In vitro susceptibilities of tropical strains of Aeromonas species from Queensland, Australia, to 22 antimicrobial agents

Bacterial Causes for Mortality Syndrome in Some Marine Fish Farms with Treatment Trials

BACKGROUND AND OBJECTIVE

Bacterial fish diseases constitute a major problem in aquaculture, it was found in the environment and under stressors cause severe economic losses to fish. This work aimed to investigate the bacterial causes and suitable treatments of mass mortality in some cultured marine fish farms in Damietta governorate.

MATERIALS AND METHODS

The study was performed on 5 farms suffered from mass mortality. Total of 100 diseased fish (10 sea bass and 10 sea bream/farm) and 20 water samples were randomly collected from these farms. Bacteriological examinations were carried out followed by in vitro sensitivity tests. Treatment trial was performed using the most effective antibacterial agent on isolated bacteria.

RESULTS

From fish and water samples Pseudomonas spp., Aeromonas spp. and Vibrio spp. were isolated with the rat of (16, 10%), (22, 10%) and (28, 10%) respectively. These results were confirmed biochemically. Some virulence genes of isolated bacteria were detected using PCR; meanwhile, enrofloxacin reduced significantly the mortality rates in examined farms.

CONCLUSION

It could be concluded that, Pseudomonas spp., Aeromonas spp. and Vibrio spp. are the main bacterial species causing mass mortality in marine fish farms. These bacteria were highly sensitive to enrofloxacin in vitro and in vivo.

Population dynamics and antimicrobial susceptibility of Aeromonas spp. along a salinity gradient in an urban estuary in Northeastern Brazil

The main objective of this study was to quantify population and identify culturable species of Aeromonas in sediment and surface water collected along a salinity gradient in an urban estuary in Northeastern Brazil. Thirty sediment samples and 30 water samples were collected from 3 sampling locations (A, B and C) between October 2007 and April 2008. The Aeromonas count was 10-7050CFU/mL (A), 25-38,500CFU/mL (B) and<10CFU/mL (C) for water samples, and ∼100-37,500CFU/g (A), 1200-43,500CFU/g (B) and<10CFU/g (C) for sediment samples. Five species (Aeromonas caviae, A. sobria, A. trota, A. salmonicida and A. allosaccharophila) were identified among 41 isolates. All strains were sensitive to chloramphenicol and ceftriaxone, whereas 33 (80, 4%) strains were resistant to at least 2 of the 9 antibiotics tested. Resistance to erythromycin was mostly plasmidial. In conclusion, due to pollution, the Cocó River is contaminated by pathogenic strains of Aeromonas spp. with a high incidence of antibacterial resistance, posing a serious risk to human health.

Antimicrobial susceptibilities of Aeromonas strains isolated from clinical and environmental sources to 26 antimicrobial agents

We determined the susceptibilities of 144 clinical and 49 environmental Aeromonas strains representing 10 different species to 26 antimicrobial agents by the agar dilution method. No single species had a predominantly nonsusceptible phenotype. A multidrug nonsusceptible pattern was observed in three (2.1%) clinical strains and two (4.0%) strains recovered from diseased fish. Common clinical strains were more resistant than the corresponding environmental isolates, suggesting that resistance mechanisms may be acquired by environmental strains from clinical strains.

Aeromonas spp. clinical microbiology and disease

Members of the genus Aeromonas inhabit various aquatic environments and are responsible for, and are implicated in, a number of intestinal and extra-intestinal infections in humans as well as other animals. This review focuses on invasive human infection and disease and summarizes available findings regarding the microbiology and detection of Aeromonas spp., with emphasis on successful identification and diagnosis, and the control of disease in the population. Antimicrobial resistance and therapy of Aeromonas spp. is also discussed.

Bacteremia caused by Aeromonas species [corrected] complex in the Caribbean Islands of Martinique and Guadeloupe

Aeromonas species are Gram-negative bacilli of the water environment whose survival appears facilitated by warm climates. There have been no reports on Aeromonas species in the [corrected] Caribbean to date. Our aim was to describe clinical and bacteriological features in patients presenting with such bacteremia in Martinique and Guadeloupe. During a 14-year period, we retrospectively identified 37 patients. The mean age was 55 years and in 89% of cases underlying disease such as digestive diseases, cutaneous wounds, and malignancy were identified. One case was related to severe strongyloidiasis and one with snake bite. Polymicrobial bacteremia was identified in 38%, essentially with Enterobacteriaceae. All Aeromonas isolates were resistant to amoxicillin but extended-spectrum beta-lactam and fluoroquinolone were active against more than 95%. During hospitalization 10 patients died (27%). Older age, occurrence of multiorgan failure, and impaired renal function were associated with in-hospital mortality.

Development of imipenem resistance in an Aeromonas veronii biovar sobria clinical isolate recovered from a patient with cholangitis

Several imipenem-susceptible and -resistant Aeromonas veronii biovar sobria isolates with different morphologies and antimicrobial susceptibilities recovered from bile samples of a patient with cholangitis were analysed. These isolates belonged to the same clone and the imipenem-resistant strains showed overexpression of the imiS gene, encoding a chromosomal carbapenemase. These results should make clinicians aware of the possible emergence of multidrug-resistant A. veronii biovar sobria, perhaps as a consequence of previous treatment of a urinary tract infection with amoxicillin plus clavulanic acid.

In vitro activities of tigecycline against clinical isolates of Aeromonas, Vibrio, and Salmonella species in Taiwan

All 198 Salmonella isolates (58.6% of isolates were resistant to tetracycline), 92 Vibrio isolates (4.4% of isolates were resistant to tetracycline), and 200 of 201 Aeromonas isolates (39.3% of isolates were resistant to tetracycline; 1 A. caviae isolate had a tigecycline MIC of 4 mug/ml) in our study were susceptible to tigecycline, by U. S. Food and Drug Administration criteria for Enterobacteriaceae.

Molecular characterization of class 1 integrons and antimicrobial resistance in Aeromonas strains from foodborne outbreak-suspect samples and environmental sources in Taiwan

One hundred thirty-three Aeromonas spp. isolates were examined for multiple antibiotic resistance phenotypes and prevalence of class 1 integron sequences. Twenty-four (18.0%) of these isolates contained class 1 integron. Seven different class 1 integrons were found among 24strains, with a total of 10 different gene cassettes encoding for resistance to trimethoprim (dfr12 and dfr2d), aminoglycosides (aadA1 and aadA2), beta-lactam antibiotics (oxa2), chloramphenicol (catB3 and catB8), quaternary ammonium amines (qacE2), and 2 ORFs (orfD and orfF) with unknown function. Rate of antibiotic resistance was different between integron-positive and integron-negative strains. Trimethoprim and trimethoprim-sulphamethoxazole resistances were commonly associated with integron, and all of integron-positive isolates were multiple resistant to more than 3 agents. Resistance to as many as 10 antimicrobial agents were observed in integron-positive strains. Several cassette arrays of class 1 integrons identified in this study were not previously reported in Aeromonas strains. This study demonstrates the wide distribution of class 1 integron in Aeromonas spp. isolated from foodborne outbreak-suspect samples and environmental sources in Taiwan.

[Extraintestinal infection due to Aeromonas spp.: review of 38 cases]

INTRODUCTION

Aeromonas spp. typically cause gastroenteritis, but can occasionally produce extraintestinal infections. The aim of this study was to determine the clinical and microbiological characteristics of extraintestinal infections caused by Aeromonas spp. in our area.

PATIENTS AND METHODS

The clinical histories of patients with extraintestinal infections by Aeromonas spp. diagnosed in Hospital Universitario de Guadalajara (Guadalajara, Spain) from January 1990 to December 2005 were reviewed. Identification and susceptibility testing of the strains were performed by the MicroScan WalkAway-40 automated method (DadeBerhing).

RESULTS

Thirty-eight cases of extraintestinal infections were diagnosed: 18 abdominal infections, 11 skin and soft tissue infections, 3 urinary tract infections, and 3 episodes of bacteremia with no primary focus. The species most frequently found was A. hydrophila (16 cases). Infection occurred most often in patients with underlying diseases (76.3%), including malignancy (34.2%) and diabetes mellitus (21%). Polymicrobial infections were detected in 50% and the etiology was nosocomial in 21%. The mortality rate was 16.2%. Gentamicin, amikacin, cefotaxime and ciprofloxacin had the highest activity against the Aeromonas species isolated.

CONCLUSIONS

Aeromonas spp. as the causative infectious agent should be kept in mind in patients with infections of the biliary system, surgical wounds in the abdomen and posttraumatic cellulitis. Extraintestinal infection is usually polymicrobial, appears most commonly in patients with underlying diseases, and generally has a good prognosis. The most active antibiotics in vitro were gentamicin, amikacin, cefotaxime and ciprofloxacin.

Virulence and antibiotic susceptibility of Aeromonas spp. isolated from drinking water

Aeromonas isolates from tap water, mineral water, and artesian well water were investigated for their ability to produce different potential virulence factors or markers such as hemolysins, cytotoxins, phospholipase, DNase, hydrophobicity and their ability to adhere to epithelial cells and to abiotic surfaces. The susceptibility to antibiotics of Aeromonas isolates was also examined. Majority of the isolates displayed hemolytic activity against sheep erythrocytes, while only 7 of the 23 Aeromonas strains displayed DNase activity and 4 of the 23 Aeromonas strains tested were regarded as positive for phospholipase production. Most of the isolates showed cytotoxic activities in culture filtrate dilutions at titer of 1/8 or lower. No general relation between the strain isolated and the ability to interact with epithelial cells could be established. Using the bacterial adherence to hydrocarbons method, most of the strains were classified as highly hydrophilic. All five Aeromonas jandaei strains isolates, 9 of the 12 Aeromonas sp strains and four of the five Aeromonas hydrophila were multidrug resistant. The most active antimicrobial was ciprofloxacin (susceptible in 100% of the isolates), and the least active antibiotic was ampicillin (resistance in 92% of the isolates). The majority of the isolates tested were not killed by chlorine at 1.2 mg/l. Whether the high tolerance to chlorine of Aeromonas isolates can be linked to greater virulence is not know.

In vitro and in vivo activities of fluoroquinolones against Aeromonas hydrophila

Aeromonas hydrophila, an uncommon human pathogen, can cause invasive infections in immunocompromised individuals. As the fluoroquinolones have been shown to be active in vitro against mesophilic aeromonads and clinical experience with the use of fluoroquinolones to treat aeromonads infections is limited, the antimicrobial activities of five selected drugs (ciprofloxacin, gatifloxacin, levofloxacin, lomefloxacin, and moxifloxacin) against A. hydrophila were studied in vitro and in mice. The MICs of the fluoroquinolones (except lomefloxacin), cefotaxime, and minocycline for 90% of 64 clinical isolates of A. hydrophila tested by the agar dilution method were <or=1 microg/ml. With a clinical cefotaxime-resistant strain, Ah 2743, in an in vitro time-kill study, at an inoculum of 7 x 10(5) CFU/ml incubated with fluoroquinolones, cefotaxime, or minocycline at concentrations equal to twice the MICs, the inhibitory effect lasted for less than 6 h and regrowth occurred thereafter. In an animal model with female BALB/c mice intraperitoneally infected with an inoculum of 1.1 x 10(7) CFU of Ah 2743, more mice in the ciprofloxacin-treated group survived (72.2%) than in the cefotaxime-, minocycline-, or cefotaxime-minocycline-treated group (P < 0.00001, log rank test). However, there were similar fatality rates, ranging from 71.4 to 87.5%, among mice treated with any of five fluoroquinolones. With a larger inoculum, 4.9 x 10(7) CFU, mice in the ciprofloxacin-treated group survived longer than those in the minocycline-, cefotaxime-, or cefotaxime-minocycline-treated group (30 h versus 18, 12, and 12 h, respectively [P < 0.002, log rank test]). However, in mice infected with cefotaxime-susceptible Ah 2556, ciprofloxacin was as effective as cefotaxime-minocycline. Thus, our results suggest that ciprofloxacin is at least as effective as cefotaxime-minocycline against murine A. hydrophila infections, which warrants clinical studies to delineate its role in human infections.

Group 1 beta-lactamases of Aeromonas caviae and their resistance to beta-lactam antibiotics

The contribution of beta-lactamase production to beta-lactam antibiotic resistance was examined in an Aeromonas caviae mutant strain, selected in vitro by cefotaxime and derived from a wild-type strain isolated in our laboratory from crude sewage. Both strains produced beta-lactamase. The mutant strain (AC7m) produced beta-lactamase constitutively, in contrast to the parental strain (AC7), which was inducible by cefoxitin. AC7m was regarded as a mutant from AC7, which over-expressed beta-lactamase. The mutant strain showed a remarkable reduction in sensitivity to most of the beta-lactam antibiotics tested, such as (i) aminopenicillins and their combinations with clavulanic acid and sulbactam, (ii) carboxypenicillins, (iii) ureidopenicillins, and (iv) cephalosporins. This strain remained susceptible to ceftazidime, imipenem, and aztreonam. Isoelectric focusing of sonic extracts revealed that both strains AC7 and AC7m shared a common major beta-lactamase band at pI 6.5. The plasmid DNA assays showed that the beta-lactamases expressed by each A. caviae strain were chromosomally encoded. Based on substrate and inhibitor profiles determined in sonic extracts for AC7 and AC7m, the enzymes displayed on isoelectric focusing at pI 6.5 were assigned to chromosomal Group 1 beta-lactamases. Imipenem would therefore be the appropriate choice for therapy of infections caused by A. caviae beta-lactamase over-expressing mutants.

The role of antibiotics in the treatment of infectious diarrhea

Infectious diarrhea is a significant cause of morbidity and mortality and a common complaint in clinical practice. Routine empirical use of antibiotics for infectious diarrhea should be avoided because of the self-limited nature of most cases, the cost of antibiotics, and the potential to worsen the already significant problem of antibiotic resistance of enteric pathogens. For patients with severe invasive or prolonged diarrhea or who are at high risk of complications, such as the elderly, diabetics, cirrhotics, and immunocompromised patients, empirical treatment with a quinolone antibiotic for 3 to 5 days can be considered. Antibiotic treatment can be highly effective for Shigella, ETEC, and V. cholerae infections, and metronidazole is indicated for C. difficile colitis. The impact of antibiotics for other specific pathogens is modest, and antibiotic therapy should be reserved for the same group of patients who would be considered for empirical treatment. The most significant problem in the antibiotic treatment of infectious diarrhea is the progressive increase in resistance among enteric pathogens; only the prudent use of antimicrobials in all areas of daily practice can limit or delay the impact of this serious problem.

Clinical features and therapeutic implications of 104 episodes of monomicrobial Aeromonas bacteraemia

OBJECTIVES

Aeromonas bacteraemia is not a common infectious disease, but can cause a grave outcome in infected cases. In this study, clinical presentations and prognostic factors of cases of monomicrobial Aeromonas bacteraemia were analysed. Also, the impact of beta-lactam and aminoglycoside in combination and of emerging cephalosporin-resistance during therapy was discussed.

METHODS

From 1989 to 1998 in a medical centre in southern Taiwan, those cases with monomicrobial Aeromonas bacteraemia were included for study.

RESULTS

A total of 104 episodes of monomicrobial Aeromonas bacteraemia, accounting for 74% of all Aeromonas bacteraemia, were encountered. The infections usually occurred in the patients with hepatic cirrhosis (54%) or malignancy (21%) and were community-acquired (74%). Cases of community-acquired bacteraemia were more likely to have cirrhosis, a high severity score at onset, and a worse prognosis than those of nosocomial bacteraemia did and nosocomial isolates were less susceptible to cefoxitin and cefotaxime. Forty-three percent of cases had a concomitant infection focus, such as primary peritonitis, invasive cellulitis or necrotizing fasciitis, biliary tract or burn wound infections. Crude fatality rate within 2 weeks after the onset was 30%. Secondary bacteraemia and a higher severity score ( > or = 4) for illness at the first presentation were independently associated with a fatal outcome. The therapeutic superiority of beta-lactam and aminoglycoside in combination cannot be demonstrated in patients with Aeromonas bacteraemia. Cefotaxime resistance emerged in 3.4% of 58 patients treated with a cephalosporin for at least 72 h. None of the community-acquired isolates, but one-quarter of the nosocomial isolates, were resistant to cefotaxime.

CONCLUSIONS

Aeromonas bacteraemia usually occurred in patients with liver cirrhosis or malignancy, and heralded a poor prognosis, especially while associated with a relevant infectious source or with a higher severity score at presentation. The superiority of aminoglycoside and beta-lactam in combination cannot be demonstrated while treating those patients, and the emergence of antimicrobial resistance to cephalosporin was a rare event during cephalosporin therapy. Thus, a broad-spectrum cephalosporin remains one of the antimicrobial alternatives for invasive community-acquired Aeromonas infections.

In vitro susceptibilities of Aeromonas genomic species to 69 antimicrobial agents

A total of 217 strains representing all 14 currently described genomic species in the genus Aeromonas were tested for susceptibility to 69 antimicrobial agents by a microdilution method. All species were susceptible to tetracyclines, quinolones, chloramphenicol, and most of the aminoglycosides and the cephalosporins, but were resistant to lincosamides, vancomycin, teicoplanin and some penicillins. In general, no significant differences were found that correlated with the taxonomic designation or the origin of the isolates tested. The microdilution method proved to be easy to perform allowing susceptibility testing of extensive strain collections for a large number of antimicrobial agents.

Antimicrobial susceptibility patterns of Aeromonas jandaei, A. schubertii, A. trota, and A. veronii biotype veronii

Fifty-six isolates of four Aeromonas species, which have been documented as causative agents of human infections or isolated from human clinical specimens, were subjected to antimicrobial susceptibility testing using a MicroScan WalkAway conventional (overnight incubation) gram-negative panel. The four species tested and the number of isolates of each were as follows: Aeromonas jandaei, 17; A. schubertii, 12; A. trota, 15; and A. veronii biotype veronii, 12. All isolates of A. trota were susceptible to all antimicrobial agents tested, except cefazolin (20% of isolates were resistant) and cefoxitin (13% of isolates were resistant). All isolates of A. schubertii and A. veronii biotype veronii, as well as 88% of A. jandaei isolates, were resistant to ampicillin. Resistance to ampicillin-sulbactam ranged from 25% of A. schubertii strains to 100% of A. veronii biotype veronii strains. Cefazolin resistance ranged from 17% of A. veronii biotype veronii isolates to 59% of A. jandaei isolates. Imipenem resistance was detected in 65% of A. jandaei strains and 67% of A. veronii biotype veronii strains. A. jandaei displayed resistance to piperacillin and ticarcillin in 53 and 71% of the isolates, respectively. A. veronii biotype veronii strains were 100% susceptible to piperacillin and 100% resistant to ticarcillin. These antibiogram data may be useful in establishing the identification of these four species when members of the genus Aeromonas are isolated from human clinical sources.

Resistance to antibiotic and heavy metals of motile aeromonads from Chilean freshwater

In this work the resistance of 172 motile Aeromonas isolates recovered from raw drinking water supplies (56), irrigation waters (60) and runoff waters receiving sewage (56), to some antibiotics and heavy metals was investigated by agar diffusion and agar dilution methods. A high proportion of isolates from all water sources showed resistance to carbenicillin, erythromycin, streptomycin, cephradine and cadmium, and susceptibility to chloramphenicol, kanamycin, gentamicin, tetracycline, nalidixic acid, trimethoprim-sulphametoxazole and chromium. No amikacin-resistant Aeromonas were recovered. No relationship was found between antimicrobial resistance and Aeromonas species, with the exception of cephradine, that exhibited a significantly higher activity against the A. sobria isolates than the other Aeromonas species (P < 0.05). Moderately polluted waters showed lower antibiotic multiresistance and metal susceptibility than unpolluted and highly polluted ones. Although significant differences (P < 0.05), between resistance frequencies to erythromycin, carbenicillin, streptomycin and cephradine were found among isolates from different sources, the antimicrobial resistance patterns of aeromonads could not be related to the level of faecal pollution. These results indicate that aeromonads resistant to antibiotics and heavy metals are easily recovered from water sources in Chile, posing a potential public health risk.

Inducible beta-lactam resistance in Aeromonas hydrophila: therapeutic challenge for antimicrobial therapy

Despite the abundant amount of knowledge about inducible chromosomally mediated beta-lactamases among Aeromonas species, extended-spectrum beta-lactam-resistant A. hydrophila strains selected in clinical practice were rarely reported. In the present study, two strains of A. hydrophila, A136 and A139, with markedly different susceptibilities to extended-spectrum cephalosporins were isolated from blood and the tip segment of an arterial catheter of a burn patient. Another strain (A136m) was selected in vitro by culturing A136 in a subinhibitory concentration of cefotaxime, the beta-lactam agent administered for the treatment of Aeromonas bacteremia in this patient. Typing studies by arbitrarily primed PCR and pulsed-field gel electrophoresis indicated a clonal relationship among strains A136, A136m, and A139. These strains were identified to be of DNA hybridization group 1. Wild-type strain A136 was resistant only to ampicillin and cephamycins, but A136m and A139 were highly resistant to the expanded- and broad-spectrum cephalosporins. The presence of increased beta-lactamase activity in A139 suggests that A139 is a derepressed mutant which overexpresses beta-lactamases. These results call attention to the use of beta-lactam agents for the treatment of invasive Aeromonas infections.

Aeromonas sobria endophthalmitis

BACKGROUND

Aeromonas sobria causes a rare Gram-negative bacterial water-borne infection. It has been found in waters of North Queensland and South-east Asia. Of all Aeromonas species, A. sobria is the most virulent and invasive and has been reported to cause soft tissue infection and corneal ulcer.

METHODS

A 14-year-old Caucasian male from North Queensland presented following a penetrating eye injury in which a water bird (cormorant species) had pecked his eye while he was fishing. A fulminant endophthalmitis developed despite treatment with intravenous, intravitreal and topical antibiotics and initial wound repair. Enucleation was performed.

RESULTS

Aeromonas sobria was isolated from the vitreous aspirate.

CONCLUSION

Aeromonas sobria infection should be suspected in water-contaminated penetrating eye injuries. The prognosis in this case was poor.

Increasing antibiotic resistance in clinical isolates of Aeromonas strains in Taiwan

A total of 234 clinical isolates of Aeromonas, primarily A. hydrophila, were collected for the present study. Most were isolates from blood. By the agar dilution method, more than 90% of the Aeromonas strains were found to be susceptible to moxalactam, ceftazidime, cefepime, aztreonam, imipenem, amikacin, and fluoroquinolones, but they were more resistant to tetracycline, trimethoprim-sulfamethoxazole, some extended-spectrum cephalosporins, and aminoglycosides than strains from the United States and Australia.