Media for the isolation of Aeromonas hydrophila

Novo meio seletivo-indicador para detecção de Aeromonas e Plesiomonas: ágar UNISC

Avaliou-se um novo meio seletivo-indicador (ágar UNISC) para o isolamento de enteropatógenos clássicos e Aeromonas e Plesiomonas shigelloides. A capacidade de fermentação da xilose é indicada pela coloração amarela (fermentadores) ou azul (não fermentadores) que, aliada à prova da oxidase, constitui-se em indicador para a detecção de Aeromonas spp e Plesiomonas shigelloides. A produtividade e seletividade, avaliadas pelos índice de contagem absoluta e índice de contagem relativa indicam-no como uma alternativa aos coprocultivos clássicos porque permite, num só meio, o isolamento de Escherichia coli, Shigella spp, Salmonella spp, bem como, Aeromonas spp e Plesiomonas shigelloides, favorecendo o diagnóstico laboratorial das gastroenterites.

Use of cefoperazone MacConkey agar for selective isolation of Laribacter hongkongensis

A new selective medium, cefoperazone MacConkey agar (CMA), was developed for primary isolation of Laribacter hongkongensis from stool. Its performance in quantitative recovery and in a clinical evaluation of 4,741 human diarrheal stool specimens was superior to that of charcoal cefoperazone deoxycholate agar. In addition, with CMA, Arcobacter butzleri was unexpectedly isolated from the stools of six patients.

Selective enrichment broth for the isolation of Aeromonas sp. from chicken meat

Six selective agents (ampicillin, novobiocin, cephalothin, bile salts, brilliant green and ethanol) were tested during the development of a selective enrichment broth for the isolation of Aeromonas sp. from food. Cephalothin at 10 mg/l was found to be the best selective agent owing to its greater selectivity and efficiency in recovering stressed and lower cell concentrations of Aeromonas sp. Higher concentrations (15-25 mg/l) of cephalothin were inhibitory to some strains of A. sobria. Cephalothin (10 mg/l) was incorporated in buffered dextrin broth (BCDB-10) and alkaline peptone water (CAPW-10) and employed for the isolation of Aeromonas sp. from chicken meat naturally and artificially inoculated (with 10(9) cells/ml of A. hydrophila). The highest isolation rate (22%) with naturally contaminated chicken was achieved with CAPW-10 in comparison to 16% with BCDB-10 and 8% with APW. Similarly, from artificially inoculated samples, 100% isolation was accomplished with CAPW-10, against 80% with BCDB-10 and 50% with APW.

Comparison of seven selective media for the isolation of mesophilic Aeromonas species in fish and meat

Seven selective agar media and two enrichment broths were evaluated for their suitability for the isolation of mesophilic Aeromonas species from meat, fish, and shellfish samples. In a first trial, aeromonads were inoculated in fish and meat samples and reisolated using all selected media. For qualitative isolation, enrichment in alkaline peptone water (pH 8.7 +/- 0.1) at 28 degrees C and subsequent plating onto sheep blood agar supplemented with 30 mg/L ampicillin (ASBA 30) and bile salts-irgasan-brilliant green agar (BIBG) at 35 degrees C led to the best results. For quantitative assays, direct plating on the same agar media is recommended. In a second trial, 829 meat, fish, and shellfish samples were investigated with the same methods. The results show that BIBG is the most selective medium and that presumptive identification of aeromonads on ASBA 30 is very easy. Finally, we could confirm the opinion of other workers that optimal recovery of mesophilic Aeromonas spp. requires the use of more than one agar medium.

Etiologic agents in acute vs persistent diarrhea in children under three years of age in peri-urban Lima, Perú

In a longitudinal study of acute and persistent diarrhea in 677 children less than three years old in a peri-urban community of Lima, Perú, during 27 months of surveillance, stools were cultured at the beginning of each diarrheal episode and on each subsequent week of illness. Analyzing stool cultures only from children who had not received antibiotic treatment in the 48 h prior to the culture, no association was found between any enteropathogen and persistent diarrhea. We did not find any increase in mixed infections in persistent diarrhea episodes as compared with acute diarrhea, controlling for age, season and anthropometric status. The isolation rate for any given enteropathogen was similar during the first, second, third or later week of illness, but when the presence of a specific enteropathogen was sought in sequential stools within a single episode, no evidence of persistent infection was found. This study shows that in developing countries with a high incidence of diarrheal diseases frequent re-infections with enteropathogens prevalent in the population are one reason for prolonged illnesses. Host factors that increase susceptibility to infection or decrease recovery from illness may also play a role. Further studies of these factors, such as micronutrient deficiencies, are needed to identify a public health intervention to control persistent diarrhea, a condition associated with mortality in many developing countries.

Aeromonas and Plesiomonas as food- and waterborne pathogens

Aeromonas and Plesiomonas have become increasingly recognized as human enteropathogens. Plesiomonas shigelloides has mainly been recovered from various sea foods, whereas Aeromonas sp. have also been cultured from pigs, broilers, eggs, milk and vegetables. Aeromonas sp. also multiply rapidly at +4 degrees C which is a significant risk in food storage. Aeromonas sp. have furthermore been recovered from fresh water sources, and some isolates are resistant to chlorination which makes it a further risk factor. No large food- or waterborne outbreaks have been reported so far with Aeromonas sp. Various virulence factors involved in intestinal infections are described such as enterotoxins, cytotoxins, and adhesins.

Case report of Plesiomonas shigelloides-associated persistent dysentery and pseudomembranous colitis

An adult Bangladeshi woman had persistent bloody diarrhea. Repeated stool cultures yielded Plesiomonas shigelloides in pure growth. Tissue specimens of the colon were consistent with pseudomembranous colitis. Treatment with tetracycline, to which the isolate was susceptible, brought prompt recovery; the stool cultures became negative and the serum antibody titer against P. shigelloides lipopolysaccharide, as measured by hemagglutination inhibition with P. shigelloides lipopolysaccharide-sensitized sheep erythrocytes, declined from 1:160 to 1:40.

Clinical and epidemiologic aspects of members of Aeromonas DNA hybridization groups isolated from human feces

Between June 1982 and May 1987 Aeromonas species were isolated from 208 of 34,311 (0.61%) fecal samples submitted to a Regional Public Health Laboratory in The Netherlands. Aeromonas isolates were found most frequently in summer and rarely in winter. Of 169 Aermonas isolates that were available for further study, 19% were isolated from patients with a mixed infection, 5% from patients with underlying diseases, and 15% from patients who used medication that could predispose the intestinal tract to colonization with Aeromonas species. Aeromonas species that produced cytotoxins to Vero cells (cytotoxigenic) were found in hybridization groups 1 (11% of all isolates), 2 (1%), 3 (2%), and 8 (25%) and were identified phenotypically as A. hydrophila or A. sobria. Aeromonas species that did not produce cytotoxins to Vero cells (noncytotoxigenic) were found in hybridization groups 4 (57%) and 5A (4%) and were identified phenotypically as A. caviae. Distribution of Aeromonas species by age showed a predominance of noncytotoxigenic strains in children under the age of 5 years (46% of all noncytotoxigenic strains), while cytotoxigenic strains were mainly cultured from patients aged 50 years or older (54% of all cytotoxigenic strains). Significant correlations were found between cytotoxigenic strains and hospitalization, foreign travel, and contact with surface water. Cytotoxigenic strains were isolated significantly more often than noncytotoxigenic strains from patients with diarrhea, but in a multivariate analysis including age, previous medication, underlying disease, and foreign travel, this association was not significant.

Oral cholera vaccines containing B-subunit-killed whole cells and killed whole cells only. II. Field evaluation of cross-protection against other members of the Vibrionaceae family

Because of demonstrable cross-reactivity of cellular antigens contained in B subunit-killed whole-cell (BS-WC) and killed whole-cell-only (WC) oral cholera vaccines with antigens of various non-cholera species of the family Vibrionaceae (NCV), the protection conferred by the vaccines against diarrhoea associated with NCV was evaluated during a randomized, double-blind field trial in Bangladesh. Children aged 2-15 years and women aged greater than 15 years (62,285 in number) received three doses of BS-WC vaccine, WC-only vaccine, or a placebo consisting of Escherichia coli K12 strain (K12). During 1 year of follow-up, the incidence of treated episodes of diarrhoea associated with non-cholera vibrios known to be enteric pathogens (non-01 Vibrio cholerae, V. fluvialis, V. parahaemolyticus, V. mimicus) in the placebo group was low (1.9 cases per 10,000 recipients) and identical to that for the two vaccine groups combined. The incidence (per 10,000 recipients) of treated diarrhoeal episodes associated with Aeromonas species was considerably higher, but nearly identical in the three groups (26.1 cases for BS-WC, 26.0 cases for WC; 25.9 cases for K12). Pleisiomonas shigelloides was not isolated from any participant. It is concluded that NCV other than Aeromonas were rarely isolated from diarrhoeal patients in our study population and that killed oral vaccines which were effective against cholera exhibited no detectable cross-protection against diarrhoea associated with NCV organisms.

Growth of Aeromonas spp. on Butzler Campylobacter selective agar and evaluation of the agar for the primary isolation of Aeromonas spp. from clinical specimens

The fortuitous finding that Aeromonas spp. grew well on Butzler Campylobacter selective medium (BCSA) in a microaerobic atmosphere at 42 degrees C prompted us to evaluate the performance of BCSA for selective isolation of aeromonads in comparison with ampicillin (30 micrograms/ml) sheep blood agar (ASBA30). Overall recovery rates of aeromonads from 563 stool samples from patients with acute diarrhea were higher on ASBA30 (70.4%) than on BCSA (56.3%); however, 21 (29.5%) grew only on BCSA. The three human-associated Aeromonas spp. could be recovered on BCSA and ASBA30. We recommend the use of BCSA to laboratories reluctant to include a specific selective medium for aeromonads.

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.

Clinical significance of Aeromonas species isolated from patients with diarrhea

A total of 248 strains of Aeromonas spp. were isolated from 3,334 human fecal specimens submitted to a state public health laboratory over a 2-year period to be cultured for enteric pathogens. Cary-Blair transport medium, blood ampicillin agar, and alkaline peptone water enrichment provided optimal recovery of Aeromonas spp. A questionnaire requesting clinical and epidemiological information was sent to physicians, who submitted stool samples for testing, with each laboratory report for 107 consecutive stool isolates of Aeromonas spp. The 56 questionnaires which were completed and returned were analyzed to determine the seasonal distribution of illness and the age and sex distribution of patients; characteristic symptoms; and predisposing factors for gastrointestinal disease caused by Aeromonas spp. It was concluded that some A. hydrophila, A. sobria, and A. caviae strains are capable of causing diarrhea and that antibiotic therapy and the drinking of untreated water are significant risk factors for susceptible hosts.

Comparison of selective media for primary isolation of Aeromonas species from human and animal feces

Five selective media were evaluated for their effectiveness in the primary isolation of Aeromonas spp. from human patients with acute diarrhea and from healthy domestic animals. Sheep blood agar with 30 mg of ampicillin per liter (ASBA30) yielded a significantly higher percentage of positive specimens as compared with the four other media. The effective combination of two selective media with which 98% of all isolates were detected and with which all of the three human-associated Aeromonas spp. could be isolated was ASBA30-DNase-toluidine blue agar. ASBA30 was the most sensitive medium since it permitted more growth of Aeromonas colonies and effectively suppressed competing microflora. We recommend the use of ASBA30-DNase-toluidine blue agar for investigations in which an attempt is made to assess the significance of Aeromonas spp. in the etiology of human diarrhea.