Cross-Canada survey of resistance of 2747 aerobic blood culture isolates to piperacillin/tazobactam and other antibiotics

In vitro activity of cefepime against multidrug-resistant Gram-negative bacilli, viridans group streptococci and Streptococcus pneumoniae from a cross-Canada surveillance study

OBJECTIVE

To determine the in vitro activity of cefepime against multidrug-resistant Gram-negative bacilli and Gram-positive cocci obtained from an ongoing cross-Canada surveillance study.

DESIGN

Clinical isolates of aerobic Gram-negative bacilli with inducible and constitutive chromosomally mediated cephalosporinases, viridans group streptococci and Streptococcus pneumoniae were collected from laboratories serving hospitals, nursing homes and physician offices in the community from across Canada during 1996 and 1997. Laboratories were asked to submit only clinically relevant nonduplicate isolates for susceptibility testing. In vitro antimicrobial susceptibility testing was carried out on all isolates of Gram-negative and viridans group streptococci. S pneumoniae were characterized as penicillin susceptible, intermediately resistant or highly resistant. Nonsusceptible isolates were defined as being intermediately or highly resistant (minimal inhibitory concentrations [MIC] greater than 0.06 mg/L). Only isolates of S pneumoniae that were nonsusceptible to penicillin were selected for further study. MICs were determined using a microbroth dilution technique according to the National Committee of Clinical Laboratory Standards.

RESULTS

A total of 727 Gram-negative bacilli samples were collected. No resistance to cefepime was detected with Citrobacter freundii, Serratia marcescens, Morganella morganii and Enterobacter species. Of these strains, Enterobacter species and C freundii were the most resistant to ceftazidime, cefotaxime and ceftriaxone with MIC(90S) of 32 mg/L or greater and resistance rates of 6% or greater. Resistance rates of Pseudomonas aeruginosa and Acinetobacter species to cefepime were 4.8% and 3%, respectively. The two organisms had similar rates of resistance to ceftazidime. Less than 3% of the Gram-negative bacilli were resistant to imipenem and meropenem. There were 153 viridans group streptococci, of which 22 (14.4%) were resistant to penicillin. Of 1287 S pneumoniae samples, 193 (15%) were nonsusceptible to penicillin. Cefepime, ceftriaxone and cefotaxime had comparable activity against all isolates of viridans group streptococci and S pneumoniae.

CONCLUSIONS

Cefepime demonstrated excellent in vitro activity against Gram-negative bacilli with inducible and constitutive chromosomally mediated cephalosporinases, and had equal or superior activity versus comparator beta-lactams against all isolates of viridans group streptococci and S pneumoniae.

Methicillin-resistant Staphylococcus aureus in Canada: a historical perspective and lessons learned

The history of methicillin-resistant Staphylococcus aureus (MRSA) in Canada has many similarities to MRSA evolution worldwide, but especially to that in the United States and United Kingdom. Reports of MRSA occurred as early as 1964, and community isolates were cited in the 1970s. Nosocomial outbreaks were becoming common by 1978 and flourished gradually thereafter. Endemic institutional MRSA became predominant in the 1990s, threatening large teaching hospitals in particular. In the last decade, both hospital-acquired and community-acquired MRSA have created major medical problems in Canada. More recently, an epidemic of Canadian community-acquired MRSA-10, has led to heightened public health concerns. Canadian contributions to MRSA science are numerous, with organized surveillance continuing to mature across the nation. A typing system for epidemic clones is now available and is being judiciously applied. Estimated costs for MRSA surveillance, treatment, and control are extraordinary, paralleling the dramatic rise in the number of MRSA isolations. Whereas surveillance continues to form an essential aspect of MRSA management, control, eradication, and overall diminution, MRSA reservoirs deserve much greater attention. Such efforts, however, must be as widely publicized in the community and in patient homes as they are in medical institutions responsible for both acute and long-term care.

A review of antimicrobial resistance in Canada

Antimicrobial resistance is a global concern. Over the past 10 years, considerable efforts and resources have been expended to detect, monitor, and understand at the basic level the many different facets of emerging and increasing resistance. This review summarizes our current understanding of bacterial antimicrobial resistance issues in Canada with particular emphasis given to the Enterobacteriaceae, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus, Neisseria meningitidis, Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, and Streptococcus pyogenes. In addition, future concerns and programs for ongoing surveillance are discussed.

Trends in antibiotic resistance of staphylococci over an eight-year period: differences in the emergence of resistance between coagulase positive and coagulase-negative staphylococci

The antimicrobial susceptibilities of 1058 Staphylococcus aureus and 2,163 coagulase-negative staphylococci (CNS) isolates obtained from clinical specimen between 1988 and 1995, were determined against 13 anti-staphylococcal antibiotics. During the study period the resistance of Staphylococcus aureus to ciprofloxacin, ceftazidime, and norfloxacin increased significantly by 7%, 4%, and 6%, respectively (p < or = 0.001). By comparison, the antibiotic resistance of CNS to ceftazidime, oxacillin, norfloxacin, ciprofloxacin, fusidic acid, and cefoxitin increased by 20%, 17%, 15%, 14%, 12% and 10%, respectively (p < or = 0.001). Invasive and noninvasive S. aureus had similar antibiotic resistance, whereas CNS invasive isolates were more resistant than noninvasive isolates to every antibiotics, except vancomycin and fusidic acid. These differences were significant (p < 0.001) for oxacillin, cefoxitin, and clindamycin. Our observations confirm that staphylococci and particularly CNS isolates show an important rate of increased resistance to the standard antimicrobials used for therapy, and that the rate of emergence of resistance differ considerably between coagulase-positive and coagulase-negative staphylococci.

Piperacillin/tazobactam: an updated review of its use in the treatment of bacterial infections

Piperacillin/tazobactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity encompassing most Gram-positive and Gram-negative aerobic bacteria and anaerobic bacteria, including many pathogens producing beta-lactamases. Evidence from clinical trials in adults has shown that piperacillin/tazobactam, administered in an 8:1 ratio, is an effective treatment for patients with lower respiratory tract, intra-abdominal, urinary tract, gynaecological and skin/soft tissue infections, and for fever in patients with neutropenia. Combination regimens of piperacillin/tazobactam plus an aminoglycoside are used to treat patients with severe nosocomial (hospital-acquired) infections. In clinical trials, piperacillin/tazobactam was significantly more effective than ticarcillin/clavulanic acid in terms of clinical and microbiological outcome in patients with community-acquired pneumonia. In patients with intra-abdominal infections, clinical and bacteriological response rates were significantly higher with piperacillin/tazobactam than with imipenem/cilastatin (administered at a dosage lower than is recommended in countries outside Scandinavia). Piperacillin/tazobactam in combination with amikacin was at least as effective as ceftazidime plus amikacin in the treatment of ventilator-associated pneumonia and was significantly more effective than ceftazidime plus amikacin in the empirical treatment of febrile episodes in patients with neutropenia or granulocytopenia. In other trials, the efficacy of piperacillin/tazobactam was similar to that of standard aminoglycoside-containing and other treatment regimens in patients with intra-abdominal, skin/soft tissue or gynaecological infections. Piperacillin/tazobactam is generally well tolerated. The most frequent adverse events are gastrointestinal symptoms (most commonly diarrhoea) and skin reactions. The incidence of adverse events with piperacillin/tazobactam is higher when the combination is given in combination with an aminoglycoside than when given as monotherapy.

CONCLUSION

Because of the broad spectrum of antibacterial activity provided by piperacillin/tazobactam, it is useful for the treatment of patients with polymicrobial infections caused by aerobic or anaerobic beta-lactamase-producing bacteria. Piperacillin/tazobactam appears to have a particularly useful role in the treatment of patients with intra-abdominal infections and, in combination with amikacin, in the treatment of patients with febrile neutropenia, especially given the current prevalence of Gram-positive infections in this group.