Emergence of multidrug-resistant non-fermentative gram negative bacterial infection in hospitalized patients in a tertiary care center of Nepal

Development of a duplex droplet digital PCR assay for the detection of Burkholderia cepacia complex and Stenotrophomonas maltophilia in bloodstream infections

Burkholderia cepacia complex (BCC) and Stenotrophomonas maltophilia are nosocomial pathogens that cause various infections and exhibit high resistance to multiple antimicrobial agents. In this study, we aimed to develop a duplex droplet digital PCR (ddPCR) assay for detecting BCC and S. maltophilia in bloodstream infections. We optimized the experimental conditions by setting the annealing temperature to 51°C and determining the optimal concentrations of primers and probes, as well as the thermal cycle numbers. The feasibility of the duplex ddPCR reaction system with the optimal conditions was established and verified through parallel reactions with reference strains of BCC and S. maltophilia. The specificity of the assay, tested with 33 reference strains, was found to be 100%. The duplex ddPCR assay demonstrated good repeatability and could detect as low as 5.35 copies/reaction of BCC and 7.67 copies/reaction of S. maltophilia. This level of sensitivity was consistent in the simulated blood and blood bottle samples. We compared nucleic acid extraction methods and found that the Chelex-100 boiling method and kit extraction method exhibited similar detection sensitivity, suggesting the potential application of the Chelex-100 boiling method in the ddPCR assay. In the clinical samples, the duplex ddPCR assay accurately detected BCC and S. maltophilia in 58 cases. In conclusion, our study successfully developed a duplex ddPCR assay that provides accurate and convenient detection of BCC and S. maltophilia in bloodstream infections.IMPORTANCEBurkholderia cepacia complex (BCC) and Stenotrophomonas maltophilia are implicated in a wide range of infections, including bloodstream infections (BSIs), pneumonia, and meningitis, and often exhibit high intrinsic resistance to multiple antimicrobial agents, limiting therapeutic options. The gold standard for diagnosing bloodstream infections remains blood culture. However, current blood culture detection and positivity rates do not meet the "rapid diagnosis" required for the diagnosis and treatment of critically ill patients with BSIs. The digital droplet PCR (ddPCR) method is a potentially more powerful tool in the diagnosis of BSIs compared to other molecular methods due to its greater sensitivity, specificity, accuracy, and reproducibility. In this study, a duplex ddPCR assay for the detection of BCC and S. maltophilia in BSIs was developed.

In Vitro Assessment of Antimicrobial Activity of Novel Fluoroquinolone, Levonadifloxacin (WCK 771) Against Multi-Drug-Resistant Clinical Isolates from Cancer Patients in India

Introduction: Rapid increase in antimicrobial-resistance is leading to urgent need for newer broad-spectrum antimicrobials. Therefore, we have evaluated the antimicrobial résistance spectrum of India-discovered novel antibiotics (levonadifloxacin) against clinical isolates recovered from cancer patients. Materials and Methods: The study was conducted in the microbiology department, over a period of 1 year between May 2021 and June 2022 and 374 consecutive and nonduplicate Gram-positive (GPC) and MDR Gram Negative Bacteria (GNB) isolate were analyzed from 3,880 cancer patients in study. The identification and antimicrobial sensitivities of bacterial isolates were performed according to standard laboratory protocols by using automated identification system (VITEK-2-8.01; BioMérieux, Germany). The activity of levonadifloxacin and comparator antibiotics was evaluated using disk diffusion methods as per Clinical and Laboratory Standards Institute 2022 guidelines. Results: The mean age of the patients were 51.6 ± 14.59 years with male: female ratio of 1.2:1. The prevalence of GPC was 167 (44.65%) and MDR-GNB was 207 (55.34%). The most common GPC was Staphylococcus aureus; 97 (58.08%) followed by Enterococcus species 66 (39.52%). In GNB, Escherichia coli; 93 (44.92%) was the most common followed by Klebsiella pneumoniae; 45 (21.73%). Levonadifloxacin susceptibility was present in 98.7% methicillin-resistant S. aureus and 96% methicillin-susceptible S. aureus and 77.1% Enterococcus-species. Additionally, all the fluoroquinolones-resistant S. aureus isolates were susceptible to levonadifloxacin (WCK-771) except one isolate. Also, levonadifloxacin-(WCK-771) exhibits 100% susceptibility fluoroquinolone susceptible GNB, such as E. coli, K. pneumoniae, Pseudomonas species, and Acinetobacter species. Interestingly, all fluoroquinolones-resistant Salmonella species and Stenotrophomonas maltophilla exhibited 100% susceptibility to levonadifloxacin (WCK-771). Conclusion: Levonadifloxacin (WCK-771) possesses potent activity against all the MDR Gram-positive pathogens including the coverage of susceptible Enterobacterales and MDR S. maltophilla and Burkholderia cepacia suggesting its potential utility in the management of polymicrobial infections.

Clonal diversity, antimicrobial resistance, and genome features among nonfermenting gram-negative bacteria isolated from patients with cystic fibrosis in Russia

Nonfermenting gram-negative (NFGN) bacteria were isolated from cystic fibrosis (CF) patients and subjected to susceptibility testing and whole-genome sequencing. Among 170 enrolled CF patients, 112 (65.9%) were colonized with at least 1 key NFGN species. The species-specific infection rate was highest for Pseudomonas aeruginosa (40.6%) followed by Stenotrophomonas maltophilia (14.1%), Achromobacter spp. (9.4%), and Burkholderia cepacia complex (Bcc, 8.2%) demonstrating a significant age-dependent increase for P. aeruginosa and Achromobacter spp., but not for S. maltophilia or Bcc. P. aeruginosa sequence types (STs) related to high-risk epidemic and global CF clones were carried by 12 (7.1%) and 13 (7.6%) patients, respectively. In total, 47% NFGN isolates, predominantly P. aeruginosa, harbored at least 1 plasmid-borne resistance gene; 5 ST235 isolates carried blaVIM2. Pathogenicity island-borne virulence genes were harbored by 9% NFGN isolates. These findings in conjunction with frequent early colonization by Bcc raised serious concerns regarding infection control in Russian CF centers.

High Prevalence of Multidrug-Resistant Bacteria in the Trachea of Intensive Care Units Admitted Patients: Evidence from a Bangladeshi Hospital

Recent research has shown that antibiotic-resistant microorganisms are becoming more prevalent in intensive care units (ICUs) at an exponential rate. Patients in the ICU can get infected by pathogens due to invasive operation procedures and critical health conditions. This study primarily emphasized tracheal samples from ICU patients due to their reliance on ventilators, increasing their susceptibility to Ventilator-Associated Pneumonia (VAP). Moreover, the rise of multidrug-resistant (MDR) pathogens makes treatment strategies more challenging for these patients. In this study, we tested 200 tracheal specimens to determine the prevalence of microorganisms and analyzed the antibiotic susceptibility of these isolates against regular antibiotics, including 4th generation drugs. Among the 273 isolates, 81% were gram-negative bacteria, 10% were gram-positive bacteria, and 9% were fungi. The most prevalent gram-negative bacteria were Acinetobacter spp. (34%), Klebsiella spp. (22%), Pseudomonas spp. (14%), and Escherichia coli (9.2%). The most prevalent gram-positive bacteria were Staphylococcus aureus (5.9%), and the fungi were Candida spp. (7.3%). Among the most prevalent bacteria, except Staphylococcus aureus isolates, around 90% were resistant to multiple drugs, whereas 60% of Acinetobacter spp. and Pseudomonas spp. were extensively drug resistant. Sensitivity analysis against the gram-negative and gram-positive drug panel using a one-way ANOVA test followed by Tukey's post hoc test showed that in the in vitro assay, colistin was the most effective antibiotic against all gram-negative bacteria. In contrast, linezolid, vancomycin, and fusidic acid were most effective against all gram-positive bacteria. Regular monitoring of nosocomial infections and safe management of highly resistant bacteria can help prevent future pandemics.

Current viewpoint on the epidemiology of nonfermenting Gram-negative bacterial strains

PURPOSE OF REVIEW

This article aims to review the epidemiology of nonfermenting Gram-negative bacilli (NFGNB) based on recent literature reports, particularly, of the less common, but with emerging clinical significance species.

RECENT FINDINGS

The reported frequency of multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa is increasing, with very significant variability, however, between different countries. Apart from the major NFGNB, that is, A. baumannii and P. aeruginosa, already recognized as of critical importance healthcare risks, several other NFGNB genera have been increasingly associated with diverse severe infections, such as Stenotrophomonas maltophilia, Burkholderia spp., Elizabethkingia spp., Chryseobacterium spp., Achromobacter spp., Alcaligenes spp., Sphingomonas spp., Shewanella spp. and Ralstonia spp., among others.

SUMMARY

The exploration of the epidemiology, as well as the pathogenic potential of the of the less frequent, but emerging and increasingly reported NFGNB, is crucial, not only for immunocompromised patients, but also for critically ill patients without overt immunosuppression. As we are heading fast towards a postantibiotic era, such information would contribute to the optimal antimicrobial management, that is, providing prompt, appropriate antimicrobial coverage when needed and, at the same time, avoiding overuse and/or inappropriate use of antimicrobial therapy. Also, it would help to better understand their transmission dynamics and to develop effective prevention strategies.

Multidrug-resistant among Non-Fermenting Gram-negative Bacteria Isolated in the Department of Microbiology of a Tertiary Care Centre

Introduction

Infection caused by Non-fermenting Gram-negative bacteria (NFGNB) like Pseudomonas aeruginosa and Acinetobacter baumannii leads to life-threatening conditions. These bacteria are often multidrug-resistant which leads to limited therapeutic options leading to treatment failure. Little information is available regarding the prevalence and resistance pattern of such bacteria in our country. The aim of the study was to find out the prevalence of multidrug-resistant among non-fermenting Gram-negative bacteria isolated in the Department of Microbiology of a tertiary care centre.

Methods

A descriptive cross-sectional study was conducted in the Department of Microbiology of a tertiary care centre from 1 September 2021 to 30 August 2022 after obtaining ethical approval from the Institutional Review Committee. All samples received in the Microbiology laboratory for diagnostic purposes were included. A convenience sampling method was used. The point estimated was calculated at a 95% Confidence Interval.

Results

Among 412 non-fermenting Gram-negative bacteria, multidrug resistance was observed in 373 (90.53%) (87.70-93.36, 95% Confidence Interval) isolates. Among 373 isolates, Acinetobacter baumannii was 253 (67.83%) and Pseudomonas aeruginosa was 120 (32.17%).

Conclusions

The prevalence of multidrug-resistant non-fermenting Gram-negative bacteria was found to be higher than in the study conducted in similar settings.

Keywords

Acinetobacter baumannii; antibiotic; Pseudomonas aeruginosa; prevalence.

Emergence of Multidrug-Resistant Non-Fermenting Gram-Negative Bacilli in a Tertiary Care Teaching Hospital of Central India: Is Colistin Resistance Still a Distant Threat?

Purpose Multidrug-resistant (MDR) organisms are being increasingly reported from India. This study aimed to determine the antibiotic susceptibility pattern of non-fermenting Gram-negative bacilli (NF-GNB) isolated from all the clinical samples to estimate the prevalence of MDR MDR NF-GNB and to screen for colistin-resistance genes among all colistin-resistant strains. Materials and methods This prospective study conducted from January 2021 to July 2022 at a tertiary care teaching hospital in central India identified MDR NF-GNB from clinical samples using standard procedures and antimicrobial susceptibility testing conducted as per Clinical Laboratory Standards Institute (CLSI) guidelines. Colistin-resistant strains identified by broth microdilution were further subjected to detection of plasmid-mediated colistin-resistant genes (mcr-1, mcr-2, mcr-3) by polymerase chain reaction (PCR). Results A total 2,106 NF-GNB were isolated from 21,019 culture positive clinical samples, of which 743 (35%) were MDR. Majority of MDR NF-GNB isolated were from pus (45.50%) followed by blood (20.50%). Out of 743 non-duplicate MDR non-fermenters,the most common were Pseudomonas aeruginosa (51.7%), Acinetobacter baumannii (23.4%),and others (24.9%).Around5.2% Pseudomonas aeruginosa and 2.3% Acinetobacter baumannii were resistant to colistin, and 88.2% were resistant to ceftazidime. Burkholderia cepacia complexwas 100% susceptible to minocycline and least susceptible to ceftazidime (28.6%). Out of 11, 10 (90.9%) Stenotrophomonas maltophilia were susceptible to colistin and least susceptible to ceftazidime and minocycline (27.3%). All 33 colistin-resistant strains (minimal inhibitory concentration ≥ 4 µg/mL) were found to be negative for mcr-1, mcr-2, and mcr-3 genes. Conclusion Our study showed a significantly wide variety of NF-GNB, ranging from Pseudomonas aeruginosa (51.7%), Acinetobacter baumannii (23.4%),to Acinetobacter haemolyticus (4.6%), Pseudomonas putida (0.9%), Elizabethkingia meningoseptica (0.7%), Pseudomonas luteola (0.5%), and Ralstonia pickettii (0.4%), which have not been commonly reported in literature. Of all the non-fermenters isolated in the present study, 35.28% were MDR, raising the concern for rationalizing antibiotic use and improving infection control measures to avert or slow the emergence of antibiotic resistance.

Current Trends in Antimicrobial Resistance Patterns in Bacterial Pathogens among Adult and Pediatric Patients in the Intensive Care Unit in a Tertiary Care Hospital in Kolkata, India

Nosocomial infections by multidrug-resistant (MDR) bacteria are among the main causes of morbidity and death in patients hospitalized in intensive care units (ICUs) worldwide. Antibiotic resistance has become a major concern for treating the patients with nosocomial infections. The aim of this study was to describe the antibiotic resistance patterns of pathogens causing infections in adult and pediatric patients in the ICUs of a tertiary care hospital in Kolkata, India. A cross-sectional, retrospective study was conducted from January 2022 to October 2022 on a total of 139 adult and 146 pediatric patients. Depending on clinical symptoms of the patients, samples were collected and subjected to antibiotic sensitivity testing. The culture and sensitivity pattern of clinical isolates from blood, urine, sputum, endotracheal tube (ET) aspirate, and central line catheter insertion site swabs were analyzed. A total of 695 and 556 specimens were obtained from adult and pediatric ICU, respectively. Culture positivity rate among adults and pediatric patients were 37% and 40%, respectively. The most commonly isolated organisms were Gram-negative Enterobacterales and non-fermenters. Most of the bacterial isolates showed very high resistance against multiple antibiotics. Escherichia coli from adult and pediatricpatients were found to be resistant to second generation cephalosporins (95% and 96%, respectively), beta-lactams (95% and 63%, respectively), fluoroquinolones (95% and 81%, respectively), and cotrimoxazole (85% and 78%, respectively). Klebsiella spp. from adult patients were found to be resistant to aminoglycosides (75%), second generation cephalosporins (100%), beta-lactams (94%), fluoroquinolones (92%), carbapenems (88%), and cotrimoxazole (83%). Proteus spp., Acinetobacter baumannii, and Pseudomonas spp. werefound to be resistant to multiple antibiotics. Enterococcus spp. from ICUs showed more than 90% resistance against ampicillin and more than 75% resistance against fluoroquinolones. MDR bacterial infections are increasing in both adult and pediatric ICUs, leading to significant therapeutic challenges. A frequent study of antimicrobial resistance patterns is imperative for antibiotic stewardshipin combatting the deadly effect of the MDR bacteria in critically ill patients.

Epidemiology of Multidrug Resistant Non-Fermentative Gram Negative Bacilli in Patients with Hospital Acquired Pneumonia: An Alarming Report from Somalia

Introduction

There is a lack of data concerning hospital-acquired pneumonia (HAP) due to multidrug resistant non-fermentative gram-negative bacilli (MDR-NFGNB) in Somalia, and this study will aim to analyze the epidemiology of MDR-NFGNB among HAP patients in tertiary care hospital in Somalia.

Materials and Methods

This is a retrospective study which evaluated the presence of MDR-NFGNB among 2003 HAP patients between June 2017 and May 2022 in a tertiary care hospital in Somalia. NFGNB were cultured on blood agar and eosin methylene blue agar and were then used BBL crystal system and oxidase biochemical assays for identification. Antimicrobial sensitivity and resistance were assessed using Mueller–Hinton agar.

Results

A total of 160 confirmed cases of HAP due to NFGNB were examined. Among these, 114 (71%) were males compared to females (n = 46, 29%). The mean age was 49.49 ± 21.48. The overall prevalence rate of NFGNB among patients with HAP was 8%. It was more common in older patients and in patients with co-morbidities. Acinetobacter baumannii was the most common NFGNB with n = 93 (58%), followed by Pseudomonas aeruginosa (n = 55, 34%), and Stenotrophomonas maltophilia (n = 12, 8%). Regarding the antimicrobial sensitivity rate, Acinetobacter baumannii showed an overall resistance level of 82%, Stenotrophomonas maltophilia (81%), and Pseudomonas aeruginosa (62%). The rate of CR-NFGNB in our study was 79.4%. We found that 68.1% of NFGNB was multidrug resistant (MDR) pathogens. MDR patterns were more common in Acinetobacter baumannii infections (84%). MDR pathogens were strongly associated with ICU admissions (95% CI, 0.202–0.800, OR, 0.402, p value <0.009). Finally, the mortality rate of HAP caused by NFGNB in our study was 42.5%.

Conclusion

The prevalence of NFGNB in HAP patients was 8%. These infections were more prevalent among men and the elderly. Acinetobacter baumannii and Stenotrophomonas maltophilia exhibited the highest antibiotic resistance rate. The MDR level of these pathogens was 68.1%.

Pseudomonas aeruginosa in Nepali hospitals: poor outcomes amid 10 years of increasing antimicrobial resistance

OBJECTIVE

To determine antimicrobial resistance patterns and prevalence of multi- (MDR, i.e., resistant to ⩾3 classes of antimicrobial agents) and extensively (XDR, i.e., resistant to ⩾3, susceptible to ⩽2 groups of antibiotics) drug-resistant strains of Pseudomonas aeruginosa.

METHODS

This was a cross-sectional study conducted in Nepal Mediciti Hospital, Lalitpur, Nepal, using standard microbiological methods with Kirby Bauer disc diffusion to identify antimicrobial susceptibility.

RESULTS

P. aeruginosa (n = 447) were most frequently isolated in respiratory (n = 203, 45.4%) and urinary samples (n = 120, 26.8%). AWaRe Access antibiotics showed 25-30% resistance, Watch antibiotics 30-55%. Susceptibility to AWaRe Reserve antibiotics remains high; however, 32.8% were resistant to aztreonam. Overall, 190 (42.5%) were MDR and 99 (22.1%) XDR (first Nepali report) based on mainly non-respiratory samples. The majority of infected patients were >40 years (n = 229, 63.2%) or inpatients (n = 181, 50.0%); 36 (15.2%) had an unfavourable outcome, including death (n = 25, 10.5%). Our larger study showed a failure of improvement over eight previous studies covering 10 years.

CONCLUSION

Antibiotic resistance in P. aeruginosa occurred to all 19 AWaRe group antibiotics tested. Vulnerable patients are at significant risk from such resistant strains, with a high death rate. Sustainable and acceptable antibiotic surveillance and control are urgently needed across Nepal, as antimicrobial resistance has deteriorated over the last decade.

High drug resistance among Gram-negative bacteria in sputum samples from an intensive care unit in Nepal

SETTING

Tribhuvan University Teaching Hospital, Kathmandu, Nepal.

OBJECTIVES

1) To report the number and proportion of Pseudomonas, Acinetobacter, Burkholderia, Stenotrophomonas (PABS) species among intensive care unit (ICU) patients with sputum culture; and 2) to assess antimicrobial resistance patterns, demographic and clinical characteristics associated with resistance to at least one antibiotic and ICU discharge outcomes among those patients with PABS species admitted to hospital between 14 April 2018 and 13 April 2019.

DESIGN

This was a hospital-based, cross-sectional study using secondary data.

RESULTS

Of 166 who underwent sputum culture, 104 (63%) had bacterial growth, of which, 67 (64%) showed PABS species. Of the positive cultures, Pseudomonas, Acinetobacter, Burkholderia and Stenotrophomonas were present in respectively 32 (30.7%), 31 (29.8%), 1 (1%) and 3 (2.8%). Pseudomonas showed a high level of resistance to levofloxacin (61%), cefepime (50%) and amikacin (50%). Acinetobacter was largely resistant to cefepime (95%), imipenem (92%) and levofloxacin (86%). Of the 67 with PABS infection, 32 (48%) died.

CONCLUSION

The study showed a high prevalence of Pseudomonas and Acinetobacter and the emergence of Stenotrophomonas in sputum culture samples of ICU patients. This highlights the need for monitoring PABS and associated resistance patterns to reduce mortality in ICU patients.

High prevalence of multidrug-resistant non-fermentative Gram-negative bacilli harboring bla IMP-1 and bla VIM-1 metallo-beta-lactamase genes in Birjand, south-east Iran

Background and Objectives:

Non-fermentative Gram-negative Bacilli (NFGNB) is known as a major cause of healthcare-associated infections with high levels of antibiotic resistance. The aim of this study was to investigate the antibiotic resistance profiles and molecular characteristics of metallo-beta-lactamase (MBL)-producing NFGNB.

Materials and Methods:

In this cross-sectional study, the antibiotic resistance profile of 122 clinical NFGNB isolates was determined by the Kirby-Bauer disk diffusion and microdilution broth methods. Bacterial isolates were investigated for the detection of MBLs production using the combination disk diffusion Test (CDDT). The existence of bla_IMP, bla_VIM, and bla_NDM genes in all carbapenem-resistant isolates was determined employing polymerase chain reaction (PCR) assays.

Results:

High resistance in Pseudomonas aeruginosa was reported to cefotaxime and minocycline, whereas Acinetobacter baumannii isolates were highly resistant to all antibiotics except colistin. Multidrug resistance (MDR)-NFGNB (66% vs. 12.5%, P=0.0004) and extensively drug resistant (XDR)-NFGNB (55.7% vs. 12.5%, P=0.001) isolates were significantly more common in hospitalized patients than in outpatients. The production of MBL was seen in 40% of P. aeruginosa and 93.3% of A. baumannii isolates. It was found that 33.3% and 46.7% of carbapenem-resistant P. aeruginosa isolates, and 13.3% and 28.9% of carbapenem-resistant A. baumannii isolates were harboring bla_IMP-1 and bla_VIM-1 genes, respectively. The incidence of MDR (98.2% vs. 28.3%, P<0.001) and XDR (96.4% vs. 11.7%, P<0.001) in MBL-producing NFGNB isolates was significantly higher than non-MBL-producing isolates.

Conclusion:

This study demonstrated a higher rate of resistance among NFGNB isolates with an additional burden of MBL production within them, warranting a need for robust microbiological surveillance and accurate detection of MBL producers among the NFGNB.

Antimicrobial resistance trends of non-fermenter Gram negative bacteria in Saudi Arabia: A six-year national study

BACKGROUND

Antimicrobial resistance (AMR) of non-fermenting Gram-negative bacteria (NFGNB) is increasingly recognized as urgent healthcare threat. Trend data on AMR of NFGNB in Saudi Arabia are either old or limited. The objective was to estimate the prevalence and resistance trends of isolated NFGNB in Saudi Arabia.

METHODS

A retrospective multicenter study involving seven tertiary care hospitals in Saudi Arabia was conducted between 2011 and 2016. Susceptibility testing for non-duplicate isolates was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines in College of American Pathologists accredited diagnostic microbiology laboratories in the participating hospitals.

RESULTS

Out of 461,274 isolates, 100,132 (21.7%) were NFGNB which represented 30% of gram-negative pathogens. Pseudomonas aeruginosa was the most common (73.6%), followed by Acinetobacter baumannii (21.0%) and Stenotrophomonas maltophilia (5.3%). Resistance trends of P. aeruginosa were increasing for aztreonam (absolute increase during the study was 17.3%), imipenem (12.3%), and meropenem (11.6%). A. baumannii was fully resistant to several beta lactam drugs, and resistance trends were increasing for potential treatments such as tigecycline (25.1%) and tobramycin (15.5%). S. maltophilia was >90% resistant to trimethoprim/ sulfamethoxazole and ciprofloxacin by the end of the study.

CONCLUSION

We are reporting high and/or increasing resistance of NFGNB to common treatment options. The current findings call for urgent actions to combat the increasing resistance of NFGNB. Large scale sharing of AMR data collected at different hospitals with the Saudi AMR committee would be critical to set priorities and monitor progress.

Synergistic Effect between Usnic Acid and Polymyxin B against Resistant Clinical Isolates of Pseudomonas aeruginosa

The present study aimed to characterize the susceptibility profile of Pseudomonas aeruginosa and Acinetobacter spp. clinical isolates to polymyxin B in a public hospital in Recife-PE, Brazil, between the years of 2018 and 2019, as well as to search for the presence of the mcr-1 gene and evaluate the interaction between polymyxin B and usnic acid against these isolates. The strains were identified using the BD Phoenix™ automated system and the agar-spot test was used to determine the susceptibility profile to polymyxin B. The minimum inhibitory concentrations (MICs) of usnic acid and polymyxin B were determined through the broth microdilution method according to the Clinical and Laboratory Standards Institute (CLSI). Subsequently, Polymerase Chain Reaction (PCR) was performed to detect the mcr-1 gene in the isolates. The interaction between usnic acid and polymyxin B was evaluated by the Checkerboard assay. Among 34 isolates of P. aeruginosa, 26.5% (9/34) were positive for the polymyxin B agar-spot test, and 11.8% (4/34) presented an intermediate susceptibility (MIC = 4 μg/mL), while 14.7% (5/34) presented antimicrobial resistance with MIC values ranging from 8 to 32 μg/mL. Among 38 isolates of Acinetobacter spp., 13.2% (5/38) were positive for the polymyxin B agar-spot test and all of them were resistant to polymyxin B with a MIC value > 32 μg/mL. The mcr-1 gene was not detected in the clinical isolates. Regarding usnic acid, it presented a moderate antibacterial activity against two P. aeruginosa isolates (MIC = 250 μg/mL) and no activity was detected against the others. A synergistic effect between usnic acid and polymyxin B was observed against three clinical isolates of P. aeruginosa which were resistant to polymyxin B (FICI ≤ 0.5). Therefore, it was possible to observe that usnic acid is a promising candidate to be used in combination with polymyxin B against infections caused by resistant P. aeruginosa.