Evaluation of four phenotypic methods to detect plasmid-mediated AmpC β-lactamases in clinical isolates

House Flies (Musca domestica) from Swine and Poultry Farms Carrying Antimicrobial Resistant Enterobacteriaceae and Salmonella

The house fly (Musca domestica) is a very common insect, abundantly present in farm settings. These insects are attracted by organic substrates and can easily be contaminated by several pathogenic and nonpathogenic bacteria. The aim of this survey was to evaluate the presence of Salmonella spp. and other Enterobacteriaceae in house flies captured in small-medium size farms, located in Northwest Tuscany, Central Italy, and to evaluate their antimicrobial resistance; furthermore, isolates were tested for extended spectrum β-lactamase and carbapenems resistance, considering the importance these antimicrobials have in human therapy. A total of 35 traps were placed in seven poultry and 15 swine farms; three different kinds of samples were analyzed from each trap, representing attractant substrate, insect body surface, and insect whole bodies. Enterobacteriaceae were isolated from 86.36% of farms, 82.87% of traps, and 60.95% of samples; high levels of resistance were detected for ampicillin (61.25% of resistant isolates) and tetracycline (42.5% of resistant isolates). One extended spectrum β-lactamase producer strain was isolated, carrying the blaTEM-1 gene. Salmonella spp. was detected in 36.36% of farms, 25.71% of traps, and 15.24% of samples. Five different serovars were identified: Kentucky, Kisarawe, London, Napoli, and Rubislaw; some isolates were in R phase. Resistance was detected mainly for ampicillin (31.21%) and tetracycline (31.21%). House flies could represent a serious hazard for biosecurity plans at the farm level, carrying and sharing relevant pathogenic and antimicrobial resistant bacteria.

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.

Impact of Carbapenem Heteroresistance Among Multidrug-Resistant ESBL/AmpC-Producing Klebsiella pneumoniae Clinical Isolates on Antibiotic Treatment in Experimentally Infected Mice

Purpose

Antibiotic resistance is a growing health crisis that is further complicated by treatment failures caused by bacteria that exhibit heterogeneous susceptibility to antibiotics. The aim of this study was to describe imipenem (IPM)-heteroresistant strains among multidrug-resistant (MDR) ESBL/AmpC-producing Klebsiella pneumoniae clinical isolates, investigate their molecular phenotypic characteristics, and elucidate the outcome of antibiotic treatment in mice infected with the heteroresistant isolates.

Materials and Methods

Antimicrobial susceptibility of K. pneumoniae isolates was determined by the disk diffusion and E-test methods. Heteroresistance to IPM was confirmed by population analysis profile (PAP) assays. PCR and sequencing were employed to detect MDR determinants. Molecular differences between the susceptible and resistant subpopulations were evaluated by sequencing and quantitative real-time reverse transcription PCR (qRT-PCR) analysis. The effect of the carbapenem-heteroresistant strains on antibiotic treatment was assessed using a mouse model of peritonitis with heteroresistant K. pneumoniae and subsequent treatment with IPM.

Results

In total, 37 MDR ESBL/AmpC-producing clinical isolates of K. pneumoniae were identified between September 2018 and December 2019. These strains were notably resistant to conventional antimicrobials other than carbapenems. Among the isolates, three strains exhibited heteroresistance to IPM and carried several ESBL and/or AmpC genes. Mice infected with a lethal dose of any of the three heteroresistant isolates were unable to survive in the presence of IPM treatment, as the percentage of the IPM-resistant subpopulation of each strain was increased in the peritoneum of these mice at 24 h after infection. The resistant subpopulation of the strains presented pulsed-field gel electrophoresis (PFGE) profiles that were identical to those of the susceptible subpopulation, but ompK36 porin showed a reduction in gene expression (0.09- to 0.50-fold) in the resistant subpopulation.

Conclusion

Carbapenem-heteroresistant strains were present among the MDR K. pneumoniae isolates producing ESBL/AmpC β-lactamases, and these heteroresistant strains failed IPM therapy in experimentally infected mice.

Genetic diversity and co-prevalence of ESBLs and PMQR genes among plasmid-mediated AmpC β-lactamase-producing Klebsiella pneumoniae isolates causing urinary tract infection

Klebsiella pneumoniae is an opportunistic pathogen that frequently causes nosocomial urinary tract infection (UTI). The aim of this study was to investigate the prevalence of extended-spectrum β-lactamases (ESBL), plasmid-mediated quinolone resistance (PMQR) genes, in acquired AmpC (ac-AmpC) β‑lactamase‑producing K. pneumoniae isolates from patients with nosocomial UTI and to characterize the transmissibility of plasmids harbouring multiple resistance genes. From January 2017 to June 2018, we collected 46 ac-AmpC-producing K. pneumoniae isolates causing UTI from a tertiary care hospital in China. Antimicrobial susceptibility assays showed that non-susceptibility of all isolates to third-generation cephalosporin and fluoroquinolone was very high (>80%). Diverse types of ESBLs and PMQR genes, including bla_SHV-12 (n = 23), bla_SHV-27 (n = 1)_, bla_SHV-28 (n = 2)_, bla_SHV-33 (n = 4), bla_CTX-M-3 (n = 24)_, bla_CTX-M-14 (n = 6)_, bla_CTX-M-15 (n = 6)_, bla_CTX-M-22 (n = 1) and bla_OXA-10 (n = 26)_, as well as qnrA (n = 2), qnrB (n = 39) and qnrS (n = 2) genes were identified amongst AmpC-producing K. pneumoniae isolates. The bla_AmpC, qnrB and several ESBLs genes from six strains harbouring multiple AmpC (at least two ampC) were co-transferrable to recipients via conjugation or electroporation, with IncFIA, IncFIB and IncA/C being the dominant replicons. Conserved genetic context associated with the mobilization of bla_ampC genes was detected. Forty-six isolates were categorized into 25 enterobacterial repetitive intergenic consensus (ERIC) types, and the 6 isolates harbouring multiple AmpC genes belonged to ST1 lineage. This work reports that the emergence of plasmids co-harbouring multiple resistance determinants and mediating the local prevalence in K. pneumoniae causing UTI in China.

Detection and occurrence of plasmid-mediated AmpC in highly resistant gram-negative rods

OBJECTIVES

The aim of this study was to compare the current screening methods and to evaluate confirmation tests for phenotypic plasmidal AmpC (pAmpC) detection.

METHODS

For this evaluation we used 503 Enterobacteriaceae from 18 Dutch hospitals and 21 isolates previously confirmed to be pAmpC positive. All isolates were divided into three groups: isolates with 1) reduced susceptibility to ceftazidime and/or cefotaxime; 2) reduced susceptibility to cefoxitin; 3) reduced susceptibility to ceftazidime and/or cefotaxime combined with reduced susceptibility to cefoxitin. Two disk-based tests, with cloxacillin or boronic acid as inhibitor, and Etest with cefotetan-cefotetan/cloxacillin were used for phenotypic AmpC confirmation. Finally, presence of pAmpC genes was tested by multiplex and singleplex PCR.

RESULTS

We identified 13 pAmpC producing Enterobacteriaceae isolates among the 503 isolates (2.6%): 9 CMY-2, 3 DHA-1 and 1 ACC-1 type in E. coli isolates. The sensitivity and specificity of reduced susceptibility to ceftazidime and/or cefotaxime in combination with cefoxitin was 97% (33/34) and 90% (289/322) respectively. The disk-based test with cloxacillin showed the best performance as phenotypic confirmation method for AmpC production.

CONCLUSIONS

For routine phenotypic detection of pAmpC the screening for reduced susceptibility to third generation cephalosporins combined with reduced susceptibility to cefoxitin is recommended. Confirmation via a combination disk diffusion test using cloxacillin is the best phenotypic option. The prevalence found is worrisome, since, due to their plasmidal location, pAmpC genes may spread further and increase in prevalence.

Characterization of plasmid-mediated β-lactamases in fecal colonizing patients in the hospital and community setting in Spain

AIM

Active surveillance of plasmid-mediated β-lactamase-producing Enterobacteriaceae (PMBL-E) in fecal carriers in the hospital and in the community setting in a non-outbreak period of time.

METHODS

Patients were screened for carriage of Enterobacteriaceae resistant to expanded-spectrum cephalosporins and PMBL-E were characterized (extended-spectrum-β-lactamase [ESBL], plasmid-mediated AmpC β-lactamase [pAmpC], and carbapenemases) by PCR and sequencing.

RESULTS

The prevalence of ESBL and pAmpC carriers was 5.06% and 0.59%, respectively. Overall, CTX-M-like enzymes were the ESBL dominate enzymes (96.15%). The group CTX-M-9 was the most prevalent (81, 54%) [CTX-M-14 (74, 91.35%), CTX-M-9 (5, 6.17%), CTX-M-24 (1, 1.23%), and CTX-M-27 (1, 1.23%)] followed by the group CTX-M-1 (64, 42.67%) [CTX-M-15 (42, 65.63%), CTX-M-1 (13, 20.31%), CTX-M-32 (8, 12.5%), and CTX-M-3 (1, 1.56%)]. One CTX-M-10, one CTX-M-59, and three CTX-M-8 were also found. A very small representation of SHV or TEM ESBL enzymes was found (3.2% and 0.64%, respectively). pAmpC characterization revealed a predominance of CMY-2 (81.25%), followed by DHA-1 (18.75%). We did not detect the presence of carbapenemase producers.

CONCLUSIONS

The prevalence of ESBL-producers from fecal carriers is stable in our area, but colonization by pAmpC producers has emerged recently as we have confirmed. Periodic active surveillance is useful to identify these human reservoirs and control the evolution of PMBL carriage in a community over time.