Evaluation of the Haemophilus influenzae EUCAST and CLSI disc diffusion methods to recognize aminopenicillin and amoxicillin/clavulanate resistance

Ampicillin susceptibility testing of Haemophilus influenzae in the routine clinical laboratory by the EUCAST methodology compared to broth microdilution and the presence of ftsI gene mutations

OBJECTIVES

To investigate the prevalence of ampicillin resistance in Haemophilus influenzae and the diagnostic accuracy of the EUCAST recommended disc diffusion method to detect the increasingly prevalent ampicillin resistance due to the presence of PBP3 alterations based on mutations in the ftsI gene.

METHODS

During a 6-month period all consecutive non-duplicate H. influenzae isolates were prospectively collected and stored. MICs of ampicillin were determined by broth microdilution (BMD). PCR was performed to detect mutations in the ftsI gene. Results of routine disc diffusion susceptibility testing, including the penicillin screening test in accordance with the current EUCAST methodology, as well as additional Etest results, were compared to the BMD as the reference method.

RESULTS

In 102 isolates, the prevalence of ampicillin resistance was 28% (29/102) by BMD. There was a good correlation between MICs of ampicillin and the presence of a β-lactamase and/or an ftsI gene mutation. The prevalence of ampicillin resistance was overestimated using the EUCAST method (33% (34/102)) and underestimated when an additional Etest was used (24% (24/102)) (not significant). The sensitivity and specificity of the EUCAST methodology for the detection of ampicillin resistance were 97% ((28/29); 95% CI, 82-100%) and 92% ((67/73); 95% CI, 83-97%), respectively.

CONCLUSIONS

The prevalence of ampicillin resistance was 28%, as determined by BMD. Although the overall diagnostic accuracy of the EUCAST ampicillin disc diffusion was high, misclassification of ampicillin susceptibility may still occur.

Haemophilus influenzae blood-stream infection and third-generation cephalosporin susceptibility testing: a comparative case study using EUCAST and CLSI guidelines

Introduction

In this comparative case study, we discuss clinically relevant discrepancies of antimicrobial susceptibility testing (AST) interpretation for ceftriaxone against a non-typable, beta-lactamase negative, ampicillin-resistant (BLNAR) Haemophilus influenzae isolated from a blood culture.

Case report

A 74-year-old man presented with a 3 day illness characterized by shortness of breath and dry cough, and was noted to be febrile and hypoxic on admission. A blood culture bottle flagged positive with Gram-negative coccobacilli, later identified as Haemophilus influenzae with the patient commenced on ceftriaxone. The isolate was beta-lactamase negative and antibiotic susceptibility testing (AST) using disc diffusion revealed the isolate resistant to ceftriaxone and ampicillin by EUCAST methodology, with the patient subsequently changed to amoxicillin/clavulanate. Further AST using the CLSI methodology in parallel demonstrated discrepant results between the two susceptibility methods. The patient recovered without complications.

Conclusion

This discrepancy could lead to inconsistent reporting of susceptibilities between laboratories, and consequently antibiotic prescribing, especially for invasive isolates. As more laboratories adopt EUCAST methodologies for AST interpretation in Australia and globally, it is important for clinicians to consider the clinical implications of these methodological discrepancies.

Antimicrobial, antioxidant, antiviral activity, and gas chromatographic analysis of Varanus griseus oil extracts

There is an urgent need to develop natural antimicrobials for the control of rapidly mutating drug-resistant bacteria and poultry viruses. Five extracts were prepared using diethyl ether, ethyl acetate, methanol, 1-butanol and n-hexane from abdominal fats of Varanus griseus locally known as Indian desert monitor. Antibacterial, antioxidant and antiviral activities from oil extracts were done through disc diffusion method, stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay and in ovo antiviral assay, respectively. The gas chromatography mass spectrometry (GC-MS) analyses were used to determine principal active compounds and chemical profile of each oil extract. n-Hexane extract showed clear zones of inhibition (ZOI) against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae (12 ± 0.5 mm, 9 ± 0.5 mm, and 9 ± 0.5 mm) while diethyl ether extract exhibited significant antibacterial activity (11 ± 0.5 mm) against Proteus vulgaris only. In case of drug-resistant strains, methanol extract was active (6 ± 0.5 mm) against Staphylococcus aureus, whereas n-hexane extract has shown ZOI 11 ± 0.5 mm against P. aeruginosa. Range of percentage scavenging activity of V. griseus oil extracts from DPPH free radical assay was 34.9-70.7%. For antiviral potential, growth of new castle disease virus (NDV) was effectively inhibited by all five extracts (HA titer = 0-4). The highest antiviral activity against avian influenza virus (H9N2) was observed from methanol, diethyl ether and 1-Butanol oil extracts with HA titers of 2, 2 and 0, respectively. Methanol, diethyl ether, 1-butanol and n-hexane oil extracts produced best hemagglutination assay (HA) titer values (0, 0, 4 and 0) against infectious bronchitis virus (IBV). Ethyl acetate and 1-Butanol extract exhibited good antiviral potential against infectious bursal disease virus (IBDV) with indirect hemagglutination assay (IHA) titers of 8 and 4, respectively. Main classes of identified compounds through gas chromatography were aldehydes, fatty acids, phenols and esters. GC-MS identified 11 bioactive compounds in V. griseus oil extracts. It is summarized that V. griseus oil has strong antioxidant activity and good antimicrobial potential because of its bioactive compounds.

Interrogation of Essentiality in the Reconstructed Haemophilus influenzae Metabolic Network Identifies Lipid Metabolism Antimicrobial Targets: Preclinical Evaluation of a FabH β-Ketoacyl-ACP Synthase Inhibitor

Expediting drug discovery to fight antibacterial resistance requires holistic approaches at system levels. In this study, we focused on the human-adapted pathogen Haemophilus influenzae, and by constructing a high-quality genome-scale metabolic model, we rationally identified new metabolic drug targets in this organism. Contextualization of available gene essentiality data within in silico predictions identified most genes involved in lipid metabolism as promising targets. We focused on the β-ketoacyl-acyl carrier protein synthase III FabH, responsible for catalyzing the first step in the FASII fatty acid synthesis pathway and feedback inhibition. Docking studies provided a plausible three-dimensional model of FabH in complex with the synthetic inhibitor 1-(5-(2-fluoro-5-(hydroxymethyl)phenyl)pyridin-2-yl)piperidine-4-acetic acid (FabHi). Validating our in silico predictions, FabHi reduced H. influenzae viability in a dose- and strain-dependent manner, and this inhibitory effect was independent of fabH gene expression levels. fabH allelic variation was observed among H. influenzae clinical isolates. Many of these polymorphisms, relevant for stabilization of the dimeric active form of FabH and/or activity, may modulate the inhibitory effect as part of a complex multifactorial process with the overall metabolic context emerging as a key factor tuning FabHi activity. Synergies with antibiotics were not observed and bacteria were not prone to develop resistance. Inhibitor administration during H. influenzae infection on a zebrafish septicemia infection model cleared bacteria without signs of host toxicity. Overall, we highlight the potential of H. influenzae metabolism as a source of drug targets, metabolic models as target-screening tools, and FASII targeting suitability to counteract this bacterial infection. IMPORTANCE Antimicrobial resistance drives the need of synergistically combined powerful computational tools and experimental work to accelerate target identification and drug development. Here, we present a high-quality metabolic model of H. influenzae and show its usefulness both as a computational framework for large experimental data set contextualization and as a tool to discover condition-independent drug targets. We focus on β-ketoacyl-acyl carrier protein synthase III FabH chemical inhibition by using a synthetic molecule with good synthetic and antimicrobial profiles that specifically binds to the active site. The mechanistic complexity of FabH inhibition may go beyond allelic variation, and the strain-dependent effect of the inhibitor tested supports the impact of metabolic context as a key factor driving bacterial cell behavior. Therefore, this study highlights the systematic metabolic evaluation of individual strains through computational frameworks to identify secondary metabolic hubs modulating drug response, which will facilitate establishing synergistic and/or more precise and robust antibacterial treatments.

An antimicrobial activity of oil extracted from Saara hardwickii

Present research work represents antiviral and antibacterial value of body fat of Saara hardwickii commonly called as spiny tailed lizard. Oil was extracted from body fats located in the ventral region of this animal using hydrocarbons e.g., n-hexane, methanol, butanol and ethyl acetate as a solvent. The antibacterial activity of lizard oil was tested against standard as well as multi-resistant lines ofEscherichia coli, Styphalococcus aureus, Pseudomonas aeruginosa and Proteus vulgaris alone and with antibiotic ampicillin. For antibacterial potential, Ethyl acetate and Butanol solvent extract showed best zone of inhibition (7mm) with P. aeruginosa and S. aureus respectively. For antiviral potential, Butanol and Methanol extract showed best HA (Hemagglutination) titer of 04 with NDV and IBV viral strain respectively. It is concluded that lizard oil has antimicrobial potential against different pathogens strains (virus, bacteria).