Phenotypic detection of extended-spectrum and AmpC beta-lactamases by a new spot-inoculation method and modified three-dimensional extract test: comparison with the conventional three-dimensional extract test

Novel Biocompatible Green Silver Nanoparticles Efficiently Eliminates Multidrug Resistant Nosocomial Pathogens and Mycobacterium Species

Bacterial infection is a major crisis of 21st era and the emergence of multidrug resistant (MDR) pathogens cause significant health problems. We developed, green chemistry-based silver nanoparticles (G-Ag NPs) using Citrus pseudolimon fruit peel extract. G-Ag NPs has a spherical shape in the range of ~ 40 nm with a surface charge of - 31 Mv. This nano-bioagent is an eco-friendly tool to combat menace of MDR. Biochemical tests prove that G-Ag NPs are compatible with human red blood cells and peripheral blood mononuclear cells. There have been many reports on the synthesis of silver nanoparticles, but this study suggests a green technique for making non-cytotoxic, non-hemolytic organometallic silver nanoparticles with a high therapeutic index for possible use in the medical field. On the same line, G-Ag NPs are very effective against Mycobacterium sp. and MDR strains including Escherichia coli, Klebsiella species, Pseudomonas aeruginosa, and Acinetobacter baumannii isolated from patient samples. Based on it, we filed a patent to Indian Patent Office (reference no. 202111048797) which can revolutionize the prevention of biomedical device borne infections in hospital pre/post-operated cases. This work could be further explored in future by in vivo experimentation with mice model to direct its possible clinical utility.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01061-0.

Characterization of Multidrug-Resistant Biofilm-Producing Escherichia coli and Klebsiella pneumoniae in Healthy Cattle and Cattle with Diarrhea

This study describes comparative occurrence and characterization of multidrug-resistant (MDR) Escherichia coli and Klebsiella pneumoniae (KP) in healthy cattle (HC) and cattle with diarrhea (DC) in India. During 2018-2020, 72 MDR isolates, including 35 E. coli (DC: 27; HC 8) and 37 K. pneumoniae (DC: 34; HC: 3), from 251 rectal swabs (DC: 219; HC: 32) were investigated for extended-spectrum beta-lactamase (ESBL), AmpC type β-lactamase and carbapenemase production, antimicrobial susceptibility profile, biofilm production, and efflux pump activity. Fifty-five MDR isolates were ESBL producers (ESBLPs) (DC: 50; HC: 5) and ESBLPs from DC were coresistant to multiple antibiotics. The blaCTX-M gene (50) was the most frequently detected β-lactamases followed by blaAmpC (22), blaTEM1 (13), blaCMY-6 (6), blaOXA1 (5), blaPER (2), blaDHA, and blaFOX and blaSHV12 (1 each). Plasmid-mediated quinolone resistance determinants qnrB, qnrS, qnrA, and qepA were detected in 18, 16, 2, and 3 isolates, respectively. Twenty three isolates revealed mutation in gyrA and parC genes. Tetracycline-resistance markers tetA, tetB, tetC, and tetE were detected in 33, 10, 3, and 2 isolates, respectively. Only one of the 41 imipenem-resistant isolates harbored blaNDM-5 and two were colistin-resistant. Altogether, 20 MDR isolates were strong biofilm producers and 19 harbored different virulence factors. This is the first ever report from India on the presence of MDR Enterobacteriaceae with resistance to even last-resort antimicrobials in the bovine diarrhea.

Effect of Synergistic Action of Bovine Lactoferrin with Antibiotics on Drug Resistant Bacterial Pathogens

Background and Objectives: The multidrug resistant (MDR) bacterial pathogenic infection is one of the chief worldwide public health threat to humanity. The development of novel antibiotics against MDR Gram negative bacteria has reduced over the last half century. Research is in progress regarding the treatment strategies that could be engaged in combination with antibiotics to extend the duration of these life-saving antibacterial agents. The current study was therefore planned to assess the synergistic effects of bovine lactoferrin (bLF) in combination with different antibiotics that are conventionally used. This synergism would provide a newer therapeutic choice against MDR pathogens. LF is present in mucosal secretions, vastly in milk. LF is considered an important constituent in host defense. In previous reports, LF has been co-administered as a combination antibiotic therapy. Materials and Methods: This study included synergistic (LF + appropriate antibiotic) exposure against 147 locally encountered bacterial pathogens, which were completely characterized strains. The anti-biofilm effects and the outcome of bLF on minimum inhibitory concentrations (MICs) of antibacterials on clinical MDR bacterial pathogens were determined by standard techniques. Results: In our study, synergism of bLF with antibacterial agents were reproducible and found to be significant. LF on its own had an important effect of inhibiting the biofilm production of some significant bacterial pathogens. Conclusion: The results of this study provides useful data on the antibacterial potential of the combination of LF with antibiotics against drug resistant pathogens.

Prevalence and characterization of beta-lactamase-producing Escherichia coli isolates from a tertiary care hospital in India

BACKGROUND:

The purpose of the study was to determine the prevalence and characterize the resistance profiles of Escherichia coli isolated from various clinical specimens by various phenotypic and genotypic methods.

MATERIALS AND METHODS:

A total of 196 consecutive, nonduplicate strains of clinically significant E. coli isolated from various clinical specimens were included in the study. Identification and antimicrobial susceptibility testing was performed by using Vitek-2 system (Biomerieux, France). Phenotypic detection of extended spectrum beta-lactamase (ESBLs), Amp-C-β lactamase (Amp C), and carbapenemase production was done by various combination of disc diffusion methods, minimum inhibitory concentration determination by E-test, followed by polymerase-chain-reaction for the detection of β-lactamase-encoding genes.

RESULTS:

Overall prevalence of ESBLs, Amp C, and carbapenemase production was found to be 88.3%, 42.2%, and 65.1% by the phenotypic detection methods. Our study also revealed high resistance rates against other antibiotics such as cefepime (89%), cefotaxime (95.4%), ceftazidime (85.4%), ceftriaxone (91.8%), cefpodoxime (92.7%), aztreonam (56.3%), piperacillin/tazobactam (89.2%), and ticarcillin/clavulanic acid (76.3%). The most prevalent ESBL gene was bla_TEM (67.30%), and least prevalent ESBL gene was bla_VEB (2.61%). In case of Amp C, bla_FOX gene (21.9%) was predominant. Among the genes encoding for carbapenemases, the most common gene was bla_NDM (61.7%) followed by bla_VIM (30.8%), bla_KPC (10.6%), bla_OXA-48 (5.3%), and bla_IMP (2.1%).

CONCLUSION:

Our findings suggest a high rate of ESBLs, Amp C, and carbapenemase production among the E. coli isolates. A combination of both phenotypic and genotypic methods would be ideal for better characterization of resistance patterns among the E. coli isolates.

Co-production of AmpC and extended spectrum beta-lactamases in cephalosporin-resistant Acinetobacter baumannii in Egypt

Acinetobacter baumannii is an opportunistic pathogen that has been held responsible for a lot of infections worldwide. Infections caused by this pathogen are difficult to control because of the widespread of antimicrobial resistance mechanisms. The aim of the present study is to assess the prevalence of extended spectrum β-lactamases (ESBLs) and AmpC β-lactamases among isolates of A. baumannii collected from different clinical sources in Mansoura University Hospitals, Egypt. Antimicrobial susceptibility testing has demonstrated elevated resistance level to β-lactams, quinolones and aminoglycosides. All isolates were sensitive to colistin and polymyxin B. ESBL activity was detected in 86% of the isolates. Among the tested ESBL encoding genes, bla_TEM gene was the most prevalent gene as it was detected in 52% of the isolates. While bla_PER, bla_SHV and bla_VEB were detected in 12%, 4%, and 2%, respectively. AmpC activity and bla_ADC gene were detected in 90% of the tested isolates. Insertion sequence ISAba1 was located 9 bp upstream of bla_ADC gene in 88.9% of the ADC-expressing isolates providing a potent promoter activity for its expression. To our knowledge this is the first report of loss of intrinsic ADC activity, in 10% of the tested isolates, as a result of insertional inactivation by an element belonging to IS5 family transposase. Co-expression of both ESBLs and AmpC β-lactamases was detected in 78% of the isolates. The study demonstrates high prevalence of resistance to β-lactam antibiotics through ESBLs and AmpC β-lactamases production among A. baumannii clinical isolates. Prevalence of β-lactamases should be detected routinely and reported in hospitals to avoid inappropriate use of antibiotics and therapeutic failure.

Presence of metallo-beta-lactamases (MBL), extended-spectrum beta-lactamase (ESBL) & AmpC positive non-fermenting Gram-negative bacilli among Intensive Care Unit patients with special reference to molecular detection of blaCTX-M & blaAmpC genes

BACKGROUND & OBJECTIVES

Non-fermenting Gram-negative bacilli (NFGNB) including Pseudomonas aeruginosa and Acinetobacter baumannii have been implicated in a variety of infections, particularly in the Intensive Care Units (ICUs). This study was aimed to overview the burden of multidrug-resistant NFGNB causing infections in ICU and also to assess the occurrence of extended-spectrum beta-lactamases (ESBLs), AmpC and metallo-beta-lactamases (MBLs) among these isolates.

METHODS

Bacterial culture, identification and antibiotic susceptibility were carried out. ESBLs and AmpC were detected both phenotypically and genotypically. MBL was detected by modified Hodge and imipenem-ethylenediaminetetraacetic acid double-disc synergy test.

RESULTS

NFGNB represented 45 (37%) of total 121 Gram negative isolates. Multidrug resistance was observed in 66.9 per cent and 72.5 per cent isolates of P. aeruginosa and A. baumannii, respectively. Detection by phenotypic methods showed presence of ESBL, AmpC and MBL in 21.4, 51.1 and 21.4 per cent isolates, respectively. When detected genotypically by polymerase chain reaction, ESBL and AmpC were detected in 21.4 and 41.4 per cent of NFGNB isolates, respectively. BlaCTX-M (21.4%) was the most prevalent gene responsible for ESBL production.

INTERPRETATION & CONCLUSIONS

Most of the NFGNB isolated from ICU patients were multidrug-resistant and producers of ESBL, AmpC and MBL. A regular surveillance is required to detect ESBL, AmpC and MBL producers, especially in ICU patients.

Incidence of Multidrug-Resistant Pseudomonas Spp. in ICU Patients with Special Reference to ESBL, AMPC, MBL and Biofilm Production

BACKGROUND

Multidrug-resistant (MDR) Pseudomonas spp. have been reported to be the important cause of ICU infections. The appearance of ESBL, AmpC and MBL genes and their spread among bacterial pathogens is a matter of great concern. Biofilm production also attributes to antimicrobial resistance due to close cell to cell contact that permits bacteria to more effectively transfer plasmids to one another. This study aimed at determining the incidence of ESBL, AmpC, MBL and biofilm producing Pseudomonas spp. in ICU patients.

MATERIAL AND METHODS

The clinical specimens were collected aseptically from 150 ICU patients from February 2012 to October 2013. Identification and antimicrobial susceptibility was performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. ESBLs and AmpC were detected phenotypically and genotypically. MBL was detected by modified Hodge and imipenem-EDTA double-disk synergy test.

RESULTS

Pseudomonas spp. 35(28%) were the most prevalent pathogen in ICU infections. Multidrug resistance and biofilm production was observed in 80.1% and 60.4% isolates, respectively. Prevalence of ESBL, AmpC and MBL was 22.9%, 42.8% and 14.4%, respectively. The average hospital stay was 25 days and was associated with 20% mortality.

CONCLUSIONS

A regular surveillance is required to detect ESBL, AmpC and MBL producers especially in ICU patients. Carbapenems should be judiciously used to prevent their spread. The effective antibiotics, such as fluoroquinolones and piperacillin-tazobactum should be used after sensitivity testing.

Diversity of the Genetic Environment of the blaKPC-2 Gene Among Klebsiella pneumoniae Clinical Isolates in a Chinese Hospital

KPC-producing Klebsiella pneumoniae (KPC-Kp) has been frequently reported worldwide and constitutes a major healthcare threat, given their extensively drug-resistant phenotypes. In this study, we report the characterization of the genetic environment of blaKPC-2 gene in KPC-Kp clinical strains from China belonging to diverse genotypes. Thirty-five nonduplicated KPC-Kp isolates collected in a Chinese hospital during 2012 were analyzed. All were multidrug resistant due to the presence of other resistance determinants, including metallo-β-lactamases (IMP-4, NDM-1), extended-spectrum β-lactamases (CTX-M-14, -15, -3, -10, and SHV-12), 16S rRNA methylases (armA and rmtB), and plasmid-mediated quinolone resistance determinants [qnrA, B, S, aac(6')-Ib-cr]. Using pulsed-field gel electrophoresis (PFGE), the 35 isolates were grouped into 12 clusters that were further identified as 15 sequence types (STs) by multilocus sequence typing. ST11 K. pneumoniae was the predominant clone attributed to the outbreak. blaKPC-2 was carried in plasmids of various sizes and incompatibility types. The genetic environment analysis, based on genetic structure in the plasmid pKP048, revealed five distinct platforms: the most prevalent structure was the continual occurrence in diverse STs (ST11, ST258, ST340, ST395, ST437, and ST494), harboring plasmid of blaKPC-2 in a genetic environment flanked by ISKpn8 and ISKpn6 like. This study highlights the continued evolution of the genetic environment of the blaKPC-2 gene in our hospital and movement to multiple plasmid backbones that results in acquisition by multiple clones of K. pneumoniae.

Prevalence of Extended-Spectrum and Metallo β-Lactamase Production in AmpC β-Lactamase Producing Pseudomonas aeruginosa Isolates From Burns

BACKGROUND

Pseudomonas aeruginosa is one of the most common causes of nosocomial infections. Resistance of P. aeruginosa to β-lactam antibiotics may be the result of acquired resistance through mutation and over production of various antibiotic inactivating enzymes. This research aimed to determine the prevalence of extended-spectrum β-lactamases (ESBL) and metallo β-lactamase (MBL) production as well as the presence of their related genes among AmpC β-lactamase producing P. aeruginosa isolated from burns.

OBJECTIVES

The current study aimed to determine the prevalence of class A ESBL and MBL production in relation to the presence of their related genes among AmpC β-lactamase producing P. aeruginosa isolated from burns.

MATERIALS AND METHODS

The antimicrobial susceptibility of 51 P. aeruginosa isolates from patients with burns was examined against 13 antibiotics by the disc diffusion method. Minimum inhibitory concentrations (MIC) for imipenem and ceftazidime were measured by the microdilution method. AmpC production was detected by AmpC disc and the modified three-dimensional extract tests. ESBL phenotype was confirmed by the double disc synergy test (DDST). Presence of β-lactamase genes was detected by specific primers and polymerase chain reaction (PCR).

RESULTS

All isolates were multidrug resistant. AmpC, ESBL and MBL production were observed in 35 (68.6%), 20 (39.2%) and 19 (37.3%) isolates, respectively. Overall, 43 isolates (84.3%) carried β-lactamase genes, out of which 31 (60.8%) harbored bla AmpC , 20 (39.2%) had bla TEM and 11 (21.6%) carried bla PER -1 genes. Among the AmpC producers, two isolates (6.5%) carried bla AmpC + bla ESBL , 13 (41.9%) had bla AmpC + bla MBL and six (19.4%) produced the three enzymes.

CONCLUSIONS

A high prevalence of multiple β-lactamase production was observed among the AmpC producers (60%), of which the majority co-produced AmpC and MBL. The current study results showed correlation between β-lactamase production and the presence of antibiotic resistance genes in the isolates.

Mechanisms of carbapenem resistance in cephalosporin-susceptible Pseudomonas aeruginosa in China

Twenty-nine Pseudomonas aeruginosa isolates, which are resistant to carbapenems but susceptible to ceftazidime or/and cefepime, were recovered from our hospital from July 2011 to October 2011. The results of Western blotting showed that the OprD was reduced or lost. None of the 29 clinical isolates produced carbapenemases, extended-spectrum β-lactamases, or Ambler class C β-lactamases enzymes by the modified 3-dimensional test. The sequencing of oprD for these isolates showed that there are multiple point mutations, large fragment substitutions, deletions, and insertions. It showed that the expression of oprD decreased while mexA and mexX increased by real-time reverse transcriptase-PCR. These results suggested that the loss of OprD and overexpression of mexXY-OprM and mexAB-OprM are associated with carbapenem resistance in cephalosporin-susceptible Pseudomonas aeruginosa.

Detection of ESBL among AmpC producing enterobacteriaceae using inhibitor-based method

Introduction

The occurrence of multiple β-lactamases among bacteria only limits the therapeutic options but also poses a challenge. A study using boronic acid (BA), an AmpC enzyme inhibitor, was designed to detect the combined expression of AmpC β-lactamases and extended-spectrum β-lactamases (ESBLs) in bacterial isolates further different phenotypic methods are compared to detect ESBL and AmpC.

Methods

A total of 259 clinical isolates of Enterobacteriaceae were isolated and screened for ESBL production by (i) CLSI double-disk diffusion method (ii) cefepime- clavulanic acid method (iii) boronic disk potentiation method. AmpC production was detected using cefoxitin alone and in combination with boronic acid and confirmation was done by three dimensional disk methods. Isolates were also subjected to detailed antibiotic susceptibility test.

Results

Among 259 isolates, 20.46% were coproducers of ESBL and AmpC, 26.45% were ESBL and 5.40% were AmpC. All of the 53 AmpC and ESBL coproducers were accurately detected by boronic acid disk potentiation method.

Conclusion

The BA disk test using Clinical and Laboratory Standards Institute methodology is simple and very efficient method that accurately detects the isolates that harbor both AmpCs and ESBLs.

ESBL, MBL and Ampc β Lactamases Producing Superbugs - Havoc in the Intensive Care Units of Punjab India

BACKGROUND

An alarming rise in the rates of the antibiotic resistance has now become a serious and an increasingly common public health concern, with severe implications, especially in the intensive care units. A variety of β-lactamases which include ESBLs, AmpC β-lactamases and metallo-βlactamases, have emerged as the most worrisome mechanism of resistance among the gram negative bacteria, which pose a therapeutic challenge to the health care settings.

MATERIALS AND METHODS

The present study was aimed at knowing the prevalence of various β-lactamases in the gram negative isolates which were obtained from ICU patients. A total 273 gram negative isolates from 913 clinical samples which were received over a period of one year were processed for their identification and their antimicrobial susceptibility pattern was determined. They were then screened for the β-lactamase production.

RESULTS

Among the 273 isolates, the β-lactamase production was observed in 193 strains. 96 (35.16%) strains were ESBL producers, followed by 30 (10.98%) metallo β- lactamase (MBL) producers and 15(5.4%) AmpC producers. The major ESBL and AmpC producer was Escherichia coli, while Klebsiella pneumonia was the predominant MBL producer. The co production of the ESBL/MBL/ AmpC β- lactamases was observed in 52 (19.04%) strains and it was more common in Escherichia coli. A multidrug resistance to the fluoroquinolones and the aminoglycosides was also observed in the β- lactamase producing organisms.

CONCLUSION

The high prevalence of the β- lactamases in the ICU isolates emphasizes the need for a continuous surveillance in the ICUs to detect the resistant strains, strict guidelines for the antibiotic therapy and the implementation of infection control measures to reduce the increasing burden of antibiotic resistance.

Burden of different beta-lactamase classes among clinical isolates of AmpC-producing Pseudomonas aeruginosa in burn patients: A prospective study

Background:

Pseudomonas aeruginosa is one of the most common pathogens causing infections in burns, and shows increasing resistance to β-lactam antibiotics by producing different classes of beta-lactamases. It is also not unusual to find a single isolate that expresses multiple β-lactamase enzymes, further complicating the treatment options. Thus, in this study, we aimed to determine the coexistence of different beta-lactamase enzymes in clinical isolates of P. aeruginosa in the burn ward.

Materials and Methods:

A total of 101 clinical isolates of P. aeruginosa from the burn ward were identified and tested for the presence of different beta-lactamase enzymes (extended spectrum beta lactamase (ESBL), Amp C and metallo β-lactamases (MBL) from October 2006 to May 2009. In vitro susceptibility pattern of antipseudomonal antibiotics was done by the Kirby Bauer disc diffusion method.

Results:

A total of 33 (32.7%) isolates were confirmed to be positive for AmpC beta-lactamase. Co-production of AmpC along with ESBL and MBL was reported in 24.5% and 45.5% isolates, respectively. A total of 12 (11.9%) isolates were resistant to three or more antibiotic classes (multidrug resistance). Imipenem and piperacillin/tazobactum showed high sensitivity, with 86.1% and 82.2%, respectively.

Conclusion:

This study reveals the high prevalence of multidrug- resistant P. aeruginosa producing beta-lactamase enzymes of different mechanisms in this region from burn patients. The emerging antimicrobial resistance in burn wound pathogens poses serious therapeutic challenge. Thus proper antibiotic policy and measures to restrict the indiscriminate use of cephalosporins and carbapenems should be taken to minimize the emergence of this multiple beta -lactamase producing pathogen.

Concurrent occurrence of blaampC families and blaCTX-M genogroups and association with mobile genetic elements ISEcp1, IS26, ISCR1, and sul1-type class 1 integrons in Escherichia coli and Klebsiella pneumoniae isolates originating from India

Cefoxitin-resistant Escherichia coli (n = 109) and Klebsiella pneumoniae (n = 16) isolates collected from patients in India in 2009 to 2010 were screened for bla(ampC) families and mobilizing elements (ISEcp1, IS26, ISCR1, and sul-1-type class 1 integrons) and their association with bla(ampC) and for the occurrence of class A beta-lactamases (BLs) (CTX-M, TEM, and SHV). The concurrent occurrences of two distinct AmpC families (bla(CIT) and bla(EBC)) and of class A with class C beta-lactamase were observed. All but one of the isolates harboring CTX-M extended-spectrum BLs (ESBLs) were carrying bla(CTX-M) genogroup 1; the remaining isolate carried bla(CTX-M) genogroup 9. The mobilizing elements occurred in different combinations in the study isolates.

Comparison of the boronic acid disk potentiation test and cefepime-clavulanic acid method for the detection of ESBL among AmpC-producing Enterobacteriaceae

PURPOSE

Extended spectrum β-lactamase (ESBL) and AmpC β-lactamase are important mechanisms of betalactam resistance among Enterobacteriaceae . The ESBL confirmation test described by Clinical Laboratory Standards Institute (CLSI) is in routine use. This method fails to detect ESBL in the presence of AmpC. Therefore, we compared two different ESBL detection methods against the CLSI confirmatory test.

MATERIALS AND METHODS

A total 200 consecutive clinical isolates of Enterobacteriaceae from various clinical samples were tested for ESBL production using (i) CLSI described phenotypic confirmatory test (PCT), (ii) boronic acid disk potentiation test and (iii) cefepime-CA disk potentiation method. AmpC confirmation was done by a modified three-dimensional test.

RESULTS

Among total 200 Enterobacteriaceae isolates, 82 were only ESBL producers, 12 were only AmpC producers, 55 were combined ESBL and AmpC producers, 14 were inducible AmpC producers and 37 isolates did not harboured any enzymes. The CLSI described PCT detected ESBL-producing organisms correctly but failed to detect 36.3% of ESBLs among combined enzyme producers. The boronic acid disk potentiation test reliably detected all ESBL, AmpC, and combined enzyme producers correctly. The cefepime-CA method detected all ESBLs correctly but another method of AmpC detection has to be adopted.

CONCLUSION

The use of boronic acid in disk diffusion testing along with the CLSI described PCT enhances ESBL detection in the presence of AmpC betalactamases.

Occurrence of Plasmid-Mediated AmpC β-Lactamases Among Escherichia coli and Klebsiella pneumoniae Clinical Isolates in a Tertiary Care Hospital in Bangalore

Therapeutic options for infections caused by gram-negative organisms expressing plasmid-mediated AmpC β-lactamases are limited because these organisms are usually resistant to all the β-lactam antibiotics, except for cefepime, cefpirome and the carbapenems. These organisms are a major concern in nosocomial infections and should therefore be monitored in surveillance studies. Hence, this study was aimed out to determine the prevalence of plasmid-mediated AmpC β-lactamases in E. coli and K. pneumoniae from a tertiary care in Bangalore. A total of 63 E. coli and 27 K. pneumoniae were collected from a tertiary care hospital in Bangalore from February 2008 to July 2008. The isolates with decreased susceptibility to cefoxitin were subjected to confirmation test with three dimensional extract tests. Minimum inhibitory concentrations (MICs) were determined by agar dilution method. Conjugation experiments, plasmid profiling and susceptibility testing were carried out to investigate the underlying mechanism of resistance. In our study, 52 (57.7%) isolates showed resistance to cefoxitin, the occurrence of AmpC was found to be 7.7% of the total isolates. Plasmid analysis of the selected isolates showed the presence of a single plasmid of 26 kb in E. coli and 2 Kb in K. pneumoniae. Plasmid-mediated AmpC β-lactamases were found in 11.1% of K. pneumoniae and in 6.3% of E. coli. Curing and conjugation experiments showed that resistance to cephamycins and cephalosporins was plasmid-mediated. Our study has demonstrated the occurrence of plasmid-mediated AmpC in E. coli and K. pneumoniae which illustrates the importance of molecular surveillance in tracking AmpC-producing strains at general hospitals and emphasizes the need for epidemiological monitoring.

Increasing secondary bacterial infections with Enterobacteriaceae harboring bla(CTX-M-15) and bla(CMY-6) in patients with bronchogenic carcinoma: an emerging point of concern

OBJECTIVE

To look for secondary bacterial infections in bronchogenic carcinoma (BC(A)) with resistant organisms harboring bla genes considering the paucity of relevant studies.

METHODS

A total of 137 confirmed cases of BC(A) and 34 healthy volunteers were studied for the occurrence and prevalence of bla(CTX-M) and and bla(AmpC) harboring-enterobacteriaceae. A subset of these patients (n=69) was previously reported for the secondary infection with the Aspergillus species. Bronchoalveolar lavages (BAL) were subjected for bacterial and fungal cultures and the bacterial isolates were screened by multiplex PCRs for the presence of bla(CTX-M) and bla(AmpC). The isolates were also screened for the association of insertion sequence (IS26) by PCR and characterized by RAPD for any clonal relatedness.

RESULTS

A total of 143 bacterial isolates were obtained from 137 BAL specimens of BC(A) patients. The Enterobacteriaceae-isolates were multidrug-resistant showing concomitant resistance to fluoroquinolones and aminoglycosides. Both bla(CTX-M) and bla(AmpC) of CIT family were detected in 77.4% and 27.4% isolates, respectively. Sequencing revealed the presence of bla(CTX-M-15) and bla(CMY-6). Twenty one percent of the isolates were simultaneously harboring bla(ampC) and bla(CTX-M-15). IS26 PCR and RAPD typing revealed the presence of diverse bacterial population but no predominant clone was identified. The present study also suggests strong association of aspergillosis with lung cancer and further strengthens the potential use of non-validated serological tests suggested earlier.

CONCLUSIONS

We emphasize that all patients of bronchogenic carcinoma should also be screened for secondary bacterial infections, along with secondary fungal infections, so as to introduce early and specific antimicrobial therapy and to prevent unwanted deaths.

Characterization of the first extended-spectrum beta-lactamase-producing nontyphoidal Salmonella strains isolated in Tehran, Iran

The infections caused by Salmonella remain a significant public health problem throughout the world. beta-Lactams and fluoroquinolones are generally used to treat invasive Salmonella infections, but emergence and spread of antibiotic-resistant strains are being increasingly notified in many countries. In particular, detection of extended-spectrum beta-lactamases (ESBLs) in Salmonella spp. is a newly emerging threat worldwide. This study was carried out to characterize beta-lactamase-producing Salmonella strains identified in Tehran, Iran. Over the 2-year period from 2007 to 2008, 6 of 136 Salmonella isolates recovered from pediatrics patients, including three Salmonella enterica serotypes Enteritidis (S. Enteritidis) and three S. Infantis, showed an ESBL-positive phenotype. Polymerase chain reaction and sequencing were used to identify the genetic determinants responsible for ESBL phenotypes. The Salmonella isolates were also compared by pulsed-field gel electrophoresis. All ESBL-producing strains, but one, carried the bla(CTX-M-15) gene. Moreover, three of four strains that proved to be positive for a bla(TEM) gene were producing a TEM-1 beta-lactamase. Two strains of S. Infantis tested positive for a previously unidentified CTX-M and TEM ESBL, respectively. All ESBL-producing strains carried the insertion sequence ISEcp1 gene. Except for one strain of serotype Infantis, all strains were able to transfer the ESBL determinants by conjugation. Distinct, but closely related, pulsed-field gel electrophoresis patterns were observed among the strains belonging to both serotypes. This study reports for the first time the emergence and characterization of ESBL-producing S. Enteritidis and Infantis strains in Iran.

AmpC beta-lactamases

SUMMARY

AmpC beta-lactamases are clinically important cephalosporinases encoded on the chromosomes of many of the Enterobacteriaceae and a few other organisms, where they mediate resistance to cephalothin, cefazolin, cefoxitin, most penicillins, and beta-lactamase inhibitor-beta-lactam combinations. In many bacteria, AmpC enzymes are inducible and can be expressed at high levels by mutation. Overexpression confers resistance to broad-spectrum cephalosporins including cefotaxime, ceftazidime, and ceftriaxone and is a problem especially in infections due to Enterobacter aerogenes and Enterobacter cloacae, where an isolate initially susceptible to these agents may become resistant upon therapy. Transmissible plasmids have acquired genes for AmpC enzymes, which consequently can now appear in bacteria lacking or poorly expressing a chromosomal bla(AmpC) gene, such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Resistance due to plasmid-mediated AmpC enzymes is less common than extended-spectrum beta-lactamase production in most parts of the world but may be both harder to detect and broader in spectrum. AmpC enzymes encoded by both chromosomal and plasmid genes are also evolving to hydrolyze broad-spectrum cephalosporins more efficiently. Techniques to identify AmpC beta-lactamase-producing isolates are available but are still evolving and are not yet optimized for the clinical laboratory, which probably now underestimates this resistance mechanism. Carbapenems can usually be used to treat infections due to AmpC-producing bacteria, but carbapenem resistance can arise in some organisms by mutations that reduce influx (outer membrane porin loss) or enhance efflux (efflux pump activation).

Evaluation of screening methods to detect plasmid-mediated AmpC in Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis

There are currently no standardized phenotypic methods for the screening and detection of AmpC enzymes. This study aimed to evaluate different methods to detect AmpC enzymes in Escherichia coli, Klebsiella spp., and Proteus spp., comparing the results from two disk-based methods and an agar dilution method. AmpC activity was determined for 255 clinical isolates by use of a three-dimensional enzyme assay combined with a multiplex PCR assay for plasmid-borne ampC genes. These results were compared against a disk-based inhibitor assay using various combinations of cefpodoxime and cefoxitin as antibiotic substrates and boronic acid or cloxacillin as an AmpC inhibitor. The presence of enzyme induction by disk approximation was evaluated using imipenem, cefoxitin, and amoxicillin-clavulanate as inducing agents against ceftazidime. Finally, an agar dilution assay was performed, using cefoxitin with and without added cloxacillin. AmpC activity was present in 49.8% of test isolates, 93.7% of which were positive for plasmid-borne ampC genes. CIT-like enzymes were predominant in E. coli, and DHA-like enzymes were predominant in Klebsiella spp. The disk-based inhibitor tests performed better than the agar dilution assay, while detection of AmpC by disk induction had a poor sensitivity. The cefoxitin-cloxacillin disk combination provided the best overall performance, with a sensitivity and specificity of 95%. This study confirmed the accuracy of disk-based inhibitor screening for AmpC enzymes, which proved reliable at detecting CIT- and DHA-like plasmid-borne ampC genes. The methods are simple enough for introduction into clinical microbiology laboratories.

Detection of CTX-M-14 extended-spectrum β-lactamase in Shigella sonnei isolates from China

Shigellosis is an important cause of acute diarrheal disease and multidrug-resistant phenotype has been reported in S. sonnei. In this study, we investigate the resistance and identify extended-spectrum beta-lactamases (ESBLs) gene in 37 S. sonnei isolates by agar dilution procedure and the modified three-dimensional test, respectively. The bla genes of ESBL-producing isolates were detected by polymerase chain reaction (PCR) and sequencing. More than 50% of these strains were resistant to tetracycline, sulfamethoxazole-trimethoprim, ampicillin, ampicillin-sulbactam, or gentamicin. However, they were still susceptible to third generation cephalosporins, fluoroquinolones, and chloramphenicol. A total of 8.1% (3/37) of the isolates with intermediate susceptibility to ceftriaxone and cefotaxime were ESBL-producers, which produced CTX-M-14 ESBLs and TEM-1 beta-lactamases. This is the first report of CTX-M-14 in S. sonnei isolates from China and it is important to closely monitor such strains.

Detection of plasmid-mediated class C β-lactamases

Plasmid-mediated class C beta-lactamases are reported from Enterobacteriaceae with increasing frequency. They likely originate from chromosomal AmpC of certain Gram-negative bacterial species and subsequently are mobilized onto transmissible plasmids. There are reports of unfavorable clinical outcomes in patients infected with these organisms and treated with broad-spectrum cephalosporins. However, unlike class A extended-spectrum beta-lactamases (ESBLs), no screening and confirmatory tests have been uniformly established for strains that produce class C beta-lactamases. Reduced susceptibility to cefoxitin is a sensitive but not specific indicator of class C beta-lactamase production. Simple confirmatory tests including tests using boronic acid compounds as specific class C beta-lactamase inhibitors have recently been developed. Their utilization will enable clinical microbiology laboratories to report those strains producing plasmid-mediated class C beta-lactamases as being resistant to all broad-spectrum cephalosporins, thus allowing physicians to prescribe appropriate antimicrobial therapy.

Evaluation of the new VITEK 2 extended-spectrum beta-lactamase (ESBL) test for rapid detection of ESBL production in Enterobacteriaceae isolates

Extended-spectrum beta-lactamases (ESBLs) are a large, rapidly evolving group of enzymes that confer resistance to oxyimino cephalosporins and monobactams and are inhibited by clavulanate. Rapid reliable detection of ESBL production is a prerequisite for successful infection management and for monitoring resistance trends and implementation of intervention strategies. We evaluated the performance of the new VITEK 2 ESBL test system (bioMérieux, Inc, Hazelwood, Mo.) in the identification of ESBL-producing Enterobacteriaceae isolates. We examined a total of 1,129 clinically relevant Enterobacteriaceae isolates (including 218 that had been previously characterized). The ESBL classification furnished by the VITEK 2 ESBL test system was concordant with that of the comparison method (molecular identification of beta-lactamase genes) for 1,121 (99.3%) of the 1,129 isolates evaluated. ESBL production was correctly detected in 306 of the 312 ESBL-producing organisms (sensitivity, 98.1%; positive predictive value, 99.3%). False-positive results emerged for 2 of the 817 ESBL-negative isolates (specificity, 99.7%; negative predictive value, 99.3%). VITEK 2 ESBL testing took 6 to 13 h (median, 7.5 h; mean +/- SD, 8.2 +/- 2.39 h). This automated short-incubation system appears to be a rapid and reliable tool for routine identification of ESBL-producing isolates of Enterobacteriaceae.

First detection of the Ambler class C 1 AmpC beta-lactamase in Citrobacter freundii by a new, simple double-disk synergy test

We report on the first detection of an AmpC-type Ambler class C 1 (ACC-1) beta-lactamase in Citrobacter freundi isolated from a patient also harboring ACC-1-producing Escherichia coli and Klebsiella pneumoniae. We propose a simple cefoxitin-based double-disk synergy test (DDST) for the specific detection of ACC-1 in members of the family Enterobacteriaceae, including natural AmpC producers, in association with a cloxacillin-based DDST as a first-line AmpC-type beta-lactamase screening test.

Evaluation of phenotypic screening methods for detecting plasmid-mediated AmpC beta-lactamases-producing isolates of Escherichia coli and Klebsiella pneumoniae

Detection of plasmid-mediated (P-M) AmpC beta-lactamase-producing isolates is considered critical for epidemiologic studies and hospital infection control, but the documents of the Clinical and Laboratory Standards Institute do not contain any recommendation for the phenotypic detection. In this study, phenotypic detection methods, cefoxitin-Hodge test and induction test, were evaluated using cefoxitin-resistant Escherichia coli and Klebsiella pneumoniae isolates. The cefoxitin-Hodge test detected all bla(CMY-10), and 97.4% of bla(CMY-2) allele-positive isolates, but only 57.3% of bla(DHA-1) allele-positive isolates. Induction test with an aztreonam and an amoxicillin-clavulanic acid disk was more sensitive than with cefoxitin disk, which detected 86.6% of bla(DHA-1) allele-positive isolates. These phenotypic tests should be useful to screen P-M AmpC beta-lactamase-producing E. coli and K. pneumoniae isolates.