Definition of "Antibiotics"
Antibiotics (abx) are antagonistic of bacteria. IVAB is shorthand for IV antibiotics
Antibiotic resistance is a growing problem, with the use of antibiotics in farming, and overprescription of antibiotics contributing to the problem.
Patient information
What is an antibiotic? Is it the same thing as an antibody?No, they're not. An antibiotic helps fight against bacteria. On the other hand, an antibody is created by the body to help remove foreign antigens, which can in turn, target bacteria, but also viruses.
- Bacteria do not contain a nucleus, rarely harbor membrane-bound organelles, are a few micrometers in length, and have a variety of shapes (spheres, rods, spirals)
- There are approximately ten times as many bacterial cells than human cells in human flora, with the largest numbers of human flora in the gut flora (followed next by the skin)
- The vast majority of bacteria are rendered harmless by the protective effects of the imune system, with some being even beneficial (i.e. being symbiotic rather than just parasitic)
- Several species of bacteria however, are pathogenic, and can cause infectious disease. The most common fatal bacterial diseases are respiratory diseases (especially TB)
- Interferes with the cell wall synthesis or function:
- Interferes with nucleic acid synthesis
- Interferes with protein synthesis
Based upon its action, but depends on concentration as well as bacterial species:
- Bactericidal, actively kills bacteria, which is usually preferred e.g. in endocarditis, meningitis, osteomyelitis, and neutropenia, but no evidence otherwise that it is superior
- Bacteriostatic, inhibits bacteria from reproducing, but doesn't kill it
Gram positive:
- Cocci, more common:
- Clusters:
- Staphylococcus (from Greek "staphyle" meaning "grape", "kokkos" meaning "granule"
, which appear under a microscope as round (cocci). This occurs as they divide along multiple axe and generate grape-like clusters of cells. Most are harmless and reside normally on the skin and mucous membranes. They are facultative anaerobes. It can be further differentiated with the coagulase test
- Staphylococcus (from Greek "staphyle" meaning "grape", "kokkos" meaning "granule"
- Chains, which can be further differentiated with a hemolysis test, and Lancefield serotyping:
- Streptococcus (from Greek "streptos" meaning "twisted, like a chain", which is a coccus (spherical) bacteria. Cell divisoin is along a single axis, so they grow in chains or pairs. Many are facultative anaerobes (i.e. can grow both aerobically and anaerobically)
- Enterococcus
- Streptococcus (from Greek "streptos" meaning "twisted, like a chain"
- Clusters:
- Coccobacilli, including:
- Listeria
Gram negative, which has an outer membrane that excludes not only the dye, but also antibiotics from penetrating the cell, meaning Gram-negative is generally more resistant to antibiotics than Gram-positive:
- Rods (GNR), more common:
- Lactose fermenting:
- E. coli (Escherichia coli) is a Gram-negative, facultative anaerobe (i.e. uses aerobic respiration if oxygen is available, but can switch to anaerobic respiration if oxygen is absent), rod shaped bacteria, found in the lower intestine. Although harmless strains are found in normal flora of the gut (and in fact benefit the host by producing vitamin K2, and prevent colonization of the intestine with pathogenic bacteria), some subtypes (usually via fecal-oral transmission) can cause serious food poisoning
- Klebsiella
- Enterobacter
- Lactose non-fermenting:
- Pseudomonas
- Proteus
- Stenotrophomonas
- Lactose slow fermenting:
- Serratia
- Citrobacter
- Lactose fermenting:
- Cocci:
- Neisseria
- Moraxella
- Coccobacilli:
- Haemophilus
- Bordetella
Patient information
Gram positive and gram negative, what's the difference? Because gram positive have a gram, I'm guessing they're stronger?No, it's actually the other way. Gram negative is stronger, because it can't be penetrated by the stain, therefore we say it's "negative". It doesn't stain because Gram negative has an extra outer layer.
What are some examples of Gram positive and Gram negative?
So Gram positive is things like staphyococcus, streptococcus, and enterococcus. Gram negative are all of the other ones, so things like E coli, Klebsiella, Pseudomonas, Neisseria, Hemophilus.
Anaerobes, which is infection by an organism which doesn't require oxygen for growth. It can react negatively or even die if oxygen is present. Whilst they are stainable via gram stain, they ar rarely referred to as either gram positive or negative. Examples include:
- Clostridium
- Bacteroides
- Peptostreptococcus
- Actinomyces
Patient information
You sometimes hear about anaerobes, what's that?They're special because these organisms either don't need, or perform badly, with oxygen. Specifically, facultative anaerobe means it doesn't require oxygen. Obligate anaerobe means it will DIE in the presence of oxygen.
Atypicals, which have unsual cell structure, morphology, biochemistry or life cycle. It includes:
- Mycoplasma, which doesn't have a cell wall
- Chlamydia, which doesn't have peptidoglycan in the cell wall
- Rickettsia, which is an obligate intracellular parasite
- Legionella, which doesn't grow on traditional media
Patient information
How about atypicals?So this is the miscellaneous categories. So it's bacteria which don't have a cell wall, have a special type of cell wall, don't grow on traditional media, and so on. So it's things like mycoplasma, chlamydia, legionella, rickettsia.
MC&S (Microscopy, culture and sensitivity, biochemical test) is a microbiological lab test, involving:
- Microscopy, where a sample is viewed under a microscope, for a quick initial report
- Culture, where a pure sample is grown to allow further identification of an organism
- Sensitivity, where various antibiotics are blotted into an agar plate with the culture. If an organism grows up to the antibiotic it is resistant [to the antibiotic], whereas if there is a clear zone the antibiotic is effective against the organism. This can thus be used to determine if a Pt is taking an effective [or unfortunately, resistant] antibiotic
Patient information
We hear the acronym MC&S a lot. What does it mean?Microscopy, culture and sensitivity. So microscopy is where you look at the bacteria under a microscope. Culture is where we take a pure sample, and try to grow more of it, so that we can identify what it is. Sensitivity is where we blot antibiotics on a plate, to see if the antibiotic prevents the organism from growing around it, meaning that it will be effective against the organism.
Gram staining (aka Gram's method) is used to differentiate bacteria into gram-positive and gram-negative. It differentiates bacteria based on properties of their cell walls by detecting peptidoglycan (i.e. thick layer in gram +ve bacteria). In the test, gram +ve bacteria retains the crystal violet dye, whilst a counterstain (commonly safranin or fuchsine) added after the crystal violet gives all Gram -ve bacteria a red/pink coloring. In the initial dye, the gram +ve bacteria retains the dye because the peptidoglycan is a thick mesh-like wall, which permits it to be stained by crystal violet. Not all bacteria can be classified by this technique however, giving rise to gram-variable and gram-indeterminant groups.
Noting that antibiotic susceptibility is affected by geography and patient population, and thus reference should be made to hospital guidelines:
- Gram positive, Tx w/:
- Beta-lactam, including:
- Penicillins
- Cephalosporins
- Glycopeptides (e.g. Vancomycin), especially effective against Staph aureus
- Beta-lactam, including:
- Gram negative, Tx w/ :
- Quinolones (e.g. Nalldixic acid), which is mainly effective against Gram-negative bacteria
- Fluoroquinolones (e.g. Ciprofloxacin), that is also effective against some Gram-positive bacteria (Bacillus anthracis)
- Broad spectrum (both positive and negative), Tx w/:
- Semisynthetic beta-lactams (e.g. Amoxicillin, Ampicillin)
- Clavulanic acid (e.g. Augmentin=Clavulanic acid+Amoxicillin)
- Monobactams (e.g. Aztreonam)
- Carboxypenems (e.g. Imipenem)
- Aminoglycosides (e.g. Gentamicin, Streptomycin), Gentamicin especially effective against Pseudomonas
- Lincomycins, especially effective against anaerobic bacteroides
- Macrolides, but not effective against [Gram positive] enterococci. Especially effective against Neisseria, Legionella, Mycoplasma
- Rifamycin (e.g. Rifampicin), especially effective against Mycobacterium tuberculosis
- Tetracycline (e.g. Tetracycline), especially effective against Rickettsias
- Semisynthetic tetracycline (e.g. Doxycycline), especially effective against Rickettsias, Ehrlichia, Borrelia
- Chloramphenicol
- Growth factor analogs (e.g. Sulfanilamide, Trimethoprim), although Isoniazid and Para-aminosalicylic acid is especially effective against Mycobacterium tuberculosis
- Anaerobes:
- Glycopeptides (e.g. Vancomycin) which is effective against both aerobic and anaerobic Gram +ve bacteria
- Lincosamides (e.g. Clindamycin) which is effective against anaerobes
- Metronidazole which is effective against anaerobes
Source: Textbook of Bacteriology
Patient information
How can you use drugs to kill bacteria?So it depends on the type of bacteria. If it stains, we use your general beta lactams, so penicillins and cephalosporins. We can also use glycopeptides like vancomycin. If it doesn't stain, so is Gram negative, we use quinolones or fluoroquinolones. If it doesn't like oxygen, you can use vancomycin, clindamycin, or metronidazole.
Are there general purpose antibiotics?
Well there's a whole heap of broad spectrums, which work against both Gram positive and negative, so things like special types of beta lactams like amoxicillin and ampicillin. Also if you add clavulanic acid to a beta lactam, so Augmentin. There's also gentamicin. Macrolides. Tetracyclines.
- Some antibiotics that shouldn't be used in pregnancy, include:
- Bactrim
- Ciprofloxacin
- Doxycycline
- Furadantin
- Macrobid
- Macrodantin
- Minocycline
- Septra
- Tetracycline
- Antibiotics that are considered safe in pregnancy, include:
- Amoxicillin
- Ampicillin
- Augmentin
- Penicillin
- Cephalexin
- Clindamycin
- Erythromycin
Source: Parents.com
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