Imipenem resistance in aerobic gram-negative bacteria

Clinical manifestations and prognostic factors of Morganella morganii bacteremia

Although Morganella morganii causes a variety of clinical infections, there are limited studies on M. morganii bacteremia after the year 2000. A total of 109 patients with M. morganii bacteremia at a medical center in Taiwan from 2003 to 2012 were studied. Among them, 30.3 % had polymicrobial bacteremia and 75.2 % had community-acquired infection. The most common underlying diseases were hypertension (62.4 %) and diabetes mellitus (38.5 %). The urinary tract (41.3 %) was the major portal of entry, followed by the hepatobiliary tract (27.5 %), skin and soft tissue (21.1 %), and primary bacteremia (10.1 %). Susceptibility testing of M. morganii isolates showed ubiquitous resistance to first-generation cephalosporins and ampicillin-clavulanate; resistance rates to gentamicin, piperacillin-tazobactam, and ciprofloxacin were 30.3 %, 1.8 %, and 10.1 %, respectively. Overall, the 14-day mortality was 14.7 %. Univariate analysis revealed that elevated blood urea nitrogen (BUN) values [p = 0.0137, odds ratio (OR) 5.26], intensive care unit (ICU) admission (p = 0.011, OR 4.4), and higher Acute Physiology and Chronic Health Evaluation II (APACHE II) scores (p < 0.001, OR 1.62) were significantly associated with mortality. The APACHE II score remained the only significant risk factor for mortality in multivariate analysis (p = 0.0012, OR 1.55). In conclusion, M. morganii bacteremia patients were mostly elderly, with one or more comorbidities. Most of the patients had community-acquired infection via the urinary and hepatobiliary tracts. Furthermore, prognosis can be predicted according to disease severity measured by the APACHE II score.

Overview of resistant gram-positive pathogens in the surgical patient

Staphylococci and enterococci are the most common pathogens in surgical-site and bloodstream infections. The emergence of drug resistance among these gram-positive bacteria thus poses a substantial threat to patients with surgical infections. Resistance to methicillin/oxacillin is frequently observed in Staphylococcus aureus isolates and is often accompanied by multidrug resistance. Vancomycin is usually the treatment of choice for infections caused by methicillin-resistant S. aureus (MRSA), so the recent appearance of S. aureus isolated with intermediate sensitivity to vancomycin is cause for concern. Vancomycin resistance has already appeared in most species of enterococci. Infections caused by vancomycin-resistant enterococci (VRE) are associated with increased mortality compared to infections caused by vancomycin-sensitive isolates. Measures for preventing vancomycin resistance include reducing the use of vancomycin and other agents that appear to be associated with VRE, including third-generation cephalosporins and anti-anaerobic drugs. Third-generation cephalosporins have also been implicated in the increased prevalence of MRSA infections. Prudent use of existing antibiotics is an essential strategy for combating the rising tide of drug-resistant gram-positive pathogens.

Current pharmacotherapy for the treatment of severe burns

The pharmacotherapy of burn care has evolved from the first topical antibiotics instituted > 30 years ago. These have helped greatly to reduce the incidence of burn wound sepsis, but a better understanding of the principles of burn care has resulted in earlier burn wound excision and complete coverage with autograft, cadaver skin, synthetic dressings, and amnion. This has markedly reduced septic complications and ameliorated the hypermetabolic response to burn injury. The hypermetabolic response, which is mediated by hugely increased levels of circulating catecholamines, prostaglandins, glucagon and cortisol, causes profound skeletal muscle catabolism, immune deficiency, peripheral lipolysis, reduced bone mineralisation, reduced linear growth, and increased energy expenditure. Supportive therapy and pharmacological manipulation, acutely and during rehabilitation, with growth hormone, insulin and related proteins, oxandrolone and propranolol can ameliorate the hypermetabolic response, improving survival and long-term outcome. Despite judicious use of topical and systemic antibiotics, opportunistic nosocomial bacterial resistance threatens to annul the improved survival of patients with severe burns. Patterns of emerging resistance encountered in burn units need to be considered, in light of a decreasing antibiotic armamentarium. A holistic approach to pharmacotherapy of severely burned patients including current practice in antimicrobial control, analgesia, sedation, and anxiety management is required. Current therapy of frequently encountered problems, such as post-burn pruritus, prophylaxis of deep venous thrombosis and peptic ulceration, and pharmacological manipulation of inhalation injury in the burned patient is described. Current pharmacotherapy to ameliorate psychosocial problems associated with burns such as acute stress disorder, depression and post traumatic stress disorder are discussed. Better analgesics, newer antibiotics and immune stimulating drugs are required to reduce mortality and morbidity in large burns.

Antimicrobial susceptibility testing of carbapenems: multicenter validity testing and accuracy levels of five antimicrobial test methods for detecting resistance in Enterobacteriaceae and Pseudomonas aeruginosa isolates

From January 1996 to May 1999, Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) received 448 nonduplicate clinical isolates of Enterobacteriaceae and Pseudomonas aeruginosa that were reported to be imipenem intermediate or resistant. However, broth microdilution (BMD) confirmatory testing at the Project ICARE central laboratory confirmed this result in only 11 of 123 (8.9%) Enterobacteriaceae isolates and 241 of 325 (74.2%) P. aeruginosa isolates. To investigate this overdetection of imipenem resistance, we tested 204 selected isolates from the Project ICARE collection plus five imipenem-resistant challenge strains at the Centers for Disease Control and Prevention against imipenem and meropenem by agar dilution, disk diffusion, Etest (AB BIODISK North America, Inc., Piscataway, N.J.), two MicroScan WalkAway conventional panels (Neg MIC Plus 3 and Neg Urine Combo 3) (Dade MicroScan, Inc., West Sacramento, Calif.), and two Vitek cards (GNS-116 containing meropenem and GNS-F7 containing imipenem) (bioMérieux Vitek, Inc., Durham, N.C.). The results of each test method were compared to the results of BMD testing using in-house-prepared panels. Seven imipenem-resistant and five meropenem-resistant isolates of Enterobacteriaceae and 43 imipenem-resistant and 21 meropenem-resistant isolates of P. aeruginosa were identified by BMD. For Enterobacteriaceae, the imipenem and meropenem test methods produced low numbers of very major and major errors. All test systems in the study produced low numbers of very major and major errors when P. aeruginosa was tested against imipenem and meropenem, except for Vitek testing (major error rate for imipenem, 20%). Further testing conducted in 11 of the participating ICARE hospital laboratories failed to pinpoint the factors responsible for the initial overdetection of imipenem resistance. However, this study demonstrated that carbapenem testing difficulties do exist and that laboratories should consider using a second, independent antimicrobial susceptibility testing method to validate carbapenem-intermediate and -resistant results.

Epidemiology, resistance, and outcomes of Acinetobacter baumannii bacteremia treated with imipenem-cilastatin or ampicillin-sulbactam

STUDY OBJECTIVE

To evaluate epidemiology, resistance, and treatment outcomes of Acinetobacter baumannii bacteremia treated with imipenem-cilastatin or ampicillin-sulbactam for 72 hours or longer.

DESIGN

Retrospective analysis.

SETTING

University teaching hospital.

PATIENTS

Forty-eight patients with A. baumannii bacteremia.

INTERVENTION

Evaluation of susceptibility and clinical data from 48 patients treated with either ampicillin-sulbactam or imipenem-cilastatin from 1987-1999.

MEASUREMENTS AND MAIN RESULTS

Comparing ampicillin-sulbactam and imipenem-cilastatin, there were no differences between days of bacteremia (4 vs 2 days, p=0.05), days to resolution of temperature or white blood cell count, success or failure during or at end of treatment, or intensive care unit total or antibiotic-related length of stay (13 vs 10 days, p=0.05). Patients treated with ampicillin-sulbactam had significantly decreased antibiotic treatment costs (1500 dollars vs 500 dollars, p=0.004).

CONCLUSION

Ampicillin-sulbactam is at least as effective as imipenem-cilastatin based on clinical response at days 2, 7, and end of treatment and is a cost-effective alternative for treatment of A. baumannii infections.

Hospital-acquired pneumonia: risk factors, microbiology, and treatment

Pneumonia complicates hospitalization in 0.5 to 2.0% of patients and is associated with considerable morbidity and mortality. Risk factors for hospital-acquired pneumonia (HAP) include mechanical ventilation for > 48 h, residence in an ICU, duration of ICU or hospital stay, severity of underlying illness, and presence of comorbidities. Pseudomonas aeruginosa, Staphylococcus aureus, and Enterobacter are the most common causes of HAP. Nearly half of HAP cases are polymicrobial. In patients receiving mechanical ventilation, P aeruginosa, Acinetobacter, methicillin-resistant S aureus, and other antibiotic-resistant bacteria assume increasing importance. Optimal therapy for HAP should take into account severity of illness, demographics, specific pathogens involved, and risk factors for antimicrobial resistance. When P aeruginosa is implicated, monotherapy, even with broad-spectrum antibiotics, is associated with rapid evolution of resistance and a high rate of clinical failures. For pseudomonal HAP, we advise combination therapy with an antipseudomonal beta-lactam plus an aminoglycoside or a fluoroquinolone (eg, ciprofloxacin).

Antibiotic resistance

Widespread resistance problems exist today in a global sense because of the incorporation of antibiotics with a high resistance potential into animal feeds and because of the uncontrolled use of antibiotics with a high resistance potential in the clinical setting. The only proven method of controlling nonoutbreak resistance problems in hospitals is to limit the hospital formulary to antibiotics with little or no resistance potential. The control of multiresistant organisms in outbreaks occurring in hospitals is best contained using appropriate infection control containment measures. Physicians treating infections in the community, with all other factors being equal, should preferentially select antibiotics with a low resistance potential. The titles and headings of much of the resistance literature are misleading. Articles should not contain fluoroquinolone resistant in the title when ciprofloxacin-resistant organisms are described. Many articles concerning penicillin-resistant pneumococci are entitled fluoroquinolone-resistant S. pneumoniae. These articles describe ciprofloxacin-resistant S. pneumoniae and not resistance to other fluoroquinolones. The same error is perpetuated in describing third-generation cephalosporins and carbapenems. Virtually all of the resistance problems associated with third-generation cephalosporins and carbapenems are due to ceftazidime or imipenem. More precise titling in the literature would remind physicians that antibiotic resistance is related to a specific agent and not class phenomena.

Imipenem resistance of enterobacter aerogenes mediated by outer membrane permeability

Multidrug-resistant Enterobacter aerogenes strains are increasingly isolated in Europe and especially in France. Treatment leads to imipenem resistance, because of a lack of porin. We studied the evolution of resistance in 29 strains isolated from four patients during their clinical course. These strains belonged to the prevalent epidemiological type observed in France in previous studies (C. Bosi, et al., J. Clin. Microbiol. 37:2165-2169, 1999; A. Davin-Regli et al., J. Clin. Microbiol. 34:1474-1480, 1996). They also harbored a TEM-24 extended-spectrum beta-lactamase-coding gene. Thirteen strains were susceptible to gentamicin and resistant to imipenem and cefepime. All of the patients showed E. aerogenes strains with this resistance after an imipenem treatment. One patient showed resistance to imipenem after a treatment with cefpirome. Twelve of these 13 strains showed a lack of porin. Cessation of treatment with imipenem for three patients was followed by reversion of susceptibility to this antibiotic and the reappearance of porins, except in one case. For one patient, we observed three times in the same day the coexistence of resistant strains lacking porin and susceptible strains possessing porin. The emergence of multidrug-resistant E. aerogenes strains is very disquieting. In our study, infection by E. aerogenes increased the severity of the patients' illnesses, causing a 100% fatality rate.

Alterations in surface hydrophobicity of Acinetobacter baumannii induced by meropenem

Six strains of Acinetobacter baumannii out of eleven strains tested revealed a strong hydrophobic character. This was demonstrated by adherence of bacteria to xylene in the range of 90-94%. Changes in surface hydrophobicity of these strains were studied after treatment with meropenem at subinhibitory concentrations (sub-MICs) (1/4, 1/8, 1/16 or 1/32 of the MICs). All strains showed a reduced adherence to xylene after the action of meropenem at 1/4 or 1/16 of the MICs. Hydrophobicity of the treated bacteria was decreased to 1.3-70% (1/16 of the MICs) or to 12-86% (1/4 of the MICs), depending on the strain. A decrease in surface hydrophobicity of three strains was also observed after their exposure to meropenem at 1/8 of the MICs (to 18-71% of the control values). Meropenem at 1/32 of the MICs practically did not affect bacterial hydrophobic properties, with the exception of one strain.