beta-Lactamases of Branhamella catarrhalis and their inhibition by clavulanic acid

EGFR and HER2 exon 20 insertions in solid tumours: from biology to treatment

Protein tyrosine kinases of the human epidermal growth factor receptor family, including EGFR and HER2, have emerged as important therapeutic targets in non-small-cell lung, breast and gastroesophageal cancers, and are of relevance for the treatment of various other malignancies (particularly colorectal cancer). Classic activating EGFR exon 19 deletions and exon 21 mutations, and HER2 amplification and/or overexpression, are predictive of response to matched molecularly targeted therapies, translating into favourable objective response rates and survival outcomes. By comparison, cancers with insertion mutations in exon 20 of either EGFR or HER2 are considerably less sensitive to the currently available tyrosine kinase inhibitors and antibodies targeting these receptors. These exon 20 insertions are structurally distinct from other EGFR and HER2 mutations, providing an explanation for this lack of sensitivity. In this Review, we first discuss the prevalence and pan-cancer distribution of EGFR and HER2 exon 20 insertions, their biology and detection, and associated responses to current molecularly targeted therapies and immunotherapies. We then focus on novel approaches that are being developed to more effectively target tumours driven by these non-classic EGFR and HER2 alterations.

Antimicrobial resistance in Haemophilus influenzae and Moraxella catarrhalis respiratory tract isolates: results of the Canadian Respiratory Organism Susceptibility Study, 1997 to 2002

A total of 7,566 unique patient isolates of Haemophilus influenzae and 2,314 unique patient isolates of Moraxella catarrhalis were collected between October 1997 and June 2002 from 25 medical centers in 9 of the 10 Canadian provinces. Among the 7,566 H. influenzae isolates, 22.5% produced beta-lactamase, while 92.4% of the 2,314 M. catarrhalis isolates produced beta-lactamase. The incidence of beta-lactamase-producing H. influenzae isolates decreased significantly over the 5-year study period, from 24.2% in 1997-1998 to 18.6% in 2001-2002 (P < 0.01). The incidence of beta-lactamase-producing M. catarrhalis isolates did not change over the study period. The overall rates of resistance to amoxicillin and amoxicillin-clavulanate for H. influenzae were 19.3 and 0.1%, respectively. The rank order of cephalosporin activity based on the MICs at which 90% of isolates were inhibited (MIC(90)s) was cefotaxime > cefixime > cefuroxime > cefprozil > cefaclor. On the basis of the MICs, azithromycin was more active than clarithromycin (14-OH clarithromycin was not tested); however, on the basis of the NCCLS breakpoints, resistance rates were 2.1 and 1.6%, respectively. Rates of resistance to other agents were as follows: doxycycline, 1.5%; trimethoprim-sulfamethoxazole, 14.2%; and chloramphenicol, 0.2%. All fluoroquinolones tested, including the investigational fluoroquinolones BMS284756 (garenoxacin) and ABT-492, displayed potent activities against H. influenzae, with MIC(90)s of < or = 0.03 microg/ml. The MIC(90)s of the investigational ketolides telithromycin and ABT-773 were 2 and 4 microg/ml, respectively, and the MIC(90) of the investigational glycylcycline GAR-936 (tigecycline) was 4 microg/ml. Among the M. catarrhalis isolates tested, the resistance rates derived by using the NCCLS breakpoint criteria for H. influenzae were <1% for all antibiotics tested except trimethoprim-sulfamethoxazole (1.5%). In summary, the incidence of beta-lactamase-positive H. influenzae strains in Canada is decreasing (18.6% in 2001-2002), while the incidence of beta-lactamase-positive M. catarrhalis strains has remained constant (90.0% in 2001-2002).

Rapid discrimination between BRO beta-lactamases from clinical isolates of Moraxella catarrhalis using restriction endonuclease analysis

An important feature of Moraxella catarrhalis is the production of beta-lactamases, which causes resistance to the penicillins. Restriction enzyme analysis was able to distinguish between the bro-1 and bro-2 beta-lactamase-encoding genes from 89 clinical isolates of M. catarrhalis. This is a rapid, simple and cost effective method of characterizing these genes.

Molecular characterization of the beta-lactamases from clinical isolates of Moraxella (Branhamella) catarrhalis obtained from 24 U.S. medical centers during 1994-1995 and 1997-1998

The beta-lactamases from 403 Moraxella (Branhamella) catarrhalis clinical isolates obtained during 1994-1995 and 1997-1998 U.S. multicenter surveillance studies were characterized by isoelectric focusing. The overall prevalences of the BRO-1 and BRO-2 enzymes among beta-lactamase-positive isolates were estimated to be 97.5 and 2.5%, respectively. The minimum inhibitory concentrations (MICs) of ampicillin for all BRO-2-producing isolates were </=1 microg/ml; however, numerous beta-lactamase-positive isolates for which the ampicillin MICs were </=1 microg/ml produced the BRO-1 enzyme (88. 1%).

A 1997-1998 national surveillance study: Moraxella catarrhalis and Haemophilus influenzae antimicrobial resistance in 34 US institutions

From November 1, 1997 to April 30, 1998, 726 Moraxella catarrhalis isolates and 1529 Haemophilus influenzae isolates were obtained from 34 medical centres throughout the United States. Rates of beta-lactamase production were 94.6% among M. catarrhalis and 31.1% among H. influenzae strains. Susceptibility rates of M. catarrhalis isolates to selected antimicrobial agents were greater than 99% for amoxycillin-clavulanate, cefixime, cefpodoxime, cefuroxime, cefaclor, loracarbef, clarithromycin, azithromycin, chloramphenicol and tetracycline, 97.8% for cefprozil, 50.4% for trimethoprim-sulphamethoxazole and 28.1% for ampicillin. Of the antimicrobials tested against H. influenzae, the only agents with susceptibility rates below 96% were loracarbef (87.6%), cefprozil (83.4%), cefaclor (82.7%), trimethoprim-sulphamethoxazole (67.3%) and ampicillin (64.7%). The clarithromycin susceptibility rate was 67.4% but this agent was not tested in the presence of its 14-OH metabolite.

Interaction of Streptococcus pneumoniae and Moraxella catarrhalis: investigation of the indirect pathogenic role of beta-lactamase-producing moraxellae by use of a continuous-culture biofilm system

The majority of clinical isolates of Moraxella catarrhalis produce beta-lactamase. The role of this enzyme in the phenomenon of indirect pathogenicity, in which a true pathogen such as Streptococcus pneumoniae is protected from the action of certain beta-lactam antibiotics, is well recognized. By using a simple continuous-culture biofilm system, it has been shown that the pneumococcus attains high titers in excess of 10(12) CFU/biofilm; furthermore, the penicillin-sensitive pneumococcus used remained susceptible to a range of beta-lactam antibiotics in these biofilms (R. K. Budhani and J. K. Struthers, J. Antimicrob. Chemother. 40:601-602, 1997). This system was used to characterize the antibiotic susceptibility of this isolate when grown with beta-lactamase-negative or -positive moraxellae. When grown with beta-lactamase-producing moraxellae in the presence of either benzylpenicillin or amoxicillin, the pneumococcus was protected in the range of the antibiotic concentrations to which it would be considered resistant. With amoxicillin-clavulanic acid the titers of the two organisms collapsed at the antibiotic concentration at which moraxellae became susceptible. The levels of beta-lactamase activity in cell-free supernatants of broth culture, in biofilm, and in biofilm effluent revealed distinct differences in this activity; levels in biofilm were significantly lower than those in broth culture supernatants. The system appears suitable for studying organisms under antibiotic stress and for investigating the interactions of bacteria under such conditions.

Moraxella catarrhalis: clinical significance, antimicrobial susceptibility and BRO beta-lactamases

Moraxella catarrhalis is an important pathogen of humans. It is a common cause of respiratory infections, particularly otitis media in children and lower respiratory tract infections in the elderly. Colonisation of the upper respiratory tract appears to be associated with infection in many cases, although this association is not well understood. Nosocomial transmission is being increasingly documented and the emergence of this organism as a cause of bacteremia is of concern. The widespread production of a beta-lactamase enzyme renders Moraxella catarrhalis resistant to the penicillins. Cephalosporins and beta-lactamase inhibitor combinations are effective for treatment of beta-lactamase producers, and the organism remains nearly universally susceptible to the macrolides, fluoroquinolones, tetracyclines and the combination of trimethoprim and sulfamethoxazole. Two major beta-lactamase forms, BRO-1 and BRO-2, have been described on the basis of their isoelectric focusing patterns. The BRO-1 enzyme is found in the majority of beta-lactamase-producing isolates and confers a higher level of resistance to strains than BRO-2. The BRO enzymes are membrane associated and their production appears to be mediated by chromosomal determinants which are transmissible by an unknown mechanism. The origin of these novel proteins is unknown.

Amoxicillin and clavulanic acid concentrations in gingival crevicular fluid

The beta-lactams are bactericidal antibiotics, but some of them may be inactivated by bacterial beta-lactamases which destroy the beta-lactam ring. The inactivation of amoxicillin by beta-lactamases of gram negative anaerobic bacteria can be circumvented by the addition of clavulanic acid, a beta-lactamases inhibitor. Thus, most of these bacteria are susceptible to this combination. The aim of this study was to investigate the concentrations of amoxicillin and clavulanic acid in gingival crevicular fluid (GCF). These concentrations were measured in 20 patients with rapidly progressive periodontitis 1 h after a dose of 500 mg (1 tablet Augmentin) on day 0 and 1 h after the 10th intake on day 3. For the sampling of GCF, Periopapers were introduced in 16 gingival sites per subject and time. The GCF volumes collected were estimated using the Periotron 6000. A high performance liquid chromatography method has been developed for the determination of amoxicillin and clavulanic acid in microsamples (1 to 10 microliters) of GCF. The concentrations of amoxicillin and clavulanic acid were respectively, 14.05 micrograms ml-1 and 0.40 microgram ml-1 at day 0, 13.93 micrograms ml-1 and 0.37 microgram ml-1 at day 3. Effective levels of amoxicillin and clavulanic acid, well above the minimal inhibitory concentrations of some susceptible periodontal anaerobes (P. intermedia) involved in destructive periodontal diseases, are achieved following the multiple administration of amoxicillin combined with clavulanic acid.

[Moraxella catarrhalis: virulence and resistance mechanisms]

It is more than a century ago that Moraxella catarrhalis was discovered and described in some detail. However, it was not until the last decade that M. catarrhalis was recognized as a facultative pathogen, namely in otitis media (predominantly in children), sinusitis and nosocomial pneumonia in the group of elderly, debilitated patients. Liberation of endotoxin, histamine, and chemotactically active factors can be considered the major pathogenicity factors. The pathogen can protect itself, on the one hand by binding of the Clq subcomponent of the complement system followed by subsequent formation of a functionally inactive complex with Cl, and on the other hand by inactivation of the terminal (lytic) complement complexes by means of a specific protein on the surface of the outer cell wall. Routine diagnostic procedures require, above all, culture of the pathogen: up to now the detection of specific IgA-antibodies has not been routinely available. More than half of the clinical isolates are known to exhibit beta-lactamase production (BRO-enzymes). This is the reason why combinations of a penicillin compound with a beta-lactamase inhibitor, the group of the newer cephalosporins (including the orally active ones), doxycycline and the macrolides are therapeutically effective.

Prevalence of antimicrobial resistance among 723 outpatient clinical isolates of Moraxella catarrhalis in the United States in 1994 and 1995: results of a 30-center national surveillance study

Seven hundred twenty-three isolates of Moraxella catarrhalis obtained from outpatients with a variety of infections in 30 medical centers in the United States between 1 November 1994 and 30 April 1995 were characterized in a central laboratory. The overall rate of beta-lactamase production was 95.3%. When the National Committee for Clinical Laboratory Standards MIC interpretive breakpoints for Haemophilus influenzae were applied, percentages of strains found to be susceptible to selected oral antimicrobial agents were as follows: azithromycin, clarithromycin, and erythromycin, 100%; tetracycline and chloramphenicol, 100%; amoxicillin-clavulanate, 100%; cefixime, 99.3%; cefpodoxime, 99.0%; cefaclor, 99.4%; loracarbef, 99.0%; cefuroxime, 98.5%; cefprozil, 94.3%; and trimethoprim-sulfamethoxazole, 93.5%.

The beta-lactamases of Moraxella (Branhamella) catarrhalis isolated from Danish children

Two distinct beta-lactamases have been isolated from Moraxella catarrhalis: the stronger acting BRO-1 enzyme and the weaker acting BRO-2. Several reports have noted an effect of penicillin and ampicillin on infections caused by M. catarrhalis in spite of the presence of beta-lactamase production. The purpose of this work was to charaterize the beta-lactamases of M. catarrhalis isolated from Danish children regarding type and susceptibility, and to relate these findings to the eradication of beta-lactamases-producing strains by use of antibiotic treatment with penicillin or ampicillin. MICs for penicillin V, ampicillin, cefuroxime and amoxicillin/clavulanic acid (2:1) were determined in 70 strains of M. catarrhalis: 46 strains from children with lower respiratory tract infection (LRTI) and 24 strains from respiratory healthy children, beta-lactamase production was found in 59 strains. The BRO-1 enzyme was identified by isoelectric focusing in 55 strains (93.2%) and BRO-2 in 3 strains (5.1%); in 1 strain no isoelectric bands were produced. All strains were susceptible to cefuroxime and amoxicillin/clavulanic acid, and non-beta-lactamase-producing strains were susceptible to penicillin and ampicillin. For the beta-lactamase-producing strains, MIC50 of penicillin was 8.0 micrograms/ml, while MIC50 of ampicillin was 1.0 microgram/ml and MIC90 of ampicillin was 2.0 micrograms/ml. M. catarrhalis was more often eradicated from the children who received antibiotic treatment with penicillin or ampicillin than from those who did not receive any treatment, indicating an in vivo effect of penicillin and ampicillin in spite of the beta-lactamase production.

Molecular characterization of the BRO beta-lactamase of Moraxella (Branhamella) catarrhalis

A rapid increase in the prevalence of beta-lactamase-producing Moraxella (Branhamella) catarrhalis strains has been noticed during the last decades. Today, more than 80% of strains isolated worldwide produce beta-lactamase. To investigate beta-lactamase(s) of M. catarrhalis at the molecular level, the BRO-1 beta-lactamase gene (bla) was isolated as part of a 4,223-bp HindIII fragment. Sequence analysis indicated that bla encodes a polypeptide of 314 amino acid residues. Insertional inactivation of bla in M. catarrhalis resulted in complete abrogation of beta-lactamase production and ampicillin resistance, demonstrating that bla is solely responsible for beta-lactam resistance. Comparison with other beta-lactamases suggested that M. catarrhalis beta-lactamase is a unique enzyme with conserved residues at the active sites. The presence of a signal sequence for lipoproteins suggested that it is lipid modified at its N terminus. In keeping with this assumption was the observation that 10% of beta-lactamase activity was found in the membrane compartment of M. catarrhalis. M. catarrhalis strains produce two types of beta-lactamase, BRO-1 and BRO-2, which differ in their isoelectric points. The BRO-1 and BRO-2 genes from two ATCC strains of M. catarrhalis were sequenced, and only one amino acid difference was found between the predicted products. However, there was a 21-bp deletion in the promoter region of the BRO-2 gene, possibly explaining the lower level of production of BRO-2. The G + C content of bla (31%) was significantly lower than those of the flanking genes (47 and 50%), and the overall G + C content of the M. catarrhalis genome (41%). These results indicate that bla was acquired by horizontal gene transfer from another, still unknown species.

[beta-Lactamases of Branhamella catarrhalis and their phenotypic implications]

Of the 50 strains of beta-lactamase-producing Branhamella catarrhalis isolated at Saint Joseph's Hospital (Paris) that were studied, 94% produced BRO-1 type beta-lactamase and 6% produced the BRO-2 type. We examined the transfer of BRO-1 and BRO-2 genes and found that, among 7 donor strains producing BRO-1, all were able to transfer the gene for BRO-1 production by conjugation. Of the 4 donor strains producing BRO-2, 2 were able to transfer the gene for BRO-2 production by conjugation. Three BRO-1 beta-lactamase-producing transformants were obtained from total DNA extracted from 3 strains producing BRO-1. Plasmid bands were demonstrated in strains of B. catarrhalis, but no change in plasmid profiles was seen in beta-lactamase-positive recombinants, supporting previous studies that suggested the beta-lactamases are chromosomal. In vitro activity of oral beta-lactams was tested for 67 strains of B. catarrhalis (56 beta-lactamase-producing strains). Cefixime, cefpodoxime and the combination ampicillin-clavulanic acid were very active against the beta-lactamase-producing strains. BRO-1 beta-lactamase appears to affect the activity of cefaclor, cefuroxime and loracarbef. BRO-2 beta-lactamases have no effect on the activity of these cephalosporins. Cefixime and cefpodoxime seemed the least affected by beta-lactamase production.

Characterization of cell-bound papain-soluble beta-lactamases in BRO-1 and BRO-2 producing strains of Moraxella (Branhamella) catarrhalis and Moraxella nonliquefaciens

In Moraxella (Branhamella) catarrhalis and Moraxella nonliquefaciens strains isolated from clinical specimens in the south of Sweden two variants of beta-lactamase were distinguished by isoelectric focusing (IEF). The BRO-1 (Ravasio type) enzyme was the most common in Branhamella catarrhalis, constituting about 90% of the beta-lactamase found in this species, while the BRO-2 enzyme (1908 type) was as common as BRO-1 in Moraxella nonliquefaciens. The determinants mediating the production of BRO-1 and BRO-2 were both transferable by conjugation. Cell-bound beta-lactamase from reference strains producing BRO-1 and BRO-2 could be solubilized by papain digestion. The isoelectric point of the solubilized enzymes differed distinctly between BRO-1 (pI 6.5) and BRO-2 (pI 6.9). The molecular species of BRO-1 and BRO-2 released by papain digestion were purified by affinity chromatography with phenylboronic acid agarose gel. They had identical molecular weights of approximately 28,000. Their kinetic constants were indistinguishable for a number of substrates and beta-lactamase inhibitors.

Antibacterial activity of cefpodoxime against Branhamella catarrhalis

The antibacterial activity of cefpodoxime against Branhamella catarrhalis was studied. All of the 65 clinical isolates tested were inhibited at and below 1.56 micrograms/ml, both at 10(7) and at 10(5) CFUs. The following was further studied on B. catarrhalis N-5 which showed average susceptibility to each drug examined. Bactericidal activity was observed at and above the MIC. Scanning and transmission electron microscopy revealed morphological changes, such as cellular swelling, bleb formation, inhibition of septum formation, and lysis, of the cells exposed to cefpodoxime at concentrations around the MIC. Cefpodoxime was poorly hydrolyzed by the beta-lactamase and it showed affinity for two penicillin-binding proteins that had approximate molecular weights of 83 and 74 kilodaltons, with I50 values of 3.7 and 2.1 micrograms/ml, respectively.

Branhamella catarrhalis: an organism gaining respect as a pathogen

Branhamella catarrhalis was formerly regarded as a common, essentially harmless inhabitant of the pharynx. This misapprehension was caused, in part, by confusion with another pharyngeal resident, Neisseria cinerea. The two organisms can now be differentiated by the positive reactions of B. catarrhalis in tests for nitrate reduction and hydrolysis of tributyrin and DNase. B. catarrhalis is currently recognized as the third most frequent cause of acute otitis media and acute sinusitis in young children. It often causes acute exacerbations of chronic bronchopulmonary disease in older or immunocompromised adults and is incriminated occasionally in meningitis, endocarditis, bacteremia, conjunctivitis, keratitis, and urogenital infections. Virulence-associated factors, such as pili, capsules, outer membrane vesicles, iron acquisition proteins, histamine-synthesizing ability, resistance to the bactericidal action of normal human serum, and binding to the C1q complement component, have been identified in some strains. beta-Lactamase producing strains, first detected in 1976, have risen to approximately 75% worldwide. Thus far, however, practically all American strains of B. catarrhalis remain susceptible to alternative antibiotics. A possible selective advantage of recent isolates is their reportedly heightened tendency for adherence to oropharyngeal cells from patients with chronic bronchopulmonary disease.

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.

In vitro activity of cefpodoxime proxetil (U-76,252; CS-807) against clinical isolates of Branhamella catarrhalis

Cefpodoxime proxetil (U-76,252; CS-807) is a new esterified oral cephem antibiotic with a broad antibacterial spectrum. Since data regarding the activity of cefpodoxime against Branhamella catarrhalis are limited, we tested its activity against 200 B. catarrhalis isolates. The drug was highly active against beta-lactamase-negative and -positive isolates; 99% of all strains tested showed a cefpodoxime proxetil MIC of less than or equal to 2.0 micrograms/ml.

Beta-lactamase inhibitors from laboratory to clinic

beta-Lactamases constitute the major defense mechanism of pathogenic bacteria against beta-lactam antibiotics. When the beta-lactam ring of this antibiotic class is hydrolyzed, antimicrobial activity is destroyed. Although beta-lactamases have been identified with clinical failures for over 40 years, enzymes with various abilities to hydrolyze specific penicillins or cephalosporins are appearing more frequently in clinical isolates. One approach to counteracting this resistance mechanism has been through the development of beta-lactamase inactivators. beta-Lactamase inhibitors include clavulanic acid and sulbactam, molecules with minimal antibiotic activity. However, when combined with safe and efficacious penicillins or cephalosporins, these inhibitors can serve to protect the familiar beta-lactam antibiotics from hydrolysis by penicillinases or broad-spectrum beta-lactamases. Both of these molecules eventually inactivate the target enzymes permanently. Although clavulanic acid exhibits more potent inhibitory activity than sulbactam, especially against the TEM-type broad-spectrum beta-lactamases, the spectrum of inhibitory activities are very similar. Neither of these inhibitors acts as a good inhibitor of the cephalosporinases. Clavulanic acid has been most frequently combined with amoxicillin in the orally active Augmentin and with ticarcillin in the parenteral beta-lactam combination Timentin. Sulbactam has been used primarily to protect ampicillin from enzymatic hydrolysis. Sulbactam has been used either in the orally absorbed prodrug form as sultamicillin or as the injectable combination ampicillin-sulbactam. Synergy has been demonstrated for these combinations for most members of the Enterobacteriaceae, although those organisms that produce cephalosporinases are not well inhibited. Synergy has also been observed for Neisseria gonorrhoeae, Haemophilus influenzae, penicillinase-producing Staphylococcus aureus, and anaerobic organisms. These antibiotic combinations have been used clinically to treat urinary tract infections, bone and soft-tissue infections, gonorrhea, respiratory infections, and otitis media. Gastrointestinal side effects have been reported for Augmentin and sultamicillin; most side effects with these agents have been mild. Although combination therapy with beta-lactamase inactivators has been used successfully, the problem of resistance development to two agents must be considered. Induction of cephalosporinases can occur with clavulanic acid. Permeability mutants could arise, especially with added pressure from a second beta-lactam.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of beta-lactamase activity among clinical isolates of Branhamella catarrhalis with six different beta-lactamase assays

A total of 74 different clinical isolates of Branhamella catarrhalis were examined for their ability to produce beta-lactamase by six different beta-lactamase assays. These included a conventional tube and disk test, in which the chromogenic cephalosporin nitrocefin was used as a substrate; a disk procedure, in which pyridinium-2-azo-p-dimethylanaline cephalosporin was used as a substrate; broth and disk acidometric methods; and a conventional tube iodometric assay. A total of 58 of the study isolates produced beta-lactamase. In all cases, positive results were obtained with the nitrocefin tube and disk assays after 1 min. With the pyridinium-2-azo-p-dimethylanaline cephalosporin disk test, 57 of the 58 beta-lactamase-producing strains yielded a positive reaction in 1 min; the remaining strain was positive after 10 min. None of the beta-lactamase-producing strains produced positive reactions by either the broth or disk acidometric methods after 1 min. With the broth test, 10 min was required for positive test results for 42 strains; 30 min was necessary for 16 strains. By the disk acidometric procedure, all 58 strains were positive after 10 min. Of 58 beta-lactamase-producing strains, 30 were positive by the iodometric assay after 1 min, 13 strains required 10 min, and 4 strains were detected as being beta-lactamase positive only after 30 min. One beta-lactamase-producing strain remained negative by the iodometric method. Among the 16 strains of B. catarrhalis that lacked beta-lactamase that were examined in this study, no false-positive results were obtained by any of the six assays.

In vitro activity of amoxicillin plus clavulanic acid against Haemophilus influenzae and Branhamella catarrhalis

The in vitro activity of amoxicillin in the presence of clavulanic acid against clinical isolates of Haemophilus influenzae and Branhamella catarrhalis was assessed in comparison with ampicillin, amoxicillin, cefaclor and erythromycin. The isolates were selected so as to yield equal numbers of beta-lactamase producing and non-beta-lactamase producing strains of the two species. MICs obtained by agar dilution indicated that amoxicillin in the presence of clavulanic acid was the most active of the drugs tested. Clavulanic acid potentiated the activity of amoxicillin against beta-lactamase-producing strains of both Haemophilus influenzae and Branhamella catarrhalis. Further studies on a few strains of each species revealed that the beta-lactamase of Haemophilus influenzae (TEM-1) rapidly inactivated ampicillin and slowly inactivated cefaclor but not cefuroxime. The Branhamella catarrhalis enzyme rapidly inactivated cefaclor, ampicillin and to some extent cefuroxime. Clavulanic acid afforded protection against the beta-lactamase action of both species when beta-lactam antibiotics were added to bacterial cultures.

Disk diffusion susceptibility of Branhamella catarrhalis and relationship of beta-lactam zone size to beta-lactamase production

We tested 231 isolates of Branhamella catarrhalis for beta-lactamase production and drug susceptibility by the National Committee for Clinical Laboratory Standards disk diffusion method. The nitrocephin disk (Cefinase) identified beta-lactamase in 98% of the enzyme-producing strains, and a zone diameter of inhibition of less than or equal to 29 mm for penicillin correctly predicted the presence of beta-lactamase in 99% of the isolates. No resistance to erythromycin, tetracycline, trimethoprim-sulfamethoxazole, or amoxicillin-clavulanic acid was observed.

Purification and properties of a beta-lactamase produced by Branhamella catarrhalis

A beta-lactamase from Branhamella catarrhalis was purified by column chromatography. The purified enzyme hydrolyzed penicillins, such as ampicillin, carbenicillin, and piperacillin, more rapidly than cephalosporins. Furthermore, the enzyme hydrolyzed cefotaxime and cefmenoxime. The molecular weight of the enzyme was 33,000. The pI was 5.4.

Detection, distribution and inhibition of Branhamella catarrhalis beta-lactamases

Beta-lactamase-producing isolates of Branhamella catarrhalis were first detected in France in 1977. The frequency of beta-lactamase producers has increased, especially since 1980. An agar iodometric test, a fast chromogenic test and an acidimetric test were used to assess the beta-lactamase-producing capabilities of 188 isolates of B. catarrhalis obtained mainly from sputum and the pharynx. Data from the first 2 procedures indicated positive beta-lactamase activity for all 49 strains of B. catarrhalis identified, but there were some discrepancies in the acidimetric test results. Evidence from a diffusion technique showed significant increases in the inhibition diameters surrounding filter discs impregnated with amoxycillin in the presence of clavulanic acid, or with ampicillin in the presence of sulbactam, compared with discs of the penicillins used alone. Two types of enzyme activity emerged from examination of isoelectric focusing patterns. Type I, having pI values of 5.35, 5.55 and 5.85, accounted for 87.2% of the enzyme-producing isolates. Type II, with pIs of 5.5, 5.9 and 6.25, occurred in 12.8% of isolates and appeared to be less widely distributed. The beta-lactamase inhibitors clavulanic acid and sulbactam in combination with benzylpenicillin produced potentiated effects, as demonstrated by significant reductions in MIC (33- and 44-fold decreases, respectively). Higher concentrations of each inhibitor similarly affected the MICs of amoxycillin. A weak synergy occurred with cefoxitin, a beta-lactamase-resistant beta-lactam antibiotic, and the 2 beta-lactamase inhibitors. Because B. catarrhalis has been shown to be a beta-lactamase-producing pathogenic organism, the addition of enzyme inhibitors, such as clavulanic acid and sulbactam, to standard therapy may be beneficial.

Inhibition of the beta-lactamases of Branhamella catarrhalis by clavulanic acid and other inhibitors

The beta-lactamases of Branhamella catarrhalis Ravasio and strain 1908 were readily inhibited by low concentrations of sulbactam, beta-halopenicillanic acids, MM 13902 and clavulanic acid. More detailed studies on the interaction of the Ravasio beta-lactamase with clavulanic acid demonstrated that the enzyme had high affinity for the inhibitor (Ki = 0.07 mumol/L) and was rapidly inhibited (t1/2 = 21 sec, kinhib. = 0.033/sec). Two types of enzyme-inhibitor complex were formed, a transiently stable species (t1/2 = 5.3 minutes at pH 7.3 and 37 degrees C) and a more stable species (t1/2 approximately equal to 2 hours at pH 7.3 and 37 degrees C). Irreversible inactivation of the enzyme was not achieved. Permeability studies on whole cells showed that beta-lactam antibiotics and beta-lactamase inhibitors readily penetrated the outer membrane of B. catarrhalis.

Plasmid-mediated beta-lactamase in Branhamella catarrhalis

The plasmid-mediated beta-lactamase in Branhamella catarrhalis (BRO-1), also occurring in Moraxella nonliquefaciens, differs from other known plasmid-mediated beta-lactamases in Gram-negative bacteria regarding substrate profile and isoelectric point. B. catarrhalis strains previously reported to produce beta-lactamases deviating from BRO-1 were tested, and the beta-lactamases did not differ significantly from BRO-1 in substrate profile, isoelectric point or relative substrate affinity index (RSAI). Further investigations of strains of various geographic origin should be undertaken. RSAI seems to be a useful tool for screening of beta-lactamases in B. catarrhalis since values for a large number of strains can easily be determined. The previously reported conjugational transfer of BRO-1 production within species B. catarrhalis and from M. nonliquefaciens to B. catarrhalis was confirmed. Four bands of extrachromosomal DNA were regularly detected by agarose gel electrophoresis in beta-lactamase-producing as well as in beta-lactamase-negative strains of B. catarrhalis and M. non-liquefaciens, provided that the excessive nuclease activity in the preparations was inhibited.

Classification of beta-lactamases from Branhamella catarrhalis in relation to penicillinases produced by other bacterial species

Branhamella catarrhalis strains resistant to commonly used penicillins, and presently isolated, produce a beta-lactamase. Most of these enzymes are chromosomally mediated, but a plasmid-mediated beta-lactamase has been described (enzyme BRO-1). With reference to isoelectric points, 7 different enzymes have been identified: 6 chromosomally mediated and 1 plasmid-mediated. Nevertheless, they have many common properties, such as being biosynthesised constitutively but with a low level of production. They have a penicillinase-type profile, and are strongly inhibited by clavulanic acid.

Analysis of the relationship between ampicillin resistance and beta-lactamase production in Branhamella catarrhalis

23 strains of Branhamella catarrhalis, mainly isolated from patients with acute exacerbations of chronic bronchitis, were studied. The strains were selected on the basis of a positive beta-lactamase reaction using the cefinase disc or the nitrocefin method. No bands were visible by isoelectric focusing of the crude enzyme extracts of strains showing a weak positive reaction with the cefinase method. In the 15 remaining strains, at least 6 different isoelectric focusing patterns could be detected. Four strains showed a pattern similar to that of the Ravasio strain, the most common type in a previous study. The most prevalent type in this study, present in 5 strains, demonstrated an isoelectric focusing pattern quite different from those described so far: a main band at pI 5.28 and 2 minor bands at pI 5.71 and 6.37. Two beta-lactamase-positive, but ampicillin-sensitive strains (MIC = 0.064 mg/L) showed different isoelectric focusing patterns, pI = 4.93 and 5.43, respectively, but similar substrate profiles.

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.

Amoxicillin-clavulanic acid in the treatment of lower respiratory tract infections caused by beta-lactamase-positive Haemophilus influenzae and Branhamella catarrhalis

Twenty-one adult patients hospitalized with lower respiratory tract infections due to Branhamella catarrhalis or Haemophilus influenzae or both were treated with the combination of oral amoxicillin and potassium clavulanate (Augmentin) in an open, noncomparative clinical trial. Diseases included pneumonia, empyema, and exacerbations of bronchiectasis and chronic lung disease. Thirteen of 16 B. catarrhalis and six of nine H. influenzae isolates were beta-lactamase positive. The patients with B. catarrhalis were treated for a mean of 5.3 days, and those with H. influenzae were treated for a mean of 7.0 days. The overall response to therapy was excellent, with 18 of 19 beta-lactamase-producing strains eradicated on therapy. One patient secondarily infected with Pseudomonas aeruginosa was a clinical failure, and two patients with H. influenzae who became culture positive again after therapy were considered microbiologic failures. Gastrointestinal side effects (especially nausea) were common, although all patients completed a course of therapy. Sputum levels of amoxicillin were surprisingly low (less than 0.05 to 0.54 micrograms/ml), a finding which may explain the high relapse rate (22%) seen with H. influenzae, as these are below the usual MICs of amoxicillin for this organism. The combination of amoxicillin plus potassium clavulanate appears to be an excellent drug for treatment of beta-lactamase-producing strains of these two species, although mild gastrointestinal side effects are common.

Multiresistance plasmid from commensal Neisseria strains

Antibiotic-resistant commensal strains of Neisseria spp. and Branhamella catarrhalis were isolated from throat cultures, on the basis of their capacity to grow in the presence of penicillin, streptomycin, or sulfamethoxazole-trimethoprim. Several strains, which belonged to different species of Neisseria, were resistant to beta-lactams, streptomycin, sulfamethoxazole, and trimethoprim, harbored a 6.0-megadalton plasmid with identical HinfI restriction patterns, and produced beta-lactamase and streptomycin phosphotransferase. The resistance determinants for beta-lactams, streptomycin, and sulfamethoxazole, but not for trimethoprim, were transferred from all these strains to Escherichia coli by conjugation or transformation. The resulting transconjugants or transformants acquired the plasmid and the capacity to produce beta-lactamase and streptomycin phosphotransferase. The 6.0-megadalton plasmid complemented a mutation which determines production of thermosensitive dihydropteroate synthetase in E. coli. We conclude that an R plasmid coding for beta-lactamase, streptomycin phosphotransferase, and a sulfonamide-resistant dihydropteroate synthetase is common to these strains.

Amoxicillin and potassium clavulanate: an antibiotic combination. Mechanism of action, pharmacokinetics, antimicrobial spectrum, clinical efficacy and adverse effects

The combination of amoxicillin and potassium clavulanate will soon be marketed in 2:1 and 4:1 fixed ratio dosage forms. In vitro and in vivo evidence suggests that clavulanic acid, a potent inhibitor of many bacterial beta-lactamase enzymes, will increase the spectrum of amoxicillin to include, at achievable serum concentrations, Haemophilus influenzae, H. ducreyi, Neisseria gonorrhoeae, Staphylococcus aureus and Branhamella catarralis and, at achievable urine levels, many beta-lactamase-producing strains of E. coli, Klebsiella, Proteus and Citrobacter. Both amoxicillin and clavulanic are well absorbed after oral administration, reach peak serum levels in 40-120 min and have similar half-lives of 45 to 90 min. This combination will be suitable for the treatment of complicated urinary tract infections, otitis media, sinusitis and respiratory tract infections. However, precise recommendations for its use will need to await further clinical trials that compare amoxicillin/clavulanate to alternative therapies.

Efficacy of BRL 25000 against Serratia marcescens, Enterobacter cloacae, and Citrobacter freundii in urinary tract infections

Synergism between amoxicillin and clavulanic acid was not expected against cephalosporinase-producing bacterial strains because clavulanic acid has little inhibitory action on cephalosporinases. However, in a clinical trial of BRL 25000 (amoxicillin-clavulanic acid), excellent results were obtained in complicated urinary tract infections caused by Serratia marcescens, Enterobacter cloacae, and Citrobacter freundii strains which produced cephalosporinase and were highly resistant to amoxicillin alone. The good clinical efficacy of BRL 25000 in such urinary tract infections was probably due to the fact that the urinary concentration of clavulanic acid was higher than its minimal inhibitory concentrations for these strains.

Biochemistry and action of clavulanic acid

The destruction of amoxycillin by beta-lactamase action represents an important mechanism of bacterial resistance to the drug. Data is presented to illustrate that clavulanic acid used in the form of its potassium salt inhibits the amoxycillin destroying action of many different types of beta-lactamase for example: the staphylococcal enzyme, the clinically important plasmid mediated enzymes of the TEM, SHV, OXA and PSE types and the chromosomally controlled enzymes produced by Proteus mirabilis and Klebsiella pneumoniae. The mechanisms by which clavulanic acid inhibits beta-lactamases and potentiates the antibacterial action of amoxycillin are discussed.