Comparison of the Respiratory Resistomes and Microbiota in Children Receiving Short versus Standard Course Treatment for Community-Acquired Pneumonia.

Pediatric community-acquired pneumonia (CAP) is often treated with 10 days of antibiotics. Shorter treatment strategies may be effective and lead to less resistance. The impact of duration of treatment on the respiratory microbiome is unknown. Data are from children (n = 171), ages 6 to 71 months, enrolled in the SCOUT-CAP trial (NCT02891915). Children with CAP were randomized to a short (5 days) versus standard (10 days) beta-lactam treatment strategy. Throat swabs were collected at enrollment and the end of the study and used for shotgun metagenomic sequencing. The number of beta-lactam and multidrug efflux resistance genes per prokaryotic cell (RGPC) was significantly lower in children receiving the short compared to standard treatment strategy at the end of the study (Wilcoxon rank sum test, P < 0.05 for each). Wilcoxon effect sizes were small for beta-lactam (r: 0.15; 95% confidence interval [CI], 0.01 to 0.29) and medium for multidrug efflux RGPC (r: 0.23; 95% CI, 0.09 to 0.37). Analyses comparing the resistome at the beginning and end of the trial indicated that in contrast to the standard strategy group, the resistome significantly differed in children receiving the short course strategy. Relative abundances of commensals such as Neisseria subflava were higher in children receiving the standard strategy, and Prevotella species and Veillonella parvula were higher in children receiving the short course strategy. We conclude that children receiving 5 days of beta-lactam therapy for CAP had a significantly lower abundance of antibiotic resistance determinants than those receiving standard 10-day treatment. These data provide an additional rationale for reductions in antibiotic use when feasible. IMPORTANCE Antibiotic resistance is a major threat to public health. Treatment strategies involving shorter antibiotic courses have been proposed as a strategy to lower the potential for antibiotic resistance. We examined relationships between the duration of antibiotic treatment and its impact on resistance genes and bacteria in the respiratory microbiome using data from a randomized controlled trial of beta-lactam therapy for pediatric pneumonia. The randomized design provides reliable evidence of the effectiveness of interventions and minimizes the potential for confounding. Children receiving 5 days of therapy for pneumonia had a lower prevalence of two different types of resistance genes than did those receiving the 10-day treatment. Our data also suggest that children receiving longer durations of therapy have a greater abundance of antibiotic resistance genes for a longer period of time than do children receiving shorter durations of therapy. These data provide an additional rationale for reductions in antibiotic use.

White Paper: Developing Antimicrobial Drugs for Resistant Pathogens, Narrow-Spectrum Indications, and Unmet Needs.

Despite progress in antimicrobial drug development, a critical need persists for new, feasible pathways to develop antibacterial agents to treat people infected with drug-resistant bacteria. Infections due to resistant gram-negative bacilli continue to cause unacceptable morbidity and mortality rates. Antibacterial agents have been historically studied in noninferiority clinical trials that focus on a single site of infection (eg, complicated urinary tract infections, intra-abdominal infections), yet these designs may not be optimal, and often are not feasible, for study of infections caused by drug-resistant bacteria. Over the past several years, multiple stakeholders have worked to develop consensus regarding paths forward with a goal of facilitating timely conduct of antimicrobial development. Here we advocate for a novel and pragmatic approach and, toward this end, present feasible trial designs for antibacterial agents that could enable conduct of narrow-spectrum, organism-specific clinical trials and ultimately approval of critically needed new antibacterial agents.

Cefazolin versus Nafcillin for Methicillin-Sensitive Staphylococcus aureus Bloodstream Infection in a California Tertiary Medical Center.

Recent observational studies have suggested possible reductions in mortality in patients receiving cefazolin versus antistaphylococcal penicillins. We examined 90-day mortality in patients receiving cefazolin compared to nafcillin for methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infection (BSI). We identified persons with MSSA BSI admitted to San Francisco General Hospital from January 2008 to July 2013 through a hospital-wide infection surveillance system and confirmed 90-day mortality using U.S. national vital registries. We included persons receiving cefazolin or nafcillin as the predominant intravenous antimicrobial agent; all participants received inpatient Infectious Diseases service consultation. We estimated the association between receipt of cefazolin and 90-day risk of death by multivariate logistic regression, including a propensity score for receiving cefazolin as the second predictor. Of 230 MSSA BSI cases, 30 received nafcillin and 70 received cefazolin as the predominant antimicrobial; 10 died within 90 days, 5 from each group. Unadjusted analysis showed substantial but not statistically significant reduced odds of death in those receiving cefazolin (odds ratio, 0.38; 95% confidence interval [CI], 0.10 to 1.44). Multivariate analysis with propensity scores found a similar adjusted odds ratio (0.40; 95% CI, 0.09 to 1.74; P = 0.22). We found a large reduction in 90-day mortality in those receiving cefazolin compared to nafcillin for MSSA BSI, but this finding was not statistically significant. The magnitude of effect seen in this and other studies justifies further study.

Ceftobiprole is superior to vancomycin, daptomycin, and linezolid for treatment of experimental endocarditis in rabbits caused by methicillin-resistant Staphylococcus aureus.

Beta lactam agents are the most active drugs for the treatment of streptococci and methicillin-susceptible Staphylococcus aureus endocarditis. However, methicillin-resistant S. aureus (MRSA) is resistant to all beta lactam agents licensed to date, and alternative treatments are limited. Ceftobiprole is a novel broad-spectrum cephalosporin that binds with high affinity to PBP 2a, the penicillin binding protein that mediates the methicillin resistance of staphylococci and is active against MRSA. Ceftobiprole was compared to vancomycin, daptomycin, and linezolid in a rabbit model of MRSA aortic valve endocarditis caused by the homogeneously methicillin-resistant laboratory strain COL. Residual organisms in vegetations were significantly fewer in ceftobiprole-treated rabbits than in any other treatment group (P<0.05 for each comparison). In addition, the numbers of organisms in spleens and in kidneys were significantly lower in ceftobiprole-treated rabbits than in linezolid- and vancomycin-treated animals (P<0.05 for each comparison). Anti-MRSA beta lactam agents such as ceftobiprole may represent a significant therapeutic advance over currently available agents for the treatment of MRSA endocarditis.

Relationship between susceptibility to daptomycin in vitro and activity in vivo in a rabbit model of aortic valve endocarditis.

Daptomycin is approved for treatment of Staphylococcus aureus bacteremia and right-sided endocarditis. Increases in daptomycin MICs have been associated with failure. A rabbit model of aortic valve endocarditis was used to determine whether MIC correlates with activity in vivo and whether a higher daptomycin dose can improve efficacy. Two related clinical S. aureus strains, one with a daptomycin MIC of 0.5 microg/ml and the other with a MIC of 2 microg/ml, were used to establish aortic valve endocarditis in rabbits. Daptomycin was administered once a day for 4 days at 12 mg/kg of body weight or 18 mg/kg to simulate doses in humans of 6 mg/kg and 10 mg/kg, respectively. Endocardial vegetations, spleens, and kidneys were harvested and quantitatively cultured. The strain with a MIC of 2 microg/ml had a survival advantage over the strain with a MIC of 0.5 microg/ml with >100 times more organisms of the former in endocardial vegetations at the 12-mg/kg dose in a dual-infection model. Both the 12-mg/kg dose and the 18-mg/kg dose completely eradicated the strain with a MIC of 0.5 from vegetations, spleens, and kidneys. The 12-mg/kg dose was ineffective against the strain with a MIC of 2 in vegetations; the 18-mg/kg dose produced a reduction of 3 log(10) units in CFU in vegetations compared to the controls, although in no rabbit were organisms completely eliminated. Increasing the dose of daptomycin may improve its efficacy for infections caused by strains with reduced daptomycin susceptibility.

Ceftobiprole: in-vivo profile of a bactericidal cephalosporin.

Resistance to antimicrobials is a significant and growing problem, limiting treatment options, especially for serious Gram-positive infections. Ceftobiprole is a novel broad-spectrum cephalosporin that is active in vitro against streptococci and staphylococci, including penicillin-resistant strains of pneumococci and methicillin-resistant Staphylococcus aureus (MRSA). It maintains the activity of extended-spectrum cephalosporins against Gram-negative bacteria, including Enterobacteriaceae. The in-vivo activity of ceftobiprole has been demonstrated in mouse sepsis and subcutaneous abscess models of infection. Its activity also has been examined in several discriminative models of infection that mimic specific diseases in humans and permit testing of antimicrobial activity under a variety of defined pharmacokinetic conditions. These include experimental pneumonia in mice, a tissue cage model of foreign body infection in rats, and endocarditis models in rats and rabbits. In these models, ceftobiprole exhibits activity equivalent or superior to that of comparators against MRSA, including vancomycin-intermediate strains. These models also confirm the in-vivo activity of ceftobiprole against Gram-negative bacteria that are susceptible in vitro. The results from animal models support the evaluation of the clinical efficacy of ceftobiprole in humans and also predict clinical efficacy in the empirical treatment of severe infections. The broad spectrum of activity may allow ceftobiprole to be used as monotherapy for serious hospital-acquired infections where combination therapy would otherwise be required.

Identifying pulmonary tuberculosis in patients with negative sputum smear results.

BACKGROUND: Clinicians need to decide whether to begin empiric therapy for patients who are suspected of having tuberculosis (TB) but have negative sputum smear results. Culture results may take weeks, and delaying treatment may allow further transmission of disease. STUDY OBJECTIVE: To identify the clinical, demographic, and radiographic characteristics that identify smear-negative patients who have TB, and to create a TB prediction rule. DESIGN: Retrospective chart review. SETTING: University-affiliated public hospital in San Francisco, CA, between 1993 and 1998. PATIENTS: Forty-seven patients with TB and 141 control patients who were hospitalized with a suspicion of pulmonary TB; all had negative sputum smear results. MEASUREMENTS AND RESULTS: Demographic, clinical, and radiographic variables were determined by chart review. In multivariate analysis, a positive tuberculin skin test result (odds ratio [OR], 4.8; 95% confidence interval [CI], 2.0 to 11.9) was independently associated with an increased risk of a positive TB culture finding. A radiographic pattern not typical of pulmonary tuberculosis (OR, 0.3; 95% CI, 0.1 to 0.7) and expectoration with cough (OR, 0.3; 95% CI, 0.1 to 0.6) were predictive of a decreased risk. An interaction between HIV seropositivity and mediastinal lymphadenopathy on the chest radiograph was also associated with a positive TB culture result (OR, 7.2; 95% CI, 1.4 to 36.0). The TB prediction score (TPS) was created with widely ranging likelihood ratios that could affect the posterior probability of TB by 30-fold. CONCLUSION: The TPS put into context with the overall prevalence of TB in a given area may help clinicians decide if a patient with negative sputum smear results should start empiric antituberculous therapy or wait for culture results. These results need prospective validation.

Chemokine receptor 2 serves an early and essential role in resistance to Mycobacterium tuberculosis.

Although the protective cellular immune response to Mycobacterium tuberculosis requires recruitment of macrophages and T lymphocytes to the site of infection, the signals that regulate this trafficking have not been defined. We investigated the role of C-C chemokine receptor 2 (CCR2)-dependent cell recruitment in the protective response to M. tuberculosis. CCR2(-/-) mice died early after infection and had 100-fold more bacteria in their lungs than did CCR2(+/+) mice. CCR2(-/-) mice exhibited an early defect in macrophage recruitment to the lung and a later defect in recruitment of dendritic cells and T cells to the lung. CCR2(-/-) mice also had fewer macrophages and dendritic cells recruited to the mediastinal lymph node (MLN) after infection. T cell migration through the MLN was similar in CCR2(-/-) and CCR2(+/+) mice. However, T cell priming was delayed in the MLNs of the CCR2(-/-) mice, and fewer CD4(+) and CD8(+) T cells primed to produce IFN-gamma accumulated in the lungs of the CCR2(-/-) mice. These data demonstrate that cellular responses mediated by activation of CCR2 are essential in the initial immune response and control of infection with M. tuberculosis.

The changing epidemiology of Staphylococcus aureus?

Strains of methicillin-resistant Staphylococcus aureus (MRSA), which had been largely confined to hospitals and long-term care facilities, are emerging in the community. The changing epidemiology of MRSA bears striking similarity to the emergence of penicillinase-mediated resistance in S. aureus decades ago. Even though the origin (hospital or the community) of the emerging MRSA strains is not known, the prevalence of these strains in the community seems likely to increase substantially.

A proteolytic transmembrane signaling pathway and resistance to beta-lactams in staphylococci.

beta-Lactamase and penicillin-binding protein 2a mediate staphylococcal resistance to beta-lactam antibiotics, which are otherwise highly clinically effective. Production of these inducible proteins is regulated by a signal-transducing integral membrane protein and a transcriptional repressor. The signal transducer is a fusion protein with penicillin-binding and zinc metalloprotease domains. The signal for protein expression is transmitted by site-specific proteolytic cleavage of both the transducer, which autoactivates, and the repressor, which is inactivated, unblocking gene transcription. Compounds that disrupt this regulatory pathway could restore the activity of beta-lactam antibiotics against drug-resistant strains of staphylococci.

Methicillin-resistant Staphylococcus aureus. Mechanisms of resistance and implications for treatment.

The frequency of methicillin-resistant Staphylococcus aureus (MRSA) continues to increase steadily, with nosocomial isolates approaching 50% of the total tested. Primarily isolated in hospitals, strains of MRSA have now spread into the community, complicating the management of this sometimes-fatal pathogen. Methicillin resistance in S aureus is mediated by the mecA gene, which encodes for a novel penicillin-binding protein (PBP), PBP-2a. In MRSA, exposure to methicillin inactivates the 4 high-binding-affinity PBPs normally present. PBP-2a, which displays a low affinity for methicillin, takes over the functions of these PBPs, permitting the cell to grow. Regulation of the methicillin-resistant phenotype and production of PBP-2a are influenced by the action of other genes. Two genes located upstream from mecA--mecR1 and mecI--control expression of PBP-2a. Antibiotics with high affinity for PBP-2a have displayed efficacy against MRSA in vivo, but none of these agents has made it beyond the investigational stage. Vancomycin remains the drug of choice for treatment of infections caused by MRSA, although it is intrinsically less active than the antistaphylococcal penicillins. Combinations of vancomycin with ss-lactam antibiotics may be synergistic in vivo against MRSA strains, including those with intermediate susceptibility to vancomycin. Given the increasing prevalence of MRSA in hospitals and in community settings, alternative approaches are needed for treatment of infections caused by MRSA.

Efficacy of levofloxacin for experimental aortic-valve endocarditis in rabbits infected with viridans group streptococcus or Staphylococcus aureus.

Levofloxacin is among the more active fluoroquinolones against streptococci and staphylococci. It is effective against moderately severe infections caused by these organisms, but its efficacy in the treatment of bacteremia and serious infections such as endocarditis is not well defined. We compared the efficacy of levofloxacin to those of standard agents in the rabbit model of aortic-valve endocarditis caused by fluoroquinolone-susceptible strains including a penicillin-susceptible strain of Streptococcus sanguis, a penicillin-resistant strain of Streptococcus mitis, a methicillin-resistant strain of Staphylococcus aureus, and a methicillin-susceptible strain of S. aureus. Levofloxacin administered intramuscularly at dosages of 20 to 40 mg/kg of body weight twice daily (b.i.d.) was completely ineffective against the penicillin-susceptible strain, with mean vegetation titers after 3 days of therapy not statistically significantly different from those for controls. Levofloxacin was no more effective than penicillin against the penicillin-resistant strain. Levofloxacin administered for 4 days at a dosage of 20 mg/kg b.i.d. was at least as effective as vancomycin administered intravenously at a dosage of 25 mg/kg b.i. d. against the methicillin-resistant S. aureus strain and was as effective as nafcillin administered intramuscularly at 100 mg three times daily against the methicillin-susceptible strain. Emergence of resistance to levofloxacin in vitro was less likely to occur than resistance to ciprofloxacin, and resistance to levofloxacin was not observed in vivo. Levofloxacin-rifampin combinations were antagonistic in vitro and in vivo. Levofloxacin was highly effective as a single agent against experimental staphylococcal endocarditis but was surprisingly ineffective against streptococcal endocarditis, suggesting that it has a potential role as treatment for serious S. aureus but not viridans group streptococcal infections in humans.

The role of glycopeptide antibiotics in the treatment of infective endocarditis.

There are several sets of guidelines for the treatment of infective endocarditis, reflecting the need for differing treatment in various countries and times. This review considers the need for differing treatment modalities and in particular the utility of the glycopeptide antibiotics vancomycin and teicoplanin. Specific recommendations are offered as to when to consider the use of glycopeptides, appropriate dosage, length of treatment course and whether to use monotherapy or combined therapy. Used judiciously, the glycopeptides give results as good as can be achieved with other antimicrobial agents without exceptional toxicity. The potential of teicoplanin for use in the outpatient treatment of infective endocarditis is considered.

A randomized clinical trial of mupirocin in the eradication of Staphylococcus aureus nasal carriage in human immunodeficiency virus disease.

Seventy-six human immunodeficiency virus (HIV)-infected patients with Staphylococcus aureus nasal carriage were randomized to treatment groups receiving intranasal mupirocin or placebo twice daily for 5 days. Nasal cultures for S. aureus were obtained at 1, 2, 6, and 10 weeks after therapy. At 1 week, 88% of mupirocin-treated patients had negative nasal cultures compared with 8% in placebo patients (P<.001). The percentage of mupirocin-treated patients with persistently negative nasal cultures decreased over time (63%, 45%, and 29% at 2, 6, and 10 weeks, respectively) but remained significantly greater than the placebo group (3% at 2, 6, and 10 weeks). In mupirocin-treated patients, most (16/19) instances of nasal recolonization were with pretreatment strains (determined by means of by pulsed field gel electrophoresis); mupirocin resistance was not observed. Five days of treatment with mupirocin eliminated S. aureus nasal carriage in HIV-infected patients for several weeks; however, since the effect waned over time, intermittent dosing regimens should be considered for long-term eradication.

Penicillin-binding protein-mediated resistance in pneumococci and staphylococci.

Target alteration underlies resistance to beta-lactam antibiotics in both Staphylococcus species and Streptococcus pneumoniae. The penicillin-binding protein (PBP) targets in penicillin-resistant strains of S. pneumoniae are modified, low-binding-affinity versions of the native PBPs. Multiple PBP targets may be modified by transformation and homologous recombination with DNA from PBP genes of viridans streptococci. The level of resistance is determined by how many and to what extent targets are modified. In contrast, methicillin resistance in staphylococci is due to expression of PBP 2a, a novel, low-affinity PBP for which there is no homologue in methicillin-susceptible strains. PBP 2a is encoded by mecA, a highly conserved gene most likely acquired by a rare transposition from Staphylococcus sciuri or a closely related ancestor. Expression of resistance can be highly variable, but this seems not to be determined by PBP modifications. Several non-PBP factors are required for high-level resistance.

Comparative efficacy of trovafloxacin in experimental endocarditis caused by ciprofloxacin-sensitive, methicillin-resistant Staphylococcus aureus.

The new fluoroquinolone trovafloxacin was tested against a ciprofloxacin-sensitive, methicillin-resistant Staphylococcus aureus strain in the rabbit model of endocarditis. Trovafloxacin was more effective than vancomycin (CFU/g of vegetation, 2.65 +/- 1.87 versus 4.54 +/- 2.80 [mean +/- standard deviation]; P < 0.05) or ampicillin-sulbactam plus rifampin (4.9 +/- 1.1 CFU/g). The addition of ampicillin-sulbactam to trovafloxacin tended to reduce titers further.

A randomized comparison of the safety and efficacy of once-daily gentamicin or thrice-daily gentamicin in combination with ticarcillin-clavulanate.

PURPOSE: The primary purpose of the clinical trial was to assess the safety and efficacy of once-a-day compared with three-times-a-day gentamicin in patients with serious infections who had protocol-determined peak serum aminoglycoside concentrations. PATIENTS AND METHODS: A total of 249 hospitalized patients with suspected or proven serious infections were randomized in a 2:2:1 ratio to gentamicin given three times a day with ticarcillin-clavulanate (TC), gentamicin once a day with TC, or ticarcillin-clavulanate (TC) alone. The gentamicin once-a-day dosage for patients with estimated creatinine clearance values of > or =80 mL/min was 5.1 mg/kg. With lower creatinine clearance estimates, the mg/kg dosage of gentamicin was decreased, and the dosage intervals (once daily or three times a day) were maintained. Evaluability required documentation of achievement of protocol-defined peak serum gentamicin levels. RESULTS: Of the total 175 evaluable patients, there were no significant differences found between treatment regimens with respect to clinical or microbiologic efficacy. Bedside audiometry proved impractical due to the frequency of altered mental state in ill patients. Based on the traditional increase in serum creatinine values from baseline values, no differences in renal toxicity between the treatment groups was identified. When changes in renal function were reanalyzed based on maintaining, as opposed to worsening, of renal function, preservation of renal function was better in the gentamicin once-a-day patients as opposed to the gentamicin three-times-a-day patients, P <0.01. CONCLUSIONS: Gentamicin once a day plus TC, gentamicin three times a day plus TC, and TC alone had similar effects in seriously ill hospitalized patients. The incidence of nephrotoxicity was similar in the three treatment groups. Using a nonvalidated post-hoc analysis, renal function was better preserved in gentamicin once-a-day + TC and TC-only patients as opposed to gentamicin three-times-a-day + TC.

Activity of amoxicillin/clavulanate in patients with tuberculosis.

Some beta-lactam antibiotics are active in vitro against Mycobacterium tuberculosis. There are anecdotal reports of successful treatment of tuberculosis caused by multiple-drug-resistant strains of M. tuberculosis with regimens that included amoxicillin/clavulanate. Reduction of M. tuberculosis in the sputum of patients with pulmonary tuberculosis during administration of amoxicillin/clavulanate was measured by a quantitative culture method to determine the activity in vivo. Patients were randomized to receive isoniazid, ofloxacin, or amoxicillin/clavulanate for 7 days. Isoniazid was the most effective agent, reducing M. tuberculosis after 2 days at a mean rate (+/- standard deviation) of 0.60 +/- 0.30 log10 cfu/mL per day, compared with 0.32 +/- 0.05 and 0.34 +/- 0.03 for ofloxacin and amoxicillin/clavulanate, respectively. The early bactericidal activity of amoxicillin/clavulanate was comparable to that reported for antituberculous agents other than isoniazid. Further studies of beta-lactam antibiotics with in vitro activity against M. tuberculosis are warranted to define their role in treatment of tuberculosis.