Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features

Molecular identification and genotyping of Acinetobacter baumannii isolated from burn patients by PCR and ERIC-PCR

BACKGROUND

Acinetobacter baumannii is one of the most important agents of hospital infections. Rapid and accurate identification and genotyping of A. baumannii is very important, especially in burn hospitals in order to prevent the spread of related nosocomial infections and to further epidemiological studies.

MATERIAL AND METHODS

For two months, 82 A. baumannii isolates were collected from burn wound swabs of patients in a major burn hospital in Tehran. A. baumannii isolates were identified by conventional microbiological test and polymerase chain reaction (PCR) using the primers of blaOXA-51 gene, while the genetic linkage of A. baumannii isolates was investigated by enterobacterial repetitive intragenic consensus (ERIC)-PCR technique. Similarity, a cut-off of ⩾ 95% was considered for classifying the genotypes.

RESULTS

The molecular test (PCR) confirmed 97.56% of phenotypic results for the detection of A. baumannii isolates. ERIC-PCR results revealed 14 different ERIC patterns (ERIC-types) including 11 common types and three unique types.

CONCLUSION

Our findings show that we can simply and quickly detect A. baumannii isolates by PCR using blaOXA genes and genetic diversity by ERIC-PCR, respectively. These rapid and simple techniques for the routine screening and identification of clinical A. baumannii isolates could be useful with epidemic potential.

Acinetobacter baumannii - a neglected pathogen in veterinary and environmental health in Germany

The emergence and global spread of drug resistant Acinetobacter (A.) baumannii is a cause of great concern. The current knowledge on antibiotic resistance in A. baumannii from animal origin is mostly based on few internationally published case reports, investigations of strain collections and several whole genome analyses. This lack of data results in a somewhat sketchy picture on how to assess the possible impact of drug resistant A. baumannii strains on veterinary and public health in Germany. Consequently, there is an urgent need to intensify the surveillance of A. baumannii in pet animals, the farm animal population and wildlife.

Variation of bacterioplankton community along an urban river impacted by touristic city: With a focus on pathogen

Bacterioplankton communities play a critical role in ecological processes in river systems, and shifts of their composition may impact microbial levels and raise public health concerns. The aim of this study was to comprehensively analyze the essential factors influencing bacterioplankton community, along with pathogen, and to estimate the health risk caused by the pathogens downstream of the Liushahe River, which is located in the famous touristic city Xishuangbanna. Results showed that wastewater treatment plants (WWTPs) and a subtropical recreational park impacted the bacterioplankton community and pathogen population, and potential pathogen identification demonstrated that 76 of 145 reference genera were present in the river. Moreover, the bacterioplankton community and pathogen were differently impacted by environmental gradients, and SRP, NO₂ and pH were main factors influencing bacterioplankton community while pathogen population was highly correlated with temperature and turbidity. In addition, it is noted that the pathogen population was dominated by bacterioplankton community and this might because the capacity of resistance invasion pathogen was determined by of bacterioplankton community diversity. Therefore, bacterioplankton community diversity can be used to control and predict the amount of pathogens. Quantitative microbial risk assessment (QMRA) also revealed that the infection risks of Escherichia coli (E. coli), Mycobacterium avium (M. avium), and Pseudomonas aeruginosa (P. aeruginosa) during five recreational activities, especially water-based activities in the touristic city, were greater than that in natural areas and mostly exceeded the U.S. EPA risk limit for recreational activities. Our study offered the first insight into the potential relationship between the bacterioplankton community and bacterial pathogens within a touristic river.

Trimethoprim-sulfamethoxazole vs. colistin or ampicillin-sulbactam for the treatment of carbapenem-resistant Acinetobacter baumannii: A retrospective matched cohort study

OBJECTIVES

This study aimed to assess the effectiveness of trimethoprim-sulfamethoxazole (TMP/SMX) as monotherapy for the treatment of carbapenem-resistant Acinobacter baumannii (A. baumannii) (CRAB) infections.

METHODS

This retrospective cohort study included patients receiving TMP/SMX as the main treatment for severe infections caused by CRAB, who were matched with patients treated with colistin or ampicillin-sulbactam (AMP/SUL) by age, Charlson score, department, and source of infection. Outcomes were compared among all patients and in a subgroup of propensity-score (PS) matched patients. The PS matching was performed using a match tolerance of 0.15 with replacement.

RESULTS

Fifty-three patients treated with TMP/SMX and 83 matched patients treated with colistin or AMP/SUL were included. Variables that were independently significantly associated with TMP/SMX treatment included admission for infection and septic shock, while abnormal cognition on admission and intensive care unit admission were associated with colistin or AMP/SUL treatment. All-cause 30-day mortality was lower with TMP/SMX compared with the comparator antibiotics among all patients (24.5%, 13 of 53 vs. 38.6%, 32 of 83, P=0.09) and in the PS-matched subgroup (29%, 9 of 31 vs. 55.2% 16 of 29, P=0.04). Treatment failure rates were not significantly different overall (34%, 18 of 53 vs. 42.4%, 35 of 83, P=0.339) and in the PS-matched subgroup (35.5%, 11 of 31 vs. 44.8%, 13 of 29, P=0.46). Time to clinical stability and hospitalization duration were significantly shorter with TMP/SMX. Patients treated with TMP/SMX probably had less severe infections than those treated with other antibiotics, even after matching.

CONCLUSIONS

TMP/SMX might be a valuable treatment option for TMP/SMX-susceptible CRAB infections. Given the very limited available treatment options, further studies assessing its effectiveness and safety are necessary.

Colistin nanoparticle assembly by coacervate complexation with polyanionic peptides for treating drug-resistant gram-negative bacteria

Amidst the ever-rising threat of antibiotics resistance, colistin, a decade-old antibiotic with lingering toxicity concern, is increasingly prescribed to treat many drug-resistant, gram-negative bacteria. With the aim of improving the safety profile while preserving the antimicrobial activity of colistin, a nanoformulation is herein developed through coacervate complexation with polyanionic peptides. Upon controlled mixing of cationic colistin with polyglutamic acids, formation of liquid coacervates was demonstrated. Subsequent stabilization by DSPE-PEG and homogenization through micro-fluidization of the liquid coacervates yielded nanoparticles 8 nm in diameter. In vitro assessment showed that the colistin antimicrobial activity against multiple drug-resistant bacterial strains was retained and, in some cases, enhanced following the nanoparticle assembly. In vivo administration in mice demonstrated improved safety of the colistin nanoparticle, which has a maximal tolerated dose of 12.5 mg/kg compared to 10 mg/kg of free colistin. Upon administration over a 7-day period, colistin nanoparticles also exhibited reduced hepatotoxicity as compared to free colistin. In mouse models of Klebsiella pneumoniae bacteremia and Acinetobacter baumannii pneumonia, treatment with colistin nanoparticles showed equivalent efficacy to free colistin. These results demonstrate coacervation-induced nanoparticle assembly as a promising approach towards improving colistin treatments against bacterial infections. STATEMENT OF SIGNIFICANCE: Improving the safety of colistin while retaining its antimicrobial activity has been a highly sought-after objective toward enhancing antibacterial treatments. Herein, we demonstrate formation of stabilized colistin nanocomplexes in the presence of anionic polypeptides and DSPE-PEG stabilizer. The nanocomplexes retain colistin's antimicrobial activity while demonstrating improved safety upon in vivo administration. The supramolecular nanoparticle assembly of colistin presents a unique approach towards designing antimicrobial nanoparticles.

Prevalence of VIM- and GIM-producing Acinetobacter baumannii from patients with severe urinary tract infection

Carbapenems are administered as the final drug of choice for treating complicated nosocomial infections caused by multidrug-resistant Acinetobacter baumannii strains. It is currently a worldwide issue that metallo-β-lactamases (MBLs) as carbapenem-hydrolyzing enzymes are one of the major drug resistance mechanisms. This investigation is thus aimed to assess the prevalence and characterize the MBL-producing strains of A. baumannii both by phenotypic assays and by genotypic characterization. A total of 73 isolates of A. baumannii were phenotypically and genotypically characterized from patients (N = 1,000) with severe urinary tract infection. Tested strains were subjected to double disc synergy testing (DDST) by Kirby-Bauer disc diffusion method with imipenem (IMP) and IMP/EDTA combination discs. Plasmid DNA was molecularly screened for MBL-encoding bla_IMP, bla_VIM, bla_GIM, and bla_NDM genes by PCR for the genetic relatedness of the MBL genes with carbapenem resistance. Carbapenem resistance profile showed 100%, 45%, and 49% non-susceptibility against imipenem, doripenem, and meropenem, respectively. Altogether 42.46% (n = 31) of the isolates showed MBL production upon double disc phenotypic test with IMP and IMP/EDTA discs. The bla_VIM and bla_GIM were detected in 34.24% (n = 25) and 16.43% (n = 12) of the isolates, respectively, while the co-occurrence of bla_VIM and bla_GIM was 2.73% among the isolates. DDST-positive isolates showed 21.19% and 9.58% strains positive for bla_VIM and bla_GIM, respectively, whereas 1.36% of the strains for both genes. None of the strains yielded bla_IMP and bla_NDM genes. The findings of this study showed prevalence of carbapenem resistance among A. baumannii from urine samples and the frequency of bla_VIM and bla_GIM.

Distinct amino acid residues confer one of three UDP-sugar substrate specificities in Acinetobacter baumannii PglC phosphoglycosyltransferases

Acinetobacter baumannii is an opportunistic human pathogen with the highest reported rates of multidrug resistance among Gram-negative pathogens. The capsular polysaccharide of A. baumannii is considered one of its most significant virulence factors providing resistance against complemented-mediated killing. Capsule synthesis in A. baumannii is usually initiated by the phosphoglycosyltransferase PglC. PglC transfers a phosphosugar from a nucleotide diphosphate-sugar to a polyprenol phosphate generating a polyprenol diphosphate-linked monosaccharide. Traditionally, PglC was thought to have stringent specificity towards UDP-N-N'-diacetylbacillosamine (UDP-diNAcBac). In this work we demonstrate that A. baumannii PglC has the ability to utilize three different UDP-sugar substrates: UDP-N-acetylglucosamine (UDP-GlcNAc), UDP-N-acetylgalactosamine (UDP-GalNAc) or UDP-diNAcBac. Using phylogenetic analyses, we first demonstrate that A. baumannii PglC orthologs separate into three distinct clades. Moreover, all members within a clade are predicted to have the same preference for one of the three possible sugar substrates. To experimentally determine the substrate specificity of each clade, we utilized in vivo complementation models and NMR analysis. We demonstrate that UDP-diNAcBac is accommodated by all PglC orthologs, but some orthologs evolved to utilize UDP-GlcNAc or UDP-GalNAc in a clade-dependent manner. Furthermore, we show that a single point mutation can modify the sugar specificity of a PglC ortholog specific for UDP-diNAcBac and that introduction of a non-native PglC ortholog into A. baumannii can generate a new capsule serotype. Collectively, these studies begin to explain why A. baumannii strains have such highly diverse glycan repertoires.

Genome sequence analysis of an extensively drug-resistant Acinetobacter baumannii indigo-pigmented strain depicts evidence of increase genome plasticity

Acinetobacter baumannii is a multidrug resistant nosocomial pathogen that shows an outstanding ability to undergo genetic exchange, thereby acquiring different traits that contribute to its success. In this work, we identified genetic features of an indigo-pigmented A. baumannii strain (Ab33405) that belongs to the clonal complex CC113B/CC79P. Ab33405 possesses a high number of genes coding for antibiotic resistance and virulence factors that may contribute to its survival, not only in the human host, but also in the hospital environment. Thirteen genes conferring resistance to different antibiotic families (trimethoprim, florfenicol, β-lactams, aminoglycosides and sulfonamide) as well as the adeIJK genes and the capsule locus (KL) and outer core locus (OCL) were identified. Ab33405 includes 250 unique genes and a significant number of elements associated with Horizontal Gene Transfer, such as insertion sequences and transposons, genomic islands and prophage sequences. Also, the indigo-pigmented uncommon phenotype that could be associated with the monooxygenase or dioxygenase enzyme coded for by the iacA gene within the iac cluster was probably conferred by insertion of a 18-kb DNA fragment into the iacG gene belonging to this cluster. The Ab33405 genome includes all type VI secretion system genes and killing assays showed the ability of Ab33045 to kill Escherichia coli. In addition, Ab33405 can modulate susceptibility antibiotics when exposed to blue light.

Bacterial community structure in atmospheric particulate matters of different sizes during the haze days in Xi'an, China

Serious air pollution events have frequently occurred in China associated with the acceleration of urbanization and industrialization in recent years. Exposure to atmospheric particulate matter (PM) of high concentration can lead to adverse effects on human health. Airborne bacteria are important constituents of microbial aerosols and contain lots of pathogens. However, variations in bacterial community structure in atmospheric PM of different sizes (PM_2.5, PM₁₀ and TSP) have not yet been explored. In this study, PM samples of different sizes were collected during the hazy days from Jul.2016 to Apr.2017 to determine bacterial diversity and community structure. Samples from soils and leaf surfaces were also collected to determine potential sources of bacterial aerosols. High-throughput sequencing technology was used generate bacterial community profiles, where we determined their diversity and abundances in the samples. Results showed that the dominant bacterial community structures in PM_2.5, PM₁₀ and TSP were strongly similar. Compared with non-haze days, the relative abundances of most bacterial pathogens on the haze days did not increase. Meanwhile, temperature, O₃ and NO₂ had more significant effects on bacterial community than the other environmental factors. Source tracking analysis indicated that the airborne bacteria might be not from local environment. It may come from the entire city or other regions by long distance airflow transport. Results of this study improved our understanding of the influence of bioaerosols on human health and the potential sources of airborne microbes.

The importance of lag time extension in determining bacterial resistance to antibiotics

It is widely appreciated that widespread antibiotic resistance has significantly reduced the utility of today's antibiotics. Many antibiotics now fail to cure infectious diseases, although they are classified as effective bactericidal agents based on antibiotic susceptibility tests. Here, via kinetic growth assays, we evaluated the effects of 12 commonly used antibiotics on the lag phase of a range of pure environmental isolates and of sludge bacterial communities with a high diversity. We show that an extended lag phase offers bacteria survival advantages and promotes regrowth upon the removal of antibiotics. By utilizing both lag phase extension and IC50, the killing efficiency of an antibiotic on a strain or a community can be easily revealed. Interestingly, for several strains of relevance to endemic nosocomial infections (e.g. Acinetobacter sp. and Pseudomonas aeruginosa) and the diverse sludge communities, tetracycline and quinolone antibiotics are most likely to be resisted via extended lag phase. This discovery is significant from a clinical point view since underestimation of bacteria resistance can lead to the recurrence of diseases.

Multiple Quorum Quenching Enzymes Are Active in the Nosocomial Pathogen Acinetobacter baumannii ATCC17978

Acinetobacter baumannii presents a typical luxI/luxR quorum sensing (QS) system (abaI/abaR) but the acyl-homoserine lactone (AHL) signal profile and factors controlling the production of QS signals in this species have not been determined yet. A very complex AHL profile was identified for A. baumannii ATCC17978 as well as for A. nosocomialis M2, but only when cultivated under static conditions, suggesting that surface or cell-to-cell contact is involved in the activation of the QS genes. The analysis of A. baumanni clinical isolates revealed a strain-specific AHL profile that was also affected by nutrient availability. The concentration of OHC12-HSL, the major AHL found in A. baumannii ATCC17978, peaked upon stationary-phase establishment and decreases steeply afterwards. Quorum quenching (QQ) activity was found in the cell extracts of A. baumannii ATCC17978, correlating with the disappearance of the AHLs from the culture media, indicating that AHL concentration may be self-regulated in this pathogen. Since QQ activity was observed in strains in which AidA, a novel α/β-hydrolase recently identified in A. baumannii, is not present, we have searched for additional QQ enzymes in A. baumannii ATCC17978. Seven putative AHL-lactonase sequences could be identified in the genome and the QQ activity of 3 of them could be confirmed. At least six of these lactonase sequences are also present in all clinical isolates as well as in A. nosocomialis M2. Surface-associated motility and biofilm formation could be blocked by the exogenous addition of the wide spectrum QQ enzyme Aii20J. The differential regulation of the QQ enzymes in A. baumannii ATCC17978 and the full dependence of important virulence factors on the QS system provides a strong evidence of the importance of the AHL-mediated QS/QQ network in this species.

Control of Biofilm Formation in Healthcare: Recent Advances Exploiting Quorum-Sensing Interference Strategies and Multidrug Efflux Pump Inhibitors

Biofilm formation in healthcare is an issue of considerable concern, as it results in increased morbidity and mortality, imposing a significant financial burden on the healthcare system. Biofilms are highly resistant to conventional antimicrobial therapies and lead to persistent infections. Hence, there is a high demand for novel strategies other than conventional antibiotic therapies to control biofilm-based infections. There are two approaches which have been employed so far to control biofilm formation in healthcare settings: one is the development of biofilm inhibitors based on the understanding of the molecular mechanism of biofilm formation, and the other is to modify the biomaterials which are used in medical devices to prevent biofilm formation. This review will focus on the recent advances in anti-biofilm approaches by interrupting the quorum-sensing cellular communication system and the multidrug efflux pumps which play an important role in biofilm formation. Research efforts directed towards these promising strategies could eventually lead to the development of better anti-biofilm therapies than the conventional treatments.

Assessing Pathogen Presence in an Intensively Tile Drained, Agricultural Watershed

Increases in swine production and concomitant manure application provide beneficial nutrients for crops but also include the potential to spread pathogenic bacteria in the environment. While manure is known to contain a variety of pathogens, little is known regarding the long-term effect of manure application on fate and transport of this diverse set of pathogens into surrounding waterways. We report on the use of 16S-rRNA gene sequencing to detect pathogen-containing genera in the agriculturally dominated South Fork Iowa River watershed, home to approximately 840,000 swine in the 76,000-ha basin. DNA was extracted from monthly grab samples collected from three surface water sites and two main artificial drainage outlets. DNA sequences from water samples were matched with sequences from genera known to contain pathogens using targeted 16S rRNA amplicon sequencing. The specific genera known to contain pathogens were quantified by combining percentage of genera sequence matches with 16S rRNA gene quantitative polymerase chain reaction results. Specifically, abundances of , , and significantly increased in surface water after typical fall manure application. Additionally, the likely transport pathways for specific genera known to contain pathogens were identified. Surface water concentrations were influenced mainly by artificial drainage, whereas was primarily transported to surface waters by runoff events. The results of this study will help us to understand environmental pathways that may be useful for mitigation of the diverse set of pathogenic genera transported in agroecosystems and the capability of manure application to alter existing microbial community structures.

Inactivation of multidrug-resistant pathogens and Yersinia enterocolitica with cold atmospheric-pressure plasma on stainless-steel surfaces

The objective of this study was to investigate the impact of cold atmospheric-pressure plasma (CAP) produced by a surface micro-discharge plasma source as a new strategy to combat the transmission of five multidrug-resistant (MDR) pathogens and Yersinia enterocolitica on typical hospital- and food-producing surfaces, e.g. stainless-steel. Approximately 10⁶ CFU/cm² of vancomycin-resistant Enterococcus faecium, methicillin-resistant Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Y. enterocolitica were inoculated on a 3.14-cm² stainless-steel surface. Bovine serum albumin (BSA) (3%) was used as a disruptive factor simulating natural organic material. The inoculated surfaces were subsequently exposed to CAP, generated by a peak-to-peak voltage of 10 kV with sinusoidal waveform and a frequency of 2 kHz, for 5, 10 and 20 min, respectively. Fluorescent staining with propidium iodide and SYTO^TM 9 was used to demonstrate the manner of bacterial cell damage. Significant (P < 0.05) inactivation of 1.68 ± 0.17 up to 2.80 ± 0.17 log steps was achieved after 5 min of CAP treatment. However, bacterial reduction could be increased to 3.35 ± 0.1 up to 5.17 ± 0.67 log steps after 20 min of CAP treatment. Bacterial cells covered with BSA were statistically significantly less inactivated by CAP. Fluorescent staining showed a predominant level of orange-stained, sublethally damaged bacterial cells after 10 min of CAP treatment. In conclusion, CAP has the ability to inactivate MDR bacterial pathogens on stainless-steel surfaces. Further research is required to investigate the clinical features of CAP.

Acinetobacter in veterinary medicine, with an emphasis on Acinetobacter baumannii

Acinetobacter spp. are aerobic, rod-shaped, Gram-negative bacteria belonging to the Moraxellaceae family of the class Gammaproteobacteria and are considered ubiquitous organisms. Among them, Acinetobacter baumannii is the most clinically significant species with an extraordinary ability to accumulate antimicrobial resistance and to survive in the hospital environment. Recent reports indicate that A. baumannii has also evolved into a veterinary nosocomial pathogen. Although Acinetobacter spp. can be identified to species level using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS) coupled with an updated database, molecular techniques are still necessary for genotyping and determination of clonal lineages. It appears that the majority of infections due to A. baumannii in veterinary medicine are nosocomial. Such isolates have been associated with several types of infection such as canine pyoderma, feline necrotizing fasciitis, urinary tract infection, equine thrombophlebitis and lower respiratory tract infection, foal sepsis, pneumonia in mink, and cutaneous lesions in hybrid falcons. Given the potential multidrug resistance of A. baumannii, treatment of diseased animals is often supportive and should preferably be based on in vitro antimicrobial susceptibility testing results. It should be noted that animal isolates show high genetic diversity and are in general distinct in their sequence types and resistance patterns from those found in humans. However, it cannot be excluded that animals may occasionally play a role as a reservoir of A. baumannii. Thus, it is of importance to implement infection control measures in veterinary hospitals to avoid nosocomial outbreaks with multidrug-resistant A. baumannii.

A Light-Regulated Type I Pilus Contributes to Acinetobacter baumannii Biofilm, Motility, and Virulence Functions

Transcriptional analyses of Acinetobacter baumannii ATCC 17978 showed that the expression of A1S_2091 was enhanced in cells cultured in darkness at 24°C through a process that depended on the BlsA photoreceptor. Disruption of A1S_2091, a component of the A1S_2088-A1S_2091 polycistronic operon predicted to code for a type I chaperone/usher pilus assembly system, abolished surface motility and pellicle formation but significantly enhanced biofilm formation on plastic by bacteria cultured in darkness. Based on these observations, the A1S_2088-A1S_2091 operon was named the photoregulated pilus ABCD (prpABCD) operon, with A1S_2091 coding for the PrpA pilin subunit. Unexpectedly, comparative analyses of ATCC 17978 and prpA isogenic mutant cells cultured at 37°C showed the expression of light-regulated biofilm biogenesis and motility functions under a temperature condition that drastically affects BlsA production and its light-sensing activity. These assays also suggest that ATCC 17978 cells produce alternative light-regulated adhesins and/or pilus systems that enhance bacterial adhesion and biofilm formation at both 24°C and 37°C on plastic as well as on the surface of polarized A549 alveolar epithelial cells, where the formation of bacterial filaments and cell chains was significantly enhanced. The inactivation of prpA also resulted in a significant reduction in virulence when tested by using the Galleria mellonella virulence model. All these observations provide strong evidence showing the capacity of A. baumannii to sense light and interact with biotic and abiotic surfaces using undetermined alternative sensing and regulatory systems as well as alternative adherence and motility cellular functions that allow this pathogen to persist in different ecological niches.

The Frequency of Antibiotic Resistance and ESBLs Among Clinically Acinetobacter baumannii Strains Isolated from Patients in a Major Hospital in Tehran, Iran

Background:

Bacterial resistance to antibiotics limits treatment options, increases morbidity and mortality, and raises the risk of antibiotic-associated adverse events. Antibacterial resistance emerges rapidly following an increase in the consumption of antibiotics against infectious diseases. The spread of ESBL producing strains has a limiting factor based on antibiotic function for the treatment of infections particularly caused by Acinetobacter baumannii (A. baumannii).

Objective:

This study was conducted to evaluate the prevalence of antimicrobial resistance and distribution of bla_TEM, bla_CTX, and bla_SHV genes among A. baumannii strains isolated from clinical samples at a major hospital in Teheran, Iran.

Methods:

A. baumannii strains were isolated and identified using standard microbiological methods. The disc diffusion and combined discs methods were used for testing antimicrobial susceptibility and to identify the strains producing Extended-Spectrum Beta-Lactamases (ESBL), respectively. DNA extraction was done by boiling method. Finally, the frequency of resistant genes including bla_TEM, bla_CTX, and bla_SHV in ESBL producing isolates was studied by PCR.

Results:

Gender distribution in this study was 53 (53%) samples for men and 47 (47%) for women. Totally, one hundred A. baumannii strains were isolated. More than 93% of the isolates were multi drug resistant. The highest to lowest antibiotic resistance was observed against amoxicillin/clavulanic acid (98%), ceftriaxone (96%), cefotaxime (94%), and ceftazidime (93%), respectively. The frequency of positive phenotypic test of ESBL was 19% and 16% for CAZ-C and CTX-C, respectively. The frequency of bla_TEM, bla_CTX, and bla_SHV genes was 52.1, 43.4, and 21.7, respectively.

Conclusion:

A. baumannii isolates exhibited an extremely worrying level of antibiotic resistance, and a high percentage of the isolates showed MDR in this study. This is a serious warning because ESBLs are a major threat to the effectiveness of antibiotics that are currently available for medical uses. The frequency of genes encoded ESBL isolates of A. baumannii may be due to overuse and misuse of antibiotics.

Acinetobacter baumannii Gastrointestinal Colonization Is Facilitated by Secretory IgA Which Is Reductively Dissociated by Bacterial Thioredoxin A

Multidrug-resistant Acinetobacter baumannii is among the most common causes of infectious complications associated with combat-related trauma in military personnel serving overseas. However, little is currently known about its pathogenesis. While the gastrointestinal (GI) tract has been found to be a major reservoir for A. baumannii, as well as to potentially contribute to development of multidrug resistance, no studies have addressed the mechanisms involved in gut colonization. In this study, we address this critical gap in knowledge by first assessing the interaction between secretory IgA (SIgA), the principal humoral immune defense on mucosal surfaces, and the A. baumannii clinical isolate Ci79. Surprisingly, SIgA appeared to enhance A. baumannii GI tract colonization, in a process mediated by bacterial thioredoxin A (TrxA), as evidenced by reduction of bacterial attachment in the presence of TrxA inhibitors. Additionally, a trxA targeted deletion mutant (ΔtrxA) showed reduced bacterial burdens within the GI tract 24 h after oral challenge by in vivo live imaging, along with loss of thiol-reductase activity. Surprisingly, not only was GI tract colonization greatly reduced but the associated 50% lethal dose (LD₅₀) of the ΔtrxA mutant was increased nearly 100-fold in an intraperitoneal sepsis model. These data suggest that TrxA not only mediates A. baumannii GI tract colonization but also may contribute to pathogenesis in A. baumannii sepsis following escape from the GI tract under conditions when the intestinal barrier is compromised, as occurs with cases of severe shock and trauma.

Acinetobacter baumannii is an emerging bacterial pathogen recently classified as a serious threat to U.S. and global health by both the Centers for Disease Control and Prevention and the World Health Organization. It also is one of the leading causes of combat-related infections associated with injured military personnel serving overseas. Little is known regarding mechanisms of gastrointestinal tract colonization despite this site being shown to serve as a reservoir for multidrug-resistant (MDR) A. baumannii isolates. Here, we establish that secretory IgA, the major immunoglobulin of mucosal surfaces, promotes A. baumannii GI tract colonization via bacterial thioredoxin A as evidenced through significant reduction in colonization in IgA-deficient animals. Additionally, bacterial colonization and mortality were significantly reduced in animals challenged with a thioredoxin A-deficient A. baumannii mutant. Combined, these data suggest that thioredoxin A is a novel virulence factor, for which antithioredoxin therapies could be developed, for this important multidrug-resistant pathogen.

Antimicrobial Susceptibility Patterns of an Emerging Multidrug Resistant Nosocomial Pathogen: Acinetobacter baumannii

Multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) bacterium, a nosocomial pathogen associated with a high mortality rate and limited therapeutic options have emerged as a serious problem throughout the world. The present study aimed to assess the current levels of antibiotic susceptibility among the isolates of Acinetobacter species. The sensitivity patterns were analysed from various clinical specimens obtained from both in-patients and outpatients of a teaching hospital. Isolation was performed on 5% sheep blood agar and MacConkey agar. Urine samples were inoculated into CLED agar. Antibiotic susceptibility was performed by the disc diffusion method. A total of 16,452 samples were collected. The total number of samples positive for Acinetobacter species was 67 (0.4%). The highest number of isolates 26 (38.8%) were obtained from urine. Majority 80.3% of the isolates exhibited resistance to three or more classes of antibiotics. All isolates were susceptible to colistin (100%). The susceptibility rate of A. baumannii isolates was 80% for tigecycline and 53.3% for carbapenem. Combination therapies including colistin and tigecycline seem to be the rational treatment for MDR A. baumannii until new alternatives come forward.

Complete Genome Sequence of Acinetobacter schindleri SGAir0122 Isolated from Singapore Air

Acinetobacter schindleri strain SGAir0122 was isolated from tropical air samples collected in Singapore. The prevalence of nosocomial infection caused by this Gram-negative bacterium indicates its clinical significance as an opportunistic human pathogen. Its complete genome consists of one chromosome of 3.105 Mb and a plasmid of 181 kb.

Characterization and Transcriptome Analysis of Acinetobacter baumannii Persister Cells

Acinetobacter baumannii is a nonfermenting Gram-negative bacillus. A. baumannii resistance is a significant obstacle to clinical infection treatment. The existence of persister cells (persisters) might represent the reason for therapy failure and relapse, and such cells may be the driving force behind rising resistance rates. In this study, A. baumannii ATCC 19606 was used as a target to explore the essential features of A. baumannii persisters. Antibiotic treatment of A. baumannii cultures at 50-fold the minimum inhibitory concentration resulted in a distinct plateau of surviving drug-tolerant persisters. The sensitive bacteria were lysed with ceftazidime, and the nonreplicating bacteria were isolated for transcriptome analysis using RNA sequencing. We analyzed the transcriptome of A. baumannii persisters and identified significantly differentially expressed genes, as well as their enriched pathways. The results showed that both the GP49 (HigB)/Cro (HigA) and DUF1044/RelB toxin/antitoxin systems were significantly increased during the persister incubation period. In addition, the activities of certain metabolic pathways (such as electron transport, adenosine triphosphate [ATP], and the citrate cycle) decreased sharply after antibiotic treatment and remained low during the persister period, while aromatic compound degradation genes were only upregulated in persisters. These results suggest the involvement of aromatic compound degradation genes in persister formation and maintenance. They further provide the first insight into the mechanism of persister formation in A. baumannii.

Effects of copper on the composition and diversity of microbial communities in laboratory-scale swine manure composting

This study investigated the effects of adding copper at 3 treatment levels (0 (control: CK), 200 (low: L), and 2000 (high: H) mg·kg−1 treatments) on the bacterial communities during swine manure composting. The abundances of the bacteria were determined by quantitative PCR and their compositions were evaluated by high-throughput sequencing. The results showed that the abundance of bacteria was inhibited by the H treatment during days 7–35, and principal component analysis clearly separated the H treatment from the CK and L treatments. Actinobacteria, Firmicutes, and Proteobacteria were the dominant bacterial taxa, and a high copper concentration decreased the abundances of bacteria that degrade cellulose and lignin (e.g., class Bacilli and genus Truepera), especially in the mesophilic and thermophilic phases. Moreover, network analysis showed that copper might alter the co-occurrence patterns of bacterial communities by changing the properties of the networks and the keystone taxa, and increase the competition by increasing negative associations between bacteria during composting. Temperature, water-soluble carbohydrates, and copper significantly affected the variations in the bacterial community according to redundancy analysis. The copper content mainly contributed to the bacterial community in the thermophilic and cooling phases, where it had positive relationships with potentially pathogenic bacteria (e.g., Corynebacterium_1 and Acinetobacter).

Chromosomally encoded and plasmid-mediated polymyxins resistance in Acinetobacter baumannii: a huge public health threat

Acinetobacter baumannii is an opportunistic pathogen associated with nosocomial and community infections of great clinical relevance. Its ability to rapidly develop resistance to antimicrobials, especially carbapenems, has re-boosted the prescription and use of polymyxins. However, the emergence of strains resistant to these antimicrobials is becoming a critical issue in several regions of the world because very few of currently available antibiotics are effective in these cases. This review summarizes the most up-to-date knowledge about chromosomally encoded and plasmid-mediated polymyxins resistance in A. baumannii. Different mechanisms are employed by A. baumannii to overcome the antibacterial effects of polymyxins. Modification of the outer membrane through phosphoethanolamine addition, loss of lipopolysaccharide, symmetric rupture, metabolic changes affecting osmoprotective amino acids, and overexpression of efflux pumps are involved in this process. Several genetic elements modulate these mechanisms, but only three of them have been described so far in A. baumannii clinical isolates such as mutations in pmrCAB, lpxACD, and lpsB. Elucidation of genotypic profiles and resistance mechanisms are necessary for control and fight against resistance to polymyxins in A. baumannii, thereby protecting this class for future treatment.

Variation pattern of terrestrial antibiotic resistances and bacterial communities in seawater/freshwater mixed microcosms

The ocean is the final place where pollutants generated by human activities are deposited. As a result, the long-range transport of the ocean can facilitate the diffusion of terrestrial contaminants, including ARGs. However, to our knowledge, little research has been devoted to discussing the content change of terrestrial ARGs and the reason for the change in coastal area. This study established various microcosms, in which seawater and freshwater were mixed at different ratio to simulate the environmental conditions of different regions in coastal areas. Four ARGs were quantified, and 16S pyrosequencing was conducted. The results showed that the terrestrial ARGs influenced the concentration of the corresponding ARGs in coastal areas, and the content change pattern of each ARG was distinct. The influence of salinity on the ARG content was limited in most cases. Moreover, most dominant bacteria from freshwater had significant positive correlation (p < 0.05) with selected ARGs, except for bla_TEM. The dominant bacteria in freshwater diminished dramatically in microcosms with a high proportion of seawater. Freshwater may have a strong impact on the bacteria composition of seawater, and the materials from freshwater may prompt the growth of some bacteria (include potential hosts of ARGs) in coastal area.

Urinary tract infection by Acinetobacter baumannii and Pseudomonas aeruginosa: evolution of antimicrobial resistance and therapeutic alternatives

Purpose. Acinetobacter baumannii and Pseudomonas aeruginosa are responsible for numerous nosocomial infections. The objective of this study was to determine the development of their susceptibility to ten antibiotics and the antibiotic consumption of patients with suspicion of urinary tract infection (UTI).Methodology. A retrospective study was conducted on the susceptibility profiles of A. baumannii and P. aeruginosa isolates from 749 urine samples gathered between January 2013 and December 2016, and on the consumption of imipenem, meropenem and piperacillin-tazobactam between 2014 and 2016.Results. Hospital patients were the source of 82 (91.1 %) of the 90 A. baumannii isolates detected and 555 (84.2 %) of the 659 P. aeruginosa isolates. Globally, the lowest percentage susceptibility values were found for fosfomycin, aztreonam and ciprofloxacin, while colistin continued to be the most active antibiotic in vitro. In 2016, the susceptibility of A. baumannii to carbapenem and piperacillin-tazobactam decreased to very low values, while the susceptibility of P. aeruginosa to carbapenem remained stable but its susceptibility to piperacillin-tazobactam decreased. There was a marked increase in the consumption of piperacillin-tazobactam.Conclusion. In our setting, it is no longer possible to use carbapenems and piperacillin-tazobactam for empirical treatment of UTI due to A. baumannii or to use piperacillin-tazobactam for empirical treatment of UTI due to P. aeruginosa. Colistin was found to be the most active antibiotic in vitro. There was a marked increase in the consumption of piperacillin-tazobactam.

Antibiofilm activity of an EDTA-containing nanoemulsion on multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii have evolved as an exceedingly troublesome pathogenic microorganisms and prevention and controlling this pathogen is considered to be a public health problem. Nanoemulsions (NE) are a distinctive type of decontaminator produced by integration of immiscible oil phase with aqueous phase under extreme shear forces. The effectiveness of NEs and their components was determined against four stains of A. baumannii by MBC, adherence assay, biofilm assay and SEM studies. NE dilutions ranging from 125 to 225 reduced adhesion by from 61.8 to 99.9% in NE-treated groups (p<.05) as determined by MBC. Four-day-old A. baumannii biofilms were treated with NE; LIVE/DEAD staining showed dead cell intensity of 56.2-92.0% in NE-treated groups. After NE treatment and observation by SEM, cell surfaces appeared to be remarkably disintegrated. Irregular boundaries were observed and margins of cell walls were unclear. The anti-adherence, anti-biofilm and morphological disruption effects of NE suggest that this material could be useful for the development of promising antimicrobial agents.

Incidence of and associated factors for bacterial colonization of intravenous catheters removed from dogs in response to clinical complications

BACKGROUND

Infection rate associated with intravenous (IV) catheter placement is emerging as an important issue in small animal veterinary medicine, mostly because of the economic costs associated with these infections. Identification of possible associated factors may provide useful information for the surveillance and prevention of such infections.

OBJECTIVES

To determine the incidence of positive bacterial cultures obtained from IV catheters used in dogs hospitalized for at least 48 hours and removed because of clinical complication. To identify the bacteria involved and factors associated with bacterial colonization.

ANIMALS

One-hundred eighty-two dogs that underwent IV catheterization from January 2015 to July 2015 at the Veterinary Teaching Hospital of Alfonso X el Sabio University of Madrid were enrolled in the study.

RESULTS

The bacterial colonization rate of all IV catheters removed in response to clinical complications was 39.6%, the cumulative proportion of catheters that remained in place at 24, 48, and 72 hours after placement was 89.5, 78, and 59.4%, respectively. Multivariable Cox proportional hazards regression indicated significant associations for staff who performed catheterization (junior, P = .002; student, P = .034) and use of steroidal anti-inflammatory drugs (P = .036). The most frequently isolated bacterium was Acinetobacter spp. (21.7%).

CONCLUSIONS AND CLINICAL IMPORTANCE

The bacterial colonization incidence related to IV catheter placement was slightly higher than the incidence described in other veterinary studies. Associated factors not previously described in veterinary medicine were found. The most frequently isolated organism was Acinetobacter spp., indicating its importance as an emerging pathogen in catheter colonization.

A high-frequency phenotypic switch links bacterial virulence and environmental survival in Acinetobacter baumannii

Antibiotic resistant infections lead to 700,000 deaths per year worldwide¹. The roles of phenotypically diverse subpopulations of clonal bacteria in the progression of diseases are unclear. We found that the increasingly pathogenic and antibiotic resistant pathogen, Acinetobacter baumannii, harbors a highly virulent subpopulation of cells responsible for disease. This virulent subpopulation possesses a thicker capsule and is resistant to host antimicrobials, which drive its enrichment during infection. Importantly, bacteria harvested from the bloodstream of human patients belong exclusively to this virulent subpopulation. Furthermore, the virulent form exhibits increased resistance to hospital disinfectants and desiccation, indicating a role in environmental persistence and the epidemic spread of disease. We identified a transcriptional “master regulator” of the switch between avirulent and virulent cells, and whose overexpression abrogated virulence. Further, the overexpression strain vaccinated mice against lethal challenge. This work highlights a phenotypic subpopulation of bacteria that drastically alters the outcome of infection, and illustrates how knowledge of the regulatory mechanisms controlling such phenotypic switches can be harnessed to attenuate bacteria and develop translational interventions.

Structural Variation in the Bacterial Community Associated with Airborne Particulate Matter in Beijing, China, during Hazy and Nonhazy Days

The structural variation of the bacterial community associated with particulate matter (PM) was assessed in an urban area of Beijing during hazy and nonhazy days. Sampling for different PM fractions (PM_2.5 [<2.5 μm], PM₁₀ [<10 μm], and total suspended particulate) was conducted using three portable air samplers from September 2014 to February 2015. The airborne bacterial community in these samples was analyzed using the Illumina MiSeq platform with bacterium-specific primers targeting the 16S rRNA gene. A total of 1,707,072 reads belonging to 6,009 operational taxonomic units were observed. The airborne bacterial community composition was significantly affected by PM fractions (R = 0.157, P < 0.01). In addition, the relative abundances of several genera significantly differed between samples with various haze levels; for example, Methylobacillus, Tumebacillus, and Desulfurispora spp. increased in heavy-haze days. Canonical correspondence analysis and permutation tests showed that temperature, SO₂ concentration, relative humidity, PM₁₀ concentration, and CO concentration were significant factors that associated with airborne bacterial community composition. Only six genera increased across PM₁₀ samples (Dokdonella, Caenimonas, Geminicoccus, and Sphingopyxis) and PM_2.5 samples (Cellulomonas and Rhizobacter), while a large number of taxa significantly increased in total suspended particulate samples, such as Paracoccus, Kocuria, and Sphingomonas Network analysis indicated that Paracoccus, Rubellimicrobium, Kocuria, and Arthrobacter were the key genera in the airborne PM samples. Overall, the findings presented here suggest that diverse airborne bacterial communities are associated with PM and provide further understanding of bacterial community structure in the atmosphere during hazy and nonhazy days.IMPORTANCE The results presented here represent an analysis of the airborne bacterial community associated with particulate matter (PM) and advance our understanding of the structural variation of these communities. We observed a shift in bacterial community composition with PM fractions but no significant difference with haze levels. This may be because the bacterial differences are obscured by high bacterial diversity in the atmosphere. However, we also observed that a few genera (such as Methylobacillus, Tumebacillus, and Desulfurispora) increased significantly on heavy-haze days. In addition, Paracoccus, Rubellimicrobium, Kocuria, and Arthrobacter were the key genera in the airborne PM samples. Accurate and real-time techniques, such as metagenomics and metatranscriptomics, should be developed for a future survey of the relationship of airborne bacteria and haze.

Postoperative infection caused by Acinetobacter baumannii misdiagnosed as a free-living amoeba species in a humeral head hemiarthroplasty patient: a case report

BACKGROUND

Acinetobacter baumannii is ubiquitous, facultative intracellular, and opportunistic bacterial pathogen. Its unique abilities allow it to survive in a diverse range of environments, including health care settings, leading to nosocomial infections. And its exceptional ability to develop resistance to multiple antibiotics leaves few drug options for treatment. It has been recognized as a leading cause of nosocomial pneumonia and bacteremia over the world.

CASE PRESENTATION

In this case, a 73-year-old woman presented with a Neer Group VI proximal humeral fracture. Six hours after a successfully performed hemiarthroplasty, she developed continuous fever. Clinical examination revealed that the vitals were regular. Laboratory and radiographic examinations revealed only elevated procalcitonin levels. Blood culture revealed no bacterial or fungal growth. Cooling treatment and empirical broad-spectrum antibiotic therapy showed no apparent effect.

CONCLUSIONS

We report a postoperative infection caused by Acinetobacter baumannii. The infectious pathogen was identified via molecular DNA sequencing and was initially misidentified as a free-living amoeba species upon microscopic examinations. The patient was mistreated with antiamebic combination therapy. Her symptoms persisted for over 4 months and were eventually followed by her death.

Evolution of carbapenem resistance in Acinetobacter baumannii during a prolonged infection

Acinetobacter baumannii is a common causative agent of hospital-acquired infections and a leading cause of infection in burns patients. Carbapenem-resistant A. baumannii is considered a major public-health threat and has been identified by the World Health Organization as the top priority organism requiring new antimicrobials. The most common mechanism for carbapenem resistance in A. baumannii is via horizontal acquisition of carbapenemase genes. In this study, we sampled 20 A. baumannii isolates from a patient with extensive burns, and characterized the evolution of carbapenem resistance over a 45 day period via Illumina and Oxford Nanopore sequencing. All isolates were multidrug resistant, carrying two genomic islands that harboured several antibiotic-resistance genes. Most isolates were genetically identical and represented a single founder genotype. We identified three novel non-synonymous substitutions associated with meropenem resistance: F136L and G288S in AdeB (part of the AdeABC efflux pump) associated with an increase in meropenem MIC to ≥8 µg ml⁻¹; and A515V in FtsI (PBP3, a penicillin-binding protein) associated with a further increase in MIC to 32 µg ml⁻¹. Structural modelling of AdeB and FtsI showed that these mutations affected their drug-binding sites and revealed mechanisms for meropenem resistance. Notably, one of the adeB mutations arose prior to meropenem therapy but following ciprofloxacin therapy, suggesting exposure to one drug whose resistance is mediated by the efflux pump can induce collateral resistance to other drugs to which the bacterium has not yet been exposed.

Clinical Characteristics of Acinetobacter baumannii Infection in Solid-Organ Transplant Recipients

OBJECTIVES

Acinetobacter baumannii, depending on the immune status of the host, may result in one of the most serious hospital infections. Infections involving A. baumannii infection have been recently rising. However, little is known about the clinical features of A. baumannii infection in solid-organ transplant recipients. We aimed to share our clinical experiences with A. baumannii infection in our transplant recipients.

MATERIALS AND METHODS

Between 2011 and 2017, 41 solid-organ transplant patients developed A. baumannii infection at Baskent University Hospital. Medical records were reviewed, and patient demographics, microbiology results, and overall outcome data were noted.

RESULTS

Of 41 solid-organ transplant patients with A. baumannii infection, 29 were male and 12 were female patients with mean age of 47.15 ± 13.24 years. Our infection rate with A. baumannii infection was 6.1%. The most common sites of infection were deep tracheal aspirate (48.8%)and bloodstream (36.6%). Onset of infection 1 year posttransplant was identified in 58.5% of recipients. Risk factors included presence of invasive procedures (56.1%) and administration of high-dose corticosteroids for rejection 1 year before infection (68.3%). Thirty-day mortality rate was 41.5% (17/41 patients) and was not associated with the infection site, microbiological cure, clinical cure, and drug resistance in our study group.

CONCLUSIONS

Acinetobacter baumannii is an important cause of hospital-acquired infection and mortality worldwide. A major problem with A. baumannii infection is delayed initiation of appropriate antibiotic treatment and the rising numbers of extensively drug-resistant organisms. Predicting the potential risk factors, especially in the already at-risk solid-organ transplant population, has an important role in patient outcomes.

Epidemiology, microbiology, and treatment patterns of pediatric patients hospitalized with pneumonia at two hospitals in China: a patient chart review study

Background

The etiology, epidemiology, treatment patterns, and clinical outcomes of neonatal and pediatric pneumonia patients in China are not well reported. This retrospective chart review study aimed to describe such information among neonatal (0 to 27 days) and pediatric (28 days to <18 years) pneumonia patients in two regions of China.

Methods

Electronic medical records of pneumonia hospitalizations (aged <18 years) admitted between 2008 and 2013 from four hospitals under Guangdong Provincial Hospital of Chinese Medicine (Southern China) and between 2010 and 2014 at Peking University People's Hospital (Beijing, Northern China) were reviewed.

Results

The average age of neonatal hospitalizations in Beijing (n=92) was 3.5 days. The mean length of hospital stay was 11.2 days, and no deaths occurred. Staphylococcus epidermidis was the most common bacteria found in Beijing patients, whereas Mycoplasma pneumoniae was the most common bacteria found in Guangdong patients. The average age of pediatric hospitalizations was 3.3 (±3.1) and 6.5 (±5.6) years in Guangdong (n=3,046) and Beijing (n=222), respectively. The mean length of hospital stay was 17.4 and 5.8 days, and overall mortality rates were 0.2% and 0.5%.

Conclusion

The findings revealed a low level of bacterial isolation and hence microbiological diagnoses. There was a low level of in-hospital mortality due to pneumonia, and the majority of hospitalizations were discharged from hospital, suggesting that current practice was generally effective. Neonatal hospitalizations were greater than pediatric hospitalizations in Beijing along with disparity in bacterial profile when compared with Guangdong, intending a need to improve neonatal pneumonia prophylaxis and selection of appropriate treatment.

Acinetobacter spp. as nosocomial pathogens: Epidemiology and resistance features

The genus Acinetobacter is a major cause of nosocomial infections; it is increasingly being associated with various epidemics and has become a widespread concern in a variety of hospitals worldwide. Multi-antibiotic resistant Acinetobacter baumannii, is now recognized to be of great clinical significance. Numerous reports relay to the spread of A. baumannii in the hospital settings which leads to enhanced nosocomial outbreaks associated with high death rates. However, many other Acinetobacter spp. also can cause nosocomial infections. This review focused on the role of Acinetobacter spp. as nosocomial pathogens in addition to their persistence, antimicrobial resistance patterns and epidemiology.

Blue light irradiation triggers the antimicrobial potential of ZnO nanoparticles on drug-resistant Acinetobacter baumannii

Photodynamic inactivation (PDI) is a non-invasive and safe therapeutic method for microbial infections. Bacterial antibiotic resistance is caused by antibiotics abuse. Drug-resistant Acinetobacter spp. is a serious problem in hospitals around the world. These pathogens from nosocomial infections have high mortality rates in frailer people, and Acinetobacter spp. is commonly found in immunocompromised patients. Visible light is safer than ultraviolet light (UV) for PDI of nosocomial pathogens with mammalian cells. Zinc oxide nanoparticles (ZnO-NPs) were used in this study as an antimicrobial agent and a photosensitizer. ZnO is recognized as safe and has extensive usage in food additives, medical and cosmetic products. In this study, we used 0.125 mg/ml ZnO-NPs combined with 10.8 J/cm² blue light (BL) on Acinetobacter baumannii (A. baumannii) that could significantly reduce microbial survival. However, individual exposure to ZnO-NPs does not affect the viability of A. baumannii. BL irradiation could trigger the antimicrobial ability of ZnO nanoparticles on A. baumannii. The mechanism of photocatalytic ZnO-NPs treatment for sterilization occurs through bacterial membrane disruptions. Otherwise, the photocatalytic ZnO-NPs treatment showed high microbial eradication in nosocomial pathogens, including colistin-resistant and imipenem-resistant A. baumannii and Klebsiella pneumoniae. Based on our results, the photocatalytic ZnO-NPs treatment could support hygiene control and clinical therapies without antibiotics to nosocomial bacterial infections.

The antimicrobial cathelicidin peptide hlF(1-11) attenuates alveolar macrophage pyroptosis induced by Acinetobacter baumannii in vivo

Acinetobacter baumannii is a Gram-negative coccobacillus found primarily in hospital settings that has recently emerged as a source of hospital-acquired infections, including bacterial pneumonia. The hLF(1-11) peptide comprising the first 11 N-terminal residues of human lactoferrin exerts antimicrobial activity in vivo and was highly effective against multidrug-resistant A. baumannii strains in vitro and in vivo. Pyroptosis is a caspase-1-dependent inflammatory cell death process and is induced by various microbial infections. In the present study, we investigated the molecular mechanisms that regulate pyroptosis induced by A. baumannii in macrophages. Our results revealed that A. baumannii induced pyroptosis through caspase-1 activation and IL-1β production. We also found that caspase-1 activation and IL-1β maturation in A. baumannii-triggered pyroptotic cell death were reduced by hLF(1-11) treatment. Moreover, hLF(1-11) inhibited the A. baumannii-induced caspase-1 activation and pyroptosis of pulmonary alveolar macrophages in vivo.

Guidance on Frequency and Location of Environmental Sampling for Acinetobacter baumannii

We assessed various locations and frequency of environmental sampling to maximize information and maintain efficiency when sampling for Acinetobacter baumannii. Although sampling sites in closer proximity to the patient were more likely positive, to fully capture environmental contamination, we found value in sampling all sites and across multiple days. Infect Control Hosp Epidemiol 2018;39:339-342.

Exposure to dairy manure leads to greater antibiotic resistance and increased mass-specific respiration in soil microbial communities

Intensifying livestock production to meet the demands of a growing global population coincides with increases in both the administration of veterinary antibiotics and manure inputs to soils. These trends have the potential to increase antibiotic resistance in soil microbial communities. The effect of maintaining increased antibiotic resistance on soil microbial communities and the ecosystem processes they regulate is unknown. We compare soil microbial communities from paired reference and dairy manure-exposed sites across the USA. Given that manure exposure has been shown to elicit increased antibiotic resistance in soil microbial communities, we expect that manure-exposed sites will exhibit (i) compositionally different soil microbial communities, with shifts toward taxa known to exhibit resistance; (ii) greater abundance of antibiotic resistance genes; and (iii) corresponding maintenance of antibiotic resistance would lead to decreased microbial efficiency. We found that bacterial and fungal communities differed between reference and manure-exposed sites. Additionally, the β-lactam resistance gene ampC was 5.2-fold greater under manure exposure, potentially due to the use of cephalosporin antibiotics in dairy herds. Finally, ampC abundance was positively correlated with indicators of microbial stress, and microbial mass-specific respiration, which increased 2.1-fold under manure exposure. These findings demonstrate that the maintenance of antibiotic resistance associated with manure inputs alters soil microbial communities and ecosystem function.

Multi-drug resistant Acinetobacter species: a seven-year experience from a tertiary care center in Lebanon

Background

Acinetobacter species have become increasingly common in the intensive care units (ICU) over the past two decades, causing serious infections. At the American University of Beirut Medical Center, the incidence of multi-drug resistant Acinetobacter baumannii (MDR-Ab) infections in the ICU increased sharply in 2007 by around 120%, and these infections have continued to cause a serious problem to this day.

Methods

We conducted a seven-year prospective cohort study between 2007 and 2014 in the ICU. Early in the epidemic, a case-control study was performed that included MDR-Ab cases diagnosed between 2007 and 2008 and uninfected controls admitted to the ICU during the same time.

Results

The total number of patients with MDR-Ab infections diagnosed between 2007 and 2014 was 128. There were also 99 patients with MDR-Ab colonization without evidence of active infection between 2011 and 2014. The incidence of MDR-Ab transmission was 315.4 cases/1000 ICU patient-days. The majority of infections were considered hospital-acquired (84%) and most consisted of respiratory infections (53.1%). The mortality rate of patients with MDR-Ab ranged from 52% to 66%.

Conclusion

MDR-Ab infections mostly consisted of ventilator-associated pneumonia and were associated with a very high mortality rate. Infection control measures should be reinforced to control the transmission of these organisms in the ICU.

Efficacy of intravenous plus intrathecal/intracerebral ventricle injection of polymyxin B for post-neurosurgical intracranial infections due to MDR/XDR Acinectobacter baumannii: a retrospective cohort study

Background

Post-neurosurgical intracranial infections caused by multidrug-resistant or extensively drug-resistant Acinetobacter baumannii are difficult to treat and associated with high mortality. In this study, we analyzed the therapeutic efficacy of intravenous combined with intrathecal/intracerebral ventricle injection of polymyxin B for this type of intracranial infection.

Methods

This retrospective study was conducted from January 2013 to September 2017 at the Second Affiliated Hospital, Zhejiang University School of Medicine (Hangzhou,China) and included 61 cases for which cerebrospinal fluid (CSF) cultures were positive for multidrug-resistant or extensively drug-resistant A. baumannii after a neurosurgical operation. Patients treated with intravenous and intrathecal/intracerebral ventricle injection of polymyxin B were assigned to the intrathecal/intracerebral group, and patients treated with other antibiotics without intrathecal/intracerebral injection were assigned to the intravenous group. Data for general information, treatment history, and the results of routine tests and biochemistry indicators in CSF, clinical efficiency, microbiological clearance rate, and the 28-day mortality were collected and analyzed.

Results

The rate of multidrug-resistant or extensively drug-resistant A. baumannii infection among patients who experienced an intracranial infection after a neurosurgical operation was 33.64% in our hospital. The isolated A. baumannii were resistant to various antibiotics, and most seriously to carbapenems (100.00% resistance rate to imipenem and meropenem), cephalosporins (resistance rates of 98.38% to cefazolin, 100.00% to ceftazidime, 100.00% to cefatriaxone, and 98.39% to cefepime). However, the isolated A. baumannii were completely sensitive to polymyxin B (sensitivity rate of 100.00%), followed by tigecycline (60.66%) and amikacin (49.18%). No significant differences in basic clinical data were observed between the two groups. Compared with the intravenous group, the intrathecal/intracerebral group had a significantly lower 28-day mortality (55.26% vs. 8.70%, P = 0.01) and higher rates of clinical efficacy and microbiological clearance (95.65% vs. 23.68%, P < 0.001; 91.30% vs. 18.42%, P < 0.001, respectively).

Conclusions

Intravenous plus intrathecal/intracerebral ventricle injection of polymyxin B is an effective regimen for treating intracranial infections caused by multidrug-resistant or extensively drug-resistant A. baumannii.

Mucin acts as a nutrient source and a signal for the differential expression of genes coding for cellular processes and virulence factors in Acinetobacter baumannii

The capacity of Acinetobacter baumannii to persist and cause infections depends on its interaction with abiotic and biotic surfaces, including those found on medical devices and host mucosal surfaces. However, the extracellular stimuli affecting these interactions are poorly understood. Based on our previous observations, we hypothesized that mucin, a glycoprotein secreted by lung epithelial cells, particularly during respiratory infections, significantly alters A. baumannii's physiology and its interaction with the surrounding environment. Biofilm, virulence and growth assays showed that mucin enhances the interaction of A. baumannii ATCC 19606T with abiotic and biotic surfaces and its cytolytic activity against epithelial cells while serving as a nutrient source. The global effect of mucin on the physiology and virulence of this pathogen is supported by RNA-Seq data showing that its presence in a low nutrient medium results in the differential transcription of 427 predicted protein-coding genes. The reduced expression of ion acquisition genes and the increased transcription of genes coding for energy production together with the detection of mucin degradation indicate that this host glycoprotein is a nutrient source. The increased expression of genes coding for adherence and biofilm biogenesis on abiotic and biotic surfaces, the degradation of phenylacetic acid and the production of an active type VI secretion system further supports the role mucin plays in virulence. Taken together, our observations indicate that A. baumannii recognizes mucin as an environmental signal, which triggers a response cascade that allows this pathogen to acquire critical nutrients and promotes host-pathogen interactions that play a role in the pathogenesis of bacterial infections.

NLRP3 inflammasome pathway has a critical role in the host immunity against clinically relevant Acinetobacter baumannii pulmonary infection

The opportunistic Gram-negative bacterium Acinetobacter baumannii (AB) is a leading cause of life-threatening nosocomial pneumonia. Outbreaks of multidrug resistant (MDR)-AB belonging to international clones (ICs) I and II with limited treatment options are major global health threats. However, the pathogenesis mechanisms of various AB clonal groups are understudied. Although inflammation-associated interleukin-1β (IL-1β) levels and IL-1 receptor antagonist polymorphisms were previously implicated in MDR-AB-related pneumonia in patients, whether inflammasomes has any role in the host defense and/or pathogenesis of clinically relevant A. baumannii infection is unknown. Using a sublethal mouse pneumonia model, we demonstrate that an extensively drug-resistant clinical isolate (ICII) of A. baumannii exhibits reduced/delayed early pulmonary neutrophil recruitment, higher lung persistence, and, most importantly, elicits enhanced IL-1β/IL-18 production and lung damage through NLRP3 inflammasome, in comparison with A. baumannii-type strain. A. baumannii infection-induced IL-1β/IL-18 production is entirely dependent on NLRP3-ASC-caspase-1/caspase-11 pathway. Using Nlrp3^-/- mice infection models, we further show that while NLRP3 inflammasome pathway contributes to host defense against A. baumannii clinical isolate, it is dispensable for protection against A. baumannii-type strain. Our study reveals a novel differential role for NLRP3 inflammasome pathway in the immunity against clinically relevant A. baumannii infections, and highlights inflammasome pathway as a potential immunomodulatory target.

Comparative Analysis of 37 Acinetobacter Bacteriophages

Members of the genus Acinetobacter are ubiquitous in the environment and the multiple-drug resistant species A. baumannii is of significant clinical concern. This clinical relevance is currently driving research on bacterial viruses infecting A. baumannii, in an effort to implement phage therapy and phage-derived antimicrobials. Initially, a total of 42 Acinetobacter phage genome sequences were available in the international nucleotide sequence databases, corresponding to a total of 2.87 Mbp of sequence information and representing all three families of the order Caudovirales and a single member of the Leviviridae. A comparative bioinformatics analysis of 37 Acinetobacter phages revealed that they form six discrete clusters and two singletons based on genomic organisation and nucleotide sequence identity. The assignment of these phages to clusters was further supported by proteomic relationships established using OrthoMCL. The 4067 proteins encoded by the 37 phage genomes formed 737 groups and 974 orphans. Notably, over half of the proteins encoded by the Acinetobacter phages are of unknown function. The comparative analysis and clustering presented enables an updated taxonomic framing of these clades.

ERIC-PCR Genotyping of Acinetobacter baumannii Isolated from Different Clinical Specimens

Background:

Acinetobacter baumannii is a major cause of hospital care-acquired infections, and this bacterium poses a significant challenge to health care worldwide. At King Fahd Hospital of the University (KFHU), Al Khobar, Saudi Arabia, there had been a significant increase in the number of cases of A. baumannii infections.

Objective:

The objective of this study was to determine the clonal relationship between A. baumannii collected from different specimens of patients admitted to KFHU using the enterobacterial repetitive intergenic consensus–polymerase chain reaction (ERIC-PCR) fingerprinting method.

Materials and Methods:

A. baumannii strains were isolated from a total of 59 specimens from inpatients admitted to KFHU between January and September 2014. These specimens were mainly collected from wound, rectal and throat swabs and transtracheal aspiration. ERIC-PCR fingerprinting was used to determine the clonal relationship between the different isolated strains.

Results:

Using ERIC-PCR fingerprinting genotype analysis, 51 strains of A. baumannii were clustered into seven groups, while the remaining 8 were single strains. The genetic relatedness of A. baumannii isolated from admitted patients was high, indicating cross-transmission within the hospitalized patients.

Conclusion:

This study found that the increase in the incidence of A. baumannii in patients at KFHU was likely due to the spread of seven epidemic clones, thereby highlighting the need for intensifying the infection control measures to prevent nosocomial transmission of A. baumannii. These results also demonstrate that ERIC-PCR is a reliable and rapid method for studying the clonal similarity between A. baumannii isolated from different clinical specimens.

Defining the interaction of the protease CpaA with its type II secretion chaperone CpaB and its contribution to virulence in Acinetobacter species

Acinetobacter baumannii, Acinetobacter nosocomialis, and Acinetobacter pittii are a frequent cause of multidrug-resistant, healthcare-associated infections. Our previous work demonstrated that A. nosocomialis M2 possesses a functional type II secretion system (T2SS) that is required for full virulence. Further, we identified the metallo-endopeptidase CpaA, which has been shown previously to cleave human Factor V and deregulate blood coagulation, as the most abundant type II secreted effector protein. We also demonstrated that its secretion is dependent on CpaB, a membrane-bound chaperone. In this study, we show that CpaA expression and secretion are conserved across several medically relevant Acinetobacter species. Additionally, we demonstrate that deletion of cpaA results in attenuation of A. nosocomialis M2 virulence in moth and mouse models. The virulence defects resulting from the deletion of cpaA were comparable with those observed upon abrogation of T2SS activity. The virulence defects resulting from the deletion of cpaA are comparable with those observed upon abrogation of T2SS activity. We also show that CpaA and CpaB strongly interact, forming a complex in a 1:1 ratio. Interestingly, deletion of the N-terminal transmembrane domain of CpaB results in robust secretion of CpaA and CpaB, indicating that the transmembrane domain is dispensable for CpaA secretion and likely functions to retain CpaB inside the cell. Limited proteolysis of spheroplasts revealed that the C-terminal domain of CpaB is exposed to the periplasm, suggesting that this is the site where CpaA and CpaB interact in vivo Last, we show that CpaB does not abolish the proteolytic activity of CpaA against human Factor V. We conclude that CpaA is, to the best of our knowledge, the first characterized, bona fide virulence factor secreted by Acinetobacter species.

The microbiomes of blowflies and houseflies as bacterial transmission reservoirs

Blowflies and houseflies are mechanical vectors inhabiting synanthropic environments around the world. They feed and breed in fecal and decaying organic matter, but the microbiome they harbour and transport is largely uncharacterized. We sampled 116 individual houseflies and blowflies from varying habitats on three continents and subjected them to high-coverage, whole-genome shotgun sequencing. This allowed for genomic and metagenomic analyses of the host-associated microbiome at the species level. Both fly host species segregate based on principal coordinate analysis of their microbial communities, but they also show an overlapping core microbiome. Legs and wings displayed the largest microbial diversity and were shown to be an important route for microbial dispersion. The environmental sequencing approach presented here detected a stochastic distribution of human pathogens, such as Helicobacter pylori, thereby demonstrating the potential of flies as proxies for environmental and public health surveillance.