PCR detection of aminoglycoside resistance genes: a rapid molecular typing method for Acinetobacter baumannii

Emergence of carbapenem resistant gram-negative pathogens with high rate of colistin resistance in Egypt: A cross sectional study to assess resistance trends during the COVID-19 pandemic

The current study investigated the temporal phenotypic and genotypic antimicrobial resistance (AMR) trends among multi-drug resistant and carbapenem-resistant Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa recovered from Egyptian clinical settings between 2020 and 2021. Bacterial identification and antimicrobial sensitivity of 111 clinical isolates against a panel of antibiotics were performed. Molecular screening for antibiotic resistance determinants along with integrons and associated gene cassettes was implemented. An alarming rate (98.2%) of these isolates were found to be phenotypically resistant to carbapenem. Although 23.9 % K. pneumoniae isolates were phenotypically resistant to colistin, no mobile colistin resistance (mcr) genes were detected. Among carbapenem-resistant isolates, blaNDM and blaOXA-48-like were the most prevalent genetic determinants and were significantly overrepresented among K. pneumoniae. Furthermore, 84.78% of K. pneumoniae isolates co-produced these two carbapenemase genes. The plasmid-mediated quinolone resistance genes (qnrS and qnrB) were detected among the bacterial species and were significantly more prevalent among K. pneumoniae. Moreover, Class 1 integron was detected in 82% of the bacterial isolates. This study alarmingly reveals elevated resistance to last-resort antibiotics such as carbapenems as well as colistin which impose a considerable burden in the health care settings in Egypt. Our future work will implement high throughput sequencing-based antimicrobial resistance surveillance analysis for characterization of novel AMR determinants. This information could be applied as a step forward to establish a robust antibiotic stewardship program in Egyptian clinical settings, thereby addressing the rising challenges of AMR.

Molecular Typing of Multidrug-Resistant Acinetobacter baumannii Isolates from Clinical Specimens by ERIC-PCR and MLVA

Acinetobacter baumannii, a Gram-negative and oxidase-negative bacterium, is a major cause of nosocomial infections, leading to high mortality rates in hospitalized patients. The use of 2 prominent molecular typing methods (i.e., enterobacterial repetitive intergenic consensus-polymerase chain reaction [ERIC-PCR] and multiple-locus variable-number tandem repeat [VNTR] analysis [MLVA]) for genotyping A. baumannii isolates has proven to be an effective approach in assessing the clonal relation of these isolates and managing their outbreaks. A total of 100 A. baumannii isolates were collected from immunocompromised patients hospitalized in the intensive care unit (ICU) of a hospital in Zanjan City, Iran. Their antibiotic resistance ability (especially aminoglycoside resistance) was studied by disc diffusion tests. The genetic typing of A. baumannii was studied using ERIC-PCR and MLVA methods. All isolates were resistant to 3 or more antibiotics and regarded as multidrug-resistant (MDR). Additionally, 32% of the isolates were resistant to all antibiotics tested, and 91% were extensively drug-resistant (XDR). The increased rate of aminoglycoside-resistant A. baumannii in ICU patients, with an increased incidence of aminoglycoside-modifying enzymes of aac (6')-Ib, ant (3″)-I, and aph (2″)-Id. ERIC-PCR has likewise shown an increased level of diversity in A. baumannii isolates. According to the ERIC-PCR patterns, isolates were classified as 4 clusters, while according to the MLVA patterns, isolates were classified as 9 distinct clusters. ERIC-PCR and MLVA assays serve as useful genotyping methods to assess the genetic variety or clonal relatedness of A. baumannii isolates.

Emergence and multi-lineages of carbapenemase-producing Acinetobacter baumannii-calcoaceticus complex from canine and feline origins

The carbapenemase-producing Acinetobacter baumannii is an important opportunistic bacterium and frequently causes hospital-acquired infections in humans. It also has increasingly been reported in veterinary medicine. This study illustrates multiple clones of carbapenemase-producing A. baumannii disseminating and causing diseases in dogs and cats in Thailand. Between 2016 and 2020, 44 A. baumannii and two A. pittii isolates exhibiting imipenem resistance (MIC≥16 μg/mL) from diagnostic samples were characterized by Pasteur multilocus sequence typing (MLST), sequence grouping (SG), repetitive extragenic palindromic element (rep)-PCR fingerprint analysis and antimicrobial resistance (AMR) profiling. All isolates contained bla_OXA-23 in the Tn2006 family, and A. baumannii showed the sequence type (ST) 16 (14/44), ST149 (12/44), ST25 (6/44), ST2 (4/44), ST1581 (3/44), ST23 (2/44), ST1575 (1/44) and ST1576 (1/44). DNA fingerprint analysis and SG illustrated clonal relationships in the STs and its single locus variants, and AMR gene profiles, including tetracycline and aminoglycoside resistance genes, showed minor variations in the clones. The findings suggest that bla_OXA-23 has been spread in multiple clones of A. baumannii and A. pittii from canine and feline hosts. With the collection of multiple AMR genes and intrinsic resistance, antimicrobial options are limited for treatment, and pets can be a potential reservoir of extensively drug-resistant, carbapenemase-producing A. baumannii in the community. Epidemiological tracking by passive and active surveillance in animals, veterinary personnel and hospital environment and preventive measurements should be promoted to decrease the risk of infection and transmission to humans.

Characterization of plasmid-mediated quinolone resistance genes and extended-spectrum beta-lactamases in non-typhoidal Salmonella enterica isolated from broiler chickens

Background and Aim:

Antibiotic-resistant Salmonella is a public health concern. Fluoroquinolones and extended-spectrum beta-lactams are widely used for the treatment of Salmonella infections. This study focused on the detection of plasmid-mediated quinolone resistance (PMQR) and extended-spectrum beta-lactamase (ESBL) genes among multidrug-resistant (MDR) Salmonella enterica isolated from broilers.

Materials and Methods:

A total of 40 non-typhoidal S. enterica isolates were collected from 28 broiler chicken farms in four Iraqi Governorates. These isolates were examined for their susceptibility to 10 antimicrobial agents by disk-diffusion method followed by polymerase chain reaction assay for the detection of PMQR determinants and ESBLs genes.

Results:

Salmonella strains revealed high levels of resistance to the following antibiotics: Nalidixic acid 100%, levofloxacin (LEV) 97.5%, amoxicillin-clavulanic acid 95.0%, tetracycline 92.5%, and nitrofurantoin 80.0%. Otherwise, all isolates were susceptible to cefotaxime and ceftriaxone. All isolates were MDR, with 15 different profiles observed. Among 38 amoxicillin/clavulanic acid-resistant Salmonella isolates, 20 (52.6%) had the blaTEM gene, while blaSHV, blaCTX-M, and blaOXA genes were not detected. Only 5 (12.8%) out of 39 LEV-resistant isolates were positive for qnrB, three of which had blaTEM. No qnrC or qnrD, qnrS, aac(6`)-Ib-cr, qunA, and oqxAB genes were found in any of the tested isolates.

Conclusion:

This study demonstrates that broiler chickens may be considered a potential source for spreading MDR non-typhoidal Salmonella and ESBL traits in poultry production. Therefore, it is important to continuously monitor ESBL and PMQR genes to avoid the spread of resistant strains in the food chain and impact public health.

Dissemination of OXA-48- and NDM-1-Producing Enterobacterales Isolates in an Algerian Hospital

Multidrug-resistant (MDR) Enterobacterales remain an increasing problem in Algeria, notably due to the emergence of carbapenemase producers. We investigated the molecular characteristics of carbapenem-resistant Enterobacterales isolates recovered from outpatients and inpatients in Eastern Algeria. Non-repetitive Enterobacterales with reduced susceptibility to carbapenems were consecutively collected from clinical specimens in Annaba University Hospital (Algeria) between April 2016 and December 2018. Isolates were characterized with regard to antibiotic resistance, resistome and virulome content, clonality, and plasmid support. Of the 168 isolates analyzed, 29 (17.3%) were carbapenemase producers and identified as K. pneumoniae (n = 23), E. coli (n = 5), and E. cloacae (n = 1). bla_OXA-48 was the most prevalent carbapenemase-encoding gene (n = 26/29), followed by bla_NDM-1 gene (n = 3/29). K. pneumoniae isolates harbored some virulence traits (entB, ugeF, ureA, mrkD, fimH), whereas E. coli had a commensal origin (E, A, and B1). Clonality analysis revealed clonal expansions of ST101 K. pneumoniae and ST758 E. coli. Plasmid analysis showed a large diversity of incompatibility groups, with a predominance of IncM (n = 26, 89.7%). A global dissemination of OXA-48-producing Enterobacterales in the Algerian hospital but also the detection of NDM-1-producing E. coli in community settings were observed. The importance of this diffusion must be absolutely investigated and controlled.

The Molecular Epidemiology of Resistance to Antibiotics among Klebsiella pneumoniae Isolates in Azerbaijan, Iran

Introduction

Klebsiella pneumoniae (K. pneumoniae) is one of the leading causes of hospital-acquired and community-acquired infections in the world. This study was conducted to investigate the molecular epidemiology of drug resistance in clinical isolates of K. pneumoniae in Azerbaijan, Iran.

Materials and Methods

A total of 100 nonduplicated isolates were obtained from the different wards of Azerbaijan state hospitals, Iran, from 2019 to 2020. Antibiotic susceptibility testing was done. The DNA was extracted, and the PCR for evaluation of the resistance genes was carried out.

Results

The highest antibiotic resistance was shown to ampicillin (96%), and the highest susceptibility was shown to tigecycline (9%), and 85% of isolates were multidrug resistant. The most frequent ESBL gene in the tested isolates was bla _SHV-1 in 58%, followed by bla _CTXM-15 (55%) and bla _{SHV-11 (}42%). The qepA, oqxB, and oqxA genes were found to be 95%, 87.5%, and 70%, respectively. We detected tetB in 42%, tetA in 32%, tetD in 21%, and tetC in 16%. Seventy isolates were resistant to co-trimoxazole, and the rate of resistance genes was sul1 in 71%, followed by sul2 (43%), dfr (29%), and sul3 (7%). The most common aminoglycoside resistance genes were ant3Ia, aac6Ib, aph3Ib, and APHs in 44%, 32%, 32%, and 31.4%, respectively. The most frequent resistance gene to fosfomycin was fosA (40%) and fosX (40%) followed by fosC (20%).

Conclusion

The results of this study indicate the high frequency of drug resistance among K. pneumoniae isolated from hospitals of Azerbaijan state. The present study shows the presence of high levels of drug-resistant genes in various antibiotics, which are usually used in the treatment of infections due to K. pneumoniae.

Co-occurrence of mcr-1, mcr-3, mcr-7 and clinically relevant antimicrobial resistance genes in environmental and fecal samples

Multidrug-resistant bacteria harboring different antimicrobial resistance genes (ARGs) have been detected worldwide. The association of plasmid-mediated colistin resistance genes (mcr-like) and other ARGs in bacteria isolated from animals is a huge concern worldwide. Therefore, this study aimed to investigate the presence of mcr-like genes and clinically relevant ARGs as well as plasmids in samples from a zoo. Fecal and environmental (soil and water) samples were collected from a zoo and the DNA of cultivable aerobic bacteria was extracted. ARGs were screened by PCR and the plasmids were detected using the PCR-based replicon typing method. A total of 74 amplicons from 27 ARGs [mcr-1, mcr-3, mcr-7.1, bla_CTX-M-Gp1, bla_CTX-M-Gp2, bla_CTX-M-Gp9, bla_VEB, bla_PER, bla_CMY, tetA, tetB, tetC, aadA, aac(6')-Ib, aph(3')-Ia, ant(2'')-Ia, qnrA, qnrB, qnrS, oqxA, oqxB, sul1, sul2, sul3, cmlA, mefAE, ermB] and 21 amplicons from eight plasmid families (IncY, ColE-like, IncF_repB, IncFIA, IncFIB, IncHI1, IncFIC, IncP) were detected. These findings reinforce that the zoo acts as a reservoir of clinically relevant ARGs, including mcr-like, and call attention to the monitoring studies in the zoo. Therefore, to the best of our knowledge, this is the first report of the world of mcr-1, mcr-3 and mcr-7.1 in environmental samples from the zoo.

Genetic Diversity of Multidrug-Resistant CMY-Producing Escherichia coli from Feces and Soil in a Small-Scale Pig Farm

Diarrheagenic Escherichia coli cause diarrheal diseases, which are a public health concern and affect mainly developing countries. Multidrug-resistant (MDR) pathogens have been spreading in different sources, including animals and the environment. E. coli strains were obtained from a small-scale pig farm and 33 antimicrobials were tested. All strains were classified as MDR and harbored several antimicrobial resistance genes (ARGs) [bla_CMY, bla_OXA-1-like, bla_SHV, tet(A), tet(B), aadA, aac(6')-Ib, aph(3')-Ia, sul1, sul2, sul3, floR, and cmlA] and plasmids. Besides, mutations in quinolone resistance-determining region of GyrA (Ser83Leu and Asp87Asn) and ParC (Glu84Asp) were detected. Among the MDR E. coli, nine strains (52%) presented diarrheagenic virulence genes, including genes related to Shiga toxin-producing E. coli (STEC), enteroinvasive E. coli (EIEC), and enteroaggregative E. coli (EAEC). The pulsed-field gel electrophoresis results showed a high genetic diversity among the MDR E. coli strains. Multilocus sequence typing (MLST) analyses revealed different sequence types phylogenetically related to each other, including ST10 and ST56. Subtyping of MLST by fimH gene showed different fimH type. This study shows a high genetic diversity among MDR ARG-producing E. coli belonging to STEC, EIEC, and EAEC pathotypes obtained from a small-scale pig farm and contributes to the monitoring of antimicrobial-resistant pathogens worldwide, mainly in environmental samples, which are associated with One Health framework.

Molecular characterization of multidrug-resistant Shiga toxin-producing Escherichia coli harboring antimicrobial resistance genes obtained from a farmhouse

Shiga toxin-producing Escherichia coli (STEC) colonize the gastrointestinal tract of animals; however, STEC may also cause severe diarrheal diseases. Food-producing animals have been acting as reservoirs and disseminators of multidrug-resistant (MDR) bacteria and antimicrobial resistance genes (ARGs); however, there are few studies characterizing molecularly bacterial isolates from sheep. Therefore, this study aimed to characterize E. coli isolates obtained from feces of sheep in a Brazilian farmhouse. A total of 14 MDR E. coli isolates were obtained from 100 feces samples, six of which were classified as non-O157 STEC (stx1, stx2 and ehxA). MDR E. coli isolates presented different ARGs [bla_CTX-M-Gp9, bla_CMY, bla_SHV, qnrS, oqxB, aac(6')-Ib, tet(A), tet(B), tet(C), sul1, sul2, and cmlA] and plasmids (IncI1, IncF_repB, IncFIB, IncFIA, IncHI1, IncK, and ColE-like). In addition, mutations in the quinolone-resistance determining region of GyrA (Ser83Leu; Asp87Asn) and ParC (Glu84Asp) were detected. PFGE showed a high genetic diversity (30.9 to 83.9%) and thirteen STs were detected (ST25, ST48, ST155, ST162, ST642, ST1247, ST1518, ST1725, ST2107, ST2522, ST3270, ST5036, and ST7100). Subtyping of the fimH gene showed seven fimH-type (25, 32, 38, 41, 54, 61, and 366). The results found in the present study showed high genetic diversity among MDR ARGs-producing E. coli obtained from a farmhouse. This study reports for the first time, the presence of MDR STEC and non-STEC belonging to ST25, ST162, ST642, ST1247, ST1518, ST1725, ST2107, ST3270, ST5036, and ST7100 in sheep, and contributes to the surveillance studies associated with One Health concept.

Association of blaNDM-1 with blaKPC-2 and aminoglycoside-modifying enzyme genes among Klebsiella pneumoniae, Proteus mirabilis and Serratia marcescens clinical isolates in Brazil

OBJECTIVES

Carbapenemase-producing Enterobacterales are frequently involved in healthcare-associated infections worldwide. The objectives of this study were to investigate (i) the frequency of the main genes encoding carbapenemases, 16S rRNA methylases and aminoglycoside-modifying enzymes (AMEs) as well as the mcr gene and (ii) the clonal relationship of enterobacteria isolates resistant to carbapenems and aminoglycosides from colonisation and infection in patients from hospitals in northeastern Brazil.

METHODS

Antimicrobial susceptibility was determined using an automated VITEK®2 system. Presence of carbapenemase, AME and 16S rRNA methylase genes as well as the mcr gene was determined by PCR and amplicon sequencing. Genetic variability was determined by ERIC-PCR.

RESULTS

A total of 35 isolates resistant to carbapenems and aminoglycosides were selected for this study. Klebsiella pneumoniae was most common (45.7%), followed by Proteus mirabilis (28.6%) and Serratia marcescens (25.7%). AME genes were found in 97.1% of isolates, most commonly aph(3')-VI and aac(6')-Ib. The bla_NDM-1 and bla_KPC-2 genes were detected in 25.7% and 88.6% of isolates, respectively; five isolates harboured these genes concomitantly. According to the literature, this is the first report of the association of bla_NDM-1 and bla_KPC-2 in P. mirabilis and S. marcescens in Brazil. The isolates showed a multiclonal profile by ERIC-PCR.

CONCLUSION

The emergence of bla_NDM-1 associated with bla_KPC-2 and AME genes in K. pneumoniae, P. mirabilis and S. marcescens isolates with a multiclonal profile is of concern as this limits therapeutic options. These results should alert medical authorities to establish rigorous detection methods to reduce the spread of these antimicrobial resistance genes.

Characterization of non-O157 Shiga toxin-producing Escherichia coli (STEC) obtained from feces of sheep in Brazil

Shiga toxin-producing Escherichia coli (STEC) are zoonotic pathogens and may induce severe diarrheagenic diseases in humans and other animals. Non-O157 STEC have been emerging as important pathogens causing outbreaks worldwide. Bacterial resistance to antimicrobials has become a global public health problem, which involves different ecological spheres, including animals. This study aimed to characterize the resistance to antimicrobials, plasmids and virulence, as well as the serotypes and phylogenetic groups in E. coli isolated from sheep in Brazil. A total of 57 isolates were obtained and showed different antimicrobial resistance profiles. Nineteen isolates presented acquired antimicrobial resistance genes (ARGs) (bla_CTX-M-Gp9, qnrB, qnrS, oqxB, oqxA, tetA, tetB, tetC, sul1 and sul2) and plasmid families (F, FIA, FIB, I1, K, HI1 and ColE-like). The stx1, stx2 and ehxA virulence genes were detected by PCR, being 50 isolates (87.7%) classified as STEC. A great diversity of serotypes was detected, being O176:HNM the most predominant. Phylogenetic group E was the most prevalent, followed by B1, A and B2. To the best of our knowledge, this is the first report in the world of bla_CTX-M-Gp9 (O75, O114, O100, O128ac and O176 serogroups), qnrB and oqxB genes in non-O157 STEC in healthy sheep. The results obtained in the present study call attention to the monitoring of antimicrobial-resistant non-O157 STEC harboring acquired ARGs worldwide and indicate a zoonotic risk due to the profile of virulence, resistance and serotype found.

Emergence of bla NDM-1 associated with the aac(6')-Ib-cr, acrB, cps, and mrkD genes in a clinical isolate of multi-drug resistant Klebsiella pneumoniae from Recife-PE, Brazil

INTRODUCTION

The emergence of New Delhi metallo-β-lactamase (NDM) is concernig because it reduces the antibiotic therapy options for bacterial infections.

METHODS

Resistant and virulent genes from an isolate of Klebsiella pneumoniae derived from a patient with sepsis in a hospital in Recife-PE, Brazil, were investigated using PCR and DNA sequencing.

RESULTS

bla NDM-1, aac(6')-Ib-cr and acrB resistance genes, and cps and mrkD virulence genes were detected.

CONCLUSIONS

To our knowledge, this is the first report on bla NDM-1 in Recife-PE. This detection alerts researchers to the need to control the spread of bla NDM-1 resistance gene by this bacterium in Brazil.

Dissemination of Genes Encoding Aminoglycoside-Modifying Enzymes and armA Among Enterobacteriaceae Isolates in Northwest Iran

INTRODUCTION

Enzymatic inactivation is one of the most important mechanisms of resistance to aminoglycosides. The aim of this study was to investigate the prevalence of armA and diversity of the genes encoding aminoglycoside-modifying enzymes (AMEs) and their associations with resistance phenotypes in Enterobacteriaceae isolates.

METHODS

Three hundred and seven Enterobacteriaceae isolates were collected from five hospitals in northwest Iran. The disk diffusion method for amikacin, gentamicin, tobramycin, kanamycin, and streptomycin, as well as the minimum inhibitory concentration for amikacin, gentamicin, tobramycin, and kanamycin were done for susceptibility testing. Thirteen AME genes and armA methylase were screened using the PCR and sequencing assays.

RESULTS

Two hundred and twenty (71.7%) of isolates were resistant to aminoglycosides and 155 (70.5%) of them were positive for aminoglycoside resistance genes. The most prevalent AME genes were ant(3″)-Ia and aph(3″)-Ib with the frequency 35.9% and 30.5%, respectively. Also, 21 (9.5%) of resistant isolates were positive for armA methylase gene.

CONCLUSIONS

The prevalence of resistance to aminoglycoside is high and AME genes frequently are disseminated in Enterobacteriaceae isolates. There is an association between phenotypic resistance and the presence of some aminoglycoside genes.

Association between the Presence of Aminoglycoside-Modifying Enzymes and In Vitro Activity of Gentamicin, Tobramycin, Amikacin, and Plazomicin against Klebsiella pneumoniae Carbapenemase- and Extended-Spectrum-β-Lactamase-Producing Enterobacter Species

We compared the in vitro activities of gentamicin (GEN), tobramycin (TOB), amikacin (AMK), and plazomicin (PLZ) against 13 Enterobacter isolates possessing both Klebsiella pneumoniae carbapenemase and extended-spectrum β-lactamase (KPC+/ESBL+) with activity against 8 KPC+/ESBL-, 6 KPC-/ESBL+, and 38 KPC-/ESBL- isolates. The rates of resistance to GEN and TOB were higher for KPC+/ESBL+ (100% for both) than for KPC+/ESBL- (25% and 38%, respectively), KPC-/ESBL+ (50% and 17%, respectively), and KPC-/ESBL- (0% and 3%, respectively) isolates. KPC+/ESBL+ isolates were more likely than others to possess an aminoglycoside-modifying enzyme (AME) (100% versus 38%, 67%, and 5%; P = 0.007, 0.06, and <0.0001, respectively) or multiple AMEs (100% versus 13%, 33%, and 0%, respectively; P < 0.01 for all). KPC+/ESBL+ isolates also had a greater number of AMEs (mean of 4.6 versus 1.5, 0.9, and 0.05, respectively; P < 0.01 for all). GEN and TOB MICs were higher against isolates with >1 AME than with ≤1 AME. The presence of at least 2/3 of KPC, SHV, and TEM predicted the presence of AMEs. PLZ MICs against all isolates were ≤4 μg/ml, regardless of KPC/ESBL pattern or the presence of AMEs. In conclusion, GEN and TOB are limited as treatment options against KPC+ and ESBL+ Enterobacter PLZ may represent a valuable addition to the antimicrobial armamentarium. A full understanding of AMEs and other aminoglycoside resistance mechanisms will allow clinicians to incorporate PLZ rationally into treatment regimens. The development of molecular assays that accurately and rapidly predict antimicrobial responses among KPC- and ESBL-producing Enterobacter spp. should be a top research priority.

Providencia stuartii Isolates from Greece: Co-Carriage of Cephalosporin (blaSHV-5, blaVEB-1), Carbapenem (blaVIM-1), and Aminoglycoside (rmtB) Resistance Determinants by a Multidrug-Resistant Outbreak Clone

Providencia stuartii has emerged as an important nosocomial pathogen. We describe an outbreak due to a multidrug-resistant strain over a 4-month period in a critical care unit in Athens. Molecular typing revealed each of the isolates to be clonally related with coresistance to cephalosporins, carbapenems, aminoglycosides, and quinolones. Each isolate contained a 220-kb multi-replicon (IncA/C and IncR) conjugative plasmid encoding TEM-1, SHV-5, VEB-1, and VIM-1 β-lactamases and the 16S rDNA methylase RmtB. Antimicrobial therapy was unsuccessful in 3 of 6 cases, and resistance was readily transmissible to susceptible strains of Escherichia coli by transformation and conjugation. This highlights the clinical importance of P. stuartii and its ability to disseminate critical resistance determinants to other bacterial pathogens.

Frequency of Aminoglycoside-Modifying Enzymes and ArmA Among Different Sequence Groups of Acinetobacter baumannii in Iran

We evaluated aminoglycoside resistance in 87 Acinetobacter baumannii strains isolated from four hospitals located in the North West region of Iran and typed them in sequence groups (SGs) using trilocus sequence-based scheme to compare their clonal relationships with international clones. Resistance toward aminoglycosides was assayed by minimum inhibitory concentration (MIC) and presence of aminoglycoside-modifying enzymes (AMEs), and ArmA-encoding genes were evaluated in different SGs. The majority of isolates belonged to SG1 (39%), SG2 (33.3%), and SG3 (12.6%), whereas the remaining ones were assigned to six novel variants of SGs. MIC determination revealed netilmicin as the most and kanamycin as the least active aminoglycosides against all groups. Among the varied SGs, isolates of SG2 showed more susceptibility toward all tested aminoglycosides. APH(3'')-VIa-encoding gene was predominant in SG1 (47%), SG2 (62%), and SG6-9 (100%). However, AAC(3')-Ia (100%) and ANT(2')-Ia (90.9%) were the dominant AMEs in SG3. There was significant association between harboring of aminoglycoside resistance genes and specific aminoglycosides: gene encoded by APH(3')-VIa was allied to resistance against amikacin and kanamycin, whereas ANT(2')-Ia was related to the resistance toward gentamicin and tobramycin in SG2. In SG1, tobramycin resistance was correlated with harboring of AAC(6')-Ib. Screening of armA demonstrated the presence of this gene in SG1 (58.8%), SG2 (10.3%), as well as SG3 (9%). Our results revealed definite correlation between the phenotypes and genotypes of aminoglycoside resistance in different clonal lineages of A. baumannii.

ESBL-producing Enterobacteriaceae in 24 neonatal units and associated networks in the south of England: no clustering of ESBL-producing Escherichia coli in units or networks

OBJECTIVES

The objectives of this study were to characterize ESBL-producing Enterobacteriaceae present in 24 neonatal units (NNUs) in eight networks participating in a multicentre probiotic study and to test the hypothesis that specific strains would cluster within individual units and networks.

METHODS

We performed analysis of stool samples for the presence of ESBL-producing Enterobacteriaceae at 2 weeks post-natal age and 36 weeks post-menstrual age. ESBL-producing Enterobacteriaceae were characterized and typed using molecular methods.

RESULTS

ESBL-producing Enterobacteriaceae (n = 71) were isolated from 67/1229 (5.5%) infants from whom we received a sample at either sampling time or both sampling times, and from infants in 18 (75%) of the 24 recruiting NNUs. Thirty-three Escherichia coli, 23 Klebsiella spp. and 6 Enterobacter spp. strains were characterized. ESBL-producing E. coli were all distinguishable within individual NNUs by antibiotic resistance genotype, serogroup (O25b), phenotype, phylotype or ST. Ten of the 33 were ST131 and 9 of the 10 ST131 isolates were ciprofloxacin resistant. Seven of the 10 ST131 isolates carried genes encoding CTX-M group 1 enzymes. ST131 isolates were isolated from centres within five of the eight NNU networks. There were clusters of indistinguishable ESBL-producing Klebsiella and Enterobacter isolates associated with specific NNUs.

CONCLUSIONS

Strains of E. coli ST131 were distributed across neonatal networks in the south of England. There was no evidence of clustering of clonally related ESBL-producing E. coli strains, by contrast with Klebsiella spp. and Enterobacter spp., which did cluster within units. The possibility that ESBL-producing E. coli strains are spread by vertical transmission requires further investigation.

Application of the multifactor dimensionality reduction method in evaluation of the roles of multiple genes/enzymes in multidrug-resistant acquisition in Pseudomonas aeruginosa strains

Multidrug-resistant Pseudomonas aeruginosa (MDRPA) infections are major threats to healthcare-associated infection control and the intrinsic molecular mechanisms of MDRPA are also unclear. We examined 348 isolates of P. aeruginosa, including 188 MDRPA and 160 non-MDRPA, obtained from five tertiary-care hospitals in Guangzhou, China. Significant correlations were found between gene/enzyme carriage and increased rates of antimicrobial resistance (P < 0·01). gyrA mutation, OprD loss and metallo-β-lactamase (MBL) presence were identified as crucial molecular risk factors for MDRPA acquisition by a combination of univariate logistic regression and a multifactor dimensionality reduction approach. The MDRPA rate was also elevated with the increase in positive numbers of those three determinants (P < 0·001). Thus, gyrA mutation, OprD loss and MBL presence may serve as predictors for early screening of MDRPA infections in clinical settings.

Limited genetic diversity and extensive antimicrobial resistance in clinical isolates of Acinetobacter baumannii in north-east Iran

This study determined the mechanisms and patterns of antimicrobial resistance among the isolates obtained from different wards of a teaching hospital in the city of Mashhad in north-east Iran. Between January 2012 and the end of June 2012, 36 isolates of Acinetobacter baumannii were collected from different wards of Ghaem Hospital. Antimicrobial susceptibility testing and epsilometer testing (E-test) were performed. The genetic resistance determinants of A, B and D classes of β-lactamases, aminoglycoside modifying enzymes (AMEs), efflux pumps and ISAba1 elements were assessed by PCR. Repetitive extragenic palindromic element (REP)-PCR was performed to find the genetic relatedness of the isolates. Colistin was the most effective antibiotic of those tested, where all isolates were susceptible. E-test results revealed high rates of resistance to imipenem, ceftazidime and ciprofloxacin. The majority of isolates (97  %) were multidrug-resistant. OXA-51, OXA-23 and tetB genes were detected in all isolates, but OXA-58, IMP and tetA were not detected. The prevalence of OXA-24, bla(TEM), bla(ADC), bla(VIM) and adeB were 64, 95, 61, 64 and 86  %, respectively. ISAba1 was found to be inserted into the 5' end of OXA-23 in 35 isolates (97  %). Of the AMEs, aadA1 (89  %) was the most prevalent, followed by aphA1 (75  %). The band patterns reproduced by REP-PCR showed that 34 out of 36 isolates belonged to one clone and two singletons were identified. The results confirmed that refractory A. baumannii isolates were widely distributed and warned the hospital infection control team to exert strict measures to control the infection. An urgent surveillance system should be implemented.

Carbapenem-resistant Klebsiella pneumoniae strains exhibit diversity in aminoglycoside-modifying enzymes, which exert differing effects on plazomicin and other agents

We measured in vitro activity of plazomicin, a next-generation aminoglycoside, and other aminoglycosides against 50 carbapenem-resistant Klebsiella pneumoniae strains from two centers and correlated the results with the presence of various aminoglycoside-modifying enzymes (AMEs). Ninety-four percent of strains were sequence type 258 (ST258) clones, which exhibited 5 ompK36 genotypes; 80% and 10% of strains produced Klebsiella pneumoniae carbapenemase 2 (KPC-2) and KPC-3, respectively. Ninety-eight percent of strains possessed AMEs, including AAC(6')-Ib (98%), APH(3')-Ia (56%), AAC(3)-IV (38%), and ANT(2")-Ia (2%). Gentamicin, tobramycin, and amikacin nonsusceptibility rates were 40, 98, and 16%, respectively. Plazomicin MICs ranged from 0.25 to 1 μg/ml. Tobramycin and plazomicin MICs correlated with gentamicin MICs (r = 0.75 and 0.57, respectively). Plazomicin exerted bactericidal activity against 17% (1× MIC) and 94% (4× MIC) of strains. All strains with AAC(6')-Ib were tobramycin-resistant; 16% were nonsusceptible to amikacin. AAC(6')-Ib combined with another AME was associated with higher gentamicin, tobramycin, and plazomicin MICs than AAC(6')-Ib alone (P = 0.01, 0.0008, and 0.046, respectively). The presence of AAC(3)-IV in a strain was also associated with higher gentamicin, tobramycin, and plazomicin MICs (P = 0.0006, P < 0.0001, and P = 0.01, respectively). The combination of AAC(6')-Ib and another AME, the presence of AAC(3)-IV, and the presence of APH(3')-Ia were each associated with gentamicin resistance (P = 0.0002, 0.003, and 0.01, respectively). In conclusion, carbapenem-resistant K. pneumoniae strains (including ST258 clones) exhibit highly diverse antimicrobial resistance genotypes and phenotypes. Plazomicin may offer a treatment option against strains resistant to other aminoglycosides. The development of molecular assays that predict antimicrobial responses among carbapenem-resistant K. pneumoniae strains should be a research priority.

Co-occurrence of carbapenem and aminoglycoside resistance genes among multidrug-resistant clinical isolates of Acinetobacter baumannii from Cracow, Poland

Background

Acinetobacter baumannii is a significant hospital pathogen, possessing a considerable degree of antimicrobial resistance. A. baumannii resistance to carbapenems and aminoglycosides is mostly conferred by class D OXA carbapenemases and aminoglycoside-modifying enzymes, respectively. The aim of this study was to determine the prevalence of selected genes encoding OXA carbapenemases and aminoglycoside-modifying enzymes in multidrug-resistant strains of A. baumannii.

Material/Methods

The study included 61 carbapenem-resistant and aminoglycoside-nonsusceptible A. baumannii isolates, collected between 2009 and 2011 in Cracow, Poland. Selected resistance genes, including: bla_OXA-51-like, bla_OXA-23-like, bla_OXA-40-like, bla_OXA-58-like, aac(6′)-Ih, aac(3)-Ia, aac(3)-IIa, aac(6′)-Ib, aph(3′)-Ia and aph(3′)-VI, were detected by PCR method.

Results

The bla_OXA-51-like genes were detected in all isolates, while acquired carbapenemase encoding genes were found in 96.7% of tested strains. Presence of bla_OXA-40-like and bla_OXA-23-like genes was observed among 65.6% and 27.9% of isolates, respectively. Assayed aminoglycoside resistance genes were found to harbor 98.4% of isolates. Among tested strains, we observed the following percentages of resistance determinants: aac(3)-Ia – 78.7%, aph(3′)-VI – 78.7% and aph(3′)-Ia – 27.9%. Analysis of co-occurrence of carbapenem and aminoglycoside resistance genes revealed the highest percentage of strains possessing bla_OXA-40-like, aac(3)-Ia, and aph(3′)-VI genes (44.3%).

Conclusions

The bla_OXA-40-like and aac(3)-Ia/aph(3′)-VI were the most prevalent genes encoding acquired OXA carbapenemases and aminoglycoside-modifying enzymes, respectively, among A. baumannii strains in Cracow, Poland. Genes conferring resistance to carbapenems and aminoglycosides coexisted in the clinical strains of A. baumannii. The phenomenon of A. baumannii resistance indicates the necessity of monitoring for the presence of the resistance genes.

Molecular epidemiology of carbapenem-resistant Pseudomonas aeruginosa clinical strains isolated from western Algeria between 2009 and 2012

Infections caused by carbapenem-resistant Pseudomonas aeruginosa strains represent a major therapeutic and epidemiological problem. The aim of this study was to characterize carbapenem resistance in 89 clinical strains of P. aeruginosa isolated from three hospitals in western Algeria between October 2009 and November 2012. Minimum inhibitory concentrations (MICs) of imipenem were determined by the Etest method. Screening for metallo-β-lactamase (MβL) was performed using Etest MβL strips, and a PCR was conducted to detect carbapenemase-encoding genes. The amplification of the oprD gene followed by a sequencing reaction was performed for all strains resistant to imipenem. The clonality of 53 P. aeruginosa strains was demonstrated using multilocus sequence typing (MLST). Among the 89 isolates, 35 (39.33%) were found to be resistant to IMP (MICs ≥16 μg/ml). The blaVIM-2 gene was detected in two strains. The remaining imipenem-resistant isolates showed the presence of oprD mutations. The MLST analysis differentiated strains into various clones and the strains from the same clone had an identical sequence of the oprD gene. We report the second detection in 2010 of blaVIM-2 in Algerian P. aeruginosa strains. We also found that oprD mutations were the major determinant of high-level imipenem resistance. We demonstrate that these oprD mutations can be used as a tool to study the clonality in P. aeruginosa isolates.

Insertion sequence disruption of adeR and ciprofloxacin resistance caused by efflux pumps and gyrA and parC mutations in Acinetobacter baumannii

Acinetobacter baumannii is a pathogenic bacterium responsible for a wide range of infections in immunocompromised patients. This study examined the role of insertional inactivation of the adeR gene and its effect on adeABC gene expression along with characterisation of the gyrA and parC mutations involved in ciprofloxacin resistance in three A. baumannii clinical isolates and their derivatives. Primers designed for the detection of adeSRABC detected the presence of ISAba16, which disrupted the adeR gene in strain Ab12M, and ISAba1, which disrupted the same gene in strains Ab18 and Ab209. A second copy of ISAba1 was detected upstream of the adeA gene in Ab209 leading to AdeABC pump expression. AdeIJK pump expression was seen in all of the isolates but was not as significant as AdeABC expression. Minimum inhibitory concentrations of ciprofloxacin were ≥256 mg/L for all of the isolates and a decrease of ≥8-fold was seen following addition of the efflux pump inhibitor 1-(1-naphthylmethyl)-piperazine. Fluorometric analysis also demonstrated active efflux, with upregulation of adeIJK and some genes of the adeABC operon in some strains. Sequencing of the quinolone resistance-determining region of the gyrA and parC genes revealed a Ser83→Leu change in the gyrA gene and a novel change of Ser80→Trp in the parC gene of Ab12, Ab12M and Ab209; in Ab18 there was a Ser80→Leu change in parC. This study shows the multifactorial contribution of different mechanisms in A. baumannii leading to ciprofloxacin resistance.

Complete nucleotide sequences of blaKPC-4- and blaKPC-5-harboring IncN and IncX plasmids from Klebsiella pneumoniae strains isolated in New Jersey

Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae have emerged as major nosocomial pathogens. bla(KPC), commonly located on Tn4401, is found in Gram-negative bacterial strains, with the two most common variants, bla(KPC-2) and bla(KPC-3), identified in plasmids with diverse genetic backgrounds. In this study, we examined bla(KPC-4)- and bla(KPC-5)-bearing plasmids recovered from two K. pneumoniae strains, which were isolated from a single New Jersey hospital in 2005 and 2006, respectively. IncN plasmid pBK31551 is 84 kb in length and harbors bla(KPC-4), bla(TEM-1), qnrB2, aac(3)-Ib, aph(3')-I, qacF, qacEΔ1, sul1, and dfrA14, which confer resistance to β-lactams, quinolones, aminoglycosides, quaternary ammonium compounds, and co-trimoxazole. The conserved regions within pBK31551 are similar to those of other IncN plasmids. Surprisingly, analysis of the Tn4401 sequence revealed a large IS110- and Tn6901-carrying element (8.3 kb) inserted into the istA gene, encoding glyoxalase/bleomycin resistance, alcohol dehydrogenase, and S-formylglutathione hydrolase. Plasmid pBK31567 is 47 kb in length and harbors bla(KPC-5), dfrA5, qacEΔ1, and sul1. pBK31567 belongs to a novel IncX subgroup (IncX5) and possesses a highly syntenic plasmid backbone like other IncX plasmids; however, sequence similarity at the nucleotide level is divergent. The bla(KPC-5) gene is carried on a Tn4401 element and differs from the genetic environment of bla(KPC-5) described in Pseudomonas aeruginosa strain P28 from Puerto Rico. This study underscores the genetic diversity of multidrug-resistant plasmids involved in the spread of bla(KPC) genes and highlights the mobility and plasticity of Tn4401. Comparative genomic analysis provides new insights into the evolution and dissemination of KPC plasmids belonging to different incompatibility groups.

Emergence of 16S rRNA methylase gene armA and cocarriage of bla(IMP-1) in Pseudomonas aeruginosa isolates from South Korea

Of the 100 multidrug-resistant Pseudomonas aeruginosa isolates from a Korean hospital, 14 isolates that were resistant to all aminoglycosides tested carried 16S rRNA methylase gene armA. Fourteen armA-positive isolates were classified into 8 pulsotypes. Seven armA-positive isolates cocarried bla(IMP-1). This study is the first report of occurrence of armA in P. aeruginosa.

Aminoglycoside resistance and susceptibility testing errors in Acinetobacter baumannii-calcoaceticus complex

Antimicrobial resistance is depleting the pharmacopeia of agents clinically useful against Gram-negative bacilli. As the number of active agents diminishes, accurate susceptibility testing becomes critical. We studied the susceptibilities of 107 isolates of the Acinetobacter baumannii-calcoaceticus complex to amikacin, gentamicin, and tobramycin using disk diffusion, Etest, as well as the Phoenix, Vitek 2, and MicroScan automated systems, and compared the results to those obtained by broth microdilution. Genes encoding aminoglycoside-modifying enzymes (AMEs) were detected by multiplex PCR, and clonal relationships were determined by pulsed-field gel electrophoresis. Tobramycin was the most active aminoglycoside (27.1% of isolates were susceptible). Disk diffusion and Etest tended to be more accurate than the Vitek 2, Phoenix, and MicroScan automated systems; but errors were noted with all methods. The Vitek 2 instrument incorrectly reported that more than one-third of the isolates were susceptible to amikacin (a very major error). Isolates were polyclonal, with 26 distinct strains, and carried multiple AME genes unrelated to the strain type. The presence of the ant(2")-Ia gene was statistically associated with resistance to each aminoglycoside. The AME genotype accounted for the resistance profile observed in a minority of isolates, suggesting the involvement of multiple resistance mechanisms. Hospital pharmacy records indicated the preferential use of amikacin over other aminoglycosides in the burn intensive care unit, where aminoglycoside resistance is prevalent. The resistance in that unit did not correlate with a predominant strain, AME genotype, or total annual aminoglycoside consumption. Susceptibility to tobramycin increased, even though susceptible isolates carried AME genotypes predicting the inactivation of tobramycin. Determination of the relative contribution of multiple concurrent resistance mechanisms may improve our understanding of aminoglycoside resistance in the Acinetobacter baumannii-calcoaceticus complex.

Genetic basis of resistance to aminoglycosides in Acinetobacter spp. and spread of armA in Acinetobacter baumannii sequence group 1 in Korean hospitals

A total of 75 Acinetobacter isolates resistant to all available aminoglycosides obtained from 2 Korean hospitals were studied for the genetic basis of resistance to aminoglycosides. The MIC(50) and MIC(90) of Acinetobacter baumannii isolates (n = 61) to amikacin, gentamicin, isepamycin spectinomycin, streptomycin, and tobramycin were higher than those of Acinetobacter genomic species 13TU isolates (n = 14). Genes encoding aminoglycoside-modifying enzymes, ant(3")-Ia, aac(6')-Ib, aph(3')-1a, aac(3)-Ia, and aph(3')-VI, and 16S ribosomal RNA (rRNA) methylase armA were detected. ant(3")-Ia and aac(6')-Ib were commonly detected in both Acinetobacter spp., but armA and aph(3")-Ia were only detected in A. baumannii. armA was located on the plasmids. A. baumannii isolates carrying armA were classified into 7 pulsotypes but belonged to sequence group 1. The combination of aminoglycoside-modifying enzymes is responsible for the moderate-level resistance to aminoglycosides in Acinetobacter genomic species 13TU, whereas armA is responsible for the high-level resistance to aminoglycosides in A. baumannii sequence group 1.

The aac(6')Ib gene in Proteus mirabilis strains resistant to aminoglycosides

The aim of this study was to evaluate the presence of aac(6')-Ib gene conferring resistance to aminoglycosides in Proteus mirabilis strains. Five isolates had aac(6')-Ib gene. In one case the gene was no-expressed. Three isolates were resistant to all aminoglycosides and minimum inhibitory concentrations were > or = 256 microg/ml. Additionally, all positive strains were resistant to tetracycline and ciprofloxacin.

Acinetobacter baumannii: an emerging multidrug-resistant threat

Amid the recent attention focused on the growing impact of methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa infections, the pathogen Acinetobacter baumannii has been stealthily gaining ground as an agent of serious nosocomial and community-acquired infection. Historically, Acinetobacter spp. have been associated with opportunistic infections that were rare and of modest severity; the last two decades have seen an increase in both the incidence and seriousness of A. baumannii infection, with the main targets being patients in intensive-care units. Although this organism appears to have a predilection for the most vulnerable patients, community-acquired A. baumannii infection is an increasing cause for concern. The increase in A. baumannii infections has paralleled the alarming development of resistance it has demonstrated. The persistence of this organism in healthcare facilities, its inherent hardiness and its resistance to antibiotics results in it being a formidable emerging pathogen. This review aims to put into perspective the threat posed by this organism in hospital and community settings, describes new information that is changing our view of Acinetobacter virulence and resistance, and calls for greater understanding of how this multifaceted organism came to be a major pathogen.

Correlation of antimicrobial resistance with beta-lactamases, the OmpA-like porin, and efflux pumps in clinical isolates of Acinetobacter baumannii endemic to New York City

Acinetobacter baumannii strains resistant to all beta-lactams, aminoglycosides, and fluoroquinolones have emerged in many medical centers. Potential mechanisms contributing to antimicrobial resistance were investigated in 40 clinical isolates endemic to New York City. The isolates were examined for the presence of various beta-lactamases, aminoglycoside-modifying enzymes, and mutations in gyrA and parC. Expression of the genes encoding the beta-lactamase AmpC, the efflux systems AdeABC and AbeM, and the OmpA-like porin was also examined by real-time reverse transcription-PCR. No VIM, IMP, KPC, OXA-23-type, OXA-24-type, or OXA-58 beta-lactamases were detected, although several isolates had acquired bla(SHV-5). Most cephalosporin-resistant isolates had increased levels of expression of ampC and/or had acquired bla(SHV-5); however, isolates without these features still had reduced susceptibility to cefepime that was mediated by the AdeABC efflux system. Although most isolates with ISAba1 upstream of the bla(OXA-51)-like carbapenemase gene were resistant to meropenem, several remained susceptible to imipenem. The presence of aminoglycoside-modifying enzymes and gyrase mutations accounted for aminoglycoside and fluoroquinolone resistance, respectively. The increased expression of adeABC was not an important contributor to aminoglycoside or fluoroquinolone resistance but did correlate with reduced susceptibility to tigecycline. The expression of abeM and ompA and phenotypic changes in OmpA did not correlate with antimicrobial resistance. A. baumannii has become a well-equipped nosocomial pathogen; defining the relative contribution of these and other mechanisms of antimicrobial resistance will require further investigation.

DNA microarray-based detection of nosocomial pathogenic Pseudomonas aeruginosa and Acinetobacter baumannii

Infection by nosocomial pathogenic bacteria is increasingly becoming a major threat to the patients in the hospital. We have developed a diagnostic DNA microarray for the detection of two important nosocomial pathogens, Pseudomonas aeruginosa and Acinetobacter baumannii. The diagnostic DNA microarray contains the species-specific probes of 15mer oligonucleotides designed based on the sequences of 23S ribosomal DNA. The performance of DNA microarray in diagnosing P. aeruginosa and A. baumannii was evaluated using reference bacteria as well as clinical specimens such as blood, stool, pus, sputum, urine and cerebrospinal fluid. Using this DNA microarray, A. baumannii could be successfully detected in 11 out of 13 clinical specimens, thus giving the sensitivity of 84.6% with the specificity of 100% and the positive predictive value of 100%. P. aeruginosa could also be detected in 25 out of 26 clinical specimens, showing the sensitivity of 96.2%, the specificity of 100%, and the positive predictive value of 100%. These results suggest that two nosocomial pathogens, P. aeruginosa and A. baumannii, can be efficiently diagnosed by using the DNA microarray developed in this study.

Molecular detection of antimicrobial resistance

The determination of antimicrobial susceptibility of a clinical isolate, especially with increasing resistance, is often crucial for the optimal antimicrobial therapy of infected patients. Nucleic acid-based assays for the detection of resistance may offer advantages over phenotypic assays. Examples are the detection of the methicillin resistance-encoding mecA gene in staphylococci, rifampin resistance in Mycobacterium tuberculosis, and the spread of resistance determinants across the globe. However, molecular assays for the detection of resistance have a number of limitations. New resistance mechanisms may be missed, and in some cases the number of different genes makes generating an assay too costly to compete with phenotypic assays. In addition, proper quality control for molecular assays poses a problem for many laboratories, and this results in questionable results at best. The development of new molecular techniques, e.g., PCR using molecular beacons and DNA chips, expands the possibilities for monitoring resistance. Although molecular techniques for the detection of antimicrobial resistance clearly are winning a place in routine diagnostics, phenotypic assays are still the method of choice for most resistance determinations. In this review, we describe the applications of molecular techniques for the detection of antimicrobial resistance and the current state of the art.