Recognizing different degrees of MDR in bacteria, the terms extensively drug-resistant (XDR) and pandrug-resistant (PDR) have been introduced. Extensively drug-resistant (XDR) is the non-susceptibility of one bacteria species to all antimicrobial agents except in two or less antimicrobial categories. Within XDR, pandrug-resistant (PDR) is the non-susceptibility of bacteria to all antimicrobial agents in all antimicrobial categories.[1] The definitions were published in 2011 in the journal Clinical Microbiology and Infection and are openly accessible.[1]
Common multidrug-resistant organisms (MDROs)[edit]
Common multidrug-resistant organisms, typically bacteria, include:[3]
Overlapping with MDRGN, a group of Gram-positive and Gram-negative bacteria of particular recent importance have been dubbed as the ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter species).[4]
Various microorganisms have survived for thousands of years by their ability to adapt to antimicrobial agents. They do so via spontaneous mutation or by DNA transfer. This process enables some bacteria to oppose the action of certain antibiotics, rendering the antibiotics ineffective.[5] These microorganisms employ several mechanisms in attaining multi-drug resistance:
Many different bacteria now exhibit multi-drug resistance, including staphylococci, enterococci, gonococci, streptococci, salmonella, as well as numerous other Gram-negative bacteria and Mycobacterium tuberculosis. Antibiotic resistant bacteria are able to transfer copies of DNA that code for a mechanism of resistance to other bacteria even distantly related to them, which then are also able to pass on the resistance genes, resulting in generations of antibiotics resistant bacteria.[11] This initial transfer of DNA is called horizontal gene transfer.[12]
Phage-resistant bacteria variants have been observed in human studies. As for antibiotics, horizontal transfer of phage resistance can be acquired by plasmid acquisition.[13]
Yeasts such as Candida species can become resistant under long-term treatment with azole preparations, requiring treatment with a different drug class.
Lomentospora prolificans infections are often fatal because of their resistance to multiple antifungal agents.[14]
HIV is the prime example of MDR against antivirals, as it mutates rapidly under monotherapy.
Influenza virus has become increasingly MDR; first to amantadines, then to neuraminidase inhibitors such as oseltamivir, (2008-2009: 98.5% of Influenza A tested resistant), also more commonly in people with weak immune systems. Cytomegalovirus can become resistant to ganciclovir and foscarnet under treatment, especially in immunosuppressed patients. Herpes simplex virus rarely becomes resistant to acyclovir preparations, mostly in the form of cross-resistance to famciclovir and valacyclovir, usually in immunosuppressed patients.[15]
Preventing the emergence of antimicrobial resistance[edit]
To limit the development of antimicrobial resistance, it has been suggested to:[citation needed]
Use the appropriate antimicrobial for an infection; e.g. no antibiotics for viral infections
Identify the causative organism whenever possible
Select an antimicrobial which targets the specific organism, rather than relying on a broad-spectrum antimicrobial
Complete an appropriate duration of antimicrobial treatment (not too short and not too long)
Use the correct dose for eradication; subtherapeutic dosing is associated with resistance, as demonstrated in food animals.
More thorough education of and by prescribers on their actions' implications globally.
The medical community relies on education of its prescribers, and self-regulation in the form of appeals to voluntary antimicrobial stewardship, which at hospitals may take the form of an antimicrobial stewardship program. It has been argued that depending on the cultural context government can aid in educating the public on the importance of restrictive use of antibiotics for human clinical use, but unlike narcotics, there is no regulation of its use anywhere in the world at this time. Antibiotic use has been restricted or regulated for treating animals raised for human consumption with success, in Denmark for example.[19]
Infection prevention is the most efficient strategy of prevention of an infection with a MDR organism within a hospital, because there are few alternatives to antibiotics in the case of an extensively resistant or panresistant infection; if an infection is localized, removal or excision can be attempted (with MDR-TB the lung for example), but in the case of a systemic infection only generic measures like boosting the immune system with immunoglobulins may be possible. The use of bacteriophages (viruses which kill bacteria) is a developing area of possible therapeutic treatments.[20]
It is necessary to develop new antibiotics over time since the selection of resistant bacteria cannot be prevented completely. This means with every application of a specific antibiotic, the survival of a few bacteria which already got a resistance gene against the substance is promoted, and the concerning bacterial population amplifies. Therefore, the resistance gene is farther distributed in the organism and the environment, and a higher percentage of bacteria means they no longer respond to a therapy with this specific antibiotic. In addition to developing new antibiotics, new strategies entirely must be implemented in order to keep the public safe from the event of total resistance. New strategies are being tested such as UV light treatments and bacteriophage utilization, however more resources must be dedicated to this cause.
^Howden BP, Slavin MA, Schwarer AP, Mijch AM (February 2003). "Successful control of disseminated Scedosporium prolificans infection with a combination of voriconazole and terbinafine". Eur. J. Clin. Microbiol. Infect. Dis. 22 (2): 111–3. doi:10.1007/s10096-002-0877-z. PMID12627286. S2CID29095136.
^Dondorp, A., Nosten, F., Yi, P., Das, D., Phyo, A., & Tarning, J. et al. (2009). Artemisinin Resistance in Plasmodium falciparum Malaria. New England Journal Of Medicine, 361, 455-467.
^Doliwa C, Escotte-Binet S, Aubert D, Velard F, Schmid A, Geers R, Villena I. Induction of sulfadiazine resistance in vitro in Toxoplasma gondii.Exp Parasitol. 2013 Feb;133(2):131-6.
^Laurenson YC, Bishop SC, Forbes AB, Kyriazakis I.Modelling the short- and long-term impacts of drenching frequency and targeted selective treatment on the performance of grazing lambs and the emergence of antihelmintic resistance.Parasitology. 2013 Feb 1:1-12.
European Centre of Disease Prevention and Control and (ECDC): Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: An international expert proposal for interim standard definitions for acquired resistance Disease Programmes Unit
