Plasmid-Mediated AmpC β-Lactamase and Underestimation of Extended-Spectrum β-Lactamase in Cefepime-Susceptible Elevated-Ceftazidime-MIC Enterobacteriaceae Isolates

Systematic Review of Plasmid AmpC Type Resistances in Escherichia coli and Klebsiella pneumoniae and Preliminary Proposal of a Simplified Screening Method for ampC

Beta-lactamase (BL) production is a major public health problem. Although not the most frequent AmpC type, AmpC-BL is increasingly isolated, especially plasmid AmpC-BL (pAmpC-BL). The objective of this study was to review information published to date on pAmpC-BL in Escherichia coli and Klebsiella pneumoniae, and on the epidemiology and detection methods used by clinical microbiology laboratories, by performing a systematic review using the MEDLINE PubMed database. The predictive capacity of a screening method to detect AmpC-BL using disks with cloxacillin (CLX) was also evaluated by studying 102 Enterobacteriaceae clinical isolates grown in CHROMID ESBL medium with the addition of cefepime (FEP), cefoxitin (FOX), ertapenem (ETP), CLX, and oxacillin with CLX. The review, which included 149 publications, suggests that certain risk factors (prolonged hospitalization and previous use of cephalosporins) are associated with infections by pAmpC-BL-producing microorganisms. The worldwide prevalence has increased over the past 10 years, with a positivity rate ranging between 0.1 and 40%, although AmpC was only detected when sought in a targeted manner. CMY-2 type has been the most prevalent pAmpC-BL-producing microorganism. The most frequently used phenotypic method has been the double-disk synergy test (using CLX disks or phenyl-boronic acid and cefotaxime [CTX] and ceftazidime) and the disk method combined with these inhibitors. In regard to screening methods, a 1-µg oxacillin disk with CLX showed 88.9% sensitivity, 100% specificity, 100% positive predictive value (PPV), 98.9% negative predictive value (NPV), and 98.9% validity index (VI). This predictive capacity is reduced with the addition of extended-spectrum beta-lactamases, showing 62.5% sensitivity, 100% specificity, 100% PPV, 93.5% NPV, and 94.1% VI. In conclusion, there has been a worldwide increase in the number of isolates with pAmpC-BL, especially in Asia, with CMY-2 being the most frequently detected pAmpC-BL-producing type of microorganism. Reduction in its spread requires routine screening with a combination of phenotypic methods (with AmpC inhibitors) and genotypic methods (multiplex PCR). In conclusion, the proposed screening technique is an easy-to-apply and inexpensive test for the detection of AmpC-producing isolates in the routine screening of multidrug-resistant microorganisms.

Pharmacokinetics of Intravitreal Vancomycin and Ceftazidime in Silicone Oil-Filled Macaque Eyes

Purpose

This study evaluated the pharmacokinetics of intravitreal vancomycin and ceftazidime in the aqueous humor of macaque eyes filled with silicone oil in the vitreous cavity.

Methods

Intravitreal vancomycin (1 mg/0.1 mL) and ceftazidime (2 mg/0.1 mL) were injected into four normal macaque eyes, four vitrectomized aphakic macaque eyes, and four previously vitrectomized aphakic macaque eyes filled with silicone oil (silicone oil-filled eyes). Aqueous humor samples (0.1 mL) were obtained just before injection and at 2 and 5 hours and 1, 2, 3, 5, 7, and 10 days after injection. In each group, corneal endothelial cell density (ECD) measurements and electroretinogram (ERG) recordings were obtained before injection and after 1 month.

Results

The half-lives of vancomycin in the aqueous humor of normal, vitrectomized, and silicone oil-filled eyes were 29.4, 21.1, and 6.8 hours, respectively, and those of ceftazidime were 20.4, 5.2, and 3.1 hours, respectively. The maximum vancomycin aqueous humor concentrations of normal, vitrectomized, and silicone oil-filled eyes were 151.4, 205.6, and 543.5 µg/mL, respectively, and the maximum ceftazidime aqueous humor concentrations are 64.6, 260.0, and 1176.3 µg/mL, respectively. There was no change in ECD, and ERG was not declined after intravitreal injection in all groups.

Conclusions

The half-lives of vancomycin and ceftazidime in the aqueous humor were shorter in silicone oil-filled eyes than in normal and vitrectomized eyes. High antibiotic concentrations in silicone oil-filled eyes seemed to be well tolerated.

Translational Relevance

This study aids in estimating how often an antibiotic should be intravitreally injected for endophthalmitis of silicone oil-filled eyes.

Detection of ESBL/AmpC-Producing and Fosfomycin-Resistant Escherichia coli From Different Sources in Poultry Production in Southern Brazil

This study discussed the use of antimicrobials in the commercial chicken production system and the possible factors influencing the presence of Extended-spectrum β-lactamase (ESBL)/AmpC producers strains in the broiler production chain. The aim of this study was to perform longitudinal monitoring of ESBL-producing and fosfomycin-resistant Escherichia coli from poultry farms in southern Brazil (Paraná and Rio Grande do Sul states) and determine the possible critical points that may be reservoirs for these strains. Samples of poultry litter, cloacal swabs, poultry feed, water, and beetles (Alphitobius sp.) were collected during three distinct samplings. Phenotypic and genotypic tests were performed for characterization of antimicrobial resistant strains. A total of 117 strains were isolated and 78 (66%) were positive for ESBL production. The poultry litter presented ESBL positive strains in all three sampled periods, whereas the cloacal swab presented positive strains only from the second period. The poultry litter represents a significant risk factor mainly at the beginning poultry production (odds ratio 6.43, 95% confidence interval 1-41.21, p < 0.05). All beetles presented ESBL positive strains. The predominant gene was bla CTX-M group 2, which occurred in approximately 55% of the ESBL-producing E. coli. The cit gene was found in approximately 13% of the ESBL-producing E. coli as AmpC type determinants. A total of 19 out of 26 fosfomycin-resistant strains showed the fosA3 gene, all of which produced ESBL. The correlation between fosA3 and bla CTX-M group 1 (bla CTX-M55 ) genes was significant among ESBL-producing E. coli isolated from Paraná (OR 3.66, 95% CI 1.9-9.68) and these genetic determinants can be transmitted by conjugation to broiler chicken microbiota strains. Our data revealed that poultry litter and beetles were critical points during poultry production and the presence of fosfomycin-resistant strains indicate the possibility of risks associated with the use of this antimicrobial during production. Furthermore, the genetic determinants encoding CTX-M and fosA3 enzymes can be transferred to E. coli strains from broiler chicken microbiota, thereby creating a risk to public health.

Performance of a novel fluorogenic probe assay for the detection of extended-spectrum-β-lactamase or plasmid AmpC β-lactamase-producing Enterobacterales directly from simulated blood culture bottles

Resistance to third generation cephalosporins is widely disseminated in Enterobacteriaceae mainly because of extended-spectrum-β-lactamases (ESBL), plasmid AmpC β-lactamases (PABL), and hyper-production of chromosomal AmpC β-lactamases. Here, we evaluated the performance of rapid test using novel fluorogenic probe assay in simulated blood cultures and compared the results with the phenol red assay using a total of 172 characterized isolates (39 ESBL producers, 13 PABL producers, and 120 susceptible isolates). We prepared a pellet by centrifugation and washing, which can also be used for identification with MALDI-TOF directly from positive blood cultures. After that, we mixed the pellet with fluorogenic probe and measured the fluorescent signal using fluorometer. The fluorogenic probe assay showed higher sensitivity than the phenol red assay (96.2% vs. 71.2%, p < .0001) in 172 simulated blood culture bottles especially in detecting PABL (84.6% vs. 0%, p = .0026) and the turnaround time was 1.5 h. This fluorogenic probe assay, combined with the direct identification of pathogens, could be very useful for rapid identification of isolates and detecting cephalosporin resistance caused by ESBL and PABL directly from positive blood cultures.