Resistance to imipenem among selected gram-negative bacilli in the United States

The Prevalence of Colonization with Carbapenem-resistant Enterobacteriaceae, E. coli, Klebsiella and Enterobacter, and Related Risk Factors in Children

Background: Carbapenems are broad-spectrum antibiotics used to treat the family of gram-negative Enterobacteriaceae, especially those that are resistant to first-line antibiotics. Because these drugs are usually prescribed as the last line of treatment, resistance to these antibiotics carries irreparable risks to treatment systems, and screening high-risk individuals in medical centers and using infection control measures are critical strategies for eliminating them. Objectives: We investigated the prevalence of colonization of different strains of Enterobacteriaceae, Klebsiella, Enterobacter, and Escherichia coli and their risk factors in hospitalized children. Methods: In this descriptive cross-sectional study, stool samples were taken from patients during the first 48 hours of hospitalization in a tertiary children’s hospital and were cultured on Makcanki culture medium or EMB. Cultured Enterobacteriaceae samples were transferred to Müller-Hinton agar medium, and their antibiotic susceptibility was evaluated with meropenem and imipenem discs by disc diffusion method. In the next step, five common carbapenemase genes, including (VIM, IMP, OXA-48, NDM-1, and SPM-1) were examined by PCR method and reported accordingly. Results: Two hundred and ninety-five stool samples were examined, of which 242 (82%) samples were cultured positively with Enterobacteriaceae. The prevalence of carbapenem resistance was reported to be 37% among 295 samples using the phenotypic method. Resistance rates were high in patients with a history of antibiotic use, with frequent hospitalizations (more than two episodes in the last six months), and in patients with an underlying disease) malignancy, GI diseases, immunodeficiency, neurologic diseases such as cerebral palsy and epilepsy, endocrine diseases. Most of the genes found were OXA-48, followed by IMP and VIM. NDM-1 was found in 3 samples, and SPM was not found in any of the samples. In 13% of resistant samples, more than one carbapenemase gene was found. Conclusions: The results of this study showed that the frequency of carbapenem resistance in stools colonized with Enterobacteriaceae is high in our patients. On the other hand, the presence of carbapenemase genes in these bacteria, which are located on the plasmids that can be rapidly spread in the hospital environment, is an alarm for the hospital infection control committee to take preventive measures in order to prevent the spread of these bacteria in the hospital.

CG258 Klebsiella pneumoniae isolates without β-lactam resistance at the onset of the carbapenem-resistant Enterobacteriaceae epidemic in New York City

Objectives

To examine the epidemiology of β-lactam resistance in 'clonal group 258' (CG258), a successful KPC clonal group, over 14 years.

Methods

Isolates were collected from 1999 to 2013 for a study of antibiotic resistance in Enterobacteriaceae in New York City; 515 bloodstream isolates had antibiotic susceptibility data available and 436 were available for a CG258 PCR assay. The 56 resulting CG258 isolates were characterized by MLST, capsular type and ESBL and KPC carriage. KPC-positive isolates were assessed for common KPC plasmid types, KPC subtype and Tn4401 isoform.

Results

RT-PCR revealed 56 isolates were CG258. Seventeen of the 56 CG258 isolates were phenotypically susceptible to all carbapenems (all KPC negative). Five out of 17 susceptible isolates were of the cps-2 (wzi154) capsule type; none was cps-1 (wzi29). Nineteen out of 28 KPC-2 isolates were cps-1 (wzi29) and 8/10 KPC-3 isolates carried cps-2 (wzi154); however, cps-2 (wzi154) predominated among KPC-2-positive isolates in 2003 and 2004. KPC-2 was first detected in 2003 and KPC-3 was first detected in 2006. KPC-harbouring plasmids pKpQIL (all Tn4401a) and pBK30683 (all Tn4401d) were detected in 16/38 and 6/38 carbapenem-resistant isolates, respectively.

Discussion

CG258-lineage Klebsiella pneumoniae isolates were completely absent in 1999, but common in 2003. Twenty-one percent of CG258 isolates were susceptible to carbapenems in addition to lacking both common ESBL and blaKPC-mediated resistance. The cps-2 (wzi154) capsule type was common in both these susceptible isolates and in early KPC-2-harbouring isolates, suggesting it was the initial capsule type in CG258. Carbapenem-resistant isolates carried common KPC-harbouring plasmids with the same KPC and Tn4401 isoforms, suggesting frequent clonal spread.

Treatment of Klebsiella pneumoniae carbapenemase (KPC) infections: a review of published case series and case reports

The emergence of Klebsiella pneumoniae carbapenemases (KPCs) producing bacteria has become a significant global public health challenge while the optimal treatment remains undefined. We performed a systematic review of published studies and reports of treatment outcomes of KPC infections using MEDLINE (2001–2011). Articles or cases were excluded if one of the following was fulfilled: no individual patient data provided, no treatment regimen specified, no treatment outcome specified, report of colonization, or greater than three antibiotics were used to treat the KPC infection. Data extracted included patient demographics, site of infection, organism, KPC subtype, antimicrobial therapy directed at KPC-infection, and treatment outcome. Statistical analysis was performed in an exploratory manner. A total of 38 articles comprising 105 cases were included in the analysis. The majority of infections were due to K. pneumoniae (89%). The most common site of infection was blood (52%), followed by respiratory (30%), and urine (10%). Forty-nine (47%) cases received monotherapy and 56 (53%) cases received combination therapy directed at the KPC-infection. Significantly more treatment failures were seen in cases that received monotherapy compared to cases who received combination therapy (49% vs 25%; p= 0.01). Respiratory infections were associated with higher rates of treatment failure with monotherapy compared to combination therapy (67% vs 29% p= 0.03). Polymyxin monotherapy was associated with higher treatment failure rates compared to polymyxin-based combination therapy (73% vs 29%; p= 0.02); similarly, higher treatment failure rates were seen with carbapenem monotherapy compared to carbapenem-based combination therapy (60% vs 26%; p= 0.03). Overall treatment failure rates were not significantly different in the three most common antibiotic-class combinations: polymyxin plus carbapenem, polymyxin plus tigecycline, polymyxin plus aminoglycoside (30%, 29%, and 25% respectively; p=0.6). In conclusion, combination therapy is recommended for the treatment of KPC infections; however, which combination of antimicrobial agents needs to be established in future prospective clinical trials.

Carbapenem-resistant Enterobacteriaceae: epidemiology and prevention

Over the past 10 years, dissemination of Klebsiella pneumoniae carbapenemase (KPC) has led to an increase in the prevalence of carbapenem-resistant Enterobacteriaceae (CRE) in the United States. Infections caused by CRE have limited treatment options and have been associated with high mortality rates. In the previous year, other carbapenemase subtypes, including New Delhi metallo-β-lactamase, have been identified among Enterobacteriaceae in the United States. Like KPC, these enzymes are frequently found on mobile genetic elements and have the potential to spread widely. As a result, preventing both CRE transmission and CRE infections have become important public health objectives. This review describes the current epidemiology of CRE in the United States and highlights important prevention strategies.

Empiric, broad-spectrum antibiotic therapy with an aggressive de-escalation strategy does not induce gram-negative pathogen resistance in ventilator-associated pneumonia

BACKGROUND

Early, empiric, broad-spectrum antibiotics followed by de-escalation to pathogen-specific therapy is the standard of care for ventilator-associated pneumonia (VAP). In our surgical intensive care unit (SICU), imipenem-cilastatin (I-C) in combination with tobramycin (TOB) or levofloxacin (LEV) has been used until quantitative bronchoalveolar lavage results are finalized, at which time de-escalation occurs to pathogen-specific agents. With this practice, however, alterations in antimicrobial resistance remain a concern. Our hypothesis was that this strict regimen does not alter antimicrobial susceptibility of common gram-negative VAP pathogens in our SICU.

METHODS

After Institutional Review Board approval, a retrospective review of SICU-specific antibiograms was performed for the sensitivities of common gram-negative VAP pathogens. Time periods were defined as early (January-June 2005) and late (July-December 2006). Chart review of empiric and de-escalation antibiotic usage was obtained. Data were collated, and statistical significance was assessed with the chi-square test using the on-line Simple Interactive Statistical Analysis tool.

RESULTS

Imipenem-cilastatin was used 198 times for empiric VAP coverage (811 patient-days), whereas TOB and LEV were given a total of 149 (564 patient-days) and 61 (320 patient-days) times, respectively. Collectively, the susceptibility of gram-negative organisms to I-C did not change (early 91.4%; late 97%; p = 0.33). Individually, non-significant trends to greater sensitivity to I-C were noted for both Pseudomonas aeruginosa (early 85.7%; late 90.9%; p = 0.73) and Acinetobacter baumannii (early 80%; late 100%; p = 0.13). Further, both TOB (early 77.1%; late 70.0%; p = 0.49) and LEV (early 74.3%; late 70.0%; p = 0.67) were found to maintain their susceptibility profiles. The frequency of resistant gram-positive VAPs was unchanged during the study period. Our de-escalation compliance (by 96 h) was 78% for I-C, 77.2% for TOB, and 59% for LEV. When infections requiring I-C were removed from the analysis, de-escalation compliance was improved to 92%.

CONCLUSIONS

In our SICU, early, empiric broad-spectrum VAP therapy followed by de-escalation to pathogen-specific agents did not alter antimicrobial resistance and is a valid practice. Further, our compliance with de-escalation practices was higher than published rates.

Correlation between antibiotic use and changes in susceptibility patterns of Pseudomonas aeruginosa in a medical-surgical intensive care unit

Context:

Multiple surveillance programmes have reported a decline in antibiotic susceptibility of P. aeruginosa.

Aim:

Our study aimed to study the relationship between the use of antipseudomonal drugs and the development of resistance of P. aerogenosa to these drugs.

Setting and Design:

Our study is retrospective. It was conducted in a medical surgical intensive care unit during a five-year period (January 1^st, 1999 to December 31, 2003), which was divided into 20 quarters. We had monitored the use of antipseudomonal agents and the resistance rates of P. aeruginosa to these drugs.

Statistical Methods:

The associations between use and resistance were quantified using non-partial and partial correlation coefficients according to Pearson and Spearman.

Results:

Over the study period, the most frequently used antipseudomonal agent was Imipenem (152 ± 46 DDD/1000 patients-day) and the resistance rate of P. aeruginosa to Imipenem was 44.3 ± 9.5% (range, 30 and 60%). In addition, Imipenem use correlated significantly with development of resistance to Imipenem in the same (P < 0.05) and in the following quarter (P < 0.05); and Ciprofloxacin use correlated significantly with resistance to Ciprofloxacin in the following quarter (P < 0.05). However, use of Ceftazidime or Amikacine had no apparent association with development of resistance.

Conclusion:

We conclude that the extensive use of imipenem or ciprofloxacin in intensive care units may lead to the emergence of imipenem- and ciprofloxacin-resistant strains of P. aeruginosa and that antibiotic prescription policy has a significant impact on P. aeruginosa resistance rates in an intensive care unit.

Imipenem-resistant Pseudomonas aeruginosa: risk factors for nosocomial infections

The aim of this study was to determine the risk factors for nosocomial infections of imipenem-resistant Pseudomonas aeruginosa (IRPA). A prospective case-control study was performed at a tertiary care hospital in Ankara from January to December 2004. The patients with nosocomial P. aeruginosa infection were included in the study. The features of the patients with IRPA infections were compared to those with imipenem-sensitive P. aeruginosa (ISPA) infections. Only the first isolation of P. aeruginosa was considered. Nosocomial infections were defined according to Center for Disease Control (CDC) criteria. IRPA was isolated from 75 (44.1%) patients, and ISPA was isolated from 95 (55.9%) patients during the study period. IRPA were most frequently isolated from endotracheal aspirate (19%) cultures (p=0.048), whereas ISPA were most frequently isolated from urine (28%) cultures (p=0.023). In multivariate analysis, a longer duration of hospital stay until P. aeruginosa isolation (odds ratio [OR], 1.027; 95% confidence interval [CI], 1.002-1.054, p=0.034), arterial catheter administration (OR, 2.508; 95% CI, 1.062-5.920, p=0.036), vancomycin (OR, 2.882; 95% CI, 1.130-7.349, p=0.027), piperacillin-tazobactam (OR, 6.425; 95% CI, 2.187-18.875, p=0.001), and imipenem (OR, 3.580; 95% CI, 1.252-10.245, p=0.017) treatment within the 14 days before isolation of IRPA were independently associated with imipenem resistance. It was concluded that treatment with imipenem, vancomycin and piperacillin-tazobactam were major risk factors for IRPA infections in hospitalized patients. The nosocomial occurrence of IRPA was also strongly related to the duration of hospital stay, arterial catheter administration.

Changes in antibiotic resistance of the most common Gram-negative bacteria isolated in intensive care units

We studied the changes in antibiotic resistance of the most common Gram-negative bacteria isolated in the intensive care units at our hospital in 2000 and 2002. Bacterial identification was performed by use of the VITEK 60 analyser, and antibiotic susceptibilities were tested by the VITEK 60 analyser and the disk diffusion agar method. The bacteria isolated most frequently were Pseudomonas aeruginosa (132 strains in 2000 and 106 in 2002), Acinetobacter calcoaceticus (98 and 109 strains, respectively) and Klebsiella pneumoniae (53 and 83 strains, respectively). Acinetobacters presented the highest percentage resistance, with significant increases in resistance to imipenem (15% in 2000 and 67% in 2002) and piperacillin/tazobactam (41% and 72%, respectively). P. aeruginosa presented a significant increase in resistance to all antibiotics, except ceftazidime. A large increase was observed in the resistance of K. pneumoniae to amikacin (from 10% to 50%), ceftazidime (from 80% to 90%) and tobramycin (from 80% to 90%). No imipenem-resistant strains of K. pneumoniae were found.

Risk Factors for the Acquisition of Carbapenem-Resistant Klebsiella pneumoniae among Hospitalized Patients

The isolation of carbapenem-resistant Klebsiella pneumoniae (CRKP) has been increasingly reported. However, no study analyzing potential risk factors for the acquisition of CRKP has been published as of now. We therefore performed a case-control study to determine the risk factors for the acquisition of CRKP. CRKP was nosocomially isolated from 30 patients between January 1997 and August 2003. Control patients were randomly selected at a ratio of 4:1 from the same medical or surgical services from which patients were receiving care when isolation of CRKP occurred. Risk factors for CRKP were previous use of carbapenem (adjusted odds ratio [AOR], 28.68; 95% confidence interval [CI], 9.08-90.55) and cephalosporin (AOR, 4.10; 95% CI, 1.35-12.43). In contrast, previous use of fluoroquinolone was negatively associated with isolation of CRKP (AOR, 0.26; 95% CI 0.07-0.97); however, the possibility of selection bias cannot be ruled out. Our results suggest that the nosocomial isolation of CRKP is strongly favored by the selection pressure of carbapenem.

Risk factors for ICU-acquired imipenem-resistant Gram-negative bacterial infections

Intensive care units (ICUs) are high-risk areas for infections caused by antibiotic-resistant bacteria. This study investigated the risk factors for ICU-acquired imipenem-resistant Gram-negative infections. It was conducted prospectively in three surgical ICUs and one medical ICU from April to December 2002. ICU-acquired Gram-negative infections were found in 128 patients. Of these, 42 had imipenem-resistant and 86 had imipenem-sensitive Gram-negative bacteria as the cause of infection. According to the univariate analysis results, hospital stay before ICU admission, hospitalization period before ICU admission, length of ICU stay, surgical ICU stay, surgical operation and previous antibiotic use were significant risk factors for the acquisition of imipenem-resistant infections. In the multivariate analysis, length of ICU stay, surgical operation and previous carbapenem use were independently associated with imipenem resistance.

In vitro and in vivo activities of novel 6-methylidene penems as beta-lactamase inhibitors

Novel penem molecules with heterocycle substitutions at the 6 position via a methylidene linkage were investigated for their activities and efficacy as beta-lactamase inhibitors. The concentrations of these molecules that resulted in 50% inhibition of enzyme activity were 0.4 to 3.1 nM for the TEM-1 enzyme, 7.8 to 72 nM for Imi-1, 1.5 to 4.8 nM for AmpC, and 14 to 260 nM for a CcrA metalloenzyme. All the inhibitors were more stable than imipenem against hydrolysis by hog and human dehydropeptidases. Piperacillin was combined with a constant 4-microg/ml concentration of each inhibitor for MIC determinations. The combinations reduced piperacillin MICs by 2- to 32-fold for extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae strains. The MICs for piperacillin-resistant (MIC of piperacillin, >64 microg/ml) strains of Enterobacter spp., Citrobacter spp., and Serratia spp. were reduced to the level of susceptibility (MIC of piperacillin, < or =16 microg/ml) when the drug was combined with 4, 2, or 1 microg of these penem inhibitors/ml. Protection against acute lethal bacterial infections with class A and C beta-lactamase- and ESBL-producing organisms in mice was also demonstrated with piperacillin plus inhibitor. Median effective doses were reduced by approximately two- to eightfold compared to those of piperacillin alone when the drug was combined with the various inhibitors at a 4:1 ratio. Pharmacokinetic analysis after intravenous administration of the various inhibitors showed mean residence times of 0.1 to 0.5 h, clearance rates of 15 to 81 ml/min/kg, and volumes of distribution between 0.4 and 2.5 liters/kg. The novel methylidene penem molecules inhibit both class A and class C enzymes and warrant further investigation for potential as therapeutic agents when used in combination with a beta-lactam antibiotic.

Epidemiological risk factors for isolation of ceftriaxone-resistant versus -susceptible citrobacter freundii in hospitalized patients

Antimicrobial resistance is an emerging problem among nosocomial bacteria. Risk factors for the recovery of ceftriaxone-resistant (CRCF) or -susceptible (CSCF) Citrobacter freundii in clinical cultures from hospitalized patients were determined by using a case-case-control study design. CRCF was isolated from 43 patients (case group 1) and CSCF was isolated from 87 patients (case group 2) over a 3-year period. Risk factors for CRCF were exposure to imipenem (odds ratio [OR], 7.5; 95% confidence interval [CI], 1.2 to 45.4), broad-spectrum cephalosporins (OR, 6.9; 95% CI, 1.8 to 26.7), vancomycin (OR, 3.0; 95% CI, 1.2 to 7.4), or piperacillin-tazobactam (OR, 2.6; 95% CI, 1.1 to 6.2), as well as hospital length of stay >or=1 week (OR, 3.6; 95% CI, 1.3 to 10.2) and intensive care unit (ICU) stay (OR, 2.6; 95% CI, 1.1 to 6.2). Risk factors for CSCF were peripheral vascular disease (OR, 23.2; 95% CI, 4.3 to 124.6), AIDS (OR, 9.5; 95% CI, 1.6 to 55.5), cerebrovascular disease (OR, 4.2; 95% CI, 1.6 to 10.8), and ICU stay (OR, 3.1; 95% CI, 1.8 to 5.4).

Retrospective analysis of antibiotic susceptibility patterns of respiratory isolates of Pseudomonas aeruginosa in a Turkish University Hospital

BACKGROUND

Lower respiratory tract infections due to Pseudomonas aeruginosa have a high mortality rate. Antibacterial activity of various antibiotics against P. aeruginosa isolated from each hospital depends on the variety or amount of antibiotics used in each hospital.

METHOD

A total of 249 respiratory isolates of Pseudomonas aeruginosa in Sivas (Turkey) were included between January-1999 and January-2002. Isolates were tested against 14 different antibiotics by a disc diffusion method or standardized microdilution technique.

RESULTS

Organisms were cultured from the following specimens: sputum (31.3%), transtracheal/endotracheal aspirates (37.8%), and bronchial lavage (30.9%). Isolates in bronchial lavage were highly susceptible to cefoperazone and aminoglycosides. Resistance to ampicillin/sulbactam was 98.8%, ticarcillin 40.1%, ticarcillin/clavulanic acid 11.2%, piperacillin 21.8%, aztreonam 66.6%, cefotaxim 75.4%, ceftriaxone 84.2%, cefoperazone 39.0%, ceftazidime 50.8%, gentamicin 57.5%, tobramycin 58.4%, amikacin 25.4%, ciprofloxacin 16.1%, and imipenem/cilastatin 21.6%. The term multidrug-resistant P. aeruginosa covered resistance to imipenem, ciprofloxacin, ceftazidime, gentamicin, and piperacillin. 1.2% of isolates were multidrug-resistant.

CONCLUSIONS

These findings suggest that amikacin resistance increases progressively in Turkey. Piperacillin and ticarcillin/clavulanate were the most active agents against both imipenem- and ciprofloxacin-resistant isolates in our region.

Prophylactic antibiotics alter the bacteriology of infected necrosis in severe acute pancreatitis

BACKGROUND

Use of appropriate prophylactic antibiotics has been shown to decrease infectious complications and mortality rate in patients with severe acute pancreatitis, but its influence on the bacteriology of secondary pancreatic infection is poorly defined.

STUDY DESIGN

Operative cultures from 61 consecutive patients with pancreatic necrosis treated during routine prophylactic antibiotic use (1993-2001) were compared with 34 consecutive patients with necrosis treated before routine antibiotic use (1977-1992).

RESULTS

The two groups of patients were similar in demographics, etiology of pancreatitis, and severity of illness. All patients in the antibiotic group received prophylactic antibiotics compared with only 38% (13 of 34) in the control group. Routine broad-spectrum prophylactic antibiotics altered the bacteriology of secondary pancreatic infection in severe acute pancreatitis from predominantly gram-negative coliforms (56% versus 26%, p = 0.005) to predominately gram-positive organisms (23% versus 52%, p = 0.009) without a significant increase in either the rate of beta-lactam resistance or fungal infections. The overall hospital stay in patients treated with prophylactic antibiotics was significantly reduced (61 +/- 24 days versus 41 +/- 28 days, p = 0.002), and there was a trend toward a decline in mortality rate in the antibiotic treatment group.

CONCLUSION

Routine broad-spectrum prophylactic antibiotic use has altered the bacteriology of secondary pancreatic infection in severe acute pancreatitis from predominantly gram-negative coliforms to predominantly gram-positive organisms without altering the rate of beta-lactam resistance or fungal superinfection.

Antimicrobial activity of imipenem against isolates from complicated urinary tract infections

Antimicrobial activity of imipenem was measured using 4725 strains isolated from patients with complicated urinary tract infections (CUTIs) between 1988 and 2000. Imipenem was inactive against methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis, Enterococcus faecium and some non-fermenting Gram-negative rods. Resistant strains (MIC>16 mg/l) were observed in Staphylococcus haemolyticus (22%), Enterococcus faecalis (4%), Enterococcus avium (8%), Serratia marcescens (5%) and Pseudomonas aeruginosa (7%). Although the prevalence of imipenem-resistant strains of S. aureus, S. epidermidis and P. aeruginosa was sporadically high in some years, no steady increase was seen over the period. Resistant strains were rare in other major uropathogenic species. These results suggest that imipenem is still one of the most reliable antimicrobial drugs.

Risk factors for piperacillin-tazobactam-resistant Pseudomonas aeruginosa among hospitalized patients

Antimicrobial resistance is an emerging problem with Pseudomonas aeruginosa. This study determined risk factors for the recovery of piperacillin-tazobactam-resistant P. aeruginosa from clinical cultures from hospitalized patients. A case-control study design was used to compare two groups of case patients with control patients. The first group of case patients was defined by nosocomial isolation of piperacillin-tazobactam-resistant P. aeruginosa, and the second group of cases yielded piperacillin-tazobactam-susceptible P. aeruginosa. Controls were selected in a 6:1 ratio from the same medical or surgical services among which piperacillin-tazobactam-resistant P. aeruginosa arose in patients. Risk factors analyzed included antimicrobial drug exposure, comorbid conditions, and demographics. Bivariate and multivariable analyses were performed. Piperacillin-tazobactam-resistant P. aeruginosa was isolated from 179 patients, and piperacillin-tazobactam-susceptible P. aeruginosa was isolated from 624 patients over a 2.5-year period. Piperacillin-tazobactam (odds ratio [OR] = 6.82; 95% confidence interval [CI], 4.56 to 10.21), imipenem (OR = 2.42; 95% CI, 1.19 to 4.94), aminoglycosides (OR = 2.18; 95% CI, 1.44 to 3.28), vancomycin (OR = 1.87; 95% CI, 1.21 to 2.89), and broad-spectrum cephalosporins (OR = 2.38; 95% CI, 1.45 to 3.88) were the antibiotics associated with the isolation of piperacillin-tazobactam-resistant P. aeruginosa. Exposure to vancomycin (OR = 1.53; 95% CI, 1.13 to 2.06) or ampicillin-sulbactam (OR = 2.28; 95% CI, 1.62 to 3.21) was associated with recovery of piperacillin-tazobactam-susceptible P. aeruginosa. In this study, antibiotics associated with piperacillin-tazobactam-susceptible P. aeruginosa were different from antibiotics associated with piperacillin-tazobactam-resistant P. aeruginosa. Piperacillin-tazobactam was a strong risk factor for piperacillin-tazobactam-resistant P. aeruginosa. Our results suggest that the nosocomial isolation of piperacillin-tazobactam-resistant P. aeruginosa may be affected by multiple antibiotics.

Risk factors for imipenem-resistant Pseudomonas aeruginosa among hospitalized patients

Risk factors for the nosocomial recovery of imipenem-resistant Pseudomonas aeruginosa (IRPA) were determined. A case-control study design was used for the comparison of 2 groups of case patients with control patients. The first group of case patients had nosocomial isolation of IRPA, and the second group had imipenem-susceptible P. aeruginosa (ISPA). Control patients were selected from the same medical or surgical services from which case patients were receiving care when isolation of IRPA occurred. Risk factors analyzed included antimicrobials used, comorbid conditions, and demographic variables. IRPA was recovered from 120 patients, and ISPA from 662 patients. Imipenem (odds ratio [OR], 4.96), piperacillin-tazobactam (OR, 2.39), vancomycin (OR, 1.80), and aminoglycosides (OR, 2.19) were associated with isolation of IRPA. Vancomycin (OR, 1.64), ampicillin-sulbactam (OR, 2.00), and second-generation cephalosporins (OR, 2.00) were associated with isolation of ISPA. Antibiotics associated with ISPA are different from antibiotics associated with IRPA. The OR for imipenem as a risk factor for IRPA is less than that reported from studies in which control group selection was suboptimal.

[Hormonal contraception and epilepsy]

Attempts to optimize quality of life in woman with epilepsy should include a reliable method for birth control, including oral contraceptives (OC). One of these methods is hormonal oral contraception. The classic antiepileptic drugs (AEDs)--Phenytoin, Phenobarbital, Ethosuximide and Carbamazepine induce hepatic microsomal enzymes and decrease the production of estradiol and progesterone, that may be compromise the effects of OC. Recommendation for women taking OC include possible use of noninducing AEDs (Valproic acid), new AEDs--Lamotrigine, Gabapentin, Topiramate, Tiagabine or for patients taking inducing AEDs use of an OC containing > or = 50 micrograms. estrogen. Patients should be warned that midcycle bleeding indicates possible OC failure and that the absence of such bleeding is not an indication of OC effectiveness. Additional contraceptive methods are also advised. The authors report their own experience in 12 women taking AEDs and OC.

Monotherapy versus combination therapy for bacterial infections

The authors discuss the latest findings regarding the use of one or more antimicrobial drugs for a variety of infections. They offer suggestions for treatment based on a host of considerations, including the synergy and antagonism of specific drugs, type of infection, potential toxicities, and cost.

Carbapenems and monobactams: imipenem, meropenem, and aztreonam

Imipenem and meropenem, members of the carbapenem class of beta-lactam antibiotics, are among the most broadly active antibiotics available for systemic use in humans. They are active against streptococci, methicillin-sensitive staphylococci, Neisseria, Haemophilus, anaerobes, and the common aerobic gram-negative nosocomial pathogens including Pseudomonas. Resistance to imipenem and meropenem may emerge during treatment of P. aeruginosa infections, as has occurred with other beta-lactam agents; Stenotrophomonas maltophilia is typically resistant to both imipenem and meropenem. Like the penicillins, the carbapenems have inhibitory activity against enterococci. In general, the in vitro activity of imipenem against aerobic gram-positive cocci is somewhat greater than that of meropenem, whereas the in vitro activity of meropenem against aerobic gram-negative bacilli is somewhat greater than that of imipenem. Daily dosages may range from 0.5 to 1 g every 6 to 8 hours in patients with normal renal function; the daily dose of meropenem, however, can be safely increased to 6 g. Infusion-related nausea and vomiting, as well as seizures, which have been the main toxic effects of imipenem, occur no more frequently during treatment with meropenem than during treatment with other beta-lactam antibiotics. The carbapenems should be considered for treatment of mixed bacterial infections and aerobic gram-negative bacteria that are not susceptible to other beta-lactam agents. Indiscriminate use of these drugs will promote resistance to them. Aztreonam, the first marketed monobactam, has activity against most aerobic gram-negative bacilli including P. aeruginosa. The drug is not nephrotoxic, is weakly immunogenic, and has not been associated with disorders of coagulation. Aztreonam may be administered intramuscularly or intravenously; the primary route of elimination is urinary excretion. In patients with normal renal function, the recommended dosing interval is every 8 hours. Patients with renal impairment require dosage adjustment. Aztreonam is used primarily as an alternative to aminoglycosides and for the treatment of aerobic gram-negative infections. It is often used in combination therapy for mixed aerobic and anaerobic infections. Approved indications for its use include infections of the urinary tract or lower respiratory tract, intra-abdominal and gynecologic infections, septicemia, and cutaneous infections caused by susceptible organisms. Concurrent initial therapy with other antimicrobial agents is recommended before the causative organism has been determined in patients who are seriously ill or at risk for gram-positive or anaerobic infection.

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.

Surveillance for the emergence and dissemination of antimicrobial resistance in bacteria

Effective surveillance of antimicrobial-resistant bacteria is important for developing rational empiric therapy guidelines and for guiding public health efforts to control and prevent the spread of infective agents. Surveillance must include a timely and thorough review of the test results generated in clinical microbiology laboratories because this data serves as the core of surveillance activities. Besides ensuring data accuracy and optimizing detection of emerging resistance, the role of clinical microbiology also includes supporting the production of informative surveillance reports, providing laboratory resources for outbreak investigations, and monitoring the performance of commonly used susceptibility testing methods. Once the accuracy of susceptibility results has been validated, the data are used by public health agencies and professional societies to monitor resistance trends on a local, state, national, and international level. This information is also used to develop policies for prudent antimicrobial use locally and nationally.

The impact of antimicrobial use on the emergence of antimicrobial-resistant bacteria in hospitals

Abundant evidence suggests a relationship between antimicrobial resistance and use, including models, consistent associations between resistance and antimicrobial use in hospitals, concomitant variation in resistance as antimicrobial use varies, and a dose-response relationship for many pathogen/antimicrobial combinations. Much of the evidence is from studies performed in single hospitals. Most multicenter studies on resistance have not included data on antimicrobial usage. Despite this substantial body of evidence, some studies have not demonstrated an association between antimicrobial resistance and use, suggesting other contributing factors such as cross transmission, interhospital transfer of resistance, a community contribution to resistance, or a complex relationship between resistance and the use of a variety of antimicrobials. Understanding the problem of antimicrobial resistance in a hospital cannot be achieved without knowledge of the hospital's pattern of antimicrobial use.

Secular trends in bloodstream infection caused by antimicrobial-resistant bacteria in New Jersey hospitals, 1991 to 1995

INTRODUCTION

Antimicrobial resistance among bacteria is an increasing public health problem. In 1991, New Jersey was the first state to establish statewide, hospital-based surveillance for antimicrobial-resistant bacteria.

METHODS

Each month, all 96 nonfederal New Jersey hospital laboratories complete a form listing the species identity and drug susceptibility results for selected antimicrobial-resistant bacteria isolated from blood cultures from hospital inpatients. Penicillin-resistant Streptococcus pneumoniae and aminoglycoside-resistant gram-negative rods were studied from 1991 to 1995. Vancomycin-resistant enterococci and imipenem-resistant gram-negative rods were studied from 1992 through 1995.

RESULTS

From 1992 to 1995, the vancomycin-resistant enterococci bloodstream infection prevalence rate increased from 11 to 29 per 100,000 hospital admissions (p < 0.001); the rate was higher at larger hospitals, urban and inner-city hospitals, and teaching hospitals. From 1991 to 1995, the penicillin-resistant S. pneumoniae bloodstream infection rate increased from 1.1 to 9.9 per 100,000 admissions (p < 0.001). In contrast, bloodstream infection rates did not change significantly for imipenem-resistant (12.5 during 1992 and 14.1 during 1995, p = 0.4) or aminoglycoside-resistant (8.0 during 1991 and 6.8 during 1995, p = 0.4) gram-negative rods.

CONCLUSIONS

We found that vancomycin-resistant enterococci and penicillin-resistant S. pneumoniae, but neither of two groups of antimicrobial-resistant gram-negative rods, are increasing rapidly in prevalence in New Jersey. Continued monitoring and interventions to slow these increases are needed.

Antibiotic resistance among gram-negative nosocomial pathogens in the intensive care unit: results of 6-year body-site monitoring

Results of 6-year body-site monitoring in an intensive care unit (ICU) are presented and antimicrobial resistance of gram-negative isolates analyzed. The study included 622 patients. Six hundred thirty-five bacterial isolates-causes of nosocomial sepsis, pneumonia, and urinary tract infections (UTIs)-were tested during the study. Gram-negative bacteria were the predominant isolates, causing 65% of cases of sepsis, 78.7% of pneumonias, and 70.2% of UTIs. Gram-negative isolates (454) were highly resistant to antimicrobials commonly used in the ICU, with the exception of imipenem. Resistance was 1.1% among pathogens responsible for UTIs, 6.7% among those causing sepsis, and 13.6% among those responsible for pneumonia. Klebsiella pneumoniae associated with pneumonia and sepsis was significantly less resistant to ciprofloxacin than were isolates from urine (22.8% and 13.9%, respectively, vs 44.4%). Pseudomonas aeruginosa strains responsible for pneumonia were less resistant to ceftazidime than were isolates causing sepsis and UTI (35.7% vs 51.3% and 51.5%, respectively). Acinetobacter calcoaceticus strains associated with UTI were significantly more resistant to netilmicin than were strains responsible for sepsis and pneumonia (83.3% vs 40.3% and 42.6%, respectively). The study confirmed that in addition to focused microbiologic surveillance, multiple-body-site monitoring can provide unique information about the sensitivity of the pathogens involved. The results suggest that antimicrobial resistance among nosocomial pathogens depends on the site of infection or the type of microbiologic specimen.

Effect of zinc concentration in Mueller-Hinton agar on susceptibility of Pseudomonas aeruginosa to imipenem

The susceptibility of Pseudomonas aeruginosa to imipenem has been shown to vary according to zinc concentration in the media. MICs of imipenem for 68 unique clinical isolates of P. aeruginosa were determined in media supplemented with zinc at concentrations between 0.5 and 6.0 micrograms/ml. In agar containing up to 3 micrograms of zinc/ml, 75 to 82% of the strains were susceptible to imipenem at an MIC of < or = 4 micrograms/ml. In agar supplemented to contain 6 micrograms of zinc/ml, however, only 40% of the strains were susceptible to imipenem. Manufacturers should ensure that the concentration of zinc in commercial media is below 3 micrograms/ml to avoid false classification of isolates as resistant to imipenem.

Imipenem/cilastatin: an update of its antibacterial activity, pharmacokinetics and therapeutic efficacy in the treatment of serious infections

The prototype carbapenem antibacterial agent imipenem has a very broad spectrum of antibacterial activity, encompassing most Gram-negative and Gram-positive aerobes and anaerobes, including most beta-lactamase-producing species. It is coadministered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Extensive clinical experience gained with imipenem/cilastatin has shown it to provide effective monotherapy for septicaemia, neutropenic fever, and intra-abdominal, lower respiratory tract, genitourinary, gynaecological, skin and soft tissues, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad-spectrum cephalosporins and other carbapenems and is at least equivalent to standard aminoglycoside-based and other combination regimens. Imipenem/cilastatin is generally well tolerated by adults and children, with local injection site events, gastrointestinal disturbances and dermatological reactions being the most common adverse events. Seizures have also been reported, occurring mostly in patients with impaired renal function or CNS pathology, or with excessive dosage. Although it is no longer a unique compound, as newer carbapenems such as meropenem are becoming available, imipenem/cilastatin nevertheless remains an important agent with established efficacy as monotherapy for moderate to severe bacterial infections. Its particular niche is in treating infections known or suspected to be caused by multiresistant pathogens.

Activity of carbapenem BMS-181139 against Pseudomonas aeruginosa is not dependent on porin protein D2

The broad antipseudomonal spectrum of the carbapenem BMS-181139 includes clinical strains and laboratory mutants of Pseudomonas aeruginosa that are resistant to imipenem. Unlike other known carbapenems (meropenem, panipenem, biapenem, and BO-2727), which have reduced activity against imipenem-resistant strains of P. aeruginosa, BMS-181139 was equally active against imipenem-susceptible (D2-sufficient) and imipenem-resistant (D2-deficient) strains. Conversely, imipenem and meropenem activities were the same against the susceptible parental strains and their BMS-181139-resistant mutants. Whereas basic amino acids antagonized the antipseudomonal activities of imipenem and meropenem, they had no effect on the activity of BMS-181139. These results suggest that the uptake of BMS-181139 into pseudomonal cells occurs by a non-D2 pathway. Compared with imipenem and meropenem, BMS-181139 may have a slightly higher affinity for penicillin-binding protein 2 (PBP-2) of P. aeruginosa. The rates of resistance development to imipenem, meropenem, and BMS-181139 in P. aeruginosa strains were similar; resistance occurred at frequencies of approximately 10(-7) to 10(-8). Resistance to BMS-181139 in P. aeruginosa is presumed to be caused by its diminished permeability since no change in their penicillin-binding protein affinities or beta-lactamase levels could be detected. In summary, BMS-181139 is a new carbapenem which differs from other known carbapenems in its lack of cross-resistance with imipenem. This difference could be explained by the permeation of BMS-181139 through a non-D2 channel, compared to the preferential uptake of other carbapenems by the D2 porin.

Clinical and molecular epidemiology of acinetobacter infections sensitive only to polymyxin B and sulbactam

A nosocomial outbreak of infections due to imipenem-resistant Acinetobacter baumannii occurred in a New York hospital after increased use of imipenem for cephalosporin-resistant klebsiella infections. We identified all A baumannii isolates over 12 months, reviewed corresponding patient records, and compared strains with different antibiotic susceptibility patterns by restriction endonuclease analysis. Environmental surveillance cultures were done before and after institution of control measures. 59 patients harboured imipenem-resistant A baumannii, and 18 were infected. Isolates from patients were resistant to all routinely tested antibiotics, including imipenem. Further studies showed susceptibility to polymyxin B and sulbactam. These isolates were identical by restriction endonuclease analysis to A baumannii isolates susceptible to imipenem alone, or to imipenem and amikacin, but differed from broadly susceptible isolates. Surveillance cultures showed hand and environmental colonisation by imipenem-resistant strains. Infection and colonisation were eliminated by intensive infection control measures, and irrigation of wounds with polymyxin B. Increased use of imipenem against cephalosporin-resistant klebsiella may lead to imipenem resistance among other species, particularly acinetobacter. Such resistance appears to derive from a prior multi-resistant clone, in contrast to one which retains susceptibility to several antibiotics.

Imipenem stability in a predried susceptibility panel

We performed a 15-month study using 11 clinical strains and 1 control strain (ATCC 27853) of Pseudomonas aeruginosa to determine whether changes in the manufacturing process of Sensititre predried panels result in a reliable test of susceptibility to imipenem. MIC and breakpoint susceptibility results remained stable during the manufacturer's recommended shelf life of 18 months and compared well with standard agar disk diffusion and broth macrodilution results. Imipenem concentrations measured by high-pressure liquid chromatography were acceptable through 15 months but declined in the breakpoint panels by approximately 50% at 18 months. Between 9 months and panel expiration, 13 of 141 (9%) of the MIC panel packages had moisture entry, as indicated by pink desiccants, with a resultant loss of imipenem activity of 32 to 100%. It appears that the new manufacturing process produces MIC panels that are reliable for imipenem susceptibility testing until the labeled expiration date, provided that packages containing pink desiccants are not used.

An overview of nosocomial infections, including the role of the microbiology laboratory

An estimated 2 million patients develop nosocomial infections in the United States annually. The increasing number of antimicrobial agent-resistant pathogens and high-risk patients in hospitals are challenges to progress in preventing and controlling these infections. While Escherichia coli and Staphylococcus aureus remain the most common pathogens isolated overall from nosocomial infections, coagulase-negative staphylococci (CoNS), organisms previously considered contaminants in most cultures, are now the predominant pathogens in bloodstream infections. The growing number of antimicrobial agent-resistant organisms is troublesome, particularly vancomycin-resistant CoNS and Enterococcus spp. and Pseudomonas aeruginosa resistant to imipenem. The active involvement and cooperation of the microbiology laboratory are important to the infection control program, particularly in surveillance and the use of laboratory services for epidemiologic purposes. Surveillance is used to identify possible infection problems, monitor infection trends, and assess the quality of care in the hospital. It requires high-quality laboratory data that are timely and easily accessible.