Selection of rifampicin-resistant Staphylococcus aureus during tuberculosis therapy: concurrent bacterial eradication and acquisition of resistance

Is there a role for suppression of infection in managing fracture-related infection following intra-medullary nailing?

BACKGROUND

The management of fracture-related infection has undergone radical progress following the development of international guidelines. However, there is limited consideration to the realities of healthcare in low-resource environments due to a lack of available evidence in the literature from these settings. Initial antimicrobial suppression to support fracture union is frequently used in low- and middle-income countries despite the lack of published clinical evidence to support its practice. This study aimed to evaluate the outcomes following initial antimicrobial suppression to support fracture union in the management of fracture-related infection.

METHODS

A retrospective review of consecutive patients treated with initial antimicrobial suppression to support fracture healing followed by definitive eradication surgery to manage fracture-related infections following intramedullary fixation was performed. Indications for this approach were; a soft tissue envelope not requiring reconstructive surgery, radiographic evidence of stable fixation with adequate alignment, and progression towards fracture union.

RESULTS

This approach was associated with successful treatment in 51/55 (93 %) patients. Fracture union was achieved in 52/55 (95 %) patients with antimicrobial suppression alone. Remission of infection was achieved in 54/55 (98 %) patients following definitive infection eradication surgery. Following antibiotic suppression, 6/46 (13 %) pathogens isolated from intra-operative samples demonstrated multi-drug resistance.

CONCLUSION

Initial antimicrobial suppression to support fracture healing followed by definitive infection eradication surgery was associated with successful treatment in 93 % of patients. The likelihood of remission of infection increases when eradication surgery is performed in a healed bone. This approach was not associated with an increased risk of developing multi-drug-resistant infections compared to contemporary bone infection cohorts in the published literature.

LEVEL OF EVIDENCE

IV.

Impact of Environmental Sub-Inhibitory Concentrations of Antibiotics, Heavy Metals, and Biocides on the Emergence of Tolerance and Effects on the Mutant Selection Window in E. coli

Bacteria's ability to withstand the detrimental effects of antimicrobials could occur as resistance or tolerance with the minimum inhibitory concentration, the mutant prevention concentration, and the mutant selection window as salient concepts. Thus, this study assessed the impact of exposure to extremely high doses of ampicillin on the level of persistence and tolerance development in isolates previously exposed to different concentrations of selected antibiotics, biocides, and heavy metals. These isolates were previously exposed to oxytetracycline (OXYTET), amoxicillin (AMX), copper (Cu), zinc (Zn), benzalkonium chloride (BAC) 10, dimethylammonium chloride (DADMAC) 12 and a combination of all the individual pollutants (ALL). The isolates were exposed to very high concentrations (25 × MIC) of ampicillin, and their tolerance was calculated as the time required to kill 99.9% of the bacterial population (MDK99.9). The MDK99.9 increased by 30 to 50% in test isolates (DADMAC, OXYTET, Zinc = 28 h; BAC, Copper = 30 h; amoxycillin, ALL = 26 h) compared to the untreated control. BAC-exposed isolates decreased from 2.5 × 108 CFU/mL to 2.5 × 104 CFU/mL on the second day, displaying the highest tolerance increase. The tolerance appeared to originate from two sources, i.e., stochastic persistence and genetic-induced persistence, involving multiple genes with diverse mechanisms. The mutant selection window of the isolates to ampicillin, amoxicillin, and oxytetracycline also slightly increased compared to the control, indicating the selective survival of persister cells during the 30-day exposure. These findings indicate that bacterial exposure to sub-inhibitory concentrations of environmental chemical stressors may not always result in the development of antimicrobial resistance but could initiate this process by selecting persisters that could evolve into resistant isolates.

Cefpirome Treatment Results in Limited Selection of Stable Derepressed Enterobacter cloacae Mutants in the Intestinal Flora of Rats Treated for an Experimental Klebsiella pneumoniae Pulmonary Infection

Background: Fourth-generation cephalosporins have been developed to improve their potency, that is, low minimal inhibitory concentrations (MICs) and to prevent resistance selection of derepressed AmpC-producing mutants in comparison to third-generation cephalosporins as ceftazidime. Objectives: We investigated the role of the administered cefpirome dose on the efficacy of treatment of a Klebsiella pneumoniae lung infection as well as in the selection of resistant Enterobacter cloacae isolates in the intestines of rats treated for a K. pneumoniae lung infection. Materials and Methods: Rats with K. pneumoniae lung infection received therapy with cefpirome doses of 0.4 to 50 mg/kg/day b.i.d. for 18 days. Resistance selection in intestinal E. cloacae was monitored during 43 days. Mutants were checked for β-lactamase activity, mutations in their structural ampC gene, ampD gene, and omp39-40 gene. Results: A 45% and 100% rat survival rate was obtained by administration of 3.1 and 12.5 mg/kg b.i.d. of cefpirome. A significant correlation was demonstrated in the reduction of the susceptible E. cloacae isolates with %fT>MIC at days 7, 14, 22, and 29. Cefpirome E. cloacae mutants, with increased cefpirome MICs, were obtained in only four rats. Conclusions: The treatment with cefpirome resulted in less selection of derepressed mutants in comparison to ceftazidime as shown by their low number per gram of feces and in a limited number of animals.

Antimicrobial resistance in Clostridium difficile ribotype 017

Introduction: Antimicrobial resistance (AMR) played an important role in the initial outbreaks of Clostridium difficile infection (CDI) in the 1970s. C. difficile ribotype (RT) 017 has emerged as the major strain of C. difficile in Asia, where antimicrobial use is poorly regulated. This strain has also caused CDI outbreaks around the world for almost 30 years. Many of these outbreaks were associated with clindamycin and fluoroquinolone resistance. AMR and selective pressure is likely to be responsible for the success of this RT and may drive future outbreaks.Areas covered: This narrative review summarizes the prevalence and mechanisms of AMR in C. difficile RT 017 and transmission of these AMR mechanisms. To address these topics, reports of outbreaks due to C. difficile RT 017, epidemiologic studies with antimicrobial susceptibility results, studies on resistance mechanisms found in C. difficile and related publications available through Pubmed until September 2019 were collated and the findings discussed.Expert opinion: Primary prevention is the key to control CDI. This should be achieved by developing antimicrobial stewardship in medical, veterinary and agricultural practices. AMR is the key factor that drives CDI outbreaks, and methods for the early detection of AMR can facilitate the control of outbreaks.

Primary subacute hematogenous osteomyelitis in children: a clearer bacteriological etiology

BACKGROUND

This study aimed to describe the spectrum of pediatric primary subacute hematogenous osteomyelitis (PSAHO) and to investigate its bacterial etiology.

METHODS

Sixty-five consecutive cases of PSAHO admitted to our institution over a 16-year period (2000-2015) were retrospectively reviewed to assess their laboratory and radiographic imaging features, as well as their bacteriological etiology.

RESULTS

On evaluation, white blood cell count and C-reactive protein were normal in 53 (81.5 %) and 34 cases (52.3 %), respectively, whereas the erythrocyte sedimentation rate was superior to 20 mm/h in 44 cases (72.1 %). Blood cultures failed to identify the pathogen in all but one patient, and classic bone sample cultures only managed to isolate the pathogen in five cases (11.6 %). Use of polymerase chain reaction (PCR) assays on bone aspirates or blood allowed the causative microorganism to be isolated in a further 22 cases. Using classic cultures and PCR assays together resulted in pathogen detection in 27 cases (62.8 % of the children bacteriologically investigated), with Kingella kingae being the most frequently reported microorganism.

CONCLUSIONS

Two distinct forms of PSAHO should be distinguished on the basis of age of patients and bacteriological etiology. The infantile form affects children aged between 6 months and 4 years and is predominantly due to K. kingae. The juvenile form involves children aged >4 years and Staphylococcus aureus appears to be the main bacteriological etiology. Appropriate nucleic amplification assays drastically improve the detection rate of the microorganisms responsible for PSAHO.

LEVEL OF EVIDENCE

Case series, level IV.

Propionibacterium acnes: from commensal to opportunistic biofilm-associated implant pathogen

Propionibacterium acnes is known primarily as a skin commensal. However, it can present as an opportunistic pathogen via bacterial seeding to cause invasive infections such as implant-associated infections. These infections have gained more attention due to improved diagnostic procedures, such as sonication of explanted foreign materials and prolonged cultivation time of up to 14 days for periprosthetic biopsy specimens, and improved molecular methods, such as broad-range 16S rRNA gene PCR. Implant-associated infections caused by P. acnes are most often described for shoulder prosthetic joint infections as well as cerebrovascular shunt infections, fibrosis of breast implants, and infections of cardiovascular devices. P. acnes causes disease through a number of virulence factors, such as biofilm formation. P. acnes is highly susceptible to a wide range of antibiotics, including beta-lactams, quinolones, clindamycin, and rifampin, although resistance to clindamycin is increasing. Treatment requires a combination of surgery and a prolonged antibiotic treatment regimen to successfully eliminate the remaining bacteria. Most authors suggest a course of 3 to 6 months of antibiotic treatment, including 2 to 6 weeks of intravenous treatment with a beta-lactam. While recently reported data showed a good efficacy of rifampin against P. acnes biofilms, prospective, randomized, controlled studies are needed to confirm evidence for combination treatment with rifampin, as has been performed for staphylococcal implant-associated infections.

Minimum inhibitory concentrations of equine Corynebacterium pseudotuberculosis isolates (1996-2012)

Background

Few studies report the minimum inhibitory concentrations for antimicrobials against equine Corynebacterium pseudotuberculosis isolates.

Hypothesis/Objectives

To evaluate trends in the in vitro activities of 20 antimicrobials against equine Corynebacterium pseudotuberculosis isolates from 1996 to 2012 and to determine if a relationship exists between the minimum inhibitory concentration (MIC) and location of the abscess.

Animals

Corynebacterium pseudotuberculosis isolates from 196 horses with naturally occurring disease.

Methods

Retrospective and cross‐sectional design. Medical records were reviewed to obtain clinical and MIC data. Minimum inhibitory concentrations were determined by the microdilution technique. The MIC results over 3 periods were compared (1996–2001, 2002–2006, 2007–2012).

Results

The MIC₉₀ values for clinically relevant antimicrobials were as follows: chloramphenicol ≤4 μg/mL, enrofloxacin ≤0.25 μg/mL, gentamicin ≤1 μg/mL, penicillin =0.25 μg/mL, rifampin ≤1 μg/mL, tetracycline ≤2 μg/mL, trimethoprim‐sulfamethoxazole (TMS) ≤0.5 μg/mL, ceftiofur =2 μg/mL, and doxycycline ≤2 μg/mL. There were no significant changes in MIC results over the study period. There was no relationship between MIC patterns and abscess location.

Conclusions and Clinical Importance

The MIC₅₀ and MIC₉₀ values of antimicrobials evaluated in this study for equine isolates of C. pseudotuberculosis did not vary over time. Abscess location was not associated with different MIC patterns in cultured isolates. Several commonly used antimicrobials are active in vitro against C. pseudotuberculosis in vitro.

Bacteriophage therapy against staphylococci

The emergence of the multi-drug-resistant Staphylococcus aureus strains has prompted interest in alternatives to conventional drugs. Among the possible options one of the most promising is the therapeutic use of bacteriophages. Over the recent decades, increasing amount of literature has validated the use of bacteriophages for therapy and prophylaxis against drug-resistant staphylococci. This work attempts to review the current knowledge on bacteriophages and their usages for treatment of staphylococcal diseases.

Tuberculous Otitis Media and Staphylococcus aureus Coinfection in a Five-Year-Old Boy with Miliary Tuberculosis

A five-year-old boy with acute on chronic ear discharge and fever was diagnosed to have tubercular otitis media (TOM) with Staphylococcus aureus co-infection. His chest X-ray was suggestive of miliary tuberculosis. The clinical presentation of the child with a brief review of the literature pertaining to the case is being discussed in this report.

Factors associated with rifampin resistance in staphylococcal periprosthetic joint infections (PJI): a matched case-control study

PURPOSE

Rifampin combination therapy plays an important role in the management of staphylococcal periprosthetic joint infection (PJI). However, the emergence of rifampin resistance is a feared complication. We retrospectively analysed predetermined potential risk factors in patients with rifampin-resistant staphylococcal PJI in a multicentre case-control study.

METHODS

Cases (n = 48) were defined as PJI caused by rifampin-resistant staphylococci. Rifampin-susceptible controls (n = 48) were matched for microorganism and type of prosthetic joint. Uni- and multivariable conditional logistic regression analyses were performed to estimate odds ratios (OR) with 95 % confidence intervals (95 % CI).

RESULTS

Forty-eight cases (31 men; median age 67 years; age range 39-88 years) with hip- (n = 29), knee- (n = 13), elbow- (n = 4), shoulder- (n = 1) or ankle-PJI (n = 1) were enrolled in the study. Staphylococcus aureus and coagulase-negative staphylococci were isolated in ten and 38 episodes, respectively. Most of the cases (n = 44, 92 %) had a previous PJI, and 93 % (n = 41) of these had been treated with rifampin. There was an independent association of emergence of rifampin resistance with male sex (OR 3.6, 95 % CI 1.2-11), ≥ 3 previous surgical revisions (OR 4.7, 95 % CI 1.6-14.2), PJI treatment with high initial bacterial load (inadequate surgical debridement, <2 weeks of intravenous treatment of the combination medication; OR 4.9, 95 % CI 1.6-15) and inadequate rifampin therapy (OR 5.4, 95 % CI 1.2-25).

CONCLUSIONS

Based on our results, extensive surgical debridement and adequate antibiotic therapy are needed to prevent the emergence of rifampin resistance.

Mutant prevention concentration-based pharmacokinetic/pharmacodynamic indices as dosing targets for suppressing the enrichment of levofloxacin-resistant subpopulations of Staphylococcus aureus

MIC- and mutant prevention concentration (MPC)-based pharmacokinetic/pharmacodynamic (PK/PD) indices were compared for suitability as attainment targets for restricting amplification of levofloxacin-resistant mutant subpopulations. When three Staphylococcus aureus strains were examined with a hollow-fiber PK/PD model, area under the concentration-time curve over 24 h (AUC24)/MPC values of >25 and maximum concentration of drug in serum (Cmax)/MPC values of >2.2 predicted resistance outcome among different isolates with an interisolate kappa coefficient of 1. MIC-based mutant-restrictive PK/PD values varied >8-fold and exhibited only a moderate interisolate agreement (kappa coefficient of 0.5). Thus, MPC-based PK/PD indices are more suitable than MIC-based indices for predicting mutant-restricting fluoroquinolone doses when multiple bacterial isolates are considered.

Novel approach for comparing the abilities of quinolones to restrict the emergence of resistant mutants during quinolone exposure

An agar-plate assay was adapted to examine aspects of quinolone structure that restrict the emergence of quinolone-mediated quinolone resistance. When Escherichia coli was applied to agar containing nalidixic acid, the number of quinolone-resistant mutants arising during incubation was decreased by raising the drug concentration and by mutations expected to block the induction of the SOS response (recA, lexA); the mutant number was increased by a mutator mutation (ung). The examination of four related fluoroquinolones then revealed that a C-8 methoxy group and an N-ethyl piperazine substituent at C-7 reduced mutant acquisition more effectively than C-8 H and C-7 C-ethyl piperazine groups. The fluoroquinolone that was most effective at restricting mutant acquisition was the most active when lethal activity was measured on agar plates or in liquid medium (as minimal bactericidal concentration). It also exhibited the lowest ratio of mutant MIC to wild-type MIC when it was tested with a set of isogenic gyrase mutants, and it had a low mutant prevention concentration (MPC) relative to MIC. However, a low MPC was less likely to be important in restricting the induced mutant accumulation because a fluoroquinolone N-ethyl piperazine substituent was more effective than a C-ethyl piperazine substituent at reducing mutant accumulation but was less effective at lowering the MPC. An 8-methoxy-quinazoline-2,4-dione was also effective at restricting the accumulation of resistant mutants on agar. Collectively, these data characterize a simple assay for detection of drug-mediated resistance that is sensitive to the structures of GyrA inhibitors. The assay provides a new method for screening quinolones and quinolone-like molecules that complements MPC-based tests for restricting the emergence of resistance.

Quinolones: action and resistance updated

The quinolones trap DNA gyrase and DNA topoisomerase IV on DNA as complexes in which the DNA is broken but constrained by protein. Early studies suggested that drug binding occurs largely along helix-4 of the GyrA (gyrase) and ParC (topoisomerase IV) proteins. However, recent X-ray crystallography shows drug intercalating between the -1 and +1 nucleotides of cut DNA, with only one end of the drug extending to helix-4. These two models may reflect distinct structural steps in complex formation. A consequence of drug-enzyme-DNA complex formation is reversible inhibition of DNA replication; cell death arises from subsequent events in which bacterial chromosomes are fragmented through two poorly understood pathways. In one pathway, chromosome fragmentation stimulates excessive accumulation of highly toxic reactive oxygen species that are responsible for cell death. Quinolone resistance arises stepwise through selective amplification of mutants when drug concentrations are above the MIC and below the MPC, as observed with static agar plate assays, dynamic in vitro systems, and experimental infection of rabbits. The gap between MIC and MPC can be narrowed by compound design that should restrict the emergence of resistance. Resistance is likely to become increasingly important, since three types of plasmid-borne resistance have been reported.

Use of gyrase resistance mutants to guide selection of 8-methoxy-quinazoline-2,4-diones

A series of 1-cyclopropyl-8-methoxy-quinazoline-2,4-diones was synthesized and evaluated for lowering the ratio of the antimicrobial MIC in gyrase resistance mutants to that in the gyr(+) (wild type) using isogenic strains of Escherichia coli. Dione features that lowered this ratio were a 3-amino group and C-7 ring structure (3-aminomethyl pyrrolidinyl < 3-aminopyrrolidinyl < diazobicyclo < 2-ethyl piperazinyl). The wild-type MIC was also lowered. With the most active derivative tested, many gyrA resistance mutant types were as susceptible as, or more susceptible than, wild-type cells. The most active 2,4-dione derivatives were also more active with two quinolone-resistant gyrB mutants than with wild-type cells. With respect to lethality, the most bacteriostatic 2,4-dione killed E. coli at a rate that was affected little by a gyrA resistance mutation, and it exhibited a rate of killing similar to its cognate fluoroquinolone at 10x the MIC. Population analysis with wild-type E. coli applied to agar showed that the mutant selection window for the most active 2,4-dione was narrower than that for the cognate fluoroquinolone or for ciprofloxacin. These data illustrate a new approach to guide early-stage antimicrobial selection. Use of antimutant activity (i.e., ratio of the antimicrobial MIC in a mutant strain to the antimicrobial MIC in a wild-type strain) as a structure-function selection criterion can be combined with traditional efforts aimed at lowering antimicrobial MICs against wild-type organisms to more effectively afford lead molecules with activity against both wild-type and mutant cells.

A unified anti-mutant dosing strategy

Antimicrobial dosing is currently attracting attention as a way to minimize the emergence of resistance. Three dose-based strategies have been advocated, each with shortcomings. Focus on killing susceptible cells overlooks resistant mutant subpopulations that may be present before treatment or generated during therapy; keeping therapeutic drug concentrations above the mutant prevention concentration (MPC; resistant mutant MIC) may be overly stringent; and dosage escalation modelling uses indirect estimates of resistant mutant subpopulation susceptibility (multiples of bulk population susceptibility, MIC) rather than direct estimates from MPC. The latter is significant because MPC and MIC are discordant with multiple pathogen isolates. Combining the strategies leads to MPC-based PK/PD thresholds (e.g. AUC(24)/MPC and t > MPC) for restricting resistant subpopulation enrichment and amplification. Using MPC-based thresholds to model dosing regimens that will restrict emergence of resistance requires generation of databases in which MPC is determined for many isolates.

Role of ceftazidime dose regimen on the selection of resistant Enterobacter cloacae in the intestinal flora of rats treated for an experimental pulmonary infection

OBJECTIVES

The effect of ceftazidime dosing increments and frequency of dosing on the selection of ceftazidime-resistant Enterobacter cloacae in the intestine was studied in rats, during treatment of a pulmonary infection caused by Klebsiella pneumoniae.

METHODS

Rats with pulmonary infection (n = 10 per group) received therapy with doses of ceftazidime at 3.1 to 400 mg/kg per day at a frequency of every 6,12 or 24 h for 18 days, starting 24 h after bacterial inoculation of the lung. Emergence of resistance in intestinal E. cloacae was monitored by culturing fresh stool specimens at days 0, 8, 15, 22, 29, 36 and 43 on agar plates with (6.4 mg/L) and without ceftazidime. Pharmacodynamic indices and time within the mutant selection window (MSW) were assessed in infected rats for each regimen. Ceftazidime-resistant E. cloacae mutants were characterized by determination of the beta-lactamase activity under cefoxitin-induced and non-induced conditions.

RESULTS

A reduction of intestinal ceftazidime-susceptible E. cloacae was observed and showed a significant correlation with the fAUC/MIC at days 8, 15 and 22 and with the fCmax on days 8, 15, 22, 29 and 36. More rats treated with 12-25 and 50-100 mg/kg per day every 6 h were found colonized with ceftazidime-resistant E. cloacae mutants than animals treated every 12 h or every 24 h. The proportion of rats colonized with ceftazidime-resistant E. cloacae mutants at days 15, 36 and 43 correlated with the time during which ceftazidime plasma concentrations were within the boundaries of the MSW. Only at day 15 was a correlation demonstrated between the fCmax and significantly fewer rats colonized with ceftazidime-resistant E. cloacae. Ceftazidime-resistant E. cloacae mutants (MIC >or= 128 mg/L) were characterized as stable derepressed mutants.

CONCLUSIONS

Colonization with stable derepressed ceftazidime-resistant E. cloacae mutants particularly occurred when rats were exposed to moderate doses of ceftazidime (12-25 or 50-100 mg/kg per day) administered every 6 h. Emergence of resistance was correlated with time within the MSW.

Mutant selection window hypothesis updated

The mutant selection window hypothesis postulates that, for each antimicrobial-pathogen combination, an antimicrobial concentration range exists in which selective amplification of single-step, drug-resistant mutants occurs. This hypothesis suggests an antimutant dosing strategy that is keyed to the upper boundary of the selection window: the mutant prevention concentration. Correlations are described between the mutant prevention concentration--a static parameter that is measured with agar plates--and fluctuating drug concentrations that restrict mutant amplification in vitro and in animals. When drug resistance is acquired stepwise, the mutant selection window increases, making the suppression of each successive mutant increasingly more difficult. For agents that kill drug-resistant mutants in a drug concentration-dependent manner, the use of the area under the 24-h time-drug concentration curve value divided by the value of the mutant prevention concentration is suggested as an index for designing antimutant dosing regimens. The need for such regimens is emphasized by a clinical example in which acquisition of drug resistance occurs concurrently with eradication of susceptible bacterial cells. These data support using the mutant selection window to optimize antimicrobial dosing regimens.