Lectura interpretada del antibiograma: una necesidad clínica

The role of the microbiology laboratory in the diagnosis of multidrug-resistant Gram-negative bacilli infections. The importance of the determination of resistance mechanisms

Early diagnosis and treatment has an important impact on the morbidity and mortality of infections caused by multidrug-resistant bacteria. Multidrug-resistant gram-negative bacilli (MR-GNB) constitute the main current threat in hospitals and especially in intensive care units (ICU). The role of the microbiology laboratory is essential in providing a rapid and effective response. This review updates the microbiology laboratory procedures for the rapid detection of BGN-MR and its resistance determinants. The role of the laboratory in the surveillance and control of outbreaks caused by these bacteria, including typing techniques, is also studied. The importance of providing standardized resistance maps that allow knowing the epidemiological situation of the different units is emphasized. Finally, the importance of effective communication systems for the transmission of results and decision making in the management of patients infected by BGN-MR is reviewed.

Reporting antimicrobial susceptibilities and resistance phenotypes in Staphylococcus spp.: a nationwide proficiency study

Objectives

To evaluate the proficiency of microbiology laboratories in Spain in antimicrobial susceptibility testing (AST) of Staphylococcus spp.

Materials and methods

Eight Staphylococcus spp. with different resistance mechanisms were selected: six Staphylococcus aureus (CC-01/mecA, CC-02/mecC, CC-03/BORSA, CC-04/MLSBi, CC-06/blaZ and CC-07/linezolid resistant, cfr); one Staphylococcus epidermidis (CC-05/linezolid resistant, 23S rRNA mutation); and one Staphylococcus capitis (CC-08/daptomycin non-susceptible). Fifty-one laboratories were asked to report: (i) AST system used; (ii) antimicrobial MICs; (iii) breakpoints used (CLSI or EUCAST); and (iv) clinical category. Minor, major and very major errors (mEs, MEs and VMEs, respectively) were determined.

Results

The greatest MIC discrepancies found were: (i) by AST method: 19.4% (gradient diffusion); (ii) by antimicrobial agent: daptomycin (21.3%) and oxacillin (20.6%); and (iii) by isolate: CC-07/cfr (48.0%). The greatest error rates were: (i) by AST method: gradient diffusion (4.3% and 5.1% VMEs, using EUCAST and CLSI, respectively); (ii) by breakpoint: 3.8% EUCAST and 2.3% CLSI; (iii) by error type: mEs (0.8% EUCAST and 1.0% CLSI), MEs (1.8% EUCAST and 0.7% CLSI) and VMEs (1.2% EUCAST and 0.6% CLSI); (iii) by antimicrobial agent: VMEs (4.7% linezolid and 4.3% oxacillin using EUCAST); MEs (14.3% fosfomycin, 9.1% tobramycin and 5.7% gentamicin using EUCAST); and mEs (22.6% amikacin using EUCAST).

Conclusions

Clinical microbiology laboratories should improve their ability to determine the susceptibility of Staphylococcus spp. to some antimicrobial agents to avoid reporting false-susceptible or false-resistant results. The greatest discrepancies and errors were associated with gradient diffusion, EUCAST breakpoints and some antimicrobials (mEs for aminoglycosides; MEs for fosfomycin, aminoglycosides and oxacillin; and VMEs for linezolid and oxacillin).

Antimicrobial Resistance in Bacteria Isolated From Cats and Dogs From the Iberian Peninsula

Pet animals are assumed to be potential reservoirs in transferring antimicrobial resistance (AMR) to humans due to the extensively applied broad-spectrum antimicrobial agents and their close contact with humans. In this study, microbiological data and antimicrobial susceptibility results of dog (n = 5,086) and cat (n = 789) clinical samples from a private Laboratory of Diagnosis in Barcelona were analyzed. Samples came from different counties of the Iberian Peninsula during 2016–2018. In dogs, clinical samples were most commonly from otitis, and in cats from wounds, respiratory tract infections and conjunctivitis. In both pet groups, Staphylococcus spp. (31% in dogs vs 30% in cats), Streptococcus spp. (19% vs 17%), Pseudomonas spp. (16% vs 10%), Escherichia coli (8% vs 5.6%), and Enterococcus spp. (5.5% vs 6.8%) were shown as the most predominant bacteria. However, higher frequencies of P. aeruginosa, P. canis, and S. pseudintermedius were found in dogs, while S. aureus and P. multocida were more prevalent in cats. The antimicrobial susceptibility testing demonstrated that Enterococcus spp. and Pseudomonas spp. presented the highest levels of AMR in both dogs and cats. Within the Enterobacteriaceae, E. coli showed low levels of AMR compared to Klebsiella, Proteus, or Enterobacter spp. Respiratory tract infections caused by K. pneumoniae presented higher AMR in cats. By contrast, Pasteurella isolates from the respiratory tract were highly sensitive to all the antimicrobials in cats and dogs. Data from this study could be used to guide empirical antimicrobial selection in companion animal veterinary practices in the Iberian Peninsula.

Recommendations of the Spanish Antibiogram Committee (COESANT) for selecting antimicrobial agents and concentrations for in vitro susceptibility studies using automated systems

Automated antimicrobial susceptibility testing devices are widely implemented in clinical microbiology laboratories in Spain, mainly using EUCAST (European Committee on Antimicrobial Susceptibility Testing) breakpoints. In 2007, a group of experts published recommendations for including antimicrobial agents and selecting concentrations in these systems. Under the patronage of the Spanish Antibiogram Committee (Comité Español del Antibiograma, COESANT) and the Study Group on Mechanisms of Action and Resistance to Antimicrobial Agents (GEMARA) from the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC), and aligned with the Spanish National Plan against Antimicrobial Resistance (PRAN), a group of experts have updated this document. The main modifications from the previous version comprise the inclusion of new antimicrobial agents, adaptation of the ranges of concentrations to cover the EUCAST breakpoints and epidemiological cut-off values (ECOFFs), and the inference of new resistance mechanisms. This proposal should be considered by different manufacturers and users when designing new panels or cards. In addition, recommendations for selective reporting are also included. With this approach, the implementation of EUCAST breakpoints will be easier, increasing the quality of antimicrobial susceptibility testing data and their microbiological interpretation. It will also benefit epidemiological surveillance studies as well as the clinical use of antimicrobials aligned with antimicrobial stewardship programs.

Knowledge regarding antibiotic use among students of three medical schools in Medellin, Colombia: a cross-sectional study

BACKGROUND

The objective of the present study was to describe the knowledge regarding the antibiotic therapy of students of three medical schools in Medellín, Colombia.

METHODS

The study population comprised medical students who were enrolled in three universities. The instrument contained questions regarding their current academic term, the university, the perceived quality of the education received on antibiotic therapy and bacterial resistance, and specific questions on upper respiratory tract infections, pneumonia, urinary tract infections, and skin and soft tissue infections. The information was analyzed by calculating frequencies and measures of dispersion and central tendency. Knowledge regarding the treatment for each type of infection was compared using the Mann-Whitney U test and the Kruskal-Wallis H test.

RESULTS

We included 536 medical students, of which 43.5% students consider that the university has not sufficiently trained them to interpret antibiograms and 29.6% students consider that the quality of information received on the subject at their university ranges from regular to poor. The mean score for knowledge regarding antibiotic therapy for upper respiratory tract infections was 44.2 (9.9) on a scale from 0 to 100. The median score with regard to the treatment of pneumonia was 52.9 (14.7), that of urinary tract infection was 58.7 (14.8), and that of skin and soft tissue infections was 63.1 (19.4). The knowledge regarding antibiotic therapy for upper respiratory tract infections, pneumonia, and urinary tract infection does not improve with the academic term, the university, or perceived quality of the education received.

CONCLUSION

A large proportion of medical students perceive that the training received from the university is insufficient with regard to antibiotic use and bacterial resistance, which is consistent with the limited knowledge reflected in the selection of antibiotic treatment for respiratory, urinary tract, and skin and soft tissue infections. Overall, the situation was identical among all universities, and it did not significantly increase with the completion of an academic term.

[Antimicrobial susceptibility cumulative reports]

Cumulative reports on antimicrobial susceptibility tests data are important for selecting empirical treatments, as an educational tool in programs on antimicrobial use, and for establishing breakpoints defining clinical categories. These reports should be based on data validated by clinical microbiologists using diagnostic samples (not surveillance samples). In order to avoid a bias derived from including several isolates obtained from the same patient, it is recommended that, for a defined period, only the first isolate is counted. A minimal number of isolates per species should be presented: a figure of >=30 isolates is statistically acceptable. The report is usually presented in a table format where, for each cell, information on clinically relevant microorganisms-antimicrobial agents is presented. Depending on particular needs, multiple tables showing data related to patients, samples, services or special pathogens can be prepared.

[Programs for optimizing the use of antibiotics (PROA) in Spanish hospitals: GEIH-SEIMC, SEFH and SEMPSPH consensus document]

The antimicrobial agents are unique drugs for several reasons. First, their efficacy is higher than other drugs in terms of reduction of morbidity and mortality. Also, antibiotics are the only group of drugs associated with ecological effects, because their administration may contribute to the emergence and spread of microbial resistance. Finally, they are used by almost all medical specialties. Appropriate use of antimicrobials is very complex because of the important advances in the management of infectious diseases and the spread of antibiotic resistance. Thus, the implementation of programs for optimizing the use of antibiotics in hospitals (called PROA in this document) is necessary. This consensus document defines the objectives of the PROA (namely, to improve the clinical results of patients with infections, to minimise the adverse events associated to the use of antimicrobials including the emergence and spread of antibiotic resistance, and to ensure the use of the most cost-efficacious treatments), and provides recommendations for the implementation of these programs in Spanish hospitals. The key aspects of the recommendations are as follows. Multidisciplinary antibiotic teams should be formed, under the auspices of the Infection Committees. The PROA need to be considered as part of institutional programs and the strategic objectives of the hospital. The PROA should include specific objectives based on measurable indicators, and activities aimed at improving the use of antimicrobials, mainly through educational activities and interventions based more on training activities directed to prescribers than just on restrictive measures.

[Current panorama of the teaching of microbiology and parasitology in Spain]

The training program of residents in microbiology and parasitology in Spain includes clinical skills, ranging from the diagnostic approach to the patient and adequate sample collection for diagnosis of infectious diseases to antimicrobial therapy and infection control measures. Training also includes new challenges in clinical microbiology that ensure residents' participation in infection control programs of health-care associated infections, training in the resolution of public health problems, and application of new molecular microbiology methods. Specialization in clinical microbiology may be undertaken by graduates in Medicine, Biology, Biochemistry and Chemistry. The training is performed in accredited microbiology laboratories at different hospitals (n = 61) across the country through 4-year residency programs. In the last few years, there has been a major imbalance between the number of intended residents (0.17 per 100,000 inhabitants) and those graduating as specialists in clinical microbiology (0.13 per 100,000 inhabitants), with wide variations across the country. The current tendency in Europe is to strengthen the role of clinical microbiologists as key figures in the diagnosis of infectious diseases and in public health microbiology. Training programs have been hampered by the practice of sending samples for microbiological tests to external, centralized multipurpose laboratories with few clinical microbiologists and without a core curriculum. Essential elements in the training of specialists in clinical microbiology are a close relationship between the laboratory and the clinical center and collaboration with other specialists.

[Interpretive reading of enterobacteria antibiograms]

The resistance pattern observed in the antibiogram of an isolate should be the sum of its natural resistance pattern, characteristic of the species, plus the acquired resistances. In Enterobacteriaceae, the production of inactivating enzymes is the main mechanism of resistance to beta-lactams and aminoglycosides. Each one of these enzymes recognizes one or more specific beta-lactams or aminoglycosides as substrate. This substrate specificity implies a specific resistance pattern from which we can deduce the enzymes present in the isolate. However, enzymatic-mediated resistance is not the only mechanism implicated and resistance is frequently multifactorial. Resistance to quinolones is mainly due to precise, sequential chromosomal mutations that can be selected by fluoroquinolone treatments. Recently, certain plasmid-mediated genes which code enzymes that modify quinolones or that are target protectors have been implicated in the low level resistance to quinolones.