[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fV9Ql9cpnR8N5rzeDBl_Xhfb_bR8UXCrMUHP9YPr2M9I":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":47},[4,8,12,16,20,24,28],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":46},"antibiotic-resistance-origin-causes-mechanism","Antibiotic Resistance: Origin, Causes, Mechanism",null,"Srijana Khanal","2017-05-30","2025-12-29",false,"bacteriology","Antibiotics are the main therapeutic tools to treat various bacterial infections. But today, more and more antibiotics are becoming less effective. It is because of the antibiotic resistance developed by bacteria due to the use and misuse of antibiotics.\n\n![Antibiotic resistance poster PAHS - Antibiotics Awareness Week: Winning Poster at OCRU Nepal\u002FPatan Hospital](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FAntibiotic-Resistance-one.jpg)\n\u003Cfigcaption>Figure: Antibiotics Awareness Week: Winning Poster at OCRU Nepal\u002FPatan Hospital\u003C\u002Ffigcaption>\n\nAntibiotic resistance is the acquired ability of a bacterium to resist the effects of an antibiotic to which it usually is susceptible. It occurs when bacteria change in a way that reduces the efficacy of antibiotics. Thus, the bacteria continue to multiply in the presence of therapeutic levels of antibiotics.\n\n> Resistant bacteria destroy the antibiotic or neutralize its effects. Antibiotic resistance is encoded by bacteria at either chromosome or plasmid.\n\nBacteria resistant to multiple antibiotics are called multidrug-resistant (MDR) bacteria or superbugs.Every living organism makes an effort to survive. If an organism adjusts to a changing environment, it survives; if not, it dies. When bacteria constantly come in contact with antibiotics, some bacteria develop a resistance mechanism. Such bacteria have a greater chance of survival than those that are susceptible. Thus, antibiotic resistance is a natural phenomenon.\n\n## Selection pressure\n\n![Selection pressure and antibiotics resistance - Selection Pressure (source: cdc.gov)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FSelection-Pressure-Antibiotic-Resistance.png)\n\u003Cfigcaption>Figure: Selection Pressure (source: cdc.gov)\u003C\u002Ffigcaption>\n\nSuppose very few bacteria are antibiotic-resistant in a large population of bacteria. The antibiotic, on its exposure, kills all the susceptible bacteria. This leads to selective pressure for the survival of resistant bacteria. The resistant bacteria can multiply rapidly, giving rise to more resistant bacteria. For example, the bacteria isolated from hospital-acquired infections are more likely to be antibiotic-resistant. It is because of excessive exposure to antibiotics.\n\nIn addition, resistant bacteria also transfer their resistant gene to susceptible bacteria. One resistant bacterium among millions of bacteria cannot cause harm. The problem arises when it transfers its resistant gene to other bacteria, ultimately making resistant bacteria a majority.\n\nToday’s significant threats are [methicillin-resistantStaphylococus aureus(MRSA),](\u002Fmrsa-emergence-types-detection\u002F) Vancomycin-resistant enterococci (VRE), multi-drug resistant *Mycobacterium tuberculosis* (MDR-TB), etc. These bacteria are resistant to most of the commonly used antibiotics.\n\n![ - Ways of gaining a resistant gene by bacteria](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FWays-of-Gaining-Antibiotic-Resistance.jpg)\n\u003Cfigcaption>Figure: Ways of gaining a resistant gene by bacteria\u003C\u002Ffigcaption>\n\n## Natural resistance\n\nSome bacteria are naturally resistant to certain antibiotics. For example, antibiotics inhibiting cell wall synthesis are useless for *Mycoplasma* as these organisms lack a cell wall. Similarly, most Gram-negative bacteria are resistant to glycopeptide antibiotics like vancomycin. These antibiotics are larger and cannot pass through the tiny pores of the Gram-negative bacteria’s outer membrane.Natural resistance to a certain antibiotic is not generally considered antibiotic-resistant because the bacteria were never susceptible to that antibiotic.\n\n## Acquired resistance\n\nIf antibiotics are unfavorable, bacterial growth either suppresses or develop resistance. If bacteria are not resistant to antibiotics naturally, they may gain resistant genes from other bacteria. Bacteria can gain resistance either by mutation or a gene transfer from resistant bacteria.\n\n### Mutation\n\nThe [mutation](\u002Fmutation\u002F) is a stable, heritable change of an organism’s gene. Different genetic mutations yield different types of resistance. Isolation of resistant cells can be from the cultures of bacteria that were susceptible to the antibiotic. This type of resistance is usually due to a mutation in a chromosomal gene.\n\n### Gene transfer\n\nResistant genes can be transferred from one bacterium to the other. The transmission of resistant genes occurs via vertical gene transfer or horizontal gene transfer.\n\n#### Vertical gene transfer\n\nResistant gene is transferred from one generation to another generation by reproduction. This is called vertical gene transfer, a usual life process.\n\n#### Horizontal gene transfer\n\nBacteria also transfer their resistant gene to susceptible bacteria by horizontal gene transfer. Bacteria may transfer resistant genes horizontally among the same species or even between different genera and species. It can occur through conjugation, transformation, and transduction.\n\n1. **Conjugation**: [Conjugation](\u002Fmechanism-conjugation-bacteria-transfer-f-plasmid\u002F) is a mating process through which genes are transferred through the temporary fusion of the mating partners. Thus, a plasmid or a portion of a chromosome that bears resistant genes can be shared. For example, the transfer of antibiotic-resistance genes in intestinal pathogens from *E. coli*.\n2. **Transformation**: Another method of gene transfer is [transformation](\u002Fbacterial-transformation-mechanism\u002F). When a bacterium containing resistant genes dies, its DNA releases outside. Then another bacterium can uptake that “free” DNA from the environment.\n3. **Transduction**: Viruses (bacteriophages) are another means for passing resistant genes between bacteria through [transduction](\u002Fbacterial-genetics-mechanism-generalized-transduction\u002F). When a bacteriophage invades an antibiotic-resistant bacterium, the resistant gene of the bacterium is packaged into the head portion of the phage. When that phage invades another (susceptible) bacterium, it injects the resistant gene into it.\n\n## Causes and spread of antibiotic resistance\n\nAntibiotic resistance is driven by various factors, ranging from contaminated bodies of water to misuse of antibiotics in food production and human medicine.\n\n![Spread of antibiotics resistance - Examples of How Antibiotic Resistance Spreads (source: CDC)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FExample-of-How-Antibiotics-Spread.jpg)\n\u003Cfigcaption>Figure: Examples of How Antibiotic Resistance Spreads (source: CDC)\u003C\u002Ffigcaption>\n\n### Indiscriminate use of antibiotics\n\nAntibiotics are used indiscriminately, like taking the wrong antibiotics or inappropriate doses and for the inappropriate duration; patients not taking an entire course of antibiotics as they stop it soon after feeling better, using antibiotics for viral diseases, etc. These types of misuse lead to the rise of antibiotic resistance.\n\n![Antibiotic resistance PAHS - Antibiotics Awareness Week: Winning Poster at OCRU Nepal\u002FPatan Hospital](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FAntibiotic-Resistance-three.jpg)\n\u003Cfigcaption>Figure: Antibiotics Awareness Week: Winning Poster at OCRU Nepal\u002FPatan Hospital\u003C\u002Ffigcaption>\n\n### Non-medical use of antibiotics\n\nAntibiotics are also given to farm animals for disease prevention and growth promotion. Such antibiotics expose many animals and, thus, bacteria for a more extended period and at lower doses. This leads to the evolution of resistance. Consuming animals as food or by close contact with such animals, humans get such resistant bacteria. Antibiotic-resistant bacteria from hospitals, poultry farms, or any other place spread in the environment. These bacteria cause infectious diseases which are difficult to treat.\n\n## Mechanism of antibiotic resistance\n\n![Mechanism of Antibiotic Resistance Development - Mechanism of Antibiotic Resistance Development](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FAntibiotic-Resistance-Mechanism.jpg)\n\u003Cfigcaption>Figure: Mechanism of Antibiotic Resistance Development\u003C\u002Ffigcaption>\n\n### Decreased permeability\u002Fuptake\n\nChanges in the number and characters of porin channels through which beta-lactam and aminoglycosides cross the outer membrane to reach penicillin-binding proteins (PBPs) of gram-negative bacteria substantially reduce the uptake of beta-lactam agents.\n\nResistance shown by some Gram-negative bacteria towards [beta-lactam antibiotics](\u002Fbeta-lactam-antibiotics-mechanism-action-resistance\u002F) (e.g., *P. aeruginosa*resistance to imipenem) and aminoglycoside resistance in various gram-negative bacteria are some of the important examples.\n\n### Efflux pump\n\nIn some bacteria, an development of efflux pump occurs. When an antibiotic enters the cell, the efflux pump throws the antibiotics outside the cell. This type of resistance is seen in tetracycline-resistant bacteria.\n\nThe efflux mechanism in various streptococci and staphylococci pumps macrolides out of the cell before target binding.\n\n### Altered target\n\nSome bacteria become resistant by modifying the target on which antibiotics bind and act. For example, when the structure of a penicillin-binding protein (PBP) in bacteria alters, penicillin can no longer bind to that protein. This makes penicillin ineffective.\n\n| Examples of Resistance | Mechanism of Resistance |\n| --- | --- |\n| Staphylococcal resistance to methicillin and other available beta-lactams. Penicillin and cephalosporin resistance in S. pneumoniae and viridans streptococci. | Mutational changes in original penicillin-binding proteins (PBPs) or acquisition of different PBPs that do not bind beta-lactams sufficiently to inhibit cell wall synthesis. |\n| Enterococcal and Staphylococcus aureus resistance to vancomycin. | Alteration in the molecular structure of cell wall precursor components decreases the binding of vancomycin, allowing cell wall synthesis to continue. |\n| Enterococcal resistance to streptomycin | Mutational changes in ribosomal binding sites diminish the ability of aminoglycoside to bind sufficiently and halt protein synthesis. This resistance may also be mediated by enzymatic modification. |\n| Gram-negative and gram-positive bacteria resistance to various quinolones | Changes in DNA gyrase subunits decrease the ability of quinolones to bind this enzyme and interfere with DNA synthesis. |\n| Resistance of various streptococci and staphylococci to macrolides (erythromycin, azithromycin, clarithromycin) | Enzymatic alteration of ribosomal target reduces drug binding. |\n\n### Enzymatic Inactivation of antibiotics\n\nSome bacteria produce enzymes that damage the structure of an antibiotic so that it cannot work. For example, bacteria producing beta-lactamase enzymes inactivate beta-lactam antibiotics such as penicillin.\n\n| Examples of Resistance | Mechanism of Resistance |\n| --- | --- |\n| Staphylococcal resistance to penicillin. Enterobacteriaceae and P. aeruginosa resistant to penicillin, cephalosporin, and aztreonam | Beta-lactamase enzymes destroy the beta-lactam ring. Thus, antibiotics cannot bind to penicillin-binding protein (PBP) and interfere with cell wall synthesis. |\n| Gram-positive and gram-negative resistance to aminoglycosides | Modifying enzymes alter various sites on the aminoglycoside molecule; thus, the ability of the drug to bind to ribosome and halt protein synthesis is greatly reduced or lost. |\n\n### Alteration of metabolic pathway\n\nBacteria change some of the metabolic processes and become resistant to the antibiotics which act on such processes. For example, sulfonamide-resistant bacteria do not require PABA to synthesize folic acid. Like mammalian cells, they directly use preformed folic acid.\n\n![ - Antibiotic Sensitivity test: Multidrug-resistantE. colionMueller Hinton Agarisolated from urine sample (1=Amoxycillin, 2=Norfloxacin, 3=Ciprofloxacin, 4=Cefixime, 5=Gentamicin, 6=Nitrofurantoin). No clear zone (and very small clear zone) was seen around different antibiotic discs; this means the bacterial cells are not inhibited by multiple antibiotics.](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FAST-Plate-300x209.png)\n\u003Cfigcaption>Figure: Antibiotic Sensitivity test: Multidrug-resistantE. colionMueller Hinton Agarisolated from urine sample (1=Amoxycillin, 2=Norfloxacin, 3=Ciprofloxacin, 4=Cefixime, 5=Gentamicin, 6=Nitrofurantoin). No clear zone (and very small clear zone) was seen around different antibiotic discs; this means the bacterial cells are not inhibited by multiple antibiotics.\u003C\u002Ffigcaption>\n\n## Prevention for antibiotic resistance\n\nEvery strain of bacteria isolated from the clinical sample must be tested for [minimum inhibiting concentration (MIC)](\u002Fminimum-inhibitory-concentration-and-minimum-bactericidal-concentration-mbc\u002F) and antibiotic sensitivity test (AST). This helps clinicians choose the correct antibiotic with the right dose and reduces the chance of resistance.\n\n![Antibiotic resistance PAHS - Antibiotics Awareness Week: Winning Poster at OCRU Nepal\u002FPatan Hospital](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FAntibiotic-resistance-two.jpg)\n\u003Cfigcaption>Figure: Antibiotics Awareness Week: Winning Poster at OCRU Nepal\u002FPatan Hospital\u003C\u002Ffigcaption>\n\nA combination of different natures of antibiotics helps to work against resistant bacteria. As these antibiotics act on different sites of bacteria, the bacteria are less likely to develop resistance. However, this may not be effective against MDR bacteria.\n\n**Some of the preventive ways are as follows:**\n\n**Prevent infection**\n\nInfection can be prevented by immunization. Vaccines increase the body’s immune system and decrease resistant pathogens. Fewer IV lines and catheter use also help prevent infection in hospitals.\n\n**Diagnose and treat effectively**\n\nPatient’s sample should be cultured in a lab to isolate and identify the causative organism. Proper antibiotics should be prescribed. It is better to prefer narrow-spectrum antibiotics which only target pathogenic bacteria.\n\n**Use antibiotic wisely**\n\nPatients should be given the correct dose of antibiotics for a suitable duration. Patients should be informed why the full course of antibiotics is necessary. The focus should be given to treating the infection, not the contamination.\n\n**Stop antibiotic therapy when unnecessary.**\n\nIf an antibiotic in use is found to be ineffective against the causative organism, it should be stopped. Sometimes antibiotics are prescribed before the culture reports; after finding negative results for bacteria, the antibiotic should be stopped as infection may be caused by a virus.\n\n**Prevent transmission of the pathogen**\n\nThe patient should maintain proper hygiene and sanitization; [hand washing](\u002Fhandwashing-hygiene-wash-hands\u002F) should be promoted, and direct contact with the patient should be avoided to prevent the spreading of communicable diseases.\n\n**References**\n\n1. Madigan MT, Martinko JM (2006). Brock Biology of Microorganisms. 11th edn. Pearson Educational International. pp. 692-698.3. Pelczar MJ, Chan ECS, Krieg NR (2007). Microbiology. 5th edn. Tata McGraw-Hill. pp. 531-532.4. Hugo WB and Russel AD (2004). Pharmaceutical Microbiology. 7th edn. Blackwell Scientific Publications, UK. pp. 220-232.5. \u003Chttp:\u002F\u002Fwww.who.int\u002Fmediacentre\u002Ffactsheets\u002Ffs194\u002Fen\u002F6>. \u003Chttp:\u002F\u002Femerald.tufts.edu\u002Fmed\u002Fapua\u002Fabout_issue\u002Fabout_antibioticres.shtml>",[],[],[],[48,55,62,67,71,75,80,85,88,92],{"slug":49,"name":50,"description":51,"image":52,"body":53,"postCount":54},"acharya-tankeshwar","Acharya Tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",433,{"slug":56,"name":57,"description":58,"image":59,"body":60,"postCount":61},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",81,{"slug":63,"name":64,"description":65,"image":37,"body":37,"postCount":66},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":68,"name":69,"description":65,"image":37,"body":37,"postCount":70},"samikshya-acharya","Samikshya Acharya",20,{"slug":72,"name":73,"description":65,"image":37,"body":37,"postCount":74},"alisha-tripathi","Alisha Tripathi",6,{"slug":76,"name":77,"description":78,"image":37,"body":37,"postCount":79},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":81,"name":82,"description":83,"image":37,"body":37,"postCount":84},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":86,"name":38,"description":65,"image":37,"body":37,"postCount":87},"srijana-khanal",18,{"slug":89,"name":90,"description":83,"image":37,"body":37,"postCount":91},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":93,"name":94,"description":65,"image":37,"body":95,"postCount":96},"nisha-rijal","Nisha Rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]