Aerococcus-like organisms: use of antibiograms for diagnostic and taxonomic purposes

Aerococcus Viridans: Case Report, Microbiology, and Literature Review

BACKGROUND Aerococcus viridans are Gram-positive, catalase and oxidase-negative, microaerophilic, and non-motile bacteria species that are rarely associated with human infections such as arthritis, bacteremia, endocarditis, and meningitis. The bacteria are also fastidious (i.e., have complex nutritional requirements) and often confused with Streptococci species or treated as a contaminant. CASE REPORT We report a case of Aerococcus septicemia in an 85-year-old female patient, who transferred from a nursing home to an acute care hospital in Washington DC, USA. She had a 2-day history of worsening mental status, fever of 38.9°C (102°F), and tachycardia. Urinalysis revealed numerous white blood cells and bacteria. Laboratory tests revealed a white blood cell count of 14 000 cells/mL (85% neutrophils, 8% lymphocytes, 5% bands, and 2% monocytes), hemoglobin of 12.6 g/dL, and serum creatinine of 0.8 mg/dL. Blood and urine cultures obtained during admission grew penicillin-resistant A. viridans, identified via matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF) on day 3 of admission. The patient received empiric vancomycin with piperacillin-tazobactam, and we deescalated to vancomycin monotherapy to complete a 14-day treatment course. CONCLUSIONS This case report highlights the role of MALDI-TOF for identifying fastidious organisms, and we were able to form a better clinical correlation between patient symptoms and causative organisms. We believe that antimicrobial therapy (in accordance with susceptibility results) should be initiated in symptomatic patients who have A. viridans isolated in significant amounts in urine or from a sterile site.

Urinary tract infection by aerococcus sanguinicola. An emerging opportunistic pathogen

Elderly patients with underlying urological disease have a greater risk of urinary tract infections due to uncommon pathogens. The disease caused by Aerococcus has been underestimated, but mass spectrometry could be a simple method for identifying this pathogen. In this study, we report 2 cases of urinary tract infection by Aerococcus sanguinicola. A descriptive clinical-microbiological study was conducted on the presence of A. sanguinicola causing urinary tract infections. The presence of A. sanguinicola occurred in elderly patients with previous urological disease and a significant count in urine obtained through bladder catheterisation. Correct identification was achieved through mass spectrometry, and the clinical outcome of administering amoxicillin and cefuroxime was satisfactory. In this study, we also report the pathogenic capacity of A. sanguinicola. When there is a significant number of alpha-haemolytic microorganisms in the urine cultures, A. sanguinicola should be ruled out before reporting a result as urogenital microbiota.

Aerococcus urinae and Aerococcus sanguinicola: Susceptibility Testing of 120 Isolates to Six Antimicrobial Agents Using Disk Diffusion (EUCAST), Etest, and Broth Microdilution Techniques

BACKGROUND

Aerococcus urinae and Aerococcus sanguinicola are relatively newcomers and emerging organisms in clinical and microbiological practice. Both species have worldwide been associated with urinary tract infections. More rarely cases of bacteremia/septicemia and infective endocarditis have been reported. Treatment options are therefore important. Just recently, European recommendations on susceptibility testing and interpretive criteria have been released.

OBJECTIVE

In this investigation 120 A. urinae and A. sanguinicola isolates were tested for susceptibility to six antimicrobial agents: Penicillin, cefotaxime, meropenem, vancomycin, linezolid, and rifampicin.

METHODS

Three susceptibility testing methods were used; disk diffusion according to The European Committee on Antimicrobial Susceptibility Testing (EUCAST) standardized disk diffusion methodology and MIC determination with Etest and broth microdilution (BMD). All testing was performed with EUCAST media for fastidious organisms.

RESULTS

Data obtained in this study were part of the background data for establishing EUCAST breakpoints. MIC values obtained by Etest and BMD were well correlated with disk diffusion results.

CONCLUSION

All isolates were found susceptible to all six antimicrobial agents: penicillin, cefotaxime, meropenem, vancomycin, linezolid, and rifampicin.

Aerococcus Viridans: A Rare Pathogen Causing Urinary Tract Infection

Aerococci are Gram-positive cocci with colony morphology similar to viridans streptococci. Most often these isolates in clinical samples are misidentified and considered insignificant. However, with the use newer techniques like Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass-Spectrometry (MALDI-TOF MS), aerococci have been recognized as significant human pathogens capable of causing a diverse spectrum of infections. Among the different species of aerococci, Aerococcus urinae is the most common agent causing Urinary Tract Infection (UTI) followed by A. sanguinocola. Aerococcus viridans (A. viridans) have been reported rarely in urinary tract infections. The antimicrobial resistance in aerococci in terms of its intrinsic resistance and evolving resistance to penicillin and vancomycin has raised the concern for better understanding of this pathogen. We recently encountered two cases of nosocomial UTI caused by A. viridans which are being reported here.

Aerococcus christensenii as Part of Severe Polymicrobial Chorioamnionitis in a Pregnant Woman

Chorioamnionitis is a potentially life threatening infection of the fetal membranes, commonly caused by ascending bacteria from the vagina and cervix. In our case, a healthy nullipara with a term pregnancy presented clinical signs of infection after induced labour with an intracervical balloon. Thick green and foul smelling amniotic fluid was observed and culture showed massive growth of Aerococcus christensenii, a facultative anaerob species found in the human vagina, previously only rarely alleged to cause invasive infection. Additional testing with 16S rRNA gene analysis also identified the presence of Gemella asaccharolytica, Snethia sanguinegens, Parvimonas micra and Streptobacillus moniliformis. The patient was treated with cefuroxime and metronidazole and recovered quickly. The newborn showed no signs of infection. This case points at the possible role of these pathogens in female genital tract infections. The case also underlines the importance of the combination of culture and culture independent diagnostic approaches to reveal possible polymicrobial natures of selected infections, in this case chorioamnionitis.

Aerococci and aerococcal infections

Aerococcus is a genus that comprises seven species, of which Aerococcus urinae, and Aerococcus sanguinicola are emerging human pathogens. Aerococci are gram positive cocci that are easily misidentified as streptococci or staphylococci, and thus the incidence of aerococcal infections has been underestimated. With the introduction of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) clinical microbiologists now have access to a rapid and accurate method to identify aerococci. A. urinae and A. sanguinicola are isolated in a small proportion of urinary specimens in many laboratories and many patients with bacteriuria with aerococci have symptoms of urinary tract infection (UTI). A. urinae, and also A. sanguinicola, cause invasive infections including infective endocarditis (IE) with many reported fatalities. Especially older men with urinary tract abnormalities are at risk for bacteraemia with A. urinae but the prognosis of bacteraemia without IE is favourable. Penicillin is appropriate for treatment of invasive infections and in IE, addition of an aminoglycoside should be considered. Treatment of UTI with aerococci is complicated by uncertainty about the effect of trimethoprim-sulphametoxazole and fluoroquinolones on aerococci. This review will discuss identification of Aerococcus spp., antibiotic resistance, the clinical presentation and management of aerococcal infections as well as the virulence mechanisms of these bacteria.

Aerococcus urinae and trimethoprim-sulfamethoxazole

Aerococcus urinae has been described as resistant to trimethoprim-sulfamethoxazole (SXT), but the test medium may affect this observation. Twenty-seven clinical isolates of A. urinae tested susceptible to SXT in cation-adjusted Mueller-Hinton broth (CAMHB) plus lysed horse blood and resistant in CAMHB plus lysed sheep blood.

Aerococcus urinae: polyphasic characterization of the species

A polyphasic characterization of Aerococcus urinae is presented. In this study the intraspecies relationships between 26 strains of varying geographical origin were examined by phenotypic tests, ribotyping and multilocus enzyme electrophoresis. The results demonstrated two main phenotypic patterns that could be distinguished in tests for hydrolysis of aesculin, and acid production from amygdalin and salicin. Strains were either negative (n=19) or positive (n=6) in these tests. One strain had a deviating pattern. Heterogeneity within the 19 pattern I strains was demonstrated especially by phenotypic tests (acid production from ribose, mannitol, sorbitol, sucrose and D-arabitol) and by multilocus enzyme electrophoresis. However, DNA sequence analysis of the 16S rRNA (n=7) and gyrB genes (n=3) from strains representing the two main patterns showed no variation in sequences among strains. Comparison of A. urinae and representatives of related taxa by 16S rDNA sequence analysis showed that the taxon is related to, but distinct from, other Aerococcus spp.

Phenotypic description and antimicrobial susceptibilities of Aerococcus sanguinicola isolates from human clinical samples

This report describes the clinical sources and phenotypic characterization of 16 isolates of Aerococcus sanguinicola. Sixteen conventional tests were used to describe and differentiate the 16 isolates of A. sanguinicola from 30 strains of Aerococcus viridans, 27 strains of Aerococcus urinae, and a single strain each of Aerococcus christensenii and Aerococcus urinaehominis. The phenotypic characterizations of the type strains for each species and 14 A. sanguinicola isolates were also compared in the two reference laboratories. A. sanguinicola are catalase-negative, vancomycin-susceptible, gram-positive cocci arranged in clusters and tetrads, as are all Aerococcus species except A. christensenii (which is arranged in short chains). All 16 isolates of A. sanguinicola were leucine aminopeptidase and pyrrolidonylarylamidase positive, which is unique to this species among the aerococci. All A. sanguinicola isolates grew in broth containing 6.5% NaCl, hydrolyzed hippurate, and were variable in the bile-esculin test. None of the isolates deaminated arginine or were Voges-Proskauer positive. The type strain of A. sanguinicola was isolated from a blood culture of a patient living in Denmark. Seven additional isolates were from patients living in Canada, all with urinary tract infections (six were female). Eight isolates were from patients living in five different states in the United States; five were from patients with urinary tract infections, and three were from blood cultures of one patient each with pneumonia, suspected endocarditis, and unknown clinical conditions. The antimicrobial susceptibility patterns were unremarkable; all isolates tested were susceptible to penicillin, amoxicillin, cefotaxime, cefuroxime, erythromycin, chloramphenicol, vancomycin, quinupristin-dalfopristin (Synercid), rifampin, linezolid, and tetracycline. Six of the 15 cultures were resistant to ciprofloxacin and levofloxacin, but all 15 strains were susceptible to sparfloxacin. High-level resistance was detected for meropenem (2 strains) and trimethoprim-sulfamethonazole (1 strain). Intermediate resistance was detected for trimethoprim-sulfamethoxazole (10 strains) and clindamycin (3 strains).

Endocarditis due to Aerococcus urinae: diagnostic tests, fatty acid composition and killing kinetics

Two cases of Aerococcus urinae endocarditis are reported. The organism is not included in any database of commercial identification systems at this time. Formation of tetrades and positive reactions for leucine arylamidase and beta-glucuronidase pointed strongly to A. urinae. The cellular fatty acid pattern was similar to that of Aerococcus viridans, with predominantly C16:0, C18:1 omega 9c and C18:0; the presence of C18:1 omega 7t differentiated our isolates from A. viridans and can support the diagnosis of A. urinae. Furthermore, susceptibility to penicillin but resistance to cotrimoxazole represents a pattern opposite to that of A. viridans. Minimal inhibition concentrations of gentamicin and netilmicin were < or = 64 mg/l but those of tobramycin were > or = 256 mg/l. Penicillin combined with either gentamicin or netilmicin showed distinct synergy in killing kinetics. These combinations seem to be the appropriate regimen to treat A. urinae endocarditis.

Urinary tract infections with Aerococcus urinae in the south of The Netherlands

Aerococcus urinae is an uncommon urinary tract pathogen that causes infections predominantly in elderly persons with local or general predisposing conditions. During a one-year study, the clinical features of Aerococcus urinae urinary tract infections (> or = 10(5) cfu/ml) were investigated in two large medical microbiology laboratories in the Netherlands. The incidence of Aerococcus urinae urinary tract infections ranged between 0.31 and 0.44% for the two laboratories. The median age (range 35-95 years) of patients with this infection was 82.5 years for women and 77.5 for men. Men had significantly (p < 0.01) more local predisposing conditions than did women. Underlying systemic diseases such as diabetes mellitus, malignancy, and dementia were found in 67.5% of patients. Most patients (97.5%) had the classic signs of a urinary tract infection, but none of them developed serious symptoms. All isolates tested were susceptible to penicillin, amoxicillin, and nitrofurantoin, 78.3% were susceptible to norfloxacin, and all were resistant to sulfonamides. The majority of patients were treated with amoxicillin, amoxicillin with clavulanic acid, or norfloxacin.