Which antibiotics and breakpoints should be used for Aeromonas susceptibility testing? Considerations from a comparison of agar dilution and disk diffusion methods using Enterobacteriaceae breakpoints

The Impact of Cefuroxime Susceptibility on Aeromonas Necrotizing Fasciitis Outcomes

Despite aggressive antibiotic therapy and surgical debridement, Aeromonas necrotizing fasciitis (NF) can lead to high amputation and mortality rates. Our study compares the different antibiotic minimum inhibitory concentrations (MICs) via Epsilometer tests (E-tests) between non-survivors and survivors of Aeromonas NF of limbs. A prospective review of 16 patients with Aeromonas NF was conducted for 3.5 years in a tertiary coastal hospital. E-tests were conducted for 15 antimicrobial agents to determine the MIC value for Aeromonas species. These patients were divided into non-survival and survival groups. The clinical outcomes, demographics, comorbidities, presenting signs and symptoms, laboratory findings, and microbiological results between the two periods were compared. A total of four patients died, whereas 12 survived, resulting in a 25% mortality rate. A higher proportion of bloodstream infections (100% vs. 41.7%; p = 0.042), monomicrobial infections (100% vs. 33.3%; p = 0.021), shock (100% vs. 33.3%; p = 0.021), serous bullae (50% vs. 0%; p = 0.009), liver cirrhosis (100% vs. 25%; p = 0.009), chronic kidney disease (100% vs. 33.3%; p = 0.021), lower susceptibility to cefuroxime (25% vs. 83.3%; p = 0.028), and ineffective antibiotic prescriptions (75% vs. 16.7%; p = 0.029) was observed in non-survivors. Aeromonas NF is an extremely rare skin and soft-tissue infection that is associated with high mortality, bacteremia, antibiotic resistance, and polymicrobial infection. Therefore, antibiotic regimen selection is rendered very challenging. To improve clinical outcomes and irrational antimicrobial usage, experienced microbiologists can help physicians identify specific pathogens and test MIC.

Plasmid-Mediated Fluoroquinolone Resistance Genes in Quinolone-Susceptible Aeromonas spp. Phenotypes Isolated From Recreational Surface Freshwater Reservoir

Aeromonas spp. are recognized as opportunistic pathogens causing diseases. Infections in humans can result mainly in gastrointestinal and wound diseases with or without progression to septicemia. Although Aeromonas spp. are not known uropathogens and they rarely cause urinary tract infection, we hypothesize that the presence of these bacteria in the water and the contact during, e.g., recreational and bathing activity can create the conditions for the colonization of the human body and may result to diseases in various locations, including the urinary tract. Our study presents the occurrence of aeromonad fluoroquinolone-susceptible phenotypes with the presence of plasmid-mediated fluoroquinolone resistance (PMQR) genes in a natural freshwater reservoir occasionally used for recreational activities. Sixty-nine isolates collected during the bathing period were identified by mass spectrometry and screened for the presence of fluoroquinolone-resistant phenotypes and genotypes. Fluoroquinolone susceptibility was determined as minimal inhibitory concentration values. PMQR qnr genes were detected by PCR. Isolates comprising eight species, namely, mainly Aeromonas veronii (50.7% isolates) and Aeromonas media (24.6% isolates) and rarely Aeromonas eucrenophila, Aeromonas caviae, Aeromonas bestiarum, Aeromonas ichthiosmia, and Aeromonas hydrophila, were selected. All isolates were phenotypically susceptible either to ciprofloxacin or levofloxacin. Unexpectedly, at least one to three of the PMQR genes were detected in 42.0% of the fluoroquinolone-susceptible Aeromonas spp. phenotypes. Mainly the qnrS (34.8% isolates) and qnrA (14.5% isolates) determinants were detected. In conclusion, the freshwater reservoir occasionally used for bathing was tainted with aeromonads, with a high occurrence of opportunistic pathogens such as A. veronii and A. media. MALDI‐TOF MS is a powerful technique for aeromonad identification. Our data reveals the mismatch phenomenon between fluoroquinolone-susceptible aeromonad phenotypes and the presence of plasmid-mediated qnr resistance genes. It suggests that phenotypically susceptible bacteria might be a potential source for the storage and transmission of these genes. The exposure during, e.g., a recreational activity may create the potential risk for causing infections, both diagnostically and therapeutically difficult, after expressing the resistance genes and quinolone-resistant strain selection.

Antimicrobial Susceptibility Profiles and Resistance Genes in Genus Aeromonas spp. Isolated from the Environment and Rainbow Trout of Two Fish Farms in France

This study presents the occurrence and abundance of Aeromonas antibiotic-resistant bacteria (ARB) and genes (ARGs) isolated from water, biofilm and fish in two commercial trout farms before and one week after flumequine treatment. Wild (WT) and non-wild (NWT) strains were determined for quinolones (flumequine, oxolinic acid and enrofloxacin), oxytetracycline (OXY), florfenicol (FFN), trimethoprim-sulfamethoxazole (TMP) and colistin (COL), and pMAR (presumptive multi-resistant) strains were classified. Forty-four ARGs for the mentioned antibiotics, β-lactams and multi-resistance were quantified for 211 isolates. BlaSHV-01, mexF and tetE were the dominant ARGs. A greater occurrence and abundance of tetA2, sul3, floR1, blaSHV-01 and mexF were observed for NWT compared to WT. The occurrence of pMAR and NWT Aeromonas for quinolones, OXY, FFN, TMP, COL and ARGs depended on the Aeromonas origin, antibiotic use and the presence of upstream activities. Our results revealed the impact of a flumequine treatment on Aeromonas present on a fish farm through an increase in NWT and pMAR strains. The link between fish and their environment was shown by the detection of identical ARB and ARGs in the two types of samples. There appears to be a high risk of resistance genes developing and spreading in aquatic environments.

Occurrence and Antimicrobial Susceptibility Profiles of Multidrug-Resistant Aeromonads Isolated from Freshwater Ornamental Fish in Chiang Mai Province

Antimicrobials are commonly used to prevent and treat disease in the ornamental fish industry. However, the indiscriminate and comprehensive overuse of unregulated antimicrobials without appropriate diagnostic examination could contribute to the development of antimicrobial-resistant strains of bacterial pathogens. Moreover, human infections caused by pathogens transmitted from fish or the aquatic environment are quite common. The frequent detection of antimicrobial resistance in ornamental fish and their environments are inevitable so as to decrease the transfer of antimicrobial-resistant bacteria from aquatic sources to other environments. This study evaluated the prevalence of common bacteria species and the antimicrobial susceptibility profile in ornamental fish that were sold in an ornamental fish shop in Chiang Mai, Thailand. Aeromonas spp. were the most dominant of the isolated species from the ornamental fish samples and accounted for 68.09% of the total. Other species detected included Vibrio spp., Pseudomonas spp., and Citrobacter spp. A high percentage of resistance to amoxicillin (93.75%), oxytetracycline (79.69%), and erythromycin (75.00%) was observed among the Aeromonas spp. The antimicrobial resistance information for ornamental fish is very limited, and the results from this study indicate that the Aeromonas spp. are highly resistant to several important antibiotics. The results suggest that additional steps should be taken to educate store owners to reduce the indiscriminate use of these antibiotics to decrease the antimicrobial resistance in ornamental fish to potentially improve public health.

Abundance and Antimicrobial Resistance of Three Bacterial Species along a Complete Wastewater Pathway

After consumption, antibiotic residues and exposed bacteria end up via the feces in wastewater, and therefore wastewater is believed to play an important role in the spread of antimicrobial resistance (AMR). We investigated the abundance and AMR profiles of three different species over a complete wastewater pathway during a one-year sampling campaign, as well as including antimicrobial consumption and antimicrobial concentrations analysis. A total of 2886 isolates (997 Escherichia coli, 863 Klebsiella spp., and 1026 Aeromonas spp.) were cultured from the 211 samples collected. The bacterial AMR profiles mirrored the antimicrobial consumption in the respective locations, which were highest in the hospital. However, the contribution of hospital wastewater to AMR found in the wastewater treatment plant (WWTP) was below 10% for all antimicrobials tested. We found high concentrations (7-8 logs CFU/L) of the three bacterial species in all wastewaters, and they survived the wastewater treatment (effluent concentrations were around 5 log CFU/L), showing an increase of E. coli in the receiving river after the WWTP discharge. Although the WWTP had no effect on the proportion of AMR, bacterial species and antimicrobial residues were still measured in the effluent, showing the role of wastewater contamination in the environmental surface water.

Aeromonas induced polyostotic osteomyelitis in a juvenile loggerhead sea turtle Caretta caretta

Bacterial bone infections have been occasionally reported in wild sea turtles. This study reports on a sub-adult Caretta caretta affected by Aeromonas hydrophila osteomyelitis, with extensive involvement of cranial and caudal flippers. The turtle was severely debilitated, had limited flipper mobility and showed signs of pain in reaction to manipulation. Radiographs and computed tomography revealed multiple lytic bone lesions. Since an infectious polyostotic osteomyelitis was suspected, the turtle was subjected to echo-assisted fine needle aspiration to characterize the etiology of the disease. Bacterial cultures and antibiotic susceptibility testing led to the isolation of Aeromonas hydrophila responsive to amikacin and doxycycline. Therefore, the turtle was treated with these antibiotics and monitored through repeat bacterial cultures and diagnostic imaging. The turtle was released 17 mo after admission, upon resolution of clinical signs. The documentation of this case provides a treatment approach that may improve the outcome of Aeromonas-associated osteomyelitis, especially in endangered wildlife species.

Waterborne Infections in Reunion Island, 2010-2017

Gram-negative bacilli Vibrio spp., Aeromonas spp., and Shewanella spp. are a major cause of severe waterborne infection. The aim of this study was to assess the clinical and microbiological characteristics and prognosis of patients hospitalized in Reunion Island for a waterborne infection. This retrospective study was conducted in the two university hospitals of Reunion Island between January 2010 and March 2017. Patients diagnosed with a Vibrio, Aeromonas, or Shewanella infection were evaluated. Over the study period, 112 aquatic strains were isolated at Reunion Island: Aeromonas spp. were found in 91 patients (81.3%), Shewanella spp. in 13 patients (11.6%), and Vibrio spp. in eight patients (7.2%). The in-hospital mortality rate was 11.6%. The main sites of infection were skin and soft tissue (44.6%) and the abdomen (19.6%). Infections were polymicrobial in 70 cases (62.5%). The most commonly prescribed empiric antibiotic regimen was amoxicillin-clavulanate (34.8%). Eighty-four percent of the aquatic strains were resistant to amoxicillin-clavulanate and more than > 95% were susceptible to third or fourth generation cephalosporins and fluoroquinolones. After multivariate analysis, the only independent risk factor of in-hospital mortality was the presence of sepsis (P < 0.0001). In Reunion Island, the most commonly isolated aquatic microorganisms were Aeromonas spp. Sepsis caused by aquatic microorganisms was frequent (> 50%) and associated with higher in-hospital mortality. This study suggests that empiric antibiotic regimens in patients with sepsis or septic shock caused by suspected aquatic microorganisms (tropical climate, skin lesion exposed to seawater…) should include broad-spectrum antibiotics (third or fourth generation cephalosporins).

Protective Effects of Bacteriophages against Aeromonas hydrophila Species Causing Motile Aeromonas Septicemia (MAS) in Striped Catfish

To determine the effectivity of bacteriophages in controlling the mass mortality of striped catfish (Pangasianodon hypophthalmus) due to infections caused by Aeromonas spp. in Vietnamese fish farms, bacteriophages against pathogenic Aeromonas hydrophila were isolated. A. hydrophila-phage 2 and A. hydrophila-phage 5 were successfully isolated from water samples from the Saigon River of Ho Chi Minh City, Vietnam. These phages, belonging to the Myoviridae family, were found to have broad activity spectra, even against the tested multiple-antibiotic-resistant Aeromonas isolates. The latent periods and burst size of phage 2 were 10 min and 213 PFU per infected host cell, respectively. The bacteriophages proved to be effective in inhibiting the growth of the Aeromonas spp. under laboratory conditions. Phage treatments applied to the pathogenic strains during infestation of catfish resulted in a significant improvement in the survival rates of the tested fishes, with up to 100% survival with MOI 100, compared to 18.3% survival observed in control experiments. These findings illustrate the potential for using phages as an effective bio-treatment method to control Motile Aeromonas Septicemia (MAS) in fish farms. This study provides further evidence towards the use of bacteriophages to effectively control disease in aquaculture operations.

Leech management before application on patient: a nationwide survey of practices in French university hospitals

Background

Leech therapy in plastic/reconstructive microsurgery significantly improves a successful outcome of flap salvage but the drawback is a risk of severe infection that results in a drop of the salvage rates from 70-80% to below 30%. We report the results of a national survey conducted in all the French university hospitals to assess the current extent of use of leech for medical practices in the hospital and to investigate maintenance, delivery practices and prevention of the risk of infection.

Methods

Data concerning conditions of storage, leech external decontamination, microbiological controls, mode of delivery and antibiotic prophylaxis were collected from all the French university hospitals in practicing leech therapy, on the basis of a standardized questionnaire.

Results

Twenty-eight of the 32 centers contacted filled the questionnaire, among which 23 practiced leech therapy, mostly with a centralized storage in the pharmacy; 39.1% of the centers declared to perform leech external decontamination and only 2 centers recurrent microbiological controls of the water storage. Leech delivery was mostly nominally performed (56.5%), but traceability of the leech batch number was achieved in only 39.1% of the cases. Only 5 centers declared that a protocol of antibiotic prophylaxis was systematically administered during leech therapy: either quinolone (2), sulfamethoxazole/trimethoprim (2) or amoxicillin/clavulanic acid (1).

Conclusions

Measures to prevent infectious complications before application to patient have to be better applied and guidelines of good practices are necessary.

Aeromonas Diversity and Antimicrobial Susceptibility in Freshwater-An Attempt to Set Generic Epidemiological Cut-Off Values

The importance of the role of environment in the dissemination of antimicrobial resistant bacteria is now well recognized. Thus, bacterial indicators to monitor the phenomena are required. The Aeromonas genus is autochthonous in the aquatic environment and easy to detect in any water type, such as freshwater, or wastewater. These microorganisms are also causing infections in humans and animals (including fish). Furthermore, as Aeromonas spp. is able to acquire antimicrobial resistance mechanisms, it is candidate for indicator bacteria to follow antimicrobial resistance dissemination in aquatic environments. Unfortunately, to date, interpretation criteria for Aeromonas spp. for antimicrobial susceptibility tests are scarce in the literature. No epidemiological cut-off values for Aeromonas are currently available at EUCAST to interpret Minimum Inhibitory Concentrations (MIC). The only interpretation criteria available are clinical breakpoints from CLSI that are adapted from Enterobacteriaceae. Based on the results of MIC distributions obtained for a collection of environmental isolates of Aeromonas, this study aimed at proposing tentative epidemiological cut-off values (CO_WT) for Aeromonas spp. assessing whether the genus is an acceptable level of definition. Thus, 233 isolates collected from 16 rivers were identified at species level using Maldi-Tof (Bruker). Eleven different species were identified, the most abundant were A. bestiarum (n = 54), A. salmonicida (n = 45), A. sobria (n = 41), and A. eucrenophila (n = 37). 96-well micro-plates containing different concentrations of 15 antimicrobials, namely cefotaxime, ceftazidime, chloramphenicol, colistin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, nalidixic acid, oxolinic acid, streptomycin, temocillin, tetracycline, and trimethoprim-sulfamethoxazole, were prepared. The broth micro-dilution method was used to determine the antimicrobial susceptibility of each isolate. The estimation of CO_WT values was satisfactory obtained at genus level for all antimicrobials except cefotaxime and erythromycin. This first step is an invitation for other research teams to increase the amount of antimicrobial resistance data collected. Then, robustness of our proposed provisional generic epidemiological cut-off values could be assessed by testing antimicrobial susceptibility of various Aeromonas collections.

Prevalence and characterization of plasmid-mediated quinolone resistance genes in Aeromonas spp. isolated from South African freshwater fish

An increasing incidence of multidrug-resistant Aeromonas spp., which are both fish and emerging opportunistic human pathogens, has been observed worldwide. Quinolone-resistant Aeromonas spp. isolates are increasingly being observed in clinical and environmental settings, and this has been attributed primarily to target gene alterations, efflux, and transferable quinolone resistance. Thirty-four Aeromonas spp., obtained from freshwater aquaculture systems, were screened for the presence of GyrA and ParC substitutions, efflux activity and the prevalence of plasmid-mediated quinolone resistance genes, qnr and aac-6'-Ib-cr. Although 44% of isolates were resistant to nalidixic acid, the majority were susceptible to ciprofloxacin and ofloxacin. The predominant GyrA substitution was Ser-83→Val among Aeromonas veronii isolates whilst Aeromonas hydrophila isolates displayed a Ser-83→Ile substitution, and Ser-80→Ile substitutions were observed in ParC. Minimum inhibitory concentrations of fluoro(quinolones) were determined in the presence and absence of the efflux pump inhibitor, phenylalanine-arginine β-naphthylamide (PAβN). Addition of PAβN had no effect on the levels of fluoro(quinolone) resistance observed for these isolates. Although no aac-6'-Ib-cr variant genes were identified, qnrB and qnrS were detected for 41% and 24% of isolates, respectively, by Southern hybridization and confirmed by PCR and sequencing. Quinolone resistance in these fish-associated Aeromonas isolates was related to mutations in the quinolone resistance determining regions of GyrA and ParC and presence of qnrB and qnrS. The presence of qnr alleles in Aeromonas spp. isolates may facilitate high-level fluoroquinolone resistance and potentially serve as reservoirs for the dissemination of qnr genes to other aquatic microbes.

Relative frequency, characteristics, and antimicrobial susceptibility patterns of Vibrio spp., Aeromonas spp., Chromobacterium violaceum, and Shewanella spp. in the northern territory of Australia, 2000-2013

Vibrio, Aeromonas, Chromobacterium violaceum, and Shewanella (VACS) are water-associated Gram-negative organisms that can cause a variety of infections. The frequency, patient characteristics, and antimicrobial susceptibilities for 468 isolates from 442 patients from the Northern Territory were reviewed. Aeromonas spp. (312 of 468; 67%) were most commonly isolated followed by Vibrio spp. (71 of 468; 15%), Shewanella spp. (61 of 468; 13%), and C. violaceum (24 of 468; 5%). A strong male predominance was found (male to female ratio of 2.3:1). Skin and soft tissue isolations (373 of 468; 80%) from lower limb infections (222 of 371; 60%) were the most common clinical manifestation. The episodes were usually polymicrobial (281 of 468; 60%). Coisolates included Staphylococcus aureus (137 of 468; 29%), β-hemolytic streptococci (74 of 468; 16%), enterobacteriaceae (111 of 468; 24%), non-fermentative Gram-negative bacilli (35 of 468; 7%), and other VACS organisms (37 of 468; 8%). Antimicrobial resistance of VACS organisms to ciprofloxacin (0-4%), cefepime (0-3%), and gentamicin (0-0.8%) and Vibrio spp., Aeromonas spp., and Shewanella to cotrimoxazole (0-3%) was rarely shown. For water-associated lower limb skin and soft tissue infections in the tropics, clinicians should consider empirical antimicrobial therapy with agents active against S. aureus and VACS organisms.