Understanding the Types of Antimicrobial Resistance
Having an understanding of the types of antimicrobial resistance can be a very useful tool in protecting yourself from illness and disease. By knowing which bacteria and fungi can be resistant to which antibiotics, you can be better prepared to treat your patients.
Efflux pumps
Efflux pumps have been implicated in the pathogenicity of bacteria and fungal pathogens. In addition, these efflux pumps may be involved in secretion of virulence factors.
Efflux pumps span the periplasm and have the ability to extrude antibiotics and other compounds out of the cell before they reach the cytoplasm. In bacteria, there are two types of efflux pumps. The first is the RND-type efflux pump. These efflux pumps are the most common efflux pumps found in bacteria. They are also known to contribute to acquired antimicrobial resistance.
RND-type efflux pumps are characterized by the presence of a periplasmic accessory protein, AcrA. AcrA is involved in the cellular cooperation between the outer membrane protein channel, TolC, and the inner membrane efflux transporter, AcrB. This system has been found to contribute to environmental adaptation and fitness. In addition, some members of the RND-type efflux system are involved in quorum sensing.
Efflux pumps are large macromolecular complexes consisting of an inner membrane efflux transporter, an outer membrane protein channel, and a periplasmic accessory protein. In Gram-negative bacteria, the outer membrane is larger than the inner membrane. Efflux pumps extrude antibiotics, host-derived antimicrobial molecules, and other compounds before reaching the cytoplasm.
Acquired genetic material
Currently, there are three known mechanisms of genetic material transfer between bacteria. These include conjugation, horizontal genetic transfer, and transformation.
Conjugation is the most well-known mechanism of gene transfer between bacteria. It is mediated by the presence of heavy metals, such as Cu(II) and Ag(I). It has been demonstrated that the presence of heavy metals promotes conjugative transfer of antibiotic resistance genes. It also contributes to rapid spread of resistance.
Horizontal genetic transfer is a process whereby a gene cassette from one bacterium can be transferred to another bacterium through cell membrane structures. This process is often used in laboratory settings to insert a new gene. This type of genetic alteration can also be used for medical and industrial applications.
In the past, integrons have been associated with antibiotic resistance. This type of gene cassette is usually found in clinical bacterial strains. They are formed by an intI gene that encodes a site-specific recombinase. The insertion site can be located on the chromosome or on a plasmid.
Biofilm formation
Various studies have indicated that antibiotic resistance is associated with biofilm formation. However, it is not clear whether biofilm formation is the cause or the consequence of antibiotic resistance. Consequently, the present study was performed to analyze the relationship between biofilm formation and antibiotic resistance.
Isolates were categorized into three groups based on their antibiotic resistance phenotypes. They were: weak biofilm producers, moderate biofilm producers and extensively drug resistant (XDR) biofilm producers. The biofilm-forming capacities of each group were determined and compared using Spearman’s rank correlation test. Biofilm biomass was then quantified using confocal microscopy imaging.
In addition, MARI (multidrug-resistant indicator) values were determined to measure the degree of antibiotic resistance. The MARI ranged from 0.4 to 1.0. The isolates from the pathology laboratory of an urban tertiary healthcare centre had the highest MARI values.
A negative correlation was observed between MIC values of selected antibiotics and the biofilm forming capacities of 24 isolates. The MIC values of the antibiotics used were tetracyclines, ciprofloxacin, cephalosporins, nitrofurans, carbapenems, b-lactam/b-lactamase inhibitors and aminoglycosides.
Global antimicrobial surveillance system based on sewage
Using untreated domestic sewage samples as the basis for a global antimicrobial resistance surveillance system has been previously investigated. Among the findings was that the resistance of some bacteria to AMR is highly variable, and the resistance of some pathogens is extensively shared between samples. This study shows that wastewater can be a promising sample source for AMR surveillance. However, the occurrence of AMR in wastewater samples is difficult to interpret because of rapid degradation in the environment.
To determine if the resistance of AMR genes is widespread in sewage samples, scientists analyzed untreated domestic sewage samples collected from sixty countries. The samples were sequenced using Illumina HiSeq. The average number of reads per sample was 0.03%, and a high percentage of reads were assigned to bacterial genes. The most common genes were plasmid-encoded carbapenemases. These genes are prone to horizontal gene transfer and are frequently detected.
Among the AMR genes commonly detected were bla KPC, bla GES, and bla VIM. The bla KPC gene was carried by Escherichia coli, bla GES by 10 different bacterial species, and bla VIM by Aeromonas hydrophila / caviae.
