Antimicrobial susceptibility of Aeromonas species isolated from patients with diarrhea

Aetiological, seasonal and antibiotic susceptibility patterns of diarrhoeal diseases in Bhutan (2016-2022): a retrospective study of surveillance data

OBJECTIVES

This study aimed to identify the aetiological spectrum, seasonal distribution and antimicrobial resistance patterns of diarrhoeal diseases in Bhutan.

STUDY DESIGN AND SETTING

The study used a cross-sectional, retrospective analysis of secondary data gathered through a passive, hospital-based sentinel surveillance for diarrhoeal disease across 12 hospitals, representing Bhutan's demographically diverse regions.

PARTICIPANTS

A total of 3429 participants' data of all age groups who presented with diarrhoea at sentinel hospitals between 1 January 1 2016 and 31 December 2022 were analysed.

RESULTS

Diarrhoeagenic Escherichia coli (DEC), Shigella, Salmonella and Aeromonas spp. were predominant bacterial pathogens, while Rotavirus, Astrovirus and Norovirus were the leading viral pathogens. Coinfections were observed in 195 cases. Children under nine were significantly affected than the other age groups. Seasonal trends revealed that bacterial pathogen incidence peaked during the summer/monsoon season, viral pathogens were more common in winter and spring, and parasites persisted year-round. Among the antibiotics tested, gentamicin, chloramphenicol, ceftriaxone and tetracycline exhibited high efficacy, with susceptibility rates of 93.4%, 87.2%, 81.5% and 69.5%, respectively. Conversely, high resistance rates were observed for amoxicillin (80.3%), ampicillin (77.4%) and nalidixic acid (69.5%). Multidrug resistance was prevalent, with β-lactamase production contributing to resistance rates of 80.7% to penicillin and 65.4% to fluoroquinolones groups. Cephalosporin resistance was also notable, with rates of 34.4% for cephalexin, 40.0% for cefazolin and 16.9% for ceftriaxone.

CONCLUSIONS

DEC and Rotavirus were identified as the leading causes of diarrhoea, with significant resistance patterns observed in common bacterial isolates. These findings underscore the need for DEC screening in paediatric cases and emphasise the need for sustained antimicrobial resistance surveillance.

A 5-year study of the bacterial pathogens associated with acute diarrhoea on the island of Crete, Greece, and their resistance to antibiotics

During a 5-year period (1995-1999) a total of 7090 stool samples obtained from patients with acute diarrhoea, mostly community-acquired, were examined for bacterial pathogens, in the Greek island of Crete. One or more enteric pathogens were isolated from 987 patients (14%). Salmonella enterica were the most commonly isolated bacteria (6%), followed by Campylobacter spp. (4.2%), and enteropathogenic Escherichia coli (EPEC) (1.8%). Yersinia enterocolitica (0.6%), Shigella spp. (0.3%), and Aeromonas hydrophila (0.04%), were less frequently isolated. Clostridium difficile was isolated from 65 out of 451 diarrhoeal specimens examined (14.4%). Toxin B was detected in all cases. No verotoxigenic E. coli strains were identified. Resistance to ampicillin was observed in 31.5% of the Salmonella, 58.3% of the Shigella and 31.5% of the EPEC isolates. Resistance to trimethoprim-sulfamethoxazole was observed in 4.4% of the Salmonella, 30.5% of the Shigella, and 18.5% of the EPEC isolates. High percentages of resistance to quinolones (44.5% to norfloxacin, and 40.5% to ciprofloxacin), were found among Campylobacter isolates, while resistance to erythromycin was observed in 14.9% of them. With the present study we continue the surveillance of bacterial pathogens associated with diarrhoeal disease on the island of Crete.

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.

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.

beta-Lactam resistance of motile Aeromonas isolates from clinical and environmental sources

The MICs of various beta-lactams for 182 isolates of Aeromonas species, i.e., A. hydrophila (n = 101), A. sobria (n = 69), and A. caviae (n = 12), from clinical and environmental sources were determined by an agar dilution technique. All strains were resistant to ampicillin and susceptible to aztreonam. A. sobria and A. caviae demonstrated lower resistance rates than A. hydrophila. Penicillin-hydrolyzing beta-lactamases were detected in all strains.

In vitro activities of Ro 40-6890 against 164 predominantly intestinal members of the families Enterobacteriaceae and Vibrionaceae

The in vitro activities of Ro 40-6890, the active metabolite of a novel orally absorbable cephalosporin ester, Ro 41-3399, against 164 nonfastidious aerobic gram-negative rods of predominantly intestinal origin from patients with diarrhea were evaluated by the agar dilution method recommended by the National Committee for Clinical Laboratory Standards. Ro 40-6890 was inhibitory (MIC for 90% of isolates [MIC90], 0.12 micrograms/ml) against the majority of intestinal members of the families Enterobacteriaceae and Vibrionaceae (Vibrio spp., Aeromonas spp., and Plesiomonas shigelloides). The potency of Ro 40-6890 was very similar to that of cefotaxime (MIC90, 0.12 micrograms/ml) and distinctly higher than those of cefadroxil (MIC90, > or = 128 micrograms/ml) and amoxicillin-clavulanic acid (MIC90, 32 micrograms/ml-2 micrograms/ml).

Seasonal incidence of and antibiotic resistance among Aeromonas species isolated from domestic wastewater before and after treatment in stabilization ponds

The efficiency of stabilization pond treatment of domestic wastewater in removing culturable cells of motile Aeromonas and its influence on the incidence of resistance to seven antibiotics were investigated in this study. Removal efficiency was higher (P < 0.001) in the warm months (98.8%) than in the cold months (97%). Among the 264 isolates, 163 were Aeromonas caviae, 24 were A. hydrophila, and 54 were A. sobria. Twenty-three isolates could not be identified to the species level. In the influent, A. caviae dominated in both cold and warm months. In the water samples originating from the influent, A. sobria was present at higher percentages in the warm period. All the isolates were resistant to amoxicillin and most of them (73%) exhibited resistance to cephalothin. Of the three species tested, A. sobria was more susceptible to antibiotics than either A. caviae or A. hydrophila. The most striking difference among the species was seen in resistance to cephalothin. There were 91 % of A. caviae strains and 96% of A. hydrophila isolates that were resistant to cephalothin. However, only 9% of A. sobria strains exhibited resistance to this drug. The high incidence of resistance in raw sewage was connected with a high proportion of A. caviae, whereas in the water samples collected from the effluent during the warm months, a high proportion of A. sobria decreased the total amount of multiple-resistant bacteria. Results demonstrated the need for identification to the species level.

Use of quinolones in the treatment of gastrointestinal infections

Bacterial enteropathogens are responsible for between 40% and 80% of diarrheal illness depending upon the age of the persons affected and geographic areas where illness occurs. Antibacterial agents will shorten the illness associated with enteric infection caused by enterotoxigenic Escherichia coli, Shigella spp. and Campylobacter jejuni. These drugs also are effective in the therapy of certain clinical conditions (presumably because they are due to the same agents) which are characterized by moderate to severe diarrhea with one or more of the following: high fever, dysentery (passage of bloody mucoid stools), or high leukocyte counts in stools. Antimicrobial agents are also effective in the therapy of travelers' diarrhea. The quinolone drugs have several advantages in the management of bacterial diarrhea where strains causing illness from nearly all regions of the world will show general susceptibility: high concentrations are achieved in the intestinal lumen following oral administration and resistance development is unusual. A quinolone probably represents the optimal agent for therapy of bacterial diarrhea in adults in areas where trimethoprim-resistant enteric pathogens are common.

Amoxicillin/clavulanic acid. An update of its antibacterial activity, pharmacokinetic properties and therapeutic use

Clavulanic acid enhances the antibacterial spectrum of amoxicillin by rendering most beta-lactamase-producing isolates susceptible to the drug. In clinical trials amoxicillin/clavulanic acid is clinically and bacteriologically superior to amoxicillin alone and at least as effective as numerous other comparative agents, such as orally administered cephalosporins, cotrimoxazole, doxycycline and bacampicillin, in the treatment of adults and children with the most common forms of infection encountered in general practice, i.e. urinary tract infections, upper and lower respiratory tract infections, otorhinolaryngological infections, and skin and soft tissue infections. It may also provide effective treatment for uncomplicated gonorrhoea, chancroid and gynaecological infections as well as acting as a prophylactic agent against surgical infection. Thus, in general practice environments where beta-lactamase production has restricted the effectiveness of amoxicillin, the combination of clavulanic acid with amoxicillin has clearly extended the usefulness of a tried and proven first-line antibacterial agent.

Purification and characterization of inducible beta-lactamases in Aeromonas spp

beta-Lactamases from Aeromonas hydrophila and A. sobria were purified and characterized. Both species produced beta-lactamases that were inducible by either cefoxitin or imipenem. These species were resistant to ampicillin and cephalothin but not imipenem. Isoelectric focusing of sonic extracts revealed one band at pI 8.0 and a second band at pI 7.0 for A. hydrophila. Likewise, A. sobria produced two bands, one at pI 8.4 and the other at pI 7.0. Two enzymes from each species were separated by flatbed electrofocusing gel and purified to homogeneity. The molecular weight of the pI 7.0 enzyme (A1) from both species was estimated to be 42,500, whereas the pI 8.0 (A2h) and 8.4 (A2s) enzymes of A. hydrophila and A. sobria had molecular weights of 31,500 and 35,000, respectively, on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The relative Vmax values for cephalothin, penicillin, and imipenem for these enzymes indicated that A1 was primarily a cephalosporinase while A2h and A2s were penicillinases highly active against carbapenems. A1 was susceptible to inhibition by cloxacillin, while the A2 enzymes were inhibited by clavulanic acid and EDTA and required zinc for activity. Thus, there appear to be two distinct inducible beta-lactamases in A. hydrophila and A. sobria that play an important role in the beta-lactam resistance of these species.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Antimicrobial susceptibility of sixty human fecal isolates of Aeromonas species

The MICs of 21 antimicrobial agents were determined for 60 strains of Aeromonas spp. isolated from human feces. All isolates tested were susceptible to aztreonam, tetracycline, imipenem, moxalactam, pipemidic acid, gentamicin, trimethoprim-sulfamethoxazole, pefloxacin and ciprofloxacin. Resistance to erythromycin and streptomycin was observed in all 60 strains. Aeromonas caviae was less susceptible to cefamandole, cefotaxime, norfloxacin, chloramphenicol, tetracycline, sulfamethoxazole and trimethoprim than was either Aeromonas hydrophila or Aeromonas sobria. It was concluded that cotrimoxazole or one of the newer quinolones can be considered for treatment of aeromonas-associated diarrhea.

Aeromonas species in aquaria: a reservoir of gastrointestinal infections?

To assess the role of aquaria in the epidemiology of aeromonas associated gastroenteritis, the prevalence and antibiotic susceptibility of aeromonads in ornamental aquaria were determined and compared to that of isolates obtained from patients with gastroenteritis. Thirty-eight (76%) of 50 aquaria, including those located in our hospital, yielded 61 isolates: 24 (39.3%) Aeromonas sorbria, 18 (29.0%) A. hydrophila, 15 (24.6%) A. caviae, and four (6.5%) which could not be speciated. In comparison, 41 (65%) of 63 faecal isolates were A. caviae. The aquarium isolates, in contrast to enteric isolates, were generally resistant to chloramphenicol, tetracycline, and trimethoprim/sulphamethoxazole. These findings indicate aquaria are unlikely sources of aeromonas-associated gastroenteritis, but their role as possible reservoirs for non-enteric infections with aeromonads needs to be defined.

Aeromonas as a human pathogen

Although the first Aeromonas strain was described by Zimmermann as early as in 1890, it took 60 years until Caselitz established human pathogenicity of strains then called "Vibrio jamaicensis". Since then, and especially in the last 10 years, there have been increasing numbers of reports on different infections caused by members of the genus Aeromonas. These include sepsis; meningitis; cellulitis; necrotizing fasciitis; ecthyma gangrenosum; pneumonia; peritonitis; conjunctivitis; corneal ulcer; endophthalmitis; osteomyelitis; suppurative arthritis; myositis; subphrenic abscess; liver abscess; cholecystitis and/or ascending cholangitis; urinary tract infection; endocarditis; ear, nose, and throat infections; balanitis; etc. The role of Aeromonas in gastrointestinal disease is very controversial. Increasing epidemiological data suggest that these organisms play a major role in enteric infections, but so far enteropathogenicity has not been demonstrable in experiments where volunteers were given high numbers of Aeromonas possessing different virulence factors. Virulence factors include hemolysin(s), enterotoxin(s), hemagglutinins, invasivity, and others; but these are not found more frequently in strains isolated from patients with diarrhea than from healthy controls. Whether there is a correlation between species and disease remains to be elucidated and requires more information about the taxonomy of this genus.

Phenotypic and genotypic characterization of tetracycline- and oxytetracycline-resistant Aeromonas hydrophila from cultured channel catfish (Ictalurus punctatus) and their environments

Oxytetracycline-resistant (OTcr) and tetracycline-resistant (Tcr) Aeromonas hydrophila were isolated commonly from catfish intestinal contents and the water and sediment of catfish culture ponds, but less frequently in market catfish. Isolates demonstrated two resistance phenotypes, Tcr OTcr and Tcs OTcr, when plated directly on to MacConkey agar containing 30 micrograms of tetracycline or oxytetracycline per ml. Tcs OTcr isolates expressed Tcr after induction by 1 h of growth in tryptic soy broth containing 1 microgram of tetracycline per ml. Over 90% of the resistant aeromonads hybridized with DNA probes for class A or class E Tcr determinants; class E was twice as prevalent as class A. The distribution of class A and E Tcr determinants varied with the Tcr phenotypes. Prior to induction, 86% of isolates with class A determinants were Tcr as well as OTcr, while only 16% with class E determinant were Tcr. Three of 5 Tcr aeromonads without class A or class E determinants and 1 of 14 with class E determinants transferred Tcr to Escherichia coli.

Ceftriaxone. A reappraisal of its antibacterial activity and pharmacokinetic properties, and an update on its therapeutic use with particular reference to once-daily administration

Since ceftriaxone was first reviewed in the Journal, further studies have confirmed its broad antibacterial spectrum in vitro and extended its clinical documentation in comparative studies with other widely used drugs in infections of the urinary and lower respiratory tract, meningitis in infants and children, uncomplicated gonorrhoea, perioperative prophylaxis in patients undergoing surgery, and in several other types of infection. As in earlier studies, which primarily used a twice-daily dosage regimen, few significant differences were found between therapeutic groups in comparative studies and results have demonstrated the efficacy of once-daily ceftriaxone in all but the most serious infections, such as sole antibiotic therapy in pseudomonal infections. Wider clinical experience has established that ceftriaxone is generally well tolerated. Thus, ceftriaxone now has a well-defined place as an appropriate alternative for the parenteral treatment of a variety of infections due to susceptible organisms, as well as for perioperative prophylaxis of surgery, and may offer advantages of greater convenience over other parenteral antibiotics which are administered more frequently.