Characterization of hypervirulent Klebsiella pneumoniae isolates in Belgium.

Hypervirulent Klebsiella pneumoniae (hvKp) raised concern worldwide. We studied 22 hvKp clinical invasive isolates referred to the Belgian national reference laboratory between 2014 and 2020. Sixty-four percent of the isolates expressed K2 capsular serotype and belonged to 7 different MLST lineages, while 32% expressed K1 (all belonging to ST23) and were associated with liver abscesses. Primary extra-hepatic infections were reported in 36% and sepsis for 95% of the patients with 30% of deaths. Improved clinical and microbiological diagnostics are required as hvKp may represent an underestimated cause of community-acquired invasive infections in Belgium.

Multicenter study of automated systems for colistin susceptibility testing.

PURPOSE: Broth microdilution (BMD) stays as the reference testing method for determination of antimicrobial susceptibility testing (AST) to colistin and is considered essential for patient management and for monitoring of colistin resistance. This multicenter study aimed to evaluate the performance of automated systems for colistin AST among Enterobacterales as an alternative for BMD since the majority of laboratories use automated systems as first-line method. METHODS: Twenty colistin resistant (COL-R) including 10 MCR producers and 10 colistin-susceptible (COL-S) Enterobacterales isolates were blindly tested for colistin susceptibility with the routine automated AST systems used by 8 laboratories (3 with BD Phoenix, 3 with Vitek2 and 2 with MicroScan). Additionally, 3 reference strains (E. coli ATCC 25922, E. coli NCTC 13846, and one COL-R mcr-negative K. pneumoniae M/14750) were tested in triplicate by each laboratory. RESULTS AND CONCLUSION: Results were compared with BMD performed at the reference laboratory. BD Phoenix and MicroScan automated AST systems provide accurate and reproducible categorical results for the testing of colistin in Enterobacterales. However, Vitek2 system showed poor performance for the detection of COL-R isolates especially those with MICs close to the susceptibility breakpoint (categorical agreement of 88% and precision categorical agreement of 81%).

Novel vancomycin resistance gene cluster in Enterococcus faecium ST1486, Belgium, June 2021.

We identified a novel van gene cluster in a clinical Enterococcus faecium isolate with vancomycin minimum inhibitory concentration (MIC) of 4 µg/mL. The ligase gene, vanP, was part of a van operon cluster of 4,589 bp on a putative novel integrative conjugative element located in a ca 98 kb genomic region presumed to be acquired by horizontal gene transfer from Clostridiumscidens and Roseburia sp. 499. Screening for van genes in E. faecium strains with borderline susceptibility to vancomycin is important.

Lateral flow immunochromatographic assay for rapid screening of faecal carriage of carbapenemase-producing Enterobacteriaceae.

Background: Rapid and effective screening of carbapenemase-producing Enterobacteriaceae (CPE) appears essential for adequate patient management and rapid implementation of infection control measures. Most of these screening techniques require a minimum of 24 h of culture. Molecular assays are an exception since these can be achieved within 1 h, but are expensive and usually require specialized facilities and trained personnel. In this context, lateral immunochromatography performed directly from rectal swab samples could represent a cost-effective alternative with a reduced turnaround time. Objectives: In this study, we assessed the performance of the OKN K-SeT test (Coris BioConcept, Gembloux, Belgium) for the rapid detection of OXA-48, KPC and NDM CPE directly from rectal swab samples. Methods: A total of 149 residual rectal swabs, routinely screened for CPE through selective culture and confirmed by PCR, were tested with a defined protocol consisting of a 2.5 h incubation of the swab in an enrichment medium containing meropenem followed by OKN K-SeT testing after centrifugation. Results: This method displayed an overall sensitivity of 96% and a specificity of 100% with a limit of detection ranging between 104 and 105 cfu/mL. Conclusions: Whereas this assay appears highly specific, it displays a reduced sensitivity compared with the standard procedure encompassing a culture step. Nonetheless, this rapid method allows an accelerated identification of most CPE carriers at a lower cost and, accordingly, the implementation of early appropriate management procedures.

Salicylidene Acylhydrazides and Hydroxyquinolines Act as Inhibitors of Type Three Secretion Systems in Pseudomonas aeruginosa by Distinct Mechanisms.

Type 3 secretion systems (T3SSs) are major virulence factors in Gram-negative bacteria. Pseudomonas aeruginosa expresses two T3SSs, namely, an injectisome (iT3SS) translocating effector proteins in the host cell cytosol and a flagellum (fT3SS) ensuring bacterial motility. Inhibiting these systems is an appealing therapeutic strategy for acute infections. This study examines the protective effects of the salicylidene acylhydrazide INP0341 and of the hydroxyquinoline INP1750 (previously described as T3SS inhibitors in other species) toward cytotoxic effects of P. aeruginosain vitro Both compounds reduced cell necrosis and inflammasome activation induced by reference strains or clinical isolates expressing T3SS toxins or only the translocation apparatus. INP0341 inhibited iT3SS transcriptional activation, including in strains with constitutive iT3SS expression, and reduced the total expression of toxins, suggesting it targets iT3SS gene transcription. INP1750 inhibited toxin secretion and flagellar motility and impaired the activity of the YscN ATPase from Yersinia pseudotuberculosis (homologous to the ATPase present in the basal body of P. aeruginosa iT3SS and fT3SS), suggesting that it rather targets a T3SS core constituent with high homology among iT3SS and fT3SS. This mode of action is similar to that previously described for INP1855, another hydroxyquinoline, against P. aeruginosa Thus, although acting by different mechanisms, INP0341 and INP1750 appear as useful inhibitors of the virulence of P. aeruginosa Hydroxyquinolines may have a broader spectrum of activity by the fact they act upon two virulence factors (iT3SS and fT3SS).

Inhibition of the Injectisome and Flagellar Type III Secretion Systems by INP1855 Impairs Pseudomonas aeruginosa Pathogenicity and Inflammasome Activation.

With the rise of multidrug resistance, Pseudomonas aeruginosa infections require alternative therapeutics. The injectisome (iT3SS) and flagellar (fT3SS) type III secretion systems are 2 virulence factors associated with poor clinical outcomes. iT3SS translocates toxins, rod, needle, or regulator proteins, and flagellin into the host cell cytoplasm and causes cytotoxicity and NLRC4-dependent inflammasome activation, which induces interleukin 1ß (IL-1ß) release and reduces interleukin 17 (IL-17) production and bacterial clearance. fT3SS ensures bacterial motility, attachment to the host cells, and triggers inflammation. INP1855 is an iT3SS inhibitor identified by in vitro screening, using Yersinia pseudotuberculosis Using a mouse model of P. aeruginosa pulmonary infection, we show that INP1855 improves survival after infection with an iT3SS-positive strain, reduces bacterial pathogenicity and dissemination and IL-1ß secretion, and increases IL-17 secretion. INP1855 also modified the cytokine balance in mice infected with an iT3SS-negative, fT3SS-positive strain. In vitro, INP1855 impaired iT3SS and fT3SS functionality, as evidenced by a reduction in secretory activity and flagellar motility and an increase in adenosine triphosphate levels. As a result, INP1855 decreased cytotoxicity mediated by toxins and by inflammasome activation induced by both laboratory strains and clinical isolates. We conclude that INP1855 acts by dual inhibition of iT3SS and fT3SS and represents a promising therapeutic approach.

Optimized Antibiotic Management of Critically Ill Patients with Severe Pneumonia Following Multiplex Polymerase Chain Reaction Testing: A Prospective Clinical Exploratory Trial.

Molecular diagnostic testing is assumed to enable fast respiratory pathogen identification and contribute to improved pneumonia management. We set up a prospective clinical trial at a tertiary hospital intensive care unit including adult patients suspected of severe pneumonia from whom a lower respiratory tract sample could be obtained. During control periods (CPs), routine testing was performed, and during intervention periods (IPs), this testing was completed with the FilmArray Pneumonia Panel plus test (FA-PNEU) executed 24/7. The main objective was to measure the impact of FA-PNEU results in terms of reduced time to targeted antimicrobial treatment administration. Over a 10-month period, analysis was performed on 35 CP and 50 IP patients. The median time to targeted antimicrobial treatment administration was reduced to 4.3 h in IPs compared to 26.4 h in CPs, with 54% of IP patients having FA-PNEU results that led to a treatment modification, of which all but one were targeted. Modifications included 10 (37%) de-escalations, 7 (25.9%) escalations, 3 (11.1%) regimen switches, and 7 (25.9%) complete antimicrobial discontinuations. FA-PNEU results were available with a 42.3 h gain compared to routine identification. This prospective study confirmed retrospective data demonstrating the benefit of FA-PNEU testing in severe pneumonia management of critically ill patients through improved antimicrobial use.

Streptococcus Pneumoniae Bacteremia with Acute Kidney Injury and Transient ADAMTS13 Deficiency.

A 43-year-old woman with a medical history of splenectomy for immune thrombocytopenic purpura was diagnosed with Streptococcus pneumoniae bacteremia. Her initial complaints were fever and more importantly painful extremities that appeared cyanotic. During her hospitalisation, she never developed cardiocirculatory failure but presented acute kidney injury (AKI) with oliguria. Laboratory investigations confirmed AKI with serum creatinine 2.55 mg/dL which peaked at 6.49 mg/dL. There was also evidence for disseminated intravascular coagulation (DIC) with decreased platelet count, low fibrinogen levels, and high D-dimer levels. There were no signs of haemolytic anaemia. The initial ADAMTS13 activity was low (17%) but slowly recovered. Renal function progressively improved with supportive therapy, as opposed to the progressing skin necrosis. The association of DIC and low ADAMTS13 activity may have contributed to the severity of microthrombotic complications, even in the absence of thrombotic microangiopathy as thrombotic thrombocytopenic purpura (TTP) or pneumococcal-associated haemolytic uremic syndrome (pa-HUS).

Impact of the COVID-19 pandemic on Clostridioides difficile infection in a tertiary healthcare institution in Belgium.

OBJECTIVES: Clostridioides difficile infection (CDI) causes the greatest number of healthcare-associated infectious diarrhoea. CDIs are transmitted by direct and indirect patient-to-patient contact and risk increases with the use of antibiotics. Since early 2020, the COVID-19 pandemic has affected healthcare systems in many ways including substantial changes in hygiene behaviour. The aim of this study was to assess whether CDI incidence differed during the COVID-19 pandemic compared to a year before. METHODS: All tests for suspected CDI cases were recorded for a hospital in Brussels, Belgium. The percentage of CDI-positive results and incidences (total and healthcare-associated (HA)-CDI)) for years 2019, 2020, 2021, and 2022 were calculated. Antibiotic consumption was analysed for years 2019 and 2020. RESULTS: Since the COVID-19 pandemic struck, a significant reduction of up to 39% was observed in the number of Clostridioides difficile stool tests in our hospital. A significant decrease in the percentage of positive tests and a 50% decrease in the incidence of CDI (total and HA-CDI) was found for 2020 compared with 2019 and confirmed for years 2021 and 2022. The decrease in CDI incidence was mostly marked in haematology, nephrology, and gastroenterology units. No significant change in the use of antibiotics was found. CONCLUSION: The global decrease in CDI incidence observed in our hospital was not associated with a change in the use of antibiotics. The control measures implemented to prevent COVID-19 transmission may explain a reduction in CDI incidence. An underdiagnosis of CDI cannot be excluded.

Performance evaluation of the FAST™ System and the FAST-PBC Prep™ cartridges for speeded-up positive blood culture testing.

Objectives: As time to appropriate antimicrobial therapy is major to reduce sepsis mortality, there is great interest in the development of tools for direct identification (ID) and antimicrobial susceptibility testing (AST) of positive blood cultures (PBC). Very recently, the FAST™ System (Qvella) has been developed to isolate and concentrate microorganisms directly from PBCs, resulting in the recovery of a Liquid Colony™ (LC) within 30 min. The LC can be used as equivalent of an overnight subcultured colony for downstream testing. We aimed to evaluate the performances of the FAST™ System and FAST-PBC Prep™ cartridges by testing the resulting LC for direct ID, AST and rapid resistance detection. Materials and methods: Prospectively, FAST™ System testing was carried out on each patient's first PBC with a monomicrobial Gram-stain result. In the second arm of the study, FAST™ System testing was carried out on blood cultures spiked with multidrug-resistant bacteria. Downstream testing using the LC included MALDI-TOF MS ID with the Bruker Biotyper® smart system, rapid resistance detection testing including the Abbott Diagnostics Clearview™ PBP2a SA Culture Colony Test (PBP2a) and the Bio-Rad ßLACTA™ Test (ßLT). AST was performed using the Becton Dickinson Phoenix™ System or by Bio-Rad disk diffusion using filter paper disk following EUCAST 2020 breakpoint criteria. Results: FAST™ System testing was completed on 198 prospective PBCs and 80 spiked blood cultures. After exclusion of polymicrobial blood cultures, performance evaluation compared with standard of care results was carried out on 266 PBCs. Concordant, erroneous and no ID results included 238/266 (89.5%), 1/266 (0.4%), 27/266 (10.2%) PBCs, respectively. Sensitivity and specificity for PBP2a were 100% (10/10) and 75% (15/20), respectively. Sensitivity and specificity for ßLT were 95.8% (23/24) and 100% (42/42), respectively. Categorical agreement for all 160 tested strains was 98% (2299/2346) with 1.2% (8/657) very major errors and 0.7% (10/1347) major errors. Conclusion: FAST™ System testing is a reliable approach for direct downstream testing of PBCs including MALDI-TOF MS ID, BD Phoenix™ and Bio-Rad disk diffusion AST as well as rapid resistance testing assays. Next steps include optimal integration of the FAST™ System in the PBC workflow with a view toward clinical studies.

How to choose the right real-time RT-PCR primer sets for the SARS-CoV-2 genome detection?

OBJECTIVES: The SARS-CoV-2 pandemic has created an unprecedented need for rapid large-scale diagnostic testing to prompt clinical and public health interventions. Currently, several quantitative reverse-transcription polymerase chain reaction (RT-qPCR) assays recommended by the World Health Organization are being used by clinical and public health laboratories and typically target regions of the RNA-dependent RNA polymerase (RdRp), envelope (E) and nucleocapsid (N) coding region. However, it is currently unclear if results from different tests are comparable. This study aimed to clarify the clinical performances of the primer/probe sets designed by US CDC and Charité/Berlin to help clinical laboratories in assay selection for SARS-CoV-2 routine detection. METHODS: We compared the clinical performances of the recommended primer/probe sets using one hundred nasopharyngeal swab specimens from patients who were clinically diagnosed with COVID-19. An additional 30 "pre-intervention screening" samples from patients who were not suspected of COVID-19 were also included in this study. We also performed sequence alignment between 31064 European SARS-CoV-2 and variants of concern genomes and the recommended primer/probe sets. RESULTS: The present study demonstrates substantial differences in SARS-CoV-2 RNA detection sensitivity among the primer/probe sets recommended by the World Health Organization especially for low-level viral loads. The alignment of thousands of SARS-CoV-2 sequences reveals that the genetic diversity remains relatively low at the primer/probe binding sites. However, multiple nucleotide mismatches might contribute to false negatives. CONCLUSION: An understanding of the limitations depending on the targeted genes and primer/probe sets may influence the selection of molecular detection assays by clinical laboratories.

Multicenter Performance Evaluation of MALDI-TOF MS for Rapid Detection of Carbapenemase Activity in Enterobacterales: The Future of Networking Data Analysis With Online Software.

In this study, we evaluate the performance of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for rapid detection of carbapenemase activity in Enterobacterales in clinical microbiology laboratories during a multicenter networking validation study. The study was divided into three different stages: "software design," "intercenter evaluation," and "clinical validation." First, a standardized procedure with an online software for data analysis was designed. Carbapenem resistance was detected by measuring imipenem hydrolysis and the results were automatically interpreted using the Clover MS data analysis software (Clover BioSoft, Spain). Second, a series of 74 genotypically characterized Enterobacterales (46 carbapenemase-producers and 28 non carbapenemase-producers) were analyzed in 8 international centers to ensure the reproducibility of the method. Finally, the methodology was evaluated independently in all centers during a 2-month period and results were compared with the reference standard for carbapenemase detection used in each center. The overall agreement rate relative to the reference method for carbapenemase resistance detection in clinical samples was 92.5%. The sensitivity was 93.9% and the specificity, 100%. Results were obtained within 60 min and accuracy ranged from 83.3 to 100% among the different centers. Further, our results demonstrate that MALDI-TOF MS is an outstanding tool for rapid detection of carbapenemase activity in Enterobacterales in clinical microbiology laboratories. The use of a simple in-house procedure with online software allows routine screening of carbapenemases in diagnostics, thereby facilitating early and appropriate antimicrobial therapy.

Immune-mediated neurological syndromes in SARS-CoV-2-infected patients.

BACKGROUND: Evidence of immune-mediated neurological syndromes associated with the severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection is limited. We therefore investigated clinical, serological and CSF features of coronavirus disease 2019 (COVID-19) patients with neurological manifestations. METHODS: Consecutive COVID-19 patients with neurological manifestations other than isolated anosmia and/or non-severe headache, and with no previous neurological or psychiatric disorders were prospectively included. Neurological examination was performed in all patients and lumbar puncture with CSF examination was performed when not contraindicated. Serum anti-gangliosides antibodies were tested when clinically indicated. RESULTS: Of the 349 COVID-19 admitted to our center between March 23rd and April 24th 2020, 15 patients (4.3%) had neurological manifestations and fulfilled the study inclusion/exclusion criteria. CSF examination was available in 13 patients and showed lymphocytic pleocytosis in 2 patients: 1 with anti-contactin-associated protein 2 (anti-Caspr2) antibody encephalitis and 1 with meningo-polyradiculitis. Increased serum titer of anti-GD1b antibodies was found in three patients and was associated with variable clinical presentations, including cranial neuropathy with meningo-polyradiculitis, brainstem encephalitis and delirium. CSF PCR for SARS-CoV-2 was negative in all patients. CONCLUSIONS: In SARS-Cov-2 infected patients with neurological manifestations, CSF pleocytosis is associated with para- or post-infectious encephalitis and polyradiculitis. Anti-GD1b and anti-Caspr2 autoantibodies can be identified in certain cases, raising the question of SARS-CoV-2-induced secondary autoimmunity.

Low performance of rapid antigen detection test as frontline testing for COVID-19 diagnosis.

BACKGROUND: Ensuring accurate diagnosis is essential to limit the spread of SARS-CoV-2 and for the clinical management of COVID-19. Although real-time reverse transcription polymerase chain reaction (RT- qPCR) is the current recommended laboratory method to diagnose SARS-CoV-2 acute infection, several factors such as requirement of special equipment and skilled staff limit the use of these time-consuming molecular techniques. Recently, several easy to perform rapid antigen detection tests were developed and recommended in some countries as the first line of diagnostic. OBJECTIVES: The aim of this study was to evaluate the performances of the Coris COVID-19 Ag Respi-Strip test, a rapid immunochromatographic test for the detection of SARS-CoV-2 antigen, in comparison to RT-qPCR. RESULTS: 148 nasopharyngeal swabs were tested. Amongst the 106 positive RT-qPCR samples, 32 were detected by the rapid antigen test, given an overall sensitivity of 30.2%. All the samples detected positive with the antigen rapid test were also positive with RT-qPCR. CONCLUSIONS: Higher viral loads are associated with better antigen detection rates. Unfortunately, the overall poor sensitivity of the COVID-19 Ag Respi-Strip does not allow using it alone as the frontline testing for COVID-19 diagnosis.

Evaluation of the automated BD Phoenix CPO Detect test for detection and classification of carbapenemases in Gram negatives.

We evaluated the performance of the automated BD Phoenix CPO Detect test (BD-CPO test) for detection and Ambler classification of carbapenemases in Enterobacteriaceae, P.aeruginosa and A.baumannii complex. A collection of 287 Gram-negative clinical isolates, with a reduced susceptibility to at least one carbapenem including 184 carbapenemase-producing organisms (CPO) and 103 non-CPO, was tested. The BD-CPO test showed an overall sensitivity of 89.7% and specificity of 83.5% for carbapenemase detection. 1/7 of class A, 82.9% of class B, and 89.8% of class D carbapenemases were correctly classified. Poor detection sensitivity of 68.9% and specificity of 62.1% in P.aeruginosa was observed. However, combination with ceftazidime/avibactam susceptibility, provided by this panel, increased the performances for P.aeruginosa. The integration of an automated carbapenemase detection and classification in routine susceptibility panels would save time and help for therapeutic management. Further developments are needed to improve the accuracy of the BD-CPO test.

Performance Evaluation of the MBT STAR®-Carba IVD Assay for the Detection of Carbapenemases With MALDI-TOF MS.

Objectives: The increasing rate of carbapenem resistance in Gram-negative bacteria is a major public health problem and rapid detection is essential for infection management. We evaluated the performances of the MBT STAR®-Carba IVD assay (Bruker Daltonics) to detect carbapenemase-producing organisms (CPO) from bacterial colonies and directly from positive blood culture bottles with MALDI-TOF MS. Methods: We analyzed 130 strains with a reduced susceptibility to at least one carbapenem including 109 CPO (6 KPC, 27 NDM, 21 VIM, 1 IMP, 41 OXA-48-like, 8 OXA-23, 2 OXA-24/-40, and 2 OXA-58) and 21 non-CPO. The assay on colonies was performed with all 130 strains while the assay on spiked blood cultures was performed with 45 strains. Samples were prepared with the MBT STAR®-CARBA IVD kit and imipenem hydrolysis by the potential carbapenemase was analyzed with the MBT STAR®-BL module (Bruker Daltonics) on MALDI-TOF MS. Results: Performed on colonies, the assay detected all carbapenemase-producing Enterobacteriaceae (n = 78), Pseudomonas spp. (n = 19) and Acinetobacter spp. (n = 12). All 21 tested non-CPO remained negative resulting in sensitivity and specificity of 100%. Performed on positive blood cultures, the assay detected all carbapenemase-producing Enterobacteriaceae (n = 23) and Pseudomonas spp. (n = 4) but missed 9/12 carbapenemase-producing Acinetobacter spp. However, a prolonged imipenem-incubation time of the strain pellet improved carbapenemase detection. Non-CPO from positive blood culture bottles remained negative (n = 5) with the assay with the exception of one Klebsiella pneumoniae isolate. Conclusion: The MBT STAR®-Carba IVD assay is a highly reliable method for the detection of carbapenemase activity in Gram-negative bacteria. However, time-consuming sample preparation steps and reagent costs need to be considered before implementation in a routine clinical microbiology laboratory.

Antibacterial Activity of 1-[(2,4-Dichlorophenethyl)amino]-3-Phenoxypropan-2-ol against Antibiotic-Resistant Strains of Diverse Bacterial Pathogens, Biofilms and in Pre-clinical Infection Models.

We recently described the novel anti-persister compound 1-[(2,4-dichlorophenethyl)amino]-3-phenoxypropan-2-ol (SPI009), capable of directly killing persister cells of the Gram-negative pathogen Pseudomonas aeruginosa. This compound also shows antibacterial effects against non-persister cells, suggesting that SPI009 could be used as an adjuvant for antibacterial combination therapy. Here, we demonstrate the broad-spectrum activity of SPI009, combined with different classes of antibiotics, against the clinically relevant ESKAPE pathogens Enterobacter aerogenes, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, P. aeruginosa, Enterococcus faecium and Burkholderia cenocepacia and Escherichia coli. Importantly, SPI009 re-enabled killing of antibiotic-resistant strains and effectively lowered the required antibiotic concentrations. The clinical potential was further confirmed in biofilm models of P. aeruginosa and S. aureus where SPI009 exhibited effective biofilm inhibition and eradication. Caenorhabditis elegans infected with P. aeruginosa also showed a significant improvement in survival when SPI009 was added to conventional antibiotic treatment. Overall, we demonstrate that SPI009, initially discovered as an anti-persister molecule in P. aeruginosa, possesses broad-spectrum activity and is highly suitable for the development of antibacterial combination therapies in the fight against chronic infections.

Targeting the Type Three Secretion System in Pseudomonas aeruginosa.

The injectisome type three secretion system (T3SS) is a major virulence factor in Pseudomonas aeruginosa. This bacterium is responsible for severe infections in immunosuppressed or cystic fibrosis patients and has become resistant to many antibiotics. Inhibitors of T3SS may therefore constitute an innovative therapeutic target. After a brief description of the T3SS and its regulation, this review presents strategies to inhibit T3SS-mediated toxicity and describes the main families of existing inhibitors. Over the past few years, 12 classes of small-molecule inhibitors and two types of antibody have been discovered and evaluated in vitro for their capacity to inhibit T3SS expression or function, and to protect host cells from T3SS-mediated cytotoxicity. While only one small molecule has been tested in vivo, a bifunctional antibody targeting both the translocation apparatus of the T3SS and a surface polysaccharide is currently in Phase II clinical trials.

In Vitro Models for the Study of the Intracellular Activity of Antibiotics.

Intracellular bacteria are poorly responsive to antibiotic treatment. Pharmacological studies are thus needed to determine which antibiotics are most potent or effective against intracellular bacteria as well as to explore the reasons for poor bacterial responsiveness. An in vitro pharmacodynamic model is described, consisting of (1) phagocytosis of pre-opsonized bacteria by eukaryotic cells; (2) elimination of non-internalized bacteria with gentamicin; (3) incubation of infected cells with antibiotics; and (4) determination of surviving bacteria by viable cell counting and normalization of the counts based on sample protein content.