High-Level Resistance to Erythromycin and Tetracycline and Dissemination of Resistance Determinants among Clinical Enterococci in Iran.

OBJECTIVES: The purpose of this study was to investigate the distribution pattern of genes responsible for erythromycin and tetracycline resistance and their association with resistance phenotypes in enterococcus isolates. MATERIALS AND METHODS: Eighty-six Enterococcus faecalis and 26 E. faecium isolates were collected from 2 hospitals in Kerman, Iran. Minimum inhibitory concentration of erythromycin and tetra-cycline was determined and then genes encoding resistance to erythromycin - erm (A-C), mef, and msr - and tetracycline - tet (M), tet (O), tet (S), tet (K), and tet (L) - were investigated. RESULTS: In all resistant isolates (n = 72, 64%), high-level resistance to both tested antibiotics was found. The most prevalent erm gene was erm (B) (77.7%), followed by erm (A) (15.2%) and erm (C) (8.3%). Genes mediating erythromycin efflux were detected in 70.8% (mef) and 9.7% (msr) of resistant isolates. Regarding tetracycline, tet (M) was detected at the highest rate (50%), followed by tet (O) (31%) and tet (S) (11%). Export of tetracycline was found in 31% (tet (K)) and 12% (tet (L)) of isolates. CONCLUSION: A high prevalence of high-level resistance to both erythromycin and tetracycline was documented. Alterations at the ribosomal level was more frequently detected in erythromycin and tetracycline resistance than efflux systems. Concurrent resistance mechanisms were more involved in resistance to erythromycin than tetracycline.

The emergence of the hypervirulent Klebsiella pneumoniae (hvKp) strains among circulating clonal complex 147 (CC147) harbouring blaNDM/OXA-48 carbapenemases in a tertiary care center of Iran.

BACKGROUND: Klebsiella pneumoniae is a public health concern because of its ability to develop multidrug resistance and hypervirulent genotypes, of those capsular types K1 and K2 cause community and nosocomial life-threatening infections. This study aimed to determine the antibiotic susceptibility patterns and genotypic traits of a collection of Klebsiella spp. isolates. Furthermore, the clonal relatedness of blaNDM producing strains was investigated. METHODS: During a 19-months  surveillance study, 122 Klebsiella spp. isolates were cultured from extraintestinal specimens of patients admitted to the tertiary referral hospital in Semnan, Iran. Isolates were identified using biochemical tests and subjected to determination of phylogroups, capsular types and virulence/resistance genes content. Hypervirulent K. pneumoniae (hvKp) strains were detected genotypically, and Enterobacterial Repetitive Intergenic Consensus (ERIC)-PCR fingerprinting was used to determine the clonality of blaNDM producing strains. RESULTS: Multidrug resistant phenotype was detected in 75 (61.5%) isolates and amikacin was found as the most potent antibiotic with the susceptibility rate of 85.2%. The carbapenemase genes were detected in 45 (36.8%) strains, including 21 (17.2%) blaOXA-48, 7 (5.6%) blaNDM-1, 14 (11.4%) blaNDM-1/OXA-48 and 3 (2.4%) blaIMP- carrying strains, while 55 (45.08%) isolates showed carbapenem resistant phenotype. The first blaNDM-1 carrying strain was cultured from a sputum specimen on March 2015, while the last positive one was recovered from blood culture on September 2016. Most of the isolates (80.3%) belonged to phylogroup I, and blaNDM-1 was identified among all three phylogroups. The ERIC-PCR clustered the 101 blaNDM negative and 21 blaNDM-1 positive isolates into 25 and five clusters, respectively, and the latter group belonged to clonal complex 147 (CC147). One K1 and 15 K2 blaNDM-1 negative isolates were detected, of those three strains were identified as hvKp. Five K2 positive strains, including four blaOXA-48 producer and one hvKp sequence type 86 (ST86) were carbapenem resistant. Among carbapenem resistant isolates, CC147 strains harboured higher rates of siderophores iutA and ybtS. CONCLUSION: The present findings showed a hospital circulation of CC147 blaNDM-1 or blaNDM-1/OXA-48 producing strains, disseminated in different wards. The hvKp/ST86 strain expressing K2 capsular type and carbapenem resistant phenotype wasn't reported from Iran so far. So, it seems that we must be aware of the emergence and spread of new K. pneumoniae clones associated with resistant and hypermucoviscous phenotypes.

Clonal diversity, virulence genes content and subclone status of Escherichia coli sequence type 131: comparative analysis of E. coli ST131 and non-ST131 isolates from Iran.

BACKGROUND: The Escherichia coli sequence type 131 (ST131) is a well established clone causing significant extraintestinal infections worldwide. However, no studies have been reported the phenotypic and molecular traits of ST131 isolates in comparison to other clones of E. coli from Iran. So, we determined the differences between 69 ST131 strains collected during a one year surveillance study and 84 non-ST131 isolates, including 56 clinical fluoroquinolone resistant and 28 broiler colibacillosis isolates in terms of clonality and genetic background. RESULTS: ST131 isolates were associated with phylogroup B2 (68 out of 69 isolates, 98.4%), while clinical non-ST131 and fluoroquinolone resistant broiler isolates mainly belonged to phylogroup A. The highest virulence score was observed in ST131 clone, while they showed less diversity in virulence profiles than other clinical isolates. Almost all of the ST131 isolates (95.6%) were ExPEC and had the highest virulence scores, but their resistance scores were less than clinical non-ST131 isolates. Broiler isolates showed higher prevalence of ExPEC-associated virulence genes and CTX-M-G1/G9 resistance determinants as compared to clinical non-ST131 isolates. While blaOXA-48/NDM carbapenemases were mostly found in ST131 clone, resistance rate against ertapenem was higher among clinical non-ST131 strains. According to ERIC-based fingerprinting, the ST131 strains were more genetically similar, followed by non-ST131 and broiler isolates. CONCLUSIONS: ST131 isolates possess the ability to make a balance between clonality and extent of resistance/virulence genes content, so this phenomenon gives a fitness advantage over other E. coli clones. The broilers E. coli population poses a potential zoonotic risk which could be transmitted to the community through the food chain. A number of factors are involved in the dissemination of and infections due to ST131 clone.

Molecular epidemiology of Acinetobacter baumannii in Iran: endemic and epidemic spread of multiresistant isolates.

OBJECTIVES: We examined the molecular epidemiology of Acinetobacter baumannii clinical isolates from two cities (Tehran and Tabriz) of Iran. METHODS: DiversiLab repetitive extragenic palindromic PCR (rep-PCR), multilocus sequence typing and sequence group multiplex PCR were performed. The presence of resistance mechanisms including metallo-ß-lactamases, extended-spectrum ß-lactamases, OXA carbapenemases, aminoglycoside-modifying enzymes and RNA methylases was also investigated. RESULTS: DiversiLab rep-PCR identified 11 clusters and 11 singleton isolates. Twelve sequence types (STs), including six novel types, were identified. Sequence groups (SGs) 1-3 as well as five additional banding patterns were detected by multiplex PCR. A local outbreak in a general hospital in Tabriz with an SG1/ST2 profile was identified. Isolates of international clone II showed the highest prevalence and the most heterogeneous combination of resistance determinants. CONCLUSIONS: Several different multiresistant strains of A. baumannii were shown to circulate in Iran. The selection and spread of the SG1/ST2 clone might have been favoured by the acquisition of resistance genes in the absence of adequate infection control measures.

The prevalence of aminoglycoside-modifying enzymes among coagulase negative staphylococci in Iranian pediatric patients.

In spite of widespread emergence of aminoglycoside resistance, these drugs are still used in the treatment of staphylococcal infections. This study aimed to investigate the distribution of aminoglycoside resistance and genes encoding aminoglycoside - modifying enzymes (AMEs) as well as Staphylococcal Cassette Chromosome mec (SCCmec) type in coagulase negative staphylococci (CoNS) in pediatric patients. Totally, 93 CoNS isolates were examined for susceptibility to aminoglycosides using disk diffusion and/or E-test methods. AMEs genes and SCCmec types were detected using multiplex PCR. Strain typing was performed using repetitive extragenic palindromic (REP) - PCR assay. The non-susceptibility rates to kanamycin, tobramycin, gentamicin, amikacin and netilmicin were 73%, 59%, 49.5%, 16% and 7.5%, respectively. aac(6')-Ie-aph(2″)-Ia, ant(4')-Ia and aph(3')-IIIa were encountered in 56 (60.2%), 38 (40.8%) and 18 (19.3%) isolates, respectively. In aac(6')-Ie-aph(2″)-Ia- positive isolates, the non- susceptibility rates to kanamycin, gentamicin, tobramycin, amikacin and netilmicin were 83%, 74%, 73%, 49% and 43%, respectively. SCCmec types included type IV (n = 31), I (n = 17), II (n = 5), III (n = 4), and V (n = 2). Three isolates had two types; I + III (n = 2) and III + IV (n = 1) whereas 11 isolates were non-typeable. AMEs genes carriers were distributed frequently into type IV. We found diverse fingerprint patterns among our isolates. In conclusion, there was a strong correlation between alarming rate of aminoglycoside resistance and methicillin resistance. Discordances between phenotypic and genotypic detection of aminoglycoside resistance were discernible. AMEs genes might be related to SCCmec types.

Expansion of a Subset Within the C2 Subclade of Escherichia coli Sequence Type 131 (ST131) Is Driving the Increasing Rates of Aminoglycoside Resistance.

BACKGROUND: Sequence type 131 (ST131) of Escherichia coli is a pandemic clone that drives the increasing rates of antibiotic resistance. While the pervasiveness of ST131 clade C, especially subclades C2 and C1-M27, has been demonstrated in numerous global surveys, no report about the ST131 clades and their virotypes has been published from Iran so far. METHODS: A collection of 73 consecutive ST131 isolates from extraintestinal specimens was investigated for determination of virotypes, antibiotic susceptibility patterns, resistance/virulence determinants, and clade subsets. RESULTS: Most of the isolates belonged to subclade C2 (33/73; 45.2%), which had the highest virulence factor (VF) scores and resistance rates, followed by C1-M27 (18; 24.6%), C1-non-M27 (14; 19.1%), and A (8; 10.9%). The distinctive profiles of subclade C2 virulence genes were revealed by principle coordinates analysis testing. The distribution of the hlyA virulence gene among subclade C2 was not uniform, so that positive strains (21; 63.6%) showed significantly higher rates of resistance (bla CTX-M-15, bla OXA-1, aac(6')-Ib-cr, aac(6')-Ib, aac(3)-IIa) and virulence (hra, tia/hek, K5, cnf, papGII, papC) markers and gentamicin/tobramycin resistance. Virotype C as the most common virotype (34; 46.5%) was predominant among the subclade C1 population, while virotypes E and F (21; 28.7%) were detected among subclade C2, which had the highest VF scores and aminoglycoside resistance rates. CONCLUSIONS: The appearance of virotypes E and F among subclade C2 strains with higher rates of aminoglycoside resistance/virulence gene content shows the shifting dynamics of this pandemic clone in response to antibiotic selection pressure by establishing subsets with higher survival potential.

Characterization of antibiotic-susceptibility patterns and virulence genes of five major sequence types of Escherichia coli isolates cultured from extraintestinal specimens: a 1-year surveillance study from Iran.

OBJECTIVES: Escherichia coli sequence types (STs) 69, 73, 95, 127, and 131 are major STs frequently causing extraintestinal infections. The prevalence of specific clones and their virulence and resistance profiles has not been described from Iran. The aim of this study was to characterize antimicrobial-susceptibility profiles and virulence traits of five major clones of E. coli recovered from human extraintestinal infections in Semnan, Iran. We compared these traits between major ST clones and also between O25b and O16 subgroups of the ST131 clone. METHODS: We characterized the five major ST clones among 335 collected E. coli isolates obtained from extraintestinal infections, and phylogenetic groups, antimicrobial susceptibility, and virulence/resistance-gene profiles of these major STs were studied. RESULTS: The highest rates of the multidrug-resistance phenotype were detected among ST131 (85.7%) and ST69 (41.7%), and trimethoprim/sulfamethoxazole resistance was detected significantly among the latter clone. Of the 151 isolates belonging to major ST clones, bla OXA-48 was detected among all except the ST127 clone, while bla NDM genes were harbored by 14 (9.2%) isolates, which all belonged to the ST131 clone. Aggregate virulence scores (median) of ST131 isolates (11) were slightly higher than ST69 (8.50) strains, but were lower than ST73 (16), ST95 (16), and ST127 (12.50) isolates. Principal-coordinate analysis revealed distinct virulence profiles with the ST131 clone. ST73, ST95 and ST131 were enriched with "urovirulence" traits, including phylogroup B2 and group B2-associated accessory traits (chuA, iutA, yfcV, papGII, usp, kpsMTII and malX) and the derived variables extraintestinal pathogenic E. coli and uropathogenic E. coli. In contrast, ST69 was depleted of these traits, but enriched with phylogroups D and E. CONCLUSION: Our data emphasize that isolates of the ST131 clone have the ability to make a balance between resistance and virulence traits to establish a wider clone in extraintestinal pathogenic E. coli.

Evaluation of the commercial combined disk test and minimum inhibitory concentration (MIC) determination for detection of carbapenemase producers among Gram-negative bacilli isolated in a region with high prevalence of blaOXA-48 and blaNDM.

Carbapenem-resistant Gram-negative bacilli (GNB) are a concern in the Middle East and worldwide. Simple screening methods have been sought to detect carbapenemase producers to determine appropriate therapeutic measures and implement infection control interventions. In this study, we evaluated the efficiency of agar disc diffusion, commercial combined disc test (Rosco), and carbapenem MIC determination in comparison to molecular detection of carbapenemase genes among 82 carbapenem non-susceptible Enterobacteriaceae (CNSE) and 37 Acinetobacter/Pseudomonas isolates. The blaOXA-48, blaNDM, blaNDM/OXA-48, and blaIMP were detected in 68 out of 82 CNSE isolates. All of the Acinetobacter baumannii isolates were positive for the blaOXA-51 (n = 23), of those some were positive for blaOXA-48 (n = 13) and blaNDM (n = 3). Sensitivities and specificities of combined disc test for detection of blaNDM and blaOXA-48 carrying Enterobacteriaceae isolates were 92.5% and 100%, and 58.5% and 100%, respectively, while those for Acinetobacter/Pseudomonas isolates were 100%, 81.8% and 96.2%, 89%, respectively. While carbapenem MIC values had excellent concordance with phenotypic combined disc test for detection of blaOXA-48 producers (area under curve > 90%), only ertapenem MIC's could precisely detect blaOXA-48 PCR-positive Enterobacteriaceae isolates (AUC 70%, sensitivity 70%, specificity 50%). The phenotypic commercial test showed excellent sensitivity for detection of blaNDM producers, but had poor sensitivity for blaOXA-48-producing Enterobacteriaceae. Ertapenem MIC values had low sensitivity and specificity for detection of the blaOXA-48-carrying Enterobacteriaceae. This is the first report of A. baumannii isolates co-harbored the blaOXA-48/blaNDM carbapenemases from Iran.

Molecular and Phenotypic Characterization of Multidrug-Resistant Clones of Staphylococcus epidermidis in Iranian Hospitals: Clonal Relatedness to Healthcare-Associated Methicillin-Resistant Isolates in Northern Europe.

The aim of the study was to investigate the molecular epidemiology of Staphylococcus epidermidis in Iranian hospitals and to compare the genotypes with a previously characterized collection of >1,300 S. epidermidis isolates of nosocomial and community origin from Northern Europe, Australia, and USA. In total, 82 clinical S. epidermidis isolates from three Iranian hospitals were examined by multilocus sequence typing, pulsed-field gel electrophoresis (PFGE) and staphylococcal cassette chromosome mec (SCCmec) typing. In addition, antimicrobial susceptibility, the presence of the ica operon, and the predilection to biofilm formation were assessed. Three predominant PFGE clones were found. The PFGE patterns of the most common sequence type (PFGE type 040-ST2) showed 80% similarity to multidrug-resistant S. epidermidis (MDRSE) clinical isolates from eight hospitals in Northern Europe. The second most common (PFGE 024-ST22) showed an unique PFGE pattern, whereas the third most predominant genotype (PFGE 011-ST5) proved indistinguishable to the PFGE Co-ST5 identified in five hospitals in Northern Europe. In conclusion, the study documented the dissemination of three MDRSE clones within and between hospitals in Iran and revealed an intercontinental spread of two clonal multidrug-resistant lineages (ST2 and ST5) in the hospital environment. Isolates of the predominant clones were significantly more frequently associated with multidrug-resistance and biofilm formation compared to nonclonal isolates. Further studies are needed to explore and characterize the genetic traits that enable these successful MDRSE clones to persist and disseminate worldwide in the healthcare settings.

Comparative Evaluation of RUT, PCR and ELISA Tests for Detection of Infection with Cytotoxigenic H. pylori.

PURPOSE: Helicobacter pylori is one of the most prevalent infectious agents in the world which causes a variety of gastrointestinal diseases including gastritis, peptic ulcer and gastric carcinoma. The objective of this study was to comparatively evaluate invasive (rapid urease test and polymerase chain reaction) and non-invasive (enzyme-linked immunosorbent assay) tests in diagnosis of infection with cytotoxigenic H. pylori. METHODS: Biopsy specimens and sera were collected from 105 patients with gastric disorders. The presence of H. pylori infection in gastric biopsies was evaluated by RUT and PCR methods using chemotaxis signal transduction protein gene (CSTP), Urea C and HP-16srRNA primers. Serum samples were used for the ELISA test. Detection of infection with cag A-positive strains was performed by PCR and cag A-IgG ELISA kit. RESULTS: Patients with at least two out of three positive results were regarded as infected. The sensitivity, specificity, predictive value and accuracy of the three different methods were evaluated. Of the 105 gastric biopsies, H. pylori were positive in 51 patients (48.57%). The best sensitivity (92.16%) belonged to RUT. The sensitivities of other tests including PCR and ELISA test were 88.24% and 90.20%, respectively. PCR showed the best specificity (94.44%), and the specificities of the other tests including RUT and ELISA test, were 90.74 % and 61.11%, respectively. Furthermore, results of PCR and cag A-IgG ELISA showed high prevalence of cag A-positive strain in the study population. CONCLUSION: Based on our findings, serum ELISA is a rapid noninvasive test for screening of H. pylori infection in the absence of endoscopy indication. In addition, considering the high prevalence of cytotoxigenic H. pylori strains, cag A is suggested as a promising target for PCR and non- invasive ELISA tests for detection of infection with toxigenic strains.

Efficient Inactivation of Multi-Antibiotics Resistant Nosocomial Enterococci by Purified Hiracin Bacteriocin.

PURPOSE: Because of the emergence of multi-antibiotic resistant bacteria, a number of infectious diseases have become a major concern to treat in health care services worldwide. This situation is worsened by the fact that very limited progress has been made in developing new and potent antibiotics in recent years. In this context antimicrobial peptides (AMPs) represent new potential therapeutic compounds with bactericidal or bacteriostatic activity against closely related bacterial strains. METHODS: In this study, a collection of enterococci (n=170) from clinical sources were investigated for their potential to inhibit multiresistant nosocomial enterococci from Iranian hospitals. RESULTS: Four isolates produced antimicrobial peptides that inhibited all the antibiotic resistant enterococci. This included three Enterococcus faecium isolates producing combinations of enterocin A, B and L50 AB. The most potent antagonism was produced by E. faecalis HO91. Purification and subsequent characterization by MALDI-TOF MS, Edman degradation and DNA-sequencing revealed that the antimicrobial compound was Hiracin. The purified Hiracin was evaluated for antibacterial activity against 12 multiresistant enterococcal isolates from clinical samples. The results demonstrated that Hiracin is highly effective towards enterococci which were resistant even to antibiotics from four distinct classes. CONCLUSION: The present research addresses Hiracin as a promising alternative to conventional antibiotics in treatment of multiresistant enterococcal infections.

Determination of antimicrobial resistance profile and inducible clindamycin resistance of coagulase negative staphylococci in pediatric patients: the first report from Iran.

BACKGROUND: Currently, coagulase negative staphylococci (CoNS) have got much attention as a serious health problem especially in neonates and children. High incidence of antibiotic resistance, in particular methicillin resistance, has complicated the treatment of these organisms. The aim of this study is to determine the susceptibility to different antimicrobial agents and the prevalence of macrolideslincosamides-streptogramins B (MLSB) resistance in CoNS isolates obtained from pediatric patients. METHODS: Totally 157 CoNS isolates from various clinical samples were examined for antibiotic resistance using disk diffusion and E-test methods. Double-disk test was applied to detect constitutive and inducible MLSB resistance (cMLSB and iMLSB) phenotypes. RESULTS: Resistance to methicillin was seen in 98 (62.4%) isolates. All isolates were susceptible to vancomycin and linezolid. The prevalence of resistance to antibiotics tested was as follows: fusidic acid (n=58, 36.9%), gentamicin (n=73, 46.5%), ciprofloxacin (n=81, 51.6%), clindamycin (n=112, 71.3%), erythromycin (n=129, 82.2%) and trimethoprim/sulfamethoxazole (n=133, 84.7%). iMLSB phenotype was seen in 14 (8.9%) isolates, and 18 (11.5%) and 98 (62.4%) isolates showed MS and cMLSB phenotypes, respectively. We observed that high overall antibiotic resistance rates were associated significantly with methicillin resistance. Conversely, iMLSB phenotype was correlated neither with methicillin resistance nor with invasiveness. CONCLUSION: Given the similarity observed between the prevalence of iMLSB and MS phenotypes, the performance of disk diffusion induction test is strongly recommended in our region.

Role of efflux pumps: MexAB-OprM and MexXY(-OprA), AmpC cephalosporinase and OprD porin in non-metallo-ß-lactamase producing Pseudomonas aeruginosa isolated from cystic fibrosis and burn patients.

PURPOSE OF THE RESEARCH: In order to gain a better understanding of the role of several mechanisms in antibiotic resistance in Pseudomonas aeruginosa clinical isolates obtained from CF and burn patients, we evaluated gene expression of efflux pumps MexAB-OprM and MexXY(-OprA), the natural ß-lactamase AmpC and outer membrane porin protein OprD. Also, the presence of genes encoding Ambler classes A, B ß-lactamases and aminoglycoside modifying enzymes (AMEs) was examined. PRINCIPAL RESULTS: Piperacillin-tazobactam and amikacin retained the highest in vitro activities among 21 CF and 27 burn P. aeruginosa isolates. Based on Enterobacterial Repetitive Intergenic Consensus (ERIC) PCR, 15 distinct patterns were detected. There were 5 CF and 6 burn isolates harbored PER-1 and VEB-1, respectively. Among AMEs, involved in resistance of anti-Pseudomonas aminoglycosides, aac(6')-Ib was the most prevalent gene. Among CF isolates, mexA overexpression was the most prevalent mechanism (47.6%) followed by mexX (42.8%), ampC (9.5%) and oprD downregulation (4.7%). Among burn isolates, the prevalence of mexX, mexA, and ampC overexpression was 62.9%, 74%, and 11.1%, respectively. Downregulation of oprD was observed in 14.8% of burn isolates. MAJOR CONCLUSIONS: Among CF isolates, mexX and mexA overexpression were the major contributing factors to aminoglycoside (gentamicin) and carbapenem (meropenem) resistance, respectively while among burn isolates, AMEs in conjunction with mexX hyperexpression were identified to be responsible for aminoglycoside resistance. Also mexA overexpression was partially associated with carbapenem resistance. Moreover, cephalosporin resistance was linked to overexpression of mexA and/or mexX. The impact of interplay between different resistance mechanisms on resistant phenotypes was more complicated among burn than CF isolates.

Dissemination of aminoglycoside-modifying enzymes and 16S rRNA methylases among acinetobacter baumannii and Pseudomonas aeruginosa isolates.

AIMS: The purpose of the present study was to investigate the diversity of the genes encoding aminoglycoside-modifying enzymes (AMEs) and their associations with resistance phenotypes and clonality in Acinetobacter baumannii and Pseudomonas aeruginosa isolates. METHODS: Seventy six P. aeruginosa and 75 A. baumannii isolates were collected from three University affiliated hospitals in Tehran. MIC determination of amikacin and gentamicin as well as the disk diffusion method for tobramycin, netilmicin, and kanamycin were carried out. Nine AMEs genes and three RNA methylases were investigated in all isolates using the PCR method. Clonality for A. baumannii and P. aeruginosa was investigated using repetitive extragenic palindromic and enterobacterial repetitive intergenic consensus PCR, respectively. RESULTS: aph(3')-VIa (90.6%) and aph(3')-IIb (61.8%) were the most prevalent AME genes in A. baumannii and P. aeruginosa, respectively. Eight (26%) amikacin highly resistant A. baumannii isolates were positive for armA methylase. Phenotypes and clonality did not link to the genetic determinants of resistance to aminoglycosides in our isolates. CONCLUSIONS: AMEs genes are disseminated in different clones of A. baumannii and P. aeruginosa isolates in Iran. Other than AMEs, there are more complex and multifactorial mechanisms that result in aminoglycoside-resistant phenotypes.

Prevalence of Ambler class A ß-lactamases and ampC expression in cephalosporin-resistant isolates of Acinetobacter baumannii.

We examined the prevalence of various cephalosporins' resistance mechanisms in Acinetobacter baumannii clinical isolates. Phenotypic and molecular detection of Ambler classes A, B and D ß-lactamases was performed on 75 isolates. Clonal relatedness was defined using Repetitive Extragenic Palindromic PCR. PCR mapping was used to examine the linkage of insertion sequences and the ampC gene, and ampC expression was analyzed by TaqMan reverse transcriptase-PCR. Twenty-six (37%) isolates carried at least one of the blaPER-1 or blaTEM-1. Sixty-nine (98.5%) out of 70 cephalosporin-resistant isolates had insertions upstream of the ampC gene, of which 48 (69%) and 6 (8%) were identified as ISAba1and ISAba125, respectively. Higher level of expression was obtained in resistant isolates lacking ISAba1/ampC combination in comparison with that in positive ones. The ability to up-regulate the expression of ampC gene in association with different insertion elements has become an important factor in A. baumannii resistance to cephalosporins.

Study of the carbapenem resistance mechanisms in clinical isolates of Acinetobacter baumannii: comparison of burn and non-burn strains.

We examined the prevalence of various carbapenem resistance mechanisms in clinical isolates of Acinetobacter baumannii collected from hospitalized burn and non-burn patients. Antimicrobial susceptibility testing was performed for 43 burn and 32 non-burn isolates. Carbapenem resistance genes were identified and repetitive extragenic palindromic PCR (REP-PCR) was used to define clonal relatedness. CarO disruption was investigated by PCR and its expression analyzed by real time reverse transcription-PCR. Of the sixty-four (85%) carbapenem resistant A. baumannii isolates, 42 (66%) and 22 (34%) strains were recovered from burn and non-burn patients, respectively. Isolates were categorized into 6 major REP-PCR patterns; with the highest prevalence of non-burn and burn isolates in pattern A (63%) and B (35%), respectively. Prevalence of blaOXA-23 was 68% and isolates harbored this element belonged to all REP clusters. The blaOXA-40-like was detected in 49% of isolates, with higher prevalence among burn isolates. Three of the four isolates lacked carO gene were cultured from burn patients and level of the carO expression was decreased in carbapenem resistant isolates. These findings show that blaOXA-23 is widely distributed in carbapenem resistant A. baumannii isolates and other resistance mechanisms such as blaOXA-40-like and loss or decreased carO expression could be added in burn strains.

Comparison of in Vitro Activity of Doripenem versus Old Carbapenems against Pseudomonas Aeruginosa Clinical Isolates from both CF and Burn Patients.

PURPOSE: The antimicrobial activity of doripenem in comparison of imipenem, meropenem and ertapenem among Pseudomonas aeruginosa isolated from burn and Cystic Fibrosis (CF) patients were determined. METHODS: Metallo-ß-lactamase (MBL) genes in imipenem non susceptible P. aeruginosa isolates were detected using PCR method. The in vitro susceptibilities of doripenem, imipenem, meropenem and ertapenem were determined by Etests. MIC50 and MIC90 for corresponding antibiotics were determined individually in burn and CF isolates. RESULTS: Among isolates which were resistant to imipenem, 16 isolates were positive for the bla IMP gene. All isolates had no bla VIM gene. All MBL producing isolates were excluded. MIC50/MIC90 of doripenem in CF and burn isolates were 0.75/>32 and >32/>32 mg/L respectively. The corresponding values for imipenem in CF and burn isolates were 2/>32 and >32/>32 mg/L, respectively. CONCLUSION: The susceptibility rate of doripenem is higher than that of imipenem and meropenem among P.aeruginosa isolated from CF patients, whereas, there is no difference between the efficiency of doripenem and old carbapenems in non MBL producing P.aeruginosa isolates in burn patients.