Activity of newer antimicrobial agents against Aeromonas hydrophila

Characterization of the digestive tract microbiota of Hirudo orientalis (medicinal leech) and antibiotic resistance profile

BACKGROUND

There are at least three distinct European leech species used medicinally: Hirudo medicinalis, H. orientalis, and H. verbana. Infection caused by leech microbiota is the most widely reported complication. Few studies have reported the culturable and unculturable bacteria and examined the antibiotic resistances in H. orientalis.

METHODS

Following stratified random sampling from a major worldwide leech supplier, Hirudo orientalis leeches were identified by visual comparison and amplification and sequencing the cox1 locus. Combined culture and culture-independent approaches were used to characterize the microbiota of the midgut, and bacterial gyrB sequences from distinct colonies were used to identify the Aeromonas isolates. Nonculturable studies involved clone libraries of 16S rRNA genes, and Etests were used to investigate antibiotic sensitivities.

RESULTS

Analysis of 16S rRNA gene clone libraries revealed the presence of several species in the intraluminal fluid of the crop, including a new finding of Morganella morganii, with Rikenella-like (35 percent) and Aeromonas veronii (38 percent) dominant members. The intestinum contained bacteria not previously isolated from the leech: Magnetospirillium species and Roseospira marina. Etests showed all A. veronii isolates were sensitive to ciprofloxacin, with either a complete or intermediate resistance to Augmentin.

CONCLUSIONS

The authors show diverse microbiota in the leech digestive tract. The pathogenic potential of the additional gut symbionts isolated in this study is yet to be elucidated; however, M. morganii, which is a known human pathogen, is a new finding. In addition to adding to the knowledge base regarding antibiotic sensitivities, this article serves as an update to the reconstructive surgeon regarding leech therapy.

Leech therapy for epidermoid cysts and review of the literature

Hirudo medicinalis sucks blood directly through the external mammalian skin. We recently observed a healthy 64-year-old Iranian man, who presented with numerous asymptomatic multilobular oval-to-round well-defined 0.5 to 1.5 cm cystic lesions with central umbilication (central black eschar) over the upper portion of his chest. We made the diagnosis of epidermoid cyst, giant comedone and leech bite on the basis of the constellation of clinical features. The patient was treated with oral ciprofloxacin at a dose of 2 g daily, and 2% topical erythromycin solution. Despite improvement, the evidence of cystic lesions persisted. There was no history of similar lesions in any other family member. There was no history of trauma. The patient was not using any topical or systemic medication. Two weeks before his visit, he had a history of leech therapy under the supervision of a general practitioner. His medical history was significant for leech therapy of the lesions, five days previously. He was followed up for another two weeks and after disappearance of the inflammation, with the patient under local anesthesia, the well-circumscribed mass was completely evacuated with a sharp curette and comedone extractor. The patient was subsequently lost to follow-up.

CONCLUSION

Considering the efficacy of leeches, it would be favorable to breed a germ-free leech. In Iran, the use of the leeches in surgery, in recent years, has been infrequent. It appears that the positive effects of this ancient remedy may now be explained through scientific methods, promising potentially even more uses of this admirable creature in medicine.

Musculoskeletal and soft tissue Aeromonas infection: an environmental disease

During a 4-year period from November 1985 to November 1989, Aeromonas was isolated from wounds and soft tissues with clinical evidence of infection in 28 patients at our institution. Of the 28 patients, 23 (82%) had sustained an acute open or penetrating injury, more than half of which (13 of the 23) were water-related trauma. One patient had Aeromonas osteomyelitis. Five patients had no history of trauma, and three of these five had an underlying chronic disease. Treatment included débridement and antimicrobial agents. Susceptibility testing on 25 isolates from 23 patients showed uniform resistance to ampicillin and considerable resistance to cefazolin sodium (68%), but all isolates were sensitive to gentamicin sulfate, cefuroxime sodium, and the third-generation cephalosporins.

Susceptibilities of motile Aeromonas sp. to antimicrobial agents

Resistance to antimicrobial agents of 106 isolates of motile Aeromonas sp. was characterized. The results indicated that in vitro susceptibilities among the three species of the motile Aeromonas sp. were similar, and only the distribution of susceptibility to cephalothin was different. The percentage of resistance of A. sobria strains was lower than the percentage of the resistant strains of A. hydrophila and A. caviae. All of the isolates were susceptible to kanamycin, nalidixic acid, tobramycin, amikacin, netilmicin, cefuroxime, ceftriaxone, cefoperazone and cefotaxime. Three of the tested strains (two A. hydrophila and one A. caviae) transferred resistance plasmids to the Aeromonas hydrophila recipient.

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.

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.