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Оглавление2: Bacteria – The Good, the Bad, and the Frightening
We have seen something of the crisis in which we find ourselves as a result of misguided use of the potentially life-saving antibiotic drugs –
because they are prescribed to treat conditions they cannot help
because they are wildly and massively overused in conditions that would get better on their own
because they are prescribed in the wrong dosage, wrong combinations (or not in combination when this would be a better strategy), wrong situations, for inappropriate lengths of time – often in the hot-house situations which exist in hospitals, the ‘superbug factories’
because they are used in agriculture, animal – dairy, meat and fish – as well as some fruit production, in a staggering and seemingly uncontrolled way.
And as a result of all of these misuses of antibiotics we are witnessing the looming crisis of bacterial infections which will be untreatable.
This monster – the totally antibiotic-resistant bacteria which are being unleashed on the human and animal kingdom – will require strategies other than more and more powerful antibiotics. These strategies form much of the remainder of this book, after examining what antibiotics actually do in Chapters 3 and 4.
In this chapter we will get to know some of the cast of characters involved in this saga – those that live in and on us, at best enormously beneficial and at worst potentially disease-causing, as well as a number of the bacteria which cause disease, sometimes mild but often with the potential, in the right circumstances (right for them, wrong for us) to cause life-threatening illness.
The (Usually) Friendly Bacteria
There are actually hundreds of different bacterial organisms and many more different strains living inside us, many doing useful jobs, as we will see. However, there are only a few which are present in really large numbers, and it is these which we will now examine briefly. For further details of their functions, what can harm them and what we can do to encourage their (and therefore our) health, see Chapters 9 and 10.
There is evidence that under the appropriate conditions, some of the friendly bacteria can become dangerous to us. One such situation can occur when there has been excessive use of antibiotics. This will be described more fully in Chapter 4.
Some of the ‘normal resident’ bacteria described below (S. faecal is, for example) have a borderline status – normally they do no harm, but they have been implicated in infection – of the bladder, for example – in some cases.
We have to remember that there is a delicate symbiotic (mutually beneficial) relationship between us and the organisms that have lived inside us for millions of years, but in the end they are looking after their own best interests and not ours; we benefit from them when all the environmental conditions are as they ought to be. One of the factors which can seriously disrupt the environment in which these bacteria live is the use of antibiotics, which while killing ‘bad’ bacteria do harm to the ‘good’ ones as well (not all antibiotics do this to the same degree, as will be seen in Chapter 4).
BIFIDOBACTERIUM BIFIDUM
These friendly bacteria inhabit the intestines – with a greater presence in the large intestine (the colon) than the small intestine. They also live in the vagina. In breastfed babies together with B, infantis and B. longum they form 99 percent of the flora of the intestines, but gradually reduce in numbers as we age. Their major roles are:
preventing colonization by hostile microorganisms by competing with them for attachment sites and nutrients
preventing yeasts from colonizing the territories which they inhabit
helping to maintain the right levels of acidity in the digestive tract to allow for good digestion
preventing substances such as nitrates from being transformed into toxic nitrites in our intestines
manufacturing some of the B-vitamins
helping detoxify the liver.
LACTOBACILLUS ACIDOPHILUS
This natural inhabitant of the intestines also lives in the mouth and vagina. Its main site of occupation is the small intestine. Its major roles are:
preventing colonization by hostile microorganisms such as yeasts by competing with them for attachment sites and nutrients
producing lactic acid (out of carbohydrates) which helps to maintain the correct environment for digestion, by suppressing hostile organisms (other bacteria and yeasts)
improving the digestion of lactose (milk sugar) by producing the enzyme lactase
assisting in the digestion and absorption of essential nutrients from food
destroying invading bacteria (note that not all strains of L. acidophilus can do this, however)
slowing down and controlling yeast invasions such as Candida albicans.
BIFIDOBACTERIUM LONGUM
This is a natural inhabitant of the human intestines and vagina. It is found in larger numbers in the large intestine than the small intestine. Together with other bifidobacteria, this is the dominant organism of breastfed infants (making up 99 percent of the microflora). In adolescence and adult life the bifidobacteria are still the dominant organism of the large intestine (when health is good). Among its main benefits are:
preventing colonization by hostile microorganisms by competing with them for attachment sites and nutrients
production of lactic and acetic acids, which inhibit invading bacteria
helping in weight gain in infants by retention of nitrogen
preventing harmful nitrites being formed from nitrates in the digestive tract
manufacturing B-vitamins
assisting in liver detoxification.
BIFIDOBACTERIUM INFANTIS
This is a natural inhabitant of the human infant’s digestive tract (as well as of the vagina, in small quantities). Its presence is far greater in the bowel of breastfed infants compared with bottle-fed infants. Among its main benefits are:
preventing colonization by hostile microorganisms by competing with them for attachment sites and nutrients
production of lactic and acetic acids, which inhibit invading bacteria
helping in weight gain in infants by retention of nitrogen
preventing harmful nitrites being formed from nitrates in the digestive tract
manufacturing B-vitamins.
LACTOBACILLUS BULGARICUS
This extremely useful friendly bacteria is not a resident of the human body, but a ‘transient’. Once it enters the body through food (yogurt, for example) it remains for several weeks before being passed, but while in the body it performs useful tasks. L. bulgaricus is a yogurt culture, as is the other main yogurt-making culture, Streptococcus thermophilus (see below), and is therefore found in some yogurts and cheeses if they have not been sterilized to kill their bacterial cultures to enhance shelf-life – after manufacture. It performs a number of useful roles, such as:
Some strains produce natural antibiotic substances.
Some strains have been shown to have anti-cancer properties.
They enhance the ability to digest milk and its products by producing the enzyme lactase, which is absent or deficient in almost half the adults on earth, and many children, especially if they are of Asian, African or Mediterranean descent.
Because they produce lactic acid (as do all bacteria with ‘lactobacillus’ as the first part of their name), they help to create an environment which encourages colonization by the bifidobacteria (they are therefore known as ‘bifidogenic’ bacteria) and by L. acidophilus, by helping to prevent colonization by other, undesirable microorganisms.
STREPTOCOCCUS THERMOPHILIC
This is a transient (non-resident) bacteria of the human intestine which together with L. bulgaricus (see above) is a yogurt culture, also found in some cheeses. It performs a number of useful roles, such as:
Some strains produce natural antibiotic substances.
They enhance the ability to digest milk and its products, by producing the enzyme lactase.
They produce lactic acid, thereby helping to create an environment which encourages colonization by the bifidobacteria and by L. acidophilus, and which discourages colonization by other, undesirable microorganisms.
STREPTOCOCCUS FAECIUM
This is a natural resident of the human intestine. It is found in human feces as well as on some plants and insects. Its characteristics include:
It is used as a part of the manufacture of cheeses (in some dairies, not all).
Its potential benefits to humans remain a possibility but not a certainty.
It manufactures lactic acid from carbohydrates and so enhances the environment for colonizing friendly bacteria.
STREPTOCOCCUS FAECALIS
This is a resident of the human intestine which is known as an enterococcus. It is found in feces, some insects and some plants. Its characteristics include:
the manufacture of lactic acid from carbohydrates, thereby enhancing the environment for colonizing friendly bacteria
the production of substances called amines, which can be toxic. Tyramine, for example, is associated with migraine headaches, and histamine with allergic and inflammatory reactions.
has been associated with urinary tract infections
overall there is little evidence that S. faecalis is beneficial for humans; on balance it would seem to have a harmful potential.
Some additional (usually useful) lactobacilli found in the digestive tract include:
L. casei – a transient bacteria of the intestine, found in cheese and other dairy products; manufactures lactic acid, so reducing the chances of invading bacteria being able to colonize the area
L. plantarum – a transient bacteria of the intestine, found in dairy products, sauerkraut, pickled vegetables; manufactures lactic acid
L. brevis – a transient bacteria of the intestine, found in dairy products (especially kefir, a fermented milk drink); manufactures lactic acid
L. salivarius – a natural resident of the mouth and digestive tract; manufactures lactic acid
L. delbrueckii – a transient bacteria of the intestine, found in grains and vegetables which have been fermented; manufactures lactic acid
L. caucasicus (known as L, kefir) – a transient bacteria of the intestine, found in kefir grains and drinks; manufactures lactic acid (as well as alcohol and carbon dioxide). It therefore inhibits undesirable bacteria.
The Not-so-friendly Bacteria and the Superbugs
The prospect of control over superbugs lies in the future; for the present we need to have a degree of understanding and awareness of the nature and potentials of the major antibiotic-resistant microorganisms.
STAPHYLOCOCCUS AUREUS
This bacterium is present in almost everyone, usually living in the nose. It is commonly involved in infections of
the skin (boils and abscesses, for example)
conjunctiva of the eyes (conjunctivitis).
When it has entered the body, often in a hospital, possibly after surgery, it can be the major cause of infections of;
the lungs (pneumonia)
the brain (meningitis)
the bones or bone marrow (osteomyelitis)
the heart (endocarditis).
Or it can be involved in some horrendous, often fatal, conditions such as:
Toxic Shock Syndrome
Scalded Skin Syndrome (SSS), in which the skin sloughs off the body as though it had been burned.
In both SSS and Toxic Shock Syndrome there seems to be a combined involvement of Staphylococcus aureus and a potentially dangerous yeast, Candida albicans (which lives in everyone on the planet, usually harmlessly). Candida often proliferates in the intestinal tract after antibiotic use, when its natural controls, including the flora of the bowel, are damaged.
Dr. Eunice Carlson of Michigan University has shown that when Candida is actively present in the system at the same time as an infectious agent such as Staphylococcus aureus, the toxic effects of Staphylococcus aureus are hugely enhanced and can result in fatal Toxic Shock Syndrome.1
As time has passed, Staphylococcus aureus has become resistant to almost all antibiotics apart from Vancomycin, which is now used specifically for the purpose of controlling it.
Vancomycin has potentially dangerous side-effects, is difficult to administer (usually via a drip) and is costly. This is the only remaining Staphylococcus aureus antibiotic. If resistance to vancomycin also develops, as is almost certain in time, there are no other antibiotic treatment methods currently available.
Other commonly resistant (to antibiotics) staphylococci include Staph, epidermidis and Staph, haemolyticus. Widespread, hospital-acquired infections involving these bacteria are now commonly treated with vancomycin, although this is often an inappropriate means of controlling them, according to leading experts.
As Professor French and Emeritus Professor Phillips, both of the Department of Microbiology at St. Thomas’s Hospital, London, say, ‘These infections often do not require antibiotic therapy, and unnecessary use of vancomycin for these organisms may be one factor in the emergence of … resistance.2
They believe that as these staphylococci acquire resistance to vancomycin they may be able to transfer this to the far more dangerous organism Staphylococcus aureus. Were this to happen, these researchers state, ‘Serious, untreatable staphylococcal infection would result.’
Once again we see, despite all the warnings that have been given, as well as the experience of the past, that inappropriate treatment is being used, with potentially disastrous consequences in store. Particular antibiotics are being used where they should not be used, and as a result resistance is likely to grow to the one antibiotic that can still control S. aureus.
CORYNEFORM BACTERIA
These bacteria are normally harmlessly present on almost everyone’s skin. In most cases they are sensitive to antibiotics. However, in hospital settings patients often become colonized with resistant strains and species which can then cause infections – if there is an opportunity, something far more likely in hospital settings, for any number of reasons including the obvious one that people in the hospital are more prone to having lowered immunity because they are already ill.
Infection with Coryneform Bacteria is most common where catheters and prostheses are involved, or in patients whose immune systems are struggling because of various blood-related and malignant diseases.
In hospitals Coryneform Bacteria are now resistant to most antibiotics and respond only to vancomycin.
STREPTOCOCCUS PNEUMONIAE
These bacteria, as their name suggests, are often involved in pneumonia, but they may also cause meningitis and are often associated with infections of the sinuses, ears, blood, and lungs.
When only low levels of resistance are found in the bacteria, high doses of penicillin will still control infections in which they are involved. However for those strains which have developed resistance to many antibiotics the treatment commonly involves the powerful drug vancomycin, or a cephalosporin antibiotic such as cefoxtaximine.
Researchers note that there are now signs that this last-mentioned class of drugs are gradually losing their power to control the bacteria, and there are major fears that this resistance will increase over time.
ENTEROCOCCI
These organisms live mainly in the bowel and may become involved in infections of this region. They can also cause infections of:
the blood (bacteraemia)
the heart muscle (endocarditis)
the urinary tract
the endometrium in the uterus.
They are frequently involved with infection associated with the use of catheters (obviously something more likely to be happening in the hospital than anywhere else), as well as in peritonitis.
In hospital settings the particular bacteria from this group which are most commonly found to be involved in serious infection are Enterococcus faecalis and Enterococcus faecium. The latter, which in the past has been considered relatively unimportant and not dangerous (and easily controlled), is now found to be increasingly resistant to most antibiotics.
To quote Professors French and Phillips, ‘These organisms are among the most important and problematic multidrug resistant pathogens of the 1990s.’
HAEMOPHILUS INFLUENZAE
This is frequently associated with infections of the:
throat
sinuses
ears
bones and joints
chest
meninges of the brain
and sometimes breast infections in women (mastitis).
This organism has gradually increased its resistance to the major drugs used to control it, including ampicillin. In one major incident in Spain in the early 1980s, resistance was demonstrated to chloramphenicol and ampicillin by around 60 percent of Haemophilus influenzae strains found in patients with meningitis.
It is, however, still very susceptible to antibiotics such as cefuroximine and cefaclor, although even in these a small degree of resistance is now being reported.
NEISSERIA GONORRHOEA
This organism is involved in:
sexually transmitted diseases such as gonorrhea
pelvic inflammatory disease
some eye infections, and
sore throats (rare), often when there is also genital infection.
Neisseria gonorrhoea is now widely resistant to penicillin-type antibiotics and also, increasingly, to tetracycline. At the moment it is demonstrating only slight resistance to commonly used antibiotics such as spectinomycin and fluorinated quinolones.
NEISSERIA MENINGITIDIS
This is involved in:
bacterial meningitis infections
acute sore throats.
For many years sulfonamide drugs were used to treat infections caused by Neisseria meningitidis; however in the 1960s resistance developed which made this form of antibiotic relatively useless. It was however still (and remains) largely controllable by penicillin, although this too is beginning to change.
Just how rapidly resistance to antibiotics can develop is illustrated by the pattern found in Spain, where in 1985 Neisseria meningitidis was not at all resistant to penicillin. However, by 1987 approximately 7 percent of the organisms were showing resistance, and by 1989 20 percent had reduced susceptibility to penicillin.
ENTEROBACTERIA
This group includes E. coli, Klebsiella, Enterobacter, Serrata spp, Shigella, Salmonella and Campylobacter. These organisms are found in almost everyone’s intestinal tract, in small numbers. It is when changes occur which allow them to become rampantly infectious that problems arise – once again we see how important the environment in which bacteria live is to how they behave, and must keep reminding ourselves that the ‘environment’ of the intestinal tract, above all other parts of the body, is capable of being seriously damaged when antibiotics are used.
The enterobacteria can be involved in infections of the:
intestinal tract, for example in food poisoning
abdomen (often following injury; also in peritonitis)
ear (acute otitis media)
blood (bacteraemia)
bones and joints
brain (often in brain abscesses; in meningitis of newborn babies)
tissues under the skin (cellulitis; a potentially very serious infection, often as a result of intravenous drip insertion)
some eye infections
lungs (pneumonia) and, not uncommonly,
infections involving transplant patients.
Many of these organisms are now resistant, to a greater or lesser degree, to a range of antibiotics. For example, E. coli (a common food poisoning agent), although usually sensitive to ampicillin and amoxycillin, has occasionally shown multiple resistance to almost all antibiotics, and this trend is expected to continue.
Klebsiella, Enterobacter and Serrata spp have in the past often caused outbreaks of infection in hospitals; these outbreaks have been controlled by the use of antibiotics such as cephalosporins and aminoglycosides. Researchers report, however, that strains of Klebsiella have now appeared which are capable of producing serious infections, especially in people with compromised immune systems, and which have become resistant to almost all antibiotics except for carbepenems.
Salmonella, one of the enterobacteria, is often a cause of food poisoning. About 80 percent of the bacteria recovered from infected patients are found to be resistant to major antibiotics. They remain susceptible to some fluoroquinolones antibiotics, although resistance is on the increase.
Professors French and Phillips add their voices to the controversy surrounding feeding animals with antibiotics. They point out that there is strong evidence that the use of antibiotics in animal feeds (to increase the animals’ growth rate) has contributed greatly to resistance in many of those enterobacteria found in human infections. This trend continues, unfortunately; as more advanced antibiotics (quinolones, see Chapter 4) are being used in farm settings, so resistance to these drugs has now appeared when humans are being treated for salmonella infection relating to food poisoning.
The use of antibiotics in animal production for food has been a cause of concern for many years. In 1986 after discovering that fully one-third of patients hospitalized with antibiotic-resistant infections had had no previous antibiotic treatment themselves, the Swedish government banned antibiotics in animal feed because of the fear that their use was breeding antibiotic-resistant microorganisms and that these were being transferred to humans when consumed in meat.
Since 1988 almost all Swedish farm animals are antibiotic-free, and they are also among the only commercial flocks which are free of salmonella as well.3,4
Unfortunately, largely because of economic factors and enormous pressure from the pharmaceutical industry, few other countries are even considering this vital step, a state of affairs which is certain to encourage the further development of antibiotic-resistant strains.
PSEUDOMONA AERUGINOSA
This bacteria is commonly involved in infections acquired while in the hospital (known scientifically as nosocomial infections – after the Greek word for hospital).
It is not uncommon to find it involved in infections of:
the blood
bones
joints
lungs
the urinary tract
the abdomen (peritonitis).
It may be introduced to the body leading to infection by means of a catheter, or during transplant surgery. It has displayed resistance to many forms of antibiotics, but at present remains treatable.
ACINETOBACTER SPP
This organism, which normally lives on the skin, can (usually in hospital settings) opportunistically become involved (perhaps after catheter use) in infections of the:
urinary tract
the lining of the brain – meningitis
and in peritonitis.
It has become widely resistant to antibiotics which previously controlled it.
MYCOBACTERIUM TUBERCULOSIS
Tuberculosis was until recently under control, at least in developed Western countries. However it has re-emerged as a major threat, and Mycobacterium tuberculosis can now be found in forms which are almost untreatable.
One of the major reasons for the development of resistance has been the tendency for some patients to fail to complete their courses of antibiotic treatment, one of the major factors that offers bacteria a chance to evolve defenses against a drug which is trying to kill them. It is as though a defending army were to show potential invaders how it proposed to defend itself and then decided to take a vacation, so allowing the invader time to work out new ways of overcoming it.
Among the most important background reasons for the emergence of multiple drug-resistant strains of Mycobacterium tuberculosis are thought to be:
failure of patients to complete courses of treatment – leading to mutant, resistant strains
deteriorating public health services due to economic constraints
poor training of health care workers in diagnosing and treating TB
delays in obtaining laboratory test results
use of only single-drug approaches to treat the infection (see below)
a dramatic increase in the numbers of susceptible people, often involving those who are impoverished and therefore malnourished, and/or homeless, and/or HIV positive and/or drug abusers
increasing migration into Western urban settings of people from areas where TB is endemic.
Many of these factors are beyond easy solution, and are political and economic in origin rather than medical. In other words, if everyone were well housed, well fed, well cared for and did not engage in practices which damage their immune systems, TB would vanish.
For successful care of TB today, there needs to he:
sound nutrition and hygiene
supervision which ensures that courses of antibiotic treatment are completed
the correct selection of a combination of antibiotic medications.
A treatment approach which involves using a combination of antibiotic drugs against the infection has been found to present the best option, since this offers multiple ways of killing or deactivating the invader.
When only single drugs are used, even if the course is followed through, Mycobacterium tuberculosis can respond with dramatically rapid genetic modifications in order to protect itself.
The number of cases in which treatment fails completely in dealing with TB is still relatively small, however when multiple drug-resistant tuberculosis (MDR-TB) does occur it is usually fatal, especially when this occurs in someone whose immune system is already compromised, for instance a person with an existing HIV infection or who is severely malnourished, such as a persistent drug abuser.
Sadly, hospital outbreaks of MDR-TB are increasing. Some of the reasons for this have been mentioned, but a summary is offered on pages of other reasons why many bacteria have become immune to attack by antibiotics.
This is the cast – the good, the bad, and the frightening – we now need to become familiar with the way medicine tries to control them.
