Phenotypic resistance of Staphylococcus aureus, selected Enterobacteriaceae, and Pseudomonas aeruginosa after single and multiple in vitro exposures to ciprofloxacin, levofloxacin, and trovafloxacin

Indole-based aryl sulfides target the cell wall of Staphylococcus aureus without detectable resistance

Sulfur-containing classes of the scaffold "Arylthioindoles" have been evaluated for antibacterial activity; they demonstrated excellent potency against methicillin-resistant Staphylococcus aureus (MRSA) as well as against vancomycin-resistant strains and a panel of clinical isolates of resistant strains. In this study, we have elucidated the mechanism of action of lead compounds, wherein they target the cell wall of S. aureus. Further, S. aureus failed to develop resistance against two lead compounds tested in a serial passage experiment in the presence of the compounds over a period of 40 days. Both the compounds demonstrated comparable in vivo efficacy with vancomycin in a neutropenic mice thigh infection model. The results of these antibacterial activities emphasize the excellent potential of thioethers for developing novel antibiotics and may fill in as a target for the adjustment of accessible molecules to develop new powerful antibacterial agents with fewer side effects.

UVC-LED-based face mask design and efficacy against common germs

During the Covid-19 pandemic, one of the best means of personal protection was using face masks. In this context, the World Health Organization has declared the attempts to produce masks inactivating airborne virus species a welcome initiative. This preliminary study aimed to prove that airborne germs passing through a mask filter cartridge can be destroyed by the rays emitted from UVC LEDs placed in such cartridge. We therefore designed such a face mask and tested the efficiency of UVC LEDs placed in its cartridge against common contaminants, gram-positive Staphylococcus aureus, gram-negative Pseudomonas aeruginosa, and the influenza A/Puerto Rico/8/1934 virus because of its similarity with SARS CoV-2. Eight UVC LEDs with a total power of 75 mW provided sufficient germicidal effect for all three germs. In terms of safety, ozone production released during UVC LED emission was negligible. Our findings are promising, as they show that well-designed UVC-based face masks can be effective against airborne germs, but further research on a greater sample may help us learn more and optimise such face masks.

Povidone-Iodine Fails to Eradicate Chronic Suppurative Otitis Media and Demonstrates Ototoxic Risk in Mice

HYPOTHESIS

Commercially available povidone-iodine solution can eliminate biofilms and persister cells rapidly in in vivo achievable concentrations without inducing ototoxicity.

BACKGROUND

Chronic suppurative otitis media (CSOM) is a substantial global problem. Current treatment options often induce a temporary remission without leading to a permanent cessation of symptoms secondary to the treatments' inability to eliminate persister cells. Povidone-iodine has been shown to be able to clear biofilm and planktonic cells in in vitro assays, but there are reports of ototoxic effects limiting its clinical utility.

METHODS

Bacterial and biofilm growth with quantification by spectrophotomer, murine auditory brainstem response (ABR), and distortion product otoacoustic emissions, immunohistochemistry, in vivo povidone-iodine treatment of murine CSOM, persister cell assay.

RESULTS

Commercially available 10% povidone-iodine solution is able to completely eradicate multiple clinical strains of Pseudomonas aeruginosa and Staphylococcus aureus in vitro with 10 minutes of exposure. Mice that have received a transtympanic injection of 1% povidone-iodine solution did not have significantly different auditory brainstem response or distortion product otoacoustic emission results compared with the control. Mice that received a povidone-iodine scrub or 10% povidone-iodine solution had significantly worsened hearing (25- and 13-dB increase in threshold, respectively; p < 0.05). In vivo CSOM infection recurred in all mice after the completion of treatment with 10% povidone-iodine solution, and there was no improvement in the bacterial load after treatment, indicating in vivo failure of therapy.

CONCLUSION

Povidone-iodine solution is effective at eliminating biofilm and persister cells in vitro at in vivo achievable concentrations but fails in vivo most likely because of kinetics of distribution in vivo. Even if drug distribution could be improved, the therapeutic window is likely to be too small given that the diluted solution does not have ototoxic potential, whereas while the scrub variant, which contains detergents, and the undiluted solution are ototoxic after a single treatment.

Comparative Studies to Uncover Mechanisms of Action of N-(1,3,4-Oxadiazol-2-yl)benzamide Containing Antibacterial Agents

Drug-resistant bacterial pathogens still cause high levels of mortality annually despite the availability of many antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA) is especially problematic, and the rise in resistance to front-line treatments like vancomycin and linezolid calls for new chemical modalities to treat chronic and relapsing MRSA infections. Halogenated N-(1,3,4-oxadiazol-2-yl)benzamides are an interesting class of antimicrobial agents, which have been described by multiple groups to be effective against different bacterial pathogens. The modes of action of a few N-(1,3,4-oxadiazol-2-yl)benzamides have been elucidated. For example, oxadiazoles KKL-35 and MBX-4132 have been described as inhibitors of trans-translation (a ribosome rescue pathway), while HSGN-94 was shown to inhibit lipoteichoic acid (LTA). However, other similarly halogenated N-(1,3,4-oxadiazol-2-yl)benzamides neither inhibit trans-translation nor LTA biosynthesis but are potent antimicrobial agents. For example, HSGN-220, -218, and -144 are N-(1,3,4-oxadiazol-2-yl)benzamides that are modified with OCF₃, SCF₃, or SF₅ and have remarkable minimum inhibitory concentrations ranging from 1 to 0.06 μg/mL against MRSA clinical isolates and show a low propensity to develop resistance to MRSA over 30 days. The mechanism of action of these highly potent oxadiazoles is however unknown. To provide insights into how these halogenated N-(1,3,4-oxadiazol-2-yl)benzamides inhibit bacterial growth, we performed global proteomics and RNA expression analysis of some essential genes of S. aureus treated with HSGN-220, -218, and -144. These studies revealed that the oxadiazoles HSGN-220, -218, and -144 are multitargeting antibiotics that regulate menaquinone biosynthesis and other essential proteins like DnaX, Pol IIIC, BirA, LexA, and DnaC. In addition, these halogenated N-(1,3,4-oxadiazol-2-yl)benzamides were able to depolarize bacterial membranes and regulate siderophore biosynthesis and heme regulation. Iron starvation appears to be part of the mechanism of action that led to bacterial killing. This study demonstrates that N-(1,3,4-oxadiazol-2-yl)benzamides are indeed privileged scaffolds for the development of antibacterial agents and that subtle modifications lead to changes to the mechanism of action.

Potent, specific MEPicides for treatment of zoonotic staphylococci

Coagulase-positive staphylococci, which frequently colonize the mucosal surfaces of animals, also cause a spectrum of opportunistic infections including skin and soft tissue infections, urinary tract infections, pneumonia, and bacteremia. However, recent advances in bacterial identification have revealed that these common veterinary pathogens are in fact zoonoses that cause serious infections in human patients. The global spread of multidrug-resistant zoonotic staphylococci, in particular the emergence of methicillin-resistant organisms, is now a serious threat to both animal and human welfare. Accordingly, new therapeutic targets that can be exploited to combat staphylococcal infections are urgently needed. Enzymes of the methylerythritol phosphate pathway (MEP) of isoprenoid biosynthesis represent potential targets for treating zoonotic staphylococci. Here we demonstrate that fosmidomycin (FSM) inhibits the first step of the isoprenoid biosynthetic pathway catalyzed by deoxyxylulose phosphate reductoisomerase (DXR) in staphylococci. In addition, we have both enzymatically and structurally determined the mechanism by which FSM elicits its effect. Using a forward genetic screen, the glycerol-3-phosphate transporter GlpT that facilitates FSM uptake was identified in two zoonotic staphylococci, Staphylococcus schleiferi and Staphylococcus pseudintermedius. A series of lipophilic ester prodrugs (termed MEPicides) structurally related to FSM were synthesized, and data indicate that the presence of the prodrug moiety not only substantially increased potency of the inhibitors against staphylococci but also bypassed the need for GlpT-mediated cellular transport. Collectively, our data indicate that the prodrug MEPicides selectively and robustly inhibit DXR in zoonotic staphylococci, and further, that DXR represents a promising, druggable target for future development.

Heritable nanosilver resistance in priority pathogen: a unique genetic adaptation and comparison with ionic silver and antibiotics

The past decade has seen the incorporation of antimicrobial nanosilver (NAg) into medical devices, and, increasingly, in everyday 'antibacterial' products. With the continued rise of antibiotic resistant bacteria, there are concerns that these priority pathogens will also develop resistance to the extensively commercialized nanoparticle antimicrobials. Herein, this work reports the emergence of stable resistance traits to NAg in the WHO-listed priority pathogen Staphylococcus aureus, which has previously been suggested to have no, or very low, capacity for silver resistance. With no native presence of genetically encoded silver defence mechanisms, the work showed that the bacterium is dependent on mutation of physiologically essential genes, including those involved in nucleotide synthesis and oxidative stress defence. While some mutations were uniquely associated with resistance to NAg, the study also found common mutations that could be protective against both NAg and ionic silver. This is consistent with the observation of NAg/ionic silver cross-resistance. These mutations were detected following withdrawal of the silver exposure, denoting heritable characteristics that allow for spread of the resistance traits even with discontinued silver use. Heritable silver resistance in priority pathogen cautions that these nanoparticle antimicrobials should only be used as needed, to preserve their efficacy for treating infections.

Adaptive Evolution of Escherichia coli to Ciprofloxacin in Controlled Stress Environments: Contrasting Patterns of Resistance in Spatially Varying versus Uniformly Mixed Concentration Conditions

A microfluidic gradient chamber (MGC) and a homogeneous batch culturing system were used to evaluate whether spatial concentration gradients of the antibiotic ciprofloxacin allow development of greater antibiotic resistance in Escherichia coli strain 307 (E. coli 307) compared to exclusively temporal concentration gradients, as indicated in an earlier study. A linear spatial gradient of ciprofloxacin and Luria-Bertani broth (LB) medium was established and maintained by diffusion over 5 days across a well array in the MGC, with relative concentrations along the gradient of 1.7-7.7× the original minimum inhibitory concentration (MIC_original). The E. coli biomass increased in wells with lower ciprofloxacin concentrations, and only a low level of resistance to ciprofloxacin was detected in the recovered cells (∼2× MIC_original). Homogeneous batch culture experiments were performed with the same temporal exposure history to ciprofloxacin concentration, the same and higher initial cell densities, and the same and higher nutrient (i.e., LB) concentrations as in the MGC. In all batch experiments, E. coli 307 developed higher ciprofloxacin resistance after exposure, ranging from 4 to 24× MIC_original in all replicates. Hence, these results suggest that the presence of spatial gradients appears to reduce the driving force for E. coli 307 adaptation to ciprofloxacin, which suggests that results from batch experiments may over predict the development of antibiotic resistance in natural environments.

Improvement of gram-negative susceptibility to fluoroquinolones after implementation of a pre-authorization policy for fluoroquinolone use: A decade-long experience

OBJECTIVE

Due to concerns over increasing fluoroquinolone (FQ) resistance among gram-negative organisms, our stewardship program implemented a preauthorization use policy. The goal of this study was to assess the relationship between hospital FQ use and antibiotic resistance.

DESIGN

Retrospective cohort.

SETTING

Large academic medical center.

METHODS

We performed a retrospective analysis of FQ susceptibility of hospital isolates for 5 common gram-negative bacteria: Acinetobacter spp., Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Primary endpoint was the change of FQ susceptibility. A Poisson regression model was used to calculate the rate of change between the preintervention period (1998-2005) and the postimplementation period (2006-2016).

RESULTS

Large rates of decline of FQ susceptibility began in 1998, particularly among P. aeruginosa, Acinetobacter spp., and E. cloacae. Our FQ restriction policy improved FQ use from 173 days of therapy (DOT) per 1,000 patient days to <60 DOT per 1,000 patient days. Fluoroquinolone susceptibility increased for Acinetobacter spp. (rate ratio [RR], 1.038; 95% confidence interval [CI], 1.005-1.072), E. cloacae (RR, 1.028; 95% CI, 1.013-1.044), and P. aeruginosa (RR, 1.013; 95% CI, 1.006-1.020). No significant change in susceptibility was detected for K. pneumoniae (RR, 1.002; 95% CI, 0.996-1.008), and the susceptibility for E. coli continued to decline, although the decline was not as steep (RR, 0.981; 95% CI, 0.975-0.987).

CONCLUSIONS

A stewardship-driven FQ restriction program stopped overall declining FQ susceptibility rates for all species except E. coli. For 3 species (ie, Acinetobacter spp, E. cloacae, and P. aeruginosa), susceptibility rates improved after implementation, and this improvement has been sustained over a 10-year period.

N-(1,3,4-oxadiazol-2-yl)benzamide analogs, bacteriostatic agents against methicillin- and vancomycin-resistant bacteria

Various reports of multidrug-resistant bacteria that are immune to all available FDA-approved drugs demand the development of novel chemical scaffolds as antibiotics. From screening a chemical library, we identified compounds with antibacterial activity. The most potent compounds, F6-5 and F6, inhibited growth of various drug-resistant Gram-positive bacterial pathogens at concentrations ranging from 1 μg/mL to 2 μg/mL. Both compounds were active against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-intermediate and vancomycin-resistant S. aureus (VISA and VRSA respectively) and vancomycin-resistant Enterococcus faecalis (VRE). Resistance generation experiments revealed that MRSA could develop resistance to the antibiotic ciprofloxacin but not to F6. Excitingly, F6 was found to be non-toxic against mammalian cells. In a mouse skin wound infection model, F6 was equipotent to the antibiotic fusidic acid in reducing MRSA burden.

Bacteriological profiling of diphenylureas as a novel class of antibiotics against methicillin-resistant Staphylococcus aureus

Bacterial resistance to antibiotics remains an imposing global public health challenge. Of the most serious pathogens, methicillin-resistant Staphylococcus aureus (MRSA) is problematic given strains have emerged that exhibit resistance to several antibiotic classes including β-lactams and agents of last resort such as vancomycin. New antibacterial agents composed of unique chemical scaffolds are needed to counter this public health challenge. The present study examines two synthetic diphenylurea compounds 1 and 2 that inhibit growth of clinically-relevant isolates of MRSA at concentrations as low as 4 µg/mL and are non-toxic to human colorectal cells at concentrations up to 128 μg/mL. Both compounds exhibit rapid bactericidal activity, completely eliminating a high inoculum of MRSA within four hours. MRSA mutants exhibiting resistance to 1 and 2 could not be isolated, indicating a low likelihood of rapid resistance emerging to these compounds. Bacterial cytological profiling revealed the diphenylureas exert their antibacterial activity by targeting bacterial cell wall synthesis. Both compounds demonstrate the ability to resensitize vancomycin-resistant Staphylococcus aureus to the effect of vancomycin. The present study lays the foundation for further investigation and development of diphenylurea compounds as a new class of antibacterial agents.

Bifunctional antimicrobial conjugates and hybrid antimicrobials

Covering: up to the end of 2016Novel antimicrobial drugs are continuously needed to counteract bacterial resistance development. An innovative molecular design strategy for novel antibiotic drugs is based on the hybridization of an antibiotic with a second functional entity. Such conjugates can be grouped into two major categories. In the first category (antimicrobial hybrids), both functional elements of the hybrid exert antimicrobial activity. Due to the dual targeting, resistance development can be significantly impaired, the pharmacokinetic properties can be superior compared to combination therapies with the single antibiotics, and the antibacterial potency is often enhanced in a synergistic manner. In the second category (antimicrobial conjugates), one functional moiety controls the accumulation of the other part of the conjugate, e.g. by mediating an active transport into the bacterial cell or blocking the efflux. This approach is mostly applied to translocate compounds across the cell envelope of Gram-negative bacteria through membrane-embedded transporters (e.g. siderophore transporters) that provide nutrition and signalling compounds to the cell. Such 'Trojan Horse' approaches can expand the antibacterial activity of compounds against Gram-negative pathogens, or offer new options for natural products that could not be developed as standalone antibiotics, e.g. due to their toxicity.

Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management

Staphylococcus aureus is a major human pathogen that causes a wide range of clinical infections. It is a leading cause of bacteremia and infective endocarditis as well as osteoarticular, skin and soft tissue, pleuropulmonary, and device-related infections. This review comprehensively covers the epidemiology, pathophysiology, clinical manifestations, and management of each of these clinical entities. The past 2 decades have witnessed two clear shifts in the epidemiology of S. aureus infections: first, a growing number of health care-associated infections, particularly seen in infective endocarditis and prosthetic device infections, and second, an epidemic of community-associated skin and soft tissue infections driven by strains with certain virulence factors and resistance to β-lactam antibiotics. In reviewing the literature to support management strategies for these clinical manifestations, we also highlight the paucity of high-quality evidence for many key clinical questions.

Evaluating synergy between marbofloxacin and gentamicin in Pseudomonas aeruginosa strains isolated from dogs with otitis externa

The aim of this study was to determine antimicrobial susceptibility of Pseudomonas aeruginosa strains to marbofloxacin and gentamicin, and investigate the possible synergistic, additive, indifferent or antagonistic effects between the two agents. P. aeruginosa strains can develop resistance quickly against certain antibiotics if used alone, thus the need emerges to find synergistic combinations. A total of 68 P. aeruginosa strains isolated from dogs were examined. In order to describe interactions between marbofloxacin and gentamicin the checkerboard microdilution method was utilized. The MICs (minimum inhibitory concentrations) for marbofloxacin and gentamicin were in the range 0.25-64 mg/L and 0.25-32 mg/L, respectively. The combination of marbofloxacin and gentamicin was more effective with a MIC range of 0.031-8 mg/L and a MIC90 of 1 mg/L, compared to 16 mg/L for marbofloxacin alone and 8 mg/L for gentamicin alone. The FIC (fractional inhibitory concentration) indices ranged from 0.0945 (pronounced synergy) to 1.0625 (indifference). Synergy between marbofloxacin and gentamicin was found in 33 isolates. The mean FIC index is 0.546, which represents a partial synergistic/additive effect close to the full synergy threshold. In vitro results indicate that marbofloxacin and gentamicin as partially synergistic agents may prove clinically useful in combination therapy against P. aeruginosa infections. Although marbofloxacin is not used in the human practice, the interactions between fluoroquinolones and aminoglycosides may have importance outside the veterinary field.

Exploiting adaptive laboratory evolution of Streptomyces clavuligerus for antibiotic discovery and overproduction

Adaptation is normally viewed as the enemy of the antibiotic discovery and development process because adaptation among pathogens to antibiotic exposure leads to resistance. We present a method here that, in contrast, exploits the power of adaptation among antibiotic producers to accelerate the discovery of antibiotics. A competition-based adaptive laboratory evolution scheme is presented whereby an antibiotic-producing microorganism is competed against a target pathogen and serially passed over time until the producer evolves the ability to synthesize a chemical entity that inhibits growth of the pathogen. When multiple Streptomyces clavuligerus replicates were adaptively evolved against methicillin-resistant Staphylococcus aureus N315 in this manner, a strain emerged that acquired the ability to constitutively produce holomycin. In contrast, no holomycin could be detected from the unevolved wild-type strain. Moreover, genome re-sequencing revealed that the evolved strain had lost pSCL4, a large 1.8 Mbp plasmid, and acquired several single nucleotide polymorphisms in genes that have been shown to affect secondary metabolite biosynthesis. These results demonstrate that competition-based adaptive laboratory evolution can constitute a platform to create mutants that overproduce known antibiotics and possibly to discover new compounds as well.

No decrease in susceptibility to NVC-422 in multiple-passage studies with methicillin-resistant Staphylococcus aureus, S. aureus, Pseudomonas aeruginosa, and Escherichia coli

Twenty-five serial passages of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus and 50 passages of methicillin-resistant Staphylococcus aureus resulted in no significant increase in NVC-422 MICs, while ciprofloxacin MICs increased 256-fold for E. coli and 32-fold for P. aeruginosa and S. aureus. Mupirocin, fusidic acid, and retapamulin MICs for MRSA increased 64-, 256-, and 16-fold, respectively. No cross-resistance to NVC-422 was observed with mupirocin-, fusidic acid-, and retapamulin-resistant strains.

Review: Staphylococcus aureus and MRSA in cystic fibrosis

BACKGROUND

Staphylococcus aureus (S. aureus) is one of the earliest bacteria detected in infants and children with cystic fibrosis (CF). The rise of methicillin resistant S. aureus (MRSA) in the last 10 years has caused a lot of attention to this organism.

RESULTS

The aim of this review is to provide a general overview of methicillin sensitive S. aureus (MSSA) and MRSA, discuss special aspects of S. aureus in cystic fibrosis, and to review treatment concepts. Microbiology of the organism will be reviewed along with data regarding the epidemiology of both MSSA and MRSA. Antibiotic treatments both in regards to acute management and eradication of MSSA and MRSA will be reviewed. Prophylaxis of MSSA in CF remains controversial. Treatment with anti-staphylococcal agents reduces the infection rate with MSSA but may lead to a higher rate of infection with P. aeruginosa. In regards to MRSA, there is a paucity of clinical data regarding approaches to eradication.

CONCLUSIONS

To advance the care of CF patients, controlled clinical trials are urgently needed to find the optimal approach to treating CF patients who are infected with either MSSA or MRSA.

Fluoroquinolone-resistant uncomplicated urinary tract infections, Chinese herbal medicine may provide help

We assessed the effects of Chinese herbs on the uncomplicated urinary tract infections (UTIs) in women caused by fluoroquinolone-resistant strains. A total of 56 pre-menopausal women with uncomplicated UTIs caused by fluoroquinolone-resistant strains were included. Urine cultures were carried out. All organisms were proved to be fluoroquinolone-resistant at baseline. The patients were orally administrated Chinese herbal concoction for ten days. Chinese herbal concoction eradicated the primary pathogen in 71.4% of the patients at the 1-week follow-up. Among the 20 patients who had bacteriologic failures in the Day 5 of treatment, 2 developed superinfection. Of the failures in the group, Proteus mirabilis, Staphylococcus epidermidis and Providencia rettgeri were implicated in 50.0%, 50.0% and 100.0% of the failures, respectively. The clinical outcomes were also good, with cure or improvement for more than 80% of all subjects. About 14% of the study subjects reported at least one potential adverse event. The adverse events most frequently reported were nausea and diarrhea. All patients tolerated the symptoms. The adverse reactions did not prevail after discontinuation of the medication. Chinese herbal therapy may be an acceptable alternative for the treatment of uncomplicated UTIs caused by fluoroquinolone-resistant uropathogens.

[Hospital fluoroquinolone prescription habits in northern France]

OBJECTIVE

The aim of the study was to assess the good use organization and fluoroquinolone prescription habits in cases of bone and joint, urinary, pulmonary, and digestive infections.

DESIGN

A declarative survey was made (questionnaire for the hospital and for the prescriber).

RESULTS

Thirty percent (44/145) of hospitals participated with 274 prescribers. Eighty percent had prescription protocols, 71 % of clinicians had access to epidemiologic data. A percentage of 30.7 (853/2,771) of prescriptions included a fluoroquinolone, 44.5 % (380/853) among these had not been recommended. The excessive prescription reached 24.4 % (116/474) in case of bone and joint infection, 14.6 % (107/731), and 20 % (157/779) in cases of digestive and respiratory infection respectively. Prescriptions for urinary infection were adequate in 47.6 % (375/787) of cases. Inadequate prescriptions were made because of bad knowledge of bacteria resistance epidemiology and pharmacology (insufficient dose, monotherapy at risk of selection), and non-application of good practice recommendations.

CONCLUSION

This study justifies the rationalization of antibiotic prescription.

Modification in prescribing practices for third-generation cephalosporins and ciprofloxacin is associated with a reduction in meticillin-resistant Staphylococcus aureus bacteraemia rate

To decrease the incidence of hospital infections caused by meticillin-resistant Staphylococcus aureus (MRSA), an educational intervention study was performed in which the use of intravenous ciprofloxacin and third-generation cephalosporins was discouraged. The effect was assessed by observing the MRSA bacteraemia rate both within the hospital and the intensive care unit for 18 months before, and 16 months after, the two-month intervention programme. MRSA bacteraemia rate throughout the hospital was reduced by 62.9% (P<0.001) by the end of the study and MRSA colonisation rate was reduced by 38.4% (not significant). There was no concomitant decrease in episodes of bacteraemia caused by meticillin-susceptible Staphylococcus aureus (MSSA) during the study period. There was a fall in hospital dispensing of both ciprofloxacin (80.4%) and third-generation cephalosporins (75.2%). The overall incidence of MRSA bloodstream infections within critical care was reduced (4.200 vs 0.272 per 1000 occupied bed-days) but this was not significant.

Risk factors associated with resistance to ciprofloxacin in clinical bacterial isolates from intensive care unit patients

OBJECTIVE

To determine risk factors and outcomes associated with ciprofloxacin resistance in clinical bacterial isolates from intensive care unit (ICU) patients.

DESIGN

Prospective cohort study.

SETTING

Twenty-bed medical-surgical ICU in a Canadian tertiary care teaching hospital.

PATIENTS

All patients admitted to the ICU with a stay of at least 72 hours between January 1 and December 31, 2003.

METHODS

Prospective surveillance to determine patient comorbidities, use of medical devices, nosocomial infections, use of antimicrobials, and outcomes. Characteristics of patients with a ciprofloxacin-resistant gram-negative bacterial organism were compared with characteristics of patients without these pathogens.

RESULTS

Ciprofloxacin-resistant organisms were recovered from 20 (6%) of 338 ICU patients, representing 38 (21%) of 178 nonduplicate isolates of gram-negative bacilli. Forty-nine percent of Pseudomonas aeruginosa isolates and 29% of Escherichia coli isolates were resistant to ciprofloxacin. In a multivariate analysis, independent risk factors associated with the recovery of a ciprofloxacin-resistant organism included duration of prior treatment with ciprofloxacin (relative risk [RR], 1.15 per day [95% confidence interval {CI}, 1.08-1.23]; P<.001), duration of prior treatment with levofloxacin (RR, 1.39 per day [95% CI, 1.01-1.91]; P=.04), and length of hospital stay prior to ICU admission (RR, 1.02 per day [95% CI, 1.01-1.03]; P=.005). Neither ICU mortality (15% of patients with a ciprofloxacin-resistant isolate vs 23% of patients with a ciprofloxacin-susceptible isolate; P=.58) nor in-hospital mortality (30% vs 34%; P=.81) were statistically significantly associated with ciprofloxacin resistance.

CONCLUSIONS

ICU patients are at risk of developing infections due to ciprofloxacin-resistant organisms. Variables associated with ciprofloxacin resistance include prior use of fluoroquinolones and duration of hospitalization prior to ICU admission. Recognition of these risk factors may influence antibiotic treatment decisions.

Community-acquired methicillin-resistant Staphylococcus aureus

Published data confirm that community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections are increasing in incidence in both urban and rural settings. The statistical risk is higher for athletes, military personnel, prison inmates, intravenous drug abusers, the homeless, children in daycare, and certain Native American groups, but the infections are by no means restricted to these populations. Roughly 85% of the infections involve the skin and subcutaneous tissue, with the most common presentations being an abscess or folliculitis. The typical associated gene cassette is quite small and codes only for methicillin resistance. Abscesses generally respond to drainage.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should recognize groups at high risk for community-acquired MSRA infections and manage these infections appropriately.

The anti-methicillin-resistant Staphylococcus aureus quinolone WCK 771 has potent activity against sequentially selected mutants, has a narrow mutant selection window against quinolone-resistant Staphylococcus aureus, and preferentially targets DNA gyrase

WCK 771 is a broad-spectrum fluoroquinolone with enhanced activity against quinolone-resistant staphylococci. To understand the impact of the target-level interactions of WCK 771 on its antistaphylococcal pharmacodynamic properties, we determined the MICs for genetically defined mutants and studied the mutant prevention concentrations (MPCs), the frequency of mutation, and the cidality against the wild type and double mutants. There was a twofold increase in the MICs of WCK 771 for single gyrA mutants, indicating that DNA gyrase is its primary target. All first- and second-step mutants selected by WCK 771 revealed gyrA and grlA mutations, respectively. The MICs of WCK 771 and clinafloxacin were found to be superior to those of other quinolones against strains with double and triple mutations. WCK 771 was also cidal for high-density double mutants at low concentrations. WCK 771 and clinafloxacin showed narrow mutant selection windows compared to those of the other quinolones. Against a panel of 50 high-level quinolone-resistant clinical isolates of staphylococci (ciprofloxacin MIC > or = 16 microg/ml), the WCK 771 MPCs were < or =2 microg/ml for 68% of the strains and < or =4 microg/ml for 28% of the strains. Our results demonstrate that gyrA is the primary target of WCK 771 and that it has pharmacodynamic properties remarkably different from those of quinolones with dual targets (garenoxacin and moxifloxacin) and topoisomerase IV-specific quinolones (trovafloxacin). WCK 771 displayed an activity profile comparable to that of clinafloxacin, a dual-acting quinolone with a high affinity to DNA gyrase. Overall, the findings signify the key role of DNA gyrase in determining the optimal antistaphylococcal features of quinolones.

Using interrupted time series analysis to assess associations of fluoroquinolone formulary changes with susceptibility of gram-negative pathogens and isolation rates of methicillin-resistant Staphylococcus aureus

The use of fluoroquinolones has been linked to increasing bacterial resistance and infection and/or colonization with already resistant pathogens both as a risk factor and based on volume of use. Changes in individual fluoroquinolones used in an institution may also be related to these clinical problems. Interrupted time series analysis, which allows for assessment of the associations of an outcome attributable to a specific event in time, was used to study the effect of changes in our hospital's fluoroquinolone formulary on fluoroquinolone susceptibility rates in select gram-negative pathogens and the methicillin-resistant Staphylococcus aureus (MRSA) isolation rate. Susceptibility rates to ciprofloxacin were considered for the period of 1993 through 2004, while the MRSA isolation rate was assessed from 1995 through 2004. Levofloxacin was added to the formulary in 1999, and gatifloxacin was substituted for levofloxacin in 2001. Statistically significant changes in the already declining rates of susceptibility of Pseudomonas aeruginosa (P, 0.042) and Escherichia coli (P, 0.004) to ciprofloxacin and in the already rising MRSA isolation rate (P, 0.001) were associated with the addition of levofloxacin to the formulary. Substitution of gatifloxacin for levofloxacin on the formulary was associated with reversals in the downward trend in E. coli susceptibility to ciprofloxacin and the upward trend in MRSA isolation rate. No associations were detected on susceptibility of Klebsiella pneumoniae or Proteus mirabilis to ciprofloxacin. These findings suggest that potential changes in susceptibility to fluoroquinolones and isolation of MRSA may vary by both drug and organism.

Évaluation de la relation consommation de fluoroquinolones et émergence de résistance chez Escherichia coli : rôles respectif et comparatif des études observationnelles et quasi expérimentales

The emergence of Escherichia coli (E. coli) resistance to fluoroquinolones (FQs) increased and spread gradually worldwide since the early 1990s. The selective pressure of FQs is the main mechanism responsible for the emergence of FQ resistance as shown by in vitro studies. Clinical trials are required to prove the causality between exposure to FQs and emergence of resistance. But this would not be ethical in humans. Non experimental studies must answer several principles to establish causality: association, anteriority, and directional change. We described and compared the contribution of observational and quasi-experimental studies implemented to answer several of these principles. Quasi-experimental studies using interventional models (ARIMA models with transfer function), can answer several of these principles, unlike observational studies. Thus, in addition to assessment of the association, they were able to show that the exposure to FQs precedes the emergence of FQ resistance to E. coli. They were also able to estimate the time necessary for the emergence of resistance and the dose effect, and to show if this association was reversible.

Pseudomonas aeruginosa, Staphylococcus aureus, and fluoroquinolone use

Increasingly resistant bacteria in sickle cell disease patients indicate need to evaluate extendedspectrum cephalosporin therapy.

Few long-term multicenter investigations have evaluated the relationships between aggregate antimicrobial drug use in hospitals and bacterial resistance. We measured fluoroquinolone use from 1999 through 2003 in a network of US hospitals. The percentages of fluoroquinolone-resistant Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) were obtained from yearly antibiograms at each hospital. Univariate linear regression showed significant associations between a hospital's volume of fluoroquinolone use and percent resistance in most individual study years (1999–2001 for P. aeruginosa, 1999–2002 for S. aureus). When the method of generalized estimating equations was used, a population-averaged longitudinal model incorporating total fluoroquinolone use and the previous year's resistance (to account for autocorrelation) did not show a significant effect of fluoroquinolone use on percent resistance for most drug-organism combinations, except for the relationship between levofloxacin use and percent MRSA. The ecologic relationship between fluoroquinolone use and resistance is complex and requires further study.

Hospital and Community Fluoroquinolone Use and Resistance in Staphylococcus aureus and Escherichia coli in 17 US Hospitals

BACKGROUND

Fluoroquinolones are widely prescribed in hospitals and the community. Previous studies have shown associations between fluoroquinolone use and isolation of fluoroquinolone-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA). We performed an ecologic-level study to determine whether variability in hospital percentages of fluoroquinolone-resistant E. coli and MRSA were associated with fluoroquinolone use in hospitals and their surrounding communities.

METHODS

We measured fluoroquinolone use in 17 US hospitals and their surrounding communities in the year 2000. Data on fluoroquinolone use in hospitals was electronically extracted from billing data. Data on fluoroquinolone use in communities was obtained from IMS health data for all prescriptions filled in pharmacies within a 16-km radius of each hospital. We used hospital antibiograms to determine the percentage of isolates that were fluoroquinolone-resistant E. coli and MRSA, and we performed linear regression to determine the relationship between percentage of resistant isolates and fluoroquinolone use in hospitals and their surrounding communities.

RESULTS

There was a significant association between total fluoroquinolone use within hospitals and percentage of S. aureus isolates that were MRSA (r=0.77; P=.0003) and between total fluoroquinolone use in the community and percentage of E. coli isolates that were fluoroquinolone-resistant E. coli (r=0.68; P=.003). Population density within the 16-km radius also correlated with MRSA percentage (r=0.57; P=.015) and fluoroquinolone-resistant E. coli percentage (r=0.85; P=.002), but associations between total fluoroquinolone use and resistance remained significant after adjustment for population density.

CONCLUSIONS

In this ecologic analysis, we found associations between fluoroquinolone use in hospitals and methicillin resistance in S. aureus and between fluoroquinolone use in communities and fluoroquinolone resistance in E. coli in hospitals. Antimicrobial use in hospitals and communities may have different relative importance with regard to resistance in different pathogens encountered in hospitals.

Pharmacodynamic modeling of the evolution of levofloxacin resistance in Staphylococcus aureus

Previously, we demonstrated the importance of low-level-resistant variants to the evolution of resistance in Staphylococcus aureus exposed to ciprofloxacin in an in vitro system and developed a pharmacodynamic model which predicted the emergence of resistance. Here, we examine and model the evolution of resistance to levofloxacin in S. aureus exposed to simulated levofloxacin pharmacokinetic profiles. Enrichment of subpopulations with mutations in grlA and low-level resistance varied with levofloxacin exposure. A regimen producing average steady-state concentrations (Cavg ss) just above the MIC selected grlA mutants with up to 16-fold increases in the MIC and often additional mutations in grlA/grlB and gyrA. A regimen providing Cavg ss between the MIC and the mutant prevention concentration (MPC) suppressed bacterial numbers to the limit of detection and prevented the appearance of bacteria with additional mutations or high-level resistance. Regimens producing Cavg ss above the MPC appeared to eradicate low-level-resistant variants in the cultures and prevent the emergence of resistance. There was no relationship between the time concentrations remained between the MIC and the MPC and the degree of resistance or the presence or type of mutations that appeared in grlA/B or gyrA. Our pharmacodynamic model described the growth and levofloxacin killing of the parent strains and the most resistant grlA mutants in the starting cultures and correctly predicted conditions that enrich subpopulations with low-level resistance. These findings suggest that the pharmacodynamic model has general applicability for describing fluoroquinolone resistance in S. aureus and further demonstrate the importance of low-level-resistant variants to the evolution of resistance.

In vitro selection of resistance in Pseudomonas aeruginosa and Acinetobacter spp. by levofloxacin and ciprofloxacin alone and in combination with β-lactams and amikacin

OBJECTIVES

The aim of this study was to evaluate the ability of levofloxacin and ciprofloxacin alone and in combination with either ceftazidime, cefepime, imipenem, piperacillin-tazobactam or amikacin to select for antibiotic-resistant mutants of Pseudomonas aeruginosa and Acinetobacter spp.

METHODS

Clinical strains of P. aeruginosa (n = 5) and Acinetobacter spp. (n = 5) susceptible to all the drugs used in the study were assayed. Development of resistance was determined by multi-step and single-step methodologies. For multi-step studies, MICs were determined after five serial passages on antibiotic-gradient plates containing each antibiotic alone or in combination with levofloxacin or ciprofloxacin. Acquisition of resistance was defined as an increase of >or=4-fold from the starting MIC. In single-step studies, the frequency of spontaneous mutations was calculated after a passage on plates containing antibiotics alone and in combinations at concentrations equal to the highest NCCLS breakpoints.

RESULTS

Serial passages on medium containing single antibiotics resulted in increased MICs for each antibiotic; MIC increases were limited by antibiotics in combination. A decrease in the number of strains with MICs above the NCCLS breakpoints occurred when fluoroquinolones were combined with a second antibiotic for both P. aeruginosa and Acinetobacter spp. isolates. Frequencies of mutation were higher for antibiotics alone than for combinations.

CONCLUSIONS

Use of combinations of fluoroquinolones with beta-lactams and amikacin reduces the risk for in vitro selection of resistant P. aeruginosa and Acinetobacter spp.

Pharmacodynamic modeling of ciprofloxacin resistance in Staphylococcus aureus

Three pharmacodynamic models of increasing complexity, designed for two subpopulations of bacteria with different susceptibilities, were developed to describe and predict the evolution of resistance to ciprofloxacin in Staphylococcus aureus by using pharmacokinetic, viable count, subpopulation, and resistance mechanism data obtained from in vitro system experiments. A two-population model with unique growth and killing rate constants for the ciprofloxacin-susceptible and -resistant subpopulations best described the initial killing and subsequent regrowth patterns observed. The model correctly described the enrichment of subpopulations with low-level resistance in the parent cultures but did not identify a relationship between the time ciprofloxacin concentrations were in the mutant selection window (the interval between the MIC and the mutant prevention concentration) and the enrichment of these subpopulations. The model confirmed the importance of resistant variants to the emergence of resistance by successfully predicting that resistant subpopulations would not emerge when a low-density culture, with a low probability of mutants, was exposed to a clinical dosing regimen or when a high-density culture, with a higher probability of mutants, was exposed to a transient high initial concentration designed to rapidly eradicate low-level resistant grlA mutants. The model, however, did not predict or explain the origin of variants with higher levels of resistance that appeared and became the predominant subpopulation during some experiments or the persistence of susceptible bacteria in other experiments where resistance did not emerge. Continued evaluation of the present two-population pharmacodynamic model and development of alternative models is warranted.

Evolution of ciprofloxacin-resistant Staphylococcus aureus in in vitro pharmacokinetic environments

The development of novel antibacterial agents is decreasing despite increasing resistance to presently available agents among common pathogens. Insights into relationships between pharmacodynamics and resistance may provide ways to optimize the use of existing agents. The evolution of resistance was examined in two ciprofloxacin-susceptible Staphylococcus aureus strains exposed to in vitro-simulated clinical and experimental ciprofloxacin pharmacokinetic profiles for 96 h. As the average steady-state concentration (C(avg ss)) increased, the rate of killing approached a maximum, and the rate of regrowth decreased. The enrichment of subpopulations with mutations in grlA and low-level ciprofloxacin resistance also varied depending on the pharmacokinetic environment. A regimen producing values for C(avg ss) slightly above the MIC selected resistant variants with grlA mutations that did not evolve to higher levels of resistance. Clinical regimens which provided values for C(avg ss) intermediate to the MIC and mutant prevention concentration (MPC) resulted in the emergence of subpopulations with gyrA mutations and higher levels of resistance. A regimen producing values for C(avg ss) close to the MPC selected grlA mutants, but the appearance of subpopulations with higher levels of resistance was diminished. A regimen designed to maintain ciprofloxacin concentrations entirely above the MPC appeared to eradicate low-level resistant variants in the inoculum and prevent the emergence of higher levels of resistance. There was no relationship between the time that ciprofloxacin concentrations remained between the MIC and the MPC and the degree of resistance or the presence or type of ciprofloxacin-resistance mutations that appeared in grlA or gyrA. Regimens designed to eradicate low-level resistant variants in S. aureus populations may prevent the emergence of higher levels of fluoroquinolone resistance.

Predicting hospital rates of fluoroquinolone-resistant Pseudomonas aeruginosa from fluoroquinolone use in US hospitals and their surrounding communities

Rates of fluoroquinolone resistance among Pseudomonas aeruginosa in hospitals are increasing, but interhospital variability is great. We sought to determine whether this variability correlated to fluoroquinolone use in hospitals and in the surrounding community. Hospital quinolone use in 1999 (24 hospitals) through 2001 (35 hospitals) was determined from billing records. The number of fluoroquinolone prescriptions within a 10-mile (approximately 16-km) radius of each hospital was determined for 1999 and 2000. Hospital fluoroquinolone use increased from 1999 through 2001, from 137 to 163 defined daily doses (DDD)/1000 patient-days (P=.01). The rate of community fluoroquinolone use also increased, from 2.3 to 2.8 DDD/1000 inhabitant-days (P<.001). Rates of fluoroquinolone-resistant P. aeruginosa increased from 29% in 1999 to 36% in 2001 (P=.003). Both community and hospital fluoroquinolone use were predictive of rates of fluoroquinolone-resistant P. aeruginosa. Levofloxacin was associated with resistance, but ciprofloxacin was not. Most of the variability in resistance rates is explained by volume of fluoroquinolone use, both in the hospital and the surrounding community.

Evaluation of antibiotic-loaded collagen-hyaluronic acid matrix as a skin substitute

The 1-ethyl-(3-3-dimethylaminopropyl) carbodiimide hydrochloride-crosslinked collagen-hyaluronic acid (HA) matrices containing tobramycin or ciprofloxacin as an antibiotic agent were fabricated for the control of wound contamination and characterized with respect to morphology, mechanical strength, in vitro release, antibacterial activity and cytotoxicity. For the tobramycin loaded matrix, the antibacterial capacity increased with the drug loading. Tobramycin and ciprofloxacin loaded matrices maintained their antibacterial effects for over 96 and 48 h, respectively. However, cell viability testing revealed that 0.4 mg/ml of ciprofloxacin has a cytotoxic effect on fetal human dermal fibroblasts. The effects of the bilayered collagen-HA matrices containing tobramycin and growth factors were also evaluated using an in vivo full thickness dermal defect model. Though the tobramycin incorporated collagen-HA matrix had no significant effect on wound healing compared with the control, the tobramycin incorporated matrix containing basic fibroblast growth factor or platelet-derived growth factor significantly enhanced wound healing. This study demonstrates the potential efficacy of crosslinked collagen-HA matrix containing antibiotics and growth factors for defective skin tissue replacement and infection prevention.

The magnitude of the association between fluoroquinolone use and quinolone-resistant Escherichia coli and Klebsiella pneumoniae may be lower than previously reported

Case-control analyses of resistant versus susceptible isolates have implicated fluoroquinolone exposure as a strong risk factor for fluoroquinolone-resistant isolates of Enterobacteriaceae. We suspect that such methodology may overestimate this association. A total of 84 cases with fluoroquinolone-resistant isolates and 578 cases with fluoroquinolone-susceptible isolates of Escherichia coli or Klebsiella pneumoniae were compared with 608 hospitalized controls in parallel multivariable analyses. For comparison of previous estimates, the results of 10 published case-control studies of risk for fluoroquinolone resistance in isolates of Enterobacteriaceae were pooled by using a random-effects model. Exposure to fluoroquinolones was significantly positively associated with fluoroquinolone resistance (odds ratio [OR], 3.17) and negatively associated with fluoroquinolone susceptibility (OR, 0.18). Multivariable analyses yielded similar estimates (ORs, 2.04 and 0.10, respectively). As data on antibiotic exposure were limited to inpatient prescriptions, misclassification of fluoroquinolone exposure in persons who received fluoroquinolones as outpatients may have led to an underestimation of the true effect size. Pooling the results of previously published studies in which a direct comparison of fluoroquinolone-resistant and fluoroquinolone-susceptible cases was used resulted in a markedly higher effect estimate (OR, 18.7). Had we directly compared resistant and susceptible cases, our univariate OR for the association between fluoroquinolone use and the isolation of resistant Enterobacteriaceae would have been 19.3, and the multivariate OR would have been 16.5. Fluoroquinolone use is significantly associated with the isolation of fluoroquinolone-resistant Enterobacteriaceae; however, previous studies likely exaggerated the magnitude of this association.

Influence of the cell wall on ciprofloxacin susceptibility in selected wild-type Gram-negative and Gram-positive bacteria

The susceptibility of several wild-type bacteria to ciprofloxacin and accumulation of the drug in these bacteria were evaluated. Species studied included Escherichia coli, Serratia marcescens, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis and Bacillus cereus. Ciprofloxacin susceptibility was measured for each strain using two different methods: the minimal inhibitory concentration and the bactericidal index. Significant differences were observed between the results derived from these two methods. Whereas the minimal inhibitory concentration was low in all strains tested, ciprofloxacin's bactericidal activity, as indicated by the bactericidal index, varied with the species studied. To determine whether this finding was due to variations in cell envelope permeability to ciprofloxacin (i.e. to combined cell uptake and efflux), we studied ciprofloxacin accumulation using spectrofluorometry. In Gram-negative bacteria, differences in permeability can lead to altered susceptibility to antibiotics. In fact, the combination of slow uptake and efficient efflux seems to be crucial to the characteristic poor susceptibility of P. aeruginosa to ciprofloxacin. However, the low level of activity of ciprofloxacin against S. aureus and two Bacillus species may have resulted from the drug's interaction with its target enzymes (i.e. topoisomerase IV in S. aureus and DNA gyrase in Bacillus spp.) rather than diminished permeability.

BpeAB-OprB, a multidrug efflux pump in Burkholderia pseudomallei

Burkholderia pseudomallei, the causative agent of melioidosis, is intrinsically resistant to a wide range of antimicrobial agents, including beta-lactams, aminoglycosides, macrolides, and polymyxins. An operon, bpeR-bpeA-bpeB-oprB, which encodes a putative repressor, a membrane fusion protein, an inner membrane protein, and an outer membrane protein, respectively, of a multidrug efflux pump of the resistance-nodulation-division family was identified in B. pseudomallei. The divergently transcribed bpeR gene encodes a putative repressor protein of the TetR family which probably regulates the expression of the bpeAB-oprB gene cluster. Comparison of the MICs and minimal bactericidal concentrations of antimicrobials for bpeAB deletion mutant KHW Delta bpeAB and its isogenic wild-type parent, KHW, showed that the B. pseudomallei BpeAB-OprB pump is responsible for the efflux of the aminoglycosides gentamicin and streptomycin, the macrolide erythromycin, and the dye acriflavine. Antibiotic efflux by the BpeAB-OprB pump was dependent on a proton gradient and differs from that by the AmrAB-OprA pump in that it did not efflux the aminoglycoside spectinomycin or the macrolide clarithromycin. The broad-spectrum efflux pump inhibitor MC-207,110 did not potentiate the effectiveness of the antimicrobials erythromycin and streptomycin in B. pseudomallei.

Role of oral antimicrobial therapy in the management of osteomyelitis

PURPOSE OF REVIEW

Medical therapy of chronic osteomyelitis is largely based on experimental models, historical observational or non-randomized studies, and expert opinions. A minimum of 4-6 weeks of intravenous antimicrobial therapy targeting the causative organism, given in conjunction with surgery, has become the standard for chronic long-bone osteomyelitis in adults. Given the expense, inconvenience, and potential complications inherent to such a treatment program, alternative strategies including effective oral antimicrobial regimens are desirable.

RECENT FINDINGS

Several oral antimicrobial agents have undergone evaluation for the treatment of acute and chronic osteomyelitis recently. These include fluoroquinolones, clindamycin, and linezolid. For the treatment of atypical causes of Gram-positive osteomyelitis, other oral therapies have been evaluated with reported success in small numbers of patients.

SUMMARY

The standard of care for chronic osteomyelitis in adults remains intravenous antimicrobial therapy, in combination with surgery, for at least 4-6 weeks. Acute osteomyelitis in the pediatric population as well as osteomyelitis caused by atypical Gram-positive organisms and some Gram-negative organisms may be treated successfully with oral antibiotics. Some antimicrobials have equivalent concentration in serum whether administered orally or parenterally. When therapy with these antimicrobials is indicated, the oral route is preferred in compliant patients. As research continues in this area and as new drug formulations are developed, oral therapy may become an accepted alternative in additional selected patients.

Selection and characterization of fluoroquinolone-resistant mutants of Campylobacter jejuni using enrofloxacin

Significant levels of fluoroquinolone resistance were obtained in Campylobacterjejuni isolates after an unique step of selection using enrofloxacin. An Asp90-to-Asn and a Thr86-to-Ile change in the gyrase subunit GyrA were found associated with a low (MIC < or = 8 /microg/ml) or a high (MIC > or = 16 microg/ml) level of resistance to ciprofloxacin, respectively. An association of both mutations conferred a higher level of resistance (MIC > or = 128 microg/ml). Further steps of selection increased the MICs of fluoroquinolones but did not result in a multiple antibiotic resistance phenotype. The Thr86-to-Ile change was found to confer different levels of resistance, pointing out other mechanisms of resistance. However, sequencing revealed no mutation in gyrB, and several attempts did not enable any amplification of the parC gene coding for topoisomerase IV, suggesting an absence of this secondary target in C. jejuni. In addition, no difference in the major outer membrane protein expression was found among the isolates. Furthermore, the use of the recently identified efflux pump inhibitor Phe-Arg-beta-naphthylamide did not result in a significant decrease of fluoroquinolone MICs or change in the frequency of isolation of enrofloxacin-resistant mutants, and thus appears ineffective against fluoroquinolone-resistant C. jejuni isolates. Results obtained during ciprofloxacin accumulation studies confirmed that efflux probably plays a minor role in fluoroquinolone resistance of C. jejuni.

Emergence of phenotypic resistance to ciprofloxacin and levofloxacin in methicillin-resistant and methicillin-sensitive Staphylococcus aureus strains

The emergence of phenotypic resistance to ciprofloxacin and levofloxacin in methicillin-sensitive and methicillin-resistant Staphylococcus aureus (MRSA) strains was studied. Twenty MRSA and 77 methicillin-sensitive S.aureus (MSSA) strains susceptible to both quinolones were investigated for resistance after single step or serial passages. No growth of 20 MRSA strains was observed at 4xMIC of levofloxacin after 48 h incubation, but 4 of 77 (5%) MSSA strains grew at the same concentration. At 4xMIC concentration of ciprofloxacin, 10 MSSA (13%) and five MRSA (25%) strains were grown. In the serial passages of MRSA strains, resistance to ciprofloxacin was 75 and 5% for levofloxacin by the third passage. In the seventh passage this resistance was 100 and 15%, respectively. In MSSA strains, resistance to ciprofloxacin was 75 and 19% to levofloxacin at the third passage and at the seventh passage, 100 and 61%, respectively. Emergence of ciprofloxacin resistance was more common and developed more rapidly than resistance to levofloxacin in both MRSA and MSSA strains.

Maintaining fluoroquinolone class efficacy: review of influencing factors

Previous experience with antimicrobial resistance has emphasized the importance of appropriate stewardship of these pharmacotherapeutic agents. The introduction of fluoroquinolones provided potent new drugs directed primarily against gram-negative pathogens, while the newer members of this class demonstrate more activity against gram-positive species, including Streptococcus pneumoniae. Although these agents are clinically effective against a broad range of infectious agents, emergence of resistance and associated clinical failures have prompted reexamination of their use. Appropriate use revolves around two key objectives: 1) only prescribing antimicrobial therapy when it is beneficial and 2) using the agents with optimal activity against the expected pathogens. Pharmacodynamic principles and properties can be applied to achieve the latter objective when prescribing agents belonging to the fluoroquinolone class. A focused approach emphasizing "correct-spectrum" coverage may reduce development of antimicrobial resistance and maintain class efficacy.