INTRODUCTION

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Since the first description of a Facklamia species in 1997, four additional species of this genus have been described (2-5, 11). These species, Facklamia hominis, Facklamia ignava, Facklamia sourekii, and Facklamia tabaciasalis, are most often arranged in chains, whereas Facklamia languida is most often arranged in clusters with very little chaining. The identification of these bacteria is problematic since none of the rapid testing systems currently include them in their databases. In a previous study examining 120 strains of unidentified gram-positive cocci with phenotypic characteristics that eliminated them from the known genera of bacteria, such as Aerococcus, Streptococcus, Enterococcus, and Lactococcus, we identified 18 strains (21.6%) of bacteria as Facklamia species. These carbon dioxide-enhanced bacteria were included in a group of previously unidentified gram-positive cocci since they had an unusual combination of positive reactions that included only leucine aminopeptidase, L-pyrrolidonyl-B-naphthylamide, and growth in 6.5% sodium chloride for genus identification (8). The purpose of this study was to further the knowledge of the clinical syndromes caused by Facklamia species and to report on the antimicrobial susceptibility of these strains.

	MATERIALS AND METHODS

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The strains tested were taken from the culture collection of the Streptococcus laboratory at the Centers for Disease Control and Prevention. The majority of cultures were submitted to the Streptococcus laboratory for identification from various state health departments throughout the United States (Table 1). Strains were identified according to procedures previously described (10). Based on 10 tests used to identify catalase-negative, gram-positive coccal genera, four genera have similar phenotypic profiles for genus identification by conventional tests: Alloiococcus otiditis, Ignavigranum ruoffiae, Dolosigranulum pigrum, and Facklamia species (8, 10). Members of genus Alloiococcus differ from the Ignavigranum, Dolosigranulum, and Facklamia species by their aerobic nature (12). The majority of Dolosigranulum cultures are positive for esculin hydrolysis, while Ignavigranum and Facklamia species do not hydrolyze esculin. Specific identification has been published previously (10).

MICs were determined by using the methods described by the National Committee for Clinical Laboratory Standards (NCCLS) (13). The following 15 antimicrobial agents and concentration ranges were tested in customized panels (PML Microbiologicals, Wilsonville, Oreg.) by using the microdilution method in Mueller-Hinton broth supplemented with 3% lysed horse blood: penicillin, 0.03 to 16.0 µg/ml; amoxicillin, 0.03 to 8.0 µg/ml; cefotaxime, 0.06 to 16.0 µg/ml; cefuroxime, 0.12 to 32 µg/ml; erythromycin, 0.06 to 16 µg/ml; trimethoprim-sulfamethoxazole, 0.12/2.38 to 8/152 µg/ml; clindamycin, 0.06 to 2.0 µg/ml; chloramphenicol, 2.0 to 16.0 µg/ml; levofloxacin, 0.5 to 16 µg/ml; trovafloxcin, 0.25 to 8.0 µg/ml; meropenem, 0.06 to 2.0 µg/ml; vancomycin, 0.12 to 2.0 µg/ml; tetracycline, 1.0 to 8.0 µg/ml; and quinupristin-dalfopristin and rifampin only at dilutions 1.0 µg/ml and 4.0 µg/ml, respectively. The panels were incubated under 5% carbon dioxide for 22 to 24 h. The Facklamia species are facultatively anaerobic and grow best in an atmosphere of increased carbon dioxide. In most cases, the growth from a single 15- by 100-mm Trypticase soy-5% sheep blood agar plate was required to prepare a 0.5 McFarland density of the bacteria. Panels were read visually with the aid of a mirror panel viewer.

	RESULTS AND DISCUSSION

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Since it is likely that Facklamia species were previously identified as viridans streptococci, and were therefore probably included in previous studies of infections and antimicrobial susceptibility of viridans streptococci, it is of interest to note whether the clinical sources and antimicrobial susceptibility patterns of the Facklamia species differ from those of the viridans streptococci. Our studies seem to indicate that the types of infections caused by Facklamia species are similar to those caused by viridans streptococci and that the antimicrobial susceptibilities may also be similar; however, some differences are noted.

Of the 18 human isolates of the Facklamia species, 12 of the strains were isolated from blood cultures. The sources and age of the patients indicate that the Facklamia species are opportunistic pathogens, similar to the viridans streptococci. Only one nonsterile-source isolate from a vaginal swab was examined. The other five isolates were from an abscess, bone, cerebrospinal fluid, gall bladder, and an unknown source. In the original description of F. hominis, the authors described the identification of six isolates of this bacterium (2). Four of the six isolates were identified from female patients; the gender of the patients from whom the other two strains were isolated was not given (1). Of the 18 Facklamia cultures, the gender of 14 of the patients from whom these cultures were taken was provided: 13 of the 14 cultures were from female patients (Table 1). The fact that three of the six original strains were isolated from vaginal swabs may indicate that the female genitourinary tract is the natural habitat of the Facklamia species. This speculation demonstrates a difference between Facklamia and viridans streptococci: the natural habitat of the majority of viridans streptococci is the oropharynx (9).

The interpretation of resistant, intermediate, and susceptible was determined by using the NCCLS guidelines for Streptococcus species other than Streptococcus pneumoniae (13) for penicillin, amoxicillin, cefotaxime, erythromycin, clindamycin, chloramphenicol, levofloxacin, trovofloxacin, and tetracyline. The interpretive standards for S. pneumoniae were used for presumptive susceptibility values for cefuroxime, trimethoprim-sulfamethoxazole, vancomycin, and rifampin. No interpretive standards are available for meropenem and quinupristin-dalfopristin.

The cumulative MIC data for all the Facklamia species are listed in Table 2. Seventeen percent of the strains are intermediate to penicillin, 44% are resistant to cefotaxime, and 33% are presumptively resistant to cefuroxime. There are no breakpoints for meropenem at this time. Twenty-two percent of the strains are resistant to erythromycin, and 33% are resistant to clindamycin. Twenty-eight percent of the strains are presumptively resistant to trimethoprim-sulfamethoxazole, and 17% of the strains are presumptively resistant to rifampin. These numbers are not appreciably different from those of more recent studies of viridans streptococci (1, 6, 7).

There are differences in susceptibilities among the Facklamia species to various antimicrobials. Two of five F. ignava and one of four F. hominis isolates were intermediate to penicillin while all of the F. sourekii and F. languida isolates were susceptible. While none of the strains were resistant to amoxicillin, several strains were resistant to cefotaxime and were presumptively resistant to cefuroxime. One F. ignava, one F. sourekii, and all six F. languida isolates were resistant to cefotaxime while one F. hominis and five of the six F. languida isolates were presumptively resistant to cefuroxime. More strains of F. ignava (three of five) than F. languida (two of six) were resistant to erythromycin. Strains of the other two species were susceptible to erythromycin. However, this was not true for the susceptibilities of F. ignava (one of five) and F. languida (five of six strains), which were resistant to clindamycin. Presumptive resistance, either full or intermediate, to trimethoprim-sulfamethoxazole was present in most strains. None of the isolates were resistant to chloramphenicol, levofloxacin, trovafloxacin, or vancomycin. Three of the four strains of F. hominis were presumptively resistant to rifampin while all strains of the other three species were susceptible. Resistance to tetracycline was present in three of the four species (Table 2).

Although the number of strains of the Facklamia species tested are limited, there appear to be appreciable differences in antimicrobial susceptibility between species. This finding does not differ much from that among the viridans streptococci. However, Streptococcus mitis is more likely to be resistant to penicillin (6, 14), and Streptococcus oralis and S. mitis are more resistant to the macrolides (15). It is noteworthy that the majority of isolates are from female patients. This observation merits additional attention. There is a need for the manufacturers of commercial rapid identification kits for gram-positive cocci to include Facklamia species in their databases in order for additional studies to proceed.