Antibiotic Resistance, Superbugs and Drugs

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Antibiotic resistance results, because spontaneous mutations occur so frequently that all bacteria are different.  It is just a matter of exposing enough bacteria to an antibiotic to find one that is insensitive to a particular antibiotic.  More bacteria mean a greater chance of mutations to antibiotic resistance.  The gut contains a lot of bacteria and sewage treatment plants are loaded with gut flora.

Health in Diagrams

Antibiotics are Ubiquitous

All organisms, plants, fungi and animals/humans produce chemicals that kill bacteria, i.e. antibiotics.  I have written many articles about the natural antibiotics of plants, a.k.a. phytoalexins or “antioxidant” polyphenolics, and the human defensins that are peptides with heparin binding domains.  Bacteria also produce viruses, called bacteriophages, that kill other bacteria.  All of these natural antibiotics are small molecules that interact with many different human proteins, and it is these side effects that permit their exploitation as pharmaceuticals.  Thus, statins were selected from fungal antibiotics that inhibited an enzyme needed for human synthesis of cholesterol, metformin was a phytoalexin found to reduce blood sugar and resveratrol is a grape phytoalexin.

Plant Antibiotics are Natural

The flavoring chemicals in herbs and spices have a far more important use in food preparation than titillation of taste buds, since those chemicals kill common food pathogens.  More profoundly, it is important to realize that the selective advantage of phytochemicals/polyphenols/alkaloids/essential oils to the plants that make them, is as natural antibiotics.  Plants kill bacteria, as well as fungi and insects, for a living.

Plant Chemicals Attack all Aspects of Bacteria

Most of the thousand genes that are present in a bacterium code for proteins/enzymes and most antibiotics target those enzymes.  Penicillin binds to an enzyme needed to make bacterial cell walls, streptomycin target protein synthesis, rifampicin blocks RNA synthesis, actinomycin D inhibits DNA synthesis, etc.

Mutation to Antibiotic Resistance is Automatic in Bacteria

Each time a cell replicates, mistakes are made and the new DNA molecule of each chromosome is slightly different than the original.  There are about a thousand genes on the single chromosome of a bacterium and about the same number on each of the 23 human chromosomes.  About a dozen mistakes, mutations, are made each time bacteria replicate.  The mutations that alter the gene target of an antibiotic and produce a bacterial enzyme that is unaffected by the antibiotic, yield an antibiotic resistant bacterium.  The mutant gene now codes for antibiotic resistance and the presence of several resistance genes in the same bacterium produces multiple antibiotic resistant "superbugs."

Mutations are Random, but Antibiotics Select for Resistance

Each cellular replication produces random mutations throughout the bacterial DNA, but of the billion sites along the DNA that can mutate, only a few will produce a modified enzyme that will no longer interact with a particular antibiotic and thus be resistant.  Antibiotic resistance mutants are rare, less than one in a million, but a million bacteria can grow from a single cell in a day and occupy a volume less than a crystal of salt.  Ten hours later, after ten more doublings of the million bacteria, there will be a billion, and there will be a good chance that among those will be a mutant that is resistant to a particular antibiotic.  In the pound of bacteria in the human gut, there are mutants that are resistant to most antibiotics, including the antibiotics that have not yet been developed.  Of course, most of those antibiotic resistant bacteria are just flushed down the toilet.  Treatment with antibiotics kills all of the sensitive bacteria and leaves only the resistant.  Thus, antibiotic treatments select for antibiotic resistant bacteria.

Common Use of Antibiotics Selects for Resistance on Plasmids

Genes are transferred between bacteria by bacteriophages, conjugation (a kind of bacterial sex) and transformation, which is the release of DNA from one bacterium with subsequent uptake by another.  Biofilms, which are communities of many different species of bacteria, stimulate transformation and exploit bacterial DNA as a matrix material to hold the communities together.  The human gut is lined with biofilms and the biofilm bacteria secrete vitamins as the quorum sensing signals that coordinate community activity.  Thus, some vitamins must stimulate transformation, the exchange of DNA among members of the different species of bacteria in the biofilms with evolution of new and novel species.  Rapid change in the gut environment selects for a shift in genes that provide for adaptation to the new environment to small DNA fragments, plasmids, that move most readily between bacteria.  Antibiotic treatment results in antibiotic resistance genes on plasmids.

Use of Multiple Antibiotics Selects for Multiple Antibiotic Resistance Plasmids

Persistent use of an antibiotic will spread resistance to a particular antibiotic through the gut flora, facilitated by antibiotic resistant plasmids.  Replacement of a second antibiotic will result in a new plasmid with both antibiotic resistance genes.  Hospitalization and exposure to a plethora of bacteria with multiple antibiotic resistance plasmids will result in rapid conversion of gut flora to multiple antibiotic resistance upon exposure to any antibiotics.  Hospital staff would be expected to be natural repositories for multiple resistance genes, especially if they are exposed to any antibiotic (or pharmaceutical.)

Most Pharmaceuticals Select for Multiple Antibiotic Resistance Plasmids and Superbugs

The frightening rise of superbugs resistant to all known antibiotics has been attributed to the accelerated use of antibiotics in medicine and agriculture.  Mixing megatons of bacteria in the guts of billions of people with tons of antibiotics, and still more in sewage treatment plants and agriculture, is bound to produce bacteria with every type of multiple antibiotic resistance plasmid imaginable.  But that is not the biggest problem, since fingering the commercial use and misuse of antibiotics ignores biggest exposure of bacteria to antibiotics.  It ignores the fact that most popular pharmaceuticals, NSAIDs, statins, anti-depressants, anti-diabetics, etc., also have substantial antibiotic activity.  Most of these pharmaceuticals started out as phytoalexins and then were found to also have pharmaceutical activity.  Pharmaceuticals are just repurposed natural antibiotics.  When you take an aspirin or Metformin or a statin, you are taking an antibiotic.  When you take a pharmaceutical, you are selecting for multiple antibiotic resistance plasmids in your gut flora and you may be making the next superbug.

Milk Casein, Amyloid, Pasteurization, Homogenization

Milk is a very special food for mammalian babies. It provides essential nutrients; stimulates development of the gut; promotes the growth of the unique neonate gut flora; and kills everything else. Milk is anti-bacterial, anti-fungal and anti-viral. It is used in fruit orchards as a pruning tool dip to prevent the spread of disease between trees, and it is used as a foot dip after ceremonial walking on hot coals. But is cow's milk healthy for adult humans and is milk compromised by pasteurization and homogenization?

Mother's Milk is Fierce
Milk as it is transferred from breast to baby is loaded with molecular weapons for the protection of the baby's respiratory and digestive systems. Cells from the mother are transferred along with the milk and quickly spread out on the surface of the mouth and digestive system to patrol for pathogens. The mother's immune system detects potential risks as the baby's mouth contacts the mother's lymphatic system at the breast, and the antibodies that are subsequently produced are transferred into the milk. Enzymes in the milk digest bacterial cell walls and other milk proteins are converted into anti-bacterial peptides in the baby's stomach before ultimately being digested into amino acid nutrients. Many of the fat/lipid nutrients in milk are also anti-bacterial or anti-viral. Most of the carbohydrate in milk is the simple disaccharide lactose that most bacteria can't use for food. The remaining 10% of the carbohydrates are extensions of the lactose to make galacto-oligosaccharides (GOS, a.k.a. bifidus factor) that are toxic to all but the few bacterial species that make up the highly specialized microbial community of the human baby gut flora. (Cow's milk has an entirely different composition, e.g. lacks bifidus factor, and supports a different gut flora.)

Milk is Liquid Fat
It is hard to transport fat in water, because it isn't soluble. That is true for blood or milk. We have all heard about good and bad cholesterol, LDL and HDL, and the problems of transporting blood lipids from gut to liver to tissues. Specialized carrier proteins are needed for lipid transport in blood and the same is true for milk. Caseins are the milk proteins that coat droplets of fats that make milk white and then form digestible curds in response to the baby's stomach acid and digestive enzymes. We exploit the natural curd forming response of milk proteins and lipid droplets to form yogurts and cheeses.

Pasteurization and Homogenization Put Milk in the Dairy Case
Milk behaves optimally when immediately transferred from the mother's mammary tissue to the baby's digestive tract. Bacteria that contaminate breast milk are quickly killed by cellular and molecular defenses of the milk itself. Thus, breast milk has a long storage life at room temperature, chilled or frozen. The natural defenses of milk also permit regional milk banks, where donated milk is minimally processed and screened, for subsequent use by hospitals to avoid problems, such as necrotizing colitis, associated with the use of artificial feeding substitutes. Commercial preservation of cow's milk in stores has resulted in attempts to extend the shelf-life by heat treatment (pasteurization) to provide additional protection from microbial contamination and homogenization to prevent curd formation.

Milk is for Babies
So why isn't milk the perfect food? Part of the reason may come from the highly specialized and essential role of milk for mammals like people. Millions of years of extreme selection pressure have made sure that every woman produces ample milk for all of her babies. Until very recently, if the baby could not successfully nurse, it would die. That made breast milk the perfect food for babies and milk was integral to the development of the baby gut, baby gut flora and baby immune system. But that didn't mean that cow's milk would be a healthy commercial food for human adults.

Milk Processing May Accentuate Casein Amyloid Fiber Formation
Proteins are made of a long sequence of a thousand amino acids. At each of those thousand positions there is one of twenty different amino acids. Some of the amino acids are hydrophilic and bind to water, whereas other amino acids are hydrophobic and bind only to lipids. Proteins in water fold and unfold in thousands of alternative configurations until the final shape is reached in which there is not enough energy in the molecular vibrations and movements of the water molecules to knock the protein into an alternative shape.

Heating/pasteurization and torturous mixing/homogenization can force milk casein and fats into new configurations that make the proteins stackable into fibers/amyloids. These milk protein fibers may be of interest, because protein fibers are important in many diseases, e.g. type I diabetes, Alzheimer's disease. The problem with amyloids, is that these fibers form a natural repetition of the same amino acid on each of the stacked proteins. This repetitive amino acid, e.g. positively charged lysine or arginine, can provide a binding site for a similarly spaced, oppositely charged molecule, such as heparin, which is involved in dragging molecules from the surface into cells. Beta amyloid fibers with positively charged amino acids in a band along their edges are what kills nerve cells in Alzheimer's disease.

Research has recently demonstrated that milk casein forms amyloid fibers in response to pasteurization and homogenization. It would be interesting to know if these fibers bind to heparin and if these fibers are toxic to intestinal cells.

I have raw cream from grass fed cows in my morning coffee and my three daughters never tasted formula.

Rosacea: Alzheimer’s of the Face

Is Rosacea Caused by Amyloid LL-37, as Alzheimer’s Is Caused by Anti-microbial Abeta?
A recent article in PLoS One (Thanks Daniel!) suggests that the amyloid beta (Abeta) proteins that aggregate to form fibrous plaques in the brain tissue of Alzheimer victims, function as typical defensive anti-microbial peptides (AMPs), similar to the LL-37 cathelicidin implicated in facial tissue in rosacea.  The structural and functional similarities of Abeta and LL-37 suggest to me that Alzheimer’s and rosacea may also be similar in initiation and treatment.  Let’s compare amyloids and AMPs.

[The figure shows a model protein (from ref.) used to examine stain binding to amyloids.  The stains appear to bind to aromatic amino acids spaced evenly between adjacent proteins, but adjacent basic amino acids (blue) are spaced the same way and provide sites for heparin binding.]

Amyloids:

• Amyloid proteins/peptides align into stacks and fibers
• Stacked beta sheets bind amyloid stains: Congo Red, Thioflavin-T
• Fibers form on anionic polymers: heparin, DNA
• Short amyloid stacks are toxic to cells
• Proteases produce multiple sizes of amyloid peptides

Anti-microbial Peptides:

• AMPS typically contain heparin-binding domains -- basic peptides/ plus charge
• Some AMPs, e.g. LL-37, form fibers on DNA, heparin (stain with amyloid stains)
• Toxic to cell membranes
• Kallikrein stimulated by gut flora migrates to face and clips LL-37 to a smaller peptide that binds to host DNA and stimulates the TLR receptor to produce inflammation
• Stomach pepsin hydrolyzes dietary proteins into anti-microbial peptides (heparin is secreted by mast cells onto to the intestinal surface to protect from any amyloid-like effects)
• Defensins, cathelicidins and other AMPs are under transcriptional control of vitamin D receptor

Abeta Is Anti-microbial Like LL-37

Amyloid beta is the well-known source of the fibrous plaques forming brain lesions in Alzheimer’s disease.  The normal function of Abeta has not been firmly established.  The recent article shows data to support Abeta as an anti-microbial peptide comparable to LL-37 against several pathogenic bacteria and yeast.  Knock-out mice deprived of a gene corresponding to Abeta are susceptible to bacterial infections.  The anti-microbial activity present in extracts from Alzheimer’s disease brains was inactivated by anti-Abeta antibodies.

Implications of Abeta as an AMP Like LL-37

The similarities between AMPs and amyloid peptides suggest some implications for both Alzheimer’s disease and rosacea.  Vitamin D is a hormone that binds to a cytoplasmic receptor and the vitD/receptor complex then acts as a transcription factor that controls the expression of defensins in the intestines, LL-37 in facial skin and perhaps Abeta in brains.

Amyloids form fibers on a scaffolding of heparan sulfate (HS).  There is usually an excess of HS on the surface of cells and the HS is rapidly recycled back into cells.  During inflammation, mast cells release heparin, short fragments of HS, that should also inhibit amyloid fiber formation on HS.   Chronic inflammation, however, reduces HS production and may set the stage for amyloid fiber formation.  HS metabolism of the brain may be vitally important to the development of Alzheimer’s disease, especially since the increasing chronic inflammation of aging people should deplete brain HS.

LL-37 forms complexes with DNA from damaged host cells in rosacea skin.  The LL-37/DNA complexes trigger TLRs and inflammation.  LL-37 may normally bind to cell surface HS and chronic inflammation of the skin may cause the shift to pathogenic autoinflammation.  Topical application or perhaps low dose IV heparin may be effective in disrupting the autoinflammation due to LL-37.  Part of the toxicity of LL-37 in the skin may be due to amyloid like structures that could form with inadequate HS and overabundant LL-37 production.  Vitamin D metabolism should also be very important, since LL-37 synthesis is controlled by vitamin D.  This is consistent with the benefits that some rosaceans observe with high doses of vitamin D3 supplements.

references:
Soscia SJ, Kirby JE, Washicosky KJ, Tucker SM, Ingelsson M, Hyman B, Burton MA, Goldstein LE, Duong S, Tanzi RE, Moir RD.  The Alzheimer's disease-associated amyloid beta-protein is an antimicrobial peptide.  PLoS One. 2010 Mar 3;5(3):e9505.

Abedini A, Tracz SM, Cho JH, Raleigh DP.  Characterization of the heparin binding site in the N-terminus of human pro-islet amyloid polypeptide: implications for amyloid formation.  Biochemistry. 2006 Aug 1;45(30):9228-37.

Biancalana M, Makabe K, Koide A, Koide S. Molecular mechanism of thioflavin-T binding to the surface of beta-rich peptide self-assemblies.  J Mol Biol. 2009 Jan 30;385(4):1052-63. Epub 2008 Nov 14.

Antimicrobial Heparin-binding Domains

Antimicrobial Digestion

Stomach enzymes produce antimicrobial peptides and intestinal enzymes inactivate heparin-binding domains of pathogens

The human digestive systems exhibits some amazing adaptations -- it can excise heparin-binding domains from ingested proteins and use them as antimicrobial peptides to inactivate ingested bacteria. Then in subsequent enzymatic steps in the intestines, the heparin-binding domains that otherwise could be used to adhere bacteria to the heparan sulfate proteoglycans of the intestinal lining, are chopped into inactive peptide fragments.

I was trying to find a cheap heparin-binding protein to use for a variety of research projects and finally found it in the form of whey lactoferrin. This protein is available in a relatively pure form for about $1 per milligram. Alternatively, I could buy it as a nutriceutical in 250 mg capsules for $0.50 per capsule or 1/500th the cost. My next step was to purify the cheap lactoferrin by binding it to chromatography beads with attached heparin. The lactoferrin stuck to the beads and other contaminating material was washed away. Finally, pure lactoferrin was released by increasing the salt concentration of the wash solution. My goal was to use proteolytic enzymes to hydrolyze the lactoferrin and produce peptide fragments containing heparin-binding domains. I naively pasted the known amino acid sequence of bovine lactoferrin into a website that would predict the cleavage locations of numerous proteases along the lactoferrin molecule. Amazingly, pepsin, the stomach protease, released a couple of peptides with heparin-binding domains, e.g. KCRRWQWRMKK, whereas trypsin, the intestinal protease, degraded all of the heparin-binding domains. I had a simple procedure for producing the peptides I wanted, but I also learned something about the beauty of the digestive system.

It took me a while to realize the utility of the alternative proteases. Production of heparin-binding peptides by pepsin enhances the sterilization of meals, because the heparin-binding domains are also generally antimicrobial. In fact, most antimicrobial peptides secreted by the skin or venom of a wide variety of organisms from primates to poison dart frogs have heparin-binding sequences. Degradation of heparin-binding domains by trypsin in the intestines is also advantageous, because numerous bacteria (e.g. E. coli O157;H7) and viruses (e.g. HIV and avian flu) use heparan sulfate regions of gut proteoglycans as receptors to immobilize these pathogens on the surface and initiate infections. Some toxins that rely on heparin-binding are also inactived in the intestines.