Resistance issues and community-acquired respiratory infections

The importance and future of antimicrobial surveillance studies

Surveillance studies provide important information that allows for the identification of trends in pathogen incidence and antimicrobial resistance, including identification of emerging pathogens at national and global levels. Routine surveillance is critical for creating and refining approaches to controlling antimicrobial resistance and for guiding clinician decisions regarding appropriate treatment. The traditional approach has been to monitor pathogen antimicrobial susceptibility; numerous large studies have been performed, and their designs have evolved over time. Longitudinal studies are particularly useful because important information can be obtained by comparing data over time. Another approach to surveillance, that of monitoring antimicrobial use, can help to identify trends in dosing, to prevent the development of resistance. Several studies have incorporated this approach into their methods, and both large and small studies have attempted to correlate antimicrobial use data with antimicrobial resistance data. Overall, care must be taken to coordinate programs for optimal utilization of resources, to avoid duplication of effort.

Azithromycin extended release: a review of its use in the treatment of acute bacterial sinusitis and community-acquired pneumonia in the US

Azithromycin is a macrolide antibacterial agent. The novel microspheres oral extended-release formulation (Zmax) is the first antibacterial drug approved in the US for administration as a single dose in adult patients with mild to moderate acute bacterial sinusitis (ABS) or community-acquired pneumonia (CAP). It has a broad spectrum of in vitro antibacterial activity against Gram-positive, Gram-negative and atypical pathogens that cause ABS and CAP infections (including Streptococcus pneumoniae), and achieves good tissue penetration. Azithromycin extended release is an effective and generally well tolerated treatment in patients with ABS or CAP. The clinical cure rates of a single 2.0 g dose of azithromycin extended release were noninferior to those obtained with a 10-day regimen of levofloxacin in patients with ABS, and with 7-day regimens of clarithromycin extended release or levofloxacin in patients with CAP. With a pharmacodynamic and pharmacokinetic profile well suited to administration as a single-dose regimen that may offer the advantage of improved compliance and convenience compared with once-daily longer-course regimens, azithromycin extended release is a new option in the empirical treatment of adult patients with mild or moderate ABS or CAP in the US.

Geographically-based evaluation of multidrug resistance trends among Streptococcus pneumoniae in the USA: findings of the FAST surveillance initiative (2003–2004)

Surveillance initiatives to track Streptococcus pneumoniae resistance trends are important for understanding the current in vitro effectiveness of available antimicrobial agents. The antimicrobial susceptibility profiles of S. pneumoniae (n=1479 isolates) collected from 17 geographical areas across the USA (2003-2004) were analysed; 36.8% of isolates were resistant to one or more agents (24.4% were multidrug-resistant, i.e. resistant to two or more antimicrobial classes). Multidrug resistance involved resistance to beta-lactams, macrolides, tetracycline and trimethoprim/sulphamethoxazole, but rarely fluoroquinolones (>96% of multidrug-resistant isolates were fluoroquinolone-susceptible). Multidrug resistance rates were prominent regardless of the geographical region surveyed. As this trend continues, the empirical therapeutic options for S. pneumoniae infections will diminish and there will be an ongoing need to evaluate the effectiveness of potent fluoroquinolones such as gemifloxacin.

Activities of ceftobiprole and other beta-lactams against Streptococcus pneumoniae clinical isolates from the United States with defined substitutions in penicillin-binding proteins PBP 1a, PBP 2b, and PBP 2x

The activities of ceftobiprole and other beta-lactams were examined with 30 Streptococcus pneumoniae isolates containing multiple pbp1a, pbp2b, and pbp2x mutations. The highest ceftobiprole MIC was 1 microg/ml, while the comparator MICs were 16 to 64 microg/ml. Fifty percent inhibitory concentrations for penicillin-binding protein 2x were 0.5 microg/ml (ceftobiprole) and 4 microg/ml (ceftriaxone) in a penicillin- and ceftriaxone-resistant isolate.

Infrequent occurrence of single mutations in topoisomerase IV and DNA gyrase genes among US levofloxacin-susceptible clinical isolates of Streptococcus pneumoniae from nine institutions (1999–2003)

OBJECTIVES

Prevalence of single quinolone-resistance determining region (QRDR) mutations in Streptococcus pneumoniae was studied from nine institutions over 5 years to track the incidence of single QRDR mutations.

METHODS

All 1106 levofloxacin-susceptible pneumococci (MICs < or = 2.0 mg/L) identified from 1112 total isolates (99.5% susceptibility) in TRUST 3 (1999), TRUST 5 (2001) and TRUST 7 (2003) surveillance studies from the same nine hospitals in nine states were screened for QRDR mutations. Using pyrosequencing, the strains were screened for mutations corresponding to hot spots Asp-78, Ser-79 and Asp-83 in ParC; Asp-80, Ser-81 and Glu-85 in GyrA; Asp-435 in ParE and Asp-435 in GyrB. DNA sequencing of QRDRs was performed to confirm mutations.

RESULTS

No QRDR mutations were found in any of the isolates with levofloxacin MICs < or = 0.5 mg/L and no gyrA or gyrB QRDR mutations were found in any of the screened isolates (MICs < or = 2 mg/L). Four single-step QRDR mutants with the following amino acid substitutions were found: ParE Asp-435 to Asn (isolated in 1999 in Colorado); ParC Asp-83 to Asn (isolated in 2001 in Kentucky); ParC Ser-79 to Phe (isolated in 2003 in Indiana) and ParC Ser-79 to Tyr (isolated in 2003 in California). These non-clonal strains had levofloxacin MICs of 1 mg/L and were non-susceptible to ciprofloxacin (MIC 2-4 mg/L).

CONCLUSIONS

Overall prevalence of single QRDR mutations in levofloxacin-susceptible S. pneumoniae with MICs of < or = 2 mg/L was 0.4% (4/1106) and has remained <1% within nine institutions over 5 years (1999-2003).

Predominance of 23S rRNA mutants among non-erm, non-mef macrolide-resistant clinical isolates of Streptococcus pneumoniae collected in the United States in 1999-2000

A total of 322 erythromycin-resistant pneumococci from TRUST 3 and TRUST 4 United States surveillance studies (1999-2000) were screened for 23S rRNA, L4, and L22 gene mutations. Nineteen isolates, two with mefA, had mutations at position 2058 or 2059 in 23S rRNA. Two had a 69GTG71-to-TPS substitution in L4; one of these also contained ermA.

Novel Ser79Leu and Ser81Ile substitutions in the quinolone resistance-determining regions of ParC topoisomerase IV and GyrA DNA gyrase subunits from recent fluoroquinolone-resistant Streptococcus pneumoniae clinical isolates

Resistance of Streptococcus pneumoniae to fluoroquinolones is caused predominantly by amino acid substitutions at positions Ser79 of ParC and Ser81 of GyrA to either Phe or Tyr encoded in the quinolone resistance-determining regions of the parC topoisomerase IV and gyrA DNA gyrase genes. Analysis of highly resistant clinical isolates identified novel second-step substitutions, Ser79Leu (ParC) and Ser81Ile (GyrA). To determine contributions of these new mutations to fluoroquinolone resistance either alone or in combination with other Ser79/81 alleles, the substitutions Ser79Leu/Phe/Tyr in ParC and Ser81Ile/Phe/Tyr in GyrA were introduced into the R6 background, resulting in 15 isogenic strains. Their level of fluoroquinolone resistance was determined by susceptibility testing for ciprofloxacin, levofloxacin, moxifloxacin, gatifloxacin, gemifloxacin, garenoxacin, and norfloxacin. Leu79 and Ile81 alone as well as 79/81Phe/Tyr substitutions did not contribute significantly to resistance, with fluoroquinolone MICs increasing two- to fourfold compared to wild type for all agents tested. Fluoroquinolone MICs for double transformants ParC Ser79Phe/Tyr/Leu-GyrA Ser81Phe/Tyr were uniformly increased by 8- to 64-fold regardless of pairs of amino acid substitutions. However, combinations including Ile81 conferred two- to fourfold-higher levels of resistance than did combinations including any other Ser81 GyrA substitution, thus demonstrating the differential effects of diverse amino acid substitutions at particular hotspots on fluoroquinolone MICs.

Antimicrobial treatment of lower respiratory tract infections in the hospital setting

Respiratory tract infections (RTIs) that may require hospitalization include acute exacerbations of chronic bronchitis (AECB), community-acquired pneumonia (CAP), and hospital-acquired pneumonia (HAP), which includes ventilator-associated pneumonia (VAP). Healthcare-associated pneumonia (HCAP) is treated similar to HAP and may be considered with HAP. For CAP requiring hospitalization, the current guidelines for the treatments of RTIs generally recommend either a beta-lactam and macrolide combination or a fluoroquinolone. The respiratory fluoroquinolones (levofloxacin, gatifloxacin, moxifloxacin, and gemifloxacin) are excellent antibiotics due to high levels of susceptibility among gram-negative, gram-positive, and atypical pathogens. The fluoroquinolones are active against > 98% of Streptococcus pneumoniae, including penicillin-resistant strains. Fluoroquinolones are also recommended for AECB requiring hospitalization. Evidence from clinical trials suggests that levofloxacin monotherapy is as efficacious as combination ceftriaxone-erythromycin therapy in the treatment of patients hospitalized with CAP. For early-onset HAP, VAP, and HCAP without the risk of multidrug resistance, ceftriaxone, ampicillin-sulbactam, ertapenem, or one of the fluoroquinolones is recommended. High-dose, short-course therapy regimens may offer improved treatment due to higher drug concentrations, more rapid killing, increased adherence, and the potential to reduce development of resistance. Recent studies have shown that short-course therapy with levofloxacin, azithromycin, or telithromycin in patients with CAP was effective, safe, and tolerable and may control the rate of resistance.