Multidrug-resistant bacteria (MDR bacteria) are

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

that are resistant to three or more classes of

antimicrobial An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...

drugs. MDR bacteria have seen an increase in prevalence in recent years and pose serious risks to

public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...

. MDR bacteria can be broken into 3 main categories:

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bact ...

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

, and other ( acid-stain). These bacteria employ various adaptations to avoid or mitigate the damage done by antimicrobials. With increased access to modern medicine there has been a sharp increase in the amount of antibiotics consumed. Given the abundant use of antibiotics there has been a considerable increase in the evolution of

antimicrobial resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. P ...

factors, now outpacing the development of new antibiotics.

Examples identified as serious threats to public health

Examples of MDR bacteria identified as serious threats to public health include: ;Gram-positive MDR bacteria * ''

Clostridioides difficile ''Clostridioides difficile'' ( syn. ''Clostridium difficile'') is a bacterium that is well known for causing serious diarrheal infections, and may also cause colon cancer. Also known as ''C. difficile'', or ''C. diff'' (), is Gram-positive spe ...

'' * '' Staphylococcus aureus'' * ''

Streptococcus pneumoniae ''Streptococcus pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under anaerobic conditions), aerotolerant anaerobic member of the genus Streptococcus. They ar ...

'' ;Gram-negative MDR bacteria *

Carbapenem Carbapenems are a class of very effective antibiotic agents most commonly used for the treatment of severe bacterial infections. This class of antibiotics is usually reserved for known or suspected multidrug-resistant (MDR) bacterial infections. ...

-resistant ''

Acinetobacter ''Acinetobacter'' is a genus of gram-negative bacteria belonging to the wider class of Gammaproteobacteria. ''Acinetobacter'' species are oxidase-negative, exhibit twitching motility, and occur in pairs under magnification. They are importan ...

'' * ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

'' * ''

Klebsiella pneumoniae ''Klebsiella pneumoniae'' is a Gram-negative, non-motile, encapsulated, lactose- fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mo ...

'' * '' Neisseria gonorrhoeae'' * '' Campylobacter'' * ''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic–facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. aerug ...

'' * '' Salmonella'' * ''

Shigella ''Shigella'' is a genus of bacteria that is Gram-negative, facultative anaerobic, non-spore-forming, nonmotile, rod-shaped, and genetically closely related to '' E. coli''. The genus is named after Kiyoshi Shiga, who first discovered it in 1 ...

'' ;Other MDR bacteria * '' Mycobacterium tuberculosis''

Microbial adaptations

MDR bacteria employ a plurality of adaptations to overcome the environmental insults caused by antibiotics. Bacteria are capable of sharing these resistance factors in a process called

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). H ...

where resistant bacteria share genetic information that encodes resistance to the naive population. * Antibiotic inactivation: bacteria create proteins that can prevent damage caused by antibiotics, they can do this in two ways. First, inactivating or modifying the antibiotic so that it can no longer interact with its target. Second, degrading the antibiotic directly. * Multidrug efflux pumps: The use of transporter proteins to expel the antibiotic. * Modification of target sites: mutating or modifying elements of the bacteria structure to prevent interaction with the antibiotic. * Structural modifications: mutating or modifying global elements of cell to adapt to Antibiotic (Such as increased acid tolerance to an acidic antimicrobial)

Alternative antimicrobial methods

Phage therapy

Bacteriophage therapy, commonly known as 'phage therapy,' uses bacteria-specific viruses to kill antibiotic resistant bacteria. Phage therapy offers considerably higher specificity as the phage can be engineered to only infect a certain bacteria species. Phage therapy also allows for the possibility of

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...

penetration in cases where antibiotics are ineffective due to the increased resistance of biofilm-forming pathogens. One major drawback to phage therapy is the evolution of phage-resistant microbes which was seen in a majority of phage therapy experiments aimed to treat sepsis and intestinal infection. Recent studies suggest that development of phage resistance comes as a trade-off for antibiotic resistance and can be used to create antibiotic-sensitive populations.

References

{{Reflist Microbiology Public health Symbiosis Antibiotics Antibiotic-resistant bacteria