was submitted to the animal homologue section of the Eighth International Workshop on Human Leukocyte Differentiation Antigens (HLDA8, Adelaide, Australia) for cross-reactivity studies in a range of vertebrate species. Each of the mAbs in this study was screened for positive reactivity with guinea pig splenocytes by flow cytometry. In the first phase of this study 36 of the total 367 mAbs (9.81%) cross-reacted with splenocyte surface molecules. The majority (26 of 36) of these cross-reactive mAbs were analysed further to confirm appropriate cell subset expression by two-color immunofluorescence. Our results indicate that 15 anti-human CD9, CD10, CD14, CD20 (two clones), CD22, CD25, CD29 (two clones), CD32, CD47 (two clones), CD49d, CD49e, and CD86 mAbs exhibit clear cross-reactivity with guinea pig splenocytes. These mAb can potentially be added to the limited repertoire of reagents available for studies in this model system. This data clearly indicates that mouse anti-human CD mAb guinea pig cross-reactions have been defined and that an aim of this HLDA8 section has been fulfilled, i.e., to identify mAbs which recognize conserved, species-independent CD epitopes. These results will contribute to the availability of mAbs and tools in veterinary medicine and immunology.

Mycobacterium bovis BCG vaccination modulates TNF-α production after pulmonary challenge with virulent Mycobacterium tuberculosis in guinea pigs

Tumor necrosis factor-alpha (TNF-alpha) plays critical and opposing roles in the pathogenesis of tuberculosis (TB). We examined the effects of Mycobacterium bovis BCG vaccination on TNF-alpha production in three distinct guinea pig leukocyte populations before and after pulmonary infection with M. tuberculosis H37Rv. Following BCG vaccination alone, and following challenge, bronchoalveolar lavage cells (BALC), resident peritoneal cells (PC), and splenocytes (SPC) were stimulated with purified protein derivative (PPD). Before virulent challenge, BCG vaccination clearly enhanced the ability of BALC, PC and SPC to produce TNF-alpha in response to PPD stimulation ex vivo. Following challenge, the TNF-alpha production of all three leukocyte populations from BCG-vaccinated animals remained relatively constant at pre-challenged levels. In sharp contrast, 5 weeks post-challenge, all three leukocyte populations from unvaccinated animals produced very high amounts of TNF-alpha in response to PPD. Three weeks post-challenge, SPC from one of the unvaccinated animals produced higher levels of TNF-alpha but the others produced lower levels of TNF-alpha than BCG-vaccinated animals. As expected, BCG vaccination reduced the levels of virulent mycobacteria in both the lungs and spleens. Thus, BCG vaccination allows guinea pigs to modulate TNF-alpha levels in conjunction with a reduction in bacillary loads in their tissues.

Evaluating the role of tumor necrosis factor-alpha in experimental pulmonary tuberculosis in the guinea pig

Tumor necrosis factor-alpha (TNF-alpha) is suggested to play multiple roles in immune and pathologic responses in tuberculosis. In this study, we have developed a system for the expression of recombinant guinea pig TNF-alpha (rgpTNF-alpha). Using rgpTNF-alpha along with neutralizing anti-rgpTNF-alpha antiserum, we tested the effect of modulating the levels of TNF-alpha on antigen-specific T cell proliferation in splenocytes. By neutralizing TNF-alpha in the supernatant of PPD-pulsed splenocytes with anti-rgpTNF-alpha, we observed hyperproliferation. Conversely, the addition of rgpTNF-alpha resulted in a significant suppression of PPD-induced lymphoproliferation. In addition, when unvaccinated and BCG-vaccinated guinea pigs were treated with polyclonal rgpTNF-alpha antiserum throughout the first 3 weeks following low-dose, pulmonary infection with Mycobacterium tuberculosis H37Rv, we observed splenomegaly in BCG-vaccinated guinea pigs. We also detected higher levels of splenic granuloma organization in the non-vaccinated group as well as a significant number of plasma cells associated with granulomata from the BCG-vaccinated group. These results suggest that modulating the availability of TNF-alpha in BCG-vaccinated guinea pigs can lead to immuno-dysregulation and, perhaps, the inappropriate enhancement of humoral immunity. Conversely, abrogating TNF-alpha activity in the context of a hyperinflammatory response in non-vaccinated guinea pigs may, in fact, rescue them from immunopathological consequences of overproducing TNF-alpha.

Recombinant guinea pig tumor necrosis factor alpha stimulates the expression of interleukin-12 and the inhibition of Mycobacterium tuberculosis growth in macrophages

Tumor necrosis factor alpha (TNF-alpha) plays an important role in the host immune response to infection with the intracellular pathogen Mycobacterium tuberculosis. It is essential for the formation of protective tuberculous granulomas and regulates the expression of other cytokines which contribute to a protective immune response. Interleukin-12 (IL-12) is known to promote a Th1 response, which is essential for antimycobacterial resistance. Recombinant guinea pig TNF-alpha (rgpTNF-alpha) protein (17 kDa) was purified, and its bioactivity was confirmed by its cytotoxicity for L929 fibroblasts. High titers of polyclonal anti-gpTNF-alpha antibody were obtained by immunization of rabbits. Resident alveolar and peritoneal macrophages were isolated from guinea pigs and infected with either the H37Ra or H37Rv strain of M. tuberculosis. The mRNA levels for TNF-alpha and IL-12 p40 were measured using real-time PCR. IL-12 p40 mRNA was up-regulated in a dose-dependent manner by rgpTNF-alpha alone. In infected macrophages, a lower dose of rgpTNF-alpha intensified the mRNA levels of TNF-alpha and IL-12 p40. However, higher doses of rgpTNF-alpha suppressed TNF-alpha and IL-12 p40 mRNA. The antimycobacterial activity of macrophages was assessed by metabolic labeling of M. tuberculosis with [3H]uracil. Resident alveolar and peritoneal macrophages treated with anti-gpTNF-alpha antibody to block endogenous TNF-alpha exhibited increased intracellular mycobacterial growth. These data suggest that the dose of TNF-alpha is crucial to the stimulation of optimal expression of protective cytokines and that TNF-alpha contributes to the control of mycobacterial replication to promote host resistance against M. tuberculosis.

The protective effect of the Mycobacterium bovis BCG vaccine is increased by coadministration with the Mycobacterium tuberculosis 72-kilodalton fusion polyprotein Mtb72F in M. tuberculosis-infected guinea pigs

A tuberculosis vaccine candidate consisting of a 72-kDa polyprotein or fusion protein based upon the Mtb32 and Mtb39 antigens of Mycobacterium tuberculosis and designated Mtb72F was tested for its protective capacity as a potential adjunct to the Mycobacterium bovis BCG vaccine in the mouse and guinea pig models of this disease. Formulation of recombinant Mtb72F (rMtb72F) in an AS02A adjuvant enhanced the Th1 response to BCG in mice but did not further reduce the bacterial load in the lungs after aerosol challenge infection. In the more stringent guinea pig disease model, rMtb72F delivered by coadministration with BCG vaccination significantly improved the survival of these animals compared to BCG alone, with some animals still alive and healthy in their appearance at >100 weeks post-aerosol challenge. A similar trend was observed with guinea pigs in which BCG vaccination was boosted by DNA vaccination, although this increase was not statistically significant due to excellent protection conferred by BCG alone. Histological examination of the lungs of test animals indicated that while BCG controls eventually died from overwhelming lung consolidation, the majority of guinea pigs receiving BCG mixed with rMtb72F or boosted twice with Mtb72F DNA had mostly clear lungs with minimal granulomatous lesions. Lesions were still prominent in guinea pigs receiving BCG and the Mtb72F DNA boost, but there was considerable evidence of lesion healing and airway remodeling and reestablishment. These data support the hypothesis that the coadministration or boosting of BCG vaccination with Mtb72F may limit the lung consolidation seen with BCG alone and may promote lesion resolution and healing. Collectively, these data suggest that enhancing BCG is a valid vaccination strategy for tuberculosis that is worthy of clinical evaluation.

Effect of neutralizing transforming growth factor beta1 on the immune response against Mycobacterium tuberculosis in guinea pigs

Transforming growth factor beta (TGF-beta) is a cytokine which has been shown to suppress the antimycobacterial immune responses of humans and experimental animals. In this study, the contributions of TGF-beta to cytokine production in vivo were investigated by using the established guinea pig model of tuberculous pleurisy. Mycobacterium bovis BCG-vaccinated guinea pigs were injected intrapleurally with heat-killed virulent Mycobacterium tuberculosis. Eight days following induction of an antigen-specific pleural effusion, guinea pigs were injected intrapleurally with anti-TGF-beta1 or isotype control antibody. The following day, pleural exudates were removed, and the fluid volume and characteristics of the infiltrating cells were determined. Pleural fluid was analyzed for total interferon (IFN) and tumor necrosis factor (TNF) protein levels by using appropriate bioassays. RNA from pleural effusion cells was examined to determine TGF-beta1, TNF-alpha, IFN-gamma, and interleukin-8 mRNA levels by using real-time PCR. Proliferative responses of pleural effusion lymphocytes were examined in response to concanavalin A and purified protein derivative (PPD) in vitro. Treatment with anti-TGF-beta1 resulted in decreased pleural fluid volume and decreased cell numbers in the pleural space along with an increased percentage of lymphocytes and a decreased percentage of neutrophils. The bioactive TNF protein levels in pleural fluid were increased in guinea pigs treated with anti-TGF-beta1, while the bioactive IFN protein concentrations were not altered. Expression of TGF-beta1 and TNF-alpha mRNA was significantly increased following TGF-beta1 neutralization. Finally, PPD-induced proliferative responses of pleural cells from anti-TGF-beta1-treated animals were significantly enhanced. Thus, TGF-beta1 may be involved in the resolution of this local, mycobacterial antigen-specific inflammatory response.

Rapid accumulation of eosinophils in lung lesions in guinea pigs infected with Mycobacterium tuberculosis

Guinea pig eosinophils were positively identified in bronchoalveolar lavage populations and in the lung granulomas of Mycobacterium tuberculosis-infected guinea pigs. It is possible that the rapid influx of these cells, and their subsequent degranulation during acute pulmonary tuberculosis, may play a key role in the susceptibility of this animal model.

Effect of Mycobacterium bovis BCG vaccination on Mycobacterium-specific cellular proliferation and tumor necrosis factor alpha production from distinct guinea pig leukocyte populations

In this study, we focused on three leukocyte-rich guinea pig cell populations, bronchoalveolar lavage (BAL) cells, resident peritoneal cells (PC), and splenocytes (SPC). BAL cells, SPC, and PC were stimulated either with live attenuated Mycobacterium tuberculosis H37Ra or with live or heat-killed virulent M. tuberculosis H37Rv (multiplicity of infection of 1:100). Each cell population was determined to proliferate in response to heat-killed virulent H37Rv, whereas no measurable proliferative response could be detected upon stimulation with live mycobacteria. Additionally, this proliferative capacity (in SPC and PC populations) was significantly enhanced upon prior vaccination with Mycobacterium bovis BCG. Accordingly, in a parallel set of experiments we found a strong positive correlation between production of antigen-specific bioactive tumor necrosis factor alpha (TNF-alpha) and prior vaccination with BCG. A nonspecific stimulus, lipopolysaccharide, failed to induce this effect on BAL cells, SPC, and PC. These results showed that production of bioactive TNF-alpha from mycobacterium-stimulated guinea pig cell cultures positively correlates with the vaccination status of the host and with the virulence of the mycobacterial strain.