Potencies of newer fluoroquinolones against Viridans group Streptococciisolated in 637 cases of bloodstream infection in the SENTRY Antimicrobial Surveillance Program (1997 to 1999): beyond Canada!

Characterization of high-level daptomycin resistance in Viridans group Streptococci developed upon in vitro exposure to daptomycin

Viridans group streptococci (VGS) are part of the normal flora that may cause bacteremia, often leading to endocarditis. We evaluated daptomycin against four clinical strains of VGS (MICs = 1 or 2 μg/ml) using an in vitro-simulated endocardial vegetation model, a simulated bacteremia model, and kill curves. Daptomycin exposure was simulated at 6 mg/kg of body weight and 8 mg/kg every 24 h for endocardial and bacteremia models. Total drug concentrations were used for analyses containing protein (albumin and pooled human serum), and free (unbound) drug concentrations (93% protein bound) were used for analyses not containing protein. Daptomycin MICs in the presence of protein were significantly higher than those in the absence of protein. Despite MICs below or at the susceptible breakpoint, all daptomycin regimens demonstrated limited kill in both pharmacodynamic models. A reduction of approximately 1 to 2 log10 CFU was seen for all isolates and dosages except daptomycin at 6 mg/kg, which achieved a reduction of 2.7 log10 CFU/g against one strain (Streptococcus gordonii 1649) in the endocardial model. Activity was similar in both pharmacodynamic models in the presence or absence of protein. Similar activity was noted in the kill curves over all multiples of the MIC. Regrowth by 24 h was seen even at 8× MIC. Postexposure daptomycin MICs for both pharmacodynamic models increased to >256 μg/ml for all isolates by 24 and 72 h. Despite susceptibility to daptomycin by standard MIC methods, these VGS developed high-level daptomycin resistance (HLDR) after a short duration following drug exposure not attributed to modification or inactivation of daptomycin. Further evaluation is warranted to determine the mechanism of resistance and clinical implications.

In vitro susceptibility of viridans group streptococci isolated from blood in southwest Finland in 1993-2004

We studied in vitro activity against invasive viridans group streptococci (VGS) of penicillin and 4 newer antibiotics, i.e. telithromycin, linezolid, levofloxacin and quinupristin-dalfopristin. Also 7 other antibiotics were tested. Antibiotic susceptibility of 263 VGS blood isolates, collected from southwest Finland during a 12-y period was determined. We wished to discover whether there is an increasing trend of antimicrobial resistance among VGS in Finland. Our results showed that penicillin is still a good choice for treating VGS infections based on the considerably low resistance percentage, 2.3%. Also newer antibiotics showed good in vitro activity: susceptibilities for telithromycin, linezolid and levofloxacin were 100%, 98.9% and 94.6%, respectively. However, quinupristin-dalfopristin was not as effective as described in previous studies, with only 57% susceptibility.

Challenges in the treatment of infections caused by gram-positive and gram-negative bacteria in patients with cancer and neutropenia

Infection is the most common complication of chemotherapy-induced neutropenia. Bacterial infections predominate during the early stages of a neutropenic episode, whereas invasive fungal infections tend to occur later. The epidemiological pattern of bacterial infection continues to evolve globally and locally at the institutional level, as do patterns of susceptibility and resistance. These trends are often associated with local treatment practices and have a significant effect on the nature of empirical antibiotic therapy. The increasing rates of antimicrobial resistance among both gram-positive and gram-negative pathogens isolated from patients with neutropenia are posing new challenges. These challenges are compounded by the fact that relatively few new drugs are being developed, particularly those that treat resistant gram-negative organisms. They also stress the increasing importance of prevention and control of infection and stewardship of antibiotics as strategies in the overall treatment of patients with febrile neutropenia. The recognition of a subset of low-risk patients with neutropenia has created new opportunities (e.g., outpatient and oral therapy) and new challenges (e.g., infrastructure, safety, and compliance). These challenges may be met, to some extent, by appropriately adapting national guidelines to local and institutional circumstances.

Viridans group streptococci: an underestimated cause of spontaneous bacterial peritonitis in cirrhotic patients with ascites

OBJECTIVES

The objective of the study was to examine the characteristics of spontaneous bacterial peritonitis (SBP) caused by streptococci, in particular viridans group streptococci (VGS), and to investigate a potential association between the long-term administration of norfloxacin and high-level resistance to fluoroquinolones in these organisms.

METHODS

We reviewed 84 episodes of SBP and bacterascites caused by streptococci that occurred in 75 patients over a 6-year period. Isolates were tested for antibiotic susceptibility by the determination of minimum inhibitory concentrations.

RESULTS

Of the 84 isolates, 46 (54.8%) were associated with SBP, 12 (14.3%) were associated with symptomatic bacterascites, and 26 (31%) were associated with asymptomatic bacterascites. VGS were responsible for 39 of the 58 episodes of SBP and symptomatic bacterascites, largely preceding group B streptococci (n=7), Streptococcus pneumoniae (n=6) and Streptococcus bovis (n=5). Most of the episodes were community acquired. An extraperitoneal site of infection was found in three patients only. Positive blood cultures were less frequent in patients with VGS infection than in those with SBP caused by other streptococci (12.8 versus 52.6%, P<0.001). The rates of susceptibility to penicillin, amoxicillin and cefotaxime were 84.5, 87.9 and 91.4%, respectively. All isolates, including those from patients receiving norfloxacin, were susceptible to levofloxacin and moxifloxacin.

CONCLUSIONS

VGS are an underestimated cause of SBP in patients with cirrhosis. Most isolates are susceptible to beta-lactam agents and new fluoroquinolones.

Reappraisal With Meta-Analysis of the Addition of Gram-Positive Prophylaxis to Fluoroquinolone in Neutropenic Patients

Purpose: Past reports and meta-analyses indicate that fluoroquinolones are highly effective in preventing Gram-negative infections in neutropenic cancer patients, but offer inadequate coverage for Gram-positive infections. We evaluated by meta-analysis the efficacy of the addition of antimicrobial agents with enhanced Gram-positive activity to prophylaxis with quinolones.

Materials and Methods: Randomized trials comparing fluoroquinolones alone (ciprofloxacin, ofloxacin, pefloxacin, or norfloxacin) with fluoroquinolone in combination with Gram-positive prophylaxis (rifampin, vancomycin, amoxicillin, roxithromycin, or penicillin) were retrieved. We pooled relative risks (RRs) using a fixed-effects model.

Results: Nine trials (1,202 patients) published between 1993 and 2000 meet inclusion criteria. Compared with fluoroquinolone alone, Gram-positive prophylaxis reduced total bacteremic episodes (RR, 1.54; 95% CI, 1.26 to 1.88), streptococcal infections (RR, 2.20; 95% CI, 1.44 to 3.37), coagulase-negative staphylococcal infections (RR, 1.46; 95% CI, 1.04 to 2.04), and rate of febrile patients (RR 1.08; 95% CI, 1.00 to 1.16). Occurrence of clinically documented infections, unexplained fever, and infectious mortality was similar in the two groups. The addition of Gram-positive prophylaxis, however, significantly increased side effects (RR, 0.46; 95% CI, 0.28 to 0.76). Rifampin use resulted in a higher incidence of undesirable effects.

Conclusion: Considering the lack of cut-clear benefit on some parameters of morbidity and mortality, routine use of Gram-positive prophylaxis is not advisable. This strategy, however, should be particularly valuable in subgroups of patients at high risk of streptococcal infection (eg, those with severe and prolonged neutropenia or mucositis, and those receiving cytarabine). Problems of tolerability and the potential for the emergence of resistant microorganisms should be considered when prescribing prophylaxis with enhanced Gram-positive activity to neutropenic patients.

Bacteremia due to viridans group Streptococci with diminished susceptibility to Levofloxacin among neutropenic patients receiving levofloxacin prophylaxis

Despite the use of levofloxacin prophylaxis during the neutropenic period after autologous peripheral blood stem cell transplantation, viridans group (VG) streptococcal bacteremia developed in 6 (16.2%) of 37 patients who underwent transplantation between 1 January and 25 February 2001 at the Mayo Clinic in Rochester, Minnesota. All 6 patients presented with fever and mucositis after a mean of 4.5 days of neutropenia, and 3 developed septic shock. All 6 VG streptococcal isolates from these patients exhibited distinct patterns on pulsed-field gel electrophoresis. All isolates had diminished susceptibility to levofloxacin, 5 to gatifloxacin, and 4 to moxifloxacin. Quinolone resistance was associated with mutations in the quinolone resistance-determining region of GyrA and (for 1 isolate) of ParC. The use of levofloxacin may select VG streptococci with diminished susceptibility to levofloxacin and other quinolones with enhanced activity against gram-positive organisms and, therefore, may not be optimal for preventing VG streptococcal bacteremia in neutropenic patients.