Rapid emergence of resistance to cefepime during treatment

Infectious Diseases Society of America Guidance on the Treatment of AmpC β-lactamase-Producing Enterobacterales, Carbapenem-Resistant Acinetobacter baumannii, and Stenotrophomonas maltophilia Infections

BACKGROUND

The Infectious Diseases Society of America (IDSA) is committed to providing up-to-date guidance on the treatment of antimicrobial-resistant infections. A previous guidance document focused on infections caused by extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa). Here, guidance is provided for treating AmpC β-lactamase-producing Enterobacterales (AmpC-E), carbapenem-resistant Acinetobacter baumannii (CRAB), and Stenotrophomonas maltophilia infections.

METHODS

A panel of six infectious diseases specialists with expertise in managing antimicrobial-resistant infections formulated questions about the treatment of AmpC-E, CRAB, and S. maltophilia infections. Answers are presented as suggestions and corresponding rationales. In contrast to guidance in the previous document, published data on optimal treatment of AmpC-E, CRAB, and S. maltophilia infections are limited. As such, guidance in this document is provided as "suggested approaches" based on clinical experience, expert opinion, and a review of the available literature. Because of differences in the epidemiology of resistance and availability of specific anti-infectives internationally, this document focuses on the treatment of infections in the United States.

RESULTS

Preferred and alternative treatment suggestions are provided, assuming the causative organism has been identified and antibiotic susceptibility results are known. Approaches to empiric treatment, duration of therapy, and other management considerations are also discussed briefly. Suggestions apply for both adult and pediatric populations.

CONCLUSIONS

The field of antimicrobial resistance is highly dynamic. Consultation with an infectious diseases specialist is recommended for the treatment of antimicrobial-resistant infections. This document is current as of September 17, 2021 and will be updated annually. The most current versions of IDSA documents, including dates of publication, are available at www.idsociety.org/practice-guideline/amr-guidance-2.0/.

A Primer on AmpC β-Lactamases: Necessary Knowledge for an Increasingly Multidrug-resistant World

Understanding the nuances of AmpC β-lactamase-mediated resistance can be challenging, even for the infectious diseases specialist. AmpC resistance can be classified into 3 categories: (1) inducible chromosomal resistance that emerges in the setting of a β-lactam compound, (2) stable derepression due to mutations in ampC regulatory genes, or (3) the presence of plasmid-mediated ampC genes. This review will mainly focus on inducible AmpC resistance in Enterobacteriaceae. Although several observational studies have explored optimal treatment for AmpC producers, few provide reliable insights into effective management approaches. Heterogeneity within the data and inherent selection bias make inferences on effective β-lactam choices problematic. Most experts agree it is prudent to avoid expanded-spectrum (ie, third-generation) cephalosporins for the treatment of organisms posing the greatest risk of ampC induction, which has best been described in the context of Enterobacter cloacae infections. The role of other broad-spectrum β-lactams and the likelihood of ampC induction by other Enterobacteriaceae are less clear. We will review the mechanisms of resistance and triggers resulting in AmpC expression, the species-specific epidemiology of AmpC production, approaches to the detection of AmpC production, and treatment options for AmpC-producing infections.

Outcomes of treating AmpC-producing Enterobacterales bacteraemia with carbapenems vs. non-carbapenems

INTRODUCTION

AmpC β-lactamases are found in Enterobacter species, Serratia species, Citrobacter freundii, Providencia species and Morganella morganii ('ESCPM'). Carbapenems are commonly used to treat severe 'ESCPM' infections. Carbapenem-sparing agents are needed because of increasing carbapenem resistance worldwide. Use of cefepime and piperacillin-tazobactam has limited supportive clinical data. We evaluated the efficacy of non-carbapenems vs. carbapenems in 'ESCPM' bacteraemia.

METHODS

A retrospective cohort study was conducted on patients with 'ESCPM' bacteraemia. Primary outcome was 30-day mortality. Analyses were performed on patients who received carbapenems vs. piperacillin-tazobactam or cefepime monotherapy as empirical and definitive therapy. Propensity score for carbapenem therapy was adjusted for in multivariate analyses for 30-day mortality.

RESULTS

A total of 241 patients were included. The most common bacterium isolated was Enterobacter species (58.1%). Common sources were urinary (22.8%) and vascular lines (22.0%). Carbapenems (28.6%) and piperacillin-tazobactam (28.6%) were the commonest empirical antibiotics. Carbapenems (54.8%) and cefepime (23.7%) were the most common definitive antibiotics. Median Pitt bacteraemia score was 1 (interquartile range [IQR], 0-2). Overall, 30-day mortality was 12.9%. Adjusted multivariate analyses for empirical and definitive antibiotic treatment models yielded risk factors for 30-day mortality, including higher Pitt bacteraemia score (empirical: adjusted OR [aOR] 1.21 for each point increase, 95% confidence interval [CI]:1.01-1.45; definitive: aOR 1.33 for each point increase, 95% CI:1.06-1.69) and age (empirical: aOR 1.04 for each year increase, 95% CI:1.01-1.08). Empirical piperacillin-tazobactam (aOR 0.29, 95% CI:0.07-1.27) and definitive cefepime (aOR 0.65, 95% CI:0.12-3.55) were not associated with 30-day mortality.

CONCLUSIONS

Compared with carbapenem therapy, empirical piperacillin-tazobactam and definitive cefepime were not associated with 30-day mortality in 'ESCPM' bacteraemia.

Risk factors and outcomes of pyogenic liver abscess in adult liver recipients: a matched case-control study

BACKGROUND

Adult liver recipients (ALR) differ from the general population with pyogenic liver abscess (PLA) as they exhibit: reconstructed biliary anatomy, recurrent hospitalizations, poor clinical condition and are subjected to immunosuppression. The aim of this study was to identify risk factors associated with PLA in ALR and to analyze the management experience of these patients.

METHODS

Between 1996 and 2016, 879 adult patients underwent liver transplantation (LT), 26 of whom developed PLA. Patients and controls were matched according to the time from transplant to abscess in a 1 to 5 relation. A logistic regression model was performed to establish PLA risk factors considering clusters for matched cases and controls. Risk factors were identified and a multivariate regression analysis performed.

RESULTS

Patients with post-LT PLA were more likely to have lower BMI (p = 0.006), renal failure (p = 0.031) and to have undergone retransplantation (p = 0.002). A history of hepatic artery thrombosis (p = 0.010), the presence of Roux en-Y hepatojejunostomy (p < 0.001) and longer organ ischemia time (p = 0.009) were independent predictors for the development of post-LT PLA. Five-year survival was 49% (95%CI 28-67%) and 89% (95%CI 78%-94%) for post-LT PLA and no post-LT PLA, respectively (p < 0.001).

CONCLUSION

history of hepatic artery thrombosis, the presence of hepatojejunostomy and a longer ischemia time represent independent predictors for the development of post-LT PLA. There was a significantly poorer survival in patients who developed post-LT PLA compared with those who did not.

Updates in the Management of Cephalosporin-Resistant Gram-Negative Bacteria

Resistance to cephalosporins is now common among Gram-negative bacterial infections, including those caused by the Enterobacteriaceae and Pseudomonas aeruginosa, posing a major threat to public health. As resistance to the traditional drugs of choice for these infections, carbapenems, has also become increasingly common, interest in cefepime and piperacillin-tazobactam as carbapenem-sparing alternatives has increased. Additionally, the availability of the novel β-lactam-β-lactamase inhibitor combinations ceftolozane-tazobactam and ceftazidime-avibactam has added to the antimicrobial armamentarium available to treat these multidrug-resistant infections. Here, we review the recent literature on the use of carbapenem-sparing alternatives and highlight the potential utility of novel antimicrobials.

The use of cefepime for treating AmpC β-lactamase-producing Enterobacteriaceae

BACKGROUND

 AmpC β-lactamase-producing organisms are associated with significant morbidity and mortality. Induction of resistance to third-generation cephalosporins after exposure to these agents complicates treatment options and carbapenems are considered optimal therapy. The role of cefepime, however, remains unclear. Our objective was to compare clinical outcomes for patients receiving cefepime compared with meropenem for invasive infections caused by organisms expressing AmpC β-lactamases.

METHODS

 Hospitalized patients with blood, bronchoalveolar lavage, or intra-abdominal fluid cultures growing Enterobacter spp, Serratia spp, or Citrobacter spp were evaluated using the cefotetan-boronic acid disk test and the cefotetan-cloxacillin Etest to identify organisms with AmpC β-lactamase production from February 2010 to January 2011. In patients with organisms hyperproducing AmpC β-lactamases (positive by both methods), clinical outcomes for patients receiving cefepime or meropenem therapy were compared. To minimize the possibility of treatment selection bias, 1:1 nearest neighbor propensity score matching was performed prior to regression analysis.

RESULTS

 Of 399 patients meeting eligibility criteria, 96 (24%) had confirmed infections with AmpC β-lactamase-producing organisms. Propensity score matching of patients infected with AmpC β-lactamase-positive organisms treated with cefepime or meropenem yielded 32 well-balanced patient pairs with no difference in 30-day mortality (odds ratio, 0.63; 95% confidence interval [CI], .23-2.11; P = .36) or length of hospital stay after infection (relative risk, 0.96; 95% CI, .79-1.26; P = .56) between the 2 groups.

CONCLUSIONS

 Cefepime may be a reasonable option for the treatment of invasive infections due to AmpC β-lactamase-producing organisms, particularly when adequate source control is achieved.

Antibiotic therapy for inducible AmpC β-lactamase-producing Gram-negative bacilli: what are the alternatives to carbapenems, quinolones and aminoglycosides?

Some bacteria that possess chromosomally determined AmpC β-lactamases may express these enzymes at a high level following exposure to β-lactams, either by induction or selection for derepressed mutants. This may lead to clinical failure even if an isolate initially tests susceptible in vitro, a phenomenon best characterised by third-generation cephalosporin therapy for Enterobacter bacteraemia or meningitis. Several other Enterobacteriaceae, such as Serratia marcescens, Citrobacter freundii, Providencia spp. and Morganella morganii (often termed the 'ESCPM' group), may also express high levels of AmpC. However, the risk of clinical failure with β-lactams that test susceptible in vitro is less clear in these species than for Enterobacter. Laboratories frequently do not report β-lactam or β-lactamase inhibitor combination drug susceptibilities for ESCPM organisms, encouraging alternative therapy with quinolones, aminoglycosides or carbapenems. However, quinolones and carbapenems present problems with selective pressure for multiresistant organisms, and aminoglycosides with potential toxicity. The risk of emergent AmpC-mediated resistance for non-Enterobacter spp. appears rare in clinical studies. Piperacillin/tazobactam may remain effective and may be less selective for AmpC derepressed mutants than cephalosporins. The potential roles for agents such as cefepime or trimethoprim/sulfamethoxazole are also discussed. Clinical studies that better define optimal treatment for this group of bacteria are required.

Method for phenotypic detection of extended-spectrum beta-lactamases in enterobacter species in the routine clinical setting

In 271 Enterobacter blood culture isolates from 12 hospitals, extended-spectrum beta-lactamase (ESBL) prevalence varied between 0% and 30% per hospital. High prevalence was associated with dissemination, indicating the potential relevance of infection control measures. Screening with cefepime or Vitek 2, followed by a cefepime/cefepime-clavulanate Etest, was an accurate strategy for ESBL detection in Enterobacter isolates (positive predictive value, 100%; negative predictive value, 99%).

Prevalence of extended-spectrum β-lactamases in isolates of the Enterobacter cloacae complex from German hospitals

In 2002, 119 isolates of the Enterobacter cloacae complex were collected randomly from 11 German laboratories nationwide. Antibiotic susceptibilities were tested by disk-diffusion tests according to CLSI guidelines, and MICs were determined using Etests. PCRs were performed to amplify all TEM and SHV, and most CTX-M and OXA beta-lactamase genes. PCR products were sequenced to identify the precise extended spectrum beta-lactamase (ESBL) types. Isoelectric focusing (IEF) and PM/PML Etests were used to confirm production of the respective ESBLs. According to susceptibility tests and CLSI criteria, 49 (40%) isolates were resistant to extended-spectrum cephalosporins. Seven (5.8%) isolates were positive in at least one of the PCR assays. Sequencing identified production of TEM-1 beta-lactamase genes by three (2.9%) isolates, and ESBL genes of the CTX-M and SHV beta-lactamase families by five (4.2%) isolates. IEF confirmed the production of beta-lactamases in the expected pI ranges of the respective ESBLs, and four of the five ESBL-producers were detected using the PM/PML Etest. All ESBL-producing isolates showed co-resistance to sulphonamides.

Efficacy of cefepime and imipenem in experimental murine pneumonia caused by porin-deficient Klebsiella pneumoniae producing CMY-2 beta-Lactamase

Previous studies have shown decreased in vitro activity of zwitterionic cephalosporins and carbapenems against porin-deficient Klebsiella pneumoniae expressing a plasmid-mediated AmpC-type beta-lactamase (PACBL). The in vitro and in vivo activities of cefepime and imipenem were evaluated against the porin-deficient strain K. pneumoniae C2 and its CMY-2-producing derivative [K. pneumoniae C2(pMG248)]. The MICs (in micrograms/milliliter) of cefepime and imipenem against K. pneumoniae C2 were 0.125 and 0.25, respectively, while the corresponding values against K. pneumoniae C2(pMG248) were 8 and 16. Cefepime showed a greater inoculum effect than imipenem against both strains. Imipenem showed a significant postantibiotic effect (>2 h) against K. pneumoniae C2(pMG248) at 1x, 2x, 4x, 6x, and 8x MIC. The maximum concentrations of drug in serum of cefepime and imipenem in a pneumonia model using mice were 124.1 and 16.9 mug/ml, respectively. DeltaT/MIC for K. pneumoniae C2 and C2(pMG248) were 1.29 h and 0.34 h for imipenem and 2.96 h and 1.27 h for cefepime. Both imipenem (30 mg/kg of body weight every 3 h) and cefepime (60 mg/kg every 4 h), administered for 72 h, increased the survival rate (86.6% and 100%) compared with untreated control animals (26.6%, P < 0.003) infected with K. pneumoniae C2. For the CMY-2-producing strain, imipenem, but not cefepime, increased the survival rate compared to the controls (86.6% and 40% versus 40%, P < 0.01). Bacterial concentration of the lungs was significantly decreased by both antimicrobials. In conclusion, imipenem was more active in terms of survival than cefepime for the treatment of murine pneumonia caused by a porin-deficient K. pneumoniae expressing PACBL CMY-2.

Activity of cefepime and carbapenems in experimental pneumonia caused by porin-deficient Klebsiella pneumoniae producing FOX-5 beta-lactamase

The in-vivo activities of cefepime, imipenem and meropenem against the porin-deficient strain Klebsiella pneumoniae C2 and its derivative K. pneumoniae C2(pMG252) coding for the AmpC-type beta-lactamase FOX-5 were determined. Bactericidal activities were determined with the kill-curve method. A pneumonia model in guinea-pigs was developed, and Cmax, t(1/2) and DeltaT/MIC were calculated for the three agents tested. Animals were treated for 72 h with sterile saline (control group) or with cefepime, imipenem or meropenem (240 mg/kg/day, intramuscularly, three times daily). Bacterial counts in lungs (log10 CFU/g tissue) were determined by serial dilution. MICs (mg/L) of cefepime, imipenem and meropenem against K. pneumoniae C2/K. pneumoniae C2(pMG252), determined by macrodilution, were: 0.5/4, 0.5/0.5 and 0.25/0.5, respectively. Bacterial counts in the lungs of animals infected with K. pneumoniae C2 and treated with antimicrobial agents were always lower than in the control group (cefepime, 4.4 +/- 0.5; imipenem, 4.6 +/- 0.4; meropenem, 4.7 +/- 0.5; control group, 5.6 +/- 0.8; p <0.01). No significant differences were observed among the groups receiving therapy (p >0.05). Bacterial lung clearance was higher in treated animals than in control animals following infection with K. pneumoniae C2(pMG252) (cefepime, 4.5 +/- 0.4; imipenem, 4.0 +/- 0.3; meropenem, 4.6 +/- 0.4; control group, 6.1 +/- 0.6; p <0.01), with imipenem producing better clearance than either cefepime or meropenem (p <0.05). Thus, in the guinea-pig pneumonia model, cefepime, imipenem and meropenem were each effective against the porin-deficient K. pneumoniae strain C2 and its derivative expressing the plasmid-mediated AmpC type beta-lactamase FOX-5.

Infected bilomas in liver transplant recipients, incidence, risk factors and implications for prevention

Bilomas, infected hepatic fluid collections, are a frequent complication of liver transplantation. We report a case-control cohort study to determine the incidence and microbiologic profile of bilomas and risk factors for biloma formation in 492 patients undergoing liver transplantation from 1994 to 2001. Fifty-seven patients (11.5%) developed one or more bilomas; 95% in the first year post-transplantation. The most common initial infecting pathogens were enterococci (37%), one-half resistant to vancomycin (VRE); coagulase-negative staphylococci (26%); and Candida species (26%). Infection by coagulase-negative staphylococci was strongly associated with the presence of a T-tube (OR 9.60, p=0.02). In stepwise logistic regression multivariable analyses, hepatic artery thrombosis (OR 90.9, p<0.0001), hepatic artery stenosis (OR 13.2, p<0.0001) and Roux-en-Y choledochojejunostomy (OR 5.8, p=0.03) were independent risk factors for biloma formation; ursodeoxycholic acid use was highly protective (OR 0.1, p=0.002). Strategies to prevent biloma formation must focus on measures to prevent hepatic artery thrombosis and colonization of liver transplant patients by multiresistant nosocomial pathogens. T-tube drainage post-transplantation bears reassessment. The protective effect of ursodeoxycholic acid found in this study warrants confirmation in a prospective multicenter, randomized trial.

Outbreak of TEM-24-producing Enterobacter aerogenes in a Spanish hospital

Organisms encoding multidrug resistance genes are becoming increasingly prevalent. During a 2-month period (December, 2000, to January, 2001), 83 consecutive isolates of Enterobacter spp. were collected in our microbiology department. Antibiotic susceptibility was determined using the Vitek II automatic system. We selected strains with decreased susceptibility to extended-spectrum cephalosporins. The double-disk potentiation test was positive in 10 of these strains, indicating the presence of extended-spectrum beta-lactamases (ESBLs). Polymerase chain reaction (PCR), isoelectric focusing (IEF), and sequencing identified TEM 24 beta-lactamase in the 10 selected E. aerogenes. Random amplification of polymorphic DNA (RAPD-PCR) revealed the same clonal origin for all the strains tested and strongly suggest an outbreak of multidrug-resistant E. aerogenes. To follow up the trends in ESBLs-producing Enterobacter infections in the hospital over time, we repeated the study 1 year later (December, 2001, to February, 2002). Only three ESBLs-producing Enterobacter were found. All of them corresponded to the previously characterized clone.

Outcome of antibiotic therapy for third-generation cephalosporin-resistant Gram-negative bacteraemia: an analysis of 249 cases caused by Citrobacter, Enterobacter and Serratia species

Two hundred and forty-nine patients with monomicrobial bacteraemia due to third-generation cephalosporin (TGC)-resistant Citrobacter freundii (42), E. aerogenes (23), E. cloacae (143), and Serratia marcescens (41) were analyzed for antibiotic therapy used and outcome. For isolates with resistance to any of the TGCs, all beta-lactams, except imipenem, were considered ineffective. Of 152 patients given appropriate treatment, the mortality rates were 10.9% for 128 patients given monotherapy and 25.0% for 24 patients given combination therapy (P=0.09). Of patients given monotherapy, there were no significant differences in mortality between imipenem, aminoglycoside, and ciprofloxacin treatment groups (P=0.57). Only shock was associated with mortality in multivariate analysis. In conclusion, for patients with TGC-resistant Gram-negative bacteraemia, no significant difference in outcome was observed between single antibiotic therapy groups or monotherapy and combination therapy groups.

Antibiotic resistance in bacteria - an emerging public health problem

The discovery and eventual introduction of anti-microbial agents to clinical medicine was one of the greatest medical triumphs of the twentieth century that revolutionized the treatment of bacterial diseases. However, the gradual emergence of populations of antibiotic-resistant bacteria resulting from use, misuse and outright abuse of antibiotics has today become a major public health problem of global proportions. This review paper examines the origins and molecular epidemiology of resistance genes, global picture of antibacterial resistance, factors that favour its spread, strategies for its control, problems of control and the consequences of failure to contain antibiotic resistance in bacteria.

Is there a rationale for the continuous infusion of cefepime? A multidisciplinary approach

This review is the fruit of multidisciplinary discussions concerning the continuous administration of beta-lactams, with a special focus on cefepime. Pooling of the analyses and viewpoints of all members of the group, based on a review of the literature on this subject, has made it possible to test the hypothesis concerning the applicability of this method of administering cefepime. Cefepime is a cephalosporin for injection which exhibits a broader spectrum of activity than that of older, third-generation cephalosporins for injection (cefotaxime, ceftriaxone, ceftazidime). The specific activity of cefepime is based on its more rapid penetration (probably due to its zwitterionic structure, this molecule being both positively and negatively charged) through the outer membrane of Gram-negative bacteria, its greater affinity for penicillin-binding proteins, its weak affinity for beta-lactamases, and its stability versus certain beta-lactamases, particularly derepressed cephalosporinases. The stability of cefepime in various solutions intended for parenteral administration has been studied, and the results obtained demonstrated the good compatibility of cefepime with these different solutions. These results thus permit the administration of cefepime in a continuous infusion over a 24-h period, using two consecutive syringes.

Hepatic abscess after liver transplantation: 1990-2000

BACKGROUND

Infections following solid-organ transplants are a major cause of morbidity and mortality. Few studies have reported the complications of hepatic abscesses.

METHODS

This investigation consisted of a retrospective chart review of all solid-organ transplant recipients from 1990 to 2000. Criteria for diagnosis included parenchymal hepatic lesions, positive cultures from liver aspirates or blood cultures, or both, and a compatible clinical presentation.

RESULTS

Of 2,175 recipients of all organ transplants (heart, lung, kidney, liver, pancreas), we identified 12 patients who had experienced 14 episodes of hepatic abscess, all in liver transplant recipients. Median time from transplant to hepatic abscess was 386 days (range 25-4,198). The most common predisposing factor was hepatic artery thrombosis (HAT), which occurred in eight patients, and was diagnosed at an average of 249 days (range 33-3,215) after transplantation. Clinical presentation of hepatic abscess was similar to that described in non-immunosuppressed patients. All but one patient showed hypoalbuminemia (<3.5 g/dL); those with HAT also had significantly elevated lactate dehydrogenase. Liver aspirates grew gram-positive aerobic bacteria (50% of isolates), gram-negative aerobic bacteria (30%), and anaerobes and yeasts (10% each). Patients received an average of 6 weeks of intravenous antibiotic therapy. Catheter drainage was successful in 70% of cases; and five patients required retransplantation. Altogether, five of the patients died, yielding a mortality rate of 42%.

CONCLUSIONS

Hepatic abscess, a rare complication after liver transplantation, was frequently associated with hepatic artery thrombosis. Mortality was higher than in patients who had not undergone transplantation. Prolonged antibiotic therapy, drainage, and even retransplantation may be required to improve the outcome in these patients.

Susceptibility Patterns of Select Gram-Negative Organisms after a Formulary Switch from Ceftazidime to Cefepime

Objective:

To document changes in susceptibility patterns of gram-negative organisms, including Pseudomonas aeruginosa, Enterobacter aerogenes, Acinetobacter calcoaceticus, and Serratia marcescens after a formulary switch from ceftazidime to cefepime.

Design, Setting:

Retrospective, observational study in a tertiary care, university teaching hospital.

Participants:

Adult surgical patients with culture and susceptibility data.

Main Outcome Measures:

Percent susceptible and median minimum inhibitory concentration values were evaluated for select gram-negative organisms from culture and susceptibility results. The time periods of one year before and two years after the formulary change were evaluated. Duplicate isolates were excluded. Different culture sites of infection were assessed for P. aeruginosa, including blood, urine, and lung.

Results:

A total of 957 samples from 489 patients were included. Susceptibility results after the formulary switch favored ceftazidime over cefepime for P. aeruginosa (79% vs. 54%; n = 485) and A. calcoaceticus (65% vs. 29%; n = 140). However, cefepime demonstrated greater kill rate with E. aerogenes isolates compared with ceftazidime (95% vs. 69%; n = 208). Susceptibility results were comparable with S. marcescens (100% for cefepime vs. 98% for ceftazidime). P. aeruginosa results from isolates taken from different culture sites did not differ from the overall results, as susceptibility was higher for ceftazidime compared with cefepime for all culture sites.

Conclusions:

Susceptibility to cefepime and ceftazidime is organism-specific; therefore, it may be appropriate to include both agents on the formulary and/or implement an antibiotic rotation policy.

Enterobacter sakazakii infections among neonates, infants, children, and adults. Case reports and a review of the literature

Enterobacter sakazakii can cause serious infections especially among the very young and the elderly. It continues to be more common among neonates and infants than adults. Its tropism for the central nervous system in neonates and infants remains a mystery. Among neonates and infants, E. sakazakii has a propensity to cause meningitis resulting in ventriculitis, brain abscess or cyst formation, and development of hydrocephalus requiring ventricular-peritoneal shunt. Computed tomography of the head is therefore useful in following patients with E. sakazakii meningitis. Mortality and morbidity of E. sakazakii meningitis is high, and virtually all patients recovering from the central nervous system infection suffered mental and physical developmental delays. The case-fatality rate decreased among patients with meningitis treated with the third-generation cephalosporins. Most adults with E. sakazakii infection had serious underlying diseases and 50% of the adults with the infection had malignancies. However there has never been a known case of meningitis. Increasing antibiotic resistance among Enterobacter species should lead one to consider using the carbapenems or the newer cephalosporins in combination with a second agent such as an aminoglycoside. Limited data suggest that trimethoprim-sulfamethoxazole may be a useful agent in the treatment of infections caused by the Enterobacter species, especially in view of the production of extended-spectrum beta-lactamases capable of inactivating the cephalosporins and extended-spectrum penicillin.

National epidemiologic surveys of Enterobacter aerogenes in Belgian hospitals from 1996 to 1998

Two national surveys were conducted to describe the incidence and prevalence of Enterobacter aerogenes in 21 Belgian hospitals in 1996 and 1997 and to characterize the genotypic diversity and the antimicrobial resistance profiles of clinical strains of E. aerogenes isolated from hospitalized patients in Belgium in 1997 and 1998. Twenty-nine hospitals collected 10 isolates of E. aerogenes, which were typed by arbitrarily primed PCR (AP-PCR) using two primers and pulsed-field gel electrophoresis. MICs of 10 antimicrobial agents were determined by the agar dilution method. Beta-lactamases were detected by the double-disk diffusion test and characterized by isoelectric point. The median incidence of E. aerogenes colonization or infection increased from 3.3 per 1,000 admissions in 1996 to 4.2 per 1000 admissions in the first half of 1997 (P < 0.01). E. aerogenes strains (n = 260) clustered in 25 AP-PCR types. Two major types, BE1 and BE2, included 36 and 38% of strains and were found in 21 and 25 hospitals, respectively. The BE1 type was indistinguishable from a previously described epidemic strain in France. Half of the strains produced an extended-spectrum beta-lactamase, either TEM-24 (in 86% of the strains) or TEM-3 (in 14% of the strains). Over 75% of the isolates were resistant to ceftazidime, piperacillin-tazobactam, and ciprofloxacin. Over 90% of the strains were susceptible to cefepime, carbapenems, and aminoglycosides. In conclusion, these data suggest a nationwide dissemination of two epidemic multiresistant E. aerogenes strains in Belgian hospitals. TEM-24 beta-lactamase was frequently harbored by one of these epidemic strains, which appeared to be genotypically related to a TEM-24-producing epidemic strain from France, suggesting international dissemination.

The new antibiotics

It is easy to become overwhelmed by the amount of information available on the new antibiotics and difficult to keep abreast of the appropriate indications for each of them. For most patients with community-acquired infections, the first-line agent is usually not one of the newer agents, but a standard regimen, or at times, no antibiotic at all. The development of resistance is likely to parallel the extent to which these agents are prescribed. They should be used only when standard treatment fails, when compliance with treatment is a real and serious issue, or when the patient has a real allergic reaction to the standard regimen.

Antifungal agents: mode of action, mechanisms of resistance, and correlation of these mechanisms with bacterial resistance

The increased use of antibacterial and antifungal agents in recent years has resulted in the development of resistance to these drugs. The significant clinical implication of resistance has led to heightened interest in the study of antimicrobial resistance from different angles. Areas addressed include mechanisms underlying this resistance, improved methods to detect resistance when it occurs, alternate options for the treatment of infections caused by resistant organisms, and strategies to prevent and control the emergence and spread of resistance. In this review, the mode of action of antifungals and their mechanisms of resistance are discussed. Additionally, an attempt is made to discuss the correlation between fungal and bacterial resistance. Antifungals can be grouped into three classes based on their site of action: azoles, which inhibit the synthesis of ergosterol (the main fungal sterol); polyenes, which interact with fungal membrane sterols physicochemically; and 5-fluorocytosine, which inhibits macromolecular synthesis. Many different types of mechanisms contribute to the development of resistance to antifungals. These mechanisms include alteration in drug target, alteration in sterol biosynthesis, reduction in the intercellular concentration of target enzyme, and overexpression of the antifungal drug target. Although the comparison between the mechanisms of resistance to antifungals and antibacterials is necessarily limited by several factors defined in the review, a correlation between the two exists. For example, modification of enzymes which serve as targets for antimicrobial action and the involvement of membrane pumps in the extrusion of drugs are well characterized in both the eukaryotic and prokaryotic cells.

Extended-spectrum beta-lactamase producing strains of Enterobacter cloacae transferring resistance to cefotaxime and ceftazidime

Transferability of ceftazidime resistance and of extended-spectrum beta-lactamase (ESBL) production was recorded in three strains of Enterobacter cloacae from Frankfurt University Clinics. All three strains were resistant to rifampicin, carbenicillin, cephaloridine, cefotaxime, ceftazidime, aztreonam, imipenem and meropenem. They transferred directly determinants of resistance to carbenicillin and cephaloridine to Escherichia coli K-12 No. 185 nal+ recipient strain. All transconjugant colonies also contained determinants of resistance to cefotaxime, ceftazidime and aztreonam. In the second cycle of transfers, determinants of resistance to carbenicillin, cephaloridine, cefotaxime, ceftazidime and aztreonam were transferred en bloc to the recipient Escherichia coli K-12 No. 3110 rif+ indicating that the "transfer factor" (tra+) mediating the process of conjugational transfer had also been co-transferred. Double-disk diffusion test showed the same pattern of production of ESBLs both in original strains and in transconjugants. Transfer of cefotaxime, ceftazidime and aztreonam was accompanied by the transfer of ESBL production.

Clinical strategies for serious infection: a North American perspective

In the United States, as in Europe, clinical strategies for serious infection are being increasingly driven by growing numbers of cephalosporin-resistant and multiresistant gram-negative bacilli. In a survey of nearly 400 hospital intensive care units in North America, resistance rates of Klebsiella to third-generation cephalosporins increased (from 3.6 to 14.4%) between 1990 and 1993. Resistance rates in Enterobacter are even higher, approaching 40%. Much of this resistance, which is due mainly to production of type-1 and extended spectrum beta-lactamases, appears to have arisen through overuse of third-generation cephalosporins and from poor hand-washing practices. In some American cities, a major reservoir of resistant organisms are nursing homes, where there is evidence of overuse of oral antibiotics. Currently, the most reliable agents available for the treatment of resistant gram-negative pathogens are the carbapenems, imipenem/cilastatin and meropenem, and the aminoglycoside, amikacin. A recent clinical study of meropenem monotherapy in patients with nosocomial pneumonia showed statistically significantly better clinical and microbiologic outcome compared with a standard regimen of ceftazidime plus tobramycin. The enhanced in vitro activity of meropenem against a number of key organisms may have been responsible for the superior results. Although the newer cephalosporins, cefepime and cefpirome, show greater stability to chromosomal type-1 beta-lactamases than ceftazidime, they have variable activity against extended spectrum beta-lactamase producers and can be rendered ineffective by permeability changes which occur in certain organisms. Carbapenems, on the other hand, possess good activity against virtually all of the pathogens which produce the clinically important beta-lactamases, and represent a reliable option for treatment.