Advances in the Applications of Clinoptilolite-Rich Tuffs.

Adsorptive, catalytic, and antibacterial properties of clinoptilolite-rich tuffs (ZT) are presented here. ZT transformed into Fe-containing ZT (Fe-ZT) removes various organic and inorganic anions from water. Fe-ZT, which contains selenium, is beneficial for growing Pleurotus ostreatus mushrooms. The fungi convert inorganic Se from Fe-ZT into a more useful organically bonded form. ZT and Fe-ZT as supplements retain nitrogen and potassium in sandy, silty loam and silty clay soils. ZT shows an affinity toward toxic metal cations, which are essential for cleaning contaminated water. The adsorption of atenolol, acetylsalicylic, and salicylic acid onto M-ZT (M-Cu2+, Mn2+, Ni2+, or Zn2+) from water solutions suggests that both the natures of M and pharmaceuticals have a significant impact on the adsorption mechanism and determine the adsorption capability of the ZT. ZT is an excellent carrier for ultrafine (2-5 nm) nano oxide particles, which have been shown to have catalytic activity in different chemical processes and photodegradation reactions of organic pollutants. ZT can also be transformed into SO4-SnO2-ZT, which is catalytically active as a solid acid. M-ZT is an effective carrier of valuable bacteria. Ag-ZT possesses beneficial bactericidal activity in disinfecting water and soil remediation.

Antibacterial activity of silver doped hydroxyapatite toward multidrug-resistant clinical isolates of Acinetobacter baumannii.

Bacteria Acinetobacter baumannii is a persistent issue in hospital-acquired infections due to its fast and potent development of multi-drug resistance. To address this urgent challenge, a novel biomaterial using silver (Ag+) ions within the hydroxyapatite (HAp) lattice has been developed to prevent infections in orthopedic surgery and bone regeneration applications without relying on antibiotics. The aim of the study was to examine the antibacterial activity of mono-substituted HAp with Ag+ ions and a mixture of mono-substituted HAps with Sr2+, Zn2+, Mg2+, SeO32- and Ag+ ions against the A. baumannii. The samples were prepared in the form of powder and disc and analyzed by disc diffusion, broth microdilution method, and scanning electron microscopy. The results from the disc-diffusion method have shown a strong antibacterial efficacy of the Ag-substituted and mixture of mono-substituted HAps (Sr, Zn, Se, Mg, Ag) toward several clinical isolates. The Minimal Inhibitory Concentrations for the powdered HAp samples ranged from 32 to 42 mg/L (Ag+ substituted) and 83-167 mg/L (mixture of mono-substituted), while the Minimal Bactericidal Concentrations after 24 h of contact ranged from 62.5 (Ag+) to 187.5-292 mg/L (ion mixture). The lower substitution level of Ag+ ions in a mixture of mono-substituted HAps was the cause of lower antibacterial effects measured in suspension. However, the inhibition zones and bacterial adhesion on the biomaterial surface were comparable. Overall, the clinical isolates of A. baumannii were effectively inhibited by substituted HAp samples, probably in the same amount as by other commercially available silver-doped materials, and such materials may provide a promising alternative or supplementation to antibiotic treatment in the prevention of infections associated with bone regeneration. The antibacterial activity of prepared samples toward A. baumannii was time-dependent and should be considered in potential applications.

Dissemination of Clinical Acinetobacter baumannii Isolate to Hospital Environment during the COVID-19 Pandemic.

The aim of this study was to find the source of Acinetobacter baumannii in the intensive care unit (ICU) after an outbreak during the coronavirus disease 2019 (COVID-19) pandemic, as there was no A. baumannii detected on usually screened susceptible surfaces. The screening of the ICU environment was done in April 2021 when eleven different samples were taken. One A. baumannii isolate was recovered from the air conditioner and was compared with four clinical A. baumannii isolates obtained from patients hospitalized in January 2021. Isolates were confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), minimum inhibitory concentrations (MICs) were determined, and the multilocus sequence typing (MLST) was performed. The molecular identification of A. baumannii isolates as ST208, the presence of the same blaOXA-23 carbapenemase gene, and the same antibiotic susceptibility profile suggest that the isolate recovered from the air conditioner is the same as the isolates recovered from hospitalized patients. The environmental isolate was recovered three months later than the clinical isolates, emphasizing the ability of A. baumannii to survive on dry abiotic surfaces. The air conditioner in the clinical environment is an important but undoubtedly neglected source of A. baumannii outbreaks, hence, frequent disinfection of hospital air conditioners with appropriate disinfectants is mandatory to mitigate the circulation of A. baumannii between patients and the hospital environment.

Molecular characterisation of colistin and carbapenem-resistant clinical isolates of Acinetobacter baumannii from Southeast Europe.

OBJECTIVES: To characterise 11 colistin- and carbapenem-resistant Acinetobacter baumannii isolates recently emerging in hospital settings. METHODS: A. baumannii isolates were collected from hospitalised patients under colistin treatment in three countries of Southeast Europe: Turkey, Croatia, and Bosnia and Herzegovina. Isolates were identified using molecular methods. RESULTS: Isolates from Turkey and Croatia belong to the sequence types ST195 or ST281 of the clone lineage 2, while the single isolate from Bosnia and Herzegovina belongs to the ST231 of clone lineage 1. All isolates turned out to be highly resistant to colistin (MIC ≥ 16 mg/L) and have point mutations in pmrCAB operon genes. The colistin-resistant isolate from Bosnia and Herzegovina had a unique P170L point mutation in the pmrB gene and the R125H point mutation in the pmrC gene. The L20S mutation in the pmrA gene was detected only in isolates from Croatia and has never been reported before in isolates from this country. CONCLUSION: Colistin resistance in A. baumannii in hospitalised patients receiving colistin treatment is a result of chromosomal mutations. The pattern of point mutations in pmrCAB genes suggests a spread of specific colistin-resistant isolates within the hospital.

Evaluation of DNA-Damaging Effects Induced by Different Tanning Agents Used in the Processing of Natural Leather-Pilot Study on HepG2 Cell Line.

For a long time, the production and processing of cowhide was based on the use of chrome tanning. However, the growing problem with chromium waste and its negative impact on human health and the environment prompted the search for more environmentally friendly processes such as vegetable tanning or aldehyde tanning. In the present study, we investigated the DNA-damaging effects induced in HepG2 cells after 24 h exposure to leather samples (cut into 1 × 1 cm2 rectangles) processed with different tanning agents. Our main objective was to determine which tanning procedure resulted in the highest DNA instability. The extent of treatment-induced DNA damage was determined using the alkaline comet assay. All tanning processes used in leather processing caused primary DNA damage in HepG2 cells compared to untreated cells. The effects measured in the exposed cells indicate that the leaching of potentially genotoxic chemicals from the same surface is variable and was highest after vegetable tanning, followed by synthetic tanning and chrome tanning. These results could be due to the complex composition of the vegetable and synthetic tanning agents. Despite all limitations, these preliminary results could be useful to gain a general insight into the genotoxic potential of the processes used in the processing of natural leather and to plan future experiments with more specific cell or tissue models.

Loss of thermotolerance in antibiotic-resistant Acinetobacter baumannii.

Bacterium Acinetobacter baumannii is a leading cause of nosocomial infections. The occurrence of antibiotic-resistant A. baumannii isolates outside hospitals suggests that monitoring of this pathogen in environmental samples is needed. Survival of pandrug-resistant A. baumannii was followed on selective plates with and without carbapenems in water and soil. After a few days of starvation, A. baumannii lost the ability to be cultivated at 44°C on plates supplemented with carbapenems. Once cultivated on plates without carbapenems and/or at 36°C, A. baumannii could grow again at 44°C in the presence of carbapenems. Comparative proteomic analysis revealed that impaired membrane integrity and reduced function of efflux pumps due to elevated temperature combined with antibiotic exposure were the main reasons for this phenomenon. Loss of thermotolerance in the presence of antibiotics points to the need for temperature adjustment in long-term monitoring of A. baumannii in environmental samples, to avoid the underestimation of viable bacteria.

Characterization of Burkholderia cepacia complex from environment influenced by human waste.

The natural environment is a primary source of infections caused by members of Burkholderia cepacia complex (BCC), but the release of human waste may in return enrich the natural environment with clinically relevant BCC. Seven BCC isolates from environment influenced by human liquid or solid waste across Croatia, and one clinical isolate was characterised. B. multivorans recovered from the soil at illegal dumpsite belonged to sequence type (ST)19; B. ambifaria from the agricultural soil fertilized with swine or poultry manure to ST927 or new ST; B. cenocepacia from creek sediment, river water and wound swab to new STs. Antimicrobial susceptibility of isolates ranged from sensitive to multidrug-resistant. A variety of blaTEM genes was confirmed in isolates. Isolates expressed the virulence factors and survived in river water during 50 days. The BCC present natural environments influenced by the human waste are of clinical relevance and a potential source of sporadic infections.

Endemicity of OXA-23 and OXA-72 in clinical isolates of Acinetobacter baumannii from three neighbouring countries in Southeast Europe.

According to the World Health Organization, bacterium Acinetobacter baumannii is the first on the critical priority list of pathogens in urgent need for new antibiotics. The increasing resistance of A. baumannii to the last-line treatment options, including carbapenems, is a global problem. We report the molecular epidemiology of 12 carbapenem-resistant clinical isolates of A. baumannii collected from hospitalised patients in three neighbouring countries in Southeast Europe: Croatia, Serbia, and Bosnia and Herzegovina, giving an insight into the molecular characterisation and evolutionary history of the acquisition of resistance genes. Besides the blaOXA-23 gene, the endemic presence of OXA-72 oxacillinase of the same origin for more than a decade as the leading mechanism of carbapenem resistance in Southeast Europe was confirmed. To the best of our knowledge, this is the first paper that investigates and analyses the phylogenetic association of the most common mechanisms of resistance to carbapenems in clinical isolates of A. baumannii originating from three neighbouring countries in Southeast Europe.

The Growth and Sporulation of Bacillus subtilis in Nanotesla Magnetic Fields.

The order of magnitude of increased growth, multiplication rate, and decreased sporulation of Bacillus subtilis after exposure to nanotesla magnetic fields (MFs) relative to control samples were observed experimentally. Earth's total magnetic field intensity was reduced from 47.9 ± 0.4 µT to cover the range from 97.5 ± 1.7 nT to 1115 ± 158 nT in eight subsequent experiments by using three pairs of Helmholtz coils combined with Mu-metal shielding. The growth, multiplication rate, sporulation, and potassium content were measured in the probe and control containing B. subtilis cultures after 24 h of exposure to nanotesla and Earth's magnetic fields, respectively. The observed effect is discussed with regard to its possible repercussions on Earth's living species during geomagnetic reversals that occurred when the magnetic field was much weaker than the field that exists today. In addition, effects on future manned voyages into deep space, an environment with reduced magnetic field intensity, are considered.

Molecular Characterization and Survival of Carbapenem-Resistant Acinetobacter baumannii Isolated from Hospitalized Patients in Mostar, Bosnia and Herzegovina.

Increasingly difficult treatment of multidrug-resistant (MDR) bacteria has become a global problem of the 21st century. Within a group of multiresistant bacteria, the Acinetobacter baumannii convincingly occupies the position at the top of the group designated as ESKAPE pathogens. In this study, 61 isolates of A. baumannii were recovered from different samples originating from various departments of the University Clinical Hospital Mostar during 2018. All of the isolates were identified using conventional phenotypic methods and the VITEK® 2 Compact System, and were confirmed by MALDI-TOF mass spectrometry. The minimum inhibitory concentrations (MICs) were determined by the microbroth dilution method using MICRONAUT-S MDR MRGN-Screening and VITEK 2 Compact System. All strains were resistant to carbapenems and classified in eight different resistotypes according to their antibiotic resistance and macrorestriction pulsed-field gel electrophoresis profiles, with all belonging to IC II. One isolate displayed resistance to colistin (MIC ≥16 mg/L). The presence of blaOXA genes encoding OXA-type carbapenemases was investigated by multiplex PCR and the Eazyplex® SuperBugAcineto system and showed 100% compatibility with the detection of acquired oxacillinases. Molecular characterization of the isolates tested in this study revealed the OXA-23- and OXA-40-like groups of acquired oxacillinases. Sequencing of two PCR products of the OXA-40-like group confirmed the presence of OXA-72. Survival assays with two selected isolates of A. baumannii encoding different mechanisms of carbapenem resistance revealed that one isolate was able to survive on a fragment of white laboratory coat during 90 days of monitoring. To the best of our knowledge, this is the first article to present the results of a comprehensive phenotypic, genotypic, and molecular analysis of A. baumannii isolates from the leading clinical hospital center in the southwestern part of Bosnia and Herzegovina, including data for the survival of this pathogen on the white laboratory coats used as compulsory medical clothing.

Novel arsenic hyper-resistant bacteria from an extreme environment, Crven Dol mine, Allchar, North Macedonia.

Novel hyper-resistant bacteria were isolated from the Crven Dol mine (Allchar, North Macedonia), arsenic-rich extreme environment. Bacteria were recovered from a secondary mineral mixture, an alteration of hydrothermal realgar rich in arsenates (pharmacolite, hornesite, and talmessite). The sample was recovered from the dark part of the mine at 28 m depth. Three bacterial strains and a bacterial consortium were isolated for their capacity to survive exposure to 32 g/L (209 mM) of arsenite, and 176 g/L (564 mM) of arsenate. The 16S rRNA gene analysis identified bacterial isolates as Stenotrophomonas sp. and two Microbacterium spp. This analysis also revealed that bacterial consortium comprise two Bacteriodetes exhibiting similarity to Olivibacter ginsengisoli and to uncultured bacterium, and one γ-proteobacteria with similarity to Luteimonas sp. Among all isolates Stenotrophomonas sp. exhibited the highest tolerance to As compound as well as the capacity to accumulate As inside the cells. Analysis of genes involved in As-resistance showed that recovered isolates possess the genes encoding the ArsB, Acr3(1) and Acr3(2) proteins, indicating that at least a part of their resistance could be ascribed to As-efflux systems described in isolates obtained from human-polluted environments.

Colistin Resistance in Environmental Isolates of Acinetobacter baumannii.

Although the molecular mechanisms of carbapenem resistance of environmental isolates of Acinetobacter baumannii are well described, data on the mechanisms of colistin resistance are scarce. In this study, we report the molecular mechanisms of colistin resistance in environmental isolates of A. baumannii. Seven clinically relevant isolates of A. baumannii belonging to ST-2Pasteur were recovered from hospital wastewater and wastewater treatment plant. The phenotypic resistance to colistin was confirmed by broth microdilution with minimum inhibitory concentration values ranging from 20 to 160 mg/L. Colistin sulfate and colistimethate sodium showed bactericidal activity against two colistin-heteroresistant isolates in vitro, but substantially recovery of population was observed after prolonged incubation. In silico genome analysis revealed nucleotide variations resulting in amino acid changes in LpxC (N286D), LpxD (E117K), PmrB (A138T, R263S, L267W, Q309P, and A444V), and EptA (F166L, I228V, R348K, A370S, and K531T). According to reverse transcription quantitative PCR, all isolates had increased levels of eptA mRNA and decreased levels of lpxA and lpxD mRNA. Isolates expressed low hydrophobicity, biofilm, and pellicle formation, but showed excellent survival in river water during 50 days of monitoring. Colistin- and pandrug-resistant A. baumannii disseminated in the environment could represent the source for the occurrence of serious community-acquired infections.

Capillary bacterial migration on non-nutritive solid surfaces.

Here we describe an additional type of bacterial migration in which bacterial cells migrate vertically across a non-nutritive solid surface carried by capillary forces. Unlike standard motility experiments, these were run on a glass slide inserted into a Falcon tube, partly immersed in a nutrient medium and partly exposed to air. Observations revealed that capillary forces initiated upward cell migration when biofilm was formed at the border between liquid and air. The movement was facilitated by the production of extracellular polymeric substances (EPS). This motility differs from earlier described swarming, twitching, gliding, sliding, or surfing, although these types of movements are not excluded. We therefore propose to call it "capillary movement of biofilm". This phenomenon may be an ecologically important mode of bacterial motility on solid surfaces.

Metal-loaded zeolite remediation of soils contaminated with pandrug-resistant Acinetobacter baumannii.

Due to the development of resistance to antimicrobial agents, bacterium Acinetobacter baumannii is nowadays a leading cause of nosocomial outbreaks. Clinically relevant A. baumannii outside hospital settings including natural soils affected by human waste represents a public-health risk for humans and animals. The aim of this study was to investigate the potential of metal-loaded zeolites to eliminate viable A. baumannii from artificially contaminated natural soils. A. baumannii isolate was subjected to the activity of natural zeolitised tuff (NZ) and Cu-modified (CuNZ) or Ag-modified zeolite (AgNZ) in wet, slightly acidic terra rossa and slightly alkaline red palaeosol. A. baumannii survived in terra rossa and red palaeosol supplemented with 1 wt% of NZ for seven days and four months, respectively. The addition of 1 wt% of CuNZ to terra rossa and red palaeosol shortened the survival of A. baumannii to three and 14 days, respectively. The addition of 0.1 wt% of AgNZ to both soils resulted in complete removal of viable A. baumannii within 1 h of contact, while the total native heterotrophic bacterial counts remained high. Since AgNZ is prepared with a simple modification of cost-effective and environmentally friendly natural zeolite, it is a promising material for the remediation of soils contaminated with pandrug-resistant A. baumannii.

The chemical species of mercury accumulated by Pseudomonas idrijaensis, a bacterium from a rock of the Idrija mercury mine, Slovenia.

A mercury-resistant bacterial strain has been isolated from a rock of the Idrija mercury mine in Slovenia. The rock had 19 g carbon and 2952 mg mercury (Hg) per kg. Mass spectrometry and DNA sequencing showed that the bacterium belongs to the Pseudomonas genus. It is called Pseudomonas idrijaensis. This bacterial strain is sensitive to methylmercury (MeHg) like the reference P. aeruginosa strain PAO1, and is resistant to divalent mercury (Hg(II)) in contrast to PAO1. This difference could be attributed to the presence of the mer operon yet deprived of the merB gene encoding the organomercurial lyase, on the basis of whole genome sequencing. The P. idrijaensis mer operon displays the RTPCADE organization and is contained in the Tn5041 transposon. This transposon identified here occurs in other Gram-negative Hg-resistant strains isolated from mercury ores, aquatic systems and soils, including Pseudomonas strains from 15,000 to 40,000 years old Siberian permafrost. When P. idrijaensis was exposed to mercury chloride, two intracellular Hg species were identified by high energy-resolution XANES spectroscopy, a dithiolate Hg(SR)2 and a tetrathiolate Hg(SR)4 complex. P. idrijaensis had a much higher [Hg(SR)2]/[Hg(SR)4] molar ratio than bacteria lacking the mer operon when exposed to 4 µg Hg2+/L - resulting in an intracellular accumulation of 4.3 µg Hg/g dw. A higher amount of the Hg(SR)2 complex provides a chemical signature for the expression of the dicysteinate Mer proteins in response to mercury toxicity.

Comparison of clinical and sewage isolates of Acinetobacter baumannii from two long-term care facilities in Zagreb; mechanisms and routes of spread.

In the previous studies OXA-23-like and OXA-24-like ß-lactamase were reported among Acinetobacter baumannii in both hospitals and long-term care facilities (LTCF) in Croatia. The aim of this study was to analyze clinical and sewage A. baumannii isolates from two nursing homes in Zagreb, with regard to antibiotic susceptibility and resistance mechanisms, to determine the route of spread of carbapenem-resistant isolates. Nine clinical isolates were collected from February to May 2017 whereas in April 2017, ten A. baumannii isolates were collected from sewage of two nursing homes in Zagreb. Antibiotics susceptibility was determined by broth microdilution method. The presence of carbapenemase and extended spectrum ß-lactamases (ESBL) encoding genes was explored by PCR. Conjugation and transformation experiments were performed as previously described. Genotyping was performed by SG determination, PFGE and MLST. Seven clinical isolates were positive for blaOXA24-like whereas two clinical and environmental carbapenem-resistant isolates, respectively, were found to possess blaOXA-23-like genes. Attempts to transfer imipenem resistance were unsuccessful indicating chromosomal location of blaOXA-23 gene. All carbapenem-resistant isolates belonged to SG- 1 (IC-2) whereas the rest of the isolates susceptible to carbapenems were allocated to SG- 2 (IC-1). PFGE analysis revealed low degree of genetic variability within both IC- I and IC- II. MLST corroborated that two environmental OXA-23 isolates belong to the ST-195. This study showed dissemination of OXA-23 producing A. baumannii from the nursing home into the urban sewage. Disinfection of nursing home sewage should be recommended in order to prevent the spread of resistance genes into the community sewage.

Removal of emerging pathogenic bacteria using metal-exchanged natural zeolite bead filter.

Hospital wastewaters can become a route for dissemination of antibiotic-resistant bacteria to the environment if not properly treated. Some of these bacteria are able to survive conventional disinfection treatments (e.g. chlorination, UV irradiation), which evokes the need for novel disinfection methods. The metal-exchanged zeolites were tested as novel antibacterial agents for wastewater treatment. The natural zeolite clinoptilolite enriched with silver (AgNZ) showed far better antibacterial activity towards hospital pathogenic bacterium Acinetobacter baumannii when compared with copper-exchanged zeolite (CuNZ), with minimal bactericidal concentration of 0.25-2 (AgNZ) compared with 32-64 mg L-1 (CuNZ) in a batch system and respective log 5.6 reduction compared with log 0.5 reduction in a flow system with pure bacterial culture. In the flow system with real effluent wastewater from the treatment plant, the removal of carbapenem-resistant bacteria using AgNZ was 90-100% during the 4 days of the experimental run. These results indicate that the AgNZ efficiently removes pathogenic bacteria from the wastewater, including A. baumannii, and is promising as a disinfectant material in a bead filter system.

Impact of biotic interactions on the survival of emerging pathogen Acinetobacter baumannii in aquatic media.

Acinetobacter baumannii is an opportunistic pathogen causing infections in immunocompromised patients. Recent studies recorded its persistence in a variety of abiotic conditions, but data regarding the biotic interactions with other microorganisms are limited. The aim was to assess the interaction of clinically relevant A. baumannii with common faecal bacteria Escherichia coli and Enterococcus faecium. Additionally, the interaction with a bdelloid rotifer Adineta vaga as a potential agent for biological control of A. baumannii was examined. Experiments were conducted in nutrient-poor spring water (SW) and nutrient-rich diluted nutrient broth (DNB) at 22 °C. A. baumannii coexisted with E. coli and E. faecium in both media, suggesting the absence of inter-bacterial competition in long-term survival. No difference in the survival of pandrug-resistant, extensively drug-resistant or antibiotic sensitive isolates of A. baumannii was observed. Rotifers contributed to the removal of all tested bacteria, particularly in SW. Rotifers were able to remove 5.5 ± 1.3 log CFU/mL of A. baumannii in SW and 3.5 ± 1.7 log CFU/mL in DNB. Additionally, no intracellular growth of A. baumannii inside A. vaga was detected. In wastewater treatment plants and drinking water facilities, grazing by rotifers might be useful for the removal of emerging human pathogens such as A. baumannii from water.

Carbapenem-Resistant Acinetobacter baumannii Recovered from Swine Manure.

Recently, concerns have been raised about the possibility of Acinetobacter baumannii transmission between animals and humans. So far, A. baumannii has been reported in animals with which people can come into contact. The presence of this pathogen in animal manure presents an equally important public health risk. In this study, we report the finding of two A. baumannii isolates in swine manure from a Croatian pig farm. Both isolates shared features with the widespread human clinical isolates: affiliation to the international clonal lineage 2 (ST-195), carbapenem, and extensive drug resistance and the plasmid-located acquired blaOXA-23 gene. These two A. baumannii isolates survived anaerobic conditions, competition with other microorganisms, and elevated concentrations of heavy metals in the stagnant swine manure for at least 2 weeks. These findings call for bacteriological analysis and disinfection of liquid swine manure before its application as a fertilizer in traditional extensive agriculture.

Survival of emerging pathogen Acinetobacter baumannii in water environment exposed to different oxygen conditions.

Bacterium Acinetobacter baumannii is a leading cause of hospital infections. Over the last decade, its occurrence in natural environments outside hospital settings has been reported. The aim was to examine the survival of A. baumannii in water media exposed to different ranges of oxygen supply in order to predict its behaviour in the environment. The abundance of five A. baumannii isolates was monitored in nutrient-depleted and nutrient-rich water media in aerated, intermediate and anaerobic conditions (oxygen saturation 96, 56 and 0%, respectively). A. baumannii survived in both media in all tested oxygen concentrations for 50 days. In nutrient-rich water survival of A. baumannii was lowest in anaerobic conditions, while in nutrient-depleted water there was no difference in survival regardless of oxygen availability. A. baumannii formed translucent small colony variants as the fast response (after 1 day) and dormant cells as the prolonged response (after 14 days) to anaerobic conditions. Transmission electron microscopy (TEM) images showed the outer membrane of coccobacillus dormant cells was up to four times thicker than in regular cells. Once in the environment, A. baumannii is able to survive regardless of the availability of dissolved oxygen, which represents a serious public health concern.