Non-fermentative Gram-negative bacteria

Rare or Unusual Non-Fermenting Gram-Negative Bacteria: Therapeutic Approach and Antibiotic Treatment Options

Non-fermenting Gram-negative bacteria (NFGNB) are a heterogeneous group of opportunistic pathogens increasingly associated with healthcare-associated infections. While Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia are well known, rarer species such as Burkholderia cepacia complex, Achromobacter spp., Chryseobacterium spp., Elizabethkingia spp., Ralstonia spp., and others pose emerging therapeutic challenges. Their intrinsic and acquired resistance mechanisms limit effective treatment options, making targeted therapy essential. Objectives: This narrative review summarizes the current understanding of rare and unusual NFGNB, their clinical significance, resistance profiles, and evidence-based therapeutic strategies. Methods: A literature review was conducted using PubMed, Scopus, and Web of Science to identify relevant studies on the epidemiology, antimicrobial resistance, and treatment approaches to rare NFGNB. Results: Rare NFGNB exhibits diverse resistance mechanisms, including β-lactamase production, efflux pumps, and porin modifications. Treatment selection depends on species-specific susceptibility patterns, but some cornerstones can be individuated. Novel β-lactam/β-lactamase inhibitors and combination therapy approaches are being explored for multidrug-resistant isolates. However, clinical data remain limited. Conclusions: The increasing incidence of rare NFGNB requires heightened awareness and a tailored therapeutic approach. Given the paucity of clinical guidelines, antimicrobial stewardship and susceptibility-guided treatment are crucial in optimizing patient outcomes.

Evaluation of Blood Culture Results in Patients with Malignancy in Erzurum Province, Turkey

Background

Bloodstream infections are a serious public health problem that requires follow-up with blood culture; this negatively affects the course of the disease and patient healthcare costs in patients with malignancy. This study aimed to determine the growth frequency of pathogens and their antibiotic resistance profiles in the blood cultures of patients with hematological and oncogenic malignancies.

Materials and methods

The results of 7451 blood cultures, obtained from 2926 patients between January 2017 and January 2022, were evaluated retrospectively. Of these cultures, 3969 were obtained from patients with malignancy (diagnostic codes C00-D48 in ICD-10) and 3482 from patients without malignancy. The hospital information management system modules were used to acquire patient data and blood culture results.

Results

Various microorganisms grew in 10.1% of blood cultures. Of these organisms, 64.1% were isolated from cases of malignancy. Of the pathogens, 49.2% were gram-negative bacteria, 47.7% were gram-positive bacteria, and 3.1% were fungi. The most frequently isolated bacteria were methicillin-resistant coagulase-negative staphylococci (3.2%), Escherichia coli (2.3%), Klebsiella pneumoniae (1.0%), methicillin-sensitive coagulase-negative staphylococci (0.7%), and Staphylococcus aureus (0.6%). Pathogen positivity was highest in the patient cultures with urinary system cancer (23.9%), thyroid and other endocrine gland cancers (20.6%), female and male genital organ cancers (18.2%/16.9%), and digestive organ cancer (14.2%). Gram-negative bacteria to ampicillin, piperacillin, and sulfamethoxazole-trimethoprim and Gram-positive bacteria to penicillin, erythromycin, and sulfamethoxazole-trimethoprim were highly resistant. Combined resistance to imipenem and meropenem was observed in 25 Gram-negative bacteria. Twelve (48%) of the carbapenem-resistant bacteria were isolated from patients with lymphoid, hematopoietic, and related tissue malignant neoplasia.

Conclusion

This study reported microorganisms and their antimicrobial resistance in the blood cultures of malignant patients, a special patient group. It pointed out that the antibiotic resistance of Staphylococcus, Klebsiella pneumoniae, and E. coli is high enough to cause problems in the treatment of patients with malignancy.

Soil-specific responses in the antibiotic resistome of culturable Acinetobacter spp. and other non-fermentative Gram-negative bacteria following experimental manure application

Acinetobacter spp. and other non-fermenting Gram-negative bacteria (NFGNB) represent an important group of opportunistic pathogens due to their propensity for multiple, intrinsic, or acquired antimicrobial resistance (AMR). Antimicrobial resistant bacteria and their genes can spread to the environment through livestock manure. This study investigated the effects of fresh manure from dairy cows under antibiotic prophylaxis on the antibiotic resistome and AMR hosts in microcosms using pasture soil. We specifically focused on culturable Acinetobacter spp. and other NFGNB using CHROMagar Acinetobacter. We conducted two 28-days incubation experiments to simulate natural deposition of fresh manure on pasture soil and evaluated the effects on antibiotic resistance genes (ARGs) and bacterial hosts through shotgun metagenomics. We found that manure application altered the abundance and composition of ARGs and their bacterial hosts, and that the effects depended on the soil source. Manure enriched the antibiotic resistome of bacteria only in the soil where native bacteria had a low abundance of ARGs. Our study highlights the role of native soil bacteria in modulating the consequences of manure deposition on soil and confirms the potential of culturable Acinetobacter spp. and other NFGNB to accumulate AMR in pasture soil receiving fresh manure.

Fructose-enabled killing of antibiotic-resistant Salmonella enteritidis by gentamicin: Insight from reprogramming metabolomics

Salmonella enterica is a food-borne pathogen that poses a severe threat to both poultry production and human health. Antibiotics are critical for the initial treatment of bacterial infections. However, the overuse and misuse of antibiotics results in the rapid evolution of antibiotic-resistant bacteria, and the discovery and development of new antibiotics are declining. Therefore, understanding antibiotic resistance mechanisms and developing novel control measures are essential. In the present study, GC-MS-based metabolomics analysis was performed to determine the metabolic profile of gentamicin sensitive (SE-S) and resistant (SE-R) S. enterica. Fructose was identified as a crucial biomarker. Further analysis demonstrated a global depressed central carbon metabolism and energy metabolism in SE-R. The decrease in the pyruvate cycle reduces the production of NADH and ATP, causing a decrease in membrane potential, which contributes to gentamicin resistance. Exogenous fructose potentiated the effectiveness of gentamicin in killing SE-R by promoting the pyruvate cycle, NADH, ATP and membrane potential, thereby increasing gentamicin intake. Further, fructose plus gentamicin improved the survival rate of chicken infected with gentamicin-resistant Salmonella in vivo. Given that metabolite structures are conserved across species, fructose identified from bacteria could be used as a biomarker for breeding disease-resistant phenotypes in chicken. Therefore, a novel strategy is proposed for fighting against antibiotic-resistant S. enterica, including exploring molecules suppressed by antibiotics and providing a new approach to find pathogen targets for disease resistance in chicken breeding.

High-Throughput Antimicrobial Susceptibility Testing of Escherichia coli by Wide-Field Mid-Infrared Photothermal Imaging of Protein Synthesis

Antimicrobial resistance poses great threats to global health and economics. Current gold-standard antimicrobial susceptibility testing (AST) requires extensive culture time (36-72 h) to determine susceptibility. There is an urgent need for rapid AST methods to slow down antimicrobial resistance. Here, we present a rapid AST method based on wide-field mid-infrared photothermal imaging of protein synthesis from ¹³C-glucose in Escherichia coli. Our wide-field approach achieved metabolic imaging for hundreds of bacteria at the single-cell resolution within seconds. The perturbed microbial protein synthesis can be probed within 1 h after antibiotic treatment in E. coli cells. The susceptibility of antibiotics with various mechanisms of action has been probed through monitoring protein synthesis, which promises great potential of the proposed platform toward clinical translation.

Epidemiology of Multidrug Resistant Non-Fermentative Gram Negative Bacilli in Patients with Hospital Acquired Pneumonia: An Alarming Report from Somalia

Introduction

There is a lack of data concerning hospital-acquired pneumonia (HAP) due to multidrug resistant non-fermentative gram-negative bacilli (MDR-NFGNB) in Somalia, and this study will aim to analyze the epidemiology of MDR-NFGNB among HAP patients in tertiary care hospital in Somalia.

Materials and Methods

This is a retrospective study which evaluated the presence of MDR-NFGNB among 2003 HAP patients between June 2017 and May 2022 in a tertiary care hospital in Somalia. NFGNB were cultured on blood agar and eosin methylene blue agar and were then used BBL crystal system and oxidase biochemical assays for identification. Antimicrobial sensitivity and resistance were assessed using Mueller–Hinton agar.

Results

A total of 160 confirmed cases of HAP due to NFGNB were examined. Among these, 114 (71%) were males compared to females (n = 46, 29%). The mean age was 49.49 ± 21.48. The overall prevalence rate of NFGNB among patients with HAP was 8%. It was more common in older patients and in patients with co-morbidities. Acinetobacter baumannii was the most common NFGNB with n = 93 (58%), followed by Pseudomonas aeruginosa (n = 55, 34%), and Stenotrophomonas maltophilia (n = 12, 8%). Regarding the antimicrobial sensitivity rate, Acinetobacter baumannii showed an overall resistance level of 82%, Stenotrophomonas maltophilia (81%), and Pseudomonas aeruginosa (62%). The rate of CR-NFGNB in our study was 79.4%. We found that 68.1% of NFGNB was multidrug resistant (MDR) pathogens. MDR patterns were more common in Acinetobacter baumannii infections (84%). MDR pathogens were strongly associated with ICU admissions (95% CI, 0.202–0.800, OR, 0.402, p value <0.009). Finally, the mortality rate of HAP caused by NFGNB in our study was 42.5%.

Conclusion

The prevalence of NFGNB in HAP patients was 8%. These infections were more prevalent among men and the elderly. Acinetobacter baumannii and Stenotrophomonas maltophilia exhibited the highest antibiotic resistance rate. The MDR level of these pathogens was 68.1%.

Occurrence of Extended Spectrum Cephalosporin-, Carbapenem- and Colistin-Resistant Gram-Negative Bacteria in Fresh Vegetables, an Increasing Human Health Concern in Algeria

The aim of this study was to screen for extended spectrum cephalosporin-, carbapenem- and colistin-resistant Gram-negative bacteria in fresh vegetables in Batna, Algeria. A total of 400 samples of fresh vegetables were collected from different retail stores. Samples were immediately subjected to selective isolation, then the representative colonies were identified using matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF–MS). Phenotypic and genotypic analyses were carried out in terms of species identification and relative antibiotic resistance. Transferability of the carbapenemase and mcr-bearing plasmids was verified by conjugation. The clonal relationships of carbapenemase and mcr-positive Escherichia coli isolates were studied by multi-locus sequence typing (MLST). Sixty-seven isolates were characterised and were mostly isolated from green leafy vegetables, where the dominant species identified included Citrobacter freundii, Klebsiella pneumoniae, Enterobacter cloacae, Stenotrophomona maltophilia, E. coli and Citrobacter braakii. PCR and sequencing results showed that E. coli was the bacterial species presenting the highest antibiotic resistance level in parallel to bla_TEM (n = 16) and bla_CTX-M-15 (n = 11), which were the most detected genes. Moreover, five isolates carried carbapenemase genes, including the bla_OXA-48 and/or bla_VIM-4 genes. The mcr-1 gene was detected in two E. coli isolates. MLST analysis revealed three different E. coli sequence types: ST101 (n = 1), ST216 (n = 1) and ST2298 (n = 1). Conjugation assays confirmed the transferability of the bla_OXA-48 and mcr-1 genes. In this study we report, for the first time, the detection of the bla_OXA-48 gene in E. coli and C. braakii isolates and the bla_VIM-4 gene in vegetables. To the best of our knowledge, this is the first report on the detection of mcr-1 genes from vegetables in Algeria.

An Update of Mobile Colistin Resistance in Non-Fermentative Gram-Negative Bacilli

Colistin, the last resort for multidrug and extensively drug-resistant bacterial infection treatment, was reintroduced after being avoided in clinical settings from the 1970s to the 1990s because of its high toxicity. Colistin is considered a crucial treatment option for Acinetobacter baumannii and Pseudomonas aeruginosa, which are listed as critical priority pathogens for new antibiotics by the World Health Organization. The resistance mechanisms of colistin are considered to be chromosomally encoded, and no horizontal transfer has been reported. Nevertheless, in November 2015, a transmissible resistance mechanism of colistin, called mobile colistin resistance (MCR), was discovered. Up to ten families with MCR and more than 100 variants of Gram-negative bacteria have been reported worldwide. Even though few have been reported from Acinetobacter spp. and Pseudomonas spp., it is important to closely monitor the epidemiology of mcr genes in these pathogens. Therefore, this review focuses on the most recent update on colistin resistance and the epidemiology of mcr genes among non-fermentative Gram-negative bacilli, especially Acinetobacter spp. and P. aeruginosa.

Antimicrobial activities of sitafloxacin and comparators against the clinical isolates of less common nonfermenting Gram-negative bacteria

The in vitro antimicrobial activities of sitafloxacin and comparators against 320 clinical isolates of less common nonfermenting Gram-negative bacteria (NFGNB) were assessed by determining the minimum inhibitory concentrations (MICs) using broth microdilution method. In terms of MIC_50/90 values, sitafloxacin was highly active against Stenotrophomonas maltophilia (0.25/1 mg/L), Burkholderia cepacia complex (0.25/2 mg/L), Achromobacter xylosoxidans (0.25/1 mg/L), and Chryseobacterium gleum (1/2 mg/L), but less active for Elizabethkingia (1/8 mg/L) and Chryseobacterium indologenes (16/32 mg/L). Sitafloxacin was more active than other fluoroquinolones against these NFGNB except Chryseobacterium. The results are helpful for clinicians to be aware of the role of sitafloxacin in managing the infections caused by these NFGNB.

Coming from the Wild: Multidrug Resistant Opportunistic Pathogens Presenting a Primary, Not Human-Linked, Environmental Habitat

The use and misuse of antibiotics have made antibiotic-resistant bacteria widespread nowadays, constituting one of the most relevant challenges for human health at present. Among these bacteria, opportunistic pathogens with an environmental, non-clinical, primary habitat stand as an increasing matter of concern at hospitals. These organisms usually present low susceptibility to antibiotics currently used for therapy. They are also proficient in acquiring increased resistance levels, a situation that limits the therapeutic options for treating the infections they cause. In this article, we analyse the most predominant opportunistic pathogens with an environmental origin, focusing on the mechanisms of antibiotic resistance they present. Further, we discuss the functions, beyond antibiotic resistance, that these determinants may have in the natural ecosystems that these bacteria usually colonize. Given the capacity of these organisms for colonizing different habitats, from clinical settings to natural environments, and for infecting different hosts, from plants to humans, deciphering their population structure, their mechanisms of resistance and the role that these mechanisms may play in natural ecosystems is of relevance for understanding the dissemination of antibiotic resistance under a One-Health point of view.

A 10-year single-center experience on Stenotrophomonas maltophilia resistotyping in Szeged, Hungary

Stenotrophomonas maltophilia is an aerobic, oxidase-negative and catalase-positive bacillus. S. maltophilia is a recognized opportunistic pathogen. Due to the advancements in invasive medical procedures, organ transplantation and chemotherapy of malignant illnesses, the relevance of this pathogen increased significantly. The therapy of S. maltophilia infections is challenging, as these bacteria show intrinsic resistance to multiple classes of antibiotics, the first-choice drug is sulfamethoxazole/trimethoprim. Our aim was to assess the epidemiology of S. maltophilia from various clinical samples and the characterization of resistance-levels and resistotyping of these samples over a long surveillance period. The study included S. maltophilia bacterial isolates from blood culture samples, respiratory samples and urine samples and the data for the samples, received between January 2008 until December 2017, a total of 817 S. maltophilia isolates were identified (respiratory samples n = 579, 70.9%, blood culture samples n = 175, 21.4% and urine samples n = 63, 7.7%). Levofloxacin and colistin-susceptibility rates were the highest (92.2%; n = 753), followed by tigecycline (90.5%, n = 739), the first-line agent sulfamethoxazole/trimethoprim (87.4%, n = 714), while phenotypic resistance rate was highest for amikacin (72.5% of isolates were resistant, n = 592). The clinical problem of sulfamethoxazole/trimethoprim-resistance is a complex issue, because there is no guideline available for the therapy of these infections.

Carbapenem-Resistant but Cephalosporin-Susceptible Pseudomonas aeruginosa in Urinary Tract Infections: Opportunity for Colistin Sparing

This paper briefly reports the occurrence and epidemiology of carbapenem-resistant but cephalosporin-susceptible (Car-R/Ceph-S) Pseudomonas aeruginosa isolates from urinary tract infections (UTIs) in a tertiary-care hospital in the Southern Region of Hungary, and the phenotypic characterization of the possible resistance mechanisms in these isolates. Isolates and data were collected regarding P. aeruginosa UTIs corresponding to the period between 2008 and 2017. Susceptibility testing was performed using the Kirby-Bauer disk diffusion method; minimum inhibitory concentrations (MICs) of the isolates were determined using E-tests. The phenotypic detection of ampicillin C-type (AmpC) β-lactamases, efflux pump overexpression and carbapenemase production was also performed. P. aeruginosa represented n = 575 (2.72% ± 0.64%) from outpatient, and n = 1045 (5.43% ± 0.81%) from inpatient urinary samples, respectively. Based on the disk diffusion test, n = 359 (22.16%) were carbapenem-resistant; in addition to carbapenems, n = (64.34%) were also resistant to ciprofloxacin; n = (60.17%) to gentamicin/tobramycin; n = (58.51%) to levofloxacin; and n = (27.57%) to amikacin. From among the carbapenem-resistant isolates, n = 56 (15.59%) isolates were multidrug-resistant, while n = 16 (4.46%) were extensively drug-resistant. From among the Car-R/Ceph-S isolates (n = 57), overexpression of AmpC was observed in n = 7 cases (12.28%); carbapenemase production in n = 4 (7.02%); while overexpression of efflux pumps was present in n = 31 (54.39%) isolates. To spare last-resort agents, e.g., colistin, the use of broad-spectrum cephalosporins or safe, alternative agents should be considered in these infections.

Resistance Levels and Epidemiology of Non-Fermenting Gram-Negative Bacteria in Urinary Tract Infections of Inpatients and Outpatients (RENFUTI): A 10-Year Epidemiological Snapshot

Background: Urinary tract infections (UTIs) are one of the most common infections in the human medicine, both among outpatients and inpatients. There is an increasing appreciation for the pathogenic role of non-fermenting Gram-negative bacteria (NFGNBs) in UTIs, particularly in the presence of underlying illnesses. Methods: The study was carried out using data regarding a 10-year period (2008-2017). The antimicrobial susceptibility testing was performed using the disk diffusion method, E-tests, and broth microdilution. Results: NFGNB represented 3.46% ± 0.93% for the outpatients, while 6.43% ± 0.81% of all positive urine samples for the inpatients (p < 0.001). In both groups, Pseudomonas spp. (78.7% compared to 85.1%) and Acinetobacter spp. (19.6% compared to 10.9%), were the most prevalent. The Acinetobacter resistance levels were significantly higher in inpatients isolates (p values ranging between 0.046 and <0.001), while the differences in the resistance levels of Pseudomonas was not as pronounced. The β-lactam-resistance levels were between 15-25% and 12-28% for the Acinetobacter and Pseudomonas spp., respectively. 4.71% of Acinetobacter and 1.67% of Pseudomonas were extensively drug resistant (XDR); no colistin-resistant isolates were recovered. Conclusions: Increasing resistance levels of the Acinetobacter spp. from 2013 onward, but not in the case of the Pseudomonas spp. Although rare, the drug resistant NFGNB in UTIs present a concerning therapeutic challenge to clinicians with few therapeutic options left.

Epidemiological investigation of non-fermentative bacterial infection in cirrhotic patients

Background: This study aimed to describe the clinical characteristics of NFGNB in patients with cirrhosis as well as the risk factors for short-term mortality. Methods: A retrospective analysis was performed in patients with cirrhosis and NFGNB infections from 2011 to 2016 . Results: 144 episodes in 134 patients with liver cirrhosis and NFGNB infections were found in total. Of these, 81.2% were hospital-acquired or healthcare- associated infections, while only 18.8% of NFGNB infections originated from the community. A. baumannii were the most frequently isolated bacteria (39 episodes), followed by S. maltophilia (38 episodes) and P. aeruginosa (31 episodes). MDR- and non-MDR-NFGNB comprised 62.5% and 37.5% of infections respectively. The Kaplan-Meier survival curve showed no significant difference between MDR and non-MDR NFGNB patients (74.1% vs 75.5%, P = 0.811). Neither MDR or the subgroup of common NFGNB (P. aeruginosa, A. baumannii, S. maltophilia) was associated with the 28-day mortality (all P >0.05). Low albumin levels and high Tbil levels were both independent risk factors for 28-day mortality (HR = 0.930, 95%CI (0.869, 0.995), P = 0.035; HR = 1.003, 95%CI (1.002, 1.005), P < 0.001, respectively). Conclusions: Diabetes increased 28-day mortality significantly, however, MDR status, site of infection and bacteria type did not.

Outbreak of nonfermentative Gram-negative bacteria (Ralstonia pickettii and Stenotrophomonas maltophilia) in a hemodialysis center

We report a case series of seven patients with nonfermentative Gram-negative bacteria infections in a single dialysis center; four patients with Ralstonia pickettii and three patients with Stenotrophomonas maltophilia. Two of the seven patients were admitted to hospital for intravenous antibiotic treatment, while the rest were treated with oral antibiotics at home. Both the admitted patients had temporary vascular catheter infections from the aforementioned pathogens. We conclude that the outbreak is due to colonization of treated reverse osmosis water, presumably through contamination via polluted filters and compounded by the usage of reprocessed dialysers in the dialysis center. This is especially relevant because contaminated treated water is directly introduced into the blood compartment of the dialysers during reprocessing. In addition, there seems to be a propensity for both organisms to cause prolonged febrile reactions in patients with temporary vascular catheters, likely through the early development of biofilm. Intensification of general sterilization procedures, servicing and replacement of old decrepit components of the water treatment system and temporary cessation of dialyser reuse practice seem to have halted the outbreak. Due to the virulent nature and difficult resistant profile of nonfermentative Gram-negative bacteria, we strongly recommend meticulous vigilance in the surveillance of culture isolates in routine microbiological specimens from dialysis centers, especially if there is a senescent water treatment system and a practice of reprocessing dialysers.

Prevalence and antimicrobial susceptibility of non-fermenting Gram-negative bacilli isolated from clinical samples at a tertiary care hospital

INTRODUCTION:

We compared the prevalence and antimicrobial susceptibility of non-fermenting gram-negative bacilli (NFGNB) isolated from clinical samples at a Brazilian tertiary care hospital in 2008 and 2013.

METHODS:

Collected data included patient's name, age, sex, inpatient unit, laboratory record number, type of biological material, culture test result, and antimicrobial susceptibility of isolated strains.

RESULTS:

Out of 19,112 culture tests analyzed, 926 (4.8%) were positive for NFGNB. Among these, 45.2% were metallo-beta-lactamase (MBL) producing strains.

CONCLUSION:

Between 2008 and 2013, the number of MBL-producing NFGNB isolates increased by 21.5%, which was accompanied by a consequent reduction in susceptibility to antimicrobials.

Ralstonia mannitolilytica infections in an oncologic day ward: description of a cluster among high-risk patients

BACKGROUND

Ralstonia spp, an environmental microorganism, has been occasionally associated with healthcare infections. The aim of this study was to investigate an outbreak caused by Ralstonia mannitolilytica in oncology patients.

METHODS

Case definition: Oncology outpatients attending a day ward, with positive blood and/or central venous catheter (CVC) culture for Ralstonia spp from September 2013 - June 2014. We analysed medical records, procedures and environmental samples. R. mannitolilytica was identified by 16S rRNA sequencing, and typed by Pulsed Field Gel Electrophoresis (PFGE); resistance to carbapenemes was investigated by phenotypic and molecular methods.

RESULTS

The patients (N = 22) had different malignancies and received different therapy; all had a CVC and 16 patients presented chills and/or fever. R. mannitolilytica was isolated from both blood and CVC (n = 12) or only blood (n = 6) or CVC tips (n = 4). The isolates had indistinguishable PFGE profile, and showed resistance to carbapenems. All the isolates were negative for carbapenemase genes while phenotypic tests suggests the presence of an AmpC β-lactamase activity,responsible for carbapenem resistance. All patients had had CVC flushed with saline to keep the venous access pervious or before receiving chemotherapy at various times before the onset of symptoms. After the first four cases occurred, the multi-dose saline bottles used for CVC flushing were replaced with single-dose vials; environmental samples were negative for R. mannitolilytica.

CONCLUSIONS

Although the source of R. mannitolilytica remains unidentified, CVC flushing with contaminated saline solution seems to be the most likely origin of R. mannitolilytica CVC colonization and subsequent infections. In order to prevent similar outbreaks we recommend removal of any CVC that is no longer necessary and the use of single-dose solutions for any parenteral treatment of oncology patients.

Selected Topics in Aerobic Bacteriology

Aerobic Gram-positive and Gram-negative bacteria can be important pathogens in the immunocompromised host. These bacteria can be found in many environments, as part of the normal microbiota of the human host and animals, in soil and water, on plants, on fomites in the hospital, and on hospital equipment. This review provides information from relevant studies about what are the most common aerobic bacteria associated with patients who have cancer and/or are being treated for it, or who have other diseases which lead to immunodeficiencies, such as HIV, multiple myeloma, aplastic anemia, chronic diseases, and aging. A discussion of the appropriate laboratory tests needed for diagnosis of aerobic infections and information about antibiotics and susceptibility testing are also included.

Antibiotics resistance of Stenotrophomonas maltophilia strains isolated from various clinical specimens

BACKGROUND

A limited number of antibiotics are recommended for the therapy of Stenotrophomonas maltophilia infections due to therapy difficulties caused by its numerous mechanisms of resistance.

OBJECTIVES

In this study conducted over a period of approximately 5 years we aimed to determine resistance rates of S. maltophilia based on drug classification recommended by Clinical and Laboratory Standards Institute.

METHODS

A total of 118 S. maltophilia strains isolated from various clinical specimens between January 2006 and June 2012 were included in the study. BD Phoenixautomated microbiology system (Becton Dickinson, USA) was utilized for species level identification and antibiotic susceptibility testing.

RESULTS

Sixty seven of S. maltophilia strains were isolated from tracheal aspirate isolates, 17 from blood, 10 from sputum, 10 from wound and 14 from other clinical specimens. Levofloxacin was found to be the most effective antibiotic against S. maltophilia strains with resistance rate of 7.6%. The resistance rates to other antibiotics were as follows: chloramphenicol 18.2%, trimethoprim-sulfamethoxazole 20.3% and ceftazidime 72%.

CONCLUSION

The study revealed that S. maltophilia is resistant to many antibiotics. The treatment of infections caused by S. maltophilia should be preferred primarily as levofloxacin, chloramphenicol, and TMP-SXT, respectively.

Characterization and Genomic Analysis of Quinolone-Resistant Delftia sp. 670 Isolated from a Patient Who Died from Severe Pneumonia

Antibiotic-resistant opportunistic pathogens have become a serious concern in recent decades, as they are increasingly responsible for hospital-acquired infections. Here, we describe quinolone-resistant Delftia sp. strain 670, isolated from the sputum of a patient who died from severe pulmonary infection. The draft genome sequence of this strain was obtained by whole-genome shotgun sequencing, and was subjected to comparative genome analysis. Genome analysis revealed that one critical mutation (Ser83Ile in gyrA) might play a decisive role in quinolone resistance. The genome of Delftia sp. strain 670 contains both type II and type VI secretion systems, which were predicted to contribute to the virulence of the strain. Phylogenetic analysis, assimilation tests, and comparative genome analysis indicated that strain 670 differed from the four known Delftia species, suggesting this strain could represent a novel species. Although the study could not determine the strain 670 as the pathogen led to mortality, our findings also presented the pathogenic potential of Delftia species, and the increasing severity of antibiotic resistance among emerging opportunistic pathogens. The whole genome sequencing and comparative analysis improved our understanding of genome evolution in the genus Delftia, and provides the foundation for further study on drug resistance and virulence of Delftia strains.

Fatal Delftia acidovorans infection in an immunocompetent patient with empyema

Delftia acidovorans (earlier known as Comamonas acidovorans) is an aerobic, non-fermentative, Gram negative rod, classified in the Pseudomonas rRNA homology Group III. Reports of isolation of the organism from serious infections like central venous catheter associated bacteremia, corneal ulcers, otitis media exist. The microbiologists can identify this organism based on an orange indole reaction. This reaction demonstrates the organism's ability to produce anthranilic acid from tryptophan on addition of Kovac's reagent; which gives the media its characteristic "pumpkin orange" colour. Here we report the isolation of this organism from the Endotracheal tube aspirate of a 4 year old child. With the increasing use of invasive devices, it has become important to recognize these non fermentative gram negative bacilli as emerging source of infection even in immunocompetent individuals.

Delftia lacustris septicemia in a pheochromocytoma patient: case report and literature review

We report the first case of true Delftia lacustris bacteremia in a patient with pheochromocytoma. The organism was identified using 16S rRNA gene sequencing and biochemical tests. A peripheral intravenous catheter was the suspected source of infection, and the patient was successfully treated with piperacillin/tazobactam. We also present a review of the literature describing bacteremia caused by Delftia species.

Antimicrobial Susceptibility and Clonal Relation Between Acinetobacter baumannii Strains at a Tertiary Care Center in Turkey

Background:

Acinetobacter baumannii is an opportunistic pathogen, related with nosocomial infections such as bacteremia, urinary tract infections, and ventilator-associated pneumonia. Multidrug resistant (MDR) A. baumannii strains are first line causes of infection, especially in patients hospitalized at intensive care units (ICUs). Infection with MDR A. baumannii strains has a longer duration at ICUs and hospitals. There are studies using molecular methods which can differentiate MDR A. baumannii strains at the clonal level. This helps controlling these resistant strains and prevents their epidemy.

Objectives:

The aim of our study was to investigate the antimicrobial susceptibility and clonal relationship between the A. baumannii strains isolated from our ICU.

Materials and Methods:

The identification and antimicrobial susceptibility of 33 A. baumannii strains were performed by automatized Vitek version 2.0. The clonal relationship among A. baumannii strains was analyzed using enterobacterial repetitive intergenic consensus (ERIC) polymerase chain reaction (PCR).

Results:

A total of 33 A. baumannii strains were included in this study. A. baumannii complex strains were classified into seven clusters based on the fingerprint results. Our results revealed that two main clusters were responsible for the prevalence of A. baumannii complex strains at the ICU.

Conclusions:

MDR A. baumannii strains cause an increment in morbidity and mortality, particularly in ICUs. The use of molecular epidemiological methods can help us with the detection of the pathogen and preventing from spreading of these resistant strains.

Non-fermentative gram-negative bacteria in hospital tap water and water used for haemodialysis and bronchoscope flushing: prevalence and distribution of antibiotic resistant strains

This study provides a detailed description of the distribution of non-fermentative gram-negative bacteria (NFGNB) collected in water sources (tap water and water used for haemodialysis and bronchoscope flushing) from different wards of a tertiary care hospital. The aim is to identify risk practices for patients or to alert clinicians to the possible contamination of environment and medical devices. The resistance profile of NFGNB environmental isolates has shown that more than half (55.56%) of the strains isolated were resistant to one or more antibiotics tested in different antimicrobial categories. In particular, 38.89% of these strains were multidrug resistant (MDR) and 16.67% were extensively drug resistant (XDR). The most prevalent bacterial species recovered in water samples were Pseudomonas aeruginosa, Pseudomonas fluorescens, Ralstonia pickettii and Stenotrophomonas maltophilia. Analysis of antibiotic resistance rates has shown remarkable differences between Pseudomonadaceae (P. aeruginosa and P. fluorescens) and emerging pathogens, such as S. maltophilia and R. pickettii. Multidrug resistance can be relatively common among nosocomial isolates of P. aeruginosa, which represent the large majority of clinical isolates; moreover, our findings highlight that the emergent antibiotic resistant opportunistic pathogens, such as R. pickettii and S. maltophilia, isolated from hospital environments could be potentially more dangerous than other more known waterborne pathogens, if not subjected to surveillance to direct the decontamination procedures.

Epidemiology of bacteremia caused by uncommon non-fermentative gram-negative bacteria

Background

Prevalence of bacteremia caused by non-fermentative gram-negative bacteria (NFGNB) has been increasing over the past decade. Although many studies have already investigated epidemiology of NFGNB bacteremia, most focused only on common NFGNB including Pseudomonas aeruginosa (PA) and Acinetobacter baumannii (AB). Knowledge of uncommon NFGNB bacteremia is very limited. Our study aimed to investigate epidemiology and identify factors associated with uncommon NFGNB bacteremia.

Methods

This observational study was conducted at a university hospital in Thailand during July 1, 2007-Dec 31, 2008. All patients who had at least one blood culture positive for NFGNB and met the criteria for systemic inflammatory response syndrome within 24 hours before/after obtaining the blood culture were enrolled. The NFGNB isolates that could not be satisfactorily identified by the standard biochemical assays were further characterized by molecular sequencing methods. To identify factors associated with uncommon NFGNB bacteremia, characteristics of patients in the uncommon NFGNB group were subsequently compared to patients in the common NFGNB group (AB and PA bacteremia).

Results

Our study detected 223 clinical isolates of NFGNB in 221 unique patients. The major causative pathogens were AB (32.7%), followed by PA (27.8%), Stenotrophomonas maltophilia (5.4%), Acinetobacter lwoffii (4.9%) and Burkholderia pseudomallei (2.7%). Infection-related mortality was 63.0% in the AB group, 40.3% in the PA group and 17.4% in the uncommon NFGNB group. Factors associated with uncommon NFGNB bacteremia (OR [95% CI]; p-value) were male sex (0.28 [0.14-0.53]; p < 0.001), hospital-acquired infection (0.23 [0.11-0.51]; p < 0.001), recent aminoglycosides exposure 0.23 [0.06-0.8]; p = 0.01), primary bacteremia (6.43 [2.89-14.2]; p < 0.001]), catheter related infection (4.48 [1.54-13.06]; p < 0.001) and recent vancomycin exposure (3.88 [1.35-11.1]; p = 0.02).

Conclusions

Our distribution of causative pathogens was slightly different from other studies. The common NFGNB group had a remarkably higher ID-mortality than the uncommon NFGNB group. Knowledge of factors associated with uncommon NFGNB bacteremia would help physicians to distinguish between low vs. high risk patients.

In vitro antimicrobial activity of "last-resort" antibiotics against unusual nonfermenting Gram-negative bacilli clinical isolates

In this prospective multicentric study, we assessed the in vitro antimicrobial activity of carbapenems (imipenem, meropenem, and doripenem), tigecycline, and colistin against 166 unusual nonfermenting Gram-negative bacilli (NF-GNB) clinical isolates collected from nine French hospitals during a 6-month period (from December 1, 2008, to May 31, 2009). All NF-GNB isolates were included, except those phenotypically identified as Pseudomonas aeruginosa or Acinetobacter baumannii. Minimal inhibitory concentrations (MICs) of antimicrobial agents were determined by using the E-test technique. The following microorganisms were identified: Stenotrophomonas maltophilia (n=72), Pseudomonas spp. (n=30), Achromobacter xylosoxidans (n=25), Acinetobacter spp. (n=18), Burkholderia cepacia complex (n=9), Alcaligenes faecalis (n=7), and Delftia spp. (n=5). All isolates of Acinetobacter spp., A. faecalis, and Delftia spp. were susceptible to the three carbapenems. Imipenem exhibited the lowest MICs against Pseudomonas spp., and meropenem, as compared with imipenem and doripenem, displayed an interesting antimicrobial activity against A. xylosoxidans and B. cepacia complex isolates. Conversely, no carbapenem exhibited any activity against S. maltophilia. Except for S. maltophilia isolates, tigecycline and colistin exhibited higher MICs than carbapenems, but covered most of the microorganisms tested in this study. To our knowledge, no prior study has compared antimicrobial activity of these five antibiotics, often considered as "last-resort" treatment options for resistant Gram-negative infections, against unusual NF-GNB clinical isolates. Further studies should be carried out to assess the potential clinical use of these antibiotics for the treatment of infections due to these microorganisms.

Stenotrophomonas maltophilia--the most worrisome threat among unusual non-fermentative gram-negative bacilli from hospitalized patients: a prospective multicenter study

OBJECTIVES

Isolation rates of unusual non-fermentative Gram-negative bacilli (i.e. other than Pseudomonas aeruginosa and Acinetobacter baumannii) are increasing but studies are limited to few observations. We aimed at determining risk factors for infection and influence of antibiotic treatment on the outcome.

METHODS

A six-month (December 1, 2008-May 31, 2009) prospective multicenter cohort study was conducted in nine French teaching hospitals. Characteristics of patients colonized or infected by unusual NF-GNB, adequacy of antimicrobial therapies, and outcome were analyzed.

RESULTS

Analysis of 158 patients (median age, 62.7 years) was conducted. Stenotrophomonas maltophilia was the predominant bacterial species isolated (39%) followed by Achromobacter group (15%) and non-baumannii Acinetobacter species (13%). Compared to colonized patients, infected ones were more frequently immunocompromised [relative risk (RR) = 1.63, (95% confidence interval (CI) = 1.02-2.60, P = 0.05)], hospitalized within the last three months [RR 1.67 (95% CI 1.09-2.58, P = 0.02)], admitted in an intensive care unit with central venous catheter [RR 1.74 (95% CI 1.15-2.63, P = 0.01)]. The overall hospital mortality concerned 28 patients (18%) but no association with inadequate antimicrobial treatment was found except in the group of S. maltophilia infected cases [RR 2.81 (95% CI 1.01-7.83, P = 0.02)].

CONCLUSION

Naturally carbapenems-resistant S. maltophilia is the main unusual NF-GNB pathogen in hospitalized patients, leading to inappropriate empirical antibiotic treatment at the time of emerging extended-spectrum β-lactamase-producing bacteria.

Human infection with Delftia tsuruhatensis isolated from a central venous catheter

We present the case of a patient with catheter-related infection caused by Delftia tsuruhatensis, a newly described species closely related to Delftia acidovorans (formerly Comamonas acidovorans). To date, D. tsuruhatensis has not been described as a pathogen. To the best of our knowledge, this is the first report describing D. tsuruhatensis as the causative agent of a human infection.

Stenotrophomonas maltophilia: Significant contemporary hospital pathogen - review

Stenotrophomonas maltophilia (Sm) plays an important role as an opportunistic pathogen in immunocompromised individuals. The growing detection rates of this bacterium in hospitalized patients are associated with the invasiveness of therapeutic and diagnostic procedures and the selection pressure of antibiotic therapy. A broad range of infections that can be caused by Sm is frequently bound to biofilm. The high level of intrinsic resistance to many unrelated antibiotics and increasing acquired resistance to the drug of choice, trimethoprim-sulfamethoxazole pose a threat for the near future when our treatment options may become depleted. Prevention of colonization and infection consists in consequent implementation of the rules governing nosocomial infection control, rational use of antibiotics including the optimization of selection and testing of antimicrobial agents suitable for the treatment of stenotrophomonad infections.

Association of Stenotrophomonas maltophilia infection with lower airway disease in the horse: a retrospective case series

Stenotrophomonas maltophilia is being reported with increasing frequency as a human nosocomial pathogen, especially among immuno-compromised patients. To the authors' knowledge, this pathogen has not previously been associated with lower airway disease in the horse. In this paper the clinical findings, laboratory diagnosis and response to treatment of seven cases of respiratory infection with S. maltophilia in horses, presented at three equine referral hospitals in Denmark in 2007, are described. In all cases there was a clinical history of chronic coughing and abundant mucopurulent exudate was observed in the lower trachea on endoscopy. On culture of tracheal aspirate, grey, slow-growing colonies, identified as S. maltophilia by both API 20NE identification and 16s ribosomal DNA sequencing, were identified. All isolates had a similar antibiotic susceptibility pattern characterised by resistance to all penicillins and cephalosporins, and to imipenem, gentamicin, amikacin and rifampicin. Ribotyping and pulsed-field gel electrophoresis of the S. maltophilia isolates from different patients indicated that they were either indistinguishable or closely related. This study indicates that S. maltophilia can be associated with chronic lower airway disease in the horse and provides useful initial insights into the diagnosis, therapy and epidemiology of this novel condition.