Diversity and sources of rapidly growing mycobacteria associated with infections following cardiac surgery.

Eighty-nine isolates of rapidly growing mycobacteria associated with cardiac bypass-related infections were characterized. Isolates from sporadic infections belonged to eight taxonomic groups and displayed numerous multilocus enzyme genotypes, plasmid profiles, and heavy metal and antibiotic resistance patterns. Compared with 449 noncardiac wound isolates, 45 sporadic cardiac isolates were more likely to be Mycobacterium fortuitum and M. smegmatis and less likely to be M. chelonae. About 80% of cardiac and noncardiac isolates were from southern coastal states. Eight outbreaks of cardiac bypass-related infections were identified. Strains from each outbreak were genotypically distinctive, and five outbreaks involved more than one strain. In two outbreaks, isolates from environmental sources and noncardiac infections were similar or identical to isolates from sternal wound infections. The heterogeneity of these isolates suggests that most isolates are unrelated and are derived from local environmental sources rather than from contaminated commercial surgical materials or devices.

Ampicillin, tetracycline, and chloramphenicol resistant Haemophilus influenzae in adults with chronic lung disease. Relationship of resistance to prior antimicrobial therapy.

Antibiotic resistance in 1,003 sputum isolates of Haemophilus influenzae from adults with chronic lung disease was assessed from January 1983 through June 1986. The incidence of resistance was 3.2% for tetracycline, 0.6% for chloramphenicol, and 12.5% for ampicillin. Resistance to ampicillin or tetracycline usually occurred alone, while 100% of chloramphenicol resistant isolates were co-resistant to tetracycline or ampicillin. More than 90% of antibiotic resistant isolates were nontypable and belonged to biotypes II, III, or V. Chart reviews of 331 patients revealed that patients with ampicillin resistant isolates were more likely than control subjects to have received ampicillin in the prior 6 wk (33% versus 6%, p less than 0.0001), whereas patients with isolates resistant to tetracycline or chloramphenicol plus tetracycline were more likely to have received tetracycline than control subjects (24% and 50%, respectively, versus 5%, p less than 0.005). The incidence of ampicillin resistance and the reluctance of physicians caring for adults to use chloramphenicol suggests that a newer cephalosporin such as cefotaxime may be the initial therapy of choice for severe H. influenzae disease in our patient population.

Characterization of beta-lactamases in Mycobacterium fortuitum including a role in beta-lactam resistance and evidence of partial inducibility.

The beta-lactamases from the 3 biovariants of M. fortuitum were compared on the basis of substrate profiles, susceptibility to enzyme inhibitors, and inducibility in the presence of selected beta-lactams. Despite differences in the distribution of beta-lactamase bands observed when enzymes from different isolates were subjected to isoelectric focusing, substrate profiles for the 3 biovariants were similar. All demonstrated a comparable broad spectrum hydrolytic activity for both cephalosporins and penicillins. The MIC for amoxicillin were reduced 4- to 16-fold when combined with the beta-lactamase inhibitor clavulanic acid, but not to a clinically susceptible range. The degree of reduction in MIC for amoxicillin correlated well with the susceptibility of enzyme to inhibition by clavulanic acid as determined in an in vitro assay. Although all M. fortuitum strains produce beta-lactamase under routine growth conditions, 90% of strains demonstrated an increase in the amount of this enzyme when cultured in the presence of selected beta-lactams as potential inducers. Quantitative assays and isoelectric focusing further indicated that this apparent induction of beta-lactamase is a simple enhancement of the same enzyme(s) produced in the absence of a known inducer. This is the first demonstration of any inducibility among mycobacterial beta-lactamases and suggests that synthesis of these enzymes in M. fortuitum is under some form of regulatory control. These results indicate that the beta-lactamases have a role in resistance of M. fortuitum to the beta-lactams. Other factors, such as permeability and penicillin-binding proteins, were not evaluated.

Susceptibilities of Mycobacterium fortuitum biovariant fortuitum and the unnamed third biovariant complex to heavy-metal salts.

Fifty-three clinical isolates of Mycobacterium fortuitum were tested for susceptibility to heavy-metal salts and antimicrobial agents. The isolates exhibited a bimodal distribution for several heavy metals including mercury, whose resistance is often plasmid mediated. There was a biovariant difference in the incidence of resistance, and resistance to several metal ions was often observed together. There was no apparent relationship between resistance to heavy-metal salts and resistance to antimicrobial agents such as tetracycline.