Diversity of individual dynamic patterns of emergence of resistance to quinolones in Escherichia coli from the fecal flora of healthy volunteers exposed to ciprofloxacin

Pharmacokinetics and pharmacodynamics of azithromycin in severe malaria bacterial co-infection in African children (TABS-PKPD): a protocol for a Phase II randomised controlled trial

Background: African children with severe malaria are susceptible to Gram-negative bacterial co-infection, largely non-typhoidal Salmonellae, leading to a substantially higher rates of in-hospital and post-discharge mortality than those without bacteraemia. Current evidence for treating co-infection is lacking, and there is no consensus on the dosage or length of treatment required. We therefore aimed to establish the appropriate dose of oral dispersible azithromycin as an antimicrobial treatment for children with severe malaria and to investigate whether antibiotics can be targeted to those at greatest risk of bacterial co-infection using clinical criteria alone or in combination with rapid diagnostic biomarker tests. Methods: A Phase I/II open-label trial comparing three doses of azithromycin: 10, 15 and 20 mg/kg spanning the lowest to highest mg/kg doses previously demonstrated to be equally effective as parenteral treatment for other salmonellae infection. Children with the highest risk of bacterial infection will receive five days of azithromycin and followed for 90 days. We will generate relevant pharmacokinetic data by sparse sampling during dosing intervals. We will use population pharmacokinetic modelling to determine the optimal azithromycin dose in severe malaria and investigate azithromycin exposure to change in C-reactive protein, a putative marker of sepsis at 72 hours, and microbiological cure (seven-day), alone and as a composite with seven-day survival. We will also evaluate whether a combination of clinical, point-of-care diagnostic tests, and/or biomarkers can accurately identify the sub-group of severe malaria with culture-proven bacteraemia by comparison with a control cohort of children hospitalized with severe malaria at low risk of bacterial co-infection. Discussion: We plan to study azithromycin because of its favourable microbiological spectrum, its inherent antimalarial and immunomodulatory properties and dosing and safety profile. This study will generate new data to inform the design and sample size for definitive Phase III trial evaluation. Registration: ISRCTN49726849 (27 th October 2017).

Evolution of fluoroquinolone-resistant Escherichia coli in the gut after ciprofloxacin treatment

BACKGROUND

Three healthy volunteers carried similar quinolone-resistant E. coli (QREC) (pulsed field gel electrophoresis profiles) in their gut before and after 14 days ciprofloxacin treatment. Given the intensity of the selective pressure and the mutagenic properties of quinolones, we determined whether these strains had evolved at the phenotypic and/or genomic levels.

MATERIAL AND METHODS

Commensal QREC from before day-0 (D0), and a month after 14 days of ciprofloxacin (D42) were compared in 3 volunteers. Growth experiments were performed; acetate levels, mutation frequencies, quinolone MICs and antibiotic tolerance were measured at D0 and D42. Genomes were sequenced and single nucleotide polymorphisms (SNPs) between D0 and D42 were analyzed using DiscoSNP and breseq methods. Cytoplasmic proteins were extracted, HPLC performed and proteins identified using X!tandem software; abundances were measured by mass spectrometry using the Spectral Counting (SC) and eXtraction Ion Chromatograms (XIC) integration methods.

RESULTS

No difference was found in MICs, growth characteristics, acetate concentrations, mutation frequencies, tolerance profiles, phylogroups, O-and H-types, fimH alleles and sequence types between D0 and D42. No SNP variation was evidenced between D0 and D42 isolates for 2/3 subjects; 2 SNP variations were evidenced in one. At the protein level, very few significant protein abundance differences were identified between D0 and D42.

CONCLUSION

No fitness, tolerance, metabolic or genomic evolution of commensal QREC was observed overtime, despite massive exposure to ciprofloxacin in the gut. The three strains behaved as if they had been unaffected by ciprofloxacin, suggesting that gut may act as a sanctuary where bacteria would be protected from the effect of antibiotics and survive without any detrimental effect of stress.

Pharmacokinetics and pharmacodynamics of azithromycin in severe malaria bacterial co-infection in African children (TABS-PKPD): a protocol for a Phase II randomised controlled trial

Background: African children with severe malaria are susceptible to Gram-negative bacterial co-infection, largely non-typhoidal Salmonellae, leading to a substantially higher rates of in-hospital and post-discharge mortality than those without bacteraemia. Current evidence for treating co-infection is lacking, and there is no consensus on the dosage or length of treatment required. We therefore aimed to establish the appropriate dose of oral dispersible azithromycin as an antimicrobial treatment for children with severe malaria and to investigate whether antibiotics can be targeted to those at greatest risk of bacterial co-infection using clinical criteria alone or in combination with rapid diagnostic biomarker tests. Methods: A Phase I/II open-label trial comparing three doses of azithromycin: 10, 15 and 20 mg/kg spanning the lowest to highest mg/kg doses previously demonstrated to be equally effective as parenteral treatment for other salmonellae infection. Children with the highest risk of bacterial infection will receive five days of azithromycin and followed for 90 days. We will generate relevant pharmacokinetic data by sparse sampling during dosing intervals. We will use population pharmacokinetic modelling to determine the optimal azithromycin dose in severe malaria and investigate azithromycin exposure to change in C-reactive protein, a putative marker of sepsis at 72 hours, and microbiological cure (seven-day), alone and as a composite with seven-day survival. We will also evaluate whether a combination of clinical, point-of-care diagnostic tests, and/or biomarkers can accurately identify the sub-group of severe malaria with culture-proven bacteraemia by comparison with a control cohort of children hospitalized with severe malaria at low risk of bacterial co-infection. Discussion: We plan to study azithromycin because of its favourable microbiological spectrum, its inherent antimalarial and immunomodulatory properties and dosing and safety profile. This study will generate new data to inform the design and sample size for definitive Phase III trial evaluation. Registration: ISRCTN49726849 (27th October 2017).

Variation in antibiotic use among and within different settings: a systematic review

Objectives

Variation in antibiotic use may reflect inappropriate use. We aimed to systematically describe the variation in measures for antibiotic use among settings or providers. This study was conducted as part of the innovative medicines initiative (IMI)-funded international project DRIVE-AB.

Methods

We searched for studies published in MEDLINE from January 2004 to January 2015 reporting variation in measures for systemic antibiotic use (e.g. DDDs) in inpatient and outpatient settings. The ratio between a study's reported maximum and minimum values of a given measure [maximum:minimum ratio (MMR)] was calculated as a measure of variation. Similar measures were grouped into categories and when possible the overall median ratio and IQR were calculated.

Results

One hundred and forty-three studies were included, of which 85 (59.4%) were conducted in Europe and 12 (8.4%) in low- to middle-income countries. Most studies described the variation in the quantity of antibiotic use in the inpatient setting (81/143, 56.6%), especially among hospitals (41/81, 50.6%). The most frequent measure was DDDs with different denominators, reported in 23/81 (28.4%) inpatient studies and in 28/62 (45.2%) outpatient studies. For this measure, we found a median MMR of 3.7 (IQR 2.6-5.0) in 4 studies reporting antibiotic use in ICUs in DDDs/1000 patient-days and a median MMR of 2.3 (IQR 1.5-3.2) in 18 studies reporting outpatient antibiotic use in DDDs/1000 inhabitant-days. Substantial variation was also identified in other measures.

Conclusions

Our review confirms the large variation in antibiotic use even across similar settings and providers. Data from low- and middle-income countries are under-represented. Further studies should try to better elucidate reasons for the observed variation to facilitate interventions that reduce unwarranted practice variation. In addition, the heterogeneity of reported measures clearly shows that there is need for standardization.

Antimicrobial molecules in the lung: formulation challenges and future directions for innovation

Inhaled antimicrobials have been extremely beneficial in treating respiratory infections, particularly chronic infections in a lung with cystic fibrosis. The pulmonary delivery of antibiotics has been demonstrated to improve treatment efficacy, reduce systemic side effects and, critically, reduce drug exposure to commensal bacteria compared with systemic administration, reducing selective pressure for antimicrobial resistance. This review will explore the specific challenges of pulmonary delivery of a number of differing antimicrobial molecules, and the formulation and technological approaches that have been used to overcome these difficulties. It will also explore the future challenges being faced in the development of inhaled products and respiratory infection treatment, and identify future directions of innovation, with a particular focus on respiratory infections caused by multiple drug-resistant pathogens.

Ceftriaxone promotes the emergence of AmpC-overproducing Enterobacteriaceae in gut microbiota from hospitalized patients

Epidemiological data suggest that ceftriaxone may promote the emergence of commensal AmpC-overproducing Enterobacteriaceae because of a high biliary excretion. We tested this hypothesis in hospitalized patients either treated by ceftriaxone alone or receiving no antibiotics. Hospitalized patients with no previous antibiotics or hospitalization in the last 3 months, treated only with ceftriaxone, were prospectively included. For each ceftriaxone-treated patient, a control patient receiving no antibiotics was included. Clinical data and stools were collected at T0 (before antibiotics) and T1 (at the end of ceftriaxone treatment or at discharge) and T2 (3-6 months after T1) for the ceftriaxone-treated patients and at T0 and T1 for control patients. Third-generation cephalosporin-resistant Enterobacteriaceae were detected, identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), and characterized genetically. Clonal relatedness was evaluated by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Fifteen ceftriaxone and 22 control patients were included. Patients' characteristics did not differ. At T0, 2/15 ceftriaxone-treated versus 1/22 control patients carried third-generation cephalosporin-resistant Enterobacteriaceae (p = 0.6). At T1, 4/15 (27%) ceftriaxone-treated patients carried AmpC producers versus 0/22 control patients (p = 0.02). Additionally, two and three subjects carried extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae in the ceftriaxone and control groups, respectively (p = 1). At T2, three ceftriaxone-treated patients still carried AmpC-producing Enterobacteriaceae with the same RAPD profile as at T1. In hospitalized subjects with no other selective pressure, treatment by ceftriaxone alone promotes the gut colonization by AmpC-overproducing Enterobacteriaceae in over a quarter of patients, with a persistent carriage after the end of antibiotic exposure. The ecological impact of ceftriaxone should not be underestimated.

Effects of intramuscularly administered enrofloxacin on the susceptibility of commensal intestinal Escherichia coli in pigs (sus scrofa domestica)

BACKGROUND

In the European Union, various fluoroquinolones are authorised for the treatment of food producing animals. Each administration poses an increased risk of development and spread of antimicrobial resistance. The aim of this study was to investigate the impact of parenteral administration of enrofloxacin on the prevalence of enrofloxacin and ciprofloxacin susceptibilities in the commensal intestinal E. coli population.

METHODS

E. coli isolates from faeces of twelve healthy pigs were included. Six pigs were administered enrofloxacin on day 1 to 3 and after two weeks for further three days. The other pigs formed the control group. MIC values were determined. Virulence and resistance genes were detected by PCR. Phylogenetic grouping was performed by PCR. Enrofloxacin and ciprofloxacin were analysed in sedimentation samples by HPLC.

RESULTS

Susceptibility shifts in commensal E. coli isolates were determined in both groups. Non-wildtype E. coli could be cultivated from two animals of the experimental group for the first time one week after the first administration and from one animal of the control group on day 28. The environmental load with enrofloxacin in sedimentation samples showed the highest amount between days one and five. The repeated parenteral administration of enrofloxacin to pigs resulted in rapidly increased MIC values (day 28: MIC up to 4 mg/L, day 35: MIC ≥ 32mg/L). E. coli populations of the control group in the same stable without direct contact to the experimental group were affected.

CONCLUSION

The parenteral administration of enrofloxacin to piglets considerably reduced the number of the susceptible intestinal E. coli population which was replaced by E. coli strains with increased MIC values against enrofloxacin. Subsequently also pigs of the control were affected suggesting a transferability of strains from the experimental group through the environment to the control group especially as we could isolate the same PFGE strains from both pig groups and the environment.

Ecological impact of ciprofloxacin on commensal enterococci in healthy volunteers

Background

The ecological impact of ciprofloxacin on commensal enterococci is unknown.

Methods

Forty-eight healthy volunteers received ciprofloxacin from day (D) 0 to D14; stools were collected on D7, D14 and D42. Fluoroquinolone-susceptible and -resistant enterococci (FQ-SE and FQ-RE) were detected and quantified by culture, and identified by MALDI-TOF MS. The relative abundance of FQ-RE over FQ-SE was determined. The genetic basis of fluoroquinolone resistance was deciphered by partial sequencing of gyrA and parC genes. Clonal relatedness was determined by random amplification of polymorphic DNA PCR. Clinical trial no.: NCT00190151.

Results

Enterococci were carried by 47/48 (98%) subjects. Total counts were reduced during ciprofloxacin therapy (4.0 and 3.9 log cfu/g on D7 and D14 versus 5.9 log cfu/g before and 6.9 log cfu/g after treatment; P  < 0.05). Twenty-one out of 48 (44%) carried FQ-RE; among them, 21/21 carried Enterococcus faecium , 19 carried Enterococcus faecalis and 11 carried other species. Five out of 48 (10%) harboured FQ-RE (ciprofloxacin MIC >4 mg/L) before treatment (all E. faecium ), 6 on D7 (3 E. faecium and 3 E. faecalis ), 8 on D14 (4 E. faecium and 4 E. faecalis ) and 10 (21%) on D42 (9 E. faecium and 1 E. faecalis ). The relative abundance of FQ-RE increased from 44% on D0 to 73% and 75% on D7 and D14, respectively. No acquisition of fluoroquinolone resistance among endogenous D0 strains was evidenced. All (14/14) distinct Fluoroquinolone-resistant E. faecalis clones were gyrA / parC double mutants with high-level resistance (ciprofloxacin MIC >64 mg/L). In contrast, 34/35 E. faecium exhibited low-level resistance (ciprofloxacin MIC 4-32 mg/L) with no gyrA / parC mutation, but overexpressed the chromosomal Efm qnr gene. As compared with Fluoroquinolone-susceptible strains, Fluoroquinolone-resistant E. faecium were more frequently ampicillin resistant and Fluoroquinolone-resistant E. faecalis were more highly resistant to gentamicin.

Conclusions

Although intrinsically poorly susceptible to fluoroquinolones, gut populations of enterococci are highly impacted both quantitatively and qualitatively by ciprofloxacin.

Incomplete recovery of the fecal flora of hematological patients with neutropenia and repeated fluoroquinolone prophylaxis

Background

Routine fluoroquinolone prophylaxis in neutropenic patients with hematological malignancies is still controversial, because of antibiotic resistance concerns. The recovery of the fecal microbiota to the initial composition in patients receiving multiple courses of quinolone prophylaxis and repeated chemotherapy has not been evaluated.

Methods

We prospectively examined the changes in the fecal bacterial composition before and after levofloxacin prophylaxis. A sequential observation of bacterial resistance in patients receiving multiple prophylactic courses was also conducted.

Results

In this trial, 68 cases, including (35 with the first course and 33 with the second and subsequent courses) were registered. The disappearance of quinolone-susceptible (QS) Entero-bacteriaceae and dominant emergence of quinolone-resistant (QR) coagulase negative staphylococci (CNS) and QR Enterococci were observed after the first prophylaxis. The detection of QS Enterobacteriaceae was recovered before the second and subsequent courses to a level of the initial composition (28/35 samples, 80.0% before the first course vs 23/33 samples, 69.7% before the second and subsequent courses, P=0.41). In contrast, the detection rate of QR CNS and Enterococci significantly increased at the second and subsequent courses, even before prophylaxis (8/35 samples, 22.9% before the first course vs 20/33 samples, 60.6% before the second and subsequent courses, P=0.003). The incomplete recovery of the initial bacterial composition was associated with a prophylactic interval of within 30 days. Of the patients receiving multiple prophylactic courses, six had QR Escherichia coli, including extended-spectrum β-lactamase (ESBL) producers, at the first course, and four (66.3%) of the six patients had persistent detection of QR E. coli at the second course.

Conclusion

In patients receiving multiple courses of prophylactic quinolone, along with a common chemotherapy schedule, newly emergent resistant bacteria could be frequently persistent in their fecal flora.

Day-to-Day Dynamics of Commensal Escherichia coli in Zimbabwean Cows Evidence Temporal Fluctuations within a Host-Specific Population Structure

To get insights into the temporal pattern of commensal Escherichia coli populations, we sampled the feces of four healthy cows from the same herd in the Hwange District of Zimbabwe daily over 25 days. The cows had not received antibiotic treatment during the previous 3 months. We performed viable E. coli counts and characterized the 326 isolates originating from the 98 stool samples at a clonal level, screened them for stx and eae genes, and tested them for their antibiotic susceptibilities. We observed that E. coli counts and dominant clones were different among cows, and very few clones were shared. No clone was shared by three or four cows. Clone richness and evenness were not different between cows. Within each host, the variability in the E. coli count was evidenced between days, and no clone was found to be dominant during the entire sampling period, suggesting the existence of clonal interference. Dominant clones tended to persist longer than subdominant ones and were mainly from phylogenetic groups A and B1. Five E. coli clones were found to contain both the stx₁ and stx₂ genes, representing 6.3% of the studied isolates. All cows harbored at least one Shiga toxin-producing E. coli (STEC) strain. Resistance to tetracycline, penicillins, trimethoprim, and sulfonamides was rare and observed in three clones that were shed at low levels in two cows. This study highlights the fact that the commensal E. coli population, including the STEC population, is host specific, is highly dynamic over a short time frame, and rarely carries antibiotic resistance determinants in the absence of antibiotic treatment.IMPORTANCE The literature about the dynamics of commensal Escherichia coli populations is very scarce. Over 25 days, we followed the total E. coli counts daily and characterized the sampled clones in the feces of four cows from the same herd living in the Hwange District of Zimbabwe. This study deals with the day-to-day dynamics of both quantitative and qualitative aspects of E. coli commensal populations, with a focus on both Shiga toxin-producing E. coli and antibiotic-resistant E. coli strains. We show that the structure of these commensal populations was highly specific to the host, even though the cows ate and roamed together, and was highly dynamic between days. Such data are of importance to understand the ecological forces that drive the dynamics of the emergence of E. coli clones of particular interest within the gastrointestinal tract and their transmission between hosts.

Occurrence and Spread of Quinolone-Resistant Escherichia coli on Dairy Farms

Quinolone-resistant Escherichia coli (QREC) is common in feces from young calves, but the prevalence and genetic diversity of QREC in groups of cattle of other ages and the farm environment are unknown. The aims of the study were to obtain knowledge about the occurrence of QREC on dairy farms, the genetic diversity of QREC within and between farms, and how these relate to the number of purchased animals and geographic distances between farms. We analyzed the within-sample prevalence of QREC in individual fecal samples from preweaned dairy calves and postpartum cows and in environmental samples from 23 Swedish dairy farms. The genetic diversity of the QREC isolates on 10 of these farms was assessed. In general, QREC was more prevalent in the dairy farm environment and in postpartum cows if QREC was commonly found in calves than if QREC was rare in calves. In particular, we found more QREC organisms in feed and water troughs and in environments that may come into contact with young calves. Thus, the results suggest that QREC circulates between cattle and the farm environment and that calves are important for the maintenance of QREC. Some genotypes of QREC were widespread both within and between farms, indicating that QREC has spread within the farms and likely also between farms, possibly through purchased animals. Farms that had purchased many animals over the years had greater within-farm diversity than farms with more closed animal populations. Finally, animals on more closely located farms were more likely to share the same genotype than animals on farms located far apart.

IMPORTANCE

This study investigates the occurrence of a specific type of antimicrobial-resistant bacterium on dairy farms. It contributes to increased knowledge about the occurrence and spread of these bacteria, and the results pave the way for actions or further studies that could help mitigate the spread of these bacteria on dairy farms and in the community as a whole.

Fluoroquinolone Resistance Mechanisms and population structure of Enterobacter cloacae non-susceptible to Ertapenem in North-Eastern France

Fluoroquinolone (FQ) agents are a potential resort to treat infection due to Enterobacteriaceae producing extended spectrum β-lactamase and susceptible to FQ. In a context of increase of non-susceptibility to carbapenems among Enterobacteriaceae, we characterized FQ resistance mechanisms in 75 Enterobacter cloacae isolates non-susceptible to ertapenem in North-Eastern France in 2012 and describe the population structure by pulsed field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). Among them, 14.7% (12/75) carried a carbapenemase-encoding gene. Except one isolate producing VIM-1, the carbapenemase-producing isolates carried the well-known IncL/M pOXA48a plasmid. Most of the isolates (59/75) harbored at least a FQ-R determinant. qnr genes were predominant (40%, 30/75). The MLST study revealed that E. cloacae isolates’ clonality was wide [24 different sequence types (STs)]. The more widespread STs were ST74, ST101, ST110, ST114, and ST133. Carbapenem MICs were higher for E. cloacae ST74 than for other E. cloacae isolates. Plasmid-mediated quinolone resistance determinants were more often observed in E. cloacae ST74 isolates. These findings showed that (i) pOXA-48a is spreading in North-Eastern France, (ii) qnr is preponderant in E. cloacae, (iii) E. cloacae comprised a large amount of lineages spreading in North-Eastern France, and (iv) FQ as an alternative to β-lactams to treat ertapenem non-susceptible Enterobacteriaceae are compromised.

Comparative dynamics of the emergence of fluoroquinolone resistance in staphylococci from the nasal microbiota of patients treated with fluoroquinolones according to their environment

Fluoroquinolone-resistant staphylococci (FQRS) are primarily selected in the nasal microbiota during fluoroquinolone (FQ) treatment. To gain insight into the dynamics of the emergence of FQRS, 49 hospitalised patients (HPs) and 62 community patients (CPs) treated with FQs were studied. Nasal swabs were collected before (T0), at the end of (T1) and 1 month after (T2) FQ treatment. FQRS were identified by mass spectrometry. Antibiotic resistance was determined. Pre- and post-exposure staphylococci populations were compared phenotypically and by MLST to determine the origin of FQRS. At T0, 33/49 HPs (67%) and 24/62 CPs (39%) carried FQRS (OR=3.3, 95% CI: 1.4-7.9; P<0.001). Among patients with no FQRS at T0, 15/16 HPs (94%) and 16/38 CPs (42%) had FQRS detected at T1 and/or T2 (OR=19.6, 95% CI: 2.5-902; P<0.001). Among FQRS having emerged, co-resistance to meticillin was detected in 87% and 82% of HPs and CPs, respectively. No selection of resistance emerging from the initial microbiota was evidenced. FQRS showed decreased species diversity in favour of Staphylococcus haemolyticus and Staphylococcus epidermidis. As a consequence of FQ treatment, acquisition of FQRS in the nasal microbiota is frequent in the community and almost inevitable in hospitals. Acquisition from extranasal sites prevails. A restriction in species diversity in favour of more pathogenic and resistant species occurs. This highlights the major impact of FQ treatment on nasal microbiota, the role of the ecological environment in the emergence of FQRS, and the high-risk of dissemination of resistant staphylococci.

Impact of fluoroquinolones on human microbiota. Focus on the emergence of antibiotic resistance

The aggregate of microorganisms residing on the surface of the skin, in the oropharynx and in the GI tract, known as the human microbiota, play a major role as natural reservoirs for bacterial resistance to antibiotics. Fluoroquinolones (FQ) are among the most prescribed antibiotics and a major increase in FQ resistance is occurring worldwide. High concentrations of FQ are found in microbial ecosystems explaining their profound effect on the clinically relevant bacteria that compose them. Yet, because of different local pharmacokinetics, distinct selective pressures occur in the different microbiota. Here we review the qualitative and quantitative impact of FQ on the three main human microbiota and their consequences, particularly in terms of emergence of antibiotic resistance. Finally, we review potential actions that could decrease the impact of FQs on microbiota.

Integration of PK/PD for dose optimization of Cefquinome against Staphylococcus aureus causing septicemia in cattle

Cefquinome is a fourth generation cephalosporin with antimicrobial activity against gram negative and gram positive bacterial species, including Staphylococcus aureus. The aim of our study was to observe the ex-vivo activity of cefquinome against Staphylococcus aureus strains by using bovine serum from intravenously treated cattle. Cefquinome kinetics were measured by liquid chromatography and UV detection. In vitro post antibiotic effects (PAEs) and mutant prevention concentrations were determined with S. aureus strain ATCC 12598. Cefquinome exhibited time-dependent killing and produced in vitro PAEs increasing with concentration and time of exposure. A pharmacokinetic-pharmacodynamic model was established to simulate the efficacy of cefquinome for different dosage regimens. A dosage of 2 mg/kg every 12 h for 3 days was expected to reach a bactericidal activity against S. aureus in case of septicemia.

Development of resistance of mutans streptococci and Porphyromonas gingivalis to chlorhexidine digluconate and amine fluoride/stannous fluoride-containing mouthrinses, in vitro

OBJECTIVE

The aim if this study was to determine the minimal inhibitory concentrations of chlorhexidine digluconate and an amine fluoride/stannous fluoride-containing mouthrinse against Porphyromonas gingivalis and mutans streptococci during an experimental long-term subinhibitory exposition.

MATERIAL AND METHODS

Five P. gingivalis strains and four mutans streptococci were subcultivated for 20-30 passages in subinhibitory concentrations of chlorhexidine digluconate or an amine fluoride/stannous fluoride-containing mouthrinse.

RESULTS

Pre-passaging minimal inhibitory concentrations for chlorhexidine ranged from 0.5 to 2 mg/l for mutans streptococci and from 2 to 4 mg/l for the P. gingivalis isolates. For the amine fluoride/stannous fluoride-containing mouthrinse minimal inhibitory values from 0.125 to 0.25% for the mutans streptococci and from 0.063 to 0.125% for the P. gingivalis isolates were determined. Two- to fourfold increased minimal inhibitory concentrations against chlorhexidine were detected for two of the five P. gingivalis isolates, whereas no increase in minimal inhibitory concentrations was found for the mutans streptococci after repeated passaging through subinhibitory concentrations. Repeated exposure to subinhibitory concentrations of the amine fluoride/stannous fluoride-containing mouthrinse did not alter the minimally inhibitory concentrations of the bacterial isolates tested.

CONCLUSION

Chlorhexidine and the amine fluoride/stannous fluoride-containing mouthrinse are effective inhibitory agents against the oral bacterial isolates tested. No general development of resistance against chlorhexidine or the amine fluoride/stannous fluoride-containing mouthrinse was detected. However, some strains showed potential to develop resistance against chlorhexidine after prolonged exposure.

CLINICAL RELEVANCE

The use of chlorhexidine should be limited to short periods of time. The amine fluoride/stannous fluoride-containing mouthrinse appears to have the potential to be used on a long-term basis.

Mathematical modeling of bacterial kinetics to predict the impact of antibiotic colonic exposure and treatment duration on the amount of resistant enterobacteria excreted

Fecal excretion of antibiotics and resistant bacteria in the environment are major public health threats associated with extensive farming and modern medical care. Innovative strategies that can reduce the intestinal antibiotic concentrations during treatments are in development. However, the effect of lower exposure on the amount of resistant enterobacteria excreted has not been quantified, making it difficult to anticipate the impact of these strategies. Here, we introduce a bacterial kinetic model to capture the complex relationships between drug exposure, loss of susceptible enterobacteria and growth of resistant strains in the feces of piglets receiving placebo, 1.5 or 15 mg/kg/day ciprofloxacin, a fluoroquinolone, for 5 days. The model could well describe the kinetics of drug susceptible and resistant enterobacteria observed during treatment, and up to 22 days after treatment cessation. Next, the model was used to predict the expected amount of resistant enterobacteria excreted over an average piglet's lifetime (150 days) when varying drug exposure and treatment duration. For the clinically relevant dose of 15 mg/kg/day for 5 days, the total amount of resistant enterobacteria excreted was predicted to be reduced by 75% and 98% when reducing treatment duration to 3 and 1 day treatment, respectively. Alternatively, for a fixed 5-days treatment, the level of resistance excreted could be reduced by 18%, 33%, 57.5% and 97% if 3, 5, 10 and 30 times lower levels of colonic drug concentrations were achieved, respectively. This characterization on in vivo data of the dynamics of resistance to antibiotics in the colonic flora could provide new insights into the mechanism of dissemination of resistance and can be used to design strategies aiming to reduce it.

Fecal excretion of antibiotics and resistant bacteria in the environment are major public health threats associated with extensive farming. Innovative strategies that reduce the intestinal antibiotic concentrations during treatment are in development and could help prevent the dissemination of resistance. In order to anticipate the impact of these strategies, the effect of lower exposure on the amount of resistant enterobacteria excreted needs to be quantified precisely. Here, we introduce a bacterial kinetic model to capture the complex relationships between dosage regimen, antibiotic fecal concentrations, loss of susceptible enterobacteria and growth of resistant strains in the feces of piglets receiving different doses of ciprofloxacin for 5 days. We use this model to evaluate by simulation how much it would be necessary to reduce the antibiotic colonic concentration in order to prevent the expansion of antibiotic resistance. This approach provides new insights into the mechanism of dissemination of resistance during treatments and can be used to design strategies to reduce it.

Emergence of quinolone resistance in the microbiota of hospitalized patients treated or not with a fluoroquinolone

BACKGROUND

Quinolone resistance is a major global clinical problem. It primarily emerges in microbiota under selective pressure. Studies evaluating the incidence and risk factors for carrying quinolone-resistant bacteria in hospitalized patients treated with fluoroquinolones (FQs) are lacking.

METHODS

We prospectively included hospitalized patients treated with FQs. Nasal, throat and rectal swabs were performed before FQ treatment, at the end of FQ treatment and 30 days later. A 'reference group' of patients not receiving FQs was also included to determine the rates of quinolone resistance acquisition not linked to FQ treatment. Prevalence and incidence of quinolone-resistant strains of nasal coagulase-negative staphylococci (CoNS) and Staphylococcus aureus, pharyngeal α-haemolytic streptococci and faecal Escherichia coli, and risk factors for emergence of quinolone resistance in FQ-treated patients were assessed.

RESULTS

Four-hundred and fifty-one FQ-treated patients were included, as well as 119 subjects in the 'reference group'. Emergence of quinolone resistance occurred in 110/213 (51.6%), 50/336 (14.9%), 53/290 (18.3%) and 46/336 (13.7%) of FQ-treated patients for CoNS, S. aureus, α-haemolytic streptococci and E. coli, respectively, significantly more than for reference patients for CoNS (23/65; P < 0.05), S. aureus (5/91; P < 0.02) and E. coli (4/84; P < 0.05), but not for α-haemolytic streptococci (15/70; P = 0.55). Emergence of resistance was not associated with the type of FQ received, the duration of therapy or the duration of hospital stay, but was associated with host factors such as immunosuppression and altered performance status.

CONCLUSIONS

FQs received during hospitalization account for high rates of emergence of resistance to FQs in clinically relevant bacteria from human microbiota, reflecting the important ecological impact of FQs. Host factors outweighed treatment or hospitalization characteristics as risk factors for carrying quinolone-resistant strains.

Intestinal decontamination of multidrug-resistant Klebsiella pneumoniae after recurrent infections in an immunocompromised host

Multidrug-resistant (MDR) Enterobacteriaceae infections are associated with increased morbidity. We describe a 20-year-old hematopoietic cell transplantation recipient with recurrent MDR Klebsiella pneumoniae infection, prolonged intestinal colonization, and subsequent intestinal decontamination. Further study should evaluate stool surveillance, molecular typing, and fecal microbiota transplantation for patients with intestinal MDR Enterobacteriaceae carriage.

Dynamics of quinolone resistance in fecal Escherichia coli of finishing pigs after ciprofloxacin administration

Escherichia coli resistance to quinolones has now become a serious issue in large-scale pig farms of China. It is necessary to study the dynamics of quinolone resistance in fecal Escherichia coli of pigs after antimicrobial administration. Here, we present the hypothesis that the emergence of resistance in pigs requires drug accumulation for 7 days or more. To test this hypothesis, 26 pigs (90 days old, about 30 kg) not fed any antimicrobial after weaning were selected and divided into 2 equal groups: the experimental (EP) group and control (CP) group. Pigs in the EP group were orally treated daily with 5 mg ciprofloxacin/kg of body weight for 30 days, and pigs in the CP group were fed a normal diet. Fresh feces were collected at 16 time points from day 0 to day 61. At each time point, ten E. coli clones were tested for susceptibility to quinolones and mutations of gyrA and parC. The results showed that the minimal inhibitory concentration (MIC) for ciprofloxacin increased 16-fold compared with the initial MIC (0.5 µg/ml) after ciprofloxacin administration for 3 days and decreased 256-fold compared with the initial MIC (0.5 µg/ml) after ciprofloxacin withdrawal for 26 days. GyrA (S83L, D87N/ D87Y) and parC (S80I) substitutions were observed in all quinolone-resistant E. coli (QREC) clones with an MIC ≥8 µg/ml. This study provides scientific theoretical guidance for the rational use of antimicrobials and the control of bacterial resistance.

[Resistance to fluoroquinolones in 2013: what are the consequences in internal medicine?]

Because of their important qualities, fluoroquinolones are amongst the most prescribed antibiotics in the world. The corollary of this success is the rapid increase in resistance to fluoroquinolones, responsible for treatment failures. Moreover, fluoroquinolone-resistance is often accompanied by resistance to other classes of antibiotics. Currently, significant levels of resistance are found both in hospitals and in community settings, severely limiting possibilities for empirical use of fluoroquinolones. A major mechanism explaining the rapid emergence of resistance to fluoroquinolones is their specific impact on human microbiota and the selection of resistant strains in the microbiota, which seems to be an unavoidable ecological side effect. In order to preserve the efficiency of this important class of antibiotics, limiting their use and respecting good practice recommendations are essential.

Experimental approaches for defining functional roles of microbes in the human gut

The complex and intimate relationship between humans and their gut microbial communities is becoming less obscure, due in part to large-scale gut microbial genome-sequencing projects and culture-independent surveys of the composition and gene content of these communities. These studies build upon, and are complemented by, experimental efforts to define underlying mechanisms of host-microbe interactions in simplified model systems. This review highlights the intersection of these approaches. Experimental studies now leverage the advances in high-throughput DNA sequencing that have driven the explosion of microbial genome and community profiling projects, and the loss-of-function and gain-of-function strategies long employed in model organisms are now being extended to microbial genes, species, and communities from the human gut. These developments promise to deepen our understanding of human gut host-microbiota relationships and are readily applicable to other host-associated and free-living microbial communities.

Low or high doses of cefquinome targeting low or high bacterial inocula cure Klebsiella pneumoniae lung infections but differentially impact the levels of antibiotic resistance in fecal flora

The combination of efficacious treatment against bacterial infections and mitigation of antibiotic resistance amplification in gut microbiota is a major challenge for antimicrobial therapy in food-producing animals. In rats, we evaluated the impact of cefquinome, a fourth-generation cephalosporin, on both Klebsiella pneumoniae lung infection and intestinal flora harboring CTX-M-producing Enterobacteriaceae. Germfree rats received a fecal flora specimen from specific-pathogen-free pigs, to which a CTX-M-producing Escherichia coli strain had been added. K. pneumoniae cells were inoculated in the lungs of these gnotobiotic rats by using either a low (10(5) CFU) or a high (10(9) CFU) inoculum. Without treatment, all animals infected with the low or high K. pneumoniae inoculum developed pneumonia and died before 120 h postchallenge. In the treated groups, the low-inoculum rats received a 4-day treatment of 5 mg/kg of body weight cefquinome beginning at 24 h postchallenge (prepatent phase of the disease), and the high-inoculum rats received a 4-day treatment of 50 mg/kg cefquinome beginning when the animals expressed clinical signs of infection (patent phase of the disease). The dose of 50 mg/kg targeting the high K. pneumoniae inoculum cured all the treated rats and resulted in a massive amplification of CTX-M-producing Enterobacteriaceae. A dose of 5 mg/kg targeting the low K. pneumoniae inoculum cured all the rats and averted an outbreak of clinical disease, all without any amplification of CTX-M-producing Enterobacteriaceae. These findings might have implications for the development of new antimicrobial treatment strategies that ensure a cure for bacterial infections while avoiding the amplification of resistance genes of human concern in the gut microbiota of food-producing animals.

Pharmacokinetic/pharmacodynamic assessment of the effects of parenteral administration of a fluoroquinolone on the intestinal microbiota: comparison of bactericidal activity at the gut versus the systemic level in a pig model

Classical pharmacokinetic/pharmacodynamic studies of antimicrobial agents performed by combining plasma concentrations and minimum inhibitory concentrations (MICs) are often predictive of the activity of a drug against targeted pathogens located at infectious sites closely connected to circulating blood. However, these studies do not predict the impact of parenteral antimicrobial treatment on intestinal bacteria, which could be responsible for transmission of resistance between species or in the environment. The aim of this study was to assess the differential antibacterial activity of a fluoroquinolone against lung and gut bacteria. Plasma and intestinal concentrations of marbofloxacin were assessed in pigs following intramuscular administration, and the in vitro relationship between marbofloxacin concentrations and mean bacterial inoculum growth in standard broth and in sterilised intestinal contents was modelled. It was shown that the increased intestinal exposure to marbofloxacin compared with plasma in pigs was compensated by reduced marbofloxacin activity against Escherichia coli in the contents of the digestive tract compared with in broth. These results showed that marbofloxacin doses used to target pathogens at the lung level would similarly affect the bacterial population of the same size and with a similar MIC located in the small intestine. However, it was shown that the bactericidal activity of marbofloxacin was increased 4- to 7-fold with low (10(5)CFU/mL) compared with high (10(8)CFU/mL) inoculum sizes. This result suggests that much lower marbofloxacin doses than those classically used would potentially eradicate low pulmonary pathogenic inocula while having a minimal impact on the large gut microbiota.

Complexity of Escherichia coli bacteremia pathophysiology evidenced by comparison of isolates from blood and portal of entry within single patients

The portal of entry of Escherichia coli bacteremia, a frequent and severe disease, is most commonly the urinary tract followed by the digestive tract. Recent reports have evidenced the presence of several distinct E. coli clones within a single patient suffering of extra-intestinal infection. To explore the relationships between the blood and portal of entry strains, we thoroughly studied 98 bacteremic patients from the French prospective COLIBAFI cohort. In these patients, we compared genotypically and phenotypically E. coli strains isolated from the blood and the suspected portal of entry [non-urinary pus (n=52) and urine (n=52)]. We found genetically distinct strains exhibiting distinct antibiotypes in the blood and pus samples (8 patients; 15%) and the blood and urine samples (2 patients; 3.8%) (p=0.09). These data highlight the complexity of pathophysiology of E. coli bacteremia and should be taken into consideration when strain antibiotic susceptibility is tested, especially in bacteremia of pus origin.

Causes, consequences, and perspectives in the variations of intestinal density of colonization of multidrug-resistant enterobacteria

The intestinal microbiota is a complex environment that hosts 10¹³ to 10¹⁴ bacteria. Among these bacteria stand multidrug-resistant enterobacteria (MDRE), which intestinal densities can substantially vary, especially according to antibiotic exposure. The intestinal density of MDRE and their relative abundance (i.e., the proportion between the density of MDRE and the density of total enterobacteria) could play a major role in the infection process or patient-to-patient transmission. This review discusses the recent advances in understanding (i) what causes variations in the density or relative abundance of intestinal colonization, (ii) what are the clinical consequences of these variations, and (iii) what are the perspectives for maintaining these markers at low levels.