In vitro susceptibilities of ocular Bacillus cereus isolates to clindamycin, gentamicin, and vancomycin alone or in combination

Abstract

A broth dilution assay was used to determine the in vitro susceptibilities of 10 ocular isolates of Bacillus cereus to clindamycin, gentamicin, and vancomycin both alone and in combination. The checkerboard technique was used to determine fractional inhibitory and bactericidal concentration indices for combinations of clindamycin-gentamicin and vancomycin-gentamicin.Bacillus cereus has emerged as one of the most virulent bacteria to affect the eye, causing a destructive endophthalmitis following trauma or intravenous drug use (1, 2, 5, 8-10, 14-17, 21). Nevertheless, there is limited information available with respect to its antimicrobial agent susceptibility. Published data suggest that B. cereus isolates are susceptible in vitro to gentamicin, vancomycin, clindamycin, chloramphenicol, and erythromycin (1, 4, 12, 14, 17, 20). The purpose of the present study was to investigate the in vitro antimicrobial agent susceptibility of 10 ocular isolates of B. cereus. A checkerboard technique was used to assess the effects of clindamycin, gentamicin, and vancomycin, used both alone and in combination.The microorganisms studied were 10 B. cereus isolates recovered from ocular tissue specimens submitted to the Sid W. Richardson Ocular Microbiology Laboratory. Five isolates were recovered from vitreous, two isolates were recovered from corneal tissue, and three isolates were recovered from lids and orbital tissues. The isolates were identified by using the Minitek system.The antibiotics used were clindamycin hydrochloride, gentamicin sulfate, and vancomycin hydrochloride. These antibiotics were selected because of their activities against B. cereus as suggested by previous reports and because they are commonly used against serious ocular infections (3, 14, 20). The antibiotic concentrations ranged from 0.3 to 32 ,ug/ml in serial twofold dilutions. Each antibiotic was tested as a single agent in a broth dilution assay. The standard inoculum contained approximately 7.5 x 105 organisms in 1 ml of cation-supplemented Mueller-Hinton broth (BBL Bioquest, Cockeysville, Md.). Culture wells were incubated at 35°C for 24 h. Clindamycin-gentamicin and vancomycingentamicin were tested as combined agents by using a checkerboard technique. Controls were included in each determination. The MIC was the lowest concentration of antibiotic that completely prevented visible bacterial growth. The MBC was determined by transferring 0.01-ml broth samples to Mueller-Hinton agar plates and incubating the plates at 35°C for an additional 24 h. The lowest concentration of antibiotic that prevented macroscopic microbial growth was regarded as the MBC.The fractional inhibitory and bactericidal concentration * Corresponding author.(FIC and FBC, respectively) indices for clindamycin-gentamicin and vancomycin-gentamicin were derived by using a checkerboard technique (6). Synergy and antagonism were defined by using the established criteria of indices of <0.5 and >4.0, respectively.MICs for 50% of strains (MIC50s) Clindamycin-gentamicin demonstrated in...

Identification and antibiotic resistance of Bacillus spp. isolates from natural samples

“…Categories 2 (G S C I V S ) and 3 (G S C R V S ) were most abundant amongst the strains tested for antibiotic susceptibility. An increased incidence of resistant and intermediary resistant strains of Bacillus to clindamycin was reported earlier [34,35]. A similar strategy towards sensitivity analysis of Bacillus soil isolates to antibiotics was applied by Aslim et al [36].…”

Bacillus cereus and related species

“…Media: KG, Kim and Goepfert; MYP, mannitol-egg yolk-polymyxin; PEMBA and PEMPA, polymyxin-pyruvate-egg yolk-mannitol with bromothymol blue or bromocresol purple, respectively. 32,38,56,69,70,79,91,105,109,118,130,133,137,166,172,182). In one U.S. study of posttraumatic endophthalmitis, Bacillus species were the second most common organism isolated after Staphylococcus epidernidis (29).…”

“…Bacillus infections (probably Bacillus cereus in most cases) have been documented since the beginning of this century and probably earlier (8,42,47,81,107,110,132,136,180). Clinical infections caused by B. cereus fall into six broad groups: (i) local infections, particularly of burns, traumatic or postsurgical wounds, and the eye (1,2,7,14,25,29,38,39,56,69,73,79,84,88,92,105,131,133,137,159,165,172,178,182); (ii) bacteremia and septicemia (9,24,42,121,123,129,144,146,162,165,177); (iii) central nervous system infections, including meningitis, abscesses, and shunt-associated infections (11, 21, 42, 43, 50, 72, 85,104,…”

Microbial Community Interactions on a Chip

“…To test the efficacy of the µCI device for multi-factorial experiments with small molecules, we selected three antibiotics: gentamicin, ciprofloxacin, and vancomycin, which inhibit growth of B. cereus (37)(38)(39)(40). We first determined the minimum inhibitory concentration (MIC) of the antibiotics in the µCI device.…”