Epidemiology and clinical features of bloodstream infections caused by AmpC-type-beta-lactamase-producing Klebsiella pneumoniae

Poultry slaughterhouse wastewater as a source of bacterial antimicrobial resistance

Slaughterhouses produce huge volumes of effluents throughout the production chain that, when discharged untreated into bodies of water, can become a source of environmental contamination. This is particularly worrisome if these effluents are used for irrigation since they increase contamination levels and spread pathogens and resistance determinants to humans and animals. Therefore, in this study, we assessed antimicrobial resistance in bacteria isolated from inlet water, equalization wastewater tanks, treatment plant wastewater, and treated wastewater in slaughterhouse facilities in Rio de Janeiro, Brazil. Four samples were collected at each of the collection points, between June 2021 and July 2022. Following bacterial isolation and identification, the samples were analyzed for antimicrobial resistance using the disk diffusion method to test aminoglycoside, beta-lactam, and fluoroquinolone antimicrobials. A total of 229 bacteria were isolated, with 74 isolates selected from the genera Citrobacter (12), Enterobacter (14), Klebsiella (35), Serratia (5), and Pseudomonas (8). Inlet water had the lowest number of isolates and was the only point with gentamicin-resistant isolates. Raw effluent from the equalization tank showed the highest number of isolated bacteria and resistance levels, followed by treated wastewater and the treatment plant. Across all samples, a high rate of cefoxitin-resistance was observed among the isolated bacteria. Klebsiella pneumoniae stood out as the species that demonstrated the greatest resistance to a variety of antimicrobials. These results highlight the importance of water quality monitoring in mitigating public health and environmental risks and high antimicrobial resistance levels.

Evaluation of six commercial and in-house phenotypic tests for detection of AmpC β-lactamases: is routine detection possible?

Background

Phenotypic characterization of the prevalent AmpC β-lactamases in clinical isolates is essential for making informed empirical decisions and critical for strengthening antimicrobial stewardship programmes. This study focused on assessing six assays, two in-house and four commercial phenotypic tests for detection of AmpC, to study the feasibility of making its detection a routine diagnostic microbiology laboratory activity.

Methods

A total of 116 non-duplicate Gram-negative bacteria that were resistant to third-generation cephalosporins and amoxicillin/clavulanic acid, and resistant or susceptible to piperacillin/tazobactam and carbapenems, were screened by cefoxitin discs for AmpC. These isolates were subjected to two in-house (AmpC Tris-EDTA and disc approximation) methods and four commercial tests: D69C AmpC Detection Set; D72C ESBL, AmpC & Carbapenemase Detection Set; combination disc test: ESBL + AmpC Screen Disc Kit; and AmpC MIC Test Strip for confirmation of AmpC production. Ten whole-genome-sequenced AmpC-confirmed Gram-negative isolates were used as positive controls and one as a negative control.

Results

The prevalence of AmpC β-lactamases was 16%. Escherichia coli was a major carrier of plasmid-mediated AmpC (26.5%), followed by Klebsiella pneumoniae (23.4%). Phenotypically, 61% of AmpCs were detected by Tris-EDTA (accuracy: 73.8%), 76% by disc approximation (accuracy: 89.2%), 75% by the D69C AmpC Detection Set (accuracy: 95.4%), 74% by the D72C AmpC, ESBL & Carbapenemase Detection Set (accuracy: 95.4%), 76% by the combination disc test (accuracy: 95.4%) and 63% by AmpC MIC Test Strip (accuracy: 87.7%). The sensitivity and specificity of D69C were 97.9% and 88.2%, respectively, and 95.9% and 93.8% for the combination disc test, while for the disc approximation test and D72C they were 93.9% and 75%, and 93.9% and 100%, respectively. Screening by cefoxitin screening was less sensitive (75%) and specific (25%). Disc approximation and the combination disc test detect AmpC in Enterobacterales and also Pseudomonas aeruginosa and Acinetobacter species.

Conclusions

We recommend the in-house disc approximation test and the commercial D69C, as well as the combination disc test, as excellent tools for detection of AmpC. The cefoxitin test overcalls AmpC and cannot be considered a good stand-alone test for AmpC detection.

Phenotypic and genetic screening of Klebsiella pneumoniae isolates from human UTI patients for beta-lactamases and their genetic diversity analysis by ERIC and REP PCRs

Klebsiella pneumoniae is one of the major nosocomial pathogens responsible for pneumoniae, septicaemia, liver abscesses, and urinary tract infections. Coordinated efforts by antibiotic stewardship and clinicians are underway to curtail the emergence of antibiotic-resistant strains. The objective of the present study is to characterize K. pneumoniae strains through antibiotic resistance screening for production of beta-lactamases (β-lactamases) such as extended spectrum beta lactamases (ESBLs), AmpC β-lactamases, and carbapenemases by phenotypic and genotypic methods and genetic fingerprinting by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) and repetitive element palindromic PCR (REP-PCR). A total of 85 K. pneumoniae strains isolated from 504 human urinary tract infections (UTI) were used in this study. Only 76 isolates showed positive in phenotypic screening test (PST), while combination disc method (CDM) as phenotypic confirmatory test (PCT) confirmed 72 isolates as ESBL producers. One or more β-lactamase genes were detected by PCR in 66 isolates (91.66%, 66/72) with blaTEM gene being the most predominant (75.75%, 50/66). AmpC genes could be detected in 21 isolates (31.8%, 21/66) with FOX gene being the predominant (24.24%, 16/66), whereas NDM-I was detected in a single strain (1.51%, 1/66). Genetic fingerprinting using ERIC-PCR and REP-PCR revealed wide heterogeneity among β-lactamase producing isolates with discriminatory power of 0.9995 and 1, respectively.

Clinical characteristics, risk factors and outcomes of Klebsiella pneumoniae pneumonia developing secondary Klebsiella pneumoniae bloodstream infection

Purpose

The clinical characteristics of Klebsiella pneumoniae (KP) pneumonia and KP bloodstream infection (KP-BSI) are often reported, while the risk factors for KP pneumonia developing into secondary KP-BSI (KP-pneumonia/KP-BSI) are largely unknown. Therefore, this study attempted to investigate the clinical characteristics, risk factors and outcomes of KP-pneumonia/KP-BSI.

Methods

A retrospective observational study was conducted at a tertiary hospital between January 1, 2018, and December 31, 2020. The patients were divided into groups of KP pneumonia alone and KP pneumonia/KP-BSI, and the clinical information were collected from medical records electronic system.

Results

A total of 409 patients were finally recruited. According to the multivariate logistic regression analysis, male sex (adjusted odds ratio [aOR] 3.7; 95% CI, 1.44–9.5), immunosuppression (aOR, 13.52; 95% CI, 2.53,72.22), APACHE II score higher than 21 (aOR, 3.39; 95% CI, 1.41–8.12), serum procalcitonin (PCT) levels above 1.8 ng/ml (aOR, 6.37; 95% CI, 2.67–15.27), ICU stay of more than 2.5 days before pneumonia onset (aOR, 1.09; 95% CI, 1.02,1.17), mechanical ventilation (aOR, 4.96; 95% CI, 1.2,20.5), Klebsiella pneumoniae isolates producing extended spectrum β-lactamase (ESBL-positive KP) (aOR, 12.93; 95% CI, 5.26–31.76), and inappropriate antibacterial therapy (aOR, 12.38; 95% CI, 5.36–28.58) were independent factors of KP pneumonia/KP BSI. In comparison with the patients with KP pneumonia alone, the patients with KP pneumonia/KP BSI showed an almost 3 times higher incidence of septic shock (64.4% vs. 20.1%, p < 0.01), a longer duration of mechanical ventilation, and longer lengths of ICU stay and total hospital stay (median days, 15 vs. 4,19 vs. 6, 34 vs. 17, respectively, both p < 0.01). Additionally, the overall in-hospital crude mortality rate in the patients with KP-pneumonia/KP-BSI was more than two times higher than that in those with KP pneumonia alone (61.5% vs. 27.4%, p < 0.01).

Conclusion

Factors including male sex, immunosuppression, APACHE II score higher than 21, serum PCT levels above 1.8 ng/ml, ICU stay of more than 2.5 days before pneumonia onset, mechanical ventilation, ESBL-positive KP, and inappropriate antibacterial therapy are independent risk factors for KP pneumonia/KP-BSI. Of note, the outcomes in patients with KP pneumonia worsen once they develop secondary KP-BSI, which merits more attention.

Assessment of virulence factors and antimicrobial resistance among the Pseudomonas aeruginosa strains isolated from animal meat and carcass samples

BACKGROUND

Pseudomonas aeruginosa bacteria are emerging causes of food spoilage and foodborne diseases. Raw meat of animal species may consider a reservoir of P. aeruginosa strains.

OBJECTIVES

The present survey was done to assess the prevalence, antibiotic resistance properties and distribution of virulence factors among the P. aeruginosa strains isolated from raw meat and carcass surface swab samples of animal species.

METHODS

Five hundred and fifty raw meat and carcass surface swab samples were collected from cattle and sheep species referred to as slaughterhouses. P. aeruginosa bacteria were identified using culture and biochemical tests. The pattern of antibiotic resistance was determined by disk diffusion. The distribution of virulence and antibiotic resistance genes was determined using polymerase chain reaction.

RESULTS

Forty-seven of 550 (8.54%) examined samples were contaminated with P. aeruginosa. The prevalence of P. aeruginosa in raw meat and carcass surface swab samples were 6.57 and 12%, respectively. P. aeruginosa isolates showed the maximum resistance rate toward penicillin (87.23%), ampicillin (85.10%), tetracycline (85.10%), gentamicin (65.95%) and trimethoprim (57.44%). The most commonly detected antibiotic resistance genes were BlaCTX-M (53.19%), blaDHA (42.55%) and blaTEM (27.65%). The most commonly detected virulence factors was ExoS (42.55%), algD (31.91%), lasA (31.91%), plcH (31.91%) and exoU (25.53%).

CONCLUSIONS

Meat and carcass surface swab samples may be sources of resistant and virulent P. aeruginosa, which pose a hygienic threat in their consumption. However, further investigations are required to identify additional epidemiological features of P. aeruginosa in meat and carcass surface samples.

Prevalence, Antimicrobial Resistance, and Molecular Description of Pseudomonas aeruginosa Isolated from Meat and Meat Products

Resistant and virulent Pseudomonas aeruginosa (P. aeruginosa) bacteria are measured as the major cause of food spoilage and food-borne diseases. This survey assesses the prevalence, antibiotic resistance properties, and virulence factors distribution in P. aeruginosa bacteria isolated from meat and meat products. A total of 370 raw, frozen, and imported bovine meat samples and diverse types of meat product samples were collected from Alborz province, Iran. P. aeruginosa bacteria were identified by culture. Disk diffusion was used to assess the antibiotic resistance of bacteria. Furthermore, the PCR was used to assess the virulence and antibiotic resistance genes. Twenty nine out of 370 (7.83%) samples were contaminated with P. aeruginosa. Imported frozen bovine meat (20%) harbored the highest distribution, while sausage (2%) harbored the lowest. High resistance rates were observed toward ampicillin (89.65%), penicillin (86.20%), tetracycline (82.75%), cefoxitin (37.93%), gentamicin (34.48%), and clindamycin (31.03%). The most commonly detected antibiotic resistance genes were blaDHA (93.10%), blaCTX-M (83.65%), and blaSHV (48.27%). BlaDHA (93.10%), blaCTX-M (83.65%), and blaSHV (48.27%) were the most frequently detected resistance genes. The most commonly detected virulence genes were exoS (75.86%), lasA (68.96%), exoU (58.62%), lasB (51.72%), plcH (48.27%), and algD (44.82%). Meat and meat product samples may be sources of P. aeruginosa, which show an important threat to their consumption. Nevertheless, additional inquiries are obligatory to find supplementary epidemiological properties of P. aeruginosa in meat and meat product samples.

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.

Molecular epidemiology of cefotaxime-resistant but ceftazidime-susceptible Enterobacterales and evaluation of the in vitro bactericidal activity of ceftazidime and cefepime

Extended-spectrum β-lactamases' (ESBLs) production is the main resistance mechanism to third-generation cephalosporins (TGCs) in gram-negative bacilli. In Argentina, there is a high prevalence of cefotaximase-type ESBLs (CTX-M). For this reason, dissociated resistance phenotype (DRP) displaying a profile of resistance to cefotaxime (CTX) and susceptibility to ceftazidime (CAZ) might be detected. The aims of this study were to determine the prevalence of DRP in Enterobacterales clinical isolates, to characterize the mechanisms responsible for this phenotype and to evaluate the in vitro behaviour against different antibiotics. Sixty Enterobacterales resistant to any TGC were studied, and among them, 25% displayed a DRP. The β-lactamases associated with DRP were 5/11 CTX-M-2, 4/11 CTX-M-14, 1/11 CTX-M-15 and 1/11 CMY-2 in E. coli, 2/3 CTX-M-2 and 1/3 CMY-2 in P. mirabilis and 1/1 CTX-M-14 in K. pneumoniae. Furthermore, CTX-M-2 and CTX-M-14 were related with DRP in both wild-type isolates and the corresponding transconjugants. Time-kill experiments showed CAZ bactericidal activity on CTX-M-2-and CTX-M-14-producing strains and bacterial regrowth in those CMY-2 producers. An opposite behaviour was evident when cefepime (FEP) was used. However, CAZ and gentamicin combination showed a synergistic effect against the CMY-2 producers. We concluded that Enterobacterales with DRP responded differently to CAZ or FEP depending on the type of β-lactamase they possess, suggesting that these cephalosporins could be a therapeutic option. Therefore, the characterization of the involved resistance mechanism might contribute to define the appropriate antibiotic treatment.

The Carbapenemase BKC-1 from Klebsiella pneumoniae Is Adapted for Translocation by Both the Tat and Sec Translocons

The cell envelope of Gram-negative bacteria consists of two membranes surrounding the periplasm and peptidoglycan layer. β-Lactam antibiotics target the periplasmic penicillin-binding proteins that synthesize peptidoglycan, resulting in cell death. The primary means by which bacterial species resist the effects of β-lactam drugs is to populate the periplasmic space with β-lactamases. Resistance to β-lactam drugs is spread by lateral transfer of genes encoding β-lactamases from one species of bacteria to another. However, the resistance phenotype depends in turn on these “alien” protein sequences being recognized and exported across the cytoplasmic membrane by either the Sec or Tat protein translocation machinery of the new bacterial host. Here, we examine BKC-1, a carbapenemase from an unknown bacterial source that has been identified in a single clinical isolate of Klebsiella pneumoniae. BKC-1 was shown to be located in the periplasm, and functional in both K. pneumoniae and Escherichia coli. Sequence analysis revealed the presence of an unusual signal peptide with a twin arginine motif and a duplicated hydrophobic region. Biochemical assays showed this signal peptide directs BKC-1 for translocation by both Sec and Tat translocons. This is one of the few descriptions of a periplasmic protein that is functionally translocated by both export pathways in the same organism, and we suggest it represents a snapshot of evolution for a β-lactamase adapting to functionality in a new host.

Prevalence and Antibiotic Resistance Characteristics of Extraintestinal Pathogenic Escherichia coli among Healthy Chickens from Farms and Live Poultry Markets in China

Simple Summary

Chicken meat has been proved to be a suspected source of extraintestinal pathogenic Escherichia coli (ExPEC), causing several diseases in humans, and bacteria in healthy chickens can contaminate chicken carcasses at the slaughter; however, reports about the prevalence and molecular characteristics of ExPEC in healthy chickens are still rare. In this study, among 926 E. coli isolates from healthy chickens in China, 22 (2.4%) were qualified as ExPEC and these ExPEC isolates were clonally unrelated. A total of six serogroups were identified in this study, with O78 being the most predominant type, and all the six serogroups had been frequently reported in human ExPEC isolates in many countries. All the 22 ExPEC isolates were multidrug-resistant and most isolates carried both bla_CTX-M and fosA3 resistance genes. Notably, plasmid-borne colistin resistance gene mcr-1 was identified in six ExPEC isolates, among which two carried additional carbapenemase gene bla_NDM, compromising both the efficacies of the two critically important drugs for humans, carbapenems and colistin. These results highlight that healthy chickens can serve as a potential reservoir for multidrug resistant ExPEC isolates, including mcr-1-containing ExPEC.

Abstract

Chicken products and chickens with colibacillosis are often reported to be a suspected source of extraintestinal pathogenic Escherichia coli (ExPEC) causing several diseases in humans. Such pathogens in healthy chickens can also contaminate chicken carcasses at the slaughter and then are transmitted to humans via food supply; however, reports about the ExPEC in healthy chickens are still rare. In this study, we determined the prevalence and characteristics of ExPEC isolates in healthy chickens in China. A total of 926 E. coli isolates from seven layer farms (371 isolates), one white-feather broiler farm (78 isolates) and 17 live poultry markets (477 isolates from yellow-feather broilers) in 10 cities in China, were isolated and analyzed for antibiotic resistance phenotypes and genotypes. The molecular detection of ExPEC among these healthy chicken E. coli isolates was performed by PCRs, and the serogroups and antibiotic resistance characteristics of ExPEC were also analyzed. Pulsed-field gel electrophoresis (PFGE) and Multilocus sequence typing (MLST) were used to analyze the genetic relatedness of these ExPEC isolates. We found that the resistance rate for each of the 15 antimicrobials tested among E. coli from white-feather broilers was significantly higher than that from brown-egg layers and that from yellow-feather broilers in live poultry markets (p < 0.05). A total of 22 of the 926 E. coli isolates (2.4%) from healthy chickens were qualified as ExPEC, and the detection rate (7.7%, 6/78) of ExPEC among white-feather broilers was significantly higher than that (1.6%, 6/371) from brown-egg layers and that (2.1%, 10/477) from yellow-feather broilers (p < 0.05). PFGE and MLST analysis indicated that clonal dissemination of these ExPEC isolates was unlikely. Serogroup O78 was the most predominant type among the six serogroups identified in this study, and all the six serogroups had been frequently reported in human ExPEC isolates in many countries. All the 22 ExPEC isolates were multidrug-resistant (MDR) and the resistance rates to ampicillin (100%) and sulfamethoxazole-trimethoprim (100%) were the highest, followed by tetracycline (95.5%) and doxycycline (90.9%). bla_CTX-M was found in 15 of the 22 ExPEC isolates including 10 harboring additional fosfomycin resistance gene fosA3. Notably, plasmid-borne colistin resistance gene mcr-1 was identified in six ExPEC isolates in this study. Worryingly, two ExPEC isolates were found to carry both mcr-1 and bla_NDM, compromising both the efficacies of carbapenems and colistin. The presence of ExPEC isolates in healthy chickens, especially those carrying mcr-1 and/or bla_NDM, is alarming and will pose a threat to the health of consumers. To our knowledge, this is the first report of mcr-1-positive ExPEC isolates harboring bla_NDM from healthy chickens.

Prevalence of plasmid-mediated AmpC beta-lactamases in Enterobacteria isolated from urban and rural folks in Uganda

Background: AmpC beta-lactamase-producing bacteria are associated with increased resistance to third-generation cephalosporins. Here, we describe plasmid-mediated AmpC beta-lactamase-producing enterobacteria isolated from urban and rural dwellers in Uganda. Methods: Stool and urine from 1,448 individuals attending outpatient clinics in Kampala and two rural districts in central Uganda were processed for isolation of Escherichia coli and Klebsiella. Following antibiotic susceptibility testing, cefoxitin resistant isolates, and amoxicillin/clavulanate resistant but cefoxitin susceptible isolates, were tested for AmpC beta-lactamase production using the cefoxitin-cloxacillin double-disc synergy test. Carriage of plasmid-mediated AmpC beta-lactamase-encoding genes (pAmpC) and extended spectrum beta-lactamase (ESBL) encoding genes was determined by PCR. Results: Nine hundred and thirty E. coli and 55 Klebsiella were recovered from the cultured samples, yielding 985 isolates investigated (one per participant). One hundred and twenty-nine isolates (13.1%, 129/985) were AmpC beta-lactamase producers, of which 111 were molecularly characterized for pAmpC and ESBL gene carriage. pAmpC genes were detected in 60% (67/111) of the AmpC beta-lactamase producers; pAmpC genes were also detected in 18 AmpC beta-lactamase non-producers and in 13 isolates with reduced susceptibility to third-generation cephalosporins, yielding a total of 98 isolates that carried pAmpC genes. Overall, the prevalence of pAmpC genes in cefoxitin resistant and/or amoxicillin/clavulanate resistant E. coli and Klebsiella was 59% (93/157) and 26.1% (5/23), respectively. The overall prevalence of pAmpC-positive enterobacteria was 10% (98/985); 16.4% (45/274) in Kampala, 6.2% (25/406) Kayunga, and 9.2% (28/305) Mpigi. Ciprofloxacin use was associated with carriage of pAmpC-positive bacteria while residing in a rural district was associated with protection from carriage of pAmpC-positive bacteria. Conclusion: pAmpC beta-lactamase producing enterobacteria are prevalent in urban and rural dwellers in Uganda; therefore, cefoxitn should be considered during routine susceptibility testing in this setting.

The Novel CarbaLux Test for Carbapenemases and Carbapenem Deactivating AmpC Beta-Lactamases

Objectives

To evaluate the rapid phenotypic CarbaLux test for routine diagnostics in the medical laboratory in a proof of concept study.

Methods

isolates of Gram-negative bacteria suspicious for carbapenem resistance including Enterobacterales (67), Pseudomonas (10), Acinetobacter (5), and Stenotrophomonas (1) species, collected between 2016 and 2018 from in-patients, were tested for carbapenemase activity using a novel fluorescent carbapenem. When subjected to extracted bacterial carbapenemases its fluorescence disappears. All bacteria to be tested were cultured on Columbia blood agar and few on other commercial media. MALDI TOF MS, molecular assays, automated MIC testing, and in part, agar diffusion tests served to characterize the isolates. For comparison, few selected bacteria were also investigated by prior phenotypic tests for carbapenemase detection.

Results

Under UV light, the CarbaLux test allowed a rapid detection of 39/39 carbapenemase-producing bacteria, including 15 isolates with OXA carbapenemases (e.g., OXA-23, OXA-24/40-like OXA-48-like or OXA-181). Several isolates had low MICs but still expressed carbapenemases. Among Enterobacter spp., it detected six strains with hyper-produced AmpC beta-lactamases, which deactivated carbapenems but were not detectable by prior rapid phenotypic assays. An unexpected high carbapenemase activity appeared with these enzymes. They were identified as AmpC variants by inhibition with cloxacillin.

Conclusion

Other than prior rapid phenotypic assessments for carbapenemases, which use secondary effects such as a change of pH, the inactivation of the fluorescent carbapenem substrate can be visualized directly under UV light. The new test works at 100 to 200-fold lower, therapy-like substrate concentrations. It takes advantage of the high substrate affinity to carbapenemases allowing also the detection of less reactive resistance enzymes via a trapping mechanism, even from bacteria, which might appear unsuspicious from initial antibiograms. The novel fluorescence method allows simple and safe handling, reliable readings, and documentation and is suitable for primary testing in the clinical laboratory.

Performance of ceftriaxone susceptibility testing on the Accelerate Pheno® system of ESBL-producing isolates

The correlation of ceftriaxone nonsusceptibility and ESBL production was evaluated in 40 characterized isolates. Performance of ceftriaxone susceptibility testing on the Accelerate Pheno was evaluated and compared with reference broth microdilution in triplicate. The CLSI ESBL confirmatory test was also evaluated. Ceftriaxone categorical agreement of the Accelerate Pheno was 97.5% with 1 minor error. The ESBL confirmatory disk test resulted in 4 false-negatives and 1 false positive. The Accelerate Pheno provides an expedited and accurate method of ceftriaxone susceptibility testing allowing for optimization of antimicrobial regimens sooner. These data indicate that ESBL production has a high likelihood of ceftriaxone non-susceptibility.

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.

Exploring the genetic determinants underlying the differential production of an inducible chromosomal cephalosporinase - BlaB in Yersinia enterocolitica biotypes 1A, 1B, 2 and 4

Yersinia enterocolitica is an enteric bacterium which can cause severe gastroenteritis. Beta-lactams are the most widely used antibiotics against Y. enterocolitica. Y. enterocolitica produces two chromosomal β-lactamases, BlaA and BlaB. BlaB is an Ambler Class C inducible broad spectrum cephlaosporinase which showed differential enzyme activity in different biotypes of Y. enterocolitica. The expression of blaB is mainly regulated by ampR- the transcriptional regulator and, ampD - which helps in peptidoglycan recycling. The aim of this study was to identify and characterize genetic determinants underlying differential enzyme activity of BlaB in Y. enterocolitica biotypes 1 A, IB, 2 and 4. Thus, ampR, blaB and ampD were PCR-amplified and modeled in silico. The intercistronic region containing promoters of ampR and blaB was also investigated. Our results indicated that blaB was more inducible in biotypes 2 and 4, than in biotypes 1 A and 1B. Superimposition of in silico modeled proteins suggested that variations in amino acid sequences of AmpR, BlaB and AmpD were not responsible for hyper-production of BlaB in biotypes 2 and 4. Analysis of promoter regions of ampR and blaB revealed variations at -30, -37 and -58 positions from blaB transcription start site. Studies on relative expression levels of blaB in different biotypes by qRT-PCR indicated that nucleotide variations at these positions might contribute to a higher enzyme activity of BlaB in biotypes 2 and 4. However, this is a preliminary study and further studies including more strains of each biotype are required to strengthen our findings. Nevertheless, to the best of our knowledge, this is the first study which has investigated the genetic determinants underlying differential inducible production of BlaB in different biotypes of Y. enterocolitica.

Combined Molecular and Phenotypic Antimicrobial Susceptibility Testing Is Beneficial in Detection of ESBL and AmpC Beta-Lactamase Producing Isolates of Enterobacteriaceae in Pediatric Patients with Bloodstream Infections

Objectives: The aim was to assess the potential advantage of combined genotypic testing with phenotypic antimicrobial susceptibility testing (AST) to detect AmpC β-lactamases (AmpC) and extended-spectrum β-lactamases (ESBL) producing Enterobacteriaceae isolated from blood cultures in a pediatric population. Materials and Methods: All first-time Enterobacteriaceae isolates recovered from blood cultures of pediatric patients at the Cincinnati Children's Hospital Medical Center between January 2017 and December 2018 were evaluated. The Check-MDR CT103XL β-lactamase assay was used to determine the presence of AmpC and ESBL, while AST was performed using the VITEK 2 platform. Phenotypic ESBL resistance was defined by resistance to either ceftriaxone or ceftazidime using Clinical and Laboratory Standards Institute breakpoints, while combined cefoxitin resistance with ceftriaxone or ceftazidime resistance was used to detect AmpCs (as per European Committee on Antimicrobial Susceptibility Testing standards). Results: Overall, there were 170 isolates. Genotypically, 21 (12.4%) had AmpC and 18 (10.6%) had ESBL genes detected. Phenotypically, 11 (6.5%) isolates were AmpC and 26 (15.3%) were ESBL producing organisms. Genotypic testing identified an additional 14 AmpC and two ESBL isolates that failed to meet phenotypic criteria. Conclusions: Using combined genotypic and phenotypic methods to detect AmpC and ESBL producing organisms increased the identification of resistant organism and provided potentially clinical relevant data to guide the treatment of resistant organisms.

Molecular analysis of ampR and ampD to understand variability in inducible expression of "BlaB-like" cephalosporinase in Yersinia enterocolitica biotype 1A

Yersinia enterocolitica strains produce two chromosomal β‑lactamases, BlaA - a constitutively produced penicillinase, and BlaB - an inducible "AmpC-type" cephalosporinase. As in other members of Enterobacteriaceae, expression of ampC in Y. enterocolitica is regulated by the genes - ampR and ampD. The ampR encodes a transcriptional regulator which represses the expression of ampC and, ampD encodes a cytoplasmic N‑acetyl‑anhydromuramyl‑l‑alanine amidase which participates in recycling of peptidoglycan. Exposure of bacteria to antibiotics like imipenem and cefoxitin results in generation and accumulation of large quantities of muropeptides in cytoplasm which is beyond the recycling capability of AmpD. These muropeptides bind to AmpR, converting it into an activator of ampC expression (ampC de-repression). Earlier studies from our laboratory indicated that instead of BlaB, Y. enterocolitica biotype 1A strains produced a "BlaB-like" enzyme which was non-heterogeneous and showed a differential expression when induced with imipenem. The detection of "BlaB-like" cephalosporinase which was also induced differentially in Y. enterocolitica biotype 1A strains presented an opportunity to discern newer mechanisms, if any, which may underlie inducible expression of "AmpC-type" cephalosporinases. Thus, the objective of the present study was to understand the role of ampR and ampD in regulating differential expression of "BlaB-like" cephalosporinases in biotype 1A strains. Analysis of promoters and amino acid sequences of AmpR revealed that these were conserved in all strains of biotype 1A. Analysis of AmpD amino acid sequences revealed that five variants of AmpD were present which did not contribute to hyper-inducible production of "BlaB-like" enzyme. In-silico prediction of the mRNA secondary structures of ampD revealed significant differences, which might have affected the rate of translation of ampD and accumulation of un-recycled muropeptides inside the cell leading to hyper production of "BlaB-like" cephalosporinases in some Y. enterocolitica biotype 1A strains. The findings provide newer insights to our understanding of the mechanisms underlying regulation of expression of "AmpC-type" β‑lactamases.

Selection of hyperproduction of AmpC and SME-1 in a carbapenem-resistant Serratia marcescens isolate during antibiotic therapy

Objectives

Antibiotic selective pressure may result in changes to antimicrobial susceptibility throughout the course of infection, especially for organisms that harbour chromosomally encoded AmpC β-lactamases, notably Enterobacter spp., in which hyperexpression of ampC may be induced following treatment with cephalosporins. In this study, we document a case of bacteraemia caused by a blaSME-1-harbouring Serratia marcescens that subsequently developed resistance to expanded-spectrum cephalosporins, piperacillin/tazobactam and fluoroquinolones, over the course of several months of treatment with piperacillin/tazobactam and ciprofloxacin.

Methods

Susceptibility testing and WGS were performed on three S. marcescens isolates from the patient. β-Lactamase activity in the presence or absence of induction by imipenem was measured by nitrocefin hydrolysis assays. Expression of ampC and blaSME-1 under the same conditions was determined by real-time PCR.

Results

WGS demonstrated accumulation of missense and nonsense mutations in ampD associated with stable derepression of AmpC. Gene expression and β-lactamase activity of both AmpC and SME-1 were inducible in the initial susceptible isolate, but were constitutively high in the resistant isolate, in which total β-lactamase activity was increased by 128-fold.

Conclusions

Although development of such in vitro resistance due to selective pressure imposed by antibiotics is reportedly low in S. marcescens, our findings highlight the need to evaluate isolates on a regular basis during long-term antibiotic therapy.

Evaluation of the AID AmpC line probe assay for molecular detection of AmpC-producing Enterobacterales

OBJECTIVES

In this study, the commercially available AID AmpC line probe assay (LPA) was evaluated for detection of plasmid-mediatedbla_AmpC β-lactamase genes in Enterobacterales as well as chromosomal mutations in the bla_AmpC promoter/attenuator regions in Escherichia coli.

METHODS

Accuracy of the AID AmpC probes was assessed using Enterobacterales clinical isolates harbouring diverse plasmid-mediated AmpC enzymes (ACC, ACT, DHA, FOX, CMY and MOX) and E. coli clinical isolates with mutations in the chromosomal bla_AmpC promoter/attenuator regions. The diagnostic performance of the AID AmpC LPA for bla_AmpC detection directly from clinical specimens was determined using 99 clinical urine specimens with bacterial cell counts >10⁵CFU/mL and the results were compared with culture-based phenotypic drug susceptibility testing (DST).

RESULTS

Detection of bla_AmpC genes in Enterobacterales clinical isolates showed 100% congruence with phenotypic DST results. The AID AmpC LPA showed 100% specificity [95% confidence interval (CI) 96-100%] and 100% sensitivity (95% CI 75-100%) for detection of plasmid-meditated bla_AmpC and E. coli genomic bla_AmpC promoter/attenuator mutations directly from clinical urine specimens. The AID AmpC LPA detected three AmpC-producers in urine specimens with bacterial cell counts >10⁵CFU/mL that were missed by culture-based phenotypic DST, thereby displaying higher diagnostic sensitivity.

CONCLUSION

The AID AmpC LPA is an accurate, sensitive and easy-to-use test that can be readily implemented in any diagnostic laboratory for molecular detection of bla_AmpC genes in Enterobacterales.

Changing paradigm of antibiotic resistance amongst Escherichia coli isolates in Indian pediatric population

Antimicrobial resistance happens when microorganisms mutates in manners that render the drugs like antibacterial, antiviral, antiparasitic and antifungal, ineffective. The normal mutation process is encouraged by the improper use of antibiotics. Mutations leading to quinolone resistance occur in a highly conserved region of the quinolone resistance-determining region (QRDR) of DNA gyrAse and topoisomerase IV gene. We analyzed antibiotic resistant genes and single nucleotide polymorphism (SNP) in gyrA and parC genes in QRDR in 120 E. coli isolates (both diarrheagenic and non-pathogenic) recovered from fresh stool samples collected from children aged less than 5 years from Delhi, India. Antibiotic susceptibility testing was performed according to standard clinical and laboratory standards institute (CLSI) guidelines. Phylogenetic analysis showed the clonal diversity and phylogenetic relationships among the E. coli isolates. The SNP analysis depicted mutations in gyrA and parC genes in QRDR. The sul1 gene, responsible for sulfonamide resistance, was present in almost half (47.5%) of the isolates across the diseased and healthy samples. The presence of antibiotic resistance genes in E. coli isolates from healthy children indicate the development, dissemination and carriage of antibiotic resistance in their gut. Our observations suggest the implementation of active surveillance and stewardship programs to promote appropriate antibiotic use and minimizing further danger.

Mortality impact of empirical antimicrobial therapy in ESBL- and AmpC-producing Enterobacteriaceae bacteremia in an Australian tertiary hospital

BACKGROUND

Treatment of ESBL- and AmpC-producing Enterobacteriaceae bacteremia is often complicated by lack of appropriate antibiotics. We aimed to determine the predictors of mortality and impact of empirical antibiotics.

METHODS

A retrospective observational study was performed on consecutive adult cases of ESBL and AmpC bacteremia at the Alfred Hospital from 2014 through April 2018.

RESULTS

Among 110 patients with ESBL (88.2%) and AmpC (14.5%) bacteremia episodes, 96.4% had comorbidities such as hematological malignancy (30%). Approximately 45% were on immunosuppressive drugs, while 69% had recent antibiotic exposure. Over 84% of bacteremias were hospital acquired or healthcare associated. Urinary tract was the main source of infection (40%) with E. coli being the commonest organism (66.4%). The isolates were least resistant to gentamicin (21.8%), which was often appropriately used in empirical therapy. About 34% of patients presented with severe sepsis or shock. The 30-day mortality rate was 20% with no correlation with inappropriate empirical antibiotics (52%). There was no significant mortality difference between carbapenem use in empirical and definitive therapy. Respiratory source [OR 11.77, 95% CI 1.30-106.85; p = 0.03], severe sepsis or shock [OR 5.17, 95% CI 1.37-19.55; p = 0.02] and inappropriate definitive therapy [OR 27.93, 95%CI 3.69-211.35; p = 0.001] were independent predictors for mortality.

CONCLUSION

The choice and appropriateness of empirical therapy were not associated with mortality in ESBL and AmpC bacteremia. Prudent use of carbapenem is reasonable with gentamicin as alternative. Emphasis should be on prompt resuscitation in severe sepsis and early detection of ESBL and AmpC to facilitate appropriate switch to definitive therapy.

Molecular Characterization of Multidrug-Resistant and Extended-Spectrum Beta-Lactamase-Producing Klebsiella pneumoniae Isolated from Swine Farms in Malaysia

Aims: The high prevalence of multidrug resistance (MDR) and extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae associated with nosocomial infections has caused serious therapeutic challenges. The objectives of this study were to determine the genotypic and phenotypic characteristics of K. pneumoniae strains isolated from Malaysian swine farms and the transferability of ESBL genes by plasmids. Results: A total of 50 K. pneumoniae strains were isolated from 389 samples, which were collected from healthy and unhealthy pigs (swine rectum and oral cavities), healthy farmers (human rectum, urine, and nasal cavities), farm's environment, and animal feeds from seven Malaysian swine farms. Antimicrobial susceptibility analysis of these 50 K. pneumoniae strains showed that the majority (86%) were resistant to tetracycline, while 44% and 36% of these strains were MDR and ESBL producers, respectively. PCR and DNA sequencing of the amplicons showed the occurrence of bla_TEM (15/18), bla_SHV (15/18), bla_CTX-M-1 group (7/18), and bla_CTX-M-2 group (2/18), while only class 1 integron-encoded integrase was detected. Conjugation experiments and plasmid analysis indicated that the majority of the ESBL genes were plasmid encoded and the plasmids in 11 strains were conjugative. Genotyping by pulsed-field gel electrophoresis and repetitive extragenic palindrome-polymerase chain reaction (REP-PCR) showed that these 50 strains were genetically diverse with 44 pulsotypes and 43 REP-PCR subtypes. Conclusions: ESBL-producing K. pneumoniae strains showed high resistance to tetracycline as this antibiotic is used for prophylaxis and therapeutic purposes at the swine farms. The findings in this study have drawn attention to the issue of increasing MDR in animal husbandry and it should be taken seriously to prevent the spread and treatment failure due to antimicrobial resistance.

Prevalence of plasmid-mediated AmpC in Enterobacteriaceae isolated from humans and from retail meat in Zagazig, Egypt

Background

The objective of this study was to determine the prevalence of plasmid-mediated AmpC (pAmpC) among Enterobacteriaceae isolated from humans and from retail meat in Egypt.

Methods

Enterobacteriaceae were isolated from patients with suspected bloodstream infection, human fecal samples, retail chicken meat samples and retail sheep meat samples. All group I Enterobacteriaceae were analyzed for presence of pAmpC genes by PCR. Antibiotic susceptibility testing was performed in all pAmpC positive isolates, followed by phenotypic and genotypic ESBL and carbapenemase testing on indication.

Results

The prevalence of pAmpC among group I Enterobacteriaceae isolated from 225 patients with bloodstream infection was 5.6% [95%CI 2.2–13.4]. Among 100 patients with community-onset gastroenteritis the prevalence in fecal samples was 4.8% [95%CI 2.1–10.7]. The prevalence among 112 chicken carcasses and 100 sheep meat samples was 2.4% [95%CI 0.7–8.4] and 1.1% [95%CI 0.2–5.7], respectively. In half of the AmpC positive isolates we detected an ESBL gene and 2 isolates harbored a carbapenemase gene. In five isolates there was resistance to at least three important alternative antibiotic drugs.

Conclusions

We consider the prevalence of pAmpC in Egypt, as found in our study, moderately low. To follow future trends in prevalence of pAmpC worldwide, a standardized screening algorithm for the detection of pAmpC is needed.

The emergence of colistin-resistant Klebsiella pneumoniae strains from swine in Malaysia

OBJECTIVE

Colistin is the last line of therapy for infections caused by multidrug-resistant Gram-negative bacteria. The objective of this study was to determine the phenotypic and genotypic characteristics of colistin-resistant Klebsiella pneumoniae (K. pneumoniae) isolated from swine samples in Malaysia.

METHODS

A total of 46 swine K. pneumoniae strains isolated from 2013-2015 in Malaysia were analysed for the production of extended-spectrum β-lactamases and carbapenemase. The resistance traits and genetic diversity of these strains were characterised by polymerase chain reaction, conjugation, plasmid analysis, and pulsed-field gel electrophoresis.

RESULTS

Nineteen of 46 strains were multidrug resistant while 13 were resistant to colistin. The majority of colistin-resistant strains harboured bla_TEM gene (92.3%), followed by bla_SHV (69.23%), bla_CTXM-1 (38.46%), and bla_MCR-1 (23.08%). All three colistin-resistant strains had transferable plasmids and the colistin resistance gene bla_MCR-1. Genotyping by pulsed-field gel electrophoresis showed high genetic diversity among the K. pneumoniae and that the colistin-resistant K. pneumoniae strains were heterogenous.

CONCLUSION

It is believed that this is the first report of colistin-resistant K. pneumoniae among swine strains associated with mcr-1 plasmid in Malaysia. Due to the emergence of β-lactam, carbapenem and colistin resistance, the use of colistin in animal husbandry and agriculture should be avoided to prevent treatment failure.

Plasmids carrying DHA-1 β-lactamases

The aim of this review is to provide an update on the plasmids mediating DHA-1 cephalosporinase in Klebsiella pneumoniae. These plasmids have been mainly found in this bacterium but not only. The first was isolated from Salmonella sp. in France in the early 1990s. They are currently reported worldwide. Bla_DHA-1 beta-lactamase gene is usually co-expressed with many other antibiotic resistance genes such as extended-spectrum β-lactamases (bla_CTX-M-, bla _SHV -types), oxacillinases (bla_OXA-1, bla_OXA-30), penicillinases (bla _TEM -type), carbapenemases (bla _OXA48 , bla_KPC-2), aminoglycosides (aacA, aadA, armA), fluoroquinolones (qnrB4, aac6'-1b-cr), and sulfonamide (sul1) resistance genes. Plasmids carrying DHA-1 cephalosporinase have different sizes (22 to 313 kb), belong to diverse groups of incompatibility (R, L/M, FII(k), FIB, A/C2, HI2, HIB), and are self-transferable or not. The multidrug resistance region consists of a mosaic structure composed of resistance genes, insertion sequences, composite transposon, and integrons.

RAPD PCR Profile, Antibiotic Resistance, Prevalence of armA Gene, and Detection of KPC Enzyme in Klebsiella pneumoniae Isolates

The increasing prevalence of multidrug-resistant Klebsiella pneumoniae strains isolated from hospitals shows the limitation of recent antibiotics used for bacterial eradication. In this study, 81 K. pneumoniae isolates were collected from three hospitals in Tehran. Antibiotic susceptibility test showed the highest rates of resistance to cefotaxim (85.5%) and ceftazidime (78.3%), and the lowest rates of resistance were detected for colistin (16.9%), streptomycin (16.8%), and chloroamphenicol (21.7%). Eleven different resistance patterns were observed. Sixty-six out of 81 isolates (81.5%) were found to be multidrug resistant (MDR), and 35.8% of them belonged to A3 resistance pattern. 7.4% and 66.7% were KPC enzyme and armA gene positive, respectively. RAPD PCR assay of these bacteria showed 5 clusters, 16 single types, and 14 common types, and there was not any correlation between genetic patterns of the isolates and presence of resistance agents. Simultaneous detection of resistance-creating agents could be an important challenge for combination therapy of MDR K. pneumoniae-caused infections.

Drug-resistant gram-negative uropathogens: A review

Urinary tract infection(UTI) caused by Gram-negative bacteria is the second most common infectious presentation in community medical practice. Approximately 150 million people are diagnosed with UTI each year worldwide. Drug resistance in Gram-negative uropathogens is a major global concern which can lead to poor clinical outcomes including treatment failure, development of bacteremia, requirement for intravenous therapy, hospitalization, and extended length of hospital stay. The mechanisms of drug resistance in these bacteria are important due to they are often not identified by routine susceptibility tests and have an exceptional potential for outbreaks. Treatment of UTIs depends on the access to effective drugs, which is now threatened by antibiotic resistant Gram-negative uropathogens. Although several effective antibiotics with activity against highly resistant Gram-negatives are available, there is not a unique antibiotic with activity against the high variety of resistance. Therefore, antimicrobial susceptibility tests, correlation between clinicians and laboratories, development of more rapid diagnostic methods, and continuous monitoring of drug resistance are urgent priorities. In this review, we will discuss about the current global status of drug-resistant Gram-negative uropathogens and their mechanisms of drug resistance to provide new insights into their treatment options.

The Resistance Phenotype and Molecular Epidemiology of Klebsiella pneumoniae in Bloodstream Infections in Shanghai, China, 2012-2015

Klebsiella pneumoniae (K.pneumoniae) is a common nosocomial pathogen causing bloodstream infections. Antibiotic susceptibility surveillance and molecular characterization will facilitate prevention and management of K. pneumoniae bloodstream infections. K. pneumoniae isolates causing bloodstream infections were consecutively collected between January 2012 and December 2015 in Shanghai. Eighty isolates (20 per year) were randomly selected and enrolled in this study. Drug susceptibility were determined by the disk diffusion method. Polymerase chain reaction (PCR) was employed to detect extended-spectrum β-lactamases (ESBLs), carbapenemases, and seven housekeeping genes of K. pneumoniae. eBURST was used for multi-locus sequence typing (MLST). More than 50% isolates were resistant to cefuroxime, ampicillin-sulbactam, and piperacillin, while carbapenems had lower resistant rates than other antibiotics. Of the 80 isolates, 22 produced ESBLs, and 14 were carbapenemase producers. In the ESBL-producing K. pneumoniae isolates, the most common ESBL genes were bla_SHV and bla_CTX-M. Thirteen carbapenemase producers harbored bla_KPC-2 and one other carried bla_NDM-5. ST11 (14/80) was the most frequent sequence type (ST), followed by ST15 (7/80) and ST29 (4/80). Our data revealed high prevalence of antibiotic resistant K. pneumoniae isolates from bloodstream infections but their genetic diversity suggested no clonal dissemination in the region. Also, one K. pneumoniae isolate harbored bla_NDM-5 in this study, which was firstly reported in Shanghai.

Profiling of antimicrobial resistance and plasmid replicon types in β-lactamase producing Escherichia coli isolated from Korean beef cattle

In this study, 78 isolates of Escherichia coli isolated from Korean beef cattle farms were investigated for the production of extended-spectrum β-lactamase (ESBL) and/or AmpC β-lactamase. In the disc diffusion test with ampicillin, amoxicillin, cephalothin, ceftiofur, cefotaxime, ceftazidime, and cefoxitin, 38.5% of the isolates showed resistance to all of ampicillin, amoxicillin, and cephalothin. The double disc synergy method revealed that none of the isolates produced ESBL or AmpC β-lactamases. DNA sequencing showed that all isolates encoded genes for TEM-1-type β-lactamase. Moreover, 78.2% of the isolates transferred the TEM-1-type β-lactamase gene via conjugation. In plasmid replicon typing of all donors, IncFIB and IncFIA were identified in 71.4% and 41.0% of plasmids, respectively. In transconjugants, IncFIB and IncFIA were the most frequent types detected (61.5% and 41.0%, respectively). Overall, the present study indicates that selection pressures of antimicrobials on β-lactamases in beef cattle may be low relative to other livestock animals in Korea. Moreover, to reduce selection pressure and dissemination of β-lactamase, the long-term surveillance of antimicrobial use in domestic beef cattle should be established.

Clinical features and molecular epidemiology of plasmid-mediated DHA-type AmpC β-lactamase-producing Klebsiella pneumoniae blood culture isolates, Hong Kong

Knowledge of risk factors and clinical characteristics of bacteraemia caused by plasmid-mediated AmpC β-lactamase (pAmpC)-producing Klebsiella pneumoniae (pAmpC-Kp) is not well described. This was a retrospective cohort study of patients with K. pneumoniae bacteraemia in three Hong Kong regional hospitals. Demographic and clinical data were retrieved from medical records. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were performed for molecular epidemiology. A total of 109 patients were included, divided into four groups: bacteraemia due to K. pneumoniae with (i) DHA-type pAmpC (n=23), (ii) extended-spectrum β-lactamase (ESBL) (n=37), (iii) DHA-type pAmpC+ESBL (n=26) and (iv) controls (n=23). Nursing home residence was independently associated with pAmpC-Kp bacteraemia compared with ESBL-Kp bacteraemia [adjusted odds ratio (aOR)=7.13, 95% confidence interval (CI) 1.36-37.54] and controls (aOR=41.47, 95% CI 4.55-377.75). Compared with controls, patients with pAmpC-Kp bacteraemia also suffered from more severe illness [median Acute Physiology and Chronic Health Evaluation (APACHE) II scores 16 and 25, respectively; P=0.006]. Importantly, the pAmpC group received discordant empirical antimicrobial therapy more frequently (OR=24.00, 95% CI 5.01-114.97), resulting in higher 7-day mortality (OR=20.17, 95% CI 2.32-175.67) and 30-day mortality (OR 4.68, 95% CI 1.29-16.98). PFGE detected six pulsotypes, corresponding to the predominant sequence type 11. Severity of illness and mortality of patients with bacteraemia caused by pAmpC-Kp were high. Patients who are nursing home residents presenting nosocomial sepsis should be treated with broad-spectrum antimicrobials.

Previous Antibiotic Exposure Increases Risk of Infection with Extended-Spectrum-β-Lactamase- and AmpC-Producing Escherichia coli and Klebsiella pneumoniae in Pediatric Patients

The objective of this study was to determine whether antibiotic exposure is associated with extended-spectrum-beta-lactamase- or AmpC-producing Escherichia coli or Klebsiella pneumoniae infections in children. We collected extended-spectrum-beta-lactamase- or AmpC-producing E. coli or K. pneumoniae isolates and same-species susceptible controls from normally sterile sites of patients aged ≤21 years, along with associated clinical data, at four free-standing pediatric centers. After controlling for potential confounders, the relative risk of having an extended-spectrum-beta-lactamase-producing isolate rather than a susceptible isolate was 2.2 times higher (95% confidence interval [CI], 1.49 to 3.35) among those with antibiotic exposure in the 30 days prior to infection than in those with no antibiotic exposure. The results were similar when analyses were limited to exposure to third-generation cephalosporins, other broad-spectrum beta-lactams, or trimethoprim-sulfamethoxazole. Conversely, the relative risk of having an AmpC-producing versus a susceptible isolate was not significantly elevated with any antibiotic exposure in the 30 days prior to infection (adjusted relative risk ratio, 1.12; 95% CI, 0.65 to 1.91). However, when examining subgroups of antibiotics, the relative risk of having an AmpC-producing isolate was higher for patients with exposure to third-generation cephalosporins (adjusted relative risk ratio, 4.48; 95% CI, 1.75 to 11.43). Dose-response relationships between antibiotic exposure and extended-spectrum-beta-lactamase-producing or AmpC-producing isolates were not demonstrated. These results reinforce the need to study and implement pediatric antimicrobial stewardship strategies, and they indicate that epidemiological studies of third-generation cephalosporin-resistant E. coli and K. pneumoniae isolates should include resistance mechanisms when possible.

Detection and genotype analysis of AmpC β-lactamase in Klebsiella pneumoniae from tertiary hospitals

The aim of the present study was to investigate the phenotype and genotype of plasmid-mediated AmpC (pAmpC) β-lactamase in Klebsiella pneumoniae and its antibiotic resistance. A total of 130 non-repetitive clinical isolates of Klebsiella pneumoniae, obtained from tertiary hospitals, were phenotypically screened for pAmpC β-lactamase production with the cefoxitin disk diffusion test. β-lactamase genes in the screened isolates were detected using multiplex polymerase chain reaction (PCR); carbapenemase genes in pAmpC β-lactamase-producing isolates that were resistant to imipenem were detected using PCR. Out of the 130 isolates of Klebsiella pneumoniae, 62 strains (47.7%) were resistant to cefoxitin, including 14 strains (10.8%) positive for pAmpC β-lactamase (DHA type), among which 12 strains (85.7%) were susceptible to imipenem, and 2 strains, which were carrying Klebsiella pneumoniae carbapenemase (KPC)-2 gene, were resistant to imipenem. The pAmpC β-lactamase-producing Klebsiella pneumoniae isolates from the tertiary hospitals were mainly of DHA-1 genotype, and the majority were susceptible to carbapenems; drug-resistant strains were associated with KPC-2 expression.

Significant publications on infectious diseases pharmacotherapy in 2013

PURPOSE

The most important articles on infectious diseases (ID) pharmacotherapy published in the peer-reviewed literature in 2013, as nominated and selected by panels of pharmacists and others with ID expertise, are summarized.

SUMMARY

Members of the Houston Infectious Diseases Network were asked to nominate articles published last year in prominent biomedical journals that had a major impact in the field of ID pharmacotherapy. A list of 27 nominated articles on ID-related topics in general and 26 articles specifically focused on human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS) was compiled. In a national online survey conducted in January 2014, members of the Society of Infectious Diseases Pharmacists (SIDP) were asked to select from the list those articles that they felt had made the greatest contributions to the field of ID pharmacotherapy. Of 168 SIDP members surveyed, 108 (64%) and 53 (32%) participated in the selection of ID- and HIV/AIDS-related articles, respectively. Summaries of the top-ranked articles in both categories are presented.

CONCLUSION

Major topics explored in the top-ranked ID articles of 2013 include the use of cefepime for gram-negative infections due to AmpC or extended-spectrum β-lactamase-producing Enterobacteriaceae, optimizing antibiotic therapy through the use of extended- or continuous-infusion regimens, the use of the oral integrase inhibitor dolutegravir to combat HIV disease, and new approaches to treatment of Clostridium difficile infection and enterococcal endocarditis.

Microbiological screening is necessary to distinguish carriers of plasmid-mediated AmpC beta-lactamase-producing enterobacteriaceae and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae because of clinical similarity

Objectives

Plasmid-mediated AmpC beta-lactamase-producing (pAmpC) Enterobacteriaceae are increasing worldwide, difficult to identify and often confounded with extended-spectrum beta-lactamase (ESBL) producers. The low prevalence precludes routine universal admission screening. Therefore, we evaluated potential risk factors for carriage of pAmpC-producing Enterobacteriaceae that would allow targeted screening to improve yield and reduce cost.

Patients and methods

We performed a case control study at a tertiary care center from 1/2006 to 12/2010. Cases were adult patients in whom pAmpC-producing Enterobacteriaceae were isolated; controls were chosen among carriers of ESBL-producing Enterobacteriaceae. Both infected and colonized patients were included.

Results

Over five years, we identified 40 pAmpC producers in 39 patients among 16,247 screened consecutive isolates of Enterobacteriaceae. The pAmpC prevalence was low (0.25%), but more than 30% of pAmpC carriers received incorrect empirical antibiotic treatment. When compared with 39 ESBL controls, pAmpC carriage was associated with clinically confirmed infections in 74% (versus 51%) (p=0.035), mainly of the urinary tract, previous antibiotic exposure in 63% (versus 36%) (p=0.035) and carriage of a nasogastric tube in 23% (versus 0%) (p=0.002). In the multivariate regression analysis only clinically confirmed infections remained significantly associated with pAmpC carriage (OR 1.44 (95%CI 1.15-2.57)). No other clinical and blood test-associated risk factor allowed discrimination of pAmpC-carrying patients from ESBL controls. The type of acquisition – nosocomial versus community-acquired – was also non-informative for resistance type, as 46% of pAmpC- and 44% of ESBL-producing Enterobacteriaceae were community-acquired.

Conclusions

This study could not identify a clinical profile that would allow targeted screening for pAmpC-producing Enterobacteriaceae when compared to ESBL carriers. Because empiric antimicrobial therapy was inappropriate in more than 30%, rapid identification of pAmpC carriers is needed. New microbiological methods are therefore required to simplify rapid and reliable detection of pAmpC carriers.

Two novel CMY-2-type β-lactamases encountered in clinical Escherichia coli isolates

Background

Chromosomally encoded AmpC β-lactamases may be acquired by transmissible plasmids which consequently can disseminate into bacteria lacking or poorly expressing a chromosomal bla_AmpC gene. Nowadays, these plasmid-mediated AmpC β-lactamases are found in different bacterial species, namely Enterobacteriaceae, which typically do not express these types of β-lactamase such as Klebsiella spp. or Escherichia coli. This study was performed to characterize two E. coli isolates collected in two different Portuguese hospitals, both carrying a novel CMY-2-type β-lactamase-encoding gene.

Findings

Both isolates, INSRA1169 and INSRA3413, and their respective transformants, were non-susceptible to amoxicillin, amoxicillin plus clavulanic acid, cephalothin, cefoxitin, ceftazidime and cefotaxime, but susceptible to cefepime and imipenem, and presented evidence of synergy between cloxacilin and cefoxitin and/or ceftazidime. The genetic characterization of both isolates revealed the presence of bla_CMY-46 and bla_CMY-50 genes, respectively, and the following three resistance-encoding regions: a Citrobacter freundii chromosome-type structure encompassing a blc-sugE-bla_CMY-2-type-ampR platform; a sul1-type class 1 integron with two antibiotic resistance gene cassettes (dfrA1 and aadA1); and a truncated mercury resistance operon.

Conclusions

This study describes two new bla_CMY-2-type genes in E. coli isolates, located within a C. freundii-derived fragment, which may suggest their mobilization through mobile genetic elements. The presence of the three different resistance regions in these isolates, with diverse genetic determinants of resistance and mobile elements, may further contribute to the emergence and spread of these genes, both at a chromosomal or/and plasmid level.

A statistical approach for determination of disk diffusion-based cutoff values for systematic characterization of wild-type and non-wild-type bacterial populations in antimicrobial susceptibility testing

In this study, we introduce a new approach for determination of epidemiologic cutoffs (ECOFFs) and resistant-population cutoffs (RCOFFs) based on receiver operating characteristic (ROC) curves. As an example, the method was applied for determination of ECOFFs for seven different beta-lactam antibiotics and wild-type populations of Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae. In addition, RCOFFs were determined for bacterial populations with defined resistance mechanisms ("resistotypes"), i.e., extended-spectrum beta-lactamase (ESBL)-positive E. coli, ESBL-positive K. pneumoniae, and ESBL-positive E. cloacae; AmpC cephalosporinase-positive E. coli and AmpC-positive K. pneumoniae; and broad-spectrum beta-lactamase (BSBL)-positive E. coli. RCOFFs and ECOFFs are instrumental for a systematic characterization of associations between resistotypes and wild-type populations.

Antimicrobial resistance: impact on clinical and economic outcomes and the need for new antimicrobials

INTRODUCTION

Antimicrobial resistance is a well-recognized global threat; thus, the development of strong infection control policies coupled with antimicrobial stewardship strategies and new therapies is required to reverse this process. In its 2013 report on antimicrobial resistance, the Centers for Disease Control and Prevention focused on this problem while presenting estimated annual rates of infections with antimicrobial-resistant organisms and their related mortality rates. Whereas some resistant pathogens were considered less threatening, others such as carbapenem-resistant Enterobacteriaceae were associated with higher mortality rates owing to limited treatment options.

AREAS COVERED

An overview of the most common antimicrobial-resistant pathogens, focusing on risk factors for acquisition, clinical and economic outcomes, as well as current treatment options. Strategies to optimize antimicrobial therapy with currently available agents, in addition to newly developed antimicrobials are also discussed.

EXPERT OPINION

The emergence of pathogens with a variety of resistance mechanisms has intensified the challenges associated with infection control and treatment strategies. Therefore, prudent use of currently available antimicrobial agents, as well as implementing measures to limit spread of resistance is paramount. Although several new antimicrobials have been recently approved or are in the pipeline showing promise in the battle against resistance, the appropriate use of these agents is required as the true benefits of these treatments are to be recognized in the clinical care setting.

DHA-1 plasmid-mediated AmpC β-lactamase expression and regulation of Klebsiella pnuemoniae isolates

The present study aimed to investigate the regulatory mechanism of the AmpC enzyme by analyzing the construction and function of AmpCR, AmpE and AmpG genes in the Dhahran (DHA)‑1 plasmid of Klebsiella pneumoniae (K. pneumoniae). The production of AmpC and extended‑spectrum β‑lactamase (ESBL) were determined following the cefoxitin (FOX) inducing test for AmpC, preliminary screening and confirmation tests for ESBL in 10 DHA‑1 plasmid AmpC enzymes of K. pneumoniae strains. AmpCR, AmpD, AmpE and AmpG sequences were analyzed by polymerase chain reaction. The pACYC184‑X plasmid analysis system was established and examined by regulating the pAmpC enzyme expression. The electrophoretic bands of AmpCR, AmpD, AmpE and AmpG were expressed. Numerous mutations in AmpC + AmpR (AmpCR) and in the intergenic region cistron of AmpC‑AmpR, AmpD, AmpE and AmpG were observed. The homology of AmpC and AmpR, in relation to the Morganella morganii strain, was 99%, which was determined by comparing the gene sequences of Kp1 with those of Kp17 AmpCR. The specific combination of AmpR and labeled probe demonstrated a band retarded phenomenon and established a spatial model of AmpR. All the enzyme production strains demonstrated Val93→Ala in AmpG; six transmembrane domains were found in AmpE in all strains, with the exception of Kp1 and Kp4, which had only three transmembrane segments that were caused by mutation. The DHA‑1 plasmid AmpC enzymes encoded by plasmid are similar to the inducible chromosomal AmpC enzymes, which are also regulated by AmpD, AmpE, AmpR and AmpG.

Epidemiology and risk factors for infections due to AmpC β-lactamase-producing Escherichia coli

OBJECTIVES

To describe the prevalence and risk factors for infection due to AmpC β-lactamase-producing Escherichia coli (AmpC-EC).

METHODS

For the prevalence study, all clinical isolates of E. coli with reduced susceptibility to third-generation cephalosporins were prospectively included from June 2010 to November 2011. For risk factor analysis, a case-control study was conducted. Cases were patients with an infection due to AmpC-EC. Controls were patients infected with cephalosporin-susceptible E. coli, matched 1 : 2. Detection of blaAmpC genes was done with a multiplex AmpC-PCR, and hyperproduction of E. coli chromosomal blaAmpC by quantitative RT-PCR. Alteration of the blaAmpC promoter was studied by PCR and sequencing.

RESULTS

We identified 243 (1.1%) AmpC-EC strains out of 21 563 clinical isolates. Three cases with strains carrying ESBLs, 18 strains that were considered due to colonization and 8 cases lost to clinical follow-up were excluded. Finally, 214 cases were included in the analysis. Ninety-one cases (42.5%) and 269 (62.8%) controls were strictly community acquired (P < 0.001). Thirty-five (16.3%) cases and 186 controls (43.5%) did not have any identifiable risk factor (P < 0.001). Among cases, 158 (73.8%) were found to harbour an acquired AmpC (73.4% CMY-2). Previous use of fluoroquinolones [OR 2.6 (95% CI 1.12-3.36); P = 0.008] was independently associated with AmpC-EC in the multivariate analysis.

CONCLUSIONS

Prevalence of AmpC in E. coli remains low in our area. Plasmid acquisition (CMY type) represents the main mechanism of AmpC production. A high proportion of community-acquired isolates and patients with no identifiable risk factors were found. Previous use of fluoroquinolones was identified as a risk factor.

Escherichia coli ST131: The quintessential example of an international multiresistant high-risk clone

Escherichia coli ST131 emerged during the early to mid-2000s is an important human pathogen, has spread extensively throughout the world, and is responsible for the rapid increase in antimicrobial resistance among E. coli. ST131 is known to cause extraintestinal infections, being fluoroquinolone resistant, and is associated with ESBL production most often due to CTX-M-15. Recent molecular epidemiologic studies using whole-genome sequencing and phylogenetic analysis have demonstrated that the H30 ST131 lineage emerged in early 2000s that was followed by the rapid expansion of its sublineages H30-R and H30-Rx. Escherichia coli ST131 clearly has all of the essential characteristics that define a high-risk clone and might be the quintessential example of an international multiresistant high-risk clone. We urgently need rapid cost-effective detection methods for E. coli ST131, as well as well-designed epidemiological and molecular studies to understand the dynamics of transmission, risk factors, and reservoirs for ST131. This will provide insight into the emergence and spread of this multiresistant sequence type that will hopefully lead to information essential for preventing the spread of ST131.

Clinical management of infections caused by multidrug-resistant Enterobacteriaceae

Enterobacteriaceae showing resistance to cephalosporins due to extended-spectrum β-lactamases (ESBLs) or plasmid-mediated AmpC enzymes, and those producing carbapenemases have spread worldwide during the last decades. Many of these isolates are also resistant to other first-line agents such as fluoroquinolones or aminoglycosides, leaving few available options for therapy. Thus, older drugs such as colistin and fosfomycin are being increasingly used. Infections caused by these bacteria are associated with increased morbidity and mortality compared with those caused by their susceptible counterparts. Most of the evidence supporting the present recommendations is from in vitro data, animal studies, and observational studies. While carbapenems are considered the drugs of choice for ESBL and AmpC producers, recent data suggest that certain alternatives may be suitable for some types of infections. Combined therapy seems superior to monotherapy in the treatment of invasive infections caused by carbapenemase-producing Enterobacteriaceae. Optimization of dosage according to pharmacokinetics/pharmacodynamics data is important for the treatment of infections caused by isolates with borderline minimum inhibitory concentration due to low-level resistance mechanisms. The increasing frequency and the rapid spread of multidrug resistance among the Enterobacteriaceae is a true and complex public health problem.

Antibiotic consumption and its influence on the resistance in Enterobacteriaceae

Background

Increasing bacterial resistance to antibiotics is one of the most serious problems in current medicine. An important factor contributing to the growing prevalence of multiresistant bacteria is application of antibiotics. This study aimed at analyzing the development of resistance of Enterobacteriaceae to selected beta-lactam, fluoroquinolone and aminoglycoside antibiotics in the University Hospital Olomouc and assessing the effect of selection pressure of these antibiotics.

Methods

For the period between 1 January 2000 and 31 December 2011, resistance of Klebsiella pneumoniae, Escherichia coli, Enterobacter cloacae and Proteus mirabilis to third- and fourth-generation cephalosporins, meropenem, piperacillin/tazobactam, fluoroquinolones and aminoglycosides was retrospectively studied. For the assessment of selection pressure of antibiotics, a parameter of defined daily dose in absolute annual consumption (DDDatb) based on the ATC/DDD classification and in relative annual consumption (RDDDatb) as the number of defined daily doses per 100 bed-days was used. The relationship between frequency of strains resistant to a particular antibiotic and antibiotic consumption was assessed by linear regression analysis using Spearman’s correlation. The level of statistical significance was set at p < 0.05.

Results

A total of 113,027 isolates from the Enterobacteriaceae family were analyzed. There was a significant effect of selection pressure of the primary antibiotic in the following cases: piperacillin/tazobactam in Klebsiella pneumoniae, gentamicin in Klebsiella pneumoniae and Escherichia coli and amikacin in Escherichia coli and Enterobacter cloacae. Also, there was significant correlation between resistance to ceftazidime and consumption of piperacillin/tazobactam in Klebsiella pneumoniae and Escherichia coli. No relationship was found between consumption of third- and fourth-generation cephalosporins and resistance to ceftazidime or between fluoroquinolone consumption and resistance to ciprofloxacin.

Conclusion

The study showed the effects of both direct and indirect selection pressure on increasing resistance to gentamicin, amikacin, piperacillin/tazobactam and ceftazidime. Given the fact that no correlation was found between resistance to fluoroquinolones and consumption of either primary or secondary antibiotics, we assume that the increasing resistance to fluoroquinolones is probably due to circulation of resistance genes in the bacterial population and that this resistance was not affected by reduced use of these antibiotics.