Fluoroquinolone resistance in Bacteroides fragilis following sparfloxacin exposure

Gut bacterial species in late trimester of pregnant sows influence the occurrence of stillborn piglet through pro-inflammation response

Maternal gut microbiota is an important regulator for the metabolism and immunity of the fetus during pregnancy. Recent studies have indicated that maternal intestinal microbiota is closely linked to the development of fetus and infant health. Some bacterial metabolites are considered to be directly involved in immunoregulation of fetus during pregnancy. However, the detailed mechanisms are largely unknown. In this study, we exploited the potential correlation between the gut microbiota of pregnant sows and the occurrence of stillborn piglets by combining the 16S rRNA gene and metagenomic sequencing data, and fecal metabolome in different cohorts. The results showed that several bacterial species from Bacteroides, potential pathogens, and LPS-producing bacteria exhibited significantly higher abundances in the gut of sows giving birth to stillborn piglets. Especially, Bacteroides fragilis stood out as the key driver in both tested cohorts and showed the most significant association with the occurrence of stillborn piglets in the DN1 cohort. However, several species producing short-chain fatty acids (SCFAs), such as Prevotella copri, Clostridium butyricum and Faecalibacterium prausnitzii were enriched in the gut of normal sows. Functional capacity analysis of gut microbiome revealed that the pathways associated with infectious diseases and immune diseases were enriched in sows giving birth to stillborn piglets. However, energy metabolism had higher abundance in normal sows. Fecal metabolome profiling analysis found that Lysophosphatidylethanolamine and phosphatidylethanolamine which are the main components of cell membrane of Gram-negative bacteria showed significantly higher concentration in stillbirth sows, while SCFAs had higher concentration in normal sows. These metabolites were significantly associated with the stillborn-associated bacterial species including Bacteroides fragilis. Lipopolysaccharide (LPS), IL-1β, IL-6, FABP2, and zonulin had higher concentration in the serum of stillbirth sows, indicating increased intestinal permeability and pro-inflammatory response. The results from this study suggested that certain sow gut bacterial species in late trimester of pregnancy, e.g., an excess abundance of Bacteroides fragilis, produced high concentration of LPS which induced sow pro-inflammatory response and might cause the death of the relatively weak piglets in a farrow. This study provided novel evidences about the effect of maternal gut microbiota on the fetus development and health.

Optimal use of fluoroquinolones in the intensive care unit setting

Fluoroquinolones have become a staple antimicrobial in a variety of settings for a wide spectrum of infectious diseases. Although fluoroquinolones have been associated with a broad spectrum of adverse events, the side effect profile is generally acceptable. Their use in the intensive care unit as empiric therapy is becoming compromised due to the development of multiple drug resistant gram negative pathogens and collateral damage with C difficile & MRSA. Fluoroquinolones should be used along with another antibiotic of different chemical structure, mechanism of action, and pharmacodynamic profile to ensure adequate initial antimicrobial coverage and maximize the likelihood of a favorable clinical and microbiologic response.

Evidence for a reserpine-affected mechanism of resistance to tetracycline in Neisseria gonorrhoeae

The presence of a reserpine-affected mechanism of tetracycline resistance was investigated in 17 Neisseria gonorrhoeae clinical isolates. To establish this fact the MIC of tetracycline in the presence and absence of reserpine was determined, and, in addition, mechanisms of tetracycline resistance were analyzed by PCR. The results showed that reserpine affects the MIC of tetracycline at least 4-fold in all isolates, including those containing the tetM gene. An inhibitory effect of reserpine against the MtrCDE efflux system was ruled out by using strains either with an inactive or with an unrepressed MtrCDE system. The results suggest the presence of a constitutive system of resistance to tetracycline, by a possible efflux pump, which may be inhibited by reserpine. Further studies are required to determine the exact nature of the action of reserpine on the MIC of tetracycline.

Pharmacokinetic/pharmacodynamic relationships of antimicrobial drugs used in veterinary medicine

The rise in incidence of antimicrobial resistance, consumer demands and improved understanding of antimicrobial action has encouraged international agencies to review the use of antimicrobial drugs. More detailed understanding of relationships between the pharmacokinetics (PK) of antimicrobial drugs in target animal species and their action on target pathogens [pharmacodynamics (PD)] has led to greater sophistication in design of dosage schedules which improve the activity and reduce the selection pressure for resistance in antimicrobial therapy. This, in turn, may be informative in the pharmaceutical development of antimicrobial drugs and in their selection and clinical utility. PK/PD relationships between area under the concentration time curve from zero to 24 h (AUC(0-24)) and minimum inhibitory concentration (MIC), maximum plasma concentration (C(max)) and MIC and time during which plasma concentrations exceed the MIC have been particularly useful in optimizing efficacy and minimizing resistance. Antimicrobial drugs have been classified as concentration-dependent where increasing concentrations at the locus of infection improve bacterial kill, or time-dependent where exceeding the MIC for a prolonged percentage of the inter-dosing interval correlates with improved efficacy. For the latter group increasing the absolute concentration obtained above a threshold does not improve efficacy. The PK/PD relationship for each group of antimicrobial drugs is 'bug and drug' specific, although ratios of 125 for AUC(0-24):MIC and 10 for C(max):MIC have been recommended to achieve high efficacy for concentration-dependent antimicrobial drugs, and exceeding MIC by 1-5 multiples for between 40 and 100% of the inter-dosing interval is appropriate for most time-dependent agents. Fluoroquinolones, aminoglycosides and metronidazole are concentration-dependent and beta-lactams, macrolides, lincosamides and glycopeptides are time-dependent. For drugs of other classes there is limited and conflicting information on their classification. Resistance selection may be reduced for concentration-dependent antimicrobials by achieving an AUC(0-24):MIC ratio of greater than 100 or a C(max):MIC ratio of greater than 8. The relationships between time greater than MIC and resistance selection for time-dependent antimicrobials have not been well characterized.

Pharmacodynamics of pulse dosing versus standard dosing: in vitro metronidazole activity against Bacteroides fragilis and Bacteroides thetaiotaomicron

Pulse dosing is a novel approach to dosing that produces escalating antibiotic levels early in the dosing interval followed by a prolonged dose-free period. Antibiotic is frontloaded by means of four sequential bolus injections, after which antibiotic levels are allowed to diminish until the next dose. This study compares standard thrice-daily dosing and pulse dosing of metronidazole against Bacteroides spp. in an in vitro model. Two American Type Culture Collection Bacteroides fragilis isolates (metronidazole MIC for each organism = 1 mg/liter) were exposed to metronidazole for 48 or 96 h. Human pharmacokinetics were simulated for an oral 500-mg dose given every 8 h (maximum concentration of drug [C(max)] = 12 mg/liter; half-life = 8 h; area under the curve [AUC] = 294 mg . h/liter) and for pulse dosing. Pulses, each producing an increase in metronidazole concentration of 9 mg/liter, were administered at times 0, 2, 4, and 6 h of each 24-h cycle, with a targeted half-life of 8 h (AUC = 347 mg . h/liter). A metronidazole-resistant B. fragilis strain (metronidazole MIC = 32 mg/liter) was exposed to both dosing regimens and, additionally, to a regimen of 1,500 mg administered once daily (C(max) = 36 mg/liter; AUC = 364 mg . h/liter). Furthermore, regimens against one B. fragilis isolate and one B. thetaiotaomicron isolate corresponding to one-fourth and one-eighth of the thrice-daily and pulse dosing regimens, mimicking peak metronidazole concentrations achieved in abscesses, were simulated in 48-h experiments (metronidazole MIC = 1 mg/liter). Time-kill curves were generated for each experiment and analyzed for bactericidal activity, defined as a bacterial burden reduction >/= 3 log(10) CFU/ml. The results of paired (Wilcoxon matched-pair signed-rank test) and nonpaired (Mann-Whitney test) statistical analyses conducted on time to 3 log(10) kill data and area under the kill curve data from each of the thrice-daily dosing experiments versus each of the pulse dosing experiments were considered not significant for a given isolate-dosing regimen combination. The thrice-daily dosing, pulse dosing, and once-daily dosing regimens all exhibited bactericidal activity. Metronidazole administered in standard or pulse dosing fashion was highly active against both susceptible and resistant strains of Bacteroides spp.

Role of topoisomerase mutations and efflux in fluoroquinolone resistance of Bacteroides fragilis clinical isolates and laboratory mutants

Twelve laboratory mutants and 32 ciprofloxacin-resistant isolates of Bacteroides fragilis were examined for the mechanism(s) of fluoroquinolone resistance. Five mutants had mutations in gyrA. One mutant and two clinical isolates contained a mutation in gyrB. Eight mutants and five clinical isolates accumulated significantly less ciprofloxacin than did wild-type isolates; the mutants and clinical isolates were restored to wild-type characteristics when carbonyl cyanide m-chlorophenylhydrazone was used.

Antimicrobial susceptibility of Bacteroides fragilis group isolates in Europe

OBJECTIVE

To evaluate the activity of old and newer antianaerobic drugs against clinical isolates of Bacteroides fragilis group strains from different parts of Europe.

METHODS

Bacteroides fragilis group isolates from 37 laboratories in 19 countries were biochemically characterized. The MICs of seven antimicrobial agents were determined by the agar dilution method as recommended by the NCCLS. Production of beta-lactamase was detected by nitrocefin.

RESULTS

There were 1284 B. fragilis group isolates included in the study. Abdominal infections and wounds were the most common sources of isolation and B. fragilis was the dominating species. Ninety-nine percent of the strains were resistant to ampicillin (breakpoint 2 mg/L), 6% to cefoxitin (64 mg/L), 15% to clindamycin (8 mg/L) and 9% to moxifloxacin (8 mg/L). Less than 1% were resistant to imipenem (16 mg/L), piperacillin-tazobactam (128 mg/L) and metronidazole (32 mg/L). Ninety-six percent of the isolates were beta-lactamase producers.

CONCLUSIONS

Antimicrobial resistance among the B. fragilis group is increasing.

In vitro pharmacodynamic evaluation of the mutant selection window hypothesis using four fluoroquinolones against Staphylococcus aureus

To study the hypothesis of the mutant selection window (MSW) in a pharmacodynamic context, the susceptibility of a clinical isolate of methicillin-resistant Staphylococcus aureus exposed to moxifloxacin (MOX), gatifloxacin (GAT), levofloxacin (LEV), and ciprofloxacin (CIP) was tested daily by using an in vitro dynamic model that simulates human pharmacokinetics. A series of monoexponential pharmacokinetic profiles that mimic once-daily administration of MOX (half-life, 12 h), GAT (half-life, 7 h), and LEV (half-life, 6.8 h) and twice-daily administration of CIP (half-life, 4 h) provided peak concentrations (C(max)) that either equaled the MIC, fell between the MIC and the mutant prevention concentration (MPC) (i.e., within or "inside" the MSW), or exceeded the MPC. The respective ratios of the area under the curve (AUC) over a 24-h dosing interval (AUC(24)) to the MIC varied from 13 to 244 h, and the starting inoculum was 10(8) CFU/ml (6 x 10(9) CFU per 60-ml central compartment). With all four quinolones, the greatest increases in MIC were observed at those AUC(24)/MIC values (from 24 to 62 h) that corresponded to quinolone concentrations within the MSW over most of the dosing interval (>20%). Less-pronounced increases in MIC were associated with the smallest simulated AUC(24)/MIC values (15 to 16 h) of GAT and CIP, whose C(max) exceeded the MICs. No such increases were observed with the smallest AUC(24)/MIC values (13 to 17 h) of MOX and LEV, whose C(max) were close to the MICs. Also, less pronounced but significant increases in MIC occurred at AUC(24)/MIC values (107 to 123 h) that correspond to quinolone concentrations partly overlapping the MIC-to-MPC range. With all four drugs, no change in MIC was seen at the highest AUC(24)/MIC values (201 to 244 h), where quinolone concentrations exceeded the MPC over most of the dosing interval. These "protective" AUC(24)/MIC ratios correspond to 66% of the usual clinical dose of MOX (400 mg), 190% of a 400-mg dose of GAT, 220% of a 500-mg dose of LEV, and 420% of two 500-mg doses of CIP. Thus, MOX may protect against resistance development at subtherapeutic doses, whereas GAT, LEV, and CIP provide similar effects only at doses that exceed their usual clinical doses. These data support the concept that resistant mutants are selectively enriched when antibiotic concentrations fall inside the MSW and suggest that in vitro dynamic models can be used to predict the relative abilities of quinolones to prevent mutant selection.

In vitro activity of clinafloxacin in comparison with other quinolones against Stenotrophomonas maltophilia clinical isolates in the presence and absence of reserpine

A total of 33 Stenotrophomonas maltophilia clinical isolates were tested for their susceptibility to clinafloxacin in comparison with ciprofloxacin, levofloxacin, moxifloxacin, nalidixic acid, norfloxacin, sparfloxacin and trovafloxacin. The MIC(50) and MIC(90) were as follows: ciprofloxacin 4 and 64 microg/mL; clinafoxacin 0.5 and 4 microg/mL; levofloxacin 2 and 32 microg/mL; moxifloxacin 1 and 8 microg/mL; nalidixic acid 8 and 128 microg/mL; norfloxacin 64 and 256 microg/mL; sparfloxacin 1 and 16 microg/mL; and trovafloxacin 1 and 8 microg/mL. Clinafloxacin was the most active quinolone, with only a 15.1% of strains showing resistance. When the MICs were determined in the presence of 25 microg/ml of reserpine, the MIC(90) of trovafloxacin and moxifloxacin did not change, whereas decreased 2-fold for clinafloxacin, levofloxacin, sparfloxacin and nalidixic acid, and 4- and 8-fold for ciprofloxacin and norfloxacin respectively. No clinafloxacin-resistant strains were observed when the MIC was performed in the presence of reserpine. Therefore, clinafloxacin shows the better "in vitro"activity against these 33 strains of S.maltophilia.

Pharmacodynamics of trovafloxacin and levofloxacin against Bacteroides fragilis in an in vitro pharmacodynamic model

An in vitro pharmacodynamic investigation was conducted to explore whether the area under the concentration time curve from 0 to 24 h (AUC(0-24))/MIC ratio could predict fluoroquinolone performance against Bacteroides fragilis. An in vitro model was used to generate kill curves for trovafloxacin (TVA) and levofloxacin (LVX) at AUC(0-24)/MIC ratios of 1 to 406 against three strains of B. fragilis (ATCC 25285, ATCC 23745, and clinical isolate M97-117). TVA and LVX were bolused prior to the start of experiments to achieve the corresponding AUC(0-24)/MIC ratio. Experiments were performed in duplicate over 24 h and in an anaerobic environment. Analyses of antimicrobial performance were conducted by comparing the rates of bacterial kill (K) using nonlinear regression analysis with 95% confidence intervals. Statistical significance was defined as a lack of overlap in the 95% confidence limits generated from the slope of each kill curve. For both TVA and LVX, K was maximized once an AUC(0-24)/MIC ratio of > or =40 was achieved and was not further increased despite a 10-fold increase in AUC(0-24)/MIC from approximately 40 to 400 against all three strains of B. fragilis. No significant differences were found in K between AUC(0-24)/MIC ratios of approximately 40 to 200. In experiments where AUC(0-24)/MIC ratios that were > or = 5 and < or = 44 were conducted, 64% demonstrated regrowth at 24 h. Resistant strains were selected in 50% of those experiments, demonstrating regrowth, which resulted in increased MICs of two- to 16-fold for both TVA and LVX. Regrowth did not occur, nor were resistant strains selected in any studies with an AUC/MIC that was > 44. Our findings suggest that fluoroquinolones provide antibacterial effects against B. fragilis in a concentration-independent manner associated with an AUC(0-24)/MIC ratio of > or =40. Also, the potential for the selection of resistant strains of B. fragilis may increase with an AUC(0-24)/MIC ratio of < or =44.

What do we really know about antibiotic pharmacodynamics?

Antibiotic pharmacodynamics is an evolving science that focuses on the relationship between drug concentration and pharmacologic effect, which is an antibiotic-induced bacterial death that also can manifest as an adverse drug reaction. The pharmacologic action of antibiotics usually can be described as concentration dependent or independent, although such classifications are highly reliant on the specific antibiotic and bacterial pathogen being studied. Quantitative pharmacodynamic parameters, such as ratio of the area under the concentration-time curve during a 24-hour dosing period to minimum inhibitory concentration (AUC0-24:MIC), ratio of maximum serum antibiotic concentration to MIC (Cmax:MIC), and duration of time that antibiotic concentrations exceed MIC (T>MIC), have been proposed as likely predictors of clinical and microbiologic success or failure for different pairings of antibiotic and bacteria. Thus far, most pharmacodynamic data reported have focused on fluoroquinolones, but work has been conducted on vancomycin, beta-lactams, macrolides, aminoglycosides, and other antibiotics. Despite the development of a number of different pharmacodynamic modeling systems, remarkable agreement exists between in vitro, animal, and limited human data. Although still somewhat premature and requiring additional clinical validation, antibiotic pharmacodynamics will likely advance on four fronts: the science should prove to be extremely useful and represent a cost-effective and efficient method to help develop new antibiotics; formulary committees will likely use pharmacodynamic parameters to assist in differentiating antibiotics of the same chemical class in making antibiotic formulary selections; pharmacodynamic principles will likely be used to design optimal antibiotic strategies for patients with severe infections; and limited data to date suggest that the application of pharmacodynamic concepts may limit or prevent the development of antibiotic resistance. The study of antibiotic pharmacodynamics appears to hold great promise and will likely become a routine part of our daily clinical practices.

Fluoroquinolone resistance in anaerobic bacteria following exposure to levofloxacin, trovafloxacin, and sparfloxacin in an in vitro pharmacodynamic model

This investigation explored pharmacodynamic characteristics of fluoroquinolones against Bacteroides thetaiotamicron and the potential for development of resistance. An in vitro model was used to generate kill curves with three fluoroquinolones at various area under the concentration-time curve (AUC)/MIC ratios. Concentration-independent killing was observed. Increases in MICs were noted following exposure to fluoroquinolones at AUC/MIC ratios of 6 to 14.

Intensive care unit antimicrobial resistance and the role of the pharmacist

Over the past 20 yrs, pharmacists have successfully integrated their services and expertise to gain acceptance as full members of pediatric, surgical, medical, and intensive care unit (ICU) patient care teams. The pharmacists' training in pharmacology, pharmacokinetics, pharmacodynamics, and pharmacoeconomics complements the expertise of other members of the patient care team. Generally, a strong background in infectious diseases and critical care also provides a focal point for clinical pharmacy service intervention. Although practitioners often focus on issues exclusively related to their specific hospital or ICU, the issues surrounding antibiotic resistance are more global and societal in nature. Medical, surgical, and pharmaceutical practices inside the hospital and ICU extend their influence into the community. Customs and practices of daily living in our society coupled with use of agents capable of altering microbial flora impact our hospital and ICU when patients from the community are admitted. The misuse of antibiotics and the lack of effective infection control programs are often identified as key components in the perpetuation of these phenomena. The focus for the pharmacist and the ICU team must be on the optimization of antibiotic use and infection control guidelines. This review will address the many issues that surround the appropriate use of antibiotics and what role the pharmacist can play in ensuring the optimal use of infection control measures in the ICU and hospital.