High-level tetracycline resistance in Neisseria gonorrhoeae is result of acquisition of streptococcal tetM determinant

Rapid nucleic acid assay for detection of bacteria with tetM-mediated tetracycline resistance

A novel nucleic acid assay has been developed to screen bacterial populations for the presence of the tetM structural gene. The method involves the specific hybridization of several synthetic oligonucleotides to the gene in a crude bacterial lysate solution. As few as 1.5 x 10(4) CFU can be detected with the assay.

Tetracycline and erythromycin resistance among clinical isolates of Branhamella catarrhalis

We reviewed tetracycline and erythromycin disk diffusion susceptibility of 457 isolates of Branhamella catarrhalis. Four isolates were resistant to tetracycline, with MICs for two available isolates of 16 micrograms/ml. Sixteen isolates were in the moderately susceptible range for erythromycin, with an MIC for one available isolate being greater than 8 micrograms/ml. These are the first tetracycline- and (by MIC) erythromycin-resistant B. catarrhalis isolates reported from the United States.

Plasmid-mediated Tet M in Haemophilus ducreyi

A tetracycline-resistant Haemophilus ducreyi strain isolated in the United States was shown to carry a 34-megadalton plasmid which hybridized with the 1.8-kilobase KpnI-HindIII Tet M probe. The complete Tn916 transposon hybridized with five different bands from this plasmid, suggesting homology throughout the length of the transposon.

Associations between serotype and susceptibility to antibiotics of Neisseria gonorrhoeae

A serological classification scheme for Neisseria gonorrhoeae was used to investigate the epidemiological associations between gonococcal serotype and other bacterial and host characters. Six hundred and fifty clinical isolates of non-penicillinase producing N gonorrhoeae from the Praed Street Clinic, St Mary's Hospital, were included in this study. The strains collected represented 41 serovars, although 485 (75%) of the 650 strains belonged to five serovars. Strains of serovar IA-1/2 were commonly isolated from the cervix and tended to be sensitive to penicillin and moderately resistant to erythromycin. Strains of serovar IB-1 showed bimodal patterns of susceptibility to both penicillin and erythromycin and were obtained equally from all anatomical sites. Strains of serovar IB-2 were isolated more often from the rectum and were associated with homosexually acquired infections, whereas those of serovar IB-3 were sensitive to erythromycin and were rarely isolated from the rectum. Strains of IB-5/7 were more resistant to penicillin and erythromycin than strains of other serovars. The serological classification of N gonorrhoeae is thus a powerful tool that may be used to study biological characteristics of the gonococcus, such as susceptibility to antimicrobials and site tropism.

Chancroid and Haemophilus ducreyi

Haemophilus ducreyi is the causative agent of chancroid, one of the genital ulcerative diseases. H. ducreyi is the major cause of genital ulcer disease in Africa and Southeast Asia and is of increasing concern in the United States. Definitive diagnosis of chancroid requires the isolation and identification of H. ducreyi, but isolation of this organism is difficult and the available medium is not optimal for all strains. Fluorescent antibody and serologic tests are of limited value. In general, our knowledge of this organism is rather limited, and indeed, recent studies have questioned the placement of H. ducreyi in the genus Haemophilus. H. ducreyi has relatively few biochemical activities, and epidemiologic studies are limited because there are limited phenotypic markers available for strain typing. Specific virulence factors of H. ducreyi have yet to be identified. Antimicrobial resistance in H. ducreyi is of special concern, as this organism has acquired both gram-negative and gram-positive resistance determinants. In addition, some of these determinants can be mobilized and transferred to other Haemophilus species or to Neisseria gonorrhoeae.

Evidence for broken minocycline by NMR and HPLC techniques: a new additional resistance mechanism mediated by tetB determinant

As demonstrated by microbiological assays, a decrease in the active minocycline level occurs in spent media from each Escherichia coli K12 recipient containing one of 10 different plasmids bearing tetB determinants. No such decrease was detected when tetA, C, D or E determinants were tested under the same conditions. Likewise, no decrease in tetracycline or doxycycline levels was detected when 20 plasmids bearing tetA to E determinants were tested. Studies carried out by nuclear magnetic resonance and high pressure liquid chromatography proved that minocycline is broken by a mechanism mediated by the tetB determinant. This new mechanism can be considered as additional to the active efflux of minocycline.

Multicenter randomized study of single-dose ofloxacin versus amoxicillin-probenecid for treatment of uncomplicated gonococcal infection

The safety and efficacy of ofloxacin, 400 mg orally, were compared with those of amoxicillin, 3.0 g, plus probenecid, 1.0 g orally, as single-dose therapy in 201 heterosexual patients (101 men and 100 women) with uncomplicated gonococcal infection. Treatment groups were comparable in age, duration of symptoms, number of sexual partners within the previous month, and number of previous episodes of sexually transmitted diseases. The cure rate for men treated with ofloxacin was 98% (47 of 48), and that for women was 100% (52 of 52). Cure rates for both men and women treated with amoxicillin-probenecid were 96% (51 of 53 men; 46 of 48 women). All 13 patients with positive rectal cultures and 7 of 8 patients with positive pharyngeal cultures treated with ofloxacin were cured. Neither regimen reliably eradicated coexistent infection with Chlamydia trachomatis. The MIC of ofloxacin for all but two of 198 pretreatment isolates was 0.3 microgram/ml or less. The MIC of amoxicillin for 90% of isolates tested was 1.0 microgram/ml. Single oral doses of ofloxacin and of amoxicillin plus probenecid were equally effective for treatment of urethral and cervical gonorrhea. Ofloxacin appears promising as treatment for rectal and pharyngeal infection, but studies with larger numbers of patients with rectal or pharyngeal infection or both are required for confirmation. Relative contraindications in children and possibly pregnant women plus the potential for single-step, high-level resistance may limit the usefulness of quinolone therapy for gonorrhea.

Susceptibilities of genital mycoplasmas to the newer quinolones as determined by the agar dilution method

The increasing resistance of genital mycoplasmas to tetracycline poses a problem because tetracycline is one of the few antimicrobial agents active against Mycoplasma hominis, Ureaplasma urealyticum, chlamydiae, gonococci, and other agents of genitourinary-tract disease. Since the quinolones are a promising group of antimicrobial agents, the susceptibilities of M. hominis and U. urealyticum to the newer 6-fluoroquinolones were determined by the agar dilution method. Ciprofloxacin, difloxacin, and ofloxacin had good activity against M. hominis, with the MIC for 50% of isolates tested (MIC50) being 1 microgram/ml. Fleroxacin, lomefloxacin, pefloxacin, and rosoxacin had MIC50s of 2 micrograms/ml. Enoxacin, norfloxacin, and amifloxacin had MIC50s of 8 to 16 micrograms/ml, and cinoxacin and nalidixic acid were inactive (MIC50, greater than or equal to 256 micrograms/ml). Overall, the activities of 6-fluoroquinolones for ureaplasmas were similar to those for M. hominis, with MICs being the same or twofold greater. The most active 6-fluoroquinolones against ureaplasmas were difloxacin, ofloxacin, and pefloxacin, with MIC50s of 1 to 2 micrograms/ml. Ciprofloxacin was unusual in that the MIC50 for M. hominis was 1 microgram/ml, whereas the MIC50 for ureaplasmas was 8 micrograms/ml. Since the MIC50s for the most active quinolones approximate achievable concentrations in blood and urine, quinolones have promise in treating mycoplasmal infections.

Occurrence of the Campylobacter resistance gene tetO in Enterococcus and Streptococcus spp

The distribution of nucleotide sequences related to tetK, tetL, tetM, and tetO was studied by dot blot hybridization in 178 strains of Streptococcus and Enterococcus spp. that were resistant to tetracycline. The tetO gene, which is responsible for tetracycline resistance in Campylobacter spp., was detected in six Streptococcus strains and two Enterococcus strains, in which it was borne by similar plasmids. This observation confirms our previous proposal that tetO originated in gram-positive cocci. tetM, the most prevalent resistance gene, was present alone in 109 strains and associated with tetL in 33 strains in which the two genes contributed cooperatively to high-level tetracycline resistance. tetL was present alone in five Enterococcus strains, and tetK was detected in a single Streptococcus strain. The existence of 22 strains that did not hybridize to the probes suggest that tetracycline resistance in streptococci and enterococci involves additional gene classes as well.

Conjugative plasmid transfer from Enterococcus faecalis to Escherichia coli

The possibility of transfer of genetic information by conjugation from gram-positive to gram-negative bacteria was investigated with a pBR322-pAM beta 1 chimeric plasmid, designated pAT191. This shuttle vector, which possesses the tra functions of the streptococcal plasmid pAM beta 1, was conjugatively transferred from Enterococcus faecalis to Escherichia coli with an average frequency of 5 x 10(-9) per donor colony formed after mating.

Transfer of beta-lactamase plasmids from Neisseria gonorrhoeae to Neisseria meningitidis and commensal Neisseria species by the 25.2-megadalton conjugative plasmid

Two highly tetracycline-resistant, beta-lactamase-producing Neisseria gonorrhoeae strains were used as donors for conjugation with Neisseria meningitidis and commensal Neisseria species. We found that both strains were able to transfer the 4.4- and 3.2-megadalton beta-lactamase plasmids to the recipients tested, with frequencies between 10(-1) and 10(-9).

Tetracycline resistance and TetM in oral anaerobic bacteria and Neisseria perflava-N. sicca

Tetracycline-resistant organisms isolated from six patients with periodontal disease included Bacteroides spp., Eubacterium spp., Fusobacterium nucleatum, Neisseria perflava-N. sicca, Peptostreptococcus anaerobius, Veillonella parvula, and facultative streptococci. All but the Bacteroides spp. and Eubacterium spp. hybridized with the TetM determinant. An additional 417 bacterial strains were screened, and 4% of both the oral streptococci and the Fusobacterium spp. hybridized with the TetM probe.

Construction of shuttle cloning vectors for Bacteroides fragilis and use in assaying foreign tetracycline resistance gene expression

Shuttle vectors capable of replication in both Escherichia coli and Bacteroides fragilis have been developed. Conjugal transfer of these plasmids from E. coli to B. fragilis is facilitated by inclusion of the origin of transfer of the IncP plasmid RK2. The vectors pDK1 and pDK2 provide unique sites for cloning selectable markers in Bacteroides. pOA10 is a cosmid vector containing the replication region of pCP1 necessary for maintenance in Bacteroides. pDK3, pDK4.1, and pDK4.2 contain the Bacteroides clindamycin resistance gene allowing selection and maintenance in B. fragilis of plasmids containing inserted DNA fragments. pDK3 was used to test the expression in B. fragilis of five foreign tetracycline resistance (TcR) genes. The tetA, -B, and -C markers from facultative gram-negative bacteria, as well as a TcR determinant from Clostridium perfringens, did not express TcR in B. fragilis. The tetM gene, originally described in streptococci, encoded a small but reproducible increase of TcR in Bacteroides. These studies demonstrate the utility of shuttle vectors for introducing cloned genes into Bacteroides and underscore the differences in gene expression in these anaerobes.

Dispersal in Campylobacter spp. of aphA-3, a kanamycin resistance determinant from gram-positive cocci

DNA annealing studies indicated that kanamycin resistance in Campylobacter strains from various geographical areas is encoded by a gene structurally related to aphA-3 of gram-positive cocci. This finding confirms the transfer of genetic material between gram-positive and gram-negative bacteria under natural conditions.

Biotypes, serotypes, and susceptibility to antibiotics of 60 Haemophilus influenzae strains from genitourinary tracts

Sixty strains of Haemophilus influenzae were isolated from the genitourinary tracts of adults: 19 from cervicovaginal secretions, one from a woman with bartholinitis, 37 from urethral exudates, and three from urine. Non-capsulated strains were recovered predominantly, and biotype III accounted for 28 isolates and biotype IV for 25. Many of the H influenzae strains were found to be resistant to one or more of the antibiotics commonly used against sexually transmitted diseases. Resistance to tetracycline was prevalent and was found in 17 of the strains. Ten strains were ampicillin resistant and beta lactamase producing. Kanamycin resistance was less common (two strains). Trospectomycin (U-63366), a new spectinomycin analogue, was eight to 16 times more active than spectinomycin. All the quinolones tested were very active against all strains and may provide an effective alternative for the treatment of resistant H influenzae in genitourinary infections.

High-level tetracycline resistance resulting from TetM in strains of Neisseria spp., Kingella denitrificans, and Eikenella corrodens

Similar to Neisseria gonorrhoeae, tetracycline-resistant isolates of N. meningitidis, Kingella denitrificans, and Eikenella corrodens contained 25.2-megadalton plasmids carrying the TetM determinant. In contrast, tetracycline-resistant N. subflava biovar perflava-N. sicca and N. mucosa isolates carried the TetM determinant in the chromosome.

Evidence for natural gene transfer from gram-positive cocci to Escherichia coli

High-level resistance to macrolide-lincosamide-streptogramin type B (MLS) antibiotics in Escherichia coli BM2570 is due to the presence on the conjugative plasmid pIP1527 of the MLS resistance determinant ermBC, which is almost identical to the erm genes previously described in plasmid pAM77 from Streptococcus sanguis (ermAM) and in transposon Tn917 from Enterococcus faecalis (ermB). This gene and its regulatory region are located downstream from the insertion sequence IS1. The 23S rRNA methylase encoded by pIP1527 differs by three and six amino acids from those encoded by Tn917 and pAM77, respectively. Unlike the streptococcal elements which confer the inducible MLS phenotype, the ermBC gene is expressed constitutively in E. coli and Bacillus subtilis, due to several mutations in the regulatory region. Transcription of the ermBC gene starts from three different sites following three overlapping promoters which function in both E. coli and B. subtilis. Promoters P2 and P3 are located within the region homologous to pAM77 and Tn917, and P1 is a hybrid promoter constituted by -35 and -10 sequences located at the end of IS15 and in the streptococcal region, respectively. These results constitute evidence for the recent in vivo transfer from Streptococcus spp. to E. coli. This transfer could have been mediated by transposons such as Tn917 or Tn1545 from Streptococcus pneumoniae, which also bears an MLS determinant that is homologous to ermB. We speculate that the insertion sequences IS15 and IS1 could have played a role in the expression and dissemination of ermBC, which has been found in numerous strains of enterobacteria.

Host range of the conjugative 25.2-megadalton tetracycline resistance plasmid from Neisseria gonorrhoeae and related species

High-level tetracycline resistance in strains of Neisseria gonorrhoeae, Neisseria meningitidis, Kingella denitrificans, and Eikenella corrodens has recently been described. The resistance in each species is due to the acquisition of 25.2-megadalton conjugative plasmids that carry the tetracycline resistance determinant TetM. We examined the ability of commensal Neisseria species to serve as recipients in conjugation for these new plasmids. Most of the recipients (n = 21) tested had detectable conjugation frequencies (greater than 10(-9] with one or more of the donor strains. Transfer was not detected in Branhamella catarrhalis. Transconjugants were able to maintain the plasmids and act as donors in subsequent matings.

Use of plasmid profiles in epidemiologic surveillance of disease outbreaks and in tracing the transmission of antibiotic resistance

Plasmids are circular deoxyribonucleic acid molecules that exist in bacteria, usually independent of the chromosome. The study of plasmids is important to medical microbiology because plasmids can encode genes for antibiotic resistance or virulence factors. Plasmids can also serve as markers of various bacterial strains when a typing system referred to as plasmid profiling, or plasmid fingerprinting is used. In these methods partially purified plasma deoxyribonucleic acid species are separated according to molecular size by agarose gel electrophoresis. In a second procedure, plasmid deoxyribonucleic acid which has been cleaved by restriction endonucleases can be separated by agarose gel electrophoresis and the resulting pattern of fragments can be used to verify the identity of bacterial isolates. Because many species of bacteria contain plasmids, plasmid profile typing has been used to investigate outbreaks of many bacterial diseases and to trace inter- and intra-species spread of antibiotic resistance.

Hybridization analysis of the class P tetracycline resistance determinant from the Clostridium perfringens R-plasmid, pCW3

The tetracycline resistance determinant from pCW3, a conjugative plasmid from Clostridium perfringens, has been identified and the structural gene localized to within a 1.4-kb region. Hybridization analysis, which utilized an internal 0.8-kb specific gene probe, showed that eight nonconjugative tetracycline resistant C. perfringens strains all carried homologous resistance determinants. No homology was detected in DNA prepared from tetracycline resistant isolates of Clostridium difficile or Clostridium sporogenes. However, the one strain of Clostridium paraputrificum that was tested did contain an homologous determinant. No homology was found to any of the recognized classes of tetracycline resistance determinants. The C. perfringens tetracycline resistance determinant represents a new hybridization group, Class P.

Treatment of gonorrhoea and susceptibility to antimicrobials of PPNG and non-PPNG strains in Jamaica

Of 1400 patients in Jamaica screened for uncomplicated gonorrhoea, 54% (753 patients) were culture positive. Of the 459 patients who complied with the terms of the study, 97% (211/218) of those treated with aqueous procaine penicillin G were cured compared with 94% (227/241) of those treated with ampicillin. Penicillinase producing Neisseria gonorrhoeae (PPNG) strains were identified for the first time during the study, and 10 patients infected with PPNG strains (two treated with penicillin, eight with ampicillin) contributed to the 21 treatment failures. The in vitro susceptibility of eight antimicrobial agents for 629 non-PPNG and 20 PPNG strains was estimated. Of the non-PPNG isolates, 8% had an MIC of 1 mg/l or more of penicillin, 11% were resistant to this concentration of ampicillin, 32% to tetracycline, and under 1% to the same concentration of cefuroxime and erythromycin. Fewer than 2% of the isolates were resistant to 2 mg/l or more thiamphenicol, and all isolates were susceptible to spectinomycin and trimethoprimsulphamethoxazole (at a ratio of 1:19). Significantly more strains from the 21 treatment failures were resistant to penicillin (52%) or ampicillin (62%) compared with 7% strains resistant to penicillin and 4% to ampicillin from the successfully treated group.

Gonococcal keratoconjunctivitis

Gonococcal keratoconjunctivitis is a potentially devastating infection, because Neisseria gonorrhoeae can cause a rapid, severe, ulcerative keratitis resulting in visual loss. The therapeutic decision making process is complicated by the necessity for prompt, effective parenteral therapy, frequent coinfection with other sexually transmitted diseases, and emergence of antibiotic resistance. Because of the evolving problem of antibiotic resistance and the need for cost containment, the current recommendations of hospitalization for intravenous penicillin may need to be modified. The third generation cephalosporin, ceftriaxone, has properties that suggest it may be the best available antimicrobial agent as a single-dose treatment of gonococcal conjunctivitis. Spectinomycin may be a useful alternative in the penicillin-allergic adult patient.

DNA probes for identification of tetracycline resistance genes in Campylobacter species isolated from swine and cattle

Tetracycline-resistant strains of Campylobacter jejuni and Campylobacter coli from swine and cattle colons were isolated and characterized by hybridization with DNA probes. A probe consisting of the 1.8-kilobase (kb) HincII fragment from pUA466 was highly specific for the detection of tetracycline resistance (Tcr) in C. jejuni and C. coli. The 5-kb tetM DNA probe from Streptococcus agalactiae plasmid pJI3 which has homology with the 1.8-kb HincII fragment from pUA466 could also be used to detect Tcr Campylobacter strains. However, the tetM probe had a much lower sensitivity and required a lower stringency of hybridization. Therefore, the 1.8-kb HincII fragment appeared to be more appropriate for the classification of Tcr in Campylobacter spp. No homology was detected between the Tcr determinant from Campylobacter spp. and the tetL and tetN probes from Streptococcus spp. DNA homology was demonstrated between pUA649, a derivative of plasmid pUA466 which had lost most of the Tcr region, and Tcr plasmids from C. jejuni and C. coli isolated from animal and human sources. There was also homology between pUA649 and the chromosomes of C. jejuni and C. coli strains. In this study, all but one of the tetracycline-resistant C. coli and C. jejuni strains contained plasmids of approximately 50 kb which hybridized with the 1.8-kb HincII probe. In one C. coli strain (UA703), Tcr appeared to be chromosomally mediated.

Cloning and characterization of tetM gene from a Ureaplasma urealyticum strain

We have cloned a 4.9-kilobase (kb) HincII fragment which contains a tetracycline resistance determinant (tetM) from the chromosome of Ureaplasma urealyticum. The 4.9-kb HincII fragment contains DNA in addition to the structural gene, is closely related to the previously characterized 5.0-kb fragment from pJI3, and contains no normal ureaplasmal DNA sequences.