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Appendix D: Impact of Antimicrobials on the Microbial Ecology of the Gut
Pages 130-157

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From page 130...
... "Normal flora" is usually used collectively to describe various microbial species found by cultures or microscopy to be on the skin and mucous membranes and in certain body cavities of both healthy and sick animals. The term is also used as a synonym for "indigenous microbiota" meaning, collectively, those autochthonous microbial resi Department of Microbiology, University of Illinois, Urbana.
From page 131...
... The first suggests that all microbial types found on or in, or cultured from, certain surfaces or cavities are normal residents of habitats in those sites. However, much recent evidence supports the concept that many microbial types that can be isolated at any given time from an open ecosystem such as the gastrointestinal tract cannot be identified as indigenous to the system and must be regarded as transients.
From page 132...
... Evidence that epithelial, cryptal, and luminal habitats exist for indigenous microorganisms in all areas of the gastrointestinal tract has been provided primarily by studies of laboratory rodents (Savage, 1977~. The indigenous microbiotas of most mammalian and avian species have not been defined as well as they have for rodents.
From page 133...
... Microbes of types found in the large bowel (see below) may be identified, occasionally at high population levels, in cultures from the lower third of the gastrointestinal tract, where the content moves somewhat sluggishly and may not move at all for a tome.
From page 134...
... More than 99% of the total microbial population obligately gains its energy through anaerobic processes. In the gastrointestinal ecosystem of humans, facultative bacteria (i.e., able to use both aerobic and anaerobic processes to generate energy)
From page 135...
... . Chi ckens Staphylococcus Streptococcus Escherichia Eubacterium Bacteroides Fusobacterium Peptostreptococcus Ruminococcus Coprococcus Bifidobacterium Gemminger Clostridium Lactobacillus Humans Acidaminococcus Staphvlococcus Propionibacterium Peptococcus Desulfomonas Succinivibrio S treptococcus Es cherichia Swine: Fuller _ al., 107~; Hackman and TJilkir~s , 1975; Kinyon and Harris, 1979; Kolacz et al., 1971; tiorish~ta and Ogata, 1470; Ogata and FIorishita, 1969; ~ussell, 1979; Terarla et al., 1976.
From page 136...
... Summary There is no doubt that all mammalian and avian species have microbial floras that are indigenous to their gastrointestinal tractse In humans, calves, swine, and chickens, climax floras, such as might be found in a healthy adult, contain primarily anaerobic bacteria in most habitats of the tract. Under normal conditions those anaerobes vastly outnumber facultative microbes such as E
From page 137...
... cold were resistant to one or more antimicrobial drugs, often not only to the drug used in the feed but also to one or more other compounds. b Present at subtherapeutic levels in the feed.
From page 138...
... C2 ant imicrobial drugs, of ten not only to the drug used in tree tment but also to one or more other compounds. bused prophylactically or to treat a particular disease.
From page 139...
... CHANGES INDUCED BY SUBTHERAPEUTIC LEVELS OF ANTIBIOTICS IN FEED The Proportion of Resistant Strains in Gastrointestinal Microbiota . As suggested above, reliable information on the proportion of resistant strains in gastrointestinal microbiota is almost nonexistent for the major components of the indigenous biota.
From page 140...
... Potential Pathogens in the Gastrointestinal Microbiota . Virtually no information is available on the influence of antimicrobial drugs on the relative proportions and absolute numbers of potential pathogens in the indigenous biotas except for _.
From page 141...
... CHANGES IN FLORA RESULTING FROM THE THERAPEUTIC USE OF ANTIBIOTICS There are few definitive data concerning changes in the anaerobic components of flora resulting from the therapeutic use of antibiotics. Evidence does substantiate that therapeutic doses of certain antibiotics enable resistant strains of E
From page 142...
... Strains of such organisms may persist for a time in the human gut (Finegold, 1977~; however, there are no data pertaining to the development and persistence of resistance in the major components of the indigenous biota of the gastrointestinal tract. CHANGES IN FLORA RESULTING FROM LEVELS OF ANTIBIOTICS USED TO PROMOTE GROWTH There is no reliable information pertaining to the action of antibiotics used as growth promoters on the major components of the indigenous microbiota In viva.
From page 143...
... es peci ally in cecum Oxygen Large intestines Concentration low, if present at all Oxidation- Large intestine Low potential, especially when reduct ion microbes are present pot ent i al Enzymes Seal 1 intestines Pancreatic enzymes present Bile acids Stomach Low concentration Smal 1 intestine Conjugated bile acids present Large intestine Deconjugated bile acids present Epitlaelial All regions of Sloughing of cells necessitates turnover tract replacement of attached cells but the cel Is may provide micro bial nut rient s Urea Large intestines Can be carbon and nitrogen source to r certain microbial s pe cies
From page 144...
... No real Featur es the t Inf luence Composition of Microbiota Mucin contr ibutes to the vi scosity of the environment and may act as a microbial nutrient The diet provides microbial nutr lent s and af fe ct s the nature of habitats in the tract Inf luence i s characteris t ic of the drunks) Microbiota may be phagocyto sed ~ select ively)
From page 145...
... No real Featur es tea t In f lue nce Composition of Microbiota Ef Sect dependent upon oxidationreduct ion pot enti al F.f :fe ct s uncertain Ef fects uncertain Lay depress population levels of some facultative s pecies of bacte ria Allows microorganisms to colonize areas of the tract where peristalt ic rat e moves content s more rapidlv than bacteria can multiply , 1977, and GiLhons providence is insufficient to suggest that the factor may operate in other reg ions .
From page 146...
... Interestingly, when certain antibiotics are administered, some microbial strains may not themselves have to be resistant to the drugs to survive because resistance in another organism may enable them to do so (Hackman and Wilkins, 1975~. Humans associating with animals fed subtherapeutic doses of antibiotics may temporarily carry resistant strains of E
From page 147...
... At this time, however, this hypothesis can be neither supported nor rejected by evidence provided by studies of the major components of the indigenous microbiota -- the strictly anaerobic bacteria (Finegold, 1970~. SUMMARY Antibacterial drugs such as penicillin and the tetracyclines, when incorporated as growth promotants into the feed of animals, provide a selective environment in the gastrointestinal tract favoring the proliferation of resistant strains of Escherichia colt, Streptococcus spp., and at least some of the major (strictly anaerobic)
From page 148...
... 1975. Factors that may prevent transfer of antibiotic resistance between gram-negative bacteria in the gut.
From page 149...
... 1975. Studies on multiple antibiotic resistance in obligate anaerobes.
From page 150...
... 1959. Changes in serological type and antibiotic resistance of Lancefield group D streptococci in chickens receiving dietary chlortetracycline.
From page 151...
... 1973. Effect of oral tetracycline on the occurrence of tetracycline-resistant strains of Escherichia cold in the intestinal tract of humans.
From page 152...
... 1976. The effect of tetracycline on the coliform gut flora of broiler chickens with special reference to antibiotic resistance and O-serotypes of Escherichia colt.
From page 153...
... Vergleichende Untersuchungen uber die Laktobaz~llen aus den Faeces van Menschen, Schweinen und Huhnern. Zentralbl.
From page 154...
... Untersuchungen uber die Darmflora des Huhnes.
From page 155...
... 1977. Microbial ecology of the gastrointestinal tract.
From page 156...
... 1960. The effect of diets containing tetracyclines and penicillin on the Staphylococcus aureus flora of the nose and skin of pigs and chickens and their human attendants.
From page 157...
... 157 Welch, R


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