2
1 Antibacterials
the eukaryotes although certain early evolutionary aspects of the derivation of the
last two remain contentious (Watson 2019).
Traditionally, bacteria are categorised by how they react to staining with the
Gram stain, Gentian Violet, followed by potassium triodide as a post-mordant. Hans
Christian Gram was a Danish bacteriologist who invented the staining procedure.
Gram-positive bacteria retain the dye after an ethanol wash, while bacteria designated
as Gram-negative do not retain this purple dye but are identified by retention of
a subsequently added dye, Safranine, with the bacteria being stained red (Stinson
1996). The differential dyeing characteristics reflect cell wall differences with Grampositive bacteria having thick cross-linked polysaccharide cell walls which adsorb
the gentian violet strongly. On the other hand, the Gram-negative bacteria have thin
polysaccharide cell walls covered by a negatively-charged phospholipid layer for
adsorption of the positively charged Safranine. Other bacterial groups are comprised
of the non-stain reacting bacteria and the Mycobacteria.
Pathogenic and non-pathogenic bacteria can come from any of these different
groups above, for example the pathogenic bacterium golden staph., Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative). The
pathogenic Mycobacterium tuberculosis, the cause of tuberculosis, is neither Grampositive nor Gram-negative due to a waxy coating on the cell surface (mainly mycolic
acid) which obviates staining. Mycobacterium tuberculosis can be stained by an alternative staining procedure, however, and is classified as an acid-fast Gram-positive
due the lack of an outer cell wall membrane.
Resistance by human pathogenic bacteria to previously effective antibacterial
treatments poses an ever increasing threat to human health worldwide, a threat
which could be exacerbated by global climate change with warming temperatures
(Blair 2018; MacFadden et al. 2018). While a variety of antibacterials have been
used over the years, the vigorous counter attack by bacteria continues as emphasised in some recent reviews (World Health Organization 2017a; The Review on
Antimicrobial Resistance 2016). In early 2017, the World Health Organization
published, for the first time, a ranked threat list of bacteria or bacterial families
that posed the most pressing risk to human health and for which new antibacterials were needed (World Health Organization 2017b; and comments by Willyard
2017). Significantly the top three bacteria/families were in the Gram-negative category with the antibiotic type to which they are resistant noted in parentheses: Acinetobacter baumanii (carbapenem), Pseudomonas aeruginosa (carbapenem), and ESBL
(extended spectrum-β-lactamase)-producing Enterobacteriaceae (carbapenem; 3rd
generation cephalosporin). Watkins and Plattner (2015) have written a very good
retrospective on antibacterials, including a summary of the carbapenems as well as
covering the generations of cephalosporins. While not on the WHO ranked threat list,
the universally distributed Gram-positive Staphylococcus epidermidis, an important
cause of hospital-acquired infections, should now also be considered following the
discovery that some strains of this pathogen revealed in Europe are resistant to all
known antibiotics (Lee et al. 2018). They are thus classified as MDR (Multi Drug
Resistant) strains and are hence of significant concern.
1 Antibacterials
the eukaryotes although certain early evolutionary aspects of the derivation of the
last two remain contentious (Watson 2019).
Traditionally, bacteria are categorised by how they react to staining with the
Gram stain, Gentian Violet, followed by potassium triodide as a post-mordant. Hans
Christian Gram was a Danish bacteriologist who invented the staining procedure.
Gram-positive bacteria retain the dye after an ethanol wash, while bacteria designated
as Gram-negative do not retain this purple dye but are identified by retention of
a subsequently added dye, Safranine, with the bacteria being stained red (Stinson
1996). The differential dyeing characteristics reflect cell wall differences with Grampositive bacteria having thick cross-linked polysaccharide cell walls which adsorb
the gentian violet strongly. On the other hand, the Gram-negative bacteria have thin
polysaccharide cell walls covered by a negatively-charged phospholipid layer for
adsorption of the positively charged Safranine. Other bacterial groups are comprised
of the non-stain reacting bacteria and the Mycobacteria.
Pathogenic and non-pathogenic bacteria can come from any of these different
groups above, for example the pathogenic bacterium golden staph., Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative). The
pathogenic Mycobacterium tuberculosis, the cause of tuberculosis, is neither Grampositive nor Gram-negative due to a waxy coating on the cell surface (mainly mycolic
acid) which obviates staining. Mycobacterium tuberculosis can be stained by an alternative staining procedure, however, and is classified as an acid-fast Gram-positive
due the lack of an outer cell wall membrane.
Resistance by human pathogenic bacteria to previously effective antibacterial
treatments poses an ever increasing threat to human health worldwide, a threat
which could be exacerbated by global climate change with warming temperatures
(Blair 2018; MacFadden et al. 2018). While a variety of antibacterials have been
used over the years, the vigorous counter attack by bacteria continues as emphasised in some recent reviews (World Health Organization 2017a; The Review on
Antimicrobial Resistance 2016). In early 2017, the World Health Organization
published, for the first time, a ranked threat list of bacteria or bacterial families
that posed the most pressing risk to human health and for which new antibacterials were needed (World Health Organization 2017b; and comments by Willyard
2017). Significantly the top three bacteria/families were in the Gram-negative category with the antibiotic type to which they are resistant noted in parentheses: Acinetobacter baumanii (carbapenem), Pseudomonas aeruginosa (carbapenem), and ESBL
(extended spectrum-β-lactamase)-producing Enterobacteriaceae (carbapenem; 3rd
generation cephalosporin). Watkins and Plattner (2015) have written a very good
retrospective on antibacterials, including a summary of the carbapenems as well as
covering the generations of cephalosporins. While not on the WHO ranked threat list,
the universally distributed Gram-positive Staphylococcus epidermidis, an important
cause of hospital-acquired infections, should now also be considered following the
discovery that some strains of this pathogen revealed in Europe are resistant to all
known antibiotics (Lee et al. 2018). They are thus classified as MDR (Multi Drug
Resistant) strains and are hence of significant concern.