Mycobacterium immunogenum sp. nov., a novel species related to Mycobacterium abscessus and associated with clinical disease, pseudo-outbreaks and contaminated metalworking fluids: an international cooperative study on mycobacterial taxonomy

PCR-restriction enzyme pattern analysis of a 439 bp hsp65 gene segment identified 113 unique isolates among non-pigmented rapidly growing mycobacteria (RGM) from clinical and environmental sources that failed to match currently recognized species patterns. This group represented 40% of isolates recovered from bronchoscope contamination pseudo-outbreaks, 0% of disease-associated nosocomial outbreaks and 4% of routine clinical isolates of the Mycobacterium abscessus/Mycobacterium chelonae group submitted to the Mycobacteria/Nocardia laboratory for identification. It is grouped within the Mycobacterium fortuitum complex, with growth in less than 7 d, absence of pigmentation, positive 3-d arylsulfatase reaction and growth on MacConkey agar without crystal violet. It exhibited overlapping biochemical, antimicrobial susceptibility and HPLC characteristics of M. abscessus and M. chelonae. By 16S rRNA gene sequencing, these isolates comprised a homogeneous group with a unique hypervariable region A sequence and differed by 8 and 10 bp, respectively, from M. abscessus and M. chelonae. Surprisingly, this taxon contained two copies of the ribosomal operon, compared with single copies in the two related species. By DNA-DNA hybridization, this new group exhibited <30% homology with recognized RGM species. The name Mycobacterium immunogenum sp. nov. is proposed for this new taxon.

Mycobacterium wolinskyi sp. nov. and Mycobacterium goodii sp. nov., two new rapidly growing species related to Mycobacterium smegmatis and associated with human wound infections: a cooperative study from the International Working Group on Mycobacterial Taxonomy

Previous investigations demonstrated three taxonomic groups among 22 clinical isolates of Mycobacterium smegmatis. These studies were expanded to 71 clinical isolates, of which 35 (49%) (group 1) were identical to five ATCC reference strains including the type strain ATCC 19420T. Twenty-eight isolates (39%) were group 2, and eight isolates (11%) were group 3. Isolates of groups 2 and 3 were most often associated with post-traumatic or post-surgical wound infections including osteomyelitis, were susceptible to sulfamethoxazole, amikacin, imipenem and the tetracyclines, variably resistant to clarithromycin, and susceptible (group 1), intermediately resistant (group 2) or resistant (group 3) to tobramycin. The three groups were similar by routine biochemical and growth characteristics, but had different mycolic acid dimethoxy-4-coumarinylmethyl ester elution patterns by HPLC and different PCR-restriction enzyme patterns of a 439 bp fragment of the hsp-65 gene. Group 3 isolates differed from group 1 by 18 bp by 16S rRNA sequencing and exhibited < 25% homology by DNA-DNA hybridization, being most closely related to Mycobacterium mageritense. The 16S rRNA of group 1 and group 2 isolates differed by only 3 bp, but by DNA-DNA hybridization they exhibited only 40% homology. The following names are proposed: Mycobacterium goodii sp. nov. for group 2 isolates (type strain ATCC 700504T = MO69T), Mycobacterium wolinskyi sp. nov. for group 3 isolates (type strain ATCC 700010T = MO739T) and Mycobacterium smegmatis sensu stricto for group 1 isolates.

Clinical application of PCR-restriction enzyme pattern analysis for rapid identification of aerobic actinomycete isolates

The accuracy and practicality of PCR-restriction enzyme pattern analysis (PRA) for routine identification of aerobic actinomycete clinical isolates were evaluated for 299 cultures submitted to the Mycobacteria/Nocardia Laboratory at the University of Texas Health Center at Tyler. PRA identification using an amplified 439-bp segment (amplicon) of the 65-kDa heat shock protein gene was compared to identification by traditional methods, including growth characteristics, susceptibility patterns, biochemical testing, and high-performance liquid chromatography analysis. Microbiological examination of six cultures ruled out aerobic actinomycetes, and they were omitted from the study. Amplicons were analyzed with BstEII, HaeIII, MspI, HinfI, and BsaHI. When necessary, AciI, HhaI, and NarI were also used. From March 1995 through May 1997 (27 months), 274 of the remaining 293 (93.5%) isolates were accurately identified by PRA. Major diagnostic groups included 170 mycobacteria, 93 nocardiae, and 30 other aerobic actinomycetes. Mixed cultures were readily recognized by PRA, including a wound culture that contained two Nocardia taxa that were indistinguishable morphologically. Mycobacterium mucogenicum was identified in three cultures heavily contaminated with gram-positive cocci. The 19 isolates that produced PRA patterns that did not match those in the current PRA database were differentiated into 8 Mycobacterium species and 11 other aerobic actinomycetes by the presence or absence of BstEII recognition sites. Identification of 15 of these 19 isolates was also equivocal by traditional methods. PRA results were reportable within 2 to 5 working days and were as accurate as and faster and less expensive to obtain than those of traditional methods.

Recognition of a Nocardia transvalensis complex by resistance to aminoglycosides, including amikacin, and PCR-restriction fragment length polymorphism analysis

Amikacin resistance, rare among nocardiae, was observed in 58 clinical isolates of nocardiae. All of these isolates hydrolyzed hypoxanthine, and 75 to 100% utilized citrate, D-galactose, and D-trehalose as sole carbon sources. Based on utilization of I-erythritol, D-glucitol, i-myo-inositol, D-mannitol, and ribitol and susceptibility to amoxicillin-clavulanic acid, the 58 isolates were separable into four groups. One group was negative for I-erythritol and ribitol and included all the isolates belonging to Nocardia asteroides complex antibiogram type IV. The remaining three groups were positive for I-erythritol and ribitol and were grouped within Nocardia transvalensis. The group that included the type strain was designated N. transvalensis sensu stricto, and the other two groups were designated new taxons 1 and 2. PCR-restriction fragment length polymorphism (RFLP) analysis of a 439-bp segment of the 65-kDa heat shock protein gene with XhoI and HinfI produced identical patterns for 53 (91%) and 58 (100%) isolates, respectively, and differentiated them from all other Nocardia taxa. NarI- and HaeIII-derived RFLP patterns clearly differentiated each of the four biochemically defined taxa. These four groups were also distinguishable by using the chromogenic substrates in Dade MicroScan test panels. By high-performance liquid chromatography, these isolates exhibited the same unique mycolic acid-ester elution patterns that differed from those of all other clinically significant nocardiae. Gas-liquid chromatographic analysis of fatty acids also produced similar patterns for all isolates that distinguished them from all other Nocardia taxa, but did not differentiate the four taxa within the complex. We propose the designation N. transvalensis complex for these four groups of nocardiae, pending further genetic evaluation.

Rapid identification of clinically significant species and taxa of aerobic actinomycetes, including Actinomadura, Gordona, Nocardia, Rhodococcus, Streptomyces, and Tsukamurella isolates, by DNA amplification and restriction endonuclease analysis

A previously described PCR-restriction fragment length polymorphism (RFLP) identification schema for Nocardia that used an amplified 439-bp segment (amplicon) of the 65-kDa heat shock protein gene was evaluated for potential use with isolates of all clinically significant aerobic actinomycetes. The study included 28 reference (American Type Culture Collection) strains and 198 clinical isolates belonging to 20 taxonomic groups. Of these 198 isolates, 188 could be differentiated by this PCR-RFLP method. Amplicons from all aerobic actinomycete isolates lacked BstEII recognition sites, thereby distinguishing them from those of mycobacteria that contain one or more such sites. Of 29 restriction endonucleases, MspI plus HinfI produced RFLP patterns that differentiated 16 of the 20 taxa. A single RFLP pattern was observed for 15 of 20 taxa that included 65% of phenotypically clustered isolates. Multiple patterns were seen with Gordona bronchialis, Nocardia asteroides complex type VI, Nocardia otitidiscaviarum, Nocardia transvalensis, and Streptomyces spp. Streptomyces RFLP patterns were the most heterogeneous (five patterns among 19 isolates), but exhibited a unique HinfI fragment of > 320 bp. RFLP patterns that matched those from type strains of Streptomyces albus, Streptomyces griseus, or Streptomyces somaliensis were obtained from 14 of 19 Streptomyces isolates. Only 10 of 28 isolates of N. otitidiscaviarum failed to yield satisfactory amplicons, while only 6 of 188 (3.2%) clinical isolates exhibited patterns that failed to match one of the 21 defined RFLP patterns. These studies extended the feasibility of using PCR-RFLP analysis as a rapid method for the identification of all clinically significant species and taxa of aerobic actinomycetes.

DNA amplification and restriction endonuclease analysis for differentiation of 12 species and taxa of Nocardia, including recognition of four new taxa within the Nocardia asteroides complex

Nineteen reference and 156 clinical strains of the genus Nocardia belonging to 12 taxonomic groups were studied for restriction fragment length polymorphism (RFLP) by using an amplified 439-bp segment of the 65-kDa heat shock protein gene. Of 30 restriction endonucleases, digestion with MspI and then digestion with BsaHI produced RFLP band patterns which separated all 12 groups except N. asteroides type IV from 6 of 12 N. transvalensis isolates and N. carnea from the N. asteroides type VI isolates. Commonly encountered species such as N. nova, N. farcinica, N. brasiliensis sensu stricto, and N. otitidiscaviarum were easily separated. Each taxon resulted in a single RFLP band pattern that included > or = 96% of all biochemically grouped isolates for 9 of 12 taxa with MspI and for 8 of 12 taxa with BsaHI. With the use of both patterns, only 6 of 175 (3.4%) isolates failed to fit the biochemically defined group patterns. These studies provide the first evidence for the separate identities of four antibiogram-defined (but currently unnamed) groups within the N. asteroides complex (types I, II, IV, and VI) and the presence of two subgroups within N. transvalensis. They also provide genotypic evidence for the separate identities of N. nova and N. farcinica. The lack of BstEII recognition sites in amplicons obtained from nocardiae provides a simple and rapid method for the differentiation of nocardiae from mycobacteria. DNA amplification with RFLP analysis is the first rapid method that distinguishes all clinically significant taxa and recognized species within the genus Nocardia.

Amplification and cloning of the Mycobacterium tuberculosis dnaA gene

To identify and subsequently clone the gene encoding the DnaA protein, degenerate oligodeoxyribonucleotide (oligo) primers targeted against two highly conserved domains of the eubacterial DnaA were used to amplify a 780-bp DNA region spanning the two primers from genomic DNA preparations of Mycobacterium tuberculosis (Mt), M. bovis (Mb) and M. avium (Ma). Nucleotide (nt) sequences and deduced amino acid (aa) sequences of these fragments revealed homologies with each other and with the corresponding regions from other bacteria. Using an oligo specific to Mt dnaA as a probe, the Mt genomic DNA cosmid libraries propagated in Escherichia coli were screened and a cosmid DNA clone hybridizing with the oligo was identified. Furthermore, a 5-kb DNA fragment containing the Mt dnaA was subcloned into a pUC18 vector.

New Nocardia taxon among isolates of Nocardia brasiliensis associated with invasive disease

Nocardia brasiliensis, the second most frequently isolated aerobic actinomycete in the clinical laboratory, is usually associated with localized cutaneous infections. However, 22% of 238 N. brasiliensis isolates from the United States and 12% of 66 isolates from Queensland, Australia, which had been collected over a 17-year period, were associated with extracutaneous and/or disseminated diseases. Of the 62 invasive isolates, 37 (60%) were susceptible to ciprofloxacin and/or were susceptible to clarithromycin and resistant to minocycline, compared with only 6 (3%) of 242 localized cutaneous isolates. The 43 isolates with this susceptibility pattern appeared to define a new taxon. They were similar to Nocardia asteroides complex isolates clinically in proportions from persons with pulmonary (70%), central nervous system (23%), and/or disseminated diseases (37%) in the setting of corticosteroids (74%) or AIDS (14%). This putative new taxon differed from N. brasiliensis in the hydrolysis of adenine (92 versus 4%), beta-lactamase patterns on isoelectric focusing, and the presence of two early mycolic acid-ester peaks by high-performance liquid chromatography. Restriction analysis of a 439-bp fragment of the 65-kDa heat shock protein gene revealed that N. brasiliensis and the new taxon had different restriction patterns with 8 of the 11 enzymes tested. Screening of invasive isolates of N. brasiliensis for susceptibility to ciprofloxacin will identify most isolates of the new taxon, which likely represents a new Nocardia species.

PCR amplification and restriction endonuclease analysis of a 65-kilodalton heat shock protein gene sequence for taxonomic separation of rapidly growing mycobacteria

A total of 129 reference and clinical strains of rapidly growing mycobacteria (RGM) belonging to 10 taxonomic groups were studied for restriction fragment length polymorphism patterns from a PCR-amplified 439-bp segment of the 65-kDa heat shock protein (HSP) gene. Of 24 endonucleases evaluated, restriction fragment length polymorphism patterns produced by HaeIII and BstEII and then by AciI and CfoI gave the best separation. Sixty percent of all RGM taxa studied were differentiated by HaeIII digests alone. Single unique patterns were observed with HaeIII and/or BstEII for Mycobacterium fortuitum (100%), M. chelonae (94%), M. abscessus (96%), M. smegmatis (100%), M. mucogenicum (formerly the M. chelonae-like organism) (100%), and the sorbitol-negative third biovariant of M. fortuitum (100%). Evidence is presented in support of two subgroups within M. peregrinum, M. smegmatis, and the unnamed third biovariant of M. fortuitum (sorbitol positive and sorbitol negative). PCR-based technology provides a rapid, accurate system for the identification of clinically important species of RGM which should be particularly useful for reference laboratories.

A case of recurrent typhoid fever in the United States: importance of the grandmother connection and the use of large restriction fragment pattern analysis of genomic DNA for strain comparison

An 8-year old girl was infected for a second time with Salmonella typhi by contact with her grandmother, a known typhoid carrier. The S. typhi from both patient and grandmother had closely related genomic pulsed field gel electrophoresis patterns that differed from epidemiologically unrelated strains. The girl responded well to a 14-day course of oral trimethoprimsulfamethoxazole. The grandmother was treated successfully with a 28-day regimen of oral ciprofloxacin. Typhoid fever remains an endemic disease in the United States, largely because of recognized chronic stool carriers. Most of these carriers had typhoid in the preantibiotic era and remain potential sources of disease when they provide meals for others, not uncommonly grandchildren. The importance of this "grandmother" connection to endemic typhoid fever is reviewed, as is the potential use of pulsed field gel electrophoresis pattern analysis for comparison of strains of S. typhi.

Tetracycline resistance determinants in Mycobacterium and Streptomyces species

Two of seven tetracycline-resistant (Tcr) Mycobacterium fortuitum group isolates and six Tcr clinical Streptomyces isolates carried gram-positive Tcr determinants (Tet K and Tet L) and Streptomyces resistance determinants (Otr A, Otr B, and Otr C). This represents the first documentation of the acquisition by mycobacteria of determinants coding for antibiotic resistance and suggests the potential for the spread of antibiotic resistance determinants within mycobacterial species.

Initial clarithromycin monotherapy for Mycobacterium avium-intracellulare complex lung disease

Sputum conversion rates in Mycobacterium avium-intracellulare (MAI) complex lung disease have ranged from only 50 to 80% despite the use of three to five antituberculosis agents. We initiated a prospective, open, noncomparative trial of initial clarithromycin monotherapy at 500 mg twice a day for 4 months in HIV-negative patients with MAI lung disease. The primary study end point was microbiologic improvement. Of 30 patients enrolled, 20 completed therapy. This latter group was predominantly male (60%), smokers (70%), older than 45 yr of age (90%), infected with Mycobacterium intracellulare (70%) and with bilateral disease (85%). Of 19 patients with pretreatment minimum inhibitory concentrations (MIC) for clarithromycin < 16 micrograms/ml, 58% became sputum-negative, and 21% showed significant reductions in sputum positivity. Heavily positive sputum cultures (> 200 colonies) were reduced from 30 to 47 samples pretherapy (64%) to three of 54 (6%) post-therapy (p < 0.0001); 18 of 19 patients (95%) showed an improvement in sputum cultures, chest radiographs, or both. Only two patients (7%) discontinued the drug because of adverse events. Only three (16%) of 19 isolates developed clarithromycin resistance (MIC > 32 micrograms/ml). Clarithromycin-susceptible and -resistant MAI isolates from the same patient had identical DNA large-restriction fragment patterns. Clarithromycin is the first single agent to be shown efficacious in the treatment of MAI lung disease.

Identification of mutations in 23S rRNA gene of clarithromycin-resistant Mycobacterium intracellulare

Clarithromycin is a potent macrolide that has been used for treating infections with nontuberculous mycobacteria. Pairs of susceptible and resistant Mycobacterium intracellulare strains were obtained from patients with chronic pulmonary M. intracellulare infections undergoing monotherapy with clarithromycin. Nucleotide sequence comparisons of the peptidyltransferase region in 23S rRNAs from parental and resistant strains revealed that in three of six resistant strains, for which the MIC was > 32 micrograms/ml, a single base was mutated (Escherichia coli equivalent, A-2058-->G, C, or U). As the modification of adenine 2058 by dimethylation is a frequent cause of macrolide resistance in a variety of different bacteria, we suggest that mutation of A-2058 confers acquired resistance to clarithromycin in M. intracellulare.

Partial characterization of Nocardia farcinica beta-lactamases

The beta-lactamases obtained from culture supernatants and cell extracts of 26 clinical strains and 5 reference strains of Nocardia farcinica were partially characterized. The enzymes exhibited two patterns on isoelectric focusing (IEF). beta-Lactamases from the majority of the 31 strains (87%) including the 5 reference strains exhibited two major bands with pIs of 4.56 and 4.49. The remaining strains had two similar major bands but with slightly higher pIs. Culture supernatants and cell extracts exhibited identical patterns. The two sets of enzymes were functionally indistinguishable by substrate and inhibitor profiles and lack of inducibility. By disk testing, ampicillin, amoxicillin, ticarcillin, amoxicillin-clavulanic acid, and imipenem were highly synergistic with cefotaxime. The enzymes were primarily penicillinases and hydrolyzed cephalosporins at rates of < or = 12% of those for penicillins. N. farcinica beta-lactamases were susceptible to inhibition by clavulanic acid and BRL 42715, exhibiting 50% inhibitory concentrations of 0.025 to 0.045 micrograms/ml (0.12 to 0.22 microM) and 0.05 to 0.1 micrograms/ml (0.31 to 0.63 microM), respectively, less susceptible to tazobactam, and least susceptible to sulbactam, cloxacillin, and imipenem. The beta-lactamases of N. farcinica are believed to mediate penicillin resistance and may play a secondary role in extended-spectrum cephalosporin resistance. The close similarity among N. farcinica beta-lactamases and their distinct differences from beta-lactamases of other Nocardia species support the taxonomic identity of this species.

A membrane-bound precursor beta-lactamase in strains of Moraxella catarrhalis and Moraxella nonliquefaciens that produce periplasmic BRO-1 and BRO-2 beta-lactamases

By employing the non-ionic detergent Triton X-100, a membrane-bound beta-lactamase was extracted from strains of Moraxella (Branhamella) catarrhalis and Moraxella nonliquefaciens that produce BRO-1 and BRO-2 beta-lactamases. Unlike BRO-1 and BRO-2, which exhibit multiple major bands on isoelectric focusing (IEF), the membrane-bound enzyme focused as a single IEF band at a pI of 6.20, which was not present with either of the other two enzymes. The membrane-bound beta-lactamase could be extracted from all strains producing BRO-1 and BRO-2, including recombinant strains constructed by transformation or conjugation. The enzyme was also recovered from Escherichia coli strain HB101 carrying vector plasmid pLQ521 into which the BRO-1 beta-lactamase gene from M. catarrhalis had been cloned. All three beta-lactamases were indistinguishable by inhibitor profiles with clavulanic acid, BRL 42715, sulbactam and tazobactam. These data suggested that all three beta-lactamases were the product of a single gene in Moraxella spp., and that the membrane-bound beta-lactamase serves as a precursor of both BRO-1 and BRO-2. Species differences in cellular processing of the membrane-bound enzyme could explain the minor differences in IEF patterns that occurred with BRO-1 and BRO-2 beta-lactamases when present in different species.

Isoelectric focusing patterns of beta-lactamases in the rapidly growing mycobacteria

beta-lactamases from 259 strains of rapidly growing mycobacteria that included the third biovariant complex of Mycobacterium fortuitum, M. peregrinum, M. abscessus, M. chelonae, the M. chelonae-like organisms (MCLO), and M. smegmatis were analyzed by isoelectric focusing (IEF). All isolates produced acidic beta-lactamases with major band isoelectric points (pIs) between 4.4 and 6.0. Each of the 6 taxonomic groups exhibited 1 or 2 characteristic beta-lactamase IEF patterns. Heterogeneity among IEF patterns was evident in 5 of the 6 groups, however, and was greatest among the third biovariant complex of M. fortuitum. beta-lactamase patterns correlated with previously identified taxonomic subgroups of M. smegmatis and the third biovariant complex of M. fortuitum. beta-lactamase IEF analysis of MCLO strains isolated from two outbreaks demonstrated its possible usefulness for epidemiologic evaluation.

beta-Lactamase inhibitors and the inducibility of the beta-lactamase of Mycobacterium tuberculosis

Ten clinical isolates and the type strain (H37Rv) of Mycobacterium tuberculosis were shown to produce an intracellular beta-lactamase. Crude enzyme preparations were extracted from acetone cell powders by grinding with zirconium beads in 0.133 M glycine with 1.0% Triton X-100. The enzymes had identical patterns on isoelectric focusing, with two major bands at isoelectric points of 4.9 and 5.1. The beta-lactamase was highly susceptible to the new beta-lactamase inhibitor BRL 42715, with an I50 of 0.0001 microgram/ml. The enzyme was also susceptible to clavulanic acid with an I50 (0.05 microgram/ml), which was similar to the value for the common bacterial beta-lactamase TEM-1 (0.01 microgram/ml). The latter result is consistent with previous MIC studies with M. tuberculosis, which have shown synergy between clavulanic acid and amoxicillin. BRL 42715 and clavulanic acid were more active than sulbactam, tazobactam, and cloxacillin. These studies support the potential value of penicillin/clavulanic acid and penicillin/BRL 42715 combinations in the treatment of tuberculosis.

Mercuric reductase activity and evidence of broad-spectrum mercury resistance among clinical isolates of rapidly growing mycobacteria

Resistance to mercury was evaluated in 356 rapidly growing mycobacteria belonging to eight taxonomic groups. Resistance to inorganic Hg2+ ranged from 0% among the unnamed third biovariant complex of Mycobacterium fortuitum to 83% among M. chelonae-like organisms. With cell extracts and 203Hg(NO3)2 as the substrate, mercuric reductase (HgRe) activity was demonstrable in six of eight taxonomic groups. HgRe activity was inducible and required NADPH or NADH and a thiol donor for optimai activity. Species with HgRe activity were also resistant to organomercurial compounds, including phenylmercuric acetate. Attempts at intraspecies and intragenus transfer of HgRe activity by conjugation or transformation were unsuccessful. Mercury resistance is common in rapidly growing mycobacteria and appears to function via the same inducible enzyme systems already defined in other bacterial species. This system offers potential as a strain marker for epidemiologic investigations and for studying genetic systems in rapidly growing mycobacteria.

Clinical disease, drug susceptibility, and biochemical patterns of the unnamed third biovariant complex of Mycobacterium fortuitum

Previous studies of Mycobacterium fortuitum identified isolates that did not fit its two recognized biovariants. Eighty-five clinical isolates of this group, the "third biovariant complex", were evaluated. They represented 16% of 410 isolates of M. fortuitum submitted to a Texas laboratory and 22% of 45 isolates in Queensland, Australia. Most infections (76%) involved skin, soft tissue, or bone and occurred after metal puncture wounds or open fractures. Isolates differed from biovar fortuitum in resistance to pipemidic acid and use of mannitol and inositol as carbon sources. Two subgroups were present, and examples were deposited in the American Type Culture Collection. Isolates were resistant to doxycycline and one-third were resistant to cefoxitin. All were susceptible to amikacin, ciprofloxacin, sulfamethoxazole, and imipenem. Surgical debridement combined with drug therapy based on in vitro susceptibilities resulted in cures of cutaneous disease or osteomyelitis. DNA homology studies are needed to determine the taxonomic status of these organisms.

Acquired resistance of Nocardia brasiliensis to clavulanic acid related to a change in beta-lactamase following therapy with amoxicillin-clavulanic acid

Previous studies have demonstrated that Nocardia brasiliensis is susceptible to amoxicillin-clavulanic acid and that its beta-lactamases are inhibited in vitro by clavulanic acid. A cardiac transplant patient with disseminated infection caused by N. brasiliensis was treated with this drug combination with good response, but relapsed while still on therapy. The relapse isolate was found to be identical to the initial isolate by using genomic DNA restriction fragment patterns obtained by pulsed field gel electrophoresis, but it was resistant to amoxicillin-clavulanic acid. On isoelectric focusing, the beta-lactamase from the relapse isolate exhibited a shift in the isoelectric point (pI) of its major band from 5.10 to 5.04 compared with the enzyme from the pretreatment isolate. As determined by using values of the amount of beta-lactamase inhibitor necessary to give 50 +/- 5% inhibition of beta-lactamase-mediated hydrolysis of 50 microM nitrocefin, the beta-lactamase of the relapse isolate was also 200-fold more resistant than the enzyme from the pretreatment isolate to clavulanic acid and was more resistant to sulbactam, tazobactam, cloxacillin, and imipenem. The beta-lactamase of the relapse isolate exhibited a 10-fold decrease in hydrolytic activity for cephaloridine and other hydrolyzable cephalosporins compared with that for nitrocefin. Acquired resistance to amoxicillin-clavulanic acid in this isolate of N. brasiliensis appears to have resulted from a mutational change affecting the inhibitor and active site(s) in the beta-lactamase.

Cefotaxime-resistant Nocardia asteroides strains are isolates of the controversial species Nocardia farcinica

A recent study of Nocardia asteroides revealed that 95% of clinical strains had one of five antibiotic resistance patterns. We found the pattern of resistance to cefotaxime and cefamandole in 19% of 200 clinical N. asteroides isolates. Isolates with this drug resistance pattern were from numerous geographic sources and were associated with significant clinical disease (56% of patients had disseminated infections). Phenotypic studies revealed that these isolates were relatively homogeneous and matched previous descriptions and reference strains of the controversial species N. farcinica. Growth at 45 degrees C, acid production from rhamnose, ability to utilize acetamide as a nitrogen and carbon source, and resistance to tobramycin and cefamandole were features of N. farcinica that could be tested in the clinical laboratory and allowed their distinction from N. asteroides. The serious nature of disease due to N. farcinica and its resistance to the newer cephalosporins suggest a clinical need for laboratory identification of this species. (Current tests used in clinical laboratories do not distinguish N. farcinica from N. asteroides.) This is the first recognition that N. farcinica has a specific drug resistance pattern and confirms the previously described concept that drug resistance patterns of N. asteroides may be associated with specific taxonomic groups.

Genetic basis of tetracycline resistance in Moraxella (Branhamella) catarrhalis

Two-high-level-tetracycline-resistance Moraxella (Branhamella) catarrhalis strains were shown to carry DNA sequences which hybridized with the Tet B probe. The determinant appeared to be located in the chromosome and was nontransferable.

Antibiotic susceptibilities and drug resistance in Moraxella (Branhamella) catarrhalis

PURPOSE

To summarize current knowledge of drug susceptibility and mechanisms of drug resistance in Moraxella (Branhamella) catarrhalis.

MATERIALS AND METHODS

The current medical literature was reviewed, with careful attention to recent studies of the BRO beta-lactamases.

RESULTS

Although intrinsically resistant to a small group of drugs that included vancomycin and trimethoprim, acquired drug resistance in Branhamella catarrhalis was unknown in the early years of antimicrobial therapy. During 1976 to 1977, however, two previously unrecognized beta-lactamases appeared in this species almost simultaneously around the world. At the same time these enzymes, now known as BRO-1 and BRO-2, also appeared in two closely related commensal species of Moraxella. Within four years the BRO enzymes were found in up to 75 percent of B. catarrhalis in the United States where they provide low-level resistance to penicillin and ampicillin but not to most cephalosporins. The BRO genes appear to be chromosomal but are readily transferred by conjugation within the Moraxella genus. Resistance to aminoglycosides and trimethoprim-sulfamethoxazole has been reported from Spain, and resistance to both erythromycin and tetracycline has recently been described among United States isolates of B. catarrhalis.

CONCLUSION

Despite this drug resistance, numerous oral and parenteral agents are available and appear useful for treatment of clinical disease, including amoxicillin/clavulanic acid, erythromycin, the tetracyclines, ciprofloxacin, and trimethoprim/sulfamethoxazole. Recent changes in drug resistance in this species suggest that continued monitoring of drug resistance in B. catarrhalis is needed.

BRO beta-lactamases of Branhamella catarrhalis and Moraxella subgenus Moraxella, including evidence for chromosomal beta-lactamase transfer by conjugation in B. catarrhalis, M. nonliquefaciens, and M. lacunata

Two closely related beta-lactamases, BRO-1 and BRO-2 (formerly called Ravasio and 1908), are found in Moraxella (Branhamella) catarrhalis. We screened strains of B. catarrhalis recovered in the United States since 1952 and identified the first beta-lactamase-positive isolate in August 1976. The prevalence of the enzymes among 394 clinical isolates from one Texas hospital has averaged 75% since testing began in 1983. Screening of isolates of Moraxella subgenus Moraxella revealed the BRO enzymes in two other human respiratory tract species, M. lacunata and M. nonliquefaciens, beginning in 1978. A different beta-lactamase with a pI of 6.4 predominated in other species of subgenus Moraxella. BRO-2 had a different isoelectric focusing pattern and was produced in lesser amounts than BRO-1, but the two enzymes were indistinguishable by substrate or inhibitor profile. BRO enzymes from B. catarrhalis, M. nonliquefaciens, and M. lacunata could be transferred by conjugation and, for B. catarrhalis, also by transformation to B. catarrhalis. Plasmid bands were demonstrated in 90% of M. nonliquefaciens and in one previously reported strain of B. catarrhalis, but no change in plasmid profiles was seen in beta-lactamase-positive recombinants, supporting previous studies that suggested the beta-lactamase genes are chromosomal.

Beta-lactam resistance in Nocardia brasiliensis is mediated by beta-lactamase and reversed in the presence of clavulanic acid

Forty clinical isolates and the type strain of Nocardia brasiliensis were screened for susceptibility to 20 beta-lactams. Isolates exhibited a single pattern of resistance, with large zones of inhibition by disk diffusion and low MICs by broth and agar dilutions only to cefotaxime, ceftriaxone, ceftizoxime, Augmentin, and Timentin. All strains produced beta-lactamase, with five different enzyme patterns by isoelectric focusing. Despite the differences in their isoelectric points, the enzymes had the same substrate profiles, with equivalent activity against penicillin, ampicillin, cefamandole, cephalothin, and cephalordine. In an in vitro assay, the enzymes were highly susceptible to clavulanic acid. The MIC50 and MIC90 for the combination of amoxicillin and clavulanic acid (Augmentin) was 2 and 4 micrograms/ml, respectively, compared with 16 micrograms/ml for both values for amoxicillin alone. These studies suggest that beta-lactamase is the major mechanism of beta-lactam resistance in this species and that Augmentin is the first oral beta-lactam with good potential for treating infections due to N. brasiliensis.

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.

Isoelectric focusing of beta-lactamases from sputum and middle ear isolates of Branhamella catarrhalis recovered in the United States

Branhamella catarrhalis obtained from the sputum of 146 patients with lower respiratory tract disease and from middle ear fluids of 26 children with otitis media were evaluated for beta-lactamase activity and the enzymes were characterised by isoelectric focusing (IEF). 71% (103 of 146) of the sputum isolates and 77% (20 of 26) of the ear isolates produced beta-lactamase. By IEF, the beta-lactamases of 113 of 123 (92%) strains revealed patterns identical with the Ravasio type strain, having unique enzyme bands at pIs of 6.4 and 6.65. The remaining 10 isolates (8%) produced patterns similar to the 1908 type strain with a unique band of activity having a pI of 6.55. In addition, the 1908 types revealed a band of minor enzyme activity with a pI of 7.55 that was absent from the Ravasio types. All strains tested shared major enzyme bands with pIs of 5.1, 5.3, 5.55 and 6.1. These results indicate that the most common beta-lactamase(s) produced by clinical isolates of B. catarrhalis in the United States are similar to those produced by the Belgian Ravasio type strain.

Isoelectric focusing of beta-lactamases in Mycobacterium fortuitum. Association of a single enzyme pattern with cefoxitin resistance

The uninduced culture supernatants and cell extracts from 58 strains of the 3 biovariants (biovar) of Mycobacterium fortuitum were all positive for beta-lactamase with the chromogenic cephalosporin substrate. By analytical isoelectric focusing (IEF), 29 of 30 strains of biovar fortuitum exhibited an identical beta-lactamase pattern with 1 major band. In contrast, the beta-lactamases of biovar peregrinum and the unnamed third biovar were heterogeneous, with multiple bands and a variety of patterns. The pH range of isoelectric points for the beta-lactamases was relatively narrow, however, with most bands appearing between pH 4.3 and 5.2. Although additional genetic studies are required, these enzymes appear to be chromosomal, as they are present in all strains including some without detectable plasmids. Repeat isolates from the same patient obtained up to six months apart always had the same beta-lactamase pattern by IEF. Of the third biovar complex, 30% are cefoxitin resistant with minimal inhibitory concentrations greater than 32 micrograms/ml. All 9 cefoxitin-resistant isolates tested had the same unique beta-lactamase pattern by IEF, although this enzyme failed to hydrolyze cefoxitin while hydrolyzing cephalothin and benzylpenicillin. Thus, despite the association of cefoxitin-resistance with a single enzyme pattern, the role of this beta-lactamase in resistance is not known.

Primary immune responsiveness and other observations in mice given oral dimethyl sulfoxide

Mice were allowed to drink 5% DMSO in their drinking water ad libitum for a period of six weeks, during which time a number of variables were compared with age-, weight-, and sex-matched control mice given ordinary tap water. The amount of DMSO consumed increased from a daily average of 27 g/kg/mouse during the first week to 52 g/kg/mouse by the end of the third week. Significant decreases were observed in the treated animals for total body weight, percent spleen weight relative to total body weight, and serum volume, while serum immunoglobulin concentrations remained unchanged. Mice given 4.4 g/kg DMSO intraperitoneally for 7 days, however, revealed significant losses in serum IgG and IgA, but not IgM. The effect of DMSO on the primary humoral response was assessed following immunization of mice with sheep red blood cells either 16 days or 8 weeks after the start of DMSO. Compared with similarly immunized controls, test animals demonstrated moderate, but significant, reductions in both spontaneous and facilitated plaque-forming cells, hemagglutination titres, and serum concentrations of IgG1. Based on a comparison of the two DMSO-treated groups, the degree of immune inhibition increased and the peak of the response was delayed relative to the length of time of DMSO ingestion prior to immunization.

Selecting drug combinations for treatment of drug-resistant mycobacterial diseases

Mixtures of antituberculosis drugs were evaluated for their in vitro effects on drug-resistant isolates of Mycobacterium tuberculosis and M. avium-intracellulare. The response of individual isolates to representative drug combinations was not always predictable from the results of single-drug sensitivity assays. For the case of M. tuberculosis, combinations of drugs were often bactericidal even under conditions where two or more drugs were without effect when tested singly. The more widely drug-resistant M. avium-intracellulare demonstrated increased growth inhibition when subcultured in the presence of single drugs, particularly rifampin and streptomycin. However, these conditions favored the selection of highly resistant strains. Alternatively, multiple drugs were often bacteriostatic; and under conditions where isolates demonstrated growth inhibition, the selection of highly drug-resistant strains was delayed. These results suggest a role for multiple-drug sensitivity assays in selecting drug combinations to be used in the treatment of drug-resistant mycobacterioses.

Induction of aryl hydrocarbon hydroxylase by lymphocytes from women taking oral contraceptives

The peripheral blood lymphocytes (PBL) from two female subjects were assayed for AHH induction 40 days prior to and 30 days during ingestion of progesterone and estrogen analogues as oral contraceptives. Three habitual users of oral contraceptives were also studied. No in vitro inhibition of AHH induction was observed as a consequence of the use of these hormone analogues. Values obtained for enzyme activity suggest a slight increase in AHH induction resulting from the use of oral contraceptives. Further studies with larger numbers of subjects are required before the apparent increase in enzyme inducibility can be considered significant.