Relationship between penicillin-binding protein patterns and beta-lactamases in clinical isolates of Bacteroides fragilis with different susceptibility to beta-lactam antibiotics

Solid phase extraction technology combined with UPLC-MS/MS: a method for detecting 20 β-lactamase antibiotics traces in goat's milk

We develop and validate a method for the rapid determination and identification of 20 β-lactamase antibiotics traces in goat's milk by combining the solid phase extraction technology with ultra-high performance liquid chromatography-tandem mass spectrometry. Goat milk samples were extracted with acetonitrile twice. The supernatant was then extracted and cleaned by solid-phase extraction using divinylbenzene and N-vinylpyrrolidone copolymer. The method was validated, with limits of quantification (LOQs) of 0.3 μg kg-1, specificities of 1/3 LOQ, linearities (R2) > 0.99, recoveries of 80-110%, repeatabilities <10.0%, and intermediate precisions <10.0%. The developed method was suitable for the routine analysis of β-lactamase antibiotics residues in goat's milk and was used to test 76 goat milk samples produced in China.

Fifty years devoted to anaerobes: historical, lessons, and highlights

Renew interest and enthusiasm for anaerobes stem from both technological improvements (culture media, production of an adequate anaerobic atmosphere, identification methods) and greater awareness on the part of clinicians. Anaerobic infections were historically treated empirically, targeting the species known to be involved in each type of infection. Prevotella, fusobacteria, and Gram-positive cocci (GPAC) were considered responsible for infections above the diaphragm whereas for intra-abdominal infections, Bacteroides of the fragilis group (BFG), GPAC and clostridia were predominantly implicated. The antibiotic susceptibility of anaerobes was only taken into consideration by the clinician in the event of treatment failure or when faced with infections by multidrug-resistant bacteria (MDR). The evolution of antibiotic resistance together with clinical failures due to the absence of detection of hetero-resistant clones has resulted in a greater need for accessible antibiotic susceptibility testing (AST) and disc diffusion method. Improved isolation and identification of anaerobes, along with the availability of accessible and robust methods for performing AST, will ensure that treatment, whether empirical or guided by an antibiogram, will lead to better outcomes for anaerobic infections.

Carbapenem resistance in Bacteroides fragilis: A review of molecular mechanisms

Carbapenems are an applicable subclass of β-lactam drugs in the antibiotic therapy of anaerobic infections, especially for poly-microbial cases, due to their broad antimicrobial spectrum on aerobic and anaerobic bacteria. Bacteroides fragilis is the most commonly recovered anaerobic bacteria in the clinical laboratories from mono- and poly-microbial infections. B. fragilis is relatively non-susceptible to different antibiotics, including β-lactams, tetracyclines, fluoroquinolones, and macrolides. Carbapenems are among the most effective drugs against B. fragilis strains with high-level resistance to different antibiotics. Increased antibiotic resistance of B. fragilis strains has been reported following the overuse of an antimicrobial agent. Earlier contact with carbapenems is linked with increased resistance to them that limits the options for treatment of B. fragilis caused infections, especially in cases caused by multidrug-resistant strains. Several molecular mechanisms of resistance to carbapenems have been described for different carbapenem-resistant bacteria. Understanding the mechanisms of resistance to antimicrobial agents is necessary for selecting alternative antimicrobial agents and the application of control strategies. In the present study, we reviewed the mechanisms contributing to resistance to carbapenems in B. fragilis strains.

Resistance and Virulence Features of Bacteroides spp. Isolated from Abdominal Infections in Romanian Patients

Anaerobic bacteria are predominant residents of the normal microbiota of the skin and mucous membranes but are also known to be associated with a number of human infections including peritonitis, appendicitis, abscesses, ulcers and wound infections. Herein, we investigate the antibiotic resistance profiles as well as the genetic support of antibiotic resistance and virulence determinants of anaerobic bacteria isolated from intra-abdominal infections. The study was performed on 198 Romanian patients from which different clinical samples were taken intra-operatory and sent for microbiological analyses. From the total number of isolated strains, a subset of 75 Bacteroides spp. were selected and further investigated for antibiotic resistance and virulence features, at phenotypic and genetic level. Our results obtained through the analysis of a significant number of Bacteroides strains could shed light on the virulence potential and mechanisms by which anaerobic bacteria can cause endogenous infections.

Antimicrobial resistance and susceptibility testing of anaerobic bacteria

Infections due to anaerobic bacteria can be severe and life-threatening. Susceptibility testing of anaerobes is not frequently performed in laboratories, but such testing is important to direct appropriate therapy. Anaerobic resistance is increasing globally, and resistance trends vary by geographic region. An overview of a variety of susceptibility testing methods for anaerobes is provided, and the advantages and disadvantages of each method are reviewed. Specific clinical situations warranting anaerobic susceptibility testing are discussed.

A systematic quantitative proteomic examination of multidrug resistance in Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii strains have been examined at the DNA sequence level, but seldom using large-scale quantitative proteomics. We have compared the proteome of the multidrug resistant strain BAA-1605, with the proteome of the drug-sensitive strain ATCC 17978, using iTRAQ labeling and online 2D LC/MS/MS for peptide/protein identification. Of 1484 proteins present in at least 2 of 4 independent experiments, 114 are 2-fold to 66-fold more abundant in BAA-1605, and 99 are 2-fold to 50-fold less abundant. Proteins with 2-fold or greater abundance in the multidrug resistant strain include drug-, antibiotic-, and heavy metal-resistance proteins, stress-related proteins, porins, membrane transporters, proteins important for acquisition of foreign DNA, biofilm-related proteins, cell-wall and exopolysaccharide-related proteins, lipoproteins, metabolic proteins, and many with no annotated function. The porin CarO, inactivated in carbapenem-resistant strains, is 2.3-fold more abundant in BAA-1605. Likewise, the porin OmpW, less abundant in carbapenem- and colistin-resistant A. baumannii strains, is 3-fold more abundant in BAA-1605. Nine proteins, all present in the drug-sensitive strain but from 2.2-fold to 16-fold more abundant in the MDR strain, can potentially account for the observed resistance of BAA-1605 to 18 antibiotics.

BIOLOGICAL SIGNIFICANCE

Multidrug resistant (MDR) strains of the pathogen Acinetobacter baumannii are a significant cause of hospital-acquired infections, are associated with increased mortality and length of stay, and may be a major factor underlying the spread of this pathogen, which is difficult to eradicate from clinical settings. To obtain a better understanding of antimicrobial resistance mechanisms in MDR A. baumannii, we report the first large scale 2D LC/MS/MS-based quantitative proteomics comparison of a drug-sensitive strain and an MDR strain of this pathogen. Ca. 20% of the expressed proteome changes 2-fold or more between the compared strains, including 42 proteins with literature or informatics annotations related to resistance mechanisms, modification of xenobiotics, or drug transport. Other categories of proteins differing 2-fold or more between strains include stress-response related proteins, porins, OMPs, transporters and secretion-related proteins, cell wall- and expolysaccharide-related proteins, lipoproteins, and DNA- and plasmid-related proteins. While the compared strains also differ in other aspects than multi-drug resistance, the observed differences, combined with protein functional annotation, suggest that complex protein expression changes may accompany the MDR phenotype. Expression changes of nine proteins in the MDR strain can potentially account for the observed resistance to 18 antibiotics.

Intestinal spirochetosis: an enigmatic disease

INTRODUCTION

Intestinal spirochetosis (IS) is a condition in which colonic and appendiceal epithelial cells are colonized by one of two anaerobic spirochetes, either the Brachyspira aalborgi or Brachyspira pilosicoli. There is much debate in the literature as to whether IS is a pathogen or a commensal inhabitant. A recent case of IS at our institution prompted a retrospective database search and review of the literature.

METHODS

A pathology database search for IS was performed at Carolinas Medical Center from 2003 through 2007. After patient identification, a retrospective review of the endoscopic record and the pathology report was performed. Pathology slides were reviewed for accuracy and special silver stains and/or immunostains were performed if needed. The following data were collected for each patient when available: age, gender, nationality, HIV status, and other co-morbid conditions when noted. We attempted to determine whether patients were treated for spirochetosis and if so, the treatment regimen used as well as the results.

RESULTS

The database search detected 29 patients with biopsies showing IS. Three patients were subsequently removed due to incorrect identification. A total of 26 patients with an average age of 45 years were reviewed. The most common symptoms were abdominal pain, diarrhea, and rectal bleeding. Most patients did not exhibit inflammatory changes despite the presence of spirochetosis. Pathologic examination revealed a relative increase in intra-epithelial lymphocytes in a subset of cases, a non-specific finding. Acute colitis or architectural distortion was not seen in any of the study cases. We were only able to obtain follow-up of two patients after treatment with metronidazole and both responded to therapy.

CONCLUSIONS

To date, our study is the largest case series that includes both endoscopic and pathologic descriptions and confirms the "bland" nature of the condition. In <20 % of our patients inflammation was present microscopically and it did not correlate well with endoscopic appearance. Symptoms reported by our patients were similar to those reported in previous studies, although our lack of endoscopic changes was different from one previous paper. There is no established standard of care for the treatment of IS and our study, reflects the enigmatic nature of IS as a disease process. In the absence of rigorous literature, physicians will need to use a logical and pragmatic approach to the evaluation and treatment of IS.

In vitro activity of ceftazidime-NXL104 against 396 strains of beta-lactamase-producing anaerobes

NXL104, a novel β-lactamase inhibitor, was tested at a constant concentration of 4 μg/ml in combination with ceftazidime (CAZ), with and without added metronidazole, against 396 β-lactamase-producing strains of anaerobic bacteria. MIC(50)/MIC(90) values for Bacteroides fragilis and the B. fragilis group were 8/16 and 64/>128 μg/ml, respectively. Although CAZ-NXL104 had limited activity against most anaerobic strains, in combination with metronidazole it shows potential for treating mixed infections involving resistant Enterobacteriaceae and anaerobes.

Antimicrobial resistance in Bacteroides spp.: occurrence and dissemination

Bacteroides spp. organisms, though important human commensals, are also opportunistic pathogens when they escape the colonic milieu. Resistance to multiple antibiotics has been increasing in Bacteroides spp. for decades, and is primarily due to horizontal gene transfer of a plethora of mobile elements. The mechanistic aspects of conjugation in Bacteroides spp. are only now being elucidated at a functional level. There appear to be key differences between Bacteroides spp. and non-Bacteroides spp. conjugation systems that may contribute to promiscuous gene transfer within and from this genus. This review summarizes the mechanisms of action and resistance of antibiotics used to treat Bacteroides spp. infections, and highlights current information on conjugation-based DNA exchange.

Evaluation of a new meropenem-EDTA double-ended Etest strip for the detection of the cfiA metallo-beta-lactamase gene in clinical isolates of Bacteroides fragilis

Thirty-five Bacteroides fragilis clinical isolates with varying susceptibility to meropenem were analysed with a prototype of a double-ended Etest strip containing meropenem +/- EDTA, designed for the detection of the CfiA metallo-beta-lactamase. Phenotypic results obtained with this new Etest strip were related to the genotype and compared to the results of the Etest containing imipenem +/- EDTA. Whereas the Etest with imipenem +/- EDTA only allowed detection of isolates with high-level resistance (both MICs of imipenem and meropenem >32 mg/L), reflecting the possible underestimation of CfiA prevalence in B. fragilis, the Etest with meropenem +/- EDTA proved to be more accurate, particularly for isolates with low-level carbapenem resistance, suggesting its potential for broader detection of CfiA production.

Proteomic analysis of ampicillin-resistant oral Fusobacterium nucleatum

INTRODUCTION

Fusobacterium nucleatum represents one of the predominant anaerobic species in the oral microbiota. Penicillin-resistant F. nucleatum have been isolated from intra- and extraoral infections. This study aimed to assess ampicillin resistance in F. nucleatum by investigating the synthesis of resistance-associated proteins.

METHODS

Ampicillin-resistant and ampicillin-susceptible F. nucleatum isolates were obtained from 22 dental plaque samples. Two-dimensional gel electrophoresis and mass spectrometry were used to investigate bacterial protein synthesis. Proteins exhibiting statistically significant quantitative changes between sensitive and resistant isolates were identified using peptide mass mapping and matrix-assisted laser desorption/ionization - time of flight/time of flight (MALDI-TOF/TOF) mass spectrometry.

RESULTS

Twenty-three F. nucleatum isolates were recovered from plaque samples and their ampicillin minimum inhibitory concentrations ranged between 0.125 microg/ml and 256 microg/ml. Analysis of the bacterial cellular proteins by two-dimensional gel electrophoresis resolved 154-246 distinct protein spots (mean 212, n = 9). Between 32% and 83% of the protein spots were common for the F. nucleatum isolates. Comparisons of the protein profiles of sensitive and resistant isolates revealed the presence of a 29 kDa protein and significant increases in the synthesis of two proteins at 37 and 46 kDa in the ampicillin-resistant F. nucleatum isolates. These proteins were identified as a class D beta-lactamase, ATP-binding cassette (ABC) transporter ATP-binding protein and enolase, respectively.

CONCLUSION

Synthesis of a class D beta-lactamase by ampicillin-resistant F. nucleatum isolates could complicate antimicrobial treatment because these enzymes might confer resistance to many classes of beta-lactam antibiotics. The differences observed in protein synthesis between ampicillin-resistant and ampicillin-susceptible F. nucleatum may contribute to the antibiotic resistance and virulence of these bacteria.

Bacteroides: the good, the bad, and the nitty-gritty

SUMMARY

Bacteroides species are significant clinical pathogens and are found in most anaerobic infections, with an associated mortality of more than 19%. The bacteria maintain a complex and generally beneficial relationship with the host when retained in the gut, but when they escape this environment they can cause significant pathology, including bacteremia and abscess formation in multiple body sites. Genomic and proteomic analyses have vastly added to our understanding of the manner in which Bacteroides species adapt to, and thrive in, the human gut. A few examples are (i) complex systems to sense and adapt to nutrient availability, (ii) multiple pump systems to expel toxic substances, and (iii) the ability to influence the host immune system so that it controls other (competing) pathogens. B. fragilis, which accounts for only 0.5% of the human colonic flora, is the most commonly isolated anaerobic pathogen due, in part, to its potent virulence factors. Species of the genus Bacteroides have the most antibiotic resistance mechanisms and the highest resistance rates of all anaerobic pathogens. Clinically, Bacteroides species have exhibited increasing resistance to many antibiotics, including cefoxitin, clindamycin, metronidazole, carbapenems, and fluoroquinolones (e.g., gatifloxacin, levofloxacin, and moxifloxacin).

Penicillin-binding proteins of Bacteroides fragilis and their role in the resistance to imipenem of clinical isolates

In this study penicillin-binding proteins (PBPs) of Bacteroides fragilis and the resistance mechanisms of this micro-organism to 11 beta-lactam antibiotics were analysed. The study focused on the role of PBP2Bfr and metallo-beta-lactamase in the mechanism of resistance to imipenem. The mechanism of beta-lactam resistance in B. fragilis was strain dependent. The gene encoding the orthologue of Escherichia coli PBP3 gene (pbpBBfr, which encodes the protein PBP2Bfr) was sequenced in five of the eight strains studied, along with the ccrA (cfiA) gene in strain 119, and their implications for resistance were examined. Differences were found in the amino-acid sequence of PBP2Bfr in strains AK-2 and 119, and the production of beta-lactamases indicated that these differences may be involved in the mechanism of resistance to imipenem. In vitro binding competition assays with membrane extracts using imipenem indicated that the PBP that bound imipenem with the highest affinity was PBP2Bfr, and that increased affinity in strain 7160 may be responsible for the moderate susceptibility of this strain to imipenem. In the same way, the importance of the chromosomal class A beta-lactamase CepA in the resistance mechanism of the B. fragilis strains NCTC 9344, 7160, 2013E, AK-4, 0423 and R-212 was studied. In these strains this is the principal resistance mechanism to antimicrobial agents studied other than imipenem.

Screening of isolates from faeces for carbapenem-resistant Bacteroides strains; existence of strains with novel types of resistance mechanisms

Isolates from faecal samples (n = 224) from the UK and Hungary were screened for carbapenem-resistant Bacteroides strains and were consecutively investigated for the resistance mechanisms through detection of cfiA genes, the presence or lack of insertion sequence insertions in their upstream regions and the production of carbapenemase activities. In this way, a significant number of strains (n = 7, 3.1%) were recovered. They included 2 Bacteroides fragilis strains (one in each country) which harboured cfiA genes, but which were not activated by insertion sequence elements; this is reminiscent of some novel clinical B. fragilis strains. The cfiA-negative strains exhibited lower levels of carbapenem resistance and varying levels of carbapenemase activity, suggesting that other resistance mechanisms may also exist.