Evaluation of the VITEK 2 AST N-054 test card for the detection of extended-spectrum beta-lactamase production in Escherichia coli with CTX-M phenotypes

Advances in the detection of β-lactamase: A review

β-lactamase, an enzyme secreted by bacteria, is the main resistant mechanism of Gram-negative bacteria to β-lactam antibiotics. The resistance of bacteria to β-lactam antibiotics can be evaluated by testing the activity of β-lactamase. Traditional phenotypic detection is a golden principle, but it is time-consuming. In recent years, many new methods have emerged, which improve the efficiency by virtue of their sensitivity, low cost, easy operation, and other advantages. In this paper, we systematically review these researches and emphasize their limits of detection, sample operation, and test duration. Noteworthily, some detection systems can identify the β-lactamase subtype conveniently. We mainly divide these tests into three categories to elaborate their characteristics and application status. Both advantages and disadvantages of these methods are discussed. Additionally, we analyze the recent 5 years published researches to predict the trend of development in this field.

Evolution of the Antimicrobial resistance of Bacteria causing Urinary Tract Infections

BACKGROUND

The bacteria, Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae), are the main reasons for urinary tract infections (UTIs). This research aimed to investigate the isolation of etiologic agents from patients with UTI; it also investigates the antibiotic resistance activities and incidence of ESBL genes between different clinical separates of uropathogenic E. coli, determining their association with ESBL genes.

METHODS

The study enrolled 1000 positive growth isolates. The predominant pathogen associated with urinary tract infection, Gram-negative, were the main isolates from UTI patients, including E. coli, K. pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, Staphylococcus aureus and Enterococcus faecalis.

RESULTS

Among suspicious cases of urinary tract infection, we showed that 15.2% of the patients had UTI, and female patients in the childbearing age group were more affected. 644 E. coli (64.4%) and 322 (32.2%) K. pneumoniae were more isolated. Among 936 (93.6%) ESBL producing bacteria, 614 (61.4 %) E. coli showedhigh resistance to the antibiotics, Cefotaxime (85.7 %), Cefepime (85.7 %), Ciprofloxacin (83.1 %) and Kanamycin (77.9 %). Most ESBL-producing K. pneumoniae were multidrug-resistant (MDR). Nitrofurantoin, gentamycin, and imipenem were the most effective antibiotics for ESBL-producing E. coli isolates.

CONCLUSION

This study shows that the high rates of MDR Escherichia coli infection in our hospital were frequentative reasons for UTI. Nitrofurantoin and aminoglycosides were the most beneficial first-line drugs to be applied in the cases of UTI. It is recommended to conduct regular investigations on the drug resistance of all isolates and formulate helpful antibiotic treatment policies in China. It is important to determine the prevalence of ESBL in urine E. coli and K. pneumoniae isolates because it has a great influence on the selection of suitable antibacterial agents. In short, more than half of ESBL producers have multiple drug resistance (MDR).

The prevalence of ESBL-producing Enterobacteriaceae in a nursing home setting compared with elderly living at home: a cross-sectional comparison

Background

The aim of the study was to investigate the prevalence of faecal carriage of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae among residents living in nursing homes and to compare it with a corresponding group of elderly people living in their own homes.

Methods

A total of 160 persons participated in the study between February and April 2014, 91 were residents in nursing homes (n = 10) and the remaining 69 were elderly living in their own homes. In addition to performing faecal samples, all participants answered a standardized questionnaire regarding known risk factors for ESBL-carriage.

Results

There was no significant difference between the groups, as 10 of the 91 (11 %) residents from nursing homes were ESBL-carriers compared with 6 of 69 (8,7 %) elderly living in their own homes. There was no significant difference between the groups. The total prevalence was 10 %. A univariate analysis revealed that the only studied risk factor significantly associated with ESBL-carriage was recent foreign travel (p = 0,017). All ESBL-positive isolates were Escherichia coli and there was a high degree of co-resistance to other antibiotics. All isolates (n = 17) were susceptible to imipenem and amikacin.

Conclusion

Residents of nursing homes as well as elderly living in their own homes have high rates of faecal carriage of ESBL-producing bacteria. These findings may affect the choice of empirical antibiotic treatment of severe infections in older adults.

Expert systems in clinical microbiology

This review aims to discuss expert systems in general and how they may be used in medicine as a whole and clinical microbiology in particular (with the aid of interpretive reading). It considers rule-based systems, pattern-based systems, and data mining and introduces neural nets. A variety of noncommercial systems is described, and the central role played by the EUCAST is stressed. The need for expert rules in the environment of reset EUCAST breakpoints is also questioned. Commercial automated systems with on-board expert systems are considered, with emphasis being placed on the "big three": Vitek 2, BD Phoenix, and MicroScan. By necessity and in places, the review becomes a general review of automated system performances for the detection of specific resistance mechanisms rather than focusing solely on expert systems. Published performance evaluations of each system are drawn together and commented on critically.

Comparison of nine phenotypic methods for detection of extended-spectrum beta-lactamase production by Enterobacteriaceae

The detection of extended-spectrum β-lactamase-producing (ESBL) bacteria is of importance for infection control and epidemiological surveillance. We aimed to compare phenotypic methods available in the routine laboratory and to evaluate two-step strategies using these methods for the detection of ESBL-positive Enterobacteriaceae. Two methods used for routine susceptibility testing (Vitek2 and disk diffusion methods) and seven methods designed for the detection of ESBL production (ESBL Etests, combination disks, double-disk synergy [DDS] methods on Mueller-Hinton [MH] agar and cloxacillin-containing MH agar, and the Cica-Beta test) were tested against 107 strains of Enterobacteriaceae not susceptible to extended-spectrum cephalosporins. All strains were screened for the presence of acquired ESBL-encoding genes by PCR, and the PCR result was considered the gold standard for evaluation of the other test methods. Among the 107 strains, 52 (49%) were ESBL positive. With Vitek2, sensitivities were the highest when using extended cards (73% to 79%), but 25% to 31% of the strains yielded indeterminate results. For the disk diffusion method, sensitivities were the highest (96%) when testing at least cefotaxime, cefepime, and a third compound (ceftazidime, cefpodoxime, or aztreonam). For the specific methods, specificities ranged from 62% (ceftazidime ESBL Etest) to 100% (DDS using a disk spacing of 20 mm). When a method designed for ESBL detection was used on strains considered ESBL negative or with an indeterminate result by a first routine susceptibility method, sensitivities reached 100% for a majority of combinations. In conclusion, two-step strategies using phenotypic methods available in most clinical laboratories may reach a sensitivity of 100% for ESBL detection among a large panel of species, including AmpC producers, providing a sensible choice of tests.

[Evaluation of the MicroScan NegCombo panel Type 44 for detection of extended-spectrum beta-lactamase among clinical isolates of Escherichia coli, Klebsiella species, and Proteus mirabilis]

BACKGROUND

Accurate and rapid detection of extended-spectrum beta-lactamases (ESBLs) is important in guiding proper antimicrobial therapy for infected patients. We evaluated the performance of MicroScan NegCombo Type 44 panel (Dade Behring, USA), which was developed to confirm ESBL-producing Enterobacteriaceae using ceftazidime/clavulanate and cefotaxime/clavulanate.

METHODS

From August 30 to September 20, 2007, 206 non-duplicate clinical isolates, including 106 Escherichia coli, 81 Klebsiella pneumoniae, 11 Klebsiella oxytoca, and 8 Proteus mirabilis were subcultured and tested with Type 32 and Type 44 panels. The results were compared with those of the CLSI phenotypic confirmatory test (CLSI-PCT) and disk approximation test (DAT). Isolates not susceptible to cefotetan or flagged as "Possible ESBL, unable to interpret confirm test (Possible ESBL)" on Type 44 panel were tested with boronic acid disks to confirm AmpC beta-lactamases (AmpC) production.

RESULTS

Of the 206 isolates tested, 44 (21.4%) produced ESBL by CLSI-PCT or DAT, including 27 E. coli, 14 K. pneumoniae, 2 K. oxytoca, and 1 P. mirabilis. Thirty-eight isolates flagged as "Confirmed ESBL" on Type 44 panel were all confirmed as ESBL-producers. Of 14 K. pneumoniae flagged as "Possible ESBL", 6 were confirmed as ESBL and AmpC co-producers and 8 as AmpC-producers.

CONCLUSIONS

Type 44 panel showed an excellent performance in detecting ESBL-producing E. coli, Klebsiella spp., and P. mirabilis. When flagged as "Confirmed ESBL", no other confirmatory test was necessary to report as ESBL; however, "Possible ESBL" required a differential test for AmpC production.