Metabolic analyses reveal common adaptations in two invasive Haemophilus influenzae strains

Abstract

Non-typeable Haemophilus influenzae (NTHi) is a major pathogen in upper and lower respiratory tract infections in humans, and is increasingly also associated with invasive disease. We have examined two unrelated NTHi invasive disease isolates, R2866 and C188, in order to identify metabolic and physiological properties that distinguish them from respiratory tract disease isolates such as Hi2019. While the general use of the Hi metabolic network was similar across all three strains, the two invasive isolates secreted increased amounts of succinate, which can have anti-inflammatory properties. In addition, they showed a common shift in their carbon source utilization patterns, with strongly enhanced metabolism of nucleoside substrates, glucose and sialic acid. The latter two are major compounds present in blood and cerebrospinal fluid (CSF). Interestingly, C188 and R2866 also shared a reduced ability to invade or survive intracellularly in 16HBE14 bronchial epithelial cells relative to Hi2019 (4-fold (4 h), 25-fold (24 h) reduction). Altered metabolic properties, such as the ones observed here, could arise from genomic adaptations that NTHi undergo during infection. Together these data indicate that shifts in substrate preferences in otherwise conserved metabolic pathways may underlie strain niche specificity and thus have the potential to alter the outcomes of host–NTHi interactions.

Dual RNASeq Reveals NTHi-Macrophage Transcriptomic Changes During Intracellular Persistence

“…Although this is a small sample size, dissimilarity of NTHi strains derived from the same clinical source has also been shown in two larger studies ( Erwin et al, 2008 ; De Chiara et al, 2014 ). Furthermore, two invasive NTHi strains (C188 and R2866) displayed increased ability to metabolise diverse substrates compared to a COPD isolate (Hi2019), whereas Hi2019 was better able to invade and reside within airway cells ( Muda et al, 2019 ). This comparative analysis suggests differences in metabolic adaptations could underpin the ability of NTHi to persist in certain anatomical niches, further supported by the different levels of gene expression exhibited by the three diverse strains used in this current study.…”

Access to highly specialized growth substrates and production of epithelial immunomodulatory metabolites determine survival of Haemophilus influenzae in human airway epithelial cells

“…Optimal growth of NTHi was observed above pH 8.0, while below pH 5.5 growth was minimal. Two isolates from invasive disease patients (C188, R2866) showed some specific adaptations, including an increased ability to grow on glucose and nucleosides, and optimal growth at pH 7.0 and above, which is lower than that found for most other strains [ 32 ].…”

Learning from –omics strategies applied to uncover Haemophilus influenzae host-pathogen interactions: Current status and perspectives

“…As this being the case for H. influenzae , glucose catabolism enhances bacterial growth, but also promotes the release of end-products acting as pro-inflammatory metabolites, more specifically acetate, which may contribute to lung colonization and inflammation in chronic respiratory patients [100] . Besides the above described genomic flexibility (see Section 2 ), H. influenzae metabolic versatility among strains has also been reported, in terms of substrate utilization, histidine synthesis or urease activity, suggesting metabolic adaptive traits favoring differential access to throat, ear, lower airways or blood niches [101] , [102] , [103] , [104] .…”

“…H. influenzae possesses complete glycolysis and pentose phosphate pathways for glucose catabolism, lacks most enzymes of the oxidative branch of the Krebs cycle, and holds a respiratory chain with several dehydrogenases transferring electrons into the menaquinone pool, and terminal reductases transferring the electrons to a variety of electron acceptors, altogether driving a so-called glucose respiration-assisted fermentation, where acetate is the main end-product under aerobic growth. When oxygen is limiting, acetate is still produced but other products arise including formate and succinate, at variable rates depending on the tested strains [98] , [99] , [100] , [101] . End-product excretion profiling is informative not only from the bacterial perspective, but also due to their possible immunomodulatory roles.…”

“…Bacterial responses to gene inactivation [54] , [55] , [81] E. Metabolomic profiling E1. Bacterial responses to changing environmental conditions [99] , [100] , [101] E2. Bacterial responses to gene inactivation [81] , [100] *HITS, high-throughput insertion tracking by deep sequencing; Tn-seq, transposon sequencing; dual RNA-seq, dual RNA-sequencing.…”