Category Archives: Colloidal Silver Research

What Doctors Have Said About Colloidal Silver

energetic-peopleA fantastic article about Colloidal Silver from Kay "Violet" Hardy:

Subject: What Doctors Have Said About Colloidal Silver

Thanx Thomas for sharing…good, solid information…Don

What  Doctors Have Said About Colloidal Silver

Colloidal silver has proven particularly  effective in cases of microbial
infection. Dr. Henry Crooks found that "Silver  in the colloidal state is highly
germicidal, quite harmless to humans and  absolutely non-toxic. Rather than in
a chemical compound, the silver in the  colloidal state may be applied in a
much more concentrated form, with  correspondingly better results. All virus,
fungus, bacterium, streptococcus,  staphylococcus, and other pathogenic
organisms are killed in three or four  minutes upon contact. There are no side
effects whatsoever from the highest  concentrations."

Colloidal silver has been proven useful against all  species of fungi,
bacteria, protozoa, parasites and certain viruses, which are  often killed within
minutes. Dr. L. C. Ford, M.D. at the UCLA School of Medicine  reported in 1988
that silver solutions were effective against the following  conditions:
Streptococcus pyogenes, Staphylococcus aures, Neisseria gonorrhea,  Garnerella
vaginalis, Salmonella typhi and other enteric pathogens. He also  found that it was
fungicidal for Candida albicans, Candida globata and M.  furfur.

How Colloidal Silver Works
The most accepted theory is  that silver disables the specific enzyme that
many forms of bacteria, viruses  and fungi utilize for their metabolism. When
silver nears a virus, fungi,  bacterium or any single-celled microbe it is
effective against, it disables the  oxygen-metabolism enzyme. This destroys the
microbe's ability to "breath" and  within a few minutes, the pathogen suffocates
and dies. The dead germ and its  toxins are then cleared out of the body by
the immune, lymphatic and elimination  systems. It is not exactly clear how
silver disrupts the enzymes in these single  celled animals, but it is believed
that the silver's natural positive electrica1  charge is influential. This is
why electrically generated colloidal silver is  the absolute best form of silver
for fighting infection and related infectious  diseases.

Unlike pharmaceutical antibiotics which destroy beneficial  bodily enzymes,
colloidal silver leaves our bodies tissue and cell enzymes  intact, as they are
different than enzymes found in single celled pathogens.  Thus colloidal
silver is generally considered safe for humans, pets, plants and  all multi-celled
living matter. Some health care professionals believe silver  may be linked
to the proper functioning of our immune system and that people  with inadequate
intakes of silver may be more prone to infection. 

Dr. Robert Becker, author of the 1980's best selling book The  Body Electric,
recognized a correlation between low silver levels in the human  body, and
sickness. He said a silver deficiency in humans was responsible for  the
improper functioning of the immune system. Dr. Becker's experiments conclude  that
silver works on the full spectrum of pathogens without any side effects or 
damage to any part of the body. He also states that the silver was doing 
something more than killing disease organisms, It was also causing major growth 
stimulation of injured tissues. Burn patients and elderly patients noticed more 
rapid healing. He discovered that cancer cells change back to normal cells in 
the presence of electrically generated colloidal silver. All strains of 
pathogens he tested, even those resistant to antibiotics, were killed by  colloidal

From the article "Silver, Our Mightiest Germ  Fighter," in Science Digest,
March, 1978: "As an antibiotic, silver kills over  650 disease causing
organisms, and resistant strains fail to develop. Silver is  the best all-around germ
fighter we have and is absolutely non-toxic! Doctors  report that, taken
internally, it works against syphilis, cholera, malaria  diabetes and severe burns.
Richard L. Davies, executive director of the Silver  Institute which monitors
silver technology in 37 countries, reports: 'In four  years we've described 87
important new medical uses for silver.'

Dr.  Bjorn Nordstrom, of the Karolinska Institute, Sweden, has used 
colloidal silver in his cancer treatment method. He says the whole thing is  quite
simple. Colloidal silver, used in conjunction with other natural therapies 
developed by Dr. Nordstrom, brought rapid remission in cancer patients given up  on
by other doctors.

Uses for Colloidal Silver
Preventing and  Healing Low Grade Infections: According to many colloidal
silver researchers,  taking sufficient daily colloidal silver can saturate the
body such that the  germs simply can't gain a foothold. Many people, including
many elderly, suffer  from a general low- grade body infection that holds back
vigor and alertness.  They report that using up to an ounce or two of homemade
colloidal silver each  day often brings about an increase of energy and
alertness, as well as enjoying  better overall health throughout the year.

Parasite Infections: Some  diseases are caused by tiny worm-like organisms
that burrow through particular  organs and sometimes throughout much of the
body. They reproduce by laying eggs.  These eggs have the same enzymatic
characteristics of all of the other disease-  causing organisms that colloidal silver
suffocates. So the parasite eggs also  suffocate and the parasites can no
longer reproduce successfully in your  body.

Resistant Strains of Germs: The use of modern man-made  antibiotiqs has
increasingly led to mutant strains of germs that the antibiotics  can no longer
kill. Colloidal silver does not appear to have this problem. Why?  Because unlike
man-made antibiotics which are basically "bug poison for the  human body,"
colloidal silver is not a poison. Instead, it deals with all gerr  the same way:
it suffocates them by disabling the enzyme they need for  respiration.

Accelerated Healing: Colloidal silver reportedly  shortens the time for
healing to take place in wounds, and lessens the amount of  scar tissue. This is
apparently due to the beneficial action that colloidal  silver has on tissue
cells. It seems to cause some of their cell divisions to  produce cells that are,
in a sense, generic. These generic cells migrate  wherever they are needed in
the body. They help repair tissue damage by changing  into the type of tissue
cell needed at the wound in preference to the scar  tissue that would
normally form.

Diarrhea Diseases: Diseases like  cholera, canine parvovirus and other
conditions where the disease-causing germ  resides mainly in the large intestine
have been effectively treated by a  different approach. It is difficult for the
colloidal silver to get all the way  to the large intestine before the body
absorbs it if you take the normal daily  amount orally. An effective approach is
to take large quantities instead (i.e.  two ounces or more followed by two big
glasses of water). This will allow the  colloidal silver to make it all the
way into the large intestine so it can very  quickly take care of the problem.

What Specifically Can Colloidal  Silver Be Used For?
Here is a small sample of diseases against which  Colloidal Silver has been
used successfully (see other chapters, particularly  chapters 4, 7 and 11 of
the manual for more): acne, allergies, appendicitis,  arthritis, blood
parasites, bubonic plague, burns (colloidal silver is one of  the few treatments that
can keep severe burn patients alive), cancer, candida,  cholera, chronic
fatigue, colds and flu, conjunctivitis, diabetes, gonorrhea,  hay fever, herpes,
leprosy, leukemia, lupus, lymphangitis, lyme disease,  malaria, meningitis,
parasitic infections both viral and fungal, pneumonia,  rheumatism, ringworm,
scarlet fever, septic conditions of the eyes, ears, mouth  and throat, shingles,
skin cancer, staph infections, strep infections, syphilis,  toxemia, trenchfoot,
numerous forms of viruses, warts and stomach ulcers. 

A Colloidal Silver Primer
History of Colloidal Silver
In  ancient civilizations, the wealthy stored and ate their food from silver
vessels  to keep bacteria from growing. American settlers often put a silver
dollar in  milk containers to delay its spoilage. It was not until the late
1800's that  Western scientists were able to understand scientifically what had
been known in  ancient medicine for thousands of years… that silver is a
powerful germ  fighter! After discovering that the body's vital fluids, such as
blood, are  colloidal in nature, scientists and doctors explored the
possibilities of using  colloids in medicine. The silver solution known as "Colloidal
Silver" became  widely used in medicine as one of the main-stays of
anti-microbial treatment. 

The medical journal Lancet reported phenomenal results from colloidal  silver
in 1914. Dr. Henry Crooks showed colloidal silver to be highly germicidal 
yet absolutely harmless and non-toxic to humans. Throughout the early 1900's 
colloidal silver rapidly gained fame as one of the best infection-fighting 
agents in existence. But unfortunately its fame was short lived. The high cost  of
silver combined with the fact that silver solutions could not be patented 
motivated the development of more profitable infection-fighting drugs by the 
major pharmaceutical conglomerates. The new prescription antibiotic drugs such 
as penicillin and others became the choice in medical treatments. However, 
thirty years after the discovery of pharmaceutical antibiotics many types of 
bacteria acquired an immunity to these drugs. Frustrated doctors, tired of 
seeing their patients die from infections with antibiotic resistant pathogens, 
began looking back to the past for answers. In doing so, they have r! 
e-discovered the amazing ant ibiotic properties of colloidal silver, which had  been
known for many decades.

The Rediscovery of Silver as a Powerful  Antibiotic
According to Zane Baronowski, CN, in his booklet, Colloidal  Silver: The
Natural Antibiotic Alternative: "The comeback of silver in medicine  began in the
1970's. The late Dr. Carl Moyer, chairman of Washington University's
Department of Surgery,  received a grant to develop better treatments for burn victims.
Dr. Margraf, as  the chief biochemist, worked with Dr. Moyer and other
surgeons to find an  antiseptic strong enough, yet safe to use over large areas of
the body. Dr.  Margraf reviewed 22 antiseptic compounds and found drawbacks in
all of them.  'Mercury, for example, is an excellent antiseptic but toxic, '
he comments.  'Popular antiseptics….can be used over small areas only. '
Furthermore,  disease organisms can become resistant to antibiotics, triggering a
dangerous  super-infection. 'These compounds are also ineffective against a
number of  harmful bacteria, including the biggest killer in burn cases a
greenish-blue  bacterium called Pseudomonas aeruginosa. It almost! always shows up
in burns,  releasing a poison.'

"Reviewing the medical literature, Dr. Margraf found  repeated references to
silver. It was described as a catalyst that disables the  enzymes
microorganisms depend on to 'breathe. ' Consequently, they die.  Therefore, Dr. Margraf
decided to use the best known pharmaceutical compound of  silver: silver
nitrate. Concentrated silver nitrate was corrosive and painful.  So he diluted the
silver nitrate to a .5 percent solution and found that it  killed the
Pseudomonas aeruginosa bacteria and permitted wounds to heal.  Resistant strains did not
appear. Silver nitrate, however, was far from ideal.  It disturbed the
balance of body salts, was thick and cumbersome to use and  stained everything it
touched. Dr. Margraf searched for other preparations of  silver, and in the
process helped re-discover colloidal silver, which he found  to be highly
effective on the burns. As a result of these efforts, hundreds of  important new
medical uses for silver were found. Dr. Harry Margraf later  concluded, 'Silver is
the best all around germ-fighter we have.  '

Future uses of Colloidal Silver
Although reports on the use of  colloidal silver have spanned the past 100
years, research relating to its  recent use is limited. However, through a
growing number of physicians,  dentists, veterinarians, nutritionists and satisfied
users, information  regarding the modern day uses of colloidal silver is
mounting. It would seem  that the effective and safe use of colloidal silver in
the treatment of many  common infectious disorders is only limited by the

Some  other diseases that have been successfully treated with colloidal
silver are:  bladder infection, blood-poison, boils, bubonic plague, burns, candida
yeast  infection, chilblains, cholera, conjunctivitis, cold sores, cold &
flu,  cystitis, diabetes, dermatitis, fungal infections, herpes, HIV virus, 
indigestion, leprosy, leukemia, lupus, lymphangitis, lyrne disease, malaria (now 
making a comeback in the southern U.S. states), meningitis, neurasthenia, 
puritis ani, psoriasis, ophthalmia, rabbit fever, rhinitis, ringworm, scarlet 
fever, and septic conditions of the eyes, ears, mouth 8c throat. Plus, shingles,
 sinus infections, staph infections, syphilis, thyroid, tonsillitis, toxemia,
 trachoma, trench-foot, tuberculosis, ulcers, viruses, warts, whooping cough,
 other many other uses.

What is Colloidal Silver?
The term  "colloid" refers to a substance that consists of ultra-fine
particles suspended  within a liquid solution. Properly manufactured colloidal silver
is a liquid  solution consisting of submicroscopic particles of silver, held
in suspension in  pure water by a tiny electrical charge. In a true colloid
these particles are  about 04 to 0001 microns in diameter. These particles
cannot be seen by the  naked eye and are electrically charged.

Many references can be found  describing a "quality" colloidal silver as
being light yellow or golden in  color. However, after hundreds of hours of
searching, no medical literature  could be found describing the golden-colored
colloidal silver as being any more  therapeutically effective than clear or
silver-colored colloidal silver.  Colloidal silver made with the small
battery-operated generators is considered  to be extremely high quality, yet it is generally
clear to silverish in the  liquid suspension.

Will Colloidal Silver Kill the "Friendly Bacteria" in  Your Intestines?
Colloidal silver that contains 99.99% (pure silver) with  particles that are
.04 to ..0001 microns in diameter with a concentration of 25  ppm (parts per
million) or less have little effect on the friendly bacteria in  our digestive
tract. In small doses (i.e., preventive dosages of about one  tablespoon per
day) much of the silver itself is absorbed in the mouth or  stomach and never
reaches the intestinal area. However some researchers believe  that colloidal
silver products with higher concentrations or larger particles of  silver can
attack friendly bacteria just like some antibiotics. There is also  evidence
that when taken in high dosages, some of the colloidal silver is  evacuated
through the colon and may kill some of the friendly bacteria there.  This could
upset your natural intestinal floral balance.

The generally  accepted recommended dosage is 5 to 40 ppm, although many
researchers take  significantly higher dosages with no apparent loss of friendly
bacteria in the  gut. Nonetheless, researchers suggest that if you intend to
take larger dosages  of concentrated colloidal silver over an extend period of
time, you should also  take a "friendly bacteria" supplement such as
lactobacillus acidophilus,  available at most health food stores, in order to prevent
the possibility of  depleting the much-needed beneficial bacteria in your
stomach and digestive  system.

Nutritional Dosage for Daily Intake
Currently, there is no  federally recognized "minimum daily requirement" for
silver in the human body.  In 1940, R. A. Kehoe reported that under normal
circumstances, the average daily  intake of fruits and vegetables would provide
between 50-100 mcg of silver as a  trace element. Since that time, the
commercial farm soils of this country have  become extremely deficient in trace
minerals. According to the Earth Summit  Report, issued in 1992, the levels of soil
based minerals in North America have dropped over 85% in the last 100 yea 

Jeffrey Frankel"

Why Won’t Doctors Admit to Colloidal Silver Usage?

Be quiet, my friend. You can't tell my secrets.Over the past 16 years, Steve Barwick of has spoken at length with literally thousands of experienced colloidal silver users, as part of his research for writing and updating his 547-page book, The Ultimate Colloidal Silver Manual.

Most of these conversations have been with typical users of nutritional supplements and believers in natural health and nutrition.


But many dozens of these conversations over the years have also been with medical doctors, nurses, dentists, and other orthodox medical practitioners who actually do use colloidal silver extensively.

What's amazing is that almost to a person, when I ask these medical practitioners about the extent of their colloidal silver usage, they not only turn out to be avid users, but in most cases they are ecstatic about their results.

“Do You Use Colloidal Silver On Your Patients?”

But when asked "Do you use colloidal silver on your patients, or recommend it to them?" their answer is almost inevitably an emphatic, "No…I couldn't do that!" When asked why, they say, "I wouldn't want to get in trouble with the medical board" or "That could jeopardize my medical license."

In other words, they'll use colloidal silver themselves, in place of prescription antibiotic drugs. And most of them that Steve has spoken with have no qualms about giving colloidal silver to their family members.

But they won't use it on their patients or even recommend its usage, out of an ingrained fear of the medical bureaucrats.

Big Pharma’s Coming Silver-Based Drugs

Hopefully, the news stories coming out about Big Pharma now developing silver-based drugs will change all of that for the better.

Maybe when medical practitioners see that Big Pharma is capitalizing on silver’s well-known infection-fighting powers, they’ll be more outspoken about their usage of colloidal silver.

Maybe they’ll even start recommending it to their patients!

Hypocrisy and Conspiracy

But I wouldn’t count much on it, since the medical bureaucrats in the FDA and in other similar government agencies worldwide are still at war with colloidal silver.

And why are the medical bureaucrats so fired up against colloidal silver, when the medical community itself is developing new silver-based drugs?

It’s because these over-bearing governmental organizations – which were originally set up to protect the public from medical fraud — are now nothing more than the enforcement arm of Big Pharma, working to make sure drugs are the only healing modalities the public is allowed.

As such, they’re working to clear the way for Big Pharma’s upcoming silver-based anti-viral, anti-bacterial and anti-fungal drugs by eliminating the one and only rival to these drugs: colloidal silver.

No Competition Allowed

Big Pharma simply doesn’t want the competition from safe, natural over-the-counter products like colloidal silver.

And the medical bureaucrats are happy to oblige them by waging warfare on colloidal silver.

The world is being drawn deeper and deeper into a corporate takeover by global Big Pharma. Soon, the only way you’ll be able to heal yourself is through your local doctor. And they’ll be under the control of your health insurance company.

And you can rest assured, your local doctor won’t be offering you safe, simple, all-natural colloidal silver to cure a potentially deadly infection. Instead, he’ll be offering you a freakish silver-based Franken-drug like this one.

How Long Has Silver Been Used As A Medicine?

Silver Has Been Used in Medicine Since 69 B.C.

"The antimicrobial effects of silver (Ag) have been recognized for thousands of years. In ancient times, it was used in water containers (Grier 1983) and to prevent putrefaction of liquids and foods. In ancient times in Mexico, water and milk were kept in silver containers (Davis and Etris 1997). Silver was also mentioned in the Roman pharmacopoeia of 69 b.c. (Davis and Etris 1997)."

— Dr. Charles P. Gerba, Silver As a Disinfectant, Reviews of Environmental Contamination and Toxicology 2007, Volume 191, 23-45

National Institute of Health: Proving the Benefits of Colloidal Silver (For Breast Cancer)

Carefully read this website and look at the graphs:

Particularly, note these sections:



Colloidal silver has been used as an antimicrobial and disinfectant agent. However, there is scarce information on its antitumor potential. The aim of this study was to determine if colloidal silver had cytotoxic effects on MCF-7 breast cancer cells and its mechanism of cell death.



MCF-7 breast cancer cells were treated with colloidal silver (ranged from 1.75 to 17.5 ng/mL) for 5 h at 37°C and 5% CO2 atmosphere. Cell Viability was evaluated by trypan blue exclusion method and the mechanism of cell death through detection of mono-oligonucleosomes using an ELISA kit and TUNEL assay. The production of NO, LDH, and Gpx, SOD, CAT, and Total antioxidant activities were evaluated by colorimetric assays.



Colloidal silver had dose-dependent cytotoxic effect in MCF-7 breast cancer cells through induction of apoptosis, shown an LD50 (3.5 ng/mL) and LD100 (14 ng/mL) (*P < 0.05), significantly decreased LDH (*P < 0.05) and significantly increased SOD (*P < 0.05) activities. However, the NO production, and Gpx, CAT, and Total antioxidant activities were not affected in MCF-7 breast cancer cells. PBMC were not altered by colloidal silver.



The overall results indicated that the colloidal silver has antitumor activity through induction of apoptosis in MCF-7 breast cancer cell line, suggesting that colloidal silver might be a potential alternative agent for human breast cancer therapy.


Colloidal silver is a common substance used by the Mexican people for disinfecting foods and water for their consumption, and at this time there is not a report on potential secondary effects related to this treatment; this also agreed with a recent study in mice performed in our laboratory, where colloidal silver was provided in the water at 10- and 50-fold higher concentrations than the recommended by the manufacturer during one year without finding any alterations in the evaluated parameters (fertility, birth, and tumors development)

There you have it folks.. Colloidal Silver = positive results for breast cancer. Google searches reveal HUNDREDS more testimonials bycolloidal silver users with regards to other types of cancers and illnesses.

Shining Secret That Makes Silver Precious For Your Health


Before the discovery of antibiotics, surgeons used to stitch wounds with thread woven with silver as they believed it helped to prevent infection.

Meanwhile, bandages were laced with silver in the First World War, as it was thought to help save lives. And they were right.

As shown in more than a thousand medical studies, silver has powerful antiseptic and wound-healing properties. So just what are the health secrets of this precious metal?

'Research has shown that silver is a powerful antimicrobial agent that is non-irritating and non-toxic,' says Valerie Edwards Jones, professor of microbiology at Manchester Metropolitan University. 'Recent studies have shown that silver can kill up to 650 species of pathogenic microbes.

'The metal consists of thousands of tiny silver ions,' she says. 'These prevent bacteria, viruses and fungi from spreading by entering the cell and deactivating proteins. The microbes cannot reproduce and die, so the spread of infection is prevented.'

There has been a resurgence of medical interest in silver, according to Prof Edwards Jones, because it effectively kills antibiotic resistant bacteria such as MRSA.


More and more silver-based products that help heal wounds and combat infection are appearing on the shop shelves. So what can silver do for you?


Silver ions kill underarm bacteria responsible for causing bad odour and are non-irritating. Try Nivea for Men's Silver Protect (£2.35,


Doctors at Great Ormond Street Hospital developed socks containing silver to combat infection and blistering in a foot disease called epidermolysis bullosa. Now the socks are being marketed as they reduce foot odour ( £7.99, Crocs are launching an anti-odour sports shoe containing silver in their soles this spring.


Plasters containing silver can reduce the risk of infection and speed healing. Try Boots Advanced First Aid Faster Healing Hydrocolloid Plasters (£3.99 for 16,


Carex has just launched an antibacterial handwash containing silver. Carex Bacteria Protect (£1.38), from pharmacies and supermarkets nationwide.


Pro Colloidal Silver's atomiser (£13.95 for 250ml) is a solution of colloidal silver which acts as a non-irritating disinfectant when sprayed on to skin or wounds (


In 2007, the NHS spent more than £23million on silver dressings for leg ulcers and the Health Protection Agency has recommended that silver-coated catheters be introduced for the prevention of urinary tract infections.

Indeed, silver is set to be increasingly added to medical equipment and hospital furniture as a way of preventing hospital-based infections.

'Research with the Heart of England NHS Foundation Trust has found that silver, incorporated in the surfaces of hospital equipment furniture, can reduce bacterial levels by 99 per cent,' says Dr Richard Hastings, microbiologist for BioCote, a Wolverhampton company that makes silver-based medical products.

'This, in turn, cuts infection risk from superbugs such as MRSA, E. coli and salmonella.'

Silver is also emerging as an effective tool for the treatment of skin conditions, burns and wounds.

'Silver dressings are now widely used to aid wound healing. In the treatment of burns, where there is a high risk of irritation and infection, it has been very successful,' says Prof Edwards Jones.

'Silver could also combat skin conditions such as eczema and psoriasis – topical cream containing one per cent silver can suppress the kind of inflammation found in these allergic skin conditions.'

And silver may also one day be used as an internal antibiotic-In a study at the University of Texas, silver particles killed 100 per cent of the HIV virus within three hours. It also killed the flu virus as well as the antibiotic resistant superbug, MRSA.

However, more research needs to be conducted for the internal use of silver to be considered safe. 'A side effect when taken internally, is that you can develop blue discolouration beneath the skin,' says Prof Edwards Jones.

' Researchers would need to know more about this and any other adverse effects before it is used in this way.'


Silver Makes Antibiotics Thousands of Times More Effective

silver-makes-antibiotics-thousands-of-times-more-effective_1Like werewolves and vampires, bacteria have a weakness: silver. The precious metal has been used to fight infection for thousands of years — Hippocrates first described its antimicrobial properties in 400 bc — but how it works has been a mystery. Now, a team led by James Collins, a biomedical engineer at Boston University in Massachusetts, has described how silver can disrupt bacteria, and shown that the ancient treatment could help to deal with the thoroughly modern scourge of antibiotic resistance. The work is published today in Science Translational Medicine, and as you well know silver is the key component in Colloidal Silver.

“Resistance is growing, while the number of new antibiotics in development is dropping,” says Collins. “We wanted to find a way to make what we have work better.”

Collins and his team found that silver — in the form of dissolved ions — attacks bacterial cells in two main ways: it makes the cell membrane more permeable, and it interferes with the cell’s metabolism, leading to the overproduction of reactive, and often toxic, oxygen compounds. Both mechanisms could potentially be harnessed to make today’s antibiotics more effective against resistant bacteria, Collins says.

Resistance is futile
Many antibiotics are thought to kill their targets by producing reactive oxygen compounds, and Collins and his team showed that when boosted with a small amount of silver these drugs could kill between 10 and 1,000 times as many bacteria. The increased membrane permeability also allows more antibiotics to enter the bacterial cells, which may overwhelm the resistance mechanisms that rely on shuttling the drug back out.

That disruption to the cell membrane also increased the effectiveness of vancomycin, a large-molecule antibiotic, on Gram-negative bacteria — which have a protective outer coating. Gram-negative bacterial cells can often be impenetrable to antibiotics made of larger molecules.