Antibiotic resistance. Do we need new therapeutic approaches?

Current Issues in Gram-Negative Resistance: Extended-Spectrum Beta-Lactamases and Inducible Beta-Lactamases

The production of beta-lactamases is the most common cause of antimicrobial resistance in gram-negative bacilli. Two beta-lactamases, extended-spectrum beta-lactamases (ESBLs) and inducible beta-lactamases (IDBLs), are presently seen with increasing frequency. Treatment of severe infections due to gram-negative bacilli producing these beta-lactamases is problematic. In vitro susceptibility testing of ESBL-producing organisms remains difficult to interpret; clinical isolates sensitive to a particular antimicrobial agent at standard inoculum may become resistant when a higher inoculum is employed. Laboratory detection of IDBL-producing organisms is not yet commercially available. Due to the lack of sufficient outcome data, clinicians often have no choice but to use carbapenems empirically for the treatment of severe infections caused by organisms suspected of producing these enzymes. The widespread empiric use of carbapenems is of concern and may potentially precipitate increased bacterial resistance to this class of antimicrobial agents.

Antimicrobial resistance and serotypes of nasopharyngeal strains of Streptococcus pneumoniae in Chinese children with acute respiratory infections

This prospective, multicentre, nasal carriage study in Chinese children with upper respiratory infection was carried out over the period from 2000 to 2002. Overall, the prevalence of pneumococcal carriage was 24.9%. Antimicrobial susceptibility tests were performed for 887 isolates of Streptococcus pneumoniae of which 33.5% were intermediately susceptible to penicillin and 6.4% were resistant. Multidrug resistance was very common. Pneumococcal strains (n = 625) were serotyped, showing 72.2% were covered by the 23-valent pneumococcal polysaccharide vaccine and 57.6% by the seven-valent pneumococcal conjugate vaccine. Serogroups 19 and 23 were significantly associated with penicillin resistance, which is increasing in China. Erythromycin, tetracycline and sulphamethoxazole/trimethoprim cannot be recommended as first-line treatments for respiratory tract infection as in some other developing countries. These features of serotype distribution are of importance for surveillance in the era of the new conjugate vaccine. In particular, these features will allow for documentation of serotype replacement after the introduction of widespread vaccination.

PROTEKT 1999–2000: a multicentre study of the antimicrobial susceptibility of respiratory tract pathogens in Japan

DESIGN

A six-centre study in Japan during the winter of 1999-2000 assessed the in vitro activity of >20 antimicrobial agents against the common respiratory pathogens Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, and Moraxella catarrhalis. The minimum inhibitory concentrations (MIC) of each antimicrobial was determined against these isolates using National Committee for Clinical Laboratory Standards (NCCLS) methodology.

RESULTS

Among S. pneumoniae isolates, 44.5% were penicillin resistant. The macrolide resistance rate was 77.9% with 90.5% of penicillin-resistant strains also being macrolide resistant. Resistance mechanisms in macrolide-resistant isolates were identified as mef(A) or erm(B) in 42.5% and 52.5%, respectively. Of the fluoroquinolone-resistant isolates (1.3%), most were also penicillin and macrolide resistant. All strains were inhibited by telithromycin at <or=1mg/L. Among S. pyogenes isolates, erythromycin resistance was 17.5% overall but showed considerable variation among the six centres. For H. influenzae, 8.5% produced beta-lactamase and a single beta-lactamase-negative, ampicillin-resistant isolate (0.36%) was obtained, and there was no fluoroquinolone resistance. All isolates were susceptible to telithromycin. Most antimicrobials showed good activity against M. catarrhalis, although 96.7% were beta-lactamase positive.

CONCLUSION

The prevalence of antimicrobial resistance to macrolides, penicillin and the fluoroquinolones among the common respiratory pathogens is high in Japan.

Comparison of the efficacy and tolerability of amoxycillin/clavulanic acid 875 mg b.i.d. with cefuroxime 500 mg b.i.d. in the treatment of chronic and acute exacerbation of chronic sinusitis in adults

The efficacy and safety of amoxycillin/clavulanic acid (AMX/CA) (875/125 mg b.i.d. for 14 days) were compared with that of cefuroxime axetil (500 mg b.i.d. for 14 days) in a multicenter, open, parallel-group, randomized clinical trial in 206 adults with chronic or acute exacerbation of chronic sinusitis. Clinical response was similar, with 95% of AMX/CA-, and 88% of cefuroxime-treated, clinically evaluable patients cured (95% confidence interval; -0.6% to +15%). In bacteriologically evaluable patients, cure rates, defined as eradication of the original pathogen with or without re-colonization with non-pathogenic flora, were also similar, with 65% of AMX/CA- and 68% of cefuroxime-treated patients cured (95% confidence interval; -18% to +15%). However, clinical relapse was significantly higher in the cefuroxime group: 7% (7/89) of clinically evaluable patients, compared with 0% (0/98) in the AMX/CA (p=0.0049) group. A similar incidence of possible or definite adverse events related to the study drug was reported for both treatments (AMX/CA 4.4%, cefuroxime 4.3%), the most frequent being diarrhea. Four adverse events were recorded as serious or life-threatening with only one considered related to the study drug (urticaria, cefuroxime). AMX/CA 875/125 mg b.i.d. for 14 days is as effective and well tolerated as cefuroxime axetil 500 mg b.i.d. for 14 days in the treatment of chronic, or acute exacerbation of chronic sinusitis, but is associated with a significantly lower clinical relapse rate.

Antimicrobial susceptibility of nasopharyngeal isolates of Haemophilus influenzae from healthy children in day-care centres: results of multicentre study in Russia

Resistance of Haemophilus influenzae from clinical isolates can be predicted on the basis of results of antimicrobial susceptibility of nasopharyngeal isolates. The carriage rate and the antimicrobial susceptibility of H. influenzae isolated in healthy children attending day-care centres in Moscow, Smolensk and Yartsevo was studied. The susceptibility of ampicillin, amoxycillin/clavulanate, cefaclor, erythromycin, roxithromycin, clarithromycin and trimethoprim-sulphamethoxazole were determined by the E-test. The mean carriage rate of H. influenzae was 44%. Resistance of H. influenzae to ampicillin was 2.3%, to amoxycillin/clavulanate 0.7%, to cefaclor 0.7%, to clarithromycin 18.7% and to trimethoprim-sulphamethoxazole 21%. These included strains that showed intermediate-resistance. The antimicrobial resistance profiles varied in different centres. The clinical use of trimethoprim-sulphamethoxazole should be restricted because of the high resistance of H. influenzae to antifolate compounds.

Successful shortening from seven to four days of parenteral beta-lactam treatment for common childhood infections: a prospective and randomized study

OBJECTIVES

To explore whether 4-day parenteral beta-lactam therapy is as effective as 7-day therapy for children hospitalized for parenteral antimicrobials.

METHODS

A series of patients aged 3 months to 15 years who fulfilled strict criteria for bacterial pneumonia, other respiratory infections, sepsis-like infections, and other acute infections were prospectively randomized to receive parenteral penicillin or cefuroxime randomly for 4 or 7 days. Besides blood and throat cultures, the etiology was searched by serology for 23 different agents.

RESULTS

Of 154 children analyzed, a probable etiology was established in 96. Of those, a bacterial infection, with or without concomitant viral infection, was disclosed in 80% and 94% in the 4-day and 7-day treatment groups, respectively; pneumococcus being the commonest agent. There was one possible treatment failure in the 4-day group, but with a questionable relation to the short course. Three patients in the 4-day and two in the 7-day group underwent treatment changes, or were rehospitalized within 30 days. All children recovered entirely.

CONCLUSIONS

Shortening parenteral beta-lactam treatment to 4 days in infections for which most parenteral antimicrobials are instituted, is not only safe, but reduces costs, is ecologically sound, and minimizes the risks of nosocomial infections and other adverse effects of treatment.

The evolving threat of antibiotic resistance in Europe: new data from the Alexander Project

The Alexander Project was established in 1992 to examine the antimicrobial susceptibility of community-acquired lower respiratory tract bacterial pathogens to a range of compounds. Since then it has expanded both geographically and in the number of antimicrobial agents tested. Within Europe, the most recent data have confirmed that the prevalence of penicillin resistance among isolates of Streptococcus pneumoniae is high in France and Spain, with both intermediate (MIC 0.12-1 mg/L) and resistant (MIC > or = 2 mg/L) phenotypes, and combined resistance rates of >50%. Macrolide resistance is increasing generally both among penicillin-resistant and penicillin-susceptible isolates of S. pneumoniae and its prevalence now exceeds that of penicillin resistance, overall (16.5% and 10.4%, respectively, in 1996; 21.9% and 14.1% in 1997; 16.5% and 11.6% in 1998). Beta-lactamase production was the principal mechanism of resistance observed among isolates of Haemophilus influenzae and Moraxella catarrhalis.

Comparative in vitro potency of gemifloxacin against European respiratory tract pathogens isolated in the Alexander Project

European isolates collected in 1998 for the Alexander Project were tested for their susceptibility to ciprofloxacin, ofloxacin and a novel fluoroquinolone, gemifloxacin, which has a spectrum of activity including common and atypical respiratory pathogens. MIC90s of gemifloxacin for Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis were 0.03, 0.06 and 0.015 mg/L, respectively. On the basis of MIC90s, gemifloxacin was the most potent antimicrobial tested against S. pneumoniae and M. catarrhalis. Against H. influenzae, gemifloxacin was one tube dilution more potent than ofloxacin and one tube dilution less potent than ciprofloxacin. As resistance to currently available antimicrobial agents increases, gemifloxacin offers potential as a promising new agent for the treatment of respiratory tract infection.

The Alexander Project 1996-1997: latest susceptibility data from this international study of bacterial pathogens from community-acquired lower respiratory tract infections

The Alexander Project was established in 1992 to examine antimicrobial susceptibilities of bacterial isolates from community-acquired infections of the lower respiratory tract. Testing of a range of compounds was undertaken in a central laboratory. From 1992 to 1995, isolates were collected from geographically separated areas in countries in the European Union and various states in the USA. In 1996, the study was extended to include centres in Mexico, Brazil, Saudi Arabia, South Africa, Hong Kong and other European countries not included previously. Data generated by the project during 1996-1997 confirm France and Spain as European centres with high rates of resistance to penicillin among isolates of Streptococcus pneumoniae. Both intermediate (MIC 0. 12-1 mg/L) and resistant (MIC 2 mg/L) phenotypes are present. Combined resistance rates (intermediate and resistant) were >/=50% in 1997. Combined resistance rates in excess of 20% were found in the Republic of Ireland, Portugal, the Slovak Republic and Hungary. Penicillin resistance continues to evolve in the USA, with combined resistance rates of 16.4% (1996) and 18.6% (1997). In the new, non-European centres, e.g. Mexico and, in particular, Hong Kong (where resistant strains accounted for 50% of all isolates of S. pneumoniae in 1996 and 55.5% in 1997), there are centres where rates of resistance are high. Macrolide resistance is increasing generally among both penicillin-resistant and penicillin-susceptible isolates of S. pneumoniae. There is variation between countries, and in four out of the 16 centres for which both 1996 and 1997 data are available, rates of macrolide resistance have fallen. Overall, the percentage of S. pneumoniae strains that is resistant to macrolides exceeds the percentage that is resistant to penicillin. In 1996, 16. 5% of all S. pneumoniae isolates were resistant to macrolides compared with 10.4% resistant to penicillin, and in 1997 respective rates were 21.9% and 14.1%. beta-Lactamase production was the principal mechanism of resistance observed among isolates of Haemophilus influenzae. However, considerable variation in the percentage of isolates producing beta-lactamase (0-37.1%) was observed within this species. Within Europe, in the Republic of Ireland, France and Belgium, more than 15% of isolates were beta-lactamase producers. In Spain rates were as high as 31.7%. Outside Europe and the USA high rates were described in Mexico (25%), Saudi Arabia (27.9%, 16.7%) and Hong Kong (37.1%, 28.9%). Of H. influenzae from the USA, 30.4% were beta-lactamase producers in 1996 and 23.3% in 1997. beta-Lactamase production among isolates of Moraxella catarrhalis was observed in >90% of the isolates tested in 1996 and 1997.

Decreased antimicrobial resistance after changes in antibiotic use

Vancomycin-resistant enterococci (VRE) and methicillin-oxacillin-resistant Staphylococcus aureus (MRSA) originally predominated in large medical centers; however, these isolates are now common in community hospitals and community clinics. No simple answer is available regarding control of antimicrobial-resistant bacteria, especially VRE and MRSA, as their numbers increase and pose a more serious threat to patient care. The source of colonization is often difficult to identify because of transport of patients among different locations on the continuum of care (e.g., hospital to extended care facility to home and back). At one hospital, control strategies greatly reduced the occurrence of gram-negative bacteria such as VRE. Since 1994, VRE declined from 16% to 5%. Similarly, the number of MRSA isolates declined from 35% to 23%. These declines are attributed to a cohesive working relationship among pharmacists, microbiologists, and infectious disease physicians and personnel, and to a decision to decrease administration of cephalosporins in favor of piperacillin-tazobactam.

The Nearchus project: antibiotic susceptibility of respiratory pathogens and clinical outcome in lower respiratory tract infections at 27 centres in the UK

Community-acquired respiratory infections are usually treated empirically by the primary care physician. Increasing antibiotic resistance, for example, in pneumococci, prompted a UK survey of antibiotic susceptibility of three major lower respiratory tract pathogens, Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Each of 27 centres was asked to collect up to 100 isolates of the three species and submit them for confirmation of identity and for susceptibility testing to a central laboratory. In addition, general practitioners were asked for demographic details on the patient, their treatment and the clinical outcome. Of 1689 viable pathogens collected, there were 1078 (64%) strains of H. influenzae, 258 (15%) of M. catarrhalis and 353 (21%) of S. pneumoniae. Production of beta-lactamase was detected in 163 (15%) of 1078 isolates of H. influenzae and in 243 (94%) isolates of M. catarrhalis. For S. pneumoniae, moderate resistance to penicillin (MIC 0.12-1 mg/l) was found in 12 (3.4%) isolates and high level resistance (MIC > or = 2 mg/l) in 13 (3.7%) isolates. The most common individual treatments were amoxycillin, amoxycillin/clavulanate (amoxyclav) , and erythromycin. Complete or partial clinical resolution was achieved in 88% of 809 patients infected with H. influenzae, 83% of 197 infected with M. catarrhalis and 90% of 255 infected with S. pneumoniae.

Microbial resistance to drug therapy: a review

Microbial resistance to the antimicrobials in standard use is becoming more prevalent. A historical perspective frames further discussion. Bacterial resistance is most common, but resistance has been identified in fungi, viruses, and parasites. Resistance is a complex phenomenon that involves the microorganism, the environment, and the patient-separately and interactively. Resistance may be a characteristic of the microbe before exposure to a given drug or may arise as a consequence of therapy. Mechanisms of resistance to antibiotics are discussed. Antibiotic resistance is considered in both hospital and community settings, as ecosystems that are separate yet blending, and the major organisms demonstrating significant resistance problems are presented. A review of existing guidelines, strategies, and plans for addressing resistance and some recommendations conclude this review.

Results of the Alexander Project: a continuing, multicenter study of the antimicrobial susceptibility of community-acquired lower respiratory tract bacterial pathogens

In 1992, an ongoing, international multicenter study was established to investigate the antimicrobial susceptibility of community-acquired lower respiratory tract bacterial pathogens: the Alexander Project. Isolates cultured from patients living in geographically separated areas, ten in the European Union (EU) and five in the United States (US), were collected and tested using standard methods in a central laboratory. A total of 4,155 isolates of Haemophilus influenzae was collected during the period 1992-1994. beta-lactamase production was the principal mechanism of resistance observed with overall rates in the US (1992 = 26.3%; 1993 = 28.2%; and 1994 = 30.1%) generally twice those seen in the EU (1992 = 12.3%; 1993 = 14.4%; and 1994 = 15.5%). Chloramphenicol resistance was generally low except in Spanish centers where rates ranging from 4.0 to 15.9% were observed during the study period. One thousand one hundred ninety-three isolates of Moraxella catarrhalis were tested. beta-lactamase production was the only mechanism of resistance of any importance detected, with the vast majority of isolates producing the enzyme. Two thousand eight hundred twenty-nine isolates of Streptococcus pneumoniae were tested. French and Spanish centers provided isolates with the highest rates of either low-level (intermediate) or high-level penicillin resistance, which in 1994 ranged from 10.2 to 31.4% and 30.4 to 40.1% for each resistance category, respectively. With the exception of the fluoroquinolones, rates of resistance to other antimicrobials including the macrolides, doxycycline, chloramphenicol, and trimethoprim/sulfamethoxazole were high, generally, in centers with a high prevalence of penicillin resistance. However, in some centers (Toulouse, France and Genoa, Italy) this association was not complete for the macrolides.