ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Jan. 1991, p. 192-194
Vol. 35, No. 1
0066-4804/91/010192-03$02.00/0 Copyright © 1991, American Society for Microbiology
Comparison of the Activity of Cefixime and Activities of Other Oral Antibiotics against Adult Clinical Isolates of Moraxella (Branhamella) catarrhalis Containing BRO-1 and BRO-2 and Haemophilus influenzae DONALD R. NASH,* COLE FLANAGAN, LORRAINE C. STEELE,
AND
RICHARD J. WALLACE, JR.
Department of Microbiology, The University of Texas Health Center, Tyler, Texas 75710 Received 3 July 1990/Accepted 16 October 1990
MICs of 10 oral antibiotics were determined fQr 105 Moraxello catarrhalis and 96 Haemophilus ii#luenzae isolates from adults. A two- to fourfold increase in MICs of oral cephalosporins was seen in the presence of BRO-l but not with TEM-1 or BRO-2. The MICs of cefixime for 90% of strains of H. iiJuenzae (0.135 Lg/mI) and M. catarrhalis (0.25 gLg/ml) were 8- to 64-fold lower than those of other oral cephalosporins.
Cefixime, a new oral broad-spectrum cephalosporin, has been shown to provide good activity against a number of respiratory pathogens (4, 7, 8, 14). Alternative agents to ampicillin and amoxicillin that are resistant to 13-lactamases are important, given the presence of P-lactamase in 10 to 30% of strains of Haemophilus influenzae (5, 9, 16) and the emergence of Moraxella catarrhalis as a respiratory pathogen. M. catarrhalis contains two similar 1-lactamases, BRO-1 and BRO-2 (12, 17), which are present in 75 to 85% of current clinical isolates (6, 17). We compared the activity of cefixime with'that of other oral antibiotics against adult isolates of H. influenzae and M. catarrhalis, using isolates for the latter that were known to contain either BRO-1 or BRO-2. M. catarrhalis was recovered from the sputum of adults seen between 1983 and 1987 at the University of Texas Health Center. H. influenzae isolates were from adults seen between 1980 and 1987. All but five isolates (95%) were from sputa. Organisms were identified by using standard methods and were tested for ,-lactamase by using the chromogenic cephalosporin nitrocefin (Cefinase; BBL, Cockeysville, Md.). Details of these methods are provided elsewhere (12, 16). MICs of 10 antimicrobial agents (cefixime, cefuroxime, cephalexin, cefaclor, amoxicillin-clavulanic acid, trimethoprim-sulfamethoxazole [TMP/SMX], erythromycin, tetracycline, minocycline, and chloramphenicol) were obtained by using a microdilution' method with twofold drug dilutions in Mueller-Hinton broth plus 1% supplement B (1). The final bacterial inoculum in each well was approximately 105 CFU/ml. Plates were incubated at 37°C in 5% CO2 for 24 h. Quality control utilized Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Klebsiella pneumoniae API 5205773. Susceptibility and resistance were defined according to the guidelines of the National Committee for Clinical Laboratory Standards (13). Suggested breakpoints for cefixime are 51 ,ug/ml for susceptibility of Haemophilus spp. and sl ,ug/ml for susceptibility and .4 ,ug/ml for resistance for organisms other than Haemophilus spp. The MICs of erythromycin and tetracycline for the isolates of M. catarrhalis have been published elsewhere (2). A *
summary of this work has also been published in abstract form (3). Of 105 isolates of M. catarrhalis studied, 80 (76%) produced P-lactamase. Seventy-one of the enzyme-positive strains (89%) had previously been shown to produce BRO-1, and the remaining nine isolates (11%) produced BRO-2 (12). Ninety-six isolates of H. influenzae were studied. The strains were selected such that approximately one-half of the isolates (44%) produced p-lactamase and the others were resistant to tetracycline (17 strains) and/or chloramphenicol (8 strains). Seventy-nine of 96 H. influenzae isolates had been serotyped, and 74 (94%) of these were nontypeable. Details of these results and serotyping methods have been published elsewhere (16). The range of drug concentrations representing the MIC for 50% of strains (MIC50) and the MIC90 for P-lactamasepositive and -negative isolates of the two species tested are shown in Tables 1 and 2. Cefixime was more active against both M. catarrhalis and H. influenzae, with MIC90s of 0.25 and 0.125 pg/ml, respectively, than were cefuroxime, cephalexin, and cefaclor. For H. influenzae, TMP/SMX and cefixime with a MIC50 of sO.063 FLg/ml and a MIC90 of 0. 125 ,ug/ml demonstrated the highest activities of all drugs tested. The presence of ,3-lactamase had no effect on the MIC50 or MIC90 of any of the cephalosporins against H. influenzae. The 17 H. influenzae isolates that were intermediate (MIC, 4 ,ug/ml) or resistant (MIC, -8 p,g/ml) to tetracycline were all susceptible to minocycline. Identical MIC90s of 0.25 ,ug/ml were seen for TMP/SMX, erythromycin, tetracycline, and cefixime against M. catarrhalis, although minocycline was the most active of the agents studied. The MIC50 of cefixime for the P-lactamase-negative strains of M. catarrhalis (50.063 g/iml) was much lower than the MIC50 for the 71 BRO-1 P-lactamase-contaiing strains (0.25 ,ug/ml). A similar fourfold or greater difference was noted for cefuroxime but not for cephalexin, cefaclor, or amoxicillin-clavulanic acid. The presence of ,B-lactamase had no effect on the MIC50 or MIC9o of oral cephalosporins for H. influenzae. This finding is in agreement with those of previous studies (4, 9, 11). In contrast, the MIC50 and, in some cases, the MIC90 were twoto fourfold higher for three of four cephalosporins against BRO-1-containing strains of M. catarrhalis. Although still within the susceptibility range (MIC, -1 ,ug/ml) (13), ce-
Corresponding author. 192
VOL. 35, 1991
193
NOTES
TABLE 1. Range of MICs, MIC50s, and MIC90s of oral non-beta-lactams against adult sputum isolates of H. influenzae and M. catarrhalis MIC
Drug Range
TMP/SMX (1:19)a Erythromycin Tetracycline Minocycline Chloramphenicol
H. influenzae (n = 96) 50%o
M. catarrhalis (n = 105)
4 0.25 0.125 0.5
0.125->4 s0.063->8 8
(jig/ml) for:
90%
Range
50%
90%
0.125
s0.063-0.5 s0.063-0.25 0.125-2 s0.063 s0.063-2
0.25 0.25 0.25 s0.063 1
0.25 0.25 0.25 s0.063 1
>4 8 0.5 2
a Ratio of TMP/SMX. b Value for trimethoprim.
fixime is several dilutions less active against BRO-1-containing M. catarrhalis than against (presumed) TEM-1-containing strains of H. influenzae. In contrast, the presence of the BRO-2 enzyme in M. catarrhalis had no measurable impact on the MICs of cephalosporins or amoxicillin-clavulanic acid when compared with P-lactamase-negative strains. Previous studies have shown that BRO-2 has the same substrate profile as BRO-1 but is produced in much lower quantities than BRO-1
TABLE 2. Range of MICs, MIC50s, and
(17). This is the first study to assess beta-lactam MICs whetl the type of BRO enzyme present has been known. The H. influenzae isolates intermediate or resistant to tetracycline were susceptible to minocycline. Previous studies have shown resistance in this species to result from the Tet B determinant (10). M. catarrhalis, which also has a constitutive Tet B determinant (15), exhibits this same resistance phenotype (i.e., tetracycline resistant, ininocycline susceptible) (2).
MIC90s for oral beta-lactams against 3-lactamase-negative and ,-lactamase-positive
clinical isolates of H. influenzae and M. catarrhalis
MIC (,ug/ml)
Organism and drug
Range
50%
90%
H. influenzae ,B-Lactamase negative (n = 54) Cefixime Cefuroxime
Cephalexin Cefaclor Amoxicillin-clavulanic acid (2/1)' ,-Lactamase positive (n = 42) Cefixime Cefuroxime
Cephalexin Cefaclor Amoxicillin-clavulanic acid (2/1)
s0.063 1.00 4.00 4.00 1.00
0.125 2.00 8.00 8.00 1.00
0.250-4.0b
s0.063 1.00 8.00 4.00 1.00
0.125 2.00 8.00 8.00 2.00
Vol. 35, No. 1
0066-4804/91/010192-03$02.00/0 Copyright © 1991, American Society for Microbiology
Comparison of the Activity of Cefixime and Activities of Other Oral Antibiotics against Adult Clinical Isolates of Moraxella (Branhamella) catarrhalis Containing BRO-1 and BRO-2 and Haemophilus influenzae DONALD R. NASH,* COLE FLANAGAN, LORRAINE C. STEELE,
AND
RICHARD J. WALLACE, JR.
Department of Microbiology, The University of Texas Health Center, Tyler, Texas 75710 Received 3 July 1990/Accepted 16 October 1990
MICs of 10 oral antibiotics were determined fQr 105 Moraxello catarrhalis and 96 Haemophilus ii#luenzae isolates from adults. A two- to fourfold increase in MICs of oral cephalosporins was seen in the presence of BRO-l but not with TEM-1 or BRO-2. The MICs of cefixime for 90% of strains of H. iiJuenzae (0.135 Lg/mI) and M. catarrhalis (0.25 gLg/ml) were 8- to 64-fold lower than those of other oral cephalosporins.
Cefixime, a new oral broad-spectrum cephalosporin, has been shown to provide good activity against a number of respiratory pathogens (4, 7, 8, 14). Alternative agents to ampicillin and amoxicillin that are resistant to 13-lactamases are important, given the presence of P-lactamase in 10 to 30% of strains of Haemophilus influenzae (5, 9, 16) and the emergence of Moraxella catarrhalis as a respiratory pathogen. M. catarrhalis contains two similar 1-lactamases, BRO-1 and BRO-2 (12, 17), which are present in 75 to 85% of current clinical isolates (6, 17). We compared the activity of cefixime with'that of other oral antibiotics against adult isolates of H. influenzae and M. catarrhalis, using isolates for the latter that were known to contain either BRO-1 or BRO-2. M. catarrhalis was recovered from the sputum of adults seen between 1983 and 1987 at the University of Texas Health Center. H. influenzae isolates were from adults seen between 1980 and 1987. All but five isolates (95%) were from sputa. Organisms were identified by using standard methods and were tested for ,-lactamase by using the chromogenic cephalosporin nitrocefin (Cefinase; BBL, Cockeysville, Md.). Details of these methods are provided elsewhere (12, 16). MICs of 10 antimicrobial agents (cefixime, cefuroxime, cephalexin, cefaclor, amoxicillin-clavulanic acid, trimethoprim-sulfamethoxazole [TMP/SMX], erythromycin, tetracycline, minocycline, and chloramphenicol) were obtained by using a microdilution' method with twofold drug dilutions in Mueller-Hinton broth plus 1% supplement B (1). The final bacterial inoculum in each well was approximately 105 CFU/ml. Plates were incubated at 37°C in 5% CO2 for 24 h. Quality control utilized Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Klebsiella pneumoniae API 5205773. Susceptibility and resistance were defined according to the guidelines of the National Committee for Clinical Laboratory Standards (13). Suggested breakpoints for cefixime are 51 ,ug/ml for susceptibility of Haemophilus spp. and sl ,ug/ml for susceptibility and .4 ,ug/ml for resistance for organisms other than Haemophilus spp. The MICs of erythromycin and tetracycline for the isolates of M. catarrhalis have been published elsewhere (2). A *
summary of this work has also been published in abstract form (3). Of 105 isolates of M. catarrhalis studied, 80 (76%) produced P-lactamase. Seventy-one of the enzyme-positive strains (89%) had previously been shown to produce BRO-1, and the remaining nine isolates (11%) produced BRO-2 (12). Ninety-six isolates of H. influenzae were studied. The strains were selected such that approximately one-half of the isolates (44%) produced p-lactamase and the others were resistant to tetracycline (17 strains) and/or chloramphenicol (8 strains). Seventy-nine of 96 H. influenzae isolates had been serotyped, and 74 (94%) of these were nontypeable. Details of these results and serotyping methods have been published elsewhere (16). The range of drug concentrations representing the MIC for 50% of strains (MIC50) and the MIC90 for P-lactamasepositive and -negative isolates of the two species tested are shown in Tables 1 and 2. Cefixime was more active against both M. catarrhalis and H. influenzae, with MIC90s of 0.25 and 0.125 pg/ml, respectively, than were cefuroxime, cephalexin, and cefaclor. For H. influenzae, TMP/SMX and cefixime with a MIC50 of sO.063 FLg/ml and a MIC90 of 0. 125 ,ug/ml demonstrated the highest activities of all drugs tested. The presence of ,3-lactamase had no effect on the MIC50 or MIC90 of any of the cephalosporins against H. influenzae. The 17 H. influenzae isolates that were intermediate (MIC, 4 ,ug/ml) or resistant (MIC, -8 p,g/ml) to tetracycline were all susceptible to minocycline. Identical MIC90s of 0.25 ,ug/ml were seen for TMP/SMX, erythromycin, tetracycline, and cefixime against M. catarrhalis, although minocycline was the most active of the agents studied. The MIC50 of cefixime for the P-lactamase-negative strains of M. catarrhalis (50.063 g/iml) was much lower than the MIC50 for the 71 BRO-1 P-lactamase-contaiing strains (0.25 ,ug/ml). A similar fourfold or greater difference was noted for cefuroxime but not for cephalexin, cefaclor, or amoxicillin-clavulanic acid. The presence of ,B-lactamase had no effect on the MIC50 or MIC9o of oral cephalosporins for H. influenzae. This finding is in agreement with those of previous studies (4, 9, 11). In contrast, the MIC50 and, in some cases, the MIC90 were twoto fourfold higher for three of four cephalosporins against BRO-1-containing strains of M. catarrhalis. Although still within the susceptibility range (MIC, -1 ,ug/ml) (13), ce-
Corresponding author. 192
VOL. 35, 1991
193
NOTES
TABLE 1. Range of MICs, MIC50s, and MIC90s of oral non-beta-lactams against adult sputum isolates of H. influenzae and M. catarrhalis MIC
Drug Range
TMP/SMX (1:19)a Erythromycin Tetracycline Minocycline Chloramphenicol
H. influenzae (n = 96) 50%o
M. catarrhalis (n = 105)
4 0.25 0.125 0.5
0.125->4 s0.063->8 8
(jig/ml) for:
90%
Range
50%
90%
0.125
s0.063-0.5 s0.063-0.25 0.125-2 s0.063 s0.063-2
0.25 0.25 0.25 s0.063 1
0.25 0.25 0.25 s0.063 1
>4 8 0.5 2
a Ratio of TMP/SMX. b Value for trimethoprim.
fixime is several dilutions less active against BRO-1-containing M. catarrhalis than against (presumed) TEM-1-containing strains of H. influenzae. In contrast, the presence of the BRO-2 enzyme in M. catarrhalis had no measurable impact on the MICs of cephalosporins or amoxicillin-clavulanic acid when compared with P-lactamase-negative strains. Previous studies have shown that BRO-2 has the same substrate profile as BRO-1 but is produced in much lower quantities than BRO-1
TABLE 2. Range of MICs, MIC50s, and
(17). This is the first study to assess beta-lactam MICs whetl the type of BRO enzyme present has been known. The H. influenzae isolates intermediate or resistant to tetracycline were susceptible to minocycline. Previous studies have shown resistance in this species to result from the Tet B determinant (10). M. catarrhalis, which also has a constitutive Tet B determinant (15), exhibits this same resistance phenotype (i.e., tetracycline resistant, ininocycline susceptible) (2).
MIC90s for oral beta-lactams against 3-lactamase-negative and ,-lactamase-positive
clinical isolates of H. influenzae and M. catarrhalis
MIC (,ug/ml)
Organism and drug
Range
50%
90%
H. influenzae ,B-Lactamase negative (n = 54) Cefixime Cefuroxime
Cephalexin Cefaclor Amoxicillin-clavulanic acid (2/1)' ,-Lactamase positive (n = 42) Cefixime Cefuroxime
Cephalexin Cefaclor Amoxicillin-clavulanic acid (2/1)
s0.063 1.00 4.00 4.00 1.00
0.125 2.00 8.00 8.00 1.00
0.250-4.0b
s0.063 1.00 8.00 4.00 1.00
0.125 2.00 8.00 8.00 2.00
