Journal of Antimicrobial Chemotherapy (1986) 18, Suppl. C, 155-158
`
`The influence of antibiotics on gut colonization
`
`D. van der Waaij, H. G. de Vries-Hospers
`and G. W. Welling
`
`Laboratory for Medical Microbiology, University of Groningen, Oostersingel 59,
`9713 EZ Groningen, The Netherlands
`
`Animal and human studies have suggested the concept of "colonization resistance"
`of the gastro-intestinal tract, which can be decreased by administration of
`antibiotics that inhibit the anaerobic portion of the normal flora of the gut. This
`effect can be prevented by the production, by resistant members of the flora, of
`bacterial enzymes that inactivate or destroy the antibiotic in question. Possible
`changes in the prevailing gut flora and the implications for the incidence of different
`infecting agents and for antibiotic therapy are discussed.
`
`Introduction
`
`It has been observed frequently that colonization and infection by nosocomial Gram(cid:173)
`negative bacilli are likely to follow administration of broad spectrum antibiotics. For
`example, Myerowitz, Medeiros & O'Brien (1971) found that 75% of patients with
`hospital-associated bacteraemia caused by Gram-negative bacilli had received
`antibiotics previously, as compared with 9% of non-hospital associated cases. In such
`observations, it is difficult to rule out other factors, such as the severity of the
`underlying illness in the antibiotic-treated patients. We report here the findings in
`animal experiments, in ward observations and in human volunteer studies that have
`led us to the concept of colonization resistance (CR), the ability of the normal gut flora
`to combat colonization by extrinsic bacteria, a property which can be upset by
`antibiotic administration.
`
`Effect of antibiotics on the infective dose in mice
`
`In these experiments (van der Waaij, Berghuis-de Vries & Lekkerkerk-Van der Wees,
`1971; van der Waaij & Berghuis, 1974) groups of 20-30 conventionally raised mice
`were given oral doses of strains of Enterobacteriaceae. The number of bacteria
`necessary to establish gut colonization (which was observed two weeks later) in 50% of
`mice was compared with that necessary when the mice received an antibiotic to which
`the strain was resistant. In untreated mice the 50% infective dose was high, at least 107
`bacteria, while after antibiotic treatment 102 or fewer bacteria would set up
`colonization.
`Subsequent experiments in mice and in humans (van der Waaij et al., 1977)
`indicated that suppression of the strictly anaerobic gut flora by the antibiotic is
`necessary for a significant suppression of colonization resistance. Antibiotics that
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`© 1986 The British Society for Antimicrobial Chemotherapy
`
`0345-7453/86/18CI55 +04 $02.00/0
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`produce high concentrations of unchanged drug in the gut contents, either because
`they are not completely absorbed or because they are secreted into the gut in bile or
`other fluids, created the greatest effect. For example it was shown that parenteral, as
`well as oral, ampicillin decreased the colonization resistance in mice (van der Waaij,
`Berghuis & Lekkerkerk, 1972).
`
`Effect of antibiotics on spread of resistant bacteria in mice
`
`The spread of resistant Gram-negative bacilli between cage mates was investigated in
`pairs of groups consisting of 15 mice. One group was treated with an antibiotic while
`the other remained untreated as a control; one mouse in each group was given an oral
`colonizing dose of a Gram-negative bacillus (of the Enterobacteriaceae) resistant to the
`antibiotic in question. Spread from mouse to mouse was greatly increased by the
`antibiotic administration; for example, all 15 mice treated with ampicillin were
`excreting the resistant Gram-negative bacillus after ten days, while no spread had
`occurred in the control group (van der Waaij, 1979).
`However, when ampicillin was given for more than four weeks, the effect on the
`colonization resistance was reduced; there was no spread when the bacterium was
`introduced into one member of the group after ampicillin had been given for six weeks,
`even if high daily doses were given (Hofstra, W., personal communication). This effect
`was associated with the appearance of a strongly j1-lactamase-secreting Clostridium
`strain in the gut flora. Bacterial enzymes may rapidly degrade various antibiotics, so
`that they have no effect on the colonization resistance (Veringa & van der Waaij,
`1984).
`
`Spread of Gram-negative bacilli in patients
`
`Fortuitously, in 1971, a similar "experiment" to that carried out in mice occurred in
`the prophylactic use of antibiotics in a unit occupied by ten chronically ill paediatric
`patients. One child developed diarrhoea caused by Salmonella typhimurium, which was
`sensitive to ampicillin, and it was decided, rightly or wrongly, to treat all patients with
`ampicillin prophylactically, with the aim of preventing spread. Each patient received
`2 g of ampicillin daily, orally, for three weeks. We were able to examine twice a week,
`the faeces of all the patients, identify and biotype the Enterobacteriaceae isolated from
`them, and determine their antibiotic sensitivity pattern, and, if the specimens were
`large enough, estimate the ampicillin concentration.
`Thirteen of the 14 biotypes of Enterobacteriaceae (including the Salmonella strain)
`that were isolated from the faeces of the patient at the onset of ampicillin treatment
`disappeared from the faecal cultures during the first week of treatment. All 14 biotypes
`were sensitive to ampicillin. From day 2 onwards, however, ampicillin-, and often
`multiply-, resistant Gram-negative biotypes were isolated. The number of ampicillin(cid:173)
`resistant Gram-negative biotypes in the faeces of the patients increased almost linearly
`with time. By the end of the third and last week of treatment, 17 different ampicillin(cid:173)
`resistant biotypes had been isolated. Five of these biotypes were found in the stools of
`most (eight) patients. They had presumably spread among the group in the ward as
`had happened in the mouse experiments.
`In one patient, the original Gram-negative flora did not change during ampicillin
`treatment. This patient continued
`to excrete her original ampicillin-sensitive
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`Escherichia coli biotype and did not acquire new biotypes of Gram-negative bacteria
`during the three weeks of treatment. In the faeces of nine of the ten patients, ampicillin
`concentrations of 10-45 mg/kg faeces were found; concentrations differed among
`patients and among samples from the same patient. In the patient who retained the
`ampicilIin-sensitive strain of E. coli during treatment, no ampicillin could be detected
`in any sample. Unfortunately, at the time of this investigation only one possible
`explanation for this finding was considered: that the patient might not have taken her
`medication; this was, however denied by the attending nurses. We did not consider the
`possibility that the patient's microflora might have degraded the ampicilIin after
`ingestion. No assay was performed to determine the presence of fJ-lactamase in the
`faeces of the patients who participated in the study.
`
`Antibiotic-degrading enzymes
`
`Recently we have demonstrated antibiotic-degrading enzymes in faecal suspensions
`from 12 of 13 healthy volunteers, who had not received antibiotics recently. In
`particular, ampicillin was rapidly degraded by five of the specimens. Similar results
`have been described by Hazenberg et al. (1983).
`
`Discussion
`
`The investigations in animals and the observations in humans suggested to us that
`broad spectrum antibiotics, active against the anaerobic flora of the intestinal tract,
`decrease colonization resistance. Restraint in the administration of these agents is
`needed. Other influences, such as induction therapy for malignancy, or virus infections,
`which affect the mucous membrane or the secretions into the gut (saliva, mucus, etc.)
`may also reduce the colonization resistance.
`The effect of antibiotics can be prevented by the presence of resistant bacteria that
`produce enzymes able to inactivate or destroy the antibiotics. Unfortunately we did
`not investigate the occurrence of antibiotic-degrading enzymes at the time of our
`observations on the spread of resistant Gram-negative bacilli from patient to patient.
`It is possible that, with the use of these antibiotics in the interim, bacteria with the
`ability to produce enzymes that inactivate the antibiotic are now occurring more
`frequently in the population. One might speculate that this could be a factor
`accounting for the relative decline in infections by Gram-negative bacilli in the
`immunocompromised patient (Hennemann, 1985).
`Recently attention has been directed to the oropharynx, where this antibiotic(cid:173)
`degrading effect is less likely to occur. A decrease in the colonization resistance of the
`oropharynx has been described in patients undergoing chemotherapy for leukaemia
`(Fain stein et al., 1981) or in intensive care units. In the future, it wilI be important to
`study the effects of antibiotics on the oral flora and to determine any influence of
`bacterial enzymes in this very different ecological situation.
`
`References
`
`Fainstein, V., Rodriguez, V., Turck, M., Herman, G., Rosenbaum, B. & Bodey, G.P. (1981).
`Patterns of oropharyngeal and fecal flora in patients with acute leukaemia. Journal of
`Infectious Diseases 144, 10-8.
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`D. van der Waaij et al.
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`Hazenberg, M. P., Van de Boom, M., Bakker, M. & Van der Merwe, J. P. (1983). Binding to
`faeces and influence on human anaerobes of antimicrobial agents used for selective
`decontamination. Antonie van Leeuwenhoek 49, 111-7.
`Hcnnemann, H. H. (1985). Septikiimien bei Leukiimien und malignen Lymphomen. Klinische
`W ochenschrift 63, 821-6.
`Myerowitz, R. L., Medeiros, A. A. & O'Brien, T. F. (1971). Recent experience with bacillemia
`due to Gram-negative organisms. Journal of Infectious Diseases 124, 239-46.
`van der Waaij, D. (1979). The colonization resistance of the digestive tract in man and animals.
`Zentralblatt fur Bakteriologie Mikrobiologie und Hygiene, Suppl. 7, 155-61.
`van der Waaij, D. & Berghuis, J. M. (1974). Determination of the colonization resistance of the
`digestive tract in individual mice. Journal of Hygiene 72, 379-87.
`van der Waaij, D., Berghuis-De Vries, J. M. & Lekkerkerk-Van der Wees, J. E. C. (1971).
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`Journal of Hygiene 69, 405-11.
`van der Waaij, D., Berghuis, J. M. & Lekkerkerk, J. E. C. (1972). Colonization resistance of the
`digestive tract of mice during systemic antibiotic treatment. Journal of Hygiene 70, 605-9.
`van der Waaij, D., Vossen, 1. M., Korthals Altes, C. & Hartgrink, C.
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`Reconventionalization following antibiotic decontamination in man and animals. American
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`Veringa, E. M. & van der Waaij, D. (1984). Biological inactivation by faeces of antimicrobial
`drugs applicable in selective decontamination of the digestive tract. Journal of Antimicrobial
`Chemotherapy 14, 605-12.
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