In vitro evaluation of the susceptibility of Acinetobacter baumannii isolates to antiseptics and disinfectants: comparison between clinical and environmental isolates

Phenotypic and genotypic determination of resistance to common disinfectants among strains of Acinetobacter baumannii producing and non-producing biofilm isolated from Iran

BACKGROUND

Nosocomial infections are a global problem in hospitals all around the world. It is considered a major health problem, especially in developing countries. The increase in the patient's stay in hospitals has increased the mortality rate, and consequently, the costs drastically increase. The main purpose of using disinfectants in the hospital environment is to reduce the risk of nosocomial infections. Ethylene diamine tetra acetic acid (EDTA) causes lysis and increases susceptibility to antimicrobial agents in the planktonic form of bacteria. This substance affects the permeability of the outer membrane of bacteria. It also prevents the formation of biofilms by bacteria.

MATERIALS AND METHODS

In the current study, 120 isolates of Acinetobacter baumannii (A. baumannii) were confirmed by phenotypic and genotypic methods. Antibiogram was performed and then the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of isolates against 5% sodium hypochlorite, ethanol %70, sayasept-HP 2%, chlorhexidine 2%, dettol 4/8% were evaluated. In addition, the disinfectant effect was re-evaluated with the mixture of EDTA solution. All isolates were examined for biofilm presence by crystal violet staining method in triplicates and repeated three times for each strain. Also for all isolates detection of efflux pump genes (Qac-E, qacE-Δ1, SUG-E) by PCR technique was done.

RESULTS

Antibiogram results of A. baumannii showed that 6.7% were Multi-drug-resistant (MDR), and 89.2% were Extensively drug-resistant (XDR) isolates. The highest effect of disinfectants was related to 5% sodium hypochlorite, and the least effect was 70% ethanol. EDTA increases the efficacy of selected disinfectants significantly. The highest prevalence of the efflux pump genes was related to SUG-E (95%) and Qac-E (91.7%), and, the qacE-Δ1 gene with 12.5%. The biofilm production rate was 91.3% among all isolates.

CONCLUSION

The best and safest way to disinfect hospital floors and surfaces is to choose the right disinfectants, and learn how to use them properly. In this study, a mixture of disinfectants and EDTA had a significant effect on bactericidal activity. it was found that improper use of disinfectants, especially the use of sub-inhibitory dilutions, increases the resistance of bacteria to disinfectants.

Characterization of antibiotic and disinfectant susceptibility in biofilm-forming Acinetobacter baumannii: A focus on environmental isolates

The clinical role of Acinetobacter baumannii has been highlighted in numerous infectious syndromes with a high mortality rate, due to the high prevalence of multidrug-resistant (MDR) isolates. The treatment and eradication of this pathogen is hindered by biofilm-formation, providing protection from noxious environmental factors and antimicrobials. The aim of this study was to assess the antibiotic susceptibility, antiseptic susceptibility and biofilm-forming capacity using phenotypic methods in environmental A. baumannii isolates. One hundred and fourteen (n = 114) isolates were collected, originating from various environmental sources and geographical regions. Antimicrobial susceptibility testing was carried out using the disk diffusion method, while antiseptic susceptibility was performed using the agar dilution method. Determination of biofilm-forming capacity was carried out using a microtiter-plate based method. Resistance in environmental A. baumannii isolates were highest for ciprofloxacin (64.03%, n = 73), levofloxacin (62.18%, n = 71) and trimethoprim-sulfamethoxazole (61.40%, n = 70), while lowest for colistin (1.75%, n = 2). Efflux pump overexpression was seen in 48.25% of isolates (n = 55), 49.12% (n = 56) were classified as MDR. 6.14% (n = 7), 9.65% (n = 11), 24.65% (n = 28) and 59.65% (n = 68) of isolates were non-biofilm producers, weak, medium, and strong biofilm producers, respectively. No significant differences were observed between non-MDR vs. MDR isolates regarding their distribution of biofilm-producers (P = 0.655). The MIC ranges for the tested antiseptics were as follows: benzalkonium chloride 16-128 μg mL-1, chlorhexidine digluconate 4-128 μg mL-1, formaldehyde 64-256 μg mL-1 and triclosan 2-16 μg mL-1, respectively. The conscientious use of antiseptics, together with periodic surveillance, is essential to curb the spread of these bacteria, and to maintain current infection prevention capabilities.

Risk factors for acquiring Acinetobacter baumannii infection in the intensive care unit: experience from a Moroccan hospital

Introduction

Acinetobacter species are non-fermenting and ubiquitous Gram-negative coccobacilli, which in recent years have become the leading cause of healthcare-associated infections worldwide. Our objective here was to study the epidemiology and risk factors associated with Acinetobacter baumannii infections in the intensive care unit (ICU).

Methods

This retrospective case-control study was conducted collaboratively between the Medical Bacteriology Department and the two ICUs of the Military Hospital of Instruction Mohammed V-Rabat over a 3 month period.

Results

We included 180 patients, of whom 60 had A. baumannii infection. We observed a male predominance in both matched groups, with a sex ratio of 1.6. The median age was 67 years [interquartile range (IQR) 59.5-77]. The median length of stay in the ICU before infection was 8.5 days (IQR 5-14). Multivariate logistic regression analysis identified the risk factors statistically associated with A. baumannii infection at the ICU level as follows: duration of invasive procedures >7 days [odds ratio (OR)=1.02], parenteral nutrition (OR=3.514), mechanical ventilation (OR=3.024), imipenem (OR=18.72), colistin (OR=5.645), probabilistic antibiotic therapy >4 days (OR=9.063) and neoplastic pathology (OR=5.727).

Conclusion

Based on our results, it can be inferred that shortening the duration of stay in the resuscitation setting, implementing rational use of medical devices and optimizing antibiotic therapy could decrease the incidence of these infections.

Hospital-acquired and zoonotic bacteria from a veterinary hospital and their associated antimicrobial-susceptibility profiles: A systematic review

Background

Hospital-acquired infections (HAIs) are associated with increased mortality, morbidity, and an economic burden due to costs associated with extended hospital stays. Furthermore, most pathogens associated with HAIs in veterinary medicine are zoonotic. This study used published data to identify organisms associated with HAIs and zoonosis in veterinary medicine. Furthermore, the study also investigated the antimicrobial-susceptibility profile of these bacterial organisms.

Methods

A systematic literature review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Search terms and five electronic databases were used to identify studies published over 20 years (2000-2020). The risk of bias was assessed using the "Strengthening the Reporting of Observational Studies in Epidemiology-Vet" (STROBE-Vet) checklist.

Results

Out of the identified 628 papers, 27 met the inclusion criteria for this study. Most studies (63%, 17/27) included were either from small animal or companion animal clinics/hospitals, while 5% (4/27) were from large animal clinics/hospitals inclusive of bovine and equine hospitals. Hospital-acquired bacteria were reported from environmental surfaces (33%, 9/27), animal clinical cases (29.6%, 8/27), and fomites such as cell phones, clippers, stethoscopes, and computers (14.8%, 4/27). Staphylococcus spp. was the most (63%; 17/27) reported organism, followed by Escherichia coli (19%; 5/27), Enterococcus spp. (15%, 4/27), Salmonella spp. (15%; 4/27), Acinetobacter baumannii (15%, 4/27), Clostridioides difficile (4%, 1/27), and Pseudomonas aeruginosa (4%; 1/27). Multidrug-resistant (MDR) organisms were reported in 71% (12/17) of studies linked to Methicillin-resistant Staphylococcus aureus (MRSA), Methicillin-resistant Staphylococcus pseudintermedius (MRSP), Enterococcus spp., Salmonella Typhimurium, A. baumannii, and E. coli. The mecA gene was identified in both MRSA and MRSP, the blaCMY-2 gene in E. coli and Salmonella spp., and the vanA gene in E. faecium isolate. Six studies reported organisms from animals with similar clonal lineage to those reported in human isolates.

Conclusion

Organisms associated with hospital-acquired infections and zoonosis have been reported from clinical cases, environmental surfaces, and items used during patient treatment and care. Staphylococcus species is the most reported organism in cases of HAIs and some isolates shared similar clonal lineage to those reported in humans. Some organisms associated with HAIs exhibit a high level of resistance and contain genes associated with antibiotic resistance.

In vitro evaluation of the antimicrobial activity of antiseptics against clinical Acinetobacter baumannii strains isolated from combat wounds

Healthcare-associated infections (HCAIs) are among the most prominent medical problems worldwide. In the context of increasing antibiotic resistance globally, the use of antiseptics as the main active agent and potentiator of antibiotics for the treatment of purulent-inflammatory complications of traumatic wounds, burns, and surgical wounds can be considered to tackle opportunistic infections and their prevention during war. This study presents a comparative investigation of the antimicrobial efficacy of antiseptics used for surgical antisepsis and antiseptic treatment of skin, mucous membranes, and wounds against multidrug-resistant clinical isolates of Acinetobacter baumannii as a wound pathogen of critical priority (according to the WHO). It was found that strains of A. baumannii, which have natural and acquired resistance to antimicrobial drugs, remain susceptible to modern antiseptics. Antiseptic drugs based on decamethoxine, chlorhexidine, octenidine, polyhexanide, and povidone-iodine 10% and 2% provide effective bactericidal activity against A. baumannii within the working concentrations of these drugs. Chlorhexidine and decamethoxine can inhibit biofilm formation by A. baumannii cells. In terms of bactericidal properties and biofilm formation inhibition, chlorhexidine and decamethoxine are the most effective of all tested antiseptics.

Combined Biocidal Effect of Gaseous Ozone and Citric Acid on Acinetobacter baumannii Biofilm Formed on Ceramic Tiles and Polystyrene as a Novel Approach for Infection Prevention and Control

Acinetobacter baumannii is a prominent emerging pathogen responsible for a variety of hospital-acquired infections. It can contaminate inanimate surfaces and survive in harsh environmental conditions for prolonged periods of time in the form of biofilm. Biofilm is difficult to remove with only one method of disinfection, so combined disinfection methods and biocidal active substances are needed for biofilm eradication. Additionally, having in mind ecological demands, legislators are more prone using fewer toxic substances for disinfection that produce less solid waste and hazardous disinfection byproducts. Gaseous ozone and citric acid are natural biocidal compounds, and the purpose of this study was to determine their combined biocidal effects on A. baumannii biofilm formed on ceramics and polystyrene. Twenty-four-hour A. baumannii biofilm formed on ceramic tiles and polystyrene was exposed to different combinations of disinfection protocols with 25 ppm of gaseous ozone for 1 h exposure time and 15% citric acid for 10 min exposure. The total number of bacteria was counted afterwards and expressed as CFU/cm2. The determined disinfection protocols of A. baumannii biofilm with combined citric acid and gaseous ozone caused reduction of 2.8 to 5.89 log10 CFU (99.99% inhibition rate) of total viable bacteria for each method, with the citric acid–ozone–citric acid disinfection protocol being most successful in eradication of viable bacteria on both ceramics and polystyrene. In conclusion, gaseous ozone and citric acid showed good combined biocidal effects on A. baumannii biofilm and successfully reduced early A. baumannii biofilm from ceramic and polystyrene surfaces. The given combination of active substances can be a good option for eco-friendly disinfection of hospital inanimate surfaces from A. baumannii biofilm contamination with prior mechanical cleaning.

Inanimate Surfaces as a Source of Hospital Infections Caused by Fungi, Bacteria and Viruses with Particular Emphasis on SARS-CoV-2

The carriers of nosocomial infections are the hands of medical personnel and inanimate surfaces. Both hands and surfaces may be contaminated as a result of contact with the patient, their body fluids, and touching contaminated surfaces in the patient's surroundings. Visually clean inanimate surfaces are an important source of pathogens. Microorganisms have properties thanks to which they can survive in unfavorable conditions, from a few days to several months. Bacteria, viruses and fungi are able to transmit from inanimate surfaces to the skin of the patient and the medical staff. These pathogens include SARS-CoV-2, which can survive on various types of inanimate surfaces, being a potential source of infection. By following the recommendations related to washing and disinfecting hands and surfaces, and using appropriate washing and disinfecting agents with a broad biocidal spectrum, high material compatibility and the shortest duration of action, we contribute to breaking the chain of nosocomial infections.

Virulence Determinants and Plasmid-Mediated Colistin Resistance mcr Genes in Gram-Negative Bacteria Isolated From Bovine Milk

A major increase of bacterial resistance to colistin, a last-resort treatment for severe infections, was observed globally. Using colistin in livestock rearing is believed to be the ground of mobilized colistin resistance (mcr) gene circulation and is of crucial concern to public health. This study aimed to determine the frequency and virulence characteristics of colistin-resistant Gram-negative bacteria from the milk of mastitic cows and raw unpasteurized milk in Egypt. One hundred and seventeen strains belonging to Enterobacteriaceae (n = 90), Pseudomonas aeruginosa (n = 10), and Aeromonas hydrophila (n = 17) were screened for colistin resistance by antimicrobial susceptibility testing. The genetic characteristics of colistin-resistant strains were investigated for mcr-1-9 genes, phylogenetic groups, and virulence genes. Moreover, we evaluated four commonly used biocides in dairy farms for teat disinfection toward colistin-resistant strains. Multidrug-resistant (MDR) and extensive drug-resistant (XDR) phenotypes were detected in 82.91% (97/117) and 3.42% (4/117) of the isolates, respectively. Of the 117 tested isolates, 61 (52.14%) were colistin resistant (MIC >2 mg/L), distributed as 24/70 (34.29%) from clinical mastitis, 10/11 (90.91%) from subclinical mastitis, and 27/36 (75%) from raw milk. Of these 61 colistin-resistant isolates, 47 (19 from clinical mastitis, 8 from subclinical mastitis, and 20 from raw milk) harbored plasmid-borne mcr genes. The mcr-1 gene was identified in 31.91%, mcr-2 in 29.79%, mcr-3 in 34.04%, and each of mcr-4 and mcr-7 in 2.13% of the colistin-resistant isolates. Among these isolates, 42.55% (20/47) were E. coli, 21.28% (10/47) A. hydrophila, 19.12% (9/47) K. pneumoniae, and 17.02% (8/47) P. aeruginosa. This is the first report of mcr-3 and mcr-7 in P. aeruginosa. Conjugation experiments using the broth-mating technique showed successful transfer of colistin resistance to E. coli J53-recipient strain. Different combinations of virulence genes were observed among colistin-resistant isolates with almost all isolates harboring genes. Hydrogen peroxide has the best efficiency against all bacterial isolates even at a low concentration (10%). In conclusion, the dissemination of mobile colistin resistance mcr gene and its variants between MDR- and XDR-virulent Gram-negative isolates from dairy cattle confirms the spread of mcr genes at all levels; animals, humans, and environmental, and heralds the penetration of the last-resort antimicrobial against MDR bacteria. Consequently, a decision to ban colistin in food animals is urgently required to fight XDR and MDR bacteria.

Upregulation of abeM, amvA, and qacEΔ1 efflux pump genes associated with resistance of Acinetobacter baumannii strains to disinfectants

BACKGROUND AND AIMS

Acinetobacter baumannii is among the most concerning cause of nosocomial infections due to its high level of antibiotic resistance and high mortality. The aim of this study was to determine the role of efflux pumps in resistance of A. baumannii strains to three disinfectants, including MICROZED ID-MAX, NANOSIL D2, and OPIDEX OPA.

METHODS

Twenty-eight environmental and clinical isolates of A. baumannii were collected from selected hospitals of central Iran. The minimum inhibitory concentrations of the disinfectants were determined and real time reverse transcriptase-PCR was performed to investigate the expression level of qacEΔ1, amvA, abeM, and adeB efflux pump genes.

RESULTS

Considering both clinical and environmental isolates, there was a significant difference in the mean expression level of qacEΔ1 gene between susceptible and resistant strains to MICROZED ID-MAX disinfectant, of amvA and abeM genes between susceptible and resistant strains to NANOSIL D2 disinfectant and of abeM gene in susceptible and resistant strains to OPIDEX OPA disinfectant (all P ˂ .05). The expression levels of abeM and amvA genes were higher in the environmental isolates that were resistant to NANOSIL D2 disinfectant compared to those that were susceptible (P ˂ .05).

CONCLUSIONS

This study provided evidence for the role of abeM and amvA genes in the resistance of environmental isolates to disinfectants, particularly hydrogen peroxide derivatives.

Biocide resistance in Acinetobacter baumannii: appraising the mechanisms

A global upsurge in antibiotic-resistant Acinetobacter baumannii requires supervised selection of biocides and disinfectants to avert nosocomial infections by reducing its spread. Moreover, inadequate and improper biocides have been reported as a contributing factor in antimicrobial resistance. Regardless of the manner of administration, a biocidal concentration that does not kill the target bacteria creates a stress response, propagating the resistance mechanisms. This is an essential aspect of the disinfection programme and the overall bio-contamination management plan. Knowing the mechanisms of action of biocides and resistance modalities may open new avenues to discover novel agents. This review describes the mechanisms of action of some biocides, resistance mechanisms, and approaches to study susceptibility/resistance to these agents.

Biocide susceptibility testing of bacteria: Development of a broth microdilution method

Biocide susceptibility testing (BST) of bacteria lacks standardised methods. Based on a recently established broth macrodilution BST method, a broth microdilution method for BST was developed. To establish the respective protocol, four reference strains Staphylococcus aureus ATCC® 6538, Enterococcus hirae ATCC® 10541, Escherichia coli ATCC® 10536 and Pseudomonas aeruginosa ATCC® 15442 were investigated for their minimal inhibitory concentrations (MICs) towards quaternary ammonium compounds (benzalkonium chloride), cationic compounds (chlorhexidine), aldehydes (glutardialdehyde) and alcohols (isopropanol) using tryptic soy broth. All combinations of (i) inoculum preparation according to the German Veterinary Medical Society (DVG) or the Clinical and Laboratory Standards Institute (CLSI) with some modifications, (ii) use of 1^st subculture (SC) and 2^nd SC, (iii) direct colony suspension (DCS) with/without glass beads, and (iv) incubation at 37 °C for 24 h, 48 h, and 72 h were compared using seven independent replications. Overall, the reproducibility was high for all abovementioned strain/biocide/parameter combinations. In total, 86.9 % - 100 % of the results were within ± one dilution step of the mode value. The proposed method for a standardised BST protocol comprises (i) two different inoculum densities, (ii) the use of a fresh overnight culture (1^st SC or 2^nd SC), (iii) the preparation of the inoculum suspension by either of the two methods using DCS with or without glass beads, and (iv) the incubation at 37 °C for 24 h. This broth microdilution method will help to harmonize BST of bacterial pathogens in routine diagnostics.

Analysis of Acinetobacter baumannii survival in liquid media and on solid matrices as well as effect of disinfectants

BACKGROUND

Acinetobacter baumannii is a cause of healthcare-associated infections and has considerable potential to survive on inanimate hospital surfaces under hostile conditions (e.g. disinfection or desiccation).

AIM

To learn more about its survival strategy and capacity to persist in liquid media and on surfaces mimicking hospital environments.

METHODS

The effect of temperature, nutrient deprivation, permanence on inanimate surfaces, and exposure to disinfectants on the survival of four A. baumannii strains (ATCC 19606^T and three clinical isolates) was studied by monitoring the number of total and viable cells using fluorescent microscopy and of culturable cells by standard cultures.

FINDINGS

Bacterial survival was differentially affected by temperature (cells maintained at 20°C remained culturable at least within 30 days) and physical environment (desiccation favoured cell resistance to stress at 37°C). Moreover, persistence was associated with two adaptation patterns: one linked to entry into the viable but non-culturable state, whereas the other apparently followed a bust-and-boom model. During a study on the effect of disinfectant (commercial bleach and quaternary ammonium compounds), it was found that treatment with these antibacterial compounds did not eliminate A. baumannii populations and provoked the reduction of culturable populations, although a fraction of cells remained culturable.

CONCLUSION

The ability to persist for long periods on different surfaces, mimicking those usually found in hospitals, along with A. baumannii's capacity to survive after a disinfection process may account for the recurrent outbreaks in intensive care units.

Reduced susceptibility to disinfectants of Acinetobacter baumannii biofilms on glass and ceramic

The aim of this study was to determine the susceptibility of hospital and environmental Acinetobacter baumannii isolate biofilms on ceramics and glass to common disinfectants benzalkonium chloride and chlorhexidine. For this purpose we developed a new method for biofilm cultivation and quantification on ceramics. The biofilm bacteria were more resistant to disinfectants than the planktonic populations, as more than 50 % of the biofilm population and none of the planktonic population survived 5-minute exposure. Furthermore, biofilm populations on ceramic tiles were significantly more resistant than those on glass coverslips, even though the amount of biofilm was practically the same on ceramics and glass. The reason for reduced susceptibility of A. baumannii biofilms on ceramics may be related to surface/disinfection interactions. Our findings suggest that biofilms on ceramic surfaces can be an important source of A. baumannii infection in hospital environments.

In Vitro Bactericidal and Virucidal Efficacy of Povidone-Iodine Gargle/Mouthwash Against Respiratory and Oral Tract Pathogens

Introduction

Recent virus epidemics and rising antibiotic resistance highlight the importance of hygiene measures to prevent and control outbreaks. We investigated the in vitro bactericidal and virucidal efficacy of povidone-iodine (PVP-I) 7% gargle/mouthwash at defined dilution against oral and respiratory tract pathogens.

Methods

PVP-I was tested against Klebsiella pneumoniae and Streptococcus pneumoniae according to bactericidal quantitative suspension test EN13727 and against severe acute respiratory syndrome and Middle East respiratory syndrome coronaviruses (SARS-CoV and MERS-CoV), rotavirus strain Wa and influenza virus A subtype H1N1 according to virucidal quantitative suspension test EN14476. PVP-I 7% gargle/mouthwash was diluted 1:30 with water to a concentration of 0.23% (the recommended concentration for “real-life” use in Japan) and tested at room temperature under clean conditions [0.3 g/l bovine serum albumin (BSA), viruses only] and dirty conditions (3.0 g/l BSA + 3.0 ml/l erythrocytes) as an interfering substance for defined contact times (minimum 15 s). Rotavirus was tested without protein load. A ≥ 5 log₁₀ (99.999%) decrease of bacteria and ≥ 4 log₁₀ (99.99%) reduction in viral titre represented effective bactericidal and virucidal activity, respectively, per European standards.

Results

PVP-I gargle/mouthwash diluted 1:30 (equivalent to a concentration of 0.23% PVP-I) showed effective bactericidal activity against Klebsiella pneumoniae and Streptococcus pneumoniae and rapidly inactivated SARS-CoV, MERS-CoV, influenza virus A (H1N1) and rotavirus after 15 s of exposure.

Conclusion

PVP-I 7% gargle/mouthwash showed rapid bactericidal activity and virucidal efficacy in vitro at a concentration of 0.23% PVP-I and may provide a protective oropharyngeal hygiene measure for individuals at high risk of exposure to oral and respiratory pathogens.

Funding

Mundipharma Research GmbH & Co. KG (MRG).

Intensive care unit-acquired Acinetobacter baumannii infections in a Moroccan teaching hospital: epidemiology, risk factors and outcome

Introduction

The objective of this study was to examine the epidemiology, risk factors and outcome associated with Acinetobacter baumannii infections in the intensive care units (ICUs) in a Moroccan teaching hospital.

Methods

This is a matched case-control study conducted as a joint collaboration between the clinical Bacteriology department and the two ICUs of Mohammed V Military Teaching Hospital from January 2015 to July 2016.

Results

Among 964 patients hospitalized in the ICUs, 81 (8.4%) developed A. baumannii infections. Multivariate logistic regression analysis identified the following independent risk factors for ICU-acquired A. baumannii infections: ICU stay ≥14 days (odds ratio (OR)=6.4), prior use of central venous catheters (OR=18), prior use of mechanical ventilation (OR=9.5), duration of invasive procedures ≥7 days (OR=7.8), previous exposure to imipenem (OR=9.1), previous exposure to amikacin (OR=5.2), previous exposure to antibiotic polytherapy (OR=11.8) and previous exposure to corticotherapy (OR=5). On the other hand, the admission for post-operative care was identified as a protective factor. The crude mortality in patients with A. baumannii infection was 74.1%. Multivariate analysis showed that septic shock (OR=19.2) and older age (≥65 years) (OR=4.9) were significantly associated to mortality risk in patients with A. baumannii infection.

Conclusion

Our results show that shortening the ICU stay, rational use of medical devices and optimizing antimicrobial therapy could reduce the incidence of these infections. Elderly patients and those with septic shock have a poor prognosis. These findings highlight the need for focusing on the high-risk patients to prevent these infections and improve clinical outcome.

Molecular Characterization of Reduced Susceptibility to Biocides in Clinical Isolates of Acinetobacter baumannii

Active efflux is regarded as a common mechanism for antibiotic and biocide resistance. However, the role of many drug efflux pumps in biocide resistance in Acinetobacter baumannii remains unknown. Using biocide-resistant A. baumannii clinical isolates, we investigated the incidence of 11 known/putative antimicrobial resistance efflux pump genes (adeB, adeG, adeJ, adeT1, adeT2, amvA, abeD, abeM, qacE, qacEΔ1, and aceI) and triclosan target gene fabI through PCR and DNA sequencing. Reverse transcriptase quantitative PCR was conducted to assess the correlation between the efflux pump gene expression and the reduced susceptibility to triclosan or chlorhexidine. The A. baumannii isolates displayed high levels of reduced susceptibility to triclosan, chlorhexidine, benzalkonium, hydrogen peroxide, and ethanol. Most tested isolates were resistant to multiple antibiotics. Efflux resistance genes were widely distributed and generally expressed in A. baumannii. Although no clear relation was established between efflux pump gene expression and antibiotic resistance or reduced biocide susceptibility, triclosan non-susceptible isolates displayed relatively increased expression of adeB and adeJ whereas chlorhexidine non-susceptible isolates had increased abeM and fabI gene expression. Increased expression of adeJ and abeM was also demonstrated in multiple antibiotic resistant isolates. Exposure of isolates to subinhibitory concentrations of triclosan or chlorhexidine induced gene expression of adeB, adeG, adeJ and fabI, and adeB, respectively. A point mutation in FabI, Gly95Ser, was observed in only one triclosan-resistant isolate. Multiple sequence types with the major clone complex, CC92, were identified in high level triclosan-resistant isolates. Overall, this study showed the high prevalence of antibiotic and biocide resistance as well as the complexity of intertwined resistance mechanisms in clinical isolates of A. baumannii, which highlights the importance of antimicrobial stewardship and resistance surveillance in clinics.