Two hundred clinical isolates of Haemophilus influenzae were tested for tolerance (MBC/MIC 2 32) to ampicillin and cefotaxime by broth dilution tests. Of 200 strains, 9 were tolerant to ampicillin, and 10 were tolerant to cefotaxime. Tolerant organisms were identified in both systemic and nonsystemic infections and among different biotypes and serotypes of If. influenzae. These tolerant isolates were compared with nontolerant isolates by broth dilution and killing curves with log-phase and stationary-phase inocula. Both tolerant and nontolerant bacteria in log phase were killed more rapidly by antibiotics than bacteria in stationary-phase growth. When tested against 11 different 3-lactams, several patterns of tolerance were observed. Six of the ten strains were tolerant to aztreonam, four were tolerant to cefuroxjme, three were tolerant to cefamandole, and two were tolerant to cefoxitin. Strain H130 was tolerant to all -3-lactam antibiotics studied. None of the 10 tolerant H. influenzae isolates were tolerant to chloramphenicol, rifampin, tobramycin, ciprofloxacin, enoxacin, and trimethoprim-sulfamethoxazole. Although the clinical significance of tolerance is not determined, this study suggests that the bactericidal activity (MBC) of ,B-lactam antibiotics against H. influenzae should be determined in cases of severe infections in which clinical response is slow or unsatisfactory.The most common mechanism of ampicillin resistance in Haemophilus influenzae is the production of plasmidmediated P-lactamase (13,20,22). In addition, there have been' several 'reports of P-lactamase-negative strains of H. influenzae resistant to , B-lactam (10, 17, 27). Altered cell membrane permeability and altered penicillin-binding proteins have been suggested as mechanisms of this resistance (14,19). In the past years, we have observed that H. influenzae may be also tolerant to P-lactam antibiotics (2, 25). Antibiotic tolerance is a form of resistance that occurs when the MIC of an antibiotic is low but the MBC is high and exceeds the MIC by at least 32 times (21). The incidence and characteristics of this phenomenon have been well described previously in gram-positive bacteria, particularly in Staphylococcus aureus and Streptococcus species (3,6,9,21). A deficiency of autolytic enzyme activity has been suggested as a possible mechanism of this resistance (28,29).In the' present investigation, we have evaluated the incidence of resistance and tolerance to ampicillin and cefotaxime among 200 clinical isolates of H. influenzae. Antibiotic susceptibility of tolerant strains was compared with that of nontolerant microorganisms by broth dilution and killing curve tests with log-phase and stationary-phase inocula. The effect of storage on the stability of antimicrobial agent tolerance was also studied. to detect tryptophanase (indole), urease, and ornithine decarboxylase. Pittman serotype (a through f or nonserotypable) was determined by direct slide agglutination with polyvalent and monovalent typing sera (Difco). All isolates were teste...
In the present study, the minimal inhibitory concentrations and minimal bactericidal concentrations of moxalactam, cefamandole lithium, ampicillin, and chloramphenicol were determined, both in broth and on solid medium, against 75 non-beta-lactamase-producing and 25 beta-lactamase-producing strains of Haemophilus influenzae. Most of the 75 strains were inhibited or killed by 2 ,jg or less of ampicillin, chloramphenicol, or moxalactam per ml, but cefamandole exhibited poor bactericidal activity against 11 non-beta-lactamase-producing strains, of which 9 were non-type B H. influenzae. Most of the 25 beta-lactamaseproducing H. influenzae were resistant to 128 yg of ampicillin per ml. Both moxalactam and chloramphenicol, which had minimal inhibitory concentrations of less than 0.25 and 2 jig/ml, respectively, were more active than cefamandole, which had a minimal inhibitory concentration ranging from 2 to 2128 ,ug/ml.The widening spectrum of Haemophilus influenzae infections affecting both young children (8) and healthy adults (23) and the emergence of strains resistant to ampicillin (14,21,27) have stimulated investigators to study the in vitro efficacy of other antimicrobial agents against this microorganism (4,11,12,20,30).On the basis of these observations, cefamandole has been suggested as a useful cephalosporin for H. influenzae infections other than those affecting the central nervous system (3,6,9,25,26), but its clinical efficacy in infections due to ampicillin-or chloramphenicol-resistant strains has yet to be confirmed on a large scale.In the present study, we report the comparative in vitro activity of moxalactam, a new semisynthetic 1-oxa-beta-lactam (28, 31), cefamandole lithium, ampicillin, and chloramnphenicol.
Production of superoxide (O-.2) was measured in alveolar macrophages (AM) exposed to asbestos in vitro and in cells obtained from bronchoalveolar lavage (BAL) of rats inhaling asbestos. Steady state levels of O-.2 released by AM in vitro were dose and time dependent in response to crocidolite, chrysotile, and opsonized zymosan, a particulate used to trigger O-.2 generation. In contrast, an inhalation exposure for 1 h to crocidolite or for 6 days to either crocidolite or chrysotile asbestos resulted in a decreased production of O-.2 by BAL cells. Likewise, BAL cells from rats inhaling chrysotile for 1 h or crocidolite for 9 days exhibited a diminished capacity to secrete O-.2 when challenged with the particulate opsonized zymosan. Diminished generation of O-.2 by asbestos occurred in BAL cell populations containing either significantly increased numbers of polymorphonuclear leukocytes and lymphocytes (6- and 9-day exposures) or 99% AM (1-h exposure). Thus, these novel observations suggest that short-term inhalation of asbestos compromises the ability of BAL cells to produce O-.2 in the presence or absence of an additional phagocytic stimulus.
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