[2] Basic Microbial Concepts

• Microbes = Microorganisms
• Bacteria are single-celled microbes and its cell structure is simpler than other organisms
• Bacteria are prokaryotes which mean they have no nucleus or any other membrane-bound organelles
• Bacteria's DNA and other sites of metabolic activity are openly accessible and free floating
• Bacteria produce asexually, usually by binary fission or budding
• Bacteria has cell wall; some has capsule.
• Difference between the structure of prokaryotes and eukaryotes

  
• Bacterial morphology

  
• Most cocci (spherical or round-shaped bacteria) are gram-positive
• Most bacilli (rod-shaped) are gram-negative; Ex: Enterobacter (Klebsiella, E.coli, Salmonella)
• Exceptions! List of gram-positive bacilli:

  
• Exceptions! Gram-negative cocci

  
• Special Bacterial Morphology

  
• Spirochetes require darkfield microscopy
• Gram stain will not identify up to species level; only the bacterial cell morphology (G+ or G- bacilli or cocci)
• The color difference is based on the amount of peptidoglycan layer (Gram-positive has thicker peptidoglycan = more dye uptake = blue/violet color)
• Gram stain test can not be done on blood but other specimens like urine can
• Iodine acts as mordant which helps in the retention of

  crystal violet on the bacteria’s cell wall depending on its gram type
• Examples of gram stained species

  
• Only gram-negative organisms have outer membrane layer and lipopolysaccharides
• Lipopolysaccharides contribute to the antigenic properties and virulence of gram-negative organisms
• Difference in Cell wall properties

  
• Sepsis = body's extreme response to infection; happens when an infection you already have triggers a chain reaction throughout your body. 
• Penicillin-binding Proteins (PBPs) catalyze the synthesis of the peptidoglycan in the cell wall, thus strengthening it
• B-lactam antibiotics work by inhibiting PBPs
• Some bacteria produce enzymes that alter the PBPs

  or inactivate the B-lactam ring → resistance known as

  antimicrobial resistance
• The production of β-lactamases is the most common resistance mechanism against β-lactam antibiotics in Gram-negative bacteria
• Antimicrobial resistance = microorganisms do not become susceptible to antibiotics which is supposed to kill them; instead, they build resistance against the medicine
• Causes of AMR

  • Inappropriate dose of antibiotics
  • Misuse of antibiotics (frequent intake)
  • Incorrect antibiotic
• Superbugs are strains of bacteria, viruses, parasites and fungi that are resistant to most of the antibiotics and other medications commonly used to treat the infections they cause.
• B-lactams: type of antibiotic
• Penicillin is the most known B-lactam; act mainly on cell wall
• Efflux system - extrudes antibiotics out of the interior of the cell with the help of efflux pumps
• Porin channels: regulates the amount of B-lactam entering the cell
• mecA gene distorts the configuration of the binding protein, thus building resistance (cannot penetrate the cell)
• Methicillin-resistant Staphylococcus aureus (MRSA) strains resistant to an entire class of antibiotics called beta-lactams.
• Aerobic bacteria are oxygen-loving organisms; need oxygen to grow.
• Anaerobic bacteria fail to grow in the presence of oxygen
• Obligate anaerobes grow only in anaerobic environment (oxygen conc. must be less than 0.5%)
• Facultative anaerobes grow with or without oxygen