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.     

Glucose-nonfermenting Gram-negative bacilli associated with clinical veterinary specimens.

Glucose-nonfermenting gram-negative bacilli (NFB) have been recognized recently as opportunistic pathogens of humans. With few exceptions, strains of NFB have not been considered important enough to be identified when isolated from animals. In this study, all NFB isolated during a 1-year period in a clinical veterinary microbiology laboratory were identified to determine their prevalence. Of the 347 strains of NFB obtained, the most common species were Pseudomonas aeruginosa, Acinetobacter calcoaceticus, Bordetella bronchiseptica, and Pseudomonas pseudoalcaligenes. Of all clinical veterinary specimens submitted for cultures, 10% contained nonfermenters.     

产ESBLs、AmpC、KPC酶的葡萄糖不发酵细菌的耐药性分析及临床分布

目的了解本地区葡萄糖不发酵细菌中泛耐药菌（代表株铜绿假单胞菌、鲍曼不动杆菌、嗜麦芽窄食单胞菌）在临床标本中的分离与耐药情况,为临床合理使用抗生素提供指导。方法对临床分离的180株葡萄糖不发酵细菌进行分类鉴定和药敏试验,并用纸片扩散法筛选出产超广谱β-内酰胺酶（ESBLs）、头孢菌素酶（AmpC酶）及碳青霉烯类水解酶（KPC酶）的耐药菌株。结果在葡萄糖不发酵细菌的构成比中,其中产超广谱β-内酰胺酶（ESBLs）56株（31.1%）,产AmpC酶22株（12.2%）,KPC酶2株（1.1%）;同时产ESBLs和AmpC酶16株（8.9%）,同时产ESBLs、AmpC、KPC酶1株（0.6%）。3种主要葡萄糖不发酵细菌对头孢他啶、头孢三嗪、头孢噻肟、哌拉西林的耐药率最高,其中铜绿假单胞菌对阿米卡星、左氧氟沙星、环丙沙星耐药率较低,鲍曼不动杆菌对亚胺培南、左氧氟沙星耐药率较低,嗜麦芽窄食单胞菌对复方新诺明、环丙沙星耐药率较低。结论葡萄糖不发酵细菌中泛耐药菌特别是铜绿假单胞菌、鲍曼不动杆菌、嗜麦芽窄食单胞菌均有较高的多重耐药性,临床上应重视葡萄糖不发酵细菌引起的感染,根据药敏试验结果合理使用抗生素。     

Gram-negative bacilli in burns

In a period of two years, 865 strains of Gram-negative bacilli other than Pseudomonas aeruginosa isolated from burns were identified by a range of tests. The commonest species were Proteus mirabilis, Escherichia coli, and Enterobacter cloacae. Many strains of Klebsiella aerogenes, Enterobacter aerogenes, and Bacterium anitratum were also found.A large proportion of the strains were tested for sensitivity to nalidixic acid, ampicillin, kanamycin, chloramphenicol, tetracycline, and carbenicillin, and smaller numbers of strains were tested for sensitivity to cephaloridine, polymyxin, streptomycin, sulphadiazine, sulfamylon, and trimethoprim. The proportion of strains sensitive and resistant to different antibacterial agents varied widely with species of bacteria. A large proportion of the strains of E. coli and P. mirabilis were resistant to ampicillin, which was much used in treatment; resistance appeared least often towards nalidixic acid, kanamycin, trimethoprim, and gentamicin. Multiple resistance occurred less often among strains of E. coli than among Klebsiella spp, Enterobacter spp, and P. mirabilis.Phage and serological typing of Ps. aeruginosa showed that most infections of burns with this organism were due to strains previously found in other patients in the same ward. Taken with other evidence, this supported the view that most infections with Ps. aeruginosa were not acquired from the patient's own flora but from sources in the hospital environment.     

Sensitivity of Gram-negative bacilli to ampicillin after six years'' clinical use

A total of 1,102 clinical isolates of Gram-negative bacilli was obtained from four hospitals during 1967 and these cultures were tested for sensitivity to ampicillin. Approximately 80% of the strains of Escherichia coli and 90% of the strains of Proteus mirabilis, the two organisms most frequently isolated, were sensitive to ampicillin. Klebsiella-Enterobacter species and Pseudomonas aeruginosa were generally insensitive. Comparison of these results with data obtained in an earlier study with Gram-negative organisms isolated in 1961 showed that there had been no significant increase in the incidence of resistance of Gram-negative bacilli to ampicillin during the period 1961-67.The majority of ampicillin-resistant strains of E. coli isolated in 1967 transferred ampicillin resistance to a sensitive strain of E. coli K12. Only four ampicillin-resistant strains of E. coli isolated in 1961 were available for transferable resistance tests but all four strains transferred ampicillin resistance. Infective or transferable resistance was therefore a feature of ampicillin resistance of certain Gram-negative bacteria before ampicillin became generally available for clinical use.     

Detection of cross-transmission of multiresistant Gram-negative bacilli and Staphylococcus aureus in adult intensive care units by routine typing of clinical isolates

Objective: To determine the potential of laboratory services in identifying cross-transmission of multiresistant Gram-negative bacilli (MR GNB) and Staphylococcus aureus in adult intensive care units by routine typing of clinical isolates.
Methods: Over a 12-month period, isolates with indistinguishable PCR fingerprints were traced back to the source patients and their epidemiologic relationships were investigated. Possible episodes of cross-transmission were ascertained, and the validity of antibiograms in identifying the same cluster assessed.
Results: Of 3503 specimens received by the microbiological laboratory during 5372 patient days, 1295 cultures showed bacterial growth. Of these, 132 were primary isolates of MR GNB and 92 were primary isolates of S. aureus . Thirty-two MR GNB isolates (24%) shared fingerprints with one or more other isolates. Indistinguishable isolates from epidemiologically related patients suggested 17 episodes of cross-transmission. The positive and negative predictive values of antibiogram-based identification of these episodes were 19% and 72% respectively. S aureus displayed limited genetic diversity. The two most frequent genotypes contained 19 and 16 isolates, of which the majority appeared to be epidemiologically unrelated.
Conclusions: Endemic transmission of MR GNB occurs mainly between two patients and remains unrecognized by conventional laboratory investigation. Rapid genetic typing methods identify patients involved in cross-transmission and give an insight into the population dynamics of MR GNB on adult intensive care units.     

Integrons and gene cassettes in clinical isolates of co-trimoxazole-resistant Gram-negative bacteria

Despite a trend of declining consumption, resistance to co-trimoxazole has increased during a 12-year period in Stockholm. The molecular background to this surprising development was investigated by using PCR to screen for integrons and specific resistance genes, followed by sequence analysis of selected integrons, in 105 clinical urinary isolates of Gram-negative bacteria selected partly for trimethoprim resistance. Sixty-five integrons of class 1 or 2 were detected in a subset of 59 isolates, and of these positive isolates, all but one were resistant to trimethoprim. However, 11 isolates were resistant to trimethoprim, but negative for integrons. Isolates positive for integrons were resistant to an average of 4.2 antibiotics, compared with 1.9 antibiotics for integron-negative isolates. Despite this, the only gene cassettes identified in 19 class 1 integrons analysed were dfr and aadA cassettes. Thus, only resistance to trimethoprim, streptomycin, spectinomycin and sulphonamides could be explained by the presence of integrons in these isolates. A new dfr gene, named dfrA22, was discovered as a single gene cassette in a class 1 integron. In addition, sulphonamide resistance in many isolates was caused by carriage of sul2, which has no known association with integrons. Resistance to co-trimoxazole and many other antibiotics was thus not accounted for fully by the presence of integrons in these isolates.     

Comparison of 2 systems for identifying nonfermenting or fermenting oxidase-positive gram-negative bacilli

The N/F FLOW and API 20 NE identification systems were compared for their ability to identify 182 strains of either non-fermentative or fermentative oxidase-positive gram-negative bacilli. Agreement with the identification given by conventional methods was achieved for 91,7 per cent of strains by the API System but for only 81,9 per cent of strains by the N/F System. Complementary tests were needed to identify 35,4 per cent of strains using the API System but 65,2 per cent using the N/F System.     

Recovery of Gram-negative bacilli in stored endotracheal aspirates

This study assessed the recovery rates of Gram-negative bacilli from stored endotracheal aspirates frozen with and without glycerol. Samples frozen with glycerol showed a significant difference in isolate recovery, 89.7% versus 69.2% (P = 0.02). This study demonstrates that it is possible to achieve high recovery rates of potentially pathogenic organisms from endotracheal aspirates when stored with glycerol, thus broadening the scope of active surveillance cultures for both clinical and research purposes.     

Rapid antimicrobial susceptibility testing of Gram-negative clinical isolates with the AutoMicrobic system

Comparisons of the antimicrobial susceptibility patterns of clinical isolates of the family Enterobacteriaceae and Pseudomonas aeruginosa were made by using Kirby-Bauer disk diffusion, the MicroMedia system broth microdilution, and the AutoMicrobic system. The Kirby-Bauer system compared favorably with the MicroMedia system (95% essential correlation with 90% complete agreement). The AutoMicrobic system also compared favorably with both the Kirby-Bauer system (93% essential correlation with 87% complete agreement) and the MicroMedia system (97% essential correlation with 85% complete agreement). These data indicate that the AutoMicrobic system results are comparable to those of the MicroMedia and the Kirby-Bauer systems. Furthermore, the AutoMicrobic system offers a more rapid system (6 to 10 h), than the traditional systems, without sacrificing accuracy (16 to 24 h).     

Characteristics, epidemiology and clinical importance of emerging strains of Gram-negative bacilli producing extended-spectrum beta-lactamases

Beta-lactam antimicrobial agents represent the most common treatment for bacterial infections and continue to be the leading cause of resistance to beta-lactam antibiotics among Gram-negative bacteria worldwide. The persistent exposure of bacterial strains to a multitude of beta-lactams has induced dynamic and continuous production and mutation of beta-lactamases in these bacteria, expanding their activity even against the newly developed beta-lactam antibiotics. These enzymes are known as extended-spectrum beta-lactamases (ESBLs). The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel unrelated beta-lactamases. In recent years, there has been an increased incidence and prevalence of ESBLs. ESBLs are mainly found in strains of Escherichia coli and Klebsiella pneumoniae but have also been reported in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Infections with ESBL-producing bacterial strains are encountered singly or in outbreaks, especially in critical care units in hospitals, resulting in increasing cost of treatment and prolonged hospital stays. Not only may nursing home patients be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms, but ambulatory patients with chronic conditions may also harbor ESBL-producing organisms.     

Predominance of Gram-negative bacilli among patients with catheter-related bloodstream infections

We evaluated changes in the epidemiology of catheter-related bloodstream infections (CRBSIs) between 1996 and 2012 in a tertiary care centre in Israel. The cohort included 1754 episodes of CRBSI. The incidence of CRBSIs decreased throughout the study period, whereas 30-day mortality following bacteraemia increased. There was a linear shift toward predominance of Gram-negative bacilli throughout the study period (p for trend <0.001). In 1996, 68% (68/100) of CRBSIs were caused by Gram-positive cocci, whereas in 2012 77.8% (28/26) were caused by Gram-negative bacilli. The shift towards Gram-negative CRBSIs and the associated mortality mandates that empirical treatment for CRBSIs be directed by local epidemiology.     

Rapid detection of multidrug resistant Gram-negative bacilli by Cica-Beta-Test strips

Aim of the study

This study aimed to evaluate the sensitivity and specificity of a new system (Cica-Beta-Test, Kanto Chemical, Japan) for rapid detection of AmpC-derepressed, extended-spectrum β-lactamases (ESβL) and metallo-β-lactamases (MβL).

Methods

Two hundred Multi-Drug Resistant (MDR)-Gram-negative bacilli were studied: 170 Enterobacteriaceae and 30 Gram-negative non-fermentative bacteria. One hundred and eighteen strains produced an ESβL, seven MβL and 75 derepressed cephalosporinases. One drop of substrate was dispensed onto the filter pad of the Cica-Beta-Test strip. The bacterial colonies were spread on the filter pad of strip. The reading was performed after 2 to 15 min: turning chromogenic indicated the positive test. Three tests were used: Cica-Beta I for detection of MDR bacteria; Cica-Beta MβL for detection of MβL-producing bacteria and Cica-Beta CVA, which distinguish ESβL and AmpC-derepressed producers. Results were compared with molecular assays.

Results

Cica-Beta-Test I has detected 194 MDR (sensitivity 97%), Cica-Beta-Test MβL has shown the presence of six MβL tested (sensitivity 85.7%). Five strains were non-MβL false positive (specificity 97.3%). Cica-Beta-Test CVA allowed the differentiation of ESβL-producing strains (109/115) and AmpC-derepressed strains (56/67) (sensitivity 94.8%, specificity 83.8%).

Conclusions

Because of their epidemic nature, the MDR strains are screened and require strict hygienic measures patients. The simultaneous use of three strips can quickly determine the presence of MDR including ESβL and MβL. Rapid screening of MDR avoids transmission and limits the use of broad-spectrum antibiotics.     

Changes in antibiotic sensitivity patterns of Gram-negative bacilli in burns

Sensitivity tests with 12 antibiotics on 1,018 strains of Gram-negative bacilli isolated in a burns unit between 1969 and 1971 showed some important differences from results in similar tests on a series of strains isolated between 1965 and 1967. These changes included the emergence of a large proportion of kanamycin-resistant strains of Klebsiella aerogenes, Proteus mirabilis, and Escherichia coli and of smaller proportions of trimethoprim- and gentamicin-resistant strains; also the complete replacement of Proteus mirabilis with dissociated resistance to ampicillin by strains showing linked resistance to ampicillin and carbenicillin. The probable relationship of these changes to the emergence of an R factor determining resistance to tetracycline, kanamycin, carbenicillin, ampicillin, and cephaloridine in Enterobacteria and Pseudomonas aeruginosa is discussed.     

Carriage of multidrug-resistant Gram-negative bacilli: duration and risk factors

European Journal of Clinical Microbiology & Infectious Diseases - Identification of risk factors influencing the duration of carriage of multidrug-resistant Gram-negative bacilli (MDR-GNB) may...