In vitro efficacy of six cephalosporins tested against Enterobacteriaceae isolated at 38 North American medical centres participating in the SENTRY Antimicrobial Surveillance Program, 1997-1998

Characterization of cytotoxic Citrobacter braakii isolated from human stomach

Citrobacter braakii (C. braakii) is an anaerobic, gram-negative bacterium that has been isolated from the environment, food, and humans. Infection by C. braakii has been associated with acute mucosal inflammation in the intestine, respiratory tract, and urinary tract. However, the pathogenesis of C. braakii in the gastric mucosa has not yet been clarified. In this study, the bacterium was detected in 35.5% (61/172) of patients with chronic gastritis (CG) and was closely associated with the severity of mucosal inflammation. Citrobacter braakii P1 isolated from a patient with CG exhibited urease activity and acid resistance. It contained multiple secretion systems, including a complete type I secretion system (T1SS), T5aSS and T6SS. We then predicted the potential pilus-related adhesins. Citrobacter braakii P1 diffusely adhered to AGS cells and significantly increased lactate dehydrogenase (LDH) release; the adhesion rate and LDH release were much lower in HEp-2 cells. Strain P1 also induced markedly increased mRNA and protein expression of IL-8 and TNF-α in AGS cells, and the fold increase was much higher than that in HEp-2 cells. Our results demonstrate proinflammatory and cytotoxic role of C. braakii in gastric epithelial cells, indicating the bacterium is potentially involved in inducing gastric mucosa inflammation.

Genomic analysis of Citrobacter from Australian wastewater and silver gulls reveals novel sequence types carrying critically important antibiotic resistance genes

Antimicrobial resistance (AMR) is a major public health concern, and environmental bacteria have been recognized as important reservoirs of antimicrobial resistance genes (ARGs). Citrobacter, a common environmental bacterium and opportunistic pathogen in humans and other animals, has been largely understudied in terms of its diversity and AMR potential. Whole-genome (short-read) sequencing on a total of 77 Citrobacter isolates obtained from Australian silver gull (Chroicocephalus novaehollandiae) (n = 17) and influent wastewater samples (n = 60) was performed, revealing a diverse Citrobacter population, with seven different species and 33 sequence types, 17 of which were novel. From silver gull using non-selective media we isolated a broader range of species with little to no mobilised ARG carriage. Wastewater isolates (selected using Carbapenem- Resistant Enterobacterales (CRE) selective media) carried a heavy burden of ARGs (up to 21 ARGs, conferring resistance to nine classes of antibiotics), with several novel multidrug-resistant (MDR) lineages identified, including C. braakii ST1110, which carried ARGs conferring resistance to eight to nine classes of antibiotics, and C. freundii ST1105, which carried two carbapenemase genes, blaIMP-4 in class 1 integron structure, and blaKPC-2. Additionally, we identified an MDR C. portucalensis isolate carrying blaNDM-1, blaSHV-12, and mcr-9. We identified IncC, IncM2, and IncP6 plasmids as the likely vectors for many of the critically important mobilised ARGs. Phylogenetic analyses were performed to assess any epidemiological linkages between isolation sources, demonstrating low relatedness across sources beyond the ST level. However, these analyses did reveal some closer relationships between strains from disparate wastewater sources despite their collection some 13,000 km apart. These findings support the need for future surveillance of Citrobacter populations in wastewater and wildlife populations to monitor for potential opportunistic human pathogens.

The burden of hospital acquired infections and antimicrobial resistance

The burden of Hospital care-associated infections (HCAIs) is becoming a global concern. This is compounded by the emergence of virulent and high-risk bacterial strains such as "ESKAPE" pathogens - (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter species), especially within Intensive care units (ICUs) that house high-risk and immunocompromised patients. In this review, we discuss the contributions of AMR pathogens to the increasing burden of HCAIs and provide insights into AMR mechanisms, with a particular focus on last-resort antibiotics like polymyxins. We extensively discuss how structural modifications of surface-membrane lipopolysaccharides and cationic interactions influence and inform AMR, and subsequent severity of HCAIs. We highlight some bacterial phenotypic survival mechanisms against polymyxins. Lastly, we discuss the emergence of plasmid-mediated resistance as a phenomenon making mitigation of AMR difficult, especially within the ICUs. This review provides a balanced perspective on the burden of HCAIs, associated pathogens, implication of AMR and factors influencing emerging AMR mechanisms.

The functional repertoire of AmpR in the AmpC β-lactamase high expression and decreasing β-lactam and aminoglycosides resistance in ESBL Citrobacter freundii

Citrobacter freundii is characterized by AmpC β-lactamases that develop resistance to β-lactam antibiotics. The production of extended-spectrum β-lactamase (ESBL) is substantially high in Escherichia coli, C. freundii, Enterobacter cloacae, and Serratia marcescens, but infrequently explored in C. freundii. The present investigation characterized the ESBL C. freundii and delineated the genes involved in decrease in antibiotics resistance. We used the VITEK-2 system and Analytical Profile Index (API) kit to characterize and identify the Citrobacter isolates. The mRNA level of AmpC and AmpR was determined by RT-qPCR, and gel-shift assay was performed to evaluate protein-DNA binding. Here, a total of 26 Citrobacter strains were isolated from COVID-19 patients that showed varying degrees of antibiotic resistance. We examined and characterized the multidrug resistant C. freundii that showed ESBL production. The RT-qPCR analysis revealed that the AmpC mRNA expression is significantly high followed by a high level of AmpR. We sequenced the AmpC and AmpR genes that revealed the AmpR has four novel mutations in comparison to the reference genome namely; Thr64Ile, Arg86Ser, Asp135Val, and Ile183Leu while AmpC remained intact. The ΔAmpR mutant analysis revealed that the AmpR positively regulates oxidative stress response and decreases β-lactam and aminoglycosides resistance. The AmpC and AmpR high expression was associated with resistance to tazobactam, ampicillin, gentamicin, nitrofurantoin, and cephalosporins whereas AmpR deletion reduced β-lactam and aminoglycosides resistance. We conclude that AmpR is a positive regulator of AmpC that stimulates β-lactamases which inactivate multiple antibiotics.

Citrobacter braakii CLABSI in a hematopoietic stem cell transplant patient

INTRODUCTION

Citrobacter bacteria are gram-negative anaerobic bacilli commonly found in water, soil, food, and the intestinal tracts of animals and humans. Patients at highest risk of these nosocomial infections include neonates and adults who are ≥65 years of age, debilitated, or immunocompromised. Citrobacter braakii (C. braakii), specifically, has been reported to cause sepsis in immunocompromised patients. Herein, we describe a case of an allogeneic stem cell transplant (SCT) adult patient with C. braakii bloodstream infection.

CASE REPORT

We report our experience managing a central line-associated bloodstream infection (CLABSI) due to C. braakii in an allogeneic SCT patient.Management and Outcomes: Our patient was initially managed with cefepime. The central venous catheter (CVC) was removed. Blood cultures cleared 24 hours after antibiotic initiation. Therapy was transitioned to oral levofloxacin once susceptibilities resulted.

DISCUSSION

The course of this patient highlights the important relationship between an unusual pathogen, C. braakii, in an immunocompromised allogeneic SCT patient. In our case, the source of the bacteremia was most likely a CLABSI given the positive catheter tip cultures. Although this report describes the successful utilization of cefepime and levofloxacin in the treatment of C. braakii infection, caution should be exercised when choosing empiric antimicrobial therapy as AmpC resistance. This clinical scenario can aid health care providers in making informed treatment decisions when faced with patients diagnosed with this relatively uncommon pathogen. Further reports should be published to determine C. braakii bacteremia management in hematopoietic stem cell transplant patients.

Clinical Characteristics and Antimicrobial Susceptibility Trends in Citrobacter Bacteremia: An 11-Year Single-Center Experience

Background

Recently, Citrobacter freundii bacteremia outbreak in a neonatal intensive care unit has attracted public attention in Korea. However, Citrobacter bacteremia is uncommon and usually occurs in patients with underlying diseases such as malignancy and hepatobiliary diseases. Increase in resistance and emerging of multidrug resistance among Citrobacter species have gradually been reported. The aim of this study was to investigate the clinical characteristics and outcome of C. freundii and non-freundii bacteremia and antimicrobial susceptibility trends.

Materials and Methods

We reviewed the medical records of patients with Citrobacter bacteremia at St. Mary's Hospital, from 2007 to 2017.

Results

A total of 43 patients with a median age of 72 (24-93) years was identified and 90.7% of them had comorbidities. Twenty-nine (67.4%) patients had C. freundii bacteremia while 14 had non-freundii bacteremia (six of C. braakii, five of C. koseri, two of C. amalonaticus and one of C. youngae). A total of 26 (51.2%) patients had community-acquired infection and intra-abdominal infection including hepatobiliary tract was the most common portal of entry (24/43, 55.8%). Moreover, hepatobiliary tract was the leading primary site of nosocomial infection (9/17, 52.9%). Polymicrobial bacteremia was observed in 21 (48.8%) patients. The percentages of Citrobacter species susceptible to ampicillin, amikacin, aztreonam, cefazolin, cefoxitin, cefotaxime, cefepime, piperacillin-tazobactam, ciprofloxacin, and imipenem were 9.5%, 97.6%, 73.8%, 9.5%, 14.3%, 71.4%, 92.9%, 83.3%, 83.3% and 100%, respectively. The resistance rate did not increase during the study period. Of 39 patients treated with antibiotics, 36 (92.3%) received appropriate empirical antibiotics. Overall mortality was 18.6%. High Charlson comorbidity index and Pitt bacteremia score were significant risk factors for death in univariate analysis and showed trends in the multivariate analysis. No significant difference in clinical features and antimicrobial susceptibility rate was observed between C. freundii and non-freundii bacteremia.

Conclusion

Citrobacter bacteremia was predominant in the elderly with comorbidities, while no pediatric case was observed. Hepatobiliary tract is the leading primary focus of bacteremia both in community-acquired and nosocomial infection. The rate of susceptibility to antibiotics has not changed in the last 11 years.

A Rare Cause of Abdominal Pain in a Patient with Acute Necrotizing Pancreatitis

Introduction

Walled-off necrosis (WON) is a potentially lethal late complication of acute pancreatitis (AP) and occurs in less than 10% of AP cases. It can be located in or outside the pancreas. When infected, the mortality rate increases and can reach 100% if the collection is not drained. Its treatment is complex and includes, at the beginning, intravenous antibiotics, which permit sepsis control and a delay in the therapeutic intervention, like drainage. Nowadays, a minimally invasive approach is advised. Depending on the location of the collection, computed tomography (CT)-guided drainage or endoscopic necrosectomy are the primary options, then complemented by surgical necrosectomy if needed. Infected WON of the abdominal wall has been rarely described in the literature and there is no report of any infection with Citrobacter freundii.

Case

We present the case of a 61-year-old man with necrotizing AP complicated by WON of the left abdominal wall, infected with Citrobacter freundii that was successfully treated with CT-guided percutaneous drainage and intravenous antibiotics.

Conclusion

Infected WON accounts for considerable mortality and its location in the abdominal wall is rare; it can be treated with antibiotics and CT-guided drainage with no need for further intervention.

Citrobacter freundii bacteremia: Risk factors of mortality and prevalence of resistance genes

BACKGROUND/PURPOSE

Multidrug-resistant strains of Citrobacter have emerged, which carry Amp-C β-lactamase (Amp-C), broad-spectrum β-lactamase, extended-spectrum β-lactamase (ESBL), and other resistance mechanisms. These strains are associated with a higher rate of in-hospital mortality. The object of this study is to determine the mortality risk factors, susceptibility pattern to antibiotics, and prevalence of resistance genes in patients with Citrobacter freundii bacteremia.

METHODS

From January 2009 to December 2014, blood isolates of C. freundii were collected in MacKay Memorial Hospital, Taipei, Taiwan. PCR technique and sequencing were performed for resistance genes. Pulsed-field gel electrophoresis (PFGE) was done using XbaI restriction enzyme. The clinical characteristics and risk factors for mortality are demonstrated.

RESULTS

The 36 blood isolates of C. freundii belonged to 32 different PFGE pulsotypes, and 15 isolates (41.7%) were polymicrobial. The most common source of infection was intra-abdominal origin (61.1%), followed by unknown sources (22.2%), the urinary tract (8.3%), intravascular catheter (5.6%), and soft tissue (2.8%). High degree of antibiotic resistance was noted for cefazolin (100%), cefoxitin (97.2%), and cefuroxime (66.7%). The bla_TEM-1 resistance gene was present in 16.7% isolates. 72.2% isolates carried bla_AmpC and 5.6% isolates carried ESBL genes (bla_SHV-12 or bla_CTX-M-15). Multivariate analysis indicated that the independent risk factor for 28-day mortality was carrying the bla_TEM-1 resistance gene.

CONCLUSION

For patients with C. freundii bacteremia, carrying the bla_TEM-1 resistance gene was an independent risk factor for 28-day mortality. Carbapenems, fourth-generation cephalosporins, amikacin, and quinolones are still reliable agents for drug-resistant strains.

Characterization and genome sequencing of a Citrobacter freundii phage CfP1 harboring a lysin active against multidrug-resistant isolates

Citrobacter spp., although frequently ignored, is emerging as an important nosocomial bacterium able to cause various superficial and systemic life-threatening infections. Considered to be hard-to-treat bacterium due to its pattern of high antibiotic resistance, it is important to develop effective measures for early and efficient therapy. In this study, the first myovirus (vB_CfrM_CfP1) lytic for Citrobacter freundii was microbiologically and genomically characterized. Its morphology, activity spectrum, burst size, and biophysical stability spectrum were determined. CfP1 specifically infects C. freundii, has broad host range (>85 %; 21 strains tested), a burst size of 45 PFU/cell, and is very stable under different temperatures (-20 to 50 °C) and pH (3 to 11) values. CfP1 demonstrated to be highly virulent against multidrug-resistant clinical isolates up to 12 antibiotics, including penicillins, cephalosporins, carbapenems, and fluroquinoles. Genomically, CfP1 has a dsDNA molecule with 180,219 bp with average GC content of 43.1 % and codes for 273 CDSs. The genome architecture is organized into function-specific gene clusters typical for tailed phages, sharing 46 to 94 % nucleotide identity to other Citrobacter phages. The lysin gene encoding a predicted D-Ala-D-Ala carboxypeptidase was also cloned and expressed in Escherichia coli and its activity evaluated in terms of pH, ionic strength, and temperature. The lysine optimum activity was reached at 20 mM HEPES, pH 7 at 37 °C, and was able to significantly reduce all C. freundii (>2 logs) as well as Citrobacter koseri (>4 logs) strains tested. Interestingly, the antimicrobial activity of this enzyme was performed without the need of pretreatment with outer membrane-destabilizing agents. These results indicate that CfP1 lysin is a good candidate to control problematic Citrobacter infections, for which current antibiotics are no longer effective.

Cefepime

Cefepime (Maxipime), Maxcef, Cepimax, Cepimex, Axepim, a parenteral fourth-generation cephalosporin, is active against many organisms causative in pneumonia. Cefepime has in vitro activity against Gram-positive organisms including Staphylococcus aureus and penicillin-sensitive, -intermediate and -resistant Streptococcus pneumoniae similar to that of cefotaxime and ceftriaxone. Cefepime also has good activity against Gram-negative organisms, including Pseudomonas aeruginosa, similar to that of ceftazidime. Importantly, cefepime is stable against many of the common plasmid- and chromosome-mediated beta-lactamases and is a poor inducer of AmpC beta-lactamases. As a result, it retains activity against Enterobacteriaceae that are resistant to third-generation cephalosporins, such as derepressed mutants of Enterobacter spp. Cefepime may be hydrolyzed by the extended-spectrum beta-lactamases produced by some members of the Enterobacteriaceae, but to a lesser extent than the third-generation cephalosporins. Monotherapy with cefepime 1 or 2g, usually administered intravenously twice daily, was as effective for clinical and bacteriological response as ceftazidime, ceftriaxone or cefotaxime monotherapy (1 or 2g two or three times daily) in a number of randomized, clinical trials in hospitalized adult, or less commonly, pediatric, patients with generally moderate to severe community-acquired or nosocomial pneumonia. More limited data indicated that monotherapy with cefepime 2g three times daily was also as effective in treating patients with nosocomial pneumonia as imipenem/cilostatin 0.5g four times daily, and when combined with amikacin, cefepime was as effective as ceftazidime plus amikacin. Patients with pneumonia who failed to respond to previous antibacterial therapy with penicillins or other cephalosporins responded to treatment with cefepime. Cefepime is generally well tolerated, with a tolerability profile similar to those of other parenteral cephalosporins. In clinical trials, the majority of adverse events experienced by cefepime recipients were mild to moderate and reversible. The most common adverse events with a causal relationship to cefepime reported in clinical trials included rash and diarrhea. Other, less common, adverse events included pruritus, urticaria, nausea, vomiting oral candidiasis, colitis, headache, fever, erythema and vaginitis.

CONCLUSION

Cefepime is an established and generally well tolerated parenteral drug with a broad spectrum of antibacterial activity which, when administered twice daily, provides coverage of most of the pathogens that may be causative in pneumonia. In randomized clinical trials in hospitalized patients with generally moderate to severe community-acquired or nosocomial pneumonia, cefepime monotherapy exhibited good clinical and bacteriological efficacy. Cefepime may become a preferred antibacterial agent for infections caused by Enterobacter spp. With prudent use in order to prevent the emergence of resistant organisms, cefepime will continue to be a suitable option for the empiric treatment of pneumonia.

Clinical outcome of empiric antimicrobial therapy of bacteremia due to extended-spectrum beta-lactamase producing Escherichia coli and Klebsiella pneumoniae

Background

Prompt administration of adequate empiric antimicrobial therapy is a major determinant influencing the outcome of serious infections. The objective of this study was to describe empiric antimicrobial therapy employed and assess its effect on the outcome of patients bacteremic with extended-spectrum beta-lactamase (ESBL) producing Escherichia coli and Klebsiella pneumoniae.

Findings

A retrospective surveillance study of all patients with bacteremias caused by ESBL-producing E. coli and K. pneumoniae (EK-ESBL) from 2000-2007 in the Calgary Health Region was conducted. Data were available for 79 episodes of bacteremia among 76 patients. Forty-four (56%) were male, the median age was 70.0 yrs [interquartile range (IQR) 60.6-70.1 yrs], and 72 (91%) episodes were E. coli. Seventy-four episodes (94%) were treated with empiric therapy within the first 48 hours. A non-statistically significant increased mortality occurred in those treated empirically with a beta-lactam/beta-lactamase inhibitor combination (6/16; 38% vs. 10/53; 18%; p = 0.063) while empiric carbapenem therapy was associated with lower mortality (0/10 died vs. 16/53 (30%), p = 0.089). Only 42 (53%) episodes received adequate therapy within the first 48 hours. The median time to first adequate antibiotic therapy was 41.0 hours [IQR 5.8-59.5] (n = 75). The case-fatality rate was not different among those that received adequate compared to inadequate therapy by 48 hours as compared to inadequate empiric therapy (9/42; 21% vs. 7/37; 19%; p = 1.0).

Conclusion

Inadequate empiric therapy is common among patients with EK-ESBL bacteremia in our region but was not associated with adverse mortality outcome.

Citrobacter infections in a general hospital: characteristics and outcomes

In this investigation, we sought to investigate the characteristics of Citrobacter spp. infections. A retrospective cohort study in a 700-bed, tertiary care, university hospital was carried out during the period from June 1994 to January 2006. Seventy-eight patients (70 adults) with Citrobacter spp. isolates were identified. C. freundii was more common (71.8%), followed by C. koseri (23.1%) and C. braakii (3.8%). The most common associated clinical syndromes were urinary tract infections (52.6% of cases, including eight cases of asymptomatic bacteriuria), as well as intra-abdominal (14.1%), surgical site (7.7%), skin and soft tissue (6.4%), and respiratory tract infections (6.4%). In 29.5% of patients, Citrobacter spp. isolates were associated to polymicrobial infections, principally at sites other than the urinary tract. Antibiograms of 38 consecutive Citrobacter spp. isolates (29 C. freundii) were available. Most active agents were colistin (100%), fosfomycin (100%), imipenem (97.4%), gentamicin (89.5%), nitrofurantoin (89.5%), ciprofloxacin (80.6%), and cefepime (73.7%). Most patients (82.1%) had at least one underlying illness. Combination antimicrobial therapy was administered in 28.2% of cases. One patient died during hospitalization. The length of hospital stay was longer in patients with polymicrobial compared to monomicrobial infections (23 versus 13 days, respectively, p = 0.02). The isolation of Citrobacter species, although rather infrequent, was clinically relevant in the great majority of cases. Further attention should be paid to these pathogens.

Pathogens resistant to antimicrobial agents: epidemiology, molecular mechanisms, and clinical management

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens and resistance traits in nursing homes, the community, as well as in hospitals. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

Beta-lactam susceptibilities and prevalence of ESBL-producing isolates among more than 5000 European Enterobacteriaceae isolates

In vitro susceptibility to 15 beta-lactam antibiotics was evaluated using Enterobacteriaceae isolated during the SENTRY Antimicrobial Surveillance Program. Piperacillin/tazobactam was the most active penicillin against Escherichia coli, Proteus mirabilis, Klebsiella oxytoca and Klebsiella pneumoniae (94.9%, 98.3%, 87.4% and 82.9% of isolates susceptible). Of the cephalosporins, cefepime was most effective against Escherichia coli, Proteus mirabilis and Enterobacter cloacae (99.2%, 96.3% and 95.2% of isolates susceptible, respectively) and cefoxitin against Klebsiella oxytoca and Klebsiella pneumoniae (98.6% and 95.6% of isolates susceptible). Carbapenems had excellent activity (> or =99.5% of all isolates). ESBL-production was confirmed with the ESBL-Etest and disk diffusion test in 1.3% of Escherichia coli isolates, 18.4% of Klebsiella pneumoniae, 12.6% of Klebsiella oxytoca and 5.3% of Proteus mirabilis isolates.

Antibiotic susceptibility patterns among respiratory isolates of Gram-negative bacilli in a Turkish university hospital

Background

Gram-negative bacteria cause most nosocomial respiratory infections. At the University of Cumhuriyet, we examined 328 respiratory isolates of Enterobacteriaceae and Acinetobacter baumanii organisms in Sivas, Turkey over 3 years. We used disk diffusion or standardized microdilution to test the isolates against 18 antibiotics.

Results

We cultured organisms from sputum (54%), tracheal aspirate (25%), and bronchial lavage fluid (21%). The most common organisms were Klebsiella spp (35%), A. baumanii (27%), and Escherichia coli (15%). Imipenem was the most active agent, inhibiting 90% of Enterobacteriaceae and A. baumanii organisms. We considered approximately 12% of Klebsiella pneumoniae and 21% of E. coli isolates to be possible producers of extended-spectrum beta-lactamase. K. pneumoniae isolates of the extended-spectrum beta-lactamase phenotype were more resistant to imipenem, ciprofloxacin, and tetracycline in our study than they are in other regions of the world.

Conclusions

Our results suggest that imipenem resistance in our region is growing.

Kirby-Bauer disc approximation to detect inducible third-generation cephalosporin resistance in Enterobacteriaceae

Resistance to beta-lactam antibiotics in enteric Gram-negative bacilli may be difficult to detect using standard methods of either Kirby-Bauer disc diffusion (KBDD) or broth dilution for minimal inhibitory concentration (MIC). This difficulty is due to genetic differences in resistance determinants, differences in levels of gene expression, and variation in spectra of enzymatic activity against the substrate beta-lactams used for susceptibility testing. We have examined 95 clinical isolates reportedly susceptible to ceftazidime and ceftriaxone, as originally determined by either KBDD or MIC methods. The organisms studied here were isolated in 2002 from two pediatric hospital centers (Seattle, USA and Shanghai, China). They belong to the inducible beta-lactamase producing Gram-negative bacilli, such as Enterobacter spp., Citrobacter spp., Serratia spp., Morganella spp., Providencia spp., and Proteus vulgaris. A Kirby-Bauer disc approximation (KBDA) method identified inducible phenotypes of third-generation cephalosporin resistance in 76% of isolates, which would otherwise be considered susceptible by standard KBDD methods.

Sustained activity and spectrum of selected extended-spectrum beta-lactams (carbapenems and cefepime) against Enterobacter spp. and ESBL-producing Klebsiella spp.: report from the SENTRY antimicrobial surveillance program (USA, 1997-2000)

Enterobacter spp. and Klebsiella spp. are important clinical pathogens that frequently exhibit resistance to third-generation cephalosporins. In Enterobacter spp. strains, resistance is usually due to derepression of the Amp C locus, whereas plasmid-encoded extended-spectrum beta-lactamases (ESBLs) are primarily responsible for resistance in Klebsiella spp. Here we report the results from the SENTRY Antimicrobial Surveillance Program concerning the rates and trends of resistance to extended-spectrum beta-lactams and other antimicrobial agents in Enterobacter spp. and Klebsiella spp. isolated between 1997 and 2000 in participating hospitals in the United States. Among Enterobacter spp., resistance (MIC>or=32 mg/l) to aztreonam, ceftazidime and ceftriaxone ranged from 12.3 to 21.2% over the 4 years, whereas resistance in Klebsiella (MIC>or=2 mg/l) ranged from 5.9 to 6.8%. There was no trend toward increased resistance to these beta-lactam agents over the monitored period. Carbapenems (imipenem, meropenem) and cefepime had excellent activity against both ceftazidime-susceptible and -resistant Enterobacter spp. and Klebsiella spp. (>99% susceptible), although the minimum inhibitory concentration values of cefepime were higher in ceftazidime-resistant isolates compared with ceftazidime-susceptible isolates. Co-resistance to other antimicrobial agents was common in both tested genus groups.

Low-virulence Citrobacter species encode resistance to multiple antimicrobials

Citrobacter spp. are gram-negative commensal bacteria that infrequently cause serious nosocomial infections in compromised hosts. They are often resistant to cephalosporins due to overexpression of their chromosomal beta-lactamase. During a recent study of multidrug-resistant Enterobacteriaceae (MDRE) in solid-organ transplant patients, we found that almost half of patients colonized with MDRE carried one or more cefpodoxime-resistant Citrobacter freundii, Citrobacter braakii, or Citrobacter amalonaticus strains. Pulsed-field gel electrophoresis showed that 36 unique strains of Citrobacter were present among 32 patients. Genetic and phenotypic analysis of the resistance mechanisms of these bacteria showed that the extended-spectrum beta-lactamase (ESBL) SHV-5 or SHV-12 was encoded by 8 strains (26%) and expressed by 7 strains (19%). A number of strains were resistant to other drug classes, including aminoglycosides (28%), trimethoprim-sulfamethoxazole (31%), and fluoroquinolones (8%). PCR and DNA analysis of these multiresistant strains revealed the presence of class I integrons, including the first integrons reported for C. braakii and C. amalonaticus. The integrons encoded aminoglycoside resistance, trimethoprim resistance, or both. Despite the prevalence of MDR Citrobacter spp. in our solid-organ transplant patients, only a single infection with a colonizing strain was recorded over 18 months. Low-virulence Citrobacter spp., which can persist in the host for long periods, could influence pathogen evolution by accumulation of genes encoding resistance to multiple antimicrobial classes.

Changing pattern of bacterial susceptibility to antibiotics in hematopoietic stem cell transplant recipients

Adequate infection prophylaxis and empirical antibiotic therapy are of critical importance after hematopoietic stem cell transplantation (HSCT). We examined the evolution of bacterial susceptibility to antibiotics in 492 patients (198 allografts and 294 autografts) transplanted between 1982 and 1999 and evaluated whether ciprofloxacin prophylaxis and an empirical antibiotic regimen (glycopeptide + third-generation cephalosporin) were still valid. We collected all susceptibility tests performed during the initial hospitalization on blood cultures as well as routine surveillance cultures and analyzed susceptibility to ciprofloxacin and to major antibiotics used in our unit. Gram-positive cocci rapidly became resistant to ciprofloxacin (susceptibility around 70% in 1990 to less than 20% in 1998) but sensitivity to glycopeptides remained unaltered. There was a rapid decline in the number of patients colonized with Gram-negative bacilli in the early years of ciprofloxacin prophylaxis. However, susceptibility to ciprofloxacin fell sharply from around 90% in 1990 to around 30% in 1999. In parallel, susceptibility to ceftazidime also decreased to less than 80% in recent years. Piperacillin (+/- tazobactam) did not show any variation over time and its efficacy remained too low (about 60%). Imipenem as well as recently introduced cefepim and meropenem showed stable and excellent profiles (>90% susceptibility).

IN CONCLUSION

(1) quinolone prophylaxis has now lost most of its value; (2) the choice of a third-generation cephalosporin for empirical antibiotic therapy may no longer be the best because of the emergence of Gram-negative strains resistant to beta-lactamases, such as Enterobacter sp. More appropriate regimens of empirical antibiotic therapy in HSCT recipients may be based on the use of a carbapenem or fourth-generation cephalosporin.

Cefuroxime axetil: an updated review of its use in the management of bacterial infections

Cefuroxime axetil, a prodrug of the cephalosporin cefuroxime, has proven in vitro antibacterial activity against several gram-positive and gram-negative organisms, including those most frequently associated with various common community-acquired infections. In numerous randomised, controlled trials, 5 to 10 days' treatment with oral cefuroxime axetil (250 or 500 mg twice daily) was an effective treatment in patients with upper (URTI) and lower respiratory tract infections (LRTI) as assessed by clinical and bacteriological criteria. The drug was as effective as several other cephalosporins, quinolones, macrolides and amoxicillin/clavulanic acid. Shorter courses (5 to 10 days') of cefuroxime axetil were at least as effective as a 10 day course. Furthermore, sequential therapy with intravenous cefuroxime (750 mg 2 or 3 times daily for 2 to 5 days) followed by oral cefuroxime axetil (500 mg twice daily for 3 to 8 days) proved an effective treatment in adult patients with community-acquired pneumonia (CAP). This approach provided similar efficacy to intravenous ampicillin/sulbactam followed by oral amoxicillin/clavulanic acid, a full parenteral course of cefuroxime, or intravenous then oral azithromycin or clarithromycin. Additionally, cefuroxime axetil was an effective treatment in patients with genitourinary, skin and soft-tissue infections, and erythema migrans associated with early stage Lyme disease. The drug is well tolerated by adult and paediatric patients, with adverse effects that are consistent with those of other cephalosporins. The majority of adverse events (primarily gastrointestinal disturbances) were mild to moderate in intensity and reversible upon discontinuation of treatment, with very few serious adverse events reported.

CONCLUSIONS

Cefuroxime axetil is a broad spectrum antibacterial agent with a pharmacokinetic profile that permits convenient twice-daily administration. The drug is an effective and well tolerated treatment in patients with various infections, including otitis media, pharyngitis, sinusitis, CAP and acute exacerbations of chronic bronchitis. Cefuroxime axetil proved effective as a component of intravenous/oral sequential therapy in the treatment of CAP, although there are currently no dosage recommendations available for this regimen in some countries. Cefuroxime axetil may be considered as an empirical therapy for a range of community-acquired infections, including those in which beta-lactamase-producing strains of common respiratory pathogens are identified as the causative organisms. In an era of rapidly emerging bacterial resistance, empirical treatment with bacterial agents, potentially preventing the emergence of bacterial resistance to agents such as cefuroxime axetil may ensure the appropriate use of newer antibacterial agents, potentially preventing the emergence of bacterial resistance to these newer drugs.