Morphological and ultrastructural changes in bacterial cells as an indicator of antibacterial mechanism of action - PubMed (original) (raw)

Review

Morphological and ultrastructural changes in bacterial cells as an indicator of antibacterial mechanism of action

T P Tim Cushnie et al. Cell Mol Life Sci. 2016 Dec.

Abstract

Efforts to reduce the global burden of bacterial disease and contend with escalating bacterial resistance are spurring innovation in antibacterial drug and biocide development and related technologies such as photodynamic therapy and photochemical disinfection. Elucidation of the mechanism of action of these new agents and processes can greatly facilitate their development, but it is a complex endeavour. One strategy that has been popular for many years, and which is garnering increasing interest due to recent technological advances in microscopy and a deeper understanding of the molecular events involved, is the examination of treated bacteria for changes to their morphology and ultrastructure. In this review, we take a critical look at this approach. Variables affecting antibacterial-induced alterations are discussed first. These include characteristics of the test organism (e.g. cell wall structure) and incubation conditions (e.g. growth medium osmolarity). The main body of the review then describes the different alterations that can occur. Micrographs depicting these alterations are presented, together with information on agents that induce the change, and the sequence of molecular events that lead to the change. We close by highlighting those morphological and ultrastructural changes which are consistently induced by agents sharing the same mechanism (e.g. spheroplast formation by peptidoglycan synthesis inhibitors) and explaining how changes that are induced by multiple antibacterial classes (e.g. filamentation by DNA synthesis inhibitors, FtsZ disruptors, and other types of agent) can still yield useful mechanistic information. Lastly, recommendations are made regarding future study design and execution.

Keywords: Antibiotic; Antiseptic; Disinfectant; Mode of action; SEM; TEM.

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Figures

Fig. 1

Fig. 1

Scanning electron micrographs of a untreated Escherichia coli JP5128 and b cells of the same strain treated with 200 µg/mL chloramphenicol for 3 h (this concentration and time frame were selected because it achieved near-complete inhibition of protein synthesis). Arrow shows the location of a spheroplast. Bar 1 µm. Images from [97] by permission of Antimicrobial Agents and Chemotherapy (ASM)

Fig. 2

Fig. 2

Scanning electron micrographs of a untreated Pseudomonas aeruginosa MB3286 and b cells of the same strain treated with 2 µg/mL (2×MIC) imipenem for 3 h. All of the treated bacteria have changed to ovoid cells. Magnification ×9000. Images from [101] by permission of Innate Immunity (SAGE Publications)

Fig. 3

Fig. 3

Scanning electron micrographs of a untreated Pseudomonas aeruginosa X48 and b cells of the same strain treated with 32 µg/mL (2×MIC) of the β-lactam BL-P1654 for 4 h, and transmission electron micrographs of c untreated Escherichia coli ATCC 11303 and d cells of the same strain treated with 0.1 µg/mL (1×MIC) mitomycin C for 2 h. The number and length of filamentous cells has increased following treatment. Magnification for a ×2700, b ×2200, c ×18,000, and d ×18,000. Images a and b from [67] by permission of Antimicrobial Agents and Chemotherapy (ASM), and c and d from [133] by permission of the Journal of Bacteriology (ASM)

Fig. 4

Fig. 4

Transmission electron micrographs of a untreated Staphylococcus aureus ATCC 6538P and b cells of the same strain treated with 0.027 µg/mL (0.33×MIC) cephaloridine for 6 h. Treatment has inhibited cell separation, resulting in a pseudomulticellular form. Magnification for a ×23,500 and b ×21,500. Bar 1 µm. Images from [125] by permission of Antimicrobial Agents and Chemotherapy (ASM)

Fig. 5

Fig. 5

Scanning electron micrographs of a untreated Pseudomonas aeruginosa MB3286 and b cells of the same strain treated with 2 µg/mL (2×MIC) meropenem for 6 h, and transmission electron micrographs of c untreated Escherichia coli ATCC 12407 and d cells of the same strain treated with 5 µg/mL (~3×MIC) ampicillin for 1 h. Arrows show the location of localized swelling. Magnification for a ×9000, b ×14,000, c ×27,500, and d ×27,000. Bar 0.25 µm. Images a and b from [101] by permission of Innate Immunity (SAGE Publications), and images c and d from [169] by permission of the Journal of Bacteriology (ASM)

Fig. 6

Fig. 6

Scanning electron micrographs of a untreated Legionella pneumophila ATCC 33153 and b cells of the same strain treated with 1000 µg/mL (40×MIC) penicillin for 5 h, and negatively stained electron micrographs of c untreated L. pneumophila Nottingham N7 and d cells of the same strain treated with 1280 µg/mL (20×MIC) methicillin for 24 h. Arrows show the location of bulge formation. Bar for a 0.2 µm, b 0.4 µm, c 0.5 µm, and d 0.5 µm. Images a and b from [171] and images c and d from [83], all by permission of the Journal of Medical Microbiology (MicroSoc)

Fig. 7

Fig. 7

Scanning electron micrographs of a untreated Legionella pneumophila ATCC 33153 and b cells of the same strain treated with 1600 µg/mL (10×MIC) polymyxin B for 5 h, and transmission electron micrographs of c untreated Escherichia coli ATCC 11303 and d cells of the same strain treated with 25 µg/mL (~12.5×MIC) polymyxin B for 30 min. Arrows show the location of some of the blebs. All bars 0.2 µm. Images a and b from [171] by permission of the Journal of Medical Microbiology (MicroSoc), and images c and d from [180] by permission of the Journal of Bacteriology (ASM)

Fig. 8

Fig. 8

Transmission electron micrographs of a untreated Staphylococcus aureus ATCC 6538P and b cells of the same strain treated with 0.03 µg/mL (3×MIC) rifampicin for 4 h. Both the septal and peripheral portions of the wall appear thickened following treatment. Bar 1 µm. Images from [155] by permission of Reviews of Infectious Diseases (Oxford University Press)

Fig. 9

Fig. 9

Transmission electron micrographs of a untreated Enterobacter cloacae NCTC 1005 and b cells of the same strain treated with 12.5 µg/mL (0.83×MIC) trimethoprim for 4 h. Arrow shows where the layers of the cell envelope appear to have separated. Bar for a 0.5 µm and b 0.25 µm. Images from [195] by permission of the Journal of Medical Microbiology (MicroSoc)

Fig. 10

Fig. 10

Transmission electron micrographs of a untreated Enterobacter cloacae NCTC 1005 and b cells of the same strain treated with 12.5 µg/mL (0.83×MIC) trimethoprim for 4 h. Many of the bacterial cells have developed intracellular vacuoles following treatment. Bar 1 µm. Images from [195] by permission of the Journal of Medical Microbiology (MicroSoc)

Fig. 11

Fig. 11

Transmission electron micrographs of a an untreated clinical isolate of Proteus mirabilis and b cells of the same isolate treated with 0.78 µg/mL (0.5×MIC) ampicillin for 3 h. The number of ribosomes has decreased following treatment. Bar 1 µm. Images from [202] by permission of Proceedings of the Society for Experimental Biology and Medicine (SAGE Publications)

Fig. 12

Fig. 12

Transmission electron micrographs of a untreated Staphylococcus aureus ATCC 25923 and b cells of the same strain treated with 0.2 µg/mL (0.5×MIC) quinupristin/dalfopristin for 24 h. Arrows show the location of ghost cells. Magnification for a and b ×37,000. Images from [203] by permission of the Journal of Antimicrobial Chemotherapy (Oxford University Press)

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