Effects of cephalexin, erythromycin and clindamycin on the aerobic Gram-negative faecal flora in man

The use of first-generation cephalosporin antibiotics, cefalexin and cefradine, is not associated with induction of simulated Clostridioides difficile infection

Objectives

The use of broad-spectrum cephalosporins is associated with induction of Clostridioides difficile infection (CDI). Recent knowledge on the importance of the healthy microbiota in preventing pathogen colonization/outgrowth highlights the caution needed when prescribing broad-spectrum antibiotics. The use of historical narrow-spectrum antibiotics, such as first-generation cephalosporins, is gaining increased attention once more as they have a reduced impact on the microbiota whilst treating infections. Here, the effects of two first-generation cephalosporins, compared with a third-generation cephalosporin, on the human microbiota were investigated and their propensity to induce simulated CDI.

Methods

Three in vitro chemostat models, which simulate the physiochemical conditions of the human colon, were seeded with a human faecal slurry and instilled with either narrow-spectrum cephalosporins, cefalexin and cefradine, or a broad-spectrum cephalosporin, ceftriaxone, at concentrations reflective of colonic levels.

Results

Instillation of cefalexin was associated with reduced recoveries of Bifidobacterium and Enterobacteriaceae; however, Clostridium spp. recoveries remained unaffected. Cefradine exposure was associated with decreased recoveries of Bifidobacterium spp., Bacteroides spp. and Enterobacteriaceae. These changes were not associated with induction of CDI, as we observed a lack of C. difficile spore germination/proliferation, thus no toxin was detected. This is in contrast to a model exposed to ceftriaxone, where CDI was observed.

Conclusions

These model data suggest that the minimal impact of first-generation cephalosporins, namely cefalexin and cefradine, on the intestinal microbiota results in a low propensity to induce CDI.

Gut microbiota, body weight and histopathological examinations in experimental infection by methicillin-resistant Staphylococcus aureus: antibiotic versus bacteriocin

Bacteriocins have been steadily reported as potential agents that may contribute, in different ways, to overcome antimicrobial drug resistance. Here, holoxenic NMRI-F mice microbiota, their body weight recovery and histopathological alterations of organs like colon, spleen and liver were examined in mice intraperitoneally infected with 10⁸ cfu of a clinical methicillin-resistant Staphylococcus aureus (MRSA-1), and treated with enterocin DD14 alone (165 mg/kg), erythromycin alone (100 mg/kg) or their combination. Animals that received both antimicrobials presented a better body weight recovery than other groups. Less pronounced histopathological alterations were observed in mice MRSA-infected and treated with bacteriocin than in those MRSA-infected but untreated or MRSA-infected and treated with erythromycin. Noteworthy, these alterations were absent when mice were treated with MRSA-infected and treated with both antibacterial agents. Furthermore, the genus richness was significantly lower in mice infected and treated with erythromycin, compared to mice infected and treated with both antimicrobials. The beta-diversity analysis showed that non-infected mice and those infected and treated with both antimicrobials, stand apart from the other groups as supported in a NMDS model. This in vivo study shows the relevance of bacteriocin, or bacteriocin-antibiotic formulation in protecting colonic, liver and spleen soft tissues and controlling the mouse gut microbiota, following MRSA infection.

In vitro sensitivity of 30 anaerobic bacterial strains of the human intestinal core microbiota to antibiotics: Culture and LC-MS/MS approaches

We have a vast knowledge on human intestinal microbiota but it can still be regarded incomplete. One of the objectives of scientists using so-called "omics" techniques is to be interested in the consequences that drugs can have on the composition of the intestinal microbiota and inversely. To date, few publications have reported the effects of drugs on the growth of bacteria composing this microbiota using a "culturomics" approach. We focused on antibiotics commonly prescribed for which the only published are the susceptibility of the pathogenic strains and not that of the commensal strains. The aim of our study was to determine the sensitivity of 30 strains considered to represent the intestinal core microbiota to 8 antibiotics and to study the possible modification of these molecules by bacteria. The 30 bacterial strains were cultured under anaerobic conditions in order to determine their sensitivity to the antibiotics. After 48 h of culture, the supernatants were also analyzed via UHPLC-MS/MS in order to determine if the antibiotics have been chemically modified. Under the current experimental conditions, cefpodoxime, metronidazole, erythromycin, sulfamethozaxole, trimethoprim and the trimethoprim/sulfamethozaxole combination have little impact on the core microbiota strain growth. On the contrary, moxifloxacin and amoxicillin inhibit the growth of numerous strains of our panel. Using UHPLC-MS/MS analyses, we have shown that some antibiotics can be modifed by the bacteria composing the intestinal core microbiome. The bacteria that make up the intestinal microbiota core are impacted by the antibiotics most commonly prescribed in clinics today and inversely.

Antibiotics in the human food chain: establishing no effect levels of tetracycline, neomycin, and erythromycin using a chemostat model of the human colonic microflora

A chemostat model of the healthy human large bowel ecosystem was used to establish no effect levels for tetracycline, neomycin, and erythromycin. For each compound, the equivalent to four oral doses (0, 1.5, 15, and 150 mg/60 kg person/d) was studied. Concentrations of the test compounds in the chemostat medium were intended to simulate fecal levels that might be expected following consumption of food containing antibiotic residue and were based on published oral doses and fecal levels. We monitored the following parameters: short chain fatty acids, bile acids, sulfate reduction, azoreductase and nitroreductase activities, beta-glucosidase and beta-glucuronidase activities, a range of bacterial counts and, lastly, the susceptibility among sentinel bacteria to each test compound. Neomycin and erythromycin reduced bile acid metabolism. Neomycin elevated propionate levels and caused a marginal diminution in azoreductase activity. Based on our results, the no observed effect level (NOEL) of both tetracycline and erythromycin was 15 mg/60 kg person/d. The NOEL for neomycin was 1.5 mg/60 kg person/d.

Effect of erythromycin acistrate and erythromycin stearate on human colonic microflora

The effects of erythromycin acistrate (2'-acetyl erythromycin stearate), a new erythromycin derivative, and erythromycin stearate on the faecal microflora were compared in a randomized cross-over study. 12 healthy volunteers were given either drug 500 mg t.i.d. for 1 week. Their faeces were studied before, immediately after, and 1 week after the drug administration period. After a wash-out period of 4 weeks, the drugs were interchanged. Both erythromycin acistrate and erythromycin stearate induced changes in the normal colonic microflora to about the same extent. The most marked effect was the suppression of gram-negative anaerobic and aerobic rods. Clostridium difficile appeared in 1 subject on both drugs. Also the counts of aerobic gram-positive cocci were altered; enterococci increased in number. An increased resistance to erythromycin was noted among staphylococci and enterococci after both drugs.

Colonization resistance of the digestive tract--mechanism and clinical consequences

Potentially pathogenic bacteria and yeasts meet a number of resistance factors. These colonization resistance (CR) determining factors control the growth density of potentially pathogenic microorganisms in the various parts of the alimentary canal. The CR of the digestive tract is to be seen partially of host origin but to a greater extent due to direct and indirect activity of the (anaerobic) indigenous microflora. This implies that the CR mechanism is vulnerable to antibiotics which affect the indigenous flora during treatment. A decreased CR enhances colonization by microorganisms that are resistant to the antibiotic(s) used for therapy. Increased population densities of potentially pathogenic bacteria ("overgrowth") may correlate with invasion of the mucosal tissues often followed by translocation to remote lymphatic organs. Overgrowth also may correlate with development or acquisition of resistance to the antibiotic applied. By screening in experimental animals antibiotics have been selected which do not affect the CR. Such antimicrobial drugs have successfully been used to selectively eliminate potentially pathogenic bacteria and yeast in neutropenic patients.

Effect of amoxicillin-clavulanate and cephradine on the fecal flora of healthy volunteers not exposed to a hospital environment

A 7-day course of either cephradine or amoxicillin-clavulanate treatment caused no significant change in fecal flora composition, except that staphylococci were virtually eliminated in both groups. Some amoxicillin-resistant coliforms were isolated after treatment in both groups, but cephradine- or amoxicillin-clavulanate-resistant coliforms were rarely isolated.

Epidemiology of intestinal colonization by members of the family Enterobacteriaceae highly resistant to erythromycin in a hematology-oncology unit

Intestinal colonization by highly erythromycin-resistant members of the family Enterobacteriaceae was surveyed for 4 years in a hematology-oncology unit. Fifty-four of 555 patients (9.7%) were colonized, each with a different strain. The incidence of intestinal carriage was not correlated with erythromycin consumption in the ward but was strongly associated with individual exposure to erythromycin.

Effects of erythromycin and ciprofloxacin on chronic fecal excretion of Campylobacter species in marmosets

Ciprofloxacin was compared with erythromycin for the eradication of Campylobacter species that were chronically excreted in the stools of marmosets (Saguinus labiatus labiatus, Saguinus fuscicollis nigrifrons, and Saguinus fuscicollis illigeri). Stool cultures were negative within 48 h of the beginning of treatment with either agent. Within 10 days after the end of therapy, however, Campylobacter species were again isolated from the stools of six animals that had received erythromycin. During an 8-week follow-up period, no animal that had received ciprofloxacin relapsed. High levels of ciprofloxacin in the stool (mean, 49.2 micrograms/g) possibly contributed to the efficacy of this agent.

Effect of various antibiotics on gastrointestinal colonization and dissemination by Candida albicans

Mice were treated orally with various antibiotics to determine which members of the indigenous intestinal microflora normally suppress Candida albicans colonization and dissemination from the gastrointestinal (GI) tract. The mice were given penicillin, clindamycin, vancomycin, erythromycin, or gentamicin for 3 days, and then challenged orally with C. albicans. Penicillin, clindamycin, and vancomycin, but not gentamicin or erythromycin, decreased the total anaerobic bacterial populations in the animals ceca, and increased the enteric bacilli population levels. All three of the former antibiotics allowed C. albicans to proliferate in the gut and, subsequently, disseminate from the GI tract to visceral organs. The ability of C. albicans to associate with intestinal mucosal surfaces was also tested. It was found that antibiotics which reduced anaerobic population levels, but not enteric bacilli or aerobes, also predisposed animals to mucosal association by C. albicans. It is suggested that the strictly anaerobic bacterial populations which predominate in the gut ecosystem are responsible for the inhibition of C. albicans adhesion, colonization and dissemination from the GI tract.

Long-term antibiotic therapy for acne vulgaris: effects on the bowel flora of patients and their relatives

We have studied the effects of long-term tetracycline and erythromycin administration on the fecal flora of patients and their relatives. Tetracycline administration selects for multiply antibiotic-resistant organisms in both patients and relatives. Erythromycin exerts no such selection pressure. The mechanisms by which this may occur are discussed.

The digestive tract in immunocompromised patients: importance of maintaining its resistance to colonization, especially in hospital in-patients and those taking antibiotics

The colonization resistance (CR) of the gastrointestinal tract to potential pathogens depends partly on factors within the host but to a greater extent on the normal (anaerobic) gut flora. Its strength varies between individuals. These individual differences in resistance to colonization by pathogenic microorganisms may explain differences in susceptibility to infection. CR is lowered by remission-inducing treatment (radiation and/or chemotherapy) in leukaemia, but more severely by certain antibiotics. Development (by selection or transfer) of resistance to these antibiotics may lead to overgrowth and penetration of the mucosal lining by the overgrowing (potentially) pathogenic bacteria. Other antibiotics however, if sufficiently dosed, have been found to eliminate (potential) pathogens selectively without decreasing CR. This selective decontamination of the gastrointestinal tract has been successfully used prophylactically in neutropenic patients but needs to be monitored bacteriologically. It should perhaps be used more widely in the hospital to control development and spread of antibiotic-resistant strains.

Pharmacokinetics of multiple doses of ceftizoxime and their influence on fecal flora

The pharmacokinetics of ceftizoxime, a new beta-lactam antibiotic, were studied in eight normal volunteers after single and multiple i.v. doses of 2 X 2 g daily for eight days. The mean maximum serum concentration after the first 20 min of infusion on the first day was 176.9 +/- 32.9 micrograms/ml decreasing to 11.0 +/- 4.1 micrograms/ml after 4 h and to 0.67 +/- 0.2 micrograms/ml after 12 h. Mean 12 h urine recovery was 78.8 +/- 9.0%. The half-life of ceftizoxime was 136 +/- 36 min. Volume of distribution was 22.9 +/- 8.1 1/100 kg body weight, AUCtot 208 +/- 33 micrograms/ml x h, total body clearance 151 +/- 33 ml/min, and renal clearance 110 +/- 23 ml/min. No ceftizoxime accumulation was registered during the administration period. Computed multiple-dose values were in good agreement with the measured values, and the pharmacokinetic parameters on the first, fourth and eighth days showed no significant differences. During the study period, the fecal flora displayed a reduction of sensitive gram-negative aerobic bacteria, a slight increase in the amount of enterococci (10(6) to 10(8)/g feces), and no change in the number of Bacteroides fragilis. Some resistant gram-negative strains increased during the administration period, but most of them could no longer be detected two weeks after administration. Tolerance of ceftizoxime was good in four volunteers. Four other volunteers had gastro-intestinal symptoms and mild fever reactions. One female volunteer was assumed to have an allergic drug reaction. Biochemical, hematological, virological and serological data showed no abnormalities in seven volunteers.

Influence of erythromycin on the normal human flora and colonization of the oral cavity, throat and colon

Erythromycin stearate was given orally in doses of 500 mg twice daily for 7 days to 10 volunteers. Saliva, throat and faecal specimens were taken up to 16 days for cultivation of aerobic and anaerobic bacteria. In specimens from saliva and throat only minor changes in the numbers of bacteria were detected during the antibiotic administration period, while pronounced changes in the aerobic and anaerobic faecal flora occurred. Thus among aerobes the number of enterobacteria significantly decreased and also the numbers of most anaerobes. During the erythromycin administration period, 8 subjects were colonized by erythromycin-resistant enterobacteria in the oral cavity and throat. All subjects were colonized by erythromycin-resistant enterobacteria, clostridia or yeasts in the colon. Many of the colonizing microorganisms were potential pathogens.

Effect of erythromycin and clindamycin on the indigenous human anaerobic flora and new colonization of the gastrointestinal tract

Erythromycin and clindamycin were given orally to ten subjects in recommended doses for seven days in order to study the effects of these antibiotics on human flora. Saliva and faecal specimens were collected for up to 29 days after administration of the antibiotics. Erythromycin caused only minor changes in the saliva flora while the aerobic and anaerobic colon flora were considerably disturbed. Clindamycin depressed both the anaerobic saliva and colon flora. Both erythromycin and clindamycin induced new colonization of the oral cavity and colon. The levels of free volatile fatty acids sank in saliva and faeces when erythromycin and clindamycin were given. The ecological disturbances caused by antibiotics require further investigation and should be taken into consideration in therapy.

Susceptibility of Shigella species to erythromycin

Two of the most common causes of inflammatory enteritis are Campylobacter fetus subsp. jejuni and Shigella species. No single antimicrobial agent is recommended for treatment of both diseases. Erythromycin is used to treat C. fetus subsp. jejuni infections but has not been studied in shigellosis. For this reason, we determined the susceptibility of 22 strains of Shigella to erythromycin and found that Shigella species are susceptible to concentrations of erythromycin which are obtainable in stool.

Promotion of the translocation of enteric bacteria from the gastrointestinal tracts of mice by oral treatment with penicillin, clindamycin, or metronidazole

Specific pathogen-free mice were treated orally with antibiotics to determine whether the resulting disruption of the normal flora ecology would allow certain gram-negative enteric bacteria to overpopulate the ceca, thereby promoting the translocation of these bacteria from the gastrointestinal tract. The mice were treated orally with penicillin, clindamycin, or metronidazole for 4 days, and then the antibiotic was discontinued. The mice were tested at various intervals for viable enteric bacilli translocating from the gastrointestinal tract to the mesenteric lymph nodes. Penicillin treatment decreased the total anaerobe population levels in the ceca an average of 1,000-fold, whereas clindamycin treatment decreased these anaerobe levels only 10-fold, and metronidazole treatment slightly increased the anaerobe levels. Penicillin or metronidazole treatment slightly increased the anaerobe levels. Penicillin or metronidazole treatment increased the enteric bacilli populations in the ceca an average of 1,000-fold, whereas clindamycin treatment increased the enteric bacilli populations 100,000-fold. The peak incidence of translocation of the enteric bacilli to the mesenteric lymph nodes averaged 100% after penicillin treatment, 97% after clindamycin treatment, and 62% after metronidazole treatment. Thus, oral treatment of mice with penicillin, clindamycin, or metronidazole for only 4 days disrupts the normal flora ecology, allowing an overgrowth in the ceca of the gram-negative enteric bacilli and promoting their translocation to the mesenteric lymph nodes.