Jennifer M. Andrews

Bio: Jennifer M. Andrews is an academic researcher. The author has contributed to research in topics: Antibacterial agent & Pharmacokinetics. The author has an hindex of 9, co-authored 11 publications receiving 3830 citations.

Determination of minimum inhibitory concentrations

Abstract: Minimum inhibitory concentrations (MICs) are defined as the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation, and minimum bactericidal concentrations (MBCs) as the lowest concentration of antimicrobial that will prevent the growth of an organism after subculture on to antibiotic-free media. MICs are used by diagnostic laboratories mainly to confirm resistance, but most often as a research tool to determine the in vitro activity of new antimicrobials, and data from such studies have been used to determine MIC breakpoints. MBC determinations are undertaken less frequently and their major use has been reserved for isolates from the blood of patients with endocarditis. Standardized methods for determining MICs and MBCs are described in this paper. Like all standardized procedures, the method must be adhered to and may not be adapted by the user. The method gives information on the storage of standard antibiotic powder, preparation of stock antibiotic solutions, media, preparation of inocula, incubation conditions, and reading and interpretation of results. Tables giving expected MIC ranges for control NCTC and ATCC strains are also supplied.

BSAC standardized disc susceptibility testing method

Abstract: For nearly a decade microbiologists have used the MIC breakpoints published in the BSAC Guide to Susceptibility Testing to interpret susceptibility. Historically, and unlike the rest of Europe, the UK and Ireland have used a comparative method of disc testing to interpret susceptibility rather than one based on a correlation between MIC and zone of inhibition. Although innovative when introduced in the 1970s, Stokes' comparative method has evolved ad hoc and it has become increasingly apparent that there is a need for a standardized method of disc testing that is correlated with BSAC MIC breakpoints. The method described here, like all other standardized methods of disc testing, cannot be adapted by the user, and interpretative criteria are only applicable if the method is adhered to fully. A major advantage of this approach to susceptibility testing is that data from several sources can be combined for surveillance of resistance, a task that has been made much easier by the introduction of this method and coincides with the availability of automated zone measuring devices. It is hoped that the method described here will provide the core document for standard operating procedures; however, changes will necessarily occur over time as the method is developed and refined.

Pharmacokinetics and Inflammatory-Fluid Penetration of Moxifloxacin following Oral or Intravenous Administration

Abstract: A single 400-mg oral or intravenous (i.v.) dose of moxifloxacin was given to each of eight healthy male volunteers, and 6 weeks later the dose was administered by the other route. The concentrations of the drug in plasma, cantharidin-induced inflammatory fluid, and urine were measured over the subsequent 24 h. The mean maximum concentrations observed in plasma were 4.98 μg/ml after oral dosing and 5.09 μg/ml after i.v. dosing. The mean maximum concentrations attained in the inflammatory fluid were 2.62 and 3.23 μg/ml, respectively. The mean elimination half-lives from plasma were 8.32 and 8.17 h, respectively. The overall penetration into the inflammatory fluid was 103.4 and 104.2%. Over 24 h 15% of the drug was recovered in the urine when administered by either route.

The development of the BSAC standardized method of disc diffusion testing

Abstract: The BSAC Working Party on Susceptibility Testing has developed a standardized method of disc susceptibility testing that has been 'field tested' in 19 diagnostic laboratories in the UK and Ireland The method employs semi-defined media, a semi-confluent inoculum and relates zones of inhibition with BSAC-specified MIC breakpoints to interpret susceptibility The bacteria selected for the trial included clinical isolates and control strains from the ATCC and NCTC national collections Organisms were chosen because they had known attributes, such as being fully susceptible or having a demonstrated mechanism of resistance The results from this survey are very encouraging With the commonly isolated Enterobacteriaceae, specifically Escherichia coli, Proteus mirabilis and Klebsiella spp, no major problems were observed except with gentamicin and cefuroxime In the case of gentamicin, problems were associated with resistant strains of P mirabilis, with MICs of 2 mg/L, being falsely reported as susceptible For cefuroxime, it is not unexpected that results were unreliable, as the MIC distribution straddles the in vitro breakpoint concentration (following the results of this study the MIC and zone diameter breakpoints have been amended to improve reporting) No major problems were encountered for Pseudomonas aeruginosa with the agents studied The 'field survey' has shown that disc testing is unreliable for determining the susceptibility of coagulase-negative staphylococci to teicoplanin, and that the detection of glycopeptide resistance in enterococci is improved by incubation for a full 24 h Inconsistencies observed with fastidious organisms were associated with incorrect inocula Zone diameter data for the control strains studied provide information that can be utilized by diagnostic laboratories to monitor the daily performance of testing

Molecular and Kinetic Comparison of the Novel Extended-Spectrum β-Lactamases CTX-M-25 and CTX-M-26

Abstract: CTX-M-25 is a novel extended-spectrum β-lactamase isolated from a single Canadian Escherichia coli isolate. Susceptibility testing demonstrated that this enzyme confers resistance to both cefotaxime and ceftazidime, but the level of resistance was reduced with the addition of β-lactamase inhibitors. The blaCTX-M-25 gene was detected on a 111-kb plasmid. It is a member of the CTX-M-8 group and has the closest amino acid identity (99%; three amino acid substitutions) with CTX-M-26. The blaCTX-M-26 gene was detected on a 100-kb plasmid isolated from a Klebsiella pneumoniae strain from the United Kingdom, and plasmid profiling revealed that it showed some homology to the blaCTX-M-25-harboring plasmid. Both CTX-M genes were located downstream of ISEcp1, although the copy upstream of blaCTX-M-25 was disrupted by IS50-A. Comparative kinetic studies of recombinant CTX-M-25 and CTX-M-26 enzymes showed that CTX-M-25 has a higher level of ceftazidime hydrolysis (kcat values, 33 and 0.005 s−1 for CTX-M-25 and CTX-M-26, respectively).

Agar and broth dilution methods to determine the minimal inhibitory concentration (MIC) of antimicrobial substances

Abstract: The aim of broth and agar dilution methods is to determine the lowest concentration of the assayed antimicrobial agent (minimal inhibitory concentration, MIC) that, under defined test conditions, inhibits the visible growth of the bacterium being investigated. MIC values are used to determine susceptibilities of bacteria to drugs and also to evaluate the activity of new antimicrobial agents. Agar dilution involves the incorporation of different concentrations of the antimicrobial substance into a nutrient agar medium followed by the application of a standardized number of cells to the surface of the agar plate. For broth dilution, often determined in 96-well microtiter plate format, bacteria are inoculated into a liquid growth medium in the presence of different concentrations of an antimicrobial agent. Growth is assessed after incubation for a defined period of time (16-20 h) and the MIC value is read. This protocol applies only to aerobic bacteria and can be completed in 3 d.

Clinical relevance of the ESKAPE pathogens.

Abstract: In recent years, the Infectious Diseases Society of America has highlighted a faction of antibiotic-resistant bacteria (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) - acronymically dubbed 'the ESKAPE pathogens' - capable of 'escaping' the biocidal action of antibiotics and mutually representing new paradigms in pathogenesis, transmission and resistance. This review aims to consolidate clinically relevant background information on the ESKAPE pathogens and provide a contemporary summary of bacterial resistance, alongside pertinent microbiological considerations necessary to face the mounting threat of antimicrobial resistance.

Pseudomonas biofilm formation and antibiotic resistance are linked to phenotypic variation

Abstract: Colonization of the lungs of cystic fibrosis (CF) patients by the opportunistic bacterial pathogen Pseudomonas aeruginosa is the principal cause of mortality in CF populations1,2. Pseudomonas aeruginosa infections generally persist despite the use of long-term antibiotic therapy1,3. This has been explained by postulating that P. aeruginosa forms an antibiotic-resistant biofilm4,5 consisting of bacterial communities embedded in an exopolysaccharide matrix. Alternatively, it has been proposed that resistant P. aeruginosa variants may be selected in the CF respiratory tract by antimicrobial therapy itself1,6. Here we report that both explanations are correct, and are interrelated. We found that antibiotic-resistant phenotypic variants of P. aeruginosa with enhanced ability to form biofilms arise at high frequency both in vitro and in the lungs of CF patients. We also identified a regulatory protein (PvrR) that controls the conversion between antibiotic-resistant and antibiotic-susceptible forms. Compounds that affect PvrR function could have an important role in the treatment of CF infections.

CTX-M enzymes: origin and diffusion

Abstract: CTX-M β-lactamases are considered a paradigm in the evolution of a resistance mechanism. Incorporation of different chromosomal blaCTX-M related genes from different species of Kluyvera has derived in different CTX-M clusters. In silico analyses have shown that this event has occurred at least nine times; in CTX-M-1 cluster (3), CTX-M-2 and CTX-M-9 clusters (2 each), and CTX-M-8 and CTX-M-25 clusters (1 each). This has been mainly produced by the participation of genetic mobilization units such as insertion sequences (ISEcp1 or ISCR1) and the later incorporation in hierarchical structures associated with multifaceted genetic structures including complex class 1 integrons and transposons. The capture of these blaCTX-M genes from the environment by highly mobilizable structures could have been a random event. Moreover, after incorporation within these structures, β-lactam selective force such as that exerted by cefotaxime and ceftazidime has fuelled mutational events underscoring diversification of different clusters. Nevertheless, more variants of CTX-M-enzymes, including those not inhibited by β-lactamase inhibitors such as clavulanic acid (IR-CTX-M variants), only obtained under in in vitro experiments are still waiting to emerge in the clinical setting. Penetration and the later global spread of CTX-M producing organisms have been produced with the participation of the so called “epidemic resistance plasmids” often carried in multidrug resistant and virulent high risk clones. All these facts but also the incorporation and coselection of emerging resistance determinants within CTX-M producing bacteria, such as those encoding carbapenemases, depict the currently complex pandemic scenario of multi-drug resistant isolates.

BSAC standardized disc susceptibility testing method (version 7)

Abstract: The changes that have been made to the previous version of the recommendations (version 6) are as follows: medium and incubation condition for testing Acinetobacter spp. (Tables 1 and 6); use of cefoxitin as an indicator antibiotic for detecting methicillin/oxacillin/cefoxitin resistance in coagulase-negative staphylococci (Tables 1, 6 and 11); MIC breakpoint for co-trimoxazole based on the trimethoprim concentration in a 1:19 combination with sulfamethoxazole (Tables 7, 10, 11, 12, 15, 16 and 19); advice on the use of azithromycin for the treatment of infections with Salmonella typhi (footnote to Table 7); amendment to the recommendation for cefuroxime for the treatment of infections with Proteus mirabilis (footnote Table 7); MIC and zone diameter breakpoints for Stenotrophomonas maltophilia only (Table 10); MIC breakpoints for daptomycin (Tables 11 and 15); clarification for staphylococci that the neomycin zone diameter breakpoints are for topical use only and differentiate the isolates outside the 'wild-type' population in Table 11; clarification for beta-haemolytic streptococci that the linezolid zone diameter breakpoints relate to an MIC breakpoint of 2 mg/L as no data for the intermediate category are currently available (Table 15); clarification that strains with reduced susceptibility to fluoroquinolones give no zone of inhibition with a 30 microg nalidixic acid disc (Tables 16 and 21); erythromycin is no longer used for therapy of Neisseria gonorrhoeae, but may be tested for epidemiological purposes (Table 17); clarification that the ciprofloxacin zone diameter breakpoint for Neisseria meningitidis relates to the MIC breakpoint of 0.03 mg/L as no data for the intermediate category are currently available; clarification that the ciprofloxacin zone diameter breakpoints for Campylobacter spp. relate to an MIC breakpoint of 0.5 mg/L as no data for the intermediate category are currently available; clarification that for ciprofloxacin and vancomycin zone diameter breakpoints for coryneform organisms relate to an MIC breakpoint of 0.5 and 4 mg/L, respectively, as no data for the intermediate category are currently available; MIC and zone diameter breakpoints for Gram-negative rods isolated from urinary tract infections have been expanded to include Klebsiella spp.; and a definition of coliforms is also included (Table 26).