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Revista argentina de microbiología

versión impresa ISSN 0325-7541

Rev. argent. microbiol. vol.43 no.4 Ciudad Autónoma de Buenos Aires oct./dic. 2011

 

LETTERS TO THE EDITOR

Aerococci: hard to find and classify

 

Dear Editor,
I read with interest the case report entitled "Aerococcus viridans urinary tract infection in a pediatric patient with secondary pseudohypoaldosteronism" by Leite and coworkers in Revista Argentina de Microbiología, volume 42, number 4. This report is important since it shows that aerococci can also cause disease in pediatric patients. Previous reports indicate that aerococci mostly infect elderly people (3, 7), causing invasive disease mainly in older males (6). Since aerococci are often mistaken for streptococci, enterococci or staphylococci in clinical practice, an increased awareness of aerococci is needed and thus, the report by Leite et al. is indeed relevant.
A. viridans was described in 1953 (8) and additional aerococcal species, including Aerococcus urinae (1) and Aerococcus sanguinicola (5), have now been defned. A. viridans and A. sanguinicola have similar biochemical properties (4) but A. sanguinicola seems to be more commonly isolated from infected patients than A. viridans (2, Senneby et al. in preparation). Importantly, the GPI-Vitek2 system used by Leite et al. fails to recognize A. sanguinicola and misclassifes this species as A. viridans (2). Thus, it is possible that the organism that had caused the urinary tract infection described by Leite et al. was not A. viridans but A. sanguinicola. This potential misidentifcation may have occurred in several published cases where A. viridans was identifed only on the basis of the API or Vitek2 systems. Since biochemical typing of aerococci is diffcult, 16S rRNA gene PCR and sequencing would be
helpful to clarify which aerococcal species had caused the infection in this interesting case.

Sincerely yours
Magnus Rasmussen, M.D. Ph.D.
Division for Infection Medicine, Lund University; Sweden

 

Reply to Dr. Rasmussen

Dear Editor,
We were pleased with the compliments made by Rasmussen in his article entitled "Aerococci: hard to fnd and classify" with reference to our work, "Aerococcus viridans urinary tract infection in a pediatric patient with secondary pseudohypoaldosteronism", which was published in Revista Argentina de Microbiología, volume 42, number 4. However, we would like to clarify some aspects.
The genus Aerococcus was frst described in 1953 by Williams et al. to accommodate some gram-positive, microaerophilic, catalase-negative organisms that weren
visibly distinguishable from streptococci (6). At frst, Aerococcus viridans was the only species known, but in recent years, four additional members have been described: Aerococcus urinae [1], Aerococcus christensenii [2], Aerococcus sanguinicola [5] and Aerococcus urinaehominis [4].
Even though there are clear similarities between their morphological and biochemical characteristics, there are some reactions in each of these species that allow their own identifcation without having to resort to gene amplifcation techniques and PCR identifcation [5]. Particularly, in differentiating Aerococcus sanguinicola from other
Aerococci species, which, as suggested by Rasmussen may be diffcult, it is important to know that these organisms fail to produce acid from lactose (while the majority of A. viridans strains ferment this substrate) and produce arginine dihydrolase [5].
Unfortunately, the commercially available products distributed for the identifcation of gram-positive cocci do not have this new species in their data banks. Therefore, unlike Aerococcus viridans, the correct identifcation of these other species would be "unacceptable profle (or identifcation)," "unidentifed", or "no match" [3].
In the previously reported case of an Aerococcus viridans urinary tract infection in a child, the automatic method was used by applying both GPI-Vitek 2 (bioMérieux SA, France) and PosID-Walkaway (Dade-Behring, Germany). The concordance of results, with the clear identifcation of A. viridans after using both systems, makes a mismatch most improbable. However, genetic testing based on the uniqueness of these bacteria 16S rRNA gene sequences would be defnitely the most accurate technique [3, 5].
As the clinical case described involved a child that was already under antibiotic treatment and clinically improving when the urine culture was known, the PCR identifcation of the strain was not performed, since it would no longer be cost-effective. In fact, some authors even question whether it is clinically relevant to differentiate between the Aerococcus species or not [3].

Best regards,
Ana Luísa Leite, MD1, António Vinhas-da-Silva, MD1, Luísa Felício, MD2, António Vilarinho, MD1, Graça Ferreira, MD1

1 Department of Pediatrics, Centro Hospitalar de Vila Nova de Gaia/Espinho, EPE, 2 Department of Microbiology, Centro Hospitalar de Vila Nova de Gaia/Espinho, EPE; Rua Dr. Francisco Sá Carneiro 4400-129,Vila Nova de Gaia, Portugal
E-mail: ana.luisa20@gmail.com

REFERENCES

1. Aguirre M, Collins MD. Phylogenetic analysis of some Aerococcus like organisms from urinary tract infections: description of Aerococcus urinae sp. nov. J Gen Microbiol 1992; 138: 401-5.         [ Links ]

2. Cattoir V, Kobal A, Legrand P. Aerococcus urinae and Aerococcus sanguinicola, two frequently misidentifed uropathogens. Scand J Infect Dis 2010; 42: 775-80.         [ Links ]

3. Christensen JJ, Vibits H, Ursing J, Korner B. Aerococcus-like organism, a newly recognized potential urinary tract pathogen. J Clin Microbiol 1991; 29: 1049-53.         [ Links ]

4. Facklam RM, Lovgren P, Shewmaker L, Tyrrell G. Phenotypic description and antimicrobial susceptibilities of Aerococcus sanguinicola isolates from human clinical samples. J Clin Microbiol 2003; 41: 2587-92.         [ Links ]

5. Lawson PA, Falsen E, Truberg-Jensen K, Collins MD. Aerococcus sanguinicola sp. nov., isolated from a human clinical source. Int J Syst Evol Microbiol 2001; 51: 475-9.         [ Links ]

6. Senneby E, Petersson AC, Rasmussen M. Clinical and microbiological features of bacteremia with Aerococcus urinae. Clin Microbiol Infect 2011: DOI: 10.1111/j.1469-0691.2011.03609.x.         [ Links ]

7. Sierra-Hoffman M, Watkins K, Jinadatha C, Fader R, Carpenter JL. Clinical signifcance of Aerococcus urinae: a retrospective review. Diagn Microbiol Infect Dis 2005; 53: 289-92.         [ Links ]

8. Williams RE, Hirch A, Cowan ST. Aerococcus, a new bacterial genus. J Gen Microbiol 1953; 8: 475-80.         [ Links ]

1. Aguirre M, Collins MD. Phylogenetic analysis of some Aerococcus-like organisms from urinary tract infections: description of Aerococcus urinae sp. nov. J Gen Microbiol 1992; 138: 401-5.         [ Links ]

2. Collins MD, Rodriguez JM, Hutson RA, Ohlen M, Falsen E. Aerococcus christensenii sp. nov., from the human vagina. Int J Syst Bacteriol 1999(b); 49: 1125-8.         [ Links ]

3. Facklam R, Lovgren M, Shewmaker PL, Tyrrell G. Phenotypic description and antimicrobial susceptibilities of Aerococcus sanguinicola Isolates from human clinical samples. J Clin Microbiol 2003; 41: 2587-92.         [ Links ]

4. Lawson PA, Falsen E, Ohlen M, Collins MD. Aerococcus urinaehominis sp. nov., isolated from human urine. Int J Syst Evol Microbiol 2001; 51: 68-6.         [ Links ]

5. Lawson PA, Falsen E, Truberg-Jensen K, Collins MD. Aerococcus sanguinicola sp. nov., isolated from a human clinical source. Int J Syst Evol Microbiol 2001; 51: 475-9.         [ Links ]

6. Williams RE, Hirch A, Cowan ST. Aerococcus, a new bacterial genus. J Gen Microbiol 1953; 8: 475-80.         [ Links ]