JOAN B. MAYO AND LAURENCE R. McCARTHY1*. Infectious Disease Service, and ..... ther. 7:265-270. 5. Cavanagh, P., C.A. Morris, and N. J. Mitchell. 1975.
ANTIMICRoBIAL AGENTS AND CHIMOTHERAPY, May 1977, P. 844-847 Copyright 0 1977 American Society for Microbiology
Vol. 11, No. 5 Printed in U.S.A.
Antimicrobial Susceptibility of Haemophilus parainfluenzae JOAN B. MAYO AND LAURENCE R. McCARTHY1*
Infectious Disease Service, and the Diagnostic Microbiology Laboratory, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, and Cornell University Medical College, New York, New York 10021 Received for publication 22 November 1976
Fifty random clinical isolates of Haemophilus parainfluenzae were tested for their susceptibility to 10 antibiotics by a microtiter broth dilution method. Three of the strains tested were resistant to ampicillin, whereas eight were resistant to tetracycline. All strains tested were susceptible to chloramphenicol, kanamycin, gentamicin, cephalothin, and colistin. The ranges of minimal inhibitory concentrations for the three remaining antibiotics were: 0.5 to : 128 ,ug of penicillin G per ml, 0.03 to 4 ,ug of carbenicillin per ml, and 1 to 16 ,ug of erythromycin per ml. Elevated minimal inhibitory concentrations for penicillin and carbenicillin were noted for the three ampicillin-resistant strains. Tests for beta-lactamase production demonstrated the presence of this enzyme in each of the three ampicillin-resistant strains.
The importance of Haemophilus influenzae, especially type b, in human disease is well established (1, 21). As a consequence, a large body of research has focused on this species of the genus Haemophilus. It has been generally thought that the other three common species (H. parainfluenzae, H. parahaemolyticus, and H. haemolyticus) are a part of the upper respiratory tract normal flora and rarely cause disease. With increasing frequency, however, H. parainfluenzae has been cited as the causative agent of meningitis, epiglottitis, brain abscess, bacteremia, and endocarditis (8, 9, 12). Despite these reports that establish H. parainfluenzae as a pathogen, little is known about its susceptibility to antimicrobial agents. Studies on the antimicrobial susceptibility of H. influenzae have been well documented (19, 22). Recently, strains of H. influenzae have been isolated that demonstrate resistance to ampicillin (6, 14). As a consequence, ampicillin is no longer recommended as the drug of choice in those areas of the United States where resistant strains have been found (2). In view of these findings and the increasing role of H. parainfluenzae in human disease, this study was undertaken to determine the susceptibility of H. parainfluenzae to 10 antibiotics and to determine if ampicillin resistance is also present in this species. (This work constitutes part of a thesis in the Department of Microbiology, College of Dentistry, in partial fulfillment of the require' Present address: Department of Hospital Laboratories, North Carolina Memorial Hospital, Chapel Hill, NC 27514.
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ments for the Degree of Master of Science at New York University.) MATERIALS AND METHODS Organisms. The 50 strains of H. parainfluenzae used in this study represented random clinical isolates recovered from respiratory tract specimens taken from 50 different patients seen at the Memorial Sloan-Kettering Cancer Center between May and November 1974. Identity of the strains was confirmed by their demonstration of a V-factor requirement on Columbia agar (BBL) and their inability to produce hemolysis on 5% defibrinated rabbit blood agar. All isolates were preserved for study by freezing of bacterial suspensions in sterile defibrinated rabbit blood at -70°C. Preparation of inocula. A standardized inoculum was prepared by first streaking strains ofH. parainfluenzae onto chocolate agar (BBL). After 24 h of incubation at 35°C in 10% C02, colonies of the test bacteria were suspended in 1.0 ml of Mueller-Hinton broth (BBL) enriched with 5% supplement B (Difco). The suspension was adjusted to contain 0I colonyforming units per ml by comparison with a 0.5 MacFarland standard and subsequently diluted in the supplemented Mueller-Hinton broth to yield a final inoculum concentration of 104 colony-forming units. Susceptibility tests. Each isolate was tested for its susceptibility to chloramphenicol, tetracycline, gentamicin, kanamycin, erythromycin, colistin, penicillin, ampicillin, carben.cillin, and cephalothin. Techniques used were identical to those described by Thornsberry and Kirven (19) for antibiotic susceptibility testing of H. influenzae except that Mueller-Hinton broth was enriched with 5% supplement B rather than 5% Fildes reagent. Stock solutions of the 10 antibiotics-were prepared, and 14 serial twofold dilutions were made in sterile flat-
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bottom 120-well microtiter trays (Ames Co.) using the supplemented Mueller-Hinton broth. The last well in each row of each microtiter tray contained broth without added antibiotic and served as the growth control. All antibiotics except carbenicillin were tested over a concentration range of 0.015 to 128 ug/ml. Carbenicillin concentrations used ranged from 0.03 to 256 ,ug/ml. The inoculated trays were sealed with sterile plastic strips (Ames Co.) and incubated at 35°C without CO2 for 24 h. The minimal inhibitory concentration (MIC) was determined as the lowest concentration of an antibiotic with which there was no macroscopic evidence of growth. To assure sterility, all preparation of antibiotic dilutions and inoculation of the microtiter trays were performed under a laminar flow hood. Two selected strains of H. parainfluenzae were tested simultaneously with each new series of antibiotic dilutions to check the reproducibility of the method. Beta-lactamase tests. Tests for beta-lactamase production by ampicillin-resistant strains of H. parainfluenzae were performed using both a rapid capillary tube method (20) and an iodometric test (4). Positive controls for beta-lactamase activity for both test methods used a penicillinase-producing strain of Staphylococcus aureus and two ampicillin-resistant H. influenzae strains provided by Clyde Thornsberry of the Center for Disease Control. Ampicillinsusceptible strains of H. parainfluenzae served as negative controls. RESULTS
The MICs of the 10 antibiotics for the strains of H. parainfluenzae tested in this study are shown in Table 1. All 50 strains were susceptible to chloramphenicol. MICs ranged between 0.25 and 2.0 ug/ml with a median MIC of approximately 0.5 ,ug/ml. The results for tetracycline demonstrated that 84% of the isolates were susceptible to 0.5 ug/ml or less, whereas 16% were resistant with MICs of 8 ,g/ml. Gentamicin was the more active of the two aminoglycoside antibiotics tested. All strains of
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H. parainfluenzae yielded MICs of 1 ug or less per ml. Results for kanamycin demonstrated that 94% of the strains were susceptible with MICs less than 6 ,ug/ml, and 6% were moderately susceptible with MICs of 8 or 16 ,tg per ml. MICs for erythromycin ranged between 1 and 16 ,ug/ml. Using the National Committee for Clinical Laboratory Standards breakpoint of -2.0 ,ug/ml (15) to indicate susceptibility, it appears that only 28% of the strains were susceptible, 70% were moderately susceptible, and 2% were resistant. All strains tested were susceptible to colistin with MICs of 1 ,tg/ml or less. MICs for penicillin ranged between 0.5 and 128 ug/ml. Fifty-four percent of the strains of H. parainfluenzae were susceptible with MICs less than 1.5 ,g/ml; 40% were moderately susceptible; and 6% were resistant with MICs in excess of 32 ug/ml. MICs for ampicillin ranged between 0.25 and 128 ,ug/ml. Ninety-four percent of the strains were susceptible with MICs less than 1.5 ,ug/ml, and 6% resistant with MICs of 8 to 128 ,Lg/ml. All isolates including those demonstrating resistance to ampicillin displayed sensitivity to the beta-lactam antibiotics, carbenicillin and cephalothin. MICs for carbenicillin ranged between 0.03 and 4 ug/ml, whereas MICs for cephalothin ranged between 0.5 and 2 ,ug/ml. Slightly elevated MICs for carbenicillin were observed with those strains displaying resistance to penicillin and ampicillin. Correlation between ampicillin resistance and beta-lactamase production. The three ampicillin-resistant strains produced beta-lactamase as determined by both test methods. In contrast, 11 ampicillin-sensitive strains of H. parainfluenzae, randomly selected from the strains used in the study, showed no beta-lactamase activity with either method.
TABLE 1. MICs of 10 antibiotics for 50 strains of Haemophilus parainfluenzae No. of strains inhibited (%)
Antibiotic 0.03a
0.06
Chloramphenicol Tetracycline Gentamicin Kanamycin Erythromycin Colistin Penicillin Ampicillin Carbenicillin Cephalothin a
0.12
4 (8) 1 (2) 6 (12) 23 (46)
0.25 20 (40) 33 (66) 2 (4)
16 (32) 17 (34)
44 (88) 3 (6)
0.5 27 (54) 5 (10) 19 (38) 1 (2)
4 2 25 1 3
(8) (4) (50) (2) (6)
1
2
2 (4)
1 (2)
4
8
16
32
64
128
8 (16) 28 (56) 1 (2) 1 (2) 1 (2) 25 (50) 5 (10)
31 (62) 13 (26)
10 (20)
14 (28) 2 (4) 1 (2) 29 (58) 6 (12) 1 (2) 9 (18)
1 (2) 1 (2)
1 (2) 2 (4) 2 (4)
2 (4)
36 (72)
Minimal inhibitory concentration (micrograms per milliliter).
11 (22)
_
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ANTimicRoB. AGENTS CHEMOTHZR.
MAYO AND McCARTHY
DISCUSSION The reported pathogenicity of H. parainfluenzae, as well as the prevalence of strains of H. influenzae resistant to ampicillin, prompted us to examine the antimicrobial susceptibility of 50 strains of H. parainfluenzae. All strains were isolates from respiratory specimens of patients admitted to Memorial Sloan-Kettering Cancer Center. All isolates appeared to be a part of the normal respiratory flora for each of these patients and were not related to any disease process.
All strains tested were susceptible to chloramphenicol, gentamicin, kanamycin, colistin, carbenicillin, and cephalothin and demonstrated variable susceptibilities for tetracycline and erythromycin. Three strains of H. parainfluenzae demonstrated resistance to ampicillin and penicillin. One of these strains and seven ampicillin-susceptible strains were found to be resistant to tetracycline. These findings correlate with the incidence of tetracycline resistance in H. influenzae noted recently (22). In this study, the enzyme produced by these ampicillin-resistant H. parainfluenzae was characterized as a beta-lactamase. Thus, the mechanism of resistance appears similar to the described ampicillin-resistant strains of H. influenzae (4, 14, 20). The beta-lactamase produced by strains of H. influenzae has been characterized as a constitutive plasmid-mediated enzyme which exhibits high activity against penicillin, ampicillin, and cephaloridine substrates, low activity against penicillins such as oxacillin and methicillin, and intermediate activity against carbenicillin and cephalothin (10, 14, 18). Although oxacillin and methicillin were not tested in our study, all ampicillin-resistant strains of H. parainfluenzae demonstrated resistance to penicillin and slightly elevated MICs for carbenicillin and cephalothin. This observation suggests some similarity between the beta-lactamase enzymes of H. influenzae and H. parainfluenzae. During our study of H. parainfluenzae, we also determined the susceptibility of 14 clinical isolates of H. parahaemolyticus to ampicillin and found one strain to demonstrate a high level of ampicillin resistance (>128 ,&g/ml), which was also mediated by a beta-lactamase. Our results and the recent reports of diseases caused by ampicillin-resistant strains of H. parainfluenzae, H. haemolyticus, and H. paraphrophilus (11, 13) suggest that ampicillin resistance occurs throughout the genus. In the past ampicillin has been the drug of choice for treating meningitis due to H. influ-
enzae (3, 17): chloramphenicol and tetracycline have been acceptable alternatives (16, 17). Our results support the recommendation that chloramphenicol is the drug of choice for initial treatment of serious infections due to Haemophilus species. However, recent reports of chloramphenicol-resistant strains of H. influenzae and H. parainfluenzae have appeared (5, 7). Our results indicate that treatment of infections caused by H. parainfluenzae with ampicillin ideally should be discouraged until adequate antimicrobial susceptibility studies have been performed using carefully standardized techniques. Further studies of ampicillin resistance in H. parainfluenzae as it relates to H.
influenzae are needed to determine similarities of the beta-lactamase enzyme and whether Rfactors are responsible for ampicillin resistance in H. parainfluenzae.
ACKNOWLEDGMENTS We gratefully acknowledge the advice, encouragement, and support of Donald Armstrong, of the Infectious Disease Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center; Heiner Hoffman, of the Microbiology Department, College of Dentistry, New York University; and Clyde Thornsberry, of the Antimicrobic Investigation Unit, National Center for Disease Control. LITERATURE CITED 1. Alexander, H. E. 1965. The Hemophilus group, p. 726740. In R. J. Dubos and J. G. Hirsch (ed.), Bacterial and mycotic infections of man. J. B. Lippincott Co.,
Philadelphia. 2. American Academy of Pediatrics, Committee on Infectious Disease. 1975. Ampicillin-resistant strains of Hemophilus influenzae type b. Pediatrics 55:145-146. 3. Barrett, F. F., L. H. Taber, C. R. Morris, W. B. Stephenson, D. J. Clark, and M. D. Yow. 1972. A 12-year review of the antibiotic management of Hemophilus influenzae meningitis. Comparison of ampicillin and conventional therapy including chloramphenicol. J.
Pediatr. 81:370-377. 4. Catlin, B. W. 1975. lodometric detection of Haemophilus influenzae beta-lactamase: rapid presumptive test
5.
6. 7.
8.
9. 10.
for ampicillin resistance. Antimicrob. Agents Chemother. 7:265-270. Cavanagh, P., C. A. Morris, and N. J. Mitchell. 1975. Chloramphenicol-resistant Haemophilus. Lancet i:696. Center for Disease Control. 1975. Ampicillin-resistant Haemophilwu influenzae. Morbid. Mortal. Weekly Rep. 24:205-206. Center for Disease Control. 1976. Chloramphenicol-resistant Haemophilus influenzae. Morbid. Mortal. Weekly Rep. 25:385-386. Chow, A. W., L. L. Bushkell, T. T. Yoshikawa, and L. B. Guze. 1974. Haemophilu parainfluenzae epiglottitis with meningitis and bacteremia in an adult. Am. J. Med. Sci. 267:365-368. Dahlgren, J., F. P. Tally, G. Brothers, and J. Ruskin. 1974. Haemophilus parainfluenzae endocarditis. Am. J. Clin. Pathol. 62:607-611. Elwell, L. P., J. Degraaff, D. Seibert, and S. Falkow. 1975. Plasmid-linked ampicillin resistance in Haemo-
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philus influenzae type b. Infect. Immun. 12:404-410. 11. Groves, D. J. 1976. Ampicillin-resistant Hemophilus sp. Can. Med. J. 114:407. 12. Hable, K. A., G. B. Logan, and J. A. Washington. 1971. Three Hemophilus species. Am. J. Dis. Child. 121:3537. 13. Jones, R. N., J. Slepack, and J. Bigelow. 1976. Ampicillin-resistant Haemophilus paraphrophilus laryngoepiglottitis. J. Clin. Microbiol. 4:405-407. 14. Khan, W., S. Ross, W. Rodriguez, G. Controni, and A. K. Saz. 1974. Haemophilus influenzae type b resistant to ampicillin. A report of two cases. J. Am. Med. Assoc. 229: 298-301. 15. National Committee for Clinical Laboratory Standards. 1975. Performance standards for antimicrobial disc susceptibility tests, p. 1-11. National Committee for Laboratory Standards, 16. Nelson, K. E., S. Levin, H. W. Spies, and M. H. Lepper. 1972. Treatment of Hemophilus influenzae meningitis: a comparison of chloramphenicol and tetracycline. J. Infect. Dis. 125:459-465.
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17. Schulkind, M. L., W. A. Altemeier, and E. M. Ayoub. 1971. A comparison of ampicillin and chloramphenicol therapy in Haemophilus influenzae meningitis. Pediatrics 48:411-416. 18. Sykes, R. B., M. Matthew, and C. H. O'Callaghan. 1975. R-factor mediated beta-lactalmase production by Haemophilus influenzae. J. Med. Microbiol. 8:437441. 19. Thornsberry, C., and L. A. Kirven. 1974. Antimicrobial susceptibility of Haemophilus influenzae. Antimicrob. Agents Chemother. 6:620-624. 20. Thornsberry, C., and L. A. Kirven. 1974. Ampicillin resistance in Haemophilus influenzae as determined by a rapid test for beta-lactamase production. Anti-
microb. Agents Chemother. 6:653-654. 21. Turk, D. C., and J. R. May. 1967. Haemophilus influenzae: its clinical importance in modern medicine. English University Press, Ltd., London. 22. Williams, J. D., and J. Andrews. 1974. Sensitivity of Haemophilus influenzae to antibiotics. Br. Med. J. 1:134-137.
