Novel Antibacterial Agents SAAP-148 and Halicin Combat Gram-Negative Bacteria Colonizing Catheters.

The antibiotic management of catheter-related infections (CRIs) often fails owing to the emergence of antimicrobial-resistant strains and/or biofilm/persister apparitions. Thus, we investigated the efficacy of two novel antimicrobial agents, i.e., the synthetic peptide SAAP-148 and the novel antibiotic halicin, against Gram-negative bacteria (GNB) colonizing catheters. The antibacterial, anti-biofilm, and anti-persister activities of both agents were evaluated against Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae strains. The enrolled strains were isolated from catheters and selected based on their resistance to at least three antibiotic classes and biofilm formation potential. Furthermore, the hemolysis and endotoxin neutralization abilities of these agents were explored. The bactericidal activity of both agents was reduced in urine and plasma as compared to buffered saline. In a dose-dependent manner, SAAP-148 and halicin reduced bacterial counts in 24 h preformed biofilms on silicone elastomer discs and eliminated persisters originating from antibiotic-exposed mature 7-day biofilms, with halicin being less effective than SAAP-148. Importantly, SAAP-148 and halicin acted synergistically on E. coli and K. pneumoniae biofilms but not on A. baumannii biofilms. The peptide, but not halicin, decreased the production of IL-12p40 upon exposure to UV-killed bacteria. This preliminary study showed that SAAP-148 and halicin alone/in combination are promising candidates to fight GNB colonizing catheters.

The survival of epidemic and sporadic MRSA on human skin mimics is determined by both host and bacterial factors.

Bacterial survival on, and interactions with, human skin may explain the epidemiological success of MRSA strains. We evaluated the bacterial counts for 27 epidemic and 31 sporadic MRSA strains on 3D epidermal models based on N/TERT cells (NEMs) after 1, 2 and 8 days. In addition, the expression of antimicrobial peptides (hBD-2, RNase 7), inflammatory cytokines (IL-1ß, IL-6) and chemokine IL-8 by NEMs was assessed using immunoassays and the expression of 43 S. aureus virulence factors was determined by a multiplex competitive Luminex assay. To explore donor variation, bacterial counts for five epidemic and seven sporadic MRSA strains were determined on 3D primary keratinocyte models (LEMs) from three human donors. Bacterial survival was comparable on NEMs between the two groups, but on LEMs, sporadic strains showed significantly lower survival numbers compared to epidemic strains. Both groups triggered the expression of immune factors. Upon interaction with NEMs, only the epidemic MRSA strains expressed pore-forming toxins, including alpha-hemolysin (Hla), gamma-hemolysin (HlgB), Panton-Valentine leucocidin (LukS) and LukED. Together, these data indicate that the outcome of the interaction between MRSA and human skin mimics, depends on the unique combination of bacterial strain and host factors.

Synergism between the Synthetic Antibacterial and Antibiofilm Peptide (SAAP)-148 and Halicin.

Recently, using a deep learning approach, the novel antibiotic halicin was discovered. We compared the antibacterial activities of two novel bactericidal antimicrobial agents, i.e., the synthetic antibacterial and antibiofilm peptide (SAAP)-148 with this antibiotic halicin. Results revealed that SAAP-148 was more effective than halicin in killing planktonic bacteria of antimicrobial-resistant (AMR) Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus, especially in biologically relevant media, such as plasma and urine, and in 3D human infection models. Surprisingly, SAAP-148 and halicin were equally effective against these bacteria residing in immature and mature biofilms. As their modes of action differ, potential favorable interactions between SAAP-148 and halicin were investigated. For some specific strains of AMR E. coli and S. aureus synergism between these agents was observed, whereas for other strains, additive interactions were noted. These favorable interactions were confirmed for AMR E. coli in a 3D human bladder infection model and AMR S. aureus in a 3D human epidermal infection model. Together, combinations of these two novel antimicrobial agents hold promise as an innovative treatment for infections not effectively treatable with current antibiotics.

Procalcitonin, mid-regional proadrenomedullin and C-reactive protein in predicting treatment outcome in community-acquired febrile urinary tract infection.

BACKGROUND: A reduction in duration of antibiotic therapy is crucial in minimizing the development of antimicrobial resistance, drug-related side effects and health care costs. The minimal effective duration of antimicrobial therapy for febrile urinary tract infections (fUTI) remains a topic of uncertainty, especially in male patients, those of older age or with comorbidities. Biomarkers have the potential to objectively identify the optimal moment for cessation of therapy. METHODS: A secondary analysis of a randomized placebo-controlled trial among 35 primary care centers and 7 emergency departments of regional hospitals in the Netherlands. Women and men aged ≥18 years with a diagnosis of fUTI were randomly assigned to receive antibiotic treatment for 7 or 14 days. Patients indicated to receive antimicrobial treatment for more than 14 days were excluded from randomization. The biomarkers procalcitonin (PCT), mid-regional proadrenomedullin (MR-proADM), and C-reactive protein (CRP) were compared in their ability to predict clinical cure or failure through the 10-18 day post-treatment visit. RESULTS: Biomarker concentrations were measured in 249 patients, with a clinical cure rate of 94% in the 165 randomized and 88% in the 84 non-randomized patients. PCT, MR-proADM and CRP concentrations did not differ between patients with clinical cure and treatment failure, and did not predict treatment outcome, irrespective of 7 or 14 day treatment duration (ROCAUC 0.521; 0.515; 0.512, respectively). PCT concentrations at presentation were positively correlated with bacteraemia (τ = 0.33, p < 0.001) and presence of shaking chills (τ = 0.25, p < 0.001), and MR-proADM levels with length of hospital stay (τ = 0.40, p < 0.001), bacteraemia (τ = 0.33, p < 0.001), initial intravenous treatment (τ = 0.22, p < 0.001) and time to defervescence (τ = 0.21, p < 0.001). CRP did not display any correlation to relevant clinical parameters. CONCLUSIONS: Although the biomarkers PCT and MR-proADM were correlated to clinical parameters indicating disease severity, they did not predict treatment outcome in patients with community acquired febrile urinary tract infection who were treated for either 7 or 14 days. CRP had no added value in the management of patients with fUTI. TRIAL REGISTRATION: The study was registered at ClinicalTrials.gov [ NCT00809913 ; December 16, 2008] and trialregister.nl [ NTR1583 ; December 19, 2008].

Treatment duration of febrile urinary tract infection: a pragmatic randomized, double-blind, placebo-controlled non-inferiority trial in men and women.

BACKGROUND: In adults with febrile urinary tract infection (fUTI), data on optimal treatment duration in patients other than non-pregnant women without comorbidities are lacking. METHODS: A randomized placebo-controlled, double-blind, non-inferiority trial among 35 primary care centers and 7 emergency departments of regional hospitals in the Netherlands. Women and men aged ≥ 18 years with a diagnosis of fUTI were randomly assigned to receive antibiotic treatment for 7 or 14 days (the second week being ciprofloxacin 500 mg or placebo orally twice daily). Patients indicated to receive antimicrobial treatment for at least 14 days were excluded from randomization. The primary endpoint was the clinical cure rate through the 10- to 18-day post-treatment visit with preset subgroup analysis including sex. Secondary endpoints were bacteriologic cure rate at 10-18 days post-treatment and clinical cure at 70-84 days post-treatment. RESULTS: Of 357 patients included, 200 were eligible for randomization; 97 patients were randomly assigned to 7 days and 103 patients to 14 days of treatment. Overall, short-term clinical cure occurred in 85 (90%) patients treated for 7 days and in 94 (95%) of those treated for 14 days (difference -4.5%; 90% CI, -10.7 to 1.7; P non-inferiority = 0.072, non-inferiority not confirmed). In women, clinical cure was 94% and 93% in those treated for 7 and 14 days, respectively (difference 0.9; 90% CI, -6.9 to 8.7, P non-inferiority = 0.011, non-inferiority confirmed) and, in men, this was 86% versus 98% (difference -11.2; 90% CI -20.6 to -1.8, P superiority = 0.025, inferiority confirmed). The bacteriologic cure rate was 93% versus 97% (difference -4.3%; 90% CI, -9.7 to 1.2, P non-inferiority = 0.041) and the long-term clinical cure rate was 92% versus 91% (difference 1.6%; 90% CI, -5.3 to 8.4; P non-inferiority = 0.005) for 7 days versus 14 days of treatment, respectively. In the subgroups of men and women, long-term clinical cure rates met the criteria for non-inferiority, indicating there was no difference in the need for antibiotic retreatment for UTI during 70-84 days follow-up post-treatment. CONCLUSIONS: Women with fUTI can be treated successfully with antibiotics for 7 days. In men, 7 days of antibiotic treatment for fUTI is inferior to 14 days during short-term follow-up but it is non-inferior when looking at longer follow-up. TRIAL REGISTRATION: The study was registered at ClinicalTrials.gov [ NCT00809913 ; December 16, 2008] and trialregister.nl [ NTR1583 ; December 19, 2008].

Molecular Epidemiology and Clinical Impact of Acinetobacter calcoaceticus-baumannii Complex in a Belgian Burn Wound Center.

Multidrug resistant Acinetobacter baumannii and its closely related species A. pittii and A. nosocomialis, all members of the Acinetobacter calcoaceticus-baumannii (Acb) complex, are a major cause of hospital acquired infection. In the burn wound center of the Queen Astrid military hospital in Brussels, 48 patients were colonized or infected with Acb complex over a 52-month period. We report the molecular epidemiology of these organisms, their clinical impact and infection control measures taken. A representative set of 157 Acb complex isolates was analyzed using repetitive sequence-based PCR (rep-PCR) (DiversiLab) and a multiplex PCR targeting OXA-51-like and OXA-23-like genes. We identified 31 rep-PCR genotypes (strains). Representatives of each rep-type were identified to species by rpoB sequence analysis: 13 types to A. baumannii, 10 to A. pittii, and 3 to A. nosocomialis. It was assumed that isolates that belonged to the same rep-type also belonged to the same species. Thus, 83.4% of all isolates were identified to A. baumannii, 9.6% to A. pittii and 4.5% to A. nosocomialis. We observed 12 extensively drug resistant Acb strains (10 A. baumannii and 2 A. nosocomialis), all carbapenem-non-susceptible/colistin-susceptible and imported into the burn wound center through patients injured in North Africa. The two most prevalent rep-types 12 and 13 harbored an OXA-23-like gene. Multilocus sequence typing allocated them to clonal complex 1 corresponding to EU (international) clone I. Both strains caused consecutive outbreaks, interspersed with periods of apparent eradication. Patients infected with carbapenem resistant A. baumannii were successfully treated with colistin/rifampicin. Extensive infection control measures were required to eradicate the organisms. Acinetobacter infection and colonization was not associated with increased attributable mortality.

Identification of NDM-1 in a Putatively Novel Acinetobacter Species ("NB14") Closely Related to Acinetobacter pittii.

In this study, we describe the molecular characterization of a plasmid-located blaNDM-1 harbored by an Acinetobacter clinical isolate recovered from a patient in Turkey that putatively constitutes a novel Acinetobacter species, as shown by its distinct ARDRA (amplified 16S ribosomal DNA restriction analysis) profile and molecular sequencing techniques. blaNDM-1 was carried by a conjugative plasmid widespread among non-baumannii Acinetobacter isolates, suggesting its potential for dissemination before reaching more clinically relevant Acinetobacter species.

Urinary proteins, vitamin D and genetic polymorphisms as risk factors for febrile urinary tract infection and relation with bacteremia: a case control study.

OBJECTIVE/PURPOSE: Febrile urinary tract infection (UTI) is a common bacterial disease that may lead to substantial morbidity and mortality especially among the elderly. Little is known about biomarkers that predict a complicated course. Our aim was to determine the role of certain urinary cytokines or antimicrobial proteins, plasma vitamin D level, and genetic variation in host defense of febrile UTI and its relation with bacteremia. METHODS: A case-control study. Out of a cohort of consecutive adults with febrile UTI (n = 787) included in a multi-center observational cohort study, 46 cases with bacteremic E.coli UTI and 45 cases with non-bacteremic E.coli UTI were randomly selected and compared to 46 controls. Urinary IL-6, IL-8, LL37, ß-defensin 2 and uromodulin as well as plasma 25-hydroxyvitamin D were measured. In 440 controls and 707 UTI patients polymorphisms were genotyped in the genes CXCR1, DEFA4, DEFB1, IL6, IL8, MYD88, UMOD, TIRAP, TLR1, TLR2, TLR5 and TNF. RESULTS: IL-6, IL-8, and LL37 are different between controls and UTI patients, although these proteins do not distinguish between patients with and without bacteremia. While uromodulin did not differ between groups, inability to produce uromodulin is more common in patients with bacteremia. Most participants in the study, including the controls, had insufficient vitamin D and, at least in winter, UTI patients have lower vitamin D than controls. Associations were found between the CC genotype of IL6 SNP rs1800795 and occurrence of bacteremia and between TLR5 SNP rs5744168 and protection from UTI. The rare GG genotype of IL6 SNP rs1800795 was associated with higher ß-defensin 2 production. CONCLUSION: Although no biomarker was able to distinguish between UTI with or without bacteremia, two risk factors for bacteremia were identified. These were inability to produce uromodulin and an IL6 rs1800795 genotype.

Carbapenem resistance in a human clinical isolate identified to be closely related to Acinetobacter indicus.

Here we report a case of carbapenem resistance in a human clinical isolate that was found to be closely related to the newly described environmental species Acinetobacter indicus. This strain harboured the blaOXA-23 carbapenemase gene located on a conjugative plasmid. Partial sequencing of 16S rDNA and rpoB genes, together with matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) analysis, showed that this strain was distantly related to the Acinetobacter baumannii-calcoaceticus complex and was closely related to A. indicus.

Multidrug-resistant Acinetobacter baumannii in veterinary clinics, Germany.

An increase in prevalence of multidrug-resistant Acinetobacter spp. in hospitalized animals was observed at the Justus-Liebig-University (Germany). Genotypic analysis of 56 isolates during 2000-2008 showed 3 clusters that corresponded to European clones I-III. Results indicate spread of genotypically related strains within and among veterinary clinics in Germany.

Genotypic and phenotypic characterization of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex with the proposal of Acinetobacter pittii sp. nov. (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis sp. nov. (formerly Acinetobacter genomic species 13TU).

Acinetobacter genomic species (gen. sp.) 3 and gen. sp. 13TU are increasingly recognized as clinically important taxa within the Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex. To define the taxonomic position of these genomic species, we investigated 80 strains representing the known diversity of the ACB complex. All strains were characterized by AFLP analysis, amplified rDNA restriction analysis and nutritional or physiological testing, while selected strains were studied by 16S rRNA and rpoB gene sequence analysis, multilocus sequence analysis and whole-genome comparison. Results supported the genomic distinctness and monophyly of the individual species of the ACB complex. Despite the high phenotypic similarity among these species, some degree of differentiation between them could be made on the basis of growth at different temperatures and of assimilation of malonate, l-tartrate levulinate or citraconate. Considering the medical relevance of gen. sp. 3 and gen. sp. 13TU, we propose the formal names Acinetobacter pittii sp. nov. and Acinetobacter nosocomialis sp. nov. for these taxa, respectively. The type strain of A. pittii sp. nov. is LMG 1035(T) (=CIP 70.29(T)) and that of A. nosocomialis sp. nov. is LMG 10619(T) (=CCM 7791(T)).

Diversity and clinical impact of Acinetobacter baumannii colonization and infection at a military medical center.

The epidemiology of Acinetobacter baumannii emerging in combat casualties is poorly understood. We analyzed 65 (54 nonreplicate) Acinetobacter isolates from 48 patients (46 hospitalized and 2 outpatient trainees entering the military) from October 2004 to October 2005 for genotypic similarities, time-space relatedness, and antibiotic susceptibility. Clinical and surveillance cultures were compared by amplified fragment length polymorphism (AFLP) genomic fingerprinting to each other and to strains of a reference database. Antibiotic susceptibility was determined, and multiplex PCR was performed for OXA-23-like, -24-like, -51-like, and -58-like carbapenemases. Records were reviewed for overlapping hospital stays of the most frequent genotypes, and risk ratios were calculated for any association of genotype with severity of Acute Physiology and Chronic Health Evaluation II (APACHE II) score or injury severity score (ISS) and previous antibiotic use. Nineteen genotypes were identified; two predominated, one consistent with an emerging novel international clone and the other unique to our database. Both predominant genotypes were carbapenem resistant, were present at another hospital before patients' admission to our facility, and were associated with higher APACHE II scores, higher ISSs, and previous carbapenem antibiotics in comparison with other genotypes. One predominated in wound and respiratory isolates, and the other predominated in wound and skin surveillance samples. Several other genotypes were identified as European clones I to III. Acinetobacter genotypes from recruits upon entry to the military, unlike those in hospitalized patients, did not include carbapenem-resistant genotypes. Acinetobacter species isolated from battlefield casualties are diverse, including genotypes belonging to European clones I to III. Two carbapenem-resistant genotypes were epidemic, one of which appeared to belong to a novel international clone.

Acinetobacter bereziniae sp. nov. and Acinetobacter guillouiae sp. nov., to accommodate Acinetobacter genomic species 10 and 11, respectively.

Acinetobacter genospecies (genomic species) 10 and 11 were described by Bouvet and Grimont in 1986 on the basis of DNA-DNA reassociation studies and comprehensive phenotypic analysis. In the present study, the names Acinetobacter bereziniae sp. nov. and Acinetobacter guillouiae sp. nov., respectively, are proposed for these genomic species based on the congruence of results of polyphasic analysis of 33 strains (16 and 17 strains of genomic species 10 and 11, respectively). All strains were investigated by selective restriction fragment amplification (i.e. AFLP) analysis rpoB sequence analysis, amplified rDNA restriction analysis and tDNA intergenic length polymorphism analysis, and their nutritional and physiological properties were determined. Subsets of the strains were studied by 16S rRNA gene sequence analysis and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS or had been classified previously by DNA-DNA reassociation. Results indicate that A. bereziniae and A. guillouiae represent two phenetically and phylogenetically distinct groups within the genus Acinetobacter. Based on the comparative analysis of housekeeping genes (16S rRNA and rpoB genes), these species together represent a monophyletic branch within the genus. Despite their overall phenotypic similarity, the ability to oxidize d-glucose and to grow at 38 degrees C can be used in the presumptive differentiation of these two species from each other: with the exception of three strains that were positive for only one test, A. bereziniae strains were positive for both tests, whereas A. guillouiae strains were negative in these tests. The strains of A. bereziniae originated mainly from human clinical specimens, whereas A. guillouiae strains were isolated from different environmental sources in addition to human specimens. The type strain of A. bereziniae sp. nov. is LMG 1003(T) (=CIP 70.12(T) =ATCC 17924(T)) and that of A. guillouiae sp. nov. is LMG 988(T) (=CIP 63.46( T) =ATCC 11171(T) =CCUG 2491(T)).

Description of Acinetobacter venetianus ex Di Cello et al. 1997 sp. nov.

The name 'Acinetobacter venetianus' has been used previously to designate three marine hydrocarbon-degrading Acinetobacter strains, of which strain RAG-1 (=ATCC 31012) has industrial applications for the production of the bioemulsifier emulsan. However, to date, the name of this taxon has not been validly published. In this study, five strains were examined to corroborate the delineation of this taxon by means of phenotypic characterization, DNA-DNA hybridization, selective restriction fragment amplification (AFLP), amplified rDNA restriction analysis (ARDRA), rpoB gene sequence analysis and tRNA intergenic spacer length polymorphism analysis (tDNA-PCR) and to emend the description of 'Acinetobacter venetianus' (ex Di Cello et al. 1997). AFLP analysis showed that the five strains formed a tight cluster at 56.8+/-5.0 % genomic relatedness that was separated from strains of other haemolytic species of the genus Acinetobacter and from the type and reference strains of other Acinetobacter species at

Acinetobacter beijerinckii sp. nov. and Acinetobacter gyllenbergii sp. nov., haemolytic organisms isolated from humans.

The taxonomic status of 24 haemolytic, non-glucose acidifying Acinetobacter strains that did not belong to any previously described species was investigated by means of a polyphasic approach. Using AFLP fingerprinting, amplified rDNA restriction analysis and phenotypic characterization, the strains were classified into two phenetically coherent groups (comprising 15 and 9 strains) that were distinct from each other and from all known Acinetobacter species. Confirmation that these groups formed two separate lineages within the genus Acinetobacter was obtained from comparative analysis of partial sequences of the gene encoding the beta-subunit of RNA polymerase in all strains and also from 16S rRNA gene sequence analysis of representative strains. Previously published DNA-DNA reassociation data for some of the strains used also supported the species rank for both groups, for which the names Acinetobacter beijerinckii sp. nov. and Acinetobacter gyllenbergii sp. nov. are proposed. The strains of A. beijerinckii sp. nov. originated from human and animal specimens and from various environmental sources, whereas those of A. gyllenbergii sp. nov. were isolated exclusively from human clinical specimens. The phenotypic characteristics most useful for the differentiation of these species from other Acinetobacter species that comprise haemolytic strains were the inability of A. beijerinckii sp. nov. to grow on l-arginine and the ability of A. gyllenbergii sp. nov. to grow on azelate. The type strain of A. beijerinckii sp. nov. is NIPH 838T (=LUH 4759T=CCUG 51249T=CCM 7266T=58aT) and the type strain of A. gyllenbergii sp. nov. is NIPH 2150T (=RUH 422T=CCUG 51248T=CCM 7267T=1271T).

Emergence of carbapenem resistance in Acinetobacter baumannii in the Czech Republic is associated with the spread of multidrug-resistant strains of European clone II.

OBJECTIVES: The aim of this study was to analyse the emergence of carbapenem resistance among hospital strains of Acinetobacter in the Czech Republic. METHODS: Acinetobacter isolates were collected prospectively in 2005-06 from 19 diagnostic laboratories. They were identified to species level by AFLP, typed using AFLP, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing, and tested for susceptibility to 14 antimicrobials and for the presence of 20 genes associated with antimicrobial resistance. RESULTS: A total of 150 Acinetobacter isolates were obtained from 56 intensive care units of 20 hospitals in 15 cities. They were identified as Acinetobacter baumannii (n = 108) or other species. A. baumannii isolates were allocated to EU clone I (n = 5), EU clone II (n = 66) or other, mostly unique genotypes. Two-thirds of the clone II isolates had nearly identical AFLP and PFGE fingerprints. As many as 85% and 88% isolates were susceptible to meropenem and imipenem (or=8 mg/L were found in 23 A. baumannii isolates, of which 20 belonged to clone II. Isolates with bla(OXA-58-like) (n = 3)(,) bla(OXA-24-like) (n = 1) or ISAba1 adjacent to bla(OXA-51-like) (n = 34) had carbapenem MICs of 2 to >16 mg/L, while those without these elements showed MICs of

Reclassification of Acinetobacter grimontii Carr et al. 2003 as a later synonym of Acinetobacter junii Bouvet and Grimont 1986.

Using tDNA-PCR, the type strain CCM 7198T (<--CIP 107470T <--17A04T) of Acinetobacter grimontii was found to be indistinguishable from Acinetobacter junii strains. Therefore, the phenotypic properties, amplified fragment length polymorphism (AFLP) patterns and 16S rRNA and rpoB gene sequences of the type strain of A. grimontii (CCM 7198T) were determined. We found that the strain used l-arginine and l-glutamate, in contrast to the original description and in accordance with the phenotypic properties of A. junii. By AFLP analysis, A. grimontii CCM 7198T clustered at 50.2 % with a set of A. junii strains previously identified by DNA-DNA hybridization, which is in accordance with the previously established intraspecies values of this technique. Sequence similarity of the 16S rRNA gene between the type strains of the two species was found to be 99.9 %. Finally, DNA-DNA relatedness between the type strains of A. junii and A. grimontii was redetermined and was found to be 85 %. These findings were corroborated for a second representative of the A. grimontii type strain, DSM 14968T. These data confirm that Acinetobacter grimontii is a later heterotypic synonym of Acinetobacter junii.

Relationship between the AdeABC efflux system gene content, netilmicin susceptibility and multidrug resistance in a genotypically diverse collection of Acinetobacter baumannii strains.

OBJECTIVE: To assess the occurrence of the genes of the AdeABC efflux system and their association with antimicrobial resistance in Acinetobacter baumannii. METHODS: A set of 116 strains selected for their diversity both in genotypic properties and geographic origin was investigated for the presence of the structural (adeA, adeB and adeC) and regulatory (adeR and adeS) genes of the AdeABC system by PCR, for resistance to 11 antimicrobials by disc diffusion, for MIC of netilmicin and for the presence of aacC2 and aacA4, encoding netilmicin-modifying enzymes. RESULTS: Ninety-five strains were positive for adeA, adeB, adeR and adeS, 10 were positive for 1 to 3 of these genes and 11 were negative for all genes. The adeC gene was found in 49 strains with one or more of the other genes. Forty-one strains were resistant to a maximum of one agent and 75 strains to two or more agents. Netilmicin MICs showed an almost bimodal distribution with respective peaks of 0.5-1 and 8 mg/L; aacC2 or aacA4 was found in six strains with netilmicin MIC of >or=64 mg/L. All 61 strains with netilmicin MICs >or= 4 mg/L were both adeABRS-positive and resistant to two or more agents, whereas netilmicin MICs

Horizontal gene transfer in a polyclonal outbreak of carbapenem-resistant Acinetobacter baumannii.

In the last few years, phenotypically carbapenem resistant Acinetobacter strains have been identified throughout the world, including in many of the hospitals and intensive care units (ICUs) of Australia. Genotyping of Australian ICU outbreak-associated isolates by pulsed-field gel electrophoresis of whole genomic DNA indicated that different strains were cocirculating within one hospital. The carbapenem-resistant phenotype of these and other Australian isolates was found to be due to carbapenem-hydrolyzing activity associated with the presence of the blaOXA-23 gene. In all resistant strains examined, the blaOXA-23 gene was adjacent to the insertion sequence ISAba1 in a structure that has been found in Acinetobacter baumannii strains of a similar phenotype from around the world; blaOXA-51-like genes were also found in all A. baumannii strains but were not consistently associated with ISAba1, which is believed to provide the promoter required for expression of linked antibiotic resistance genes. Most isolates were also found to contain additional antibiotic resistance genes within the cassette arrays of class 1 integrons. The same cassette arrays, in addition to the ISAba1-blaOXA-23 structure, were found within unrelated strains, but no common plasmid carrying these accessory genetic elements could be identified. It therefore appears that antibiotic resistance genes are readily exchanged between cocirculating strains in epidemics of phenotypically indistinguishable organisms. Epidemiological investigation of major outbreaks should include whole-genome typing as well as analysis of potentially transmissible resistance genes and their vehicles.

Naturally transformable Acinetobacter sp. strain ADP1 belongs to the newly described species Acinetobacter baylyi.

Genotypic and phenotypic analyses were carried out to clarify the taxonomic position of the naturally transformable Acinetobacter sp. strain ADP1. Transfer tDNA-PCR fingerprinting, 16S rRNA gene sequence analysis, and selective restriction fragment amplification (amplified fragment length polymorphism analysis) indicate that strain ADP1 and a second transformable strain, designated 93A2, are members of the newly described species Acinetobacter baylyi. Transformation assays demonstrate that the A. baylyi type strain B2(T) and two other originally identified members of the species (C5 and A7) also have the ability to undergo natural transformation at high frequencies, confirming that these five strains belong to a separate species of the genus Acinetobacter, characterized by the high transformability of its strains that have been cultured thus far.