Probiotics for infection control

What are the key concepts of probiotics for infection control?

Microorganisms compete with one another for space, including surfaces, and nutrients. The large pool of bacteria is in the large intestine and in most studies disturbances in the gastrointestinal tract (GIT) are the targets for probiotic therapy. Most microorganisms excrete metabolites that have a negative impact on the growth of other species or strains.

The normal gastrointestinal flora consists of a stable balance between microorganisms. This is easily disturbed in illnesses and especially when antibiotics are used.

The goals of probiotic therapy are to:

• Prevent colonization and overgrowth of pathogenic microorganisms

• Restore an acute or chronic deterioration of a microbiological balance

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• Maintain a reasonable ecological balance at involved sites

• Stimulate the immune system

• Prevent or reduce side effects of antibiotics

• Improve and restore gut barrier function

• Stimulate mucus production from the gut epithelium which contributes to an improved gut barrier function

What principles regarding probiotics are necessary for effective infection control?

Proper species and strains, or mixtures of those, must be used.

Probiotic strains should be well defined and characterized.

Probiotic strains should be of human origin.

To be able to interact with the microorganisms that reside at the targeted area the added numbers must to be sufficient, i.e., in the order of 10^9 – 10^11 per dose or per day.

Treatment should be started as soon as possible. Success is greater when probiotics are used as a prophylactic measure. If one can prevent overt microbiological deteriorations or imbalances, improvement in clinical gastrointestinal illness may appear.

For the probiotics used, properties such as metabolism and capability to survive transport to and ability to establish at the aimed location must be thoroughly examined and results of these investigations must be mainly positive.

Each strain has its own properties and it cannot be assumed that one specific strain should hold all desirable characteristics. Likewise, characteristics and effects of one strain of a certain species cannot be generalized to all strains within that species.

Susceptibility to different antibiotics must be known.

Safety characteristics in general and especially for the situation of interest should be known.

When given to patients with reduced immunological capacity (perhaps the category that may benefit the most from this type of treatment) there should be an elevated alertness for signs of unexpected infections.

Freeze dried preparations should not be handled at bedside before they have been dispersed in some fluid. The risk of contamination of airways, iv-lines especially central lines with a powder being spread in the room air should not be neglected.

What conclusions of clinical trials or meta-analyses regarding probiotics guide infection control practices?

It is safe to use probiotics for most people in sickness and in health.

In some applications there is support for positive effects of the use of probiotics, but on several indications or applications there are conflicting results.

Many studies show positive results but, due to small study sizes, statistical significance is lacking.

There is a tendency to judge all probiotics as being a single entity when reviews and meta-analyses are performed. Results from different protocols with different species, strains and mixtures of those are being pooled and results validated as it was a single microorganism.

Many studies have shown positive results for the group or groups of patients that has been given active treatment. In other studies results have been inconclusive.

Although studies where probiotic treatment groups have done worse than the controls do exist, it must be considered safe to use probiotics for most people in sickness and in health.

What are the consequences of ignoring the key principles and concepts of probiotics for infection control?

Unexpected effects, such as the risk of undesired infections caused by the treatment may appear instead.

Though infections of clinical significance with microorganisms characterized as probiotic are rare, they do exist and improper use or handling of preparations can result in such infections.

Using preparations that are not pure or containing other strains than those claimed on the package could give misleading information in case of infectious complications.

There are studies showing that the contents in some dairy products were not what were printed on the label. Wrong bacterium, too small numbers of viable bacteria or in some cases the stated bacterium could not be identified.

What other information supports the research regarding probiotics for infection control, e.g., case control studies and case series?

Most of the probiotics used in healthcare are strains with human origin.

Many preparations are also sold in the grocery store or otherwise on a free market. Studies from Finland compared the observed frequency of positive findings of Lactobacillus rhannosus GG in blood cultures before and after the launch of dairy products containing that strain. No difference in the incidence of infections with the strain could be demonstrated.

Summary of current controversies.

Probiotics can never replace antibiotics but should be looked upon as a valuable complement.

Probiotics for infection control or as prophylaxis are given to patients that have some kind of disturbance in their microbiological flora or are at risk of getting one.

Added probiotics are not those commensal bacteria lost by medication with antibiotics but do in a sense replace them and will help in getting back to the premorbid state what may take months.

Are probiotics dangerous?

In general the answer is a straight NO. Microorganism classified as probiotics are generally regarded as safe.

Do they give infections difficult to treat?

In general the answer is a straight NO. The species and strains that are connected to the rare cases of infections with bacteria with probiotic characteristics are susceptible to many standard antibiotics. Most of these cases have been outpatients that have ingested the bacterium within their normal diet.

Can probiotics transfer genetic material coding for antibiotic resistance?

In theory, yes. However, no evidence has been found to support such assumptions.

Do probiotics kill people?

Under certain circumstances it has occurred! However not the bacterium per se, but the setting and the particular patient population.

Can patients benefit from probiotics or are they only benefiting the producing companies?

Probiotics can make a difference. Specific strains that are well chosen and mixtures of such strains can reduce or inhibit certain infections or clinical manifestations of such infections and the side effects of the use of antibiotics.

What is the impact of probiotics for infection control, relative to infection control by other means?

Probiotics can reduce the frequency of certain infections and attenuate symptoms of such infections.

By using probiotics the use of antibiotics may be reduced and hence contribute to a reduction or a delay of the development of multi resistant bacteria. This increasing worldwide problem has the potential to bring about a catastrophic like situation in modern healthcare.

The use of probiotics in intubated critically ill patients is equally efficient in reducing secondary infections as is the use of Selective Digestive Decontamination with antibiotics.

Using probiotics for infection control or prophylaxis is a very important complement to standard treatment of infection as we see it today.

Probiotics work on a broad basis in the competition with other species, pathogenic or non-pathogenic, and with few side effects.

Overview of all important clinical trials, meta-analyses, case control studies, case series, and individual case reports related to infection control and probiotics.

See Table I and Table II below for a summary of relevant research.