A national collaborative study of resistance to antimicrobial agents in Haenwphilus influenzae in Australian hospitals

Abstract

An Australia-wide survey of the prevalence of resistance to antimicrobial agents among Haemophilus influenzae was conducted on clinically significant isolates collected between July 1988 and September 1990. Laboratories from the capital cities of each Australian state and territory participated. Nine hundred and seventy clinical isolates were examined for beta-lactamase production and the MICs of ampicillin, coamoxiclav, chloramphenicol, cefaclor, ceftriaxone, cefotaxime, tetracycline, rifampicin, trimethoprim, sulphamethoxazole and co-trimoxazole were determined using the NCCLS agar dilution method with Haemophilus Test Medium. A smaller number of isolates were tested against penicillin V, penicillin G, ciprofloxacin, piperacillin and erythromycin in addition. The proportion of beta-lactamase producing strains was higher among invasive strains (21.6%) than non-invasive strains (14.2%) and varies considerably between states. The highest prevalence of ampicillin resistance was found in invasive strains from Canberra (40.8%), the lowest in non-invasive strains from Adelaide (5.1%). Paradoxically, in non-invasive strains, although beta-lactamase production was less common, resistance to other antimicrobials was commoner than in invasive strains and also varied between states.

Interpretive criteria and quality control parameters for testing of susceptibilities of Haemophilus influenzae and Streptococcus pneumoniae to trimethoprim and trimethoprim-sulfamethoxazole. The Antimicrobial Susceptibility Testing OC Group

“…Most strains were relatively resistant to SMX alone, and the activity of TMP-SMX was essentially due to the TMP component. This confirms previous studies that have also shown good activity of both drugs against clinical isolates of H. influenzae (5-7, 10-12, 22), and when the two have been compared simultaneously, the activity of TMP-SMX has been slightly greater than that of TMP alone (6,10,21,22). The presence or absence of ␤-lactamase production had no effect on TMP MICs (geometric mean MICs of 0.06 and 0.05 g/ml for producers and nonproducers, respectively).…”

Trimethoprim and sulfonamide resistance

“…In a collaborative European study, TMP-SUL-resistant H. influenzae isolates were most common in Spain (41%) and Italy (12%), whereas in all other countries resistance occurred at a rate of less than 8% (82). In the United States, Canada, and Australia, TMP-SUL resistance rates have been low (less than 5%) (23,45,78). In H. influenzae type b, the rate of resistance to TMP or SUL has been lower than that in nontypeable strains (23).…”

“…In the United States, Canada, and Australia, TMP-SUL resistance rates have been low (less than 5%) (23,45,78). In H. influenzae type b, the rate of resistance to TMP or SUL has been lower than that in nontypeable strains (23).…”

Epidemiology of Antibiotic Resistance inHaemophilus influenzae

“…For these reasons, results expressed as a percentage of susceptible-resistant are irrelevant and only the MICs distribution is considered to be informative. 10,16,20,22 Resistance to kanamycin and other aminoglycosides Resistance to kanamycin, which we described in 1975, is due to the production of a phosphorylating enzyme (APH 3'I) that modifies kanamycin, soframycin, and neomycin.12,16 This resistance had clinical implications when these aminoglycosides were used in intrathecal administration for the treatment of Haemophilus meningitis. Resistance to other aminoglycosides was not established.…”