Characterization of ceftriaxone-resistant Aeromonas spp. isolates from stool samples of both children and adults in Southern India

Changing epidemiological trend of Aeromonas species and ciprofloxacin sensitivity in South India

Aeromonas species can cause a wide range of clinical infections. Several reports of drug resistance among the Aeromonas species have been reported, but our observations have differed. Here we present the changing susceptibility pattern of antibiotics for Aeromonas species over 14 years (January 2010-February 2024) at a tertiary care hospital in South India.

Two colistin resistance-producing Aeromonas strains, isolated from coastal waters in Zhejiang, China: characteristics, multi-drug resistance and pathogenicity

Introduction

Aeromonas spp. are ubiquitous inhabitants of ecosystems, and many species are opportunistically pathogenic to humans and animals. Multidrug-resistant (MDR) Aeromonas species have been widely detected in hospitals, urban rivers, livestock, and aquatic animals.

Results

In this study, we identified two Aeromonas isolates, namely Aeromonas veronii 0728Q8Av and Aeromonas caviae 1029Y16Ac, from coastal waters in Zhejiang, China. Both isolates exhibited typical biochemical characteristics and conferred MDR to 11 kinds of antibiotics, remaining susceptible to ceftazidime. Whole-genome sequencing revealed that both isolates harbored multiple antibiotic resistance genes (ARGs) and several mobile genetic elements (MGEs) on the chromosomes, each containing a resistance genomic island (GI), a typical class 1 integron, a transposon, and various insertion sequences (ISs). Most ARGs were situated within the multiple resistance GI, which contained a class 1 integron and a transposon in both Aeromonas isolates. Furthermore, a chromosomal mcr-3.16 gene was identified in A. veronii 0728Q8Av, while a chromosomal mcr-3.3 was found in A. caviae 1029Y16Ac. Both mcr-3 variants were not located within but were distanced from the multidrug resistance GI on the chromosome, flanking by multiple ISs. In addition, a mcr-3-like was found adjacent to mcr-3.16 to form a tandem mcr-3.16-mcr-3-like-dgkA structure; yet, Escherichia coli carrying the recombinants of mcr-3-like did not exhibit resistance to colistin. And an incomplete mcr-3-like was found adjacent to mcr-3.3 in A. caviae 1029Y16Ac, suggesting the possibility that mcr-3 variants originated from Aeromonas species. In vivo bacterial pathogenicity test indicated that A. veronii 0728Q8Av exhibited moderate pathogenicity towards infected ayu, while A. caviae 1029Y16Ac was non-virulent.

Discussion

Thus, both Aeromonas species deserve further attention regarding their antimicrobial resistance and pathogenicity.

Antimicrobial resistance in aeromonads and new therapies targeting quorum sensing

Aeromonas species (spp.) are well-known fish pathogens, several of which have been recognized as emerging human pathogens. The organism is capable of causing a wide spectrum of diseases in humans, ranging from gastroenteritis, wound infections, and septicemia to devastating necrotizing fasciitis. The systemic form of infection is often fatal, particularly in patients with underlying chronic diseases. Indeed, recent trends demonstrate rising numbers of hospital-acquired Aeromonas infections, especially in immuno-compromised individuals. Additionally, Aeromonas-associated antibiotic resistance is an increasing challenge in combating both fish and human infections. The acquisition of antibiotic resistance is related to Aeromonas' innate transformative properties including its ability to share plasmids and integron-related gene cassettes between species and with the environment. As a result, alternatives to antibiotic treatments are desperately needed. In that vein, many treatments have been proposed and studied extensively in the fish-farming industry, including treatments that target Aeromonas quorum sensing. In this review, we discuss current strategies targeting quorum sensing inhibition and propose that such studies empower the development of novel chemotherapeutic approaches to combat drug-resistant Aeromonas spp. infections in humans. KEY POINTS: • Aeromonas notoriously acquires and maintains antimicrobial resistance, making treatment options limited. • Quorum sensing is an essential virulence mechanism in Aeromonas infections. • Inhibiting quorum sensing can be an effective strategy in combating Aeromonas infections in animals and humans.

First hybrid complete genome of Aeromonas veronii reveals chromosome-mediated novel structural variant mcr-3.30 from a human clinical sample

Recent findings demonstrate the origin of the plasmid-mediated colistin resistance gene mcr-3 from aeromonads. The present study aimed to screen for plasmid-mediated colistin resistance among 30 clinical multidrug-resistant (MDR) Aeromonas spp. PCR was used to screen for the presence of mcr-1, mcr-2, mcr-3 and mcr-4, which revealed mcr-3 in a colistin-susceptible isolate (FC951). All other isolates were negative for mcr. Sequencing of FC951 revealed that the mcr-3 (mcr-3.30) identified was different from previously reported variants and had 95.62 and 95.28 % nucleotide similarity with mcr-3.3 and mcr-3.10. Hybrid assembly using IonTorrent and MinION reads revealed structural genetic information for mcr-3.30 with an insertion of ISAs18 within the gene. Due to this, mcr-3.30 was non-expressive, which makes FC951 susceptible to colistin. Further, in silico sequence and protein structural analysis confirmed the new variant. To the best of our knowledge, this is the first report on a novel mcr-3 variant from India. The significant role of mcr-like genes in different Aeromonas species remains unknown and requires additional investigation to obtains insights into the mechanism of colistin resistance.

Distinct Antimicrobial Resistance Profiling Of Clinically Important Aeromonas Spp. In Southwest China: A Seven-Year Surveillance Study

Background

Co-evolution of host and aeromonads has diversified their spectrums of diseases and antibiograms, while a paucity of data was concerning about this diversity in China. To fill this gap, this study was aimed to investigate and compare antimicrobial resistance (AMR) patterns of clinically important Aeromonas spp. from various clinical sources.

Methods

A multicenter retrospective surveillance study was conducted in Chongqing from 2011 to 2017. Data of strains were retrieved from the database of China Antimicrobial Resistance Surveillance System (CARSS). Whonet 5.6 and Graphpad Prism 6 Software were adopted to determine and compare distribution and AMR patterns.

Results

Among 1135 Aeromonas strains, Aeromonas hydrophila complex (65.6%, 745/1135) was the most predominant species, followed by Aeromonas veronii complex (16.7%, 190/1135) and Aeromonas caviae complex (15.3%, 174/1135). Sputum was the most frequent source of strains (27.7%), followed by wound (20.8%), bloodstream (10.8%) and urine (8.8%). Urinary strains demonstrated the highest resistance rates to ceftriaxone (65.6%), ceftazidime (52.1%), cefepime (38.3%), ciprofloxacin (47.7%) and trimethoprim-sulfamethoxazole (56.6%). Similar AMR pattern was observed in intestinal strains, with corresponding resistance rates of 29.4%, 28.9%, 22.2%, 27.3% and 45%, respectively. However, respiratory, bloodstream and skin strains exhibited resistance rates of less than 20% to most of the antimicrobials tested. In terms of species, approximately 30% of Aeromonas hydrophila complex and Aeromonas caviae complex strains were resistant to ceftriaxone and trimethoprim-sulfamethoxazole, while Aeromonas veronii complex strains harbored resistance rates of less than 20% to all tested antimicrobials. Although antibiograms of these species were distinct, they remained constant from 2011 to 2017.

Conclusions

Distinct AMR patterns between species and sources highlighted the predominance of Aeromonas hydrophila complex and high resistance of strains in urine and intestine to extended-spectrum cephalosporins, ciprofloxacin and trimethoprim-sulfamethoxazole in Southwest China. Temporally constant AMR patterns should not relax the vigilance of antimicrobial resistance in clinically important Aeromonas species.

Bacteriological, Clinical and Virulence Aspects of Aeromonas-associated Diseases in Humans

Aeromonads have been isolated from varied environmental sources such as polluted and drinking water, as well as from tissues and body fluids of cold and warm-blooded animals. A phenotypically and genotypically heterogenous bacteria, aeromonads can be successfully identified by ribotyping and/or by analysing gyrB gene sequence, apart from classical biochemical characterization. Aeromonads are known to cause scepticemia in aquatic organisms, gastroenteritis and extraintestinal diseases such as scepticemia, skin, eye, wound and respiratory tract infections in humans. Several virulence and antibiotic resistance genes have been identified and isolated from this group, which if present in their mobile genetic elements, may be horizontally transferred to other naive environmental bacteria posing threat to the society. The extensive and indiscriminate use of antibiotics has given rise to many resistant varieties of bacteria. Multidrug resistance genes, such as NDM1, have been identified in this group of bacteria which is of serious health concern. Therefore, it is important to understand how antibiotic resistance develops and spreads in order to undertake preventive measures. It is also necessary to search and map putative virulence genes of Aeromonas for fighting the diseases caused by them. This review encompasses current knowledge of bacteriological, environmental, clinical and virulence aspects of the Aeromonas group and related diseases in humans and other animals of human concern.

Taxonomy, virulence genes and antimicrobial resistance of Aeromonas isolated from extra-intestinal and intestinal infections

BACKGROUND

Clinical characteristics (taxonomy, virulence genes and antimicrobial resistance ) of Aeromonas in isolated from extra-intestinal and intestinal infections were investigated to describe epidemiology, associated virulence factors and optimal therapy options.

METHODS

Clinical samples (n = 115) of Aeromonas were collected from a general hospital in Beijing between the period 2015 and 2017. Taxonomy was investigate by Multilocus phylogenetic analysis (MLPA), 10 putative virulence factors by use of polymerase chain reaction (PCR) and antimicrobial resistance to 15 antibiotics by use of the microbroth dilution method.

RESULTS

The most common species of Aeromonas detected in samples of intestinal tract included; A. caviae (43.9%), A. veronii (35.7%), and A. dhakensis (12.2%). Prevalent species of Aeromonas collected from extra-intestinal infections included; A. hydrophila (29.4%), A. caviae (29.4%), and A. dhakensis (23.5%). A. hydrophila were detected in 1% of stool samples and 29.4% (5/17) of extra-intestinal infections. A. hydrophila strains in extra-intestinal infections were related to malignancy. The most common medical conditions among patients with Aeromonas infections included malignancy and liver-transplant related cholecystitis. Multiple drug resistance (MDR) was prevalent in extra-intestinal isolates (82.3%, 14/17) and was greater than the prevalence in intestinal isolates (30.6%, 30/98) (P < 0.05). Resistant rates of extra-intestinal isolates were 70.6, 35.3, 23.5 and 5.9% for ceftriaxone, ciprofloxacin, gentamicin and imipenem, respectively, and were higher than found in previous studies. Despite differences in the number and type of virulence genes among samples of Aeromonas, no significant correlation was found between invasion and virulent genes in intestinal or extra-intestinal infections.

CONCLUSIONS

Overall results of this study support a role for Aeromonas spp. as a potential causative infectious agent of gastroenteritis, and malignancy, liver cirrhosis, post liver transplantation in immunocompromised patients. A. hydrophila was more prevalent in samples of extra-intestinal infections when compared to samples of intestinal infections, and was especially prominent in samples of patients presenting with malignancy. Aeromonas isolates from extra-intestinal samples had high rates of drug resistance but 3rd generation cephalosporins, fluoroquinolones and aminoglycosides remain as options to treat severe diarrhea. However, increasing MDR of extra-intestinal infection samples warrants monitoring.

Multidrug-resistant Aeromonas hydrophila causing fatal bilateral necrotizing fasciitis in an immunocompromised patient: a case report

BACKGROUND

Aeromonas hydrophila is a water-dwelling, gram-negative rod-shaped bacterium, associated with diarrheal illness and, less commonly, necrotizing skin and soft tissue infections, especially among immunocompromised patients. Necrotizing fasciitis is associated with a high mortality rate, especially when caused by Aeromonas spp. Our patient was infected with an extremely aggressive form of multidrug-resistant Aeromonas spp. that produced both an extended-spectrum β-lactamase and an AmpC enzyme. Aeromonads are being recognized as important emerging pathogens because of their inherent antibiotic resistance profiles compounded by other virulence factors. These difficult-to-treat organisms can have significant implications in both clinical and public health settings.

CASE PRESENTATION

A 37-year-old Caucasian male with immunosuppression due to aplastic anemia being treated with cyclosporine, presented to hospital with relapsed disease. While in hospital, he subsequently developed overwhelming sepsis secondary to bilateral lower extremity necrotizing fasciitis. The necrotizing fasciitis was caused by a multidrug-resistant strain of A. hydrophila. Despite broad-spectrum antibiotics and aggressive surgical debridement, he succumbed to this severe invasive infection.

CONCLUSIONS

Necrotizing fasciitis caused by Aeromonas spp. is a rare infection that may have a poor clinical outcome, particularly if the diagnosis is delayed and/or the organism is highly virulent and multidrug resistant. Enhanced education of clinicians and microbiologists is required to prevent unnecessary complications and improve survival.

First report of blaOXA-181-mediated carbapenem resistance in Aeromonas caviae in association with pKP3-A: Threat for rapid dissemination

OBJECTIVES

Carbapenemase-producing Aeromonas spp. are of great concern in healthcare settings and are also known to acquire clinically relevant resistance genes. In this study, carbapenem-non-susceptible Aeromonas isolates were characterised for their molecular mechanisms of resistance.

METHODS

Among 180 Aeromonas isolates, 10 carbapenem-non-susceptible isolates were selected based on their antimicrobial susceptibility profile. Carbapenemase production was investigated by the CarbaNP test. ESBL-, AmpC- and carbapenemase-encoding genes were screened by PCR. Isolates VBF557 and VBF856 with high MICs for imipenem were selected for whole-genome sequencing (WGS). Conjugation experiments were performed to determine the transmissibility of resistance.

RESULTS

WGS remarkably revealed the presence of class D β-lactamases (AmpS/AmpH), class C β-lactamases and class B2 metallo-β-lactamase (cphA3) in VBF557. In contrast, VBF856 had multiple resistance genes coding for aminoglycoside, sulphonamide, carbapenem (bla_OXA-181 class D β-lactamase), macrolide, fluoroquinolone, rifampicin, phenicol, tetracycline and trimethoprim resistance. This is the first global report of bla_OXA-181 in Aeromonas spp. Interestingly, bla_OXA-181 was identified in association with transposon Tn2013 in plasmid pKP3-A. Additionally, an IncQ2 plasmid with qnrS2 was identified. Among the tested isolates, VBF1116 and VBF888 possessed bla_NDM and bla_VEB, respectively, by PCR. None of the other isolates harboured any tested β-lactamase genes. The resistance gene was transmissible in the presence of imipenem.

CONCLUSIONS

Presence of such resistance genes in plasmids further adds complexity for control of spread of carbapenem resistance. This study reveals the emergence of carbapenem resistance among Aeromonas spp. and the importance of mobile genetic elements such as plasmids in interchanging resistance determinants between species.