Spectrochemical analyses of growth phase-related bacterial responses to low (environmentally-relevant) concentrations of tetracycline and nanoparticulate silver

Abstract

Exposure to environmental insults generally occurs at low levels, making it challenging to measure bacterial responses to such interactions. Additionally, microbial behaviour and phenotype varies in differing bacterial types or growth phases, likely giving rise to growth- or species-specific responses to environmental stimuli. The present study applied a spectrochemical tool, infrared (IR) spectral interrogation coupled with multivariate analysis, to investigate the growth- and species-specific responses of two bacterial strains, Gram-negative Pseudomonas fluorescens and Gram-positive Mycobacterium vanbaalenii, to low concentrations of tetracycline, nanoparticulate silver (AgNP) or mixtures thereof. Results indicate the tendency for tetracycline-induced biospectral alterations to occur in outer-cellular components, e.g., phospholipids or proteins, while AgNPs-induced changes are mainly associated with proteins (∼964 cm, ∼1485 cm, ∼1550 cm, ∼1650 cm). The primary altered targets are correlated with bacterial membranes or outer-cellular components. Furthermore, significant lipid changes at 1705-1750 cm were only present in P. fluorescens cells compared to M. vanbaalenii, owing to differences in cell wall structure between Gram-positive and -negative bacteria. This study also found distinct biospectral alterations in non-log phase compared to log phase, confirming bacterial growth-dependent responses to environmental exposures. It implies that previous studies on log phase only may underestimate the impacts from exposures of interest in situ, where bacteria stay in different growth stages. Our work proves the feasibility of biospectroscopy in determining bacterial responses to low-level environmental exposures in a fast and efficient manner, revealing sufficient biochemical information continuously through growth phases. As a nondestructive approach, biospectroscopy may provide deeper insights into the actual and in situ interactions between microbes and environmental stimuli, regardless of the exposure level, growth phase, or bacterial types.

Profiling antibiotic resistance in Escherichia coli strains displaying differential antibiotic susceptibilities using Raman spectroscopy

“…− stretching in nucleic acids and ring bases as well as changes in the lipids, fatty acids and proteins have been reported. [31,32] The biomolecular changes observed with rifampicin were also in line with its mode of action. It is important to mention that the bactericidal or static activity of rifampicin is organism specific [33].…”

“…In future, it will be important to correlate our findings with nutrient depletion and starvation observed in the environment. It has been shown that long-term exposure to antimicrobials often drives bacterial cells into dormant states or causes them to display additional cellular components like fatty acids, resulting in a broader range of spectral modifications compared with short-term exposure [31,32]. It is also necessary to evaluate our Raman markers with a host of other bacterial strains and/or panel of clinically-relevant antibiotics.…”

“…[30] In fact, vibrational spectroscopy has been used to understand spectral changes occurring in Gram‐positive and negative bacteria exposed to tetracycline where alterations in DNA, PO 2 − stretching in nucleic acids and ring bases as well as changes in the lipids, fatty acids and proteins have been reported. [31, 32]…”

Interrogating cadmium and lead biosorption mechanisms by Simplicillium chinense via infrared spectroscopy

“…Cultivated with carbohydrate, for instance, biospectra of S. chinense QD10 have specific biomarkers including PO 2 asymmetric (~ 1265 cm -1 ), RNA (~ 1117 cm -1 ), CH in-plane bend (~ 1510 cm -1 ), Amide I (~ 1659 cm -1 ) and C=O, lipids (~ 1740 cm -1 ), indicating the occurrence of complex carbohydrate metabolic processes during fungal growth (Figure 4). These biomarkers are significantly different from those linked with bacterial growth except for Amide I (~ 1659 cm -1 ) (Jin et al, 2018a;Jin et al, 2018b), suggesting distinct metabolite profiles between fungal and bacterial growth. Carbohydrates are reported to associate with fungal metabolism, not only providing energy for the synthesis of trehalose, polyols, glycogen, fatty acids and other cellular components, but also supplying carbon skeleton for other metabolic processes, such as hyphal growth and amino acid biosynthesis (Bago et al, 2003;Deveau et al, 2008;Rasmussen et al, 2008).…”

“…The IR bands significantly correlated with GI include 1340 cm -1 (collagen), 1136 cm -1 (collagen) and 966 cm -1 (C-C DNA, Figure 5B-5D), implying strong associations of these cellular components with fungal growth. Among them, the DNA-spectral biomarker represents DNA replication through cell reproduction process (Jin et al, 2018a;Jin et al, 2018b). Additionally, the collagen-associated spectral alterations are very likely linked to the formation of fungal fimbriae, which consist of collagen and are abundant on extracochlear surfaces (Celerin et al, 1996).…”