Neisseria gonorrhoeae with decreased susceptibility to ciprofloxacin: pulsed-field gel electrophoresis typing of strains from North America, Hawaii, and the Philippines

Review and international recommendation of methods for typing neisseria gonorrhoeae isolates and their implications for improved knowledge of gonococcal epidemiology, treatment, and biology

Gonorrhea, which may become untreatable due to multiple resistance to available antibiotics, remains a public health problem worldwide. Precise methods for typing Neisseria gonorrhoeae, together with epidemiological information, are crucial for an enhanced understanding regarding issues involving epidemiology, test of cure and contact tracing, identifying core groups and risk behaviors, and recommending effective antimicrobial treatment, control, and preventive measures. This review evaluates methods for typing N. gonorrhoeae isolates and recommends various methods for different situations. Phenotypic typing methods, as well as some now-outdated DNA-based methods, have limited usefulness in differentiating between strains of N. gonorrhoeae. Genotypic methods based on DNA sequencing are preferred, and the selection of the appropriate genotypic method should be guided by its performance characteristics and whether short-term epidemiology (microepidemiology) or long-term and/or global epidemiology (macroepidemiology) matters are being investigated. Currently, for microepidemiological questions, the best methods for fast, objective, portable, highly discriminatory, reproducible, typeable, and high-throughput characterization are N. gonorrhoeae multiantigen sequence typing (NG-MAST) or full- or extended-length porB gene sequencing. However, pulsed-field gel electrophoresis (PFGE) and Opa typing can be valuable in specific situations, i.e., extreme microepidemiology, despite their limitations. For macroepidemiological studies and phylogenetic studies, DNA sequencing of chromosomal housekeeping genes, such as multilocus sequence typing (MLST), provides a more nuanced understanding.

Strain typing and antimicrobial resistance of fluoroquinolone-resistant Neisseria gonorrhoeae causing a California infection outbreak

Antimicrobial-resistant Neisseria gonorrhoeae is an emerging public health problem as a result of the alarming limitation in treatment options. We examined an outbreak in California of fluoroquinolone-resistant Neisseria gonorrhoeae (QRNG) by evaluation of a combination of routine isolates from the Gonococcal Isolate Surveillance Project and isolates collected by expanded surveillance performed between April 2000 and June 2002. QRNG isolates were characterized by two methods: (i) determination of a combination of antibiogram, auxotype, serovar, Lip type, and patterns of amino acid alteration in the quinolone resistance-determining region of GyrA and ParC (ASLGP) and (ii) pulsed-field gel electrophoresis (PFGE). Strain typing was used to describe the QRNG outbreak strains and the associated antimicrobial resistance profiles. Among 79 isolates that were completely characterized, we identified 20 different ASLGP strain types, and 2 of the types were considered to belong to outbreak strains that comprised 65% (51/79) of the isolates. By PFGE typing, there were 24 different strain types, and 4 of these were considered outbreak types and comprised 66% (52/79) of the isolates. The overall agreement between the typing methods in distinguishing outbreak strains and non-outbreak strains was 84% (66/79). The most common QRNG ASLGP strain type had chromosomally mediated resistance to penicillin and tetracycline and an azithromycin MIC of 0.5 microg/ml. The occurrence of an outbreak caused by QRNG strains that could fail to be eradicated by most antibiotic classes reinforces the serious problem with antimicrobial resistance in Neisseria gonorrhoeae that the public health system faces. Adherence to a regimen with the recommended antibiotics at the appropriate dose is critical, and monitoring for antimicrobial susceptibility needs to be actively maintained to adapt treatment guidelines appropriately.

Application of molecular techniques to the study of hospital infection

Nosocomial infections are an important source of morbidity and mortality in hospital settings, afflicting an estimated 2 million patients in United States each year. This number represents up to 5% of hospitalized patients and results in an estimated 88,000 deaths and 4.5 billion dollars in excess health care costs. Increasingly, hospital-acquired infections with multidrug-resistant pathogens represent a major problem in patients. Understanding pathogen relatedness is essential for determining the epidemiology of nosocomial infections and aiding in the design of rational pathogen control methods. The role of pathogen typing is to determine whether epidemiologically related isolates are also genetically related. To determine molecular relatedness of isolates for epidemiologic investigation, new technologies based on DNA, or molecular analysis, are methods of choice. These DNA-based molecular methodologies include pulsed-field gel electrophoresis (PFGE), PCR-based typing methods, and multilocus sequence analysis. Establishing clonality of pathogens can aid in the identification of the source (environmental or personnel) of organisms, distinguish infectious from noninfectious strains, and distinguish relapse from reinfection. The integration of molecular typing with conventional hospital epidemiologic surveillance has been proven to be cost-effective due to the associated reduction in the number of nosocomial infections. Cost-effectiveness is maximized through the collaboration of the laboratory, through epidemiologic typing, and the infection control department during epidemiologic investigations.

Distribution of erm(F) and tet(Q) genes in 4 oral bacterial species and genotypic variation between resistant and susceptible isolates

BACKGROUND

Bacteroides forsythus, Porphyromonas gingivalis and Prevotella intermedia are Gram-negative anaerobic bacteria that are currently considered potential periopathogens. Prevotella nigrescens has recently been separated from P. intermedia and its rôle in periodontitis is unknown. The erm(F) gene codes for an rRNA methylase, conferring resistance to macrolides, lincosamides and streptogramin B (MLSB), and the tet(Q) gene for a ribosomal protection protein, conferring resistance to tetracycline. The presence of these resistance genes could impair the use of antibiotics for therapy.

PURPOSE

The aim of this study was to determine the carriage of erm(F) and tet(Q), and genetic variability of 12 Porphyromonas gingivalis, 10 Prevotella intermedia, 25 Prevotella nigrescens and 17 Bacteroides forsythus isolates from 9 different patient samples.

METHODS

We used polymerase chain reaction (PCR) for detecting antibiotic resistance genes, and pulsed-field gel electrophoresis (PFGE) for detecting genetic variability among the isolates.

RESULTS

Thirty-one (48%) isolates were resistant to both erythromycin and tetracycline and carried the erm(F) and tet(Q) genes, eight (13%) were tetracycline resistant and carried the tet(Q) gene, 9 (14%) were erythromycin resistant and carried the erm(F) gene, and 12 (19%) isolates did not carry antibiotic resistance genes. PFGE was used to compare isolates from the same patient and isolates from different patient samples digested with XbaI. No association was found between antibiotic resistance gene carriage and PFGE patterns in any species examined. All isolates of the same species from the same patient had highly related or identical PFGE patterns. Isolates of same species from different patients had unique PFGE pattern for each species tested.

CONCLUSION

All isolates of the same species from any one patient were genetically related to each other but distinct from isolates from other patients, and 66% of the patients carried antibiotic resistant isolates, which could impair antibiotic therapy.

Molecular basis of high-level ciprofloxacin resistance in Neisseria gonorrhoeae strains isolated in Denmark from 1995 to 1998

In Denmark surveillance of the in vitro susceptibility to ciprofloxacin of Neisseria gonorrhoeae was established in 1990. The proportion of N. gonorrhoeae strains with decreased susceptibility or resistance to ciprofloxacin (MIC >/= 0.06 microg/ml) was low (0.3 to 2.3%) up to 1995. Between 1995 and 1998 the rate of less-susceptible and resistant strains rose from 6.9 to 13.2%. Among ciprofloxacin-resistant strains (MIC >/= 1 microg/ml), 81% were highly resistant (MIC >/= 4 microg/ml). Thirty-five N. gonorrhoeae strains (40 isolates) for which ciprofloxacin MICs were 4 to 32 microg/ml were investigated for the frequency and patterns of mutations within the gyrA and parC genes. The quinolone resistance-determining regions of the gyrA and parC genes were amplified by PCR, and the amplicons were directly sequenced. Alterations at Ser-91 and Asp-95 in GyrA and a single or double alteration in ParC were identified in 32 strains (91%). Ser-91-to-Phe and Asp-95-to-Gly alterations in GyrA were detected in 28 strains (80%). The most common ParC alteration, Asp-86 to Asn, was found in 19 strains (54%). The strains were analyzed for genetic relationship by pulsed-field gel electrophoresis (PFGE). The analysis showed that nine strains with the same mutation pattern in the gyrA and parC genes, originating from different geographical areas over 3 years, had the same PFGE patterns after SpeI as well as NheI digestion (only one strain with one band difference in the NheI pattern), suggesting that a resistant clone had spread worldwide. The results from this study strongly suggest that double gyrA mutations plus a parC mutation(s) play an important role in the development of high-level fluoroquinolone resistance in N. gonorrhoeae.

Antibiotic susceptibility patterns of Neisseria meningitidis isolates from patients and asymptomatic carriers

The activities of seven antimicrobial agents used for treatment and prophylaxis of meningococcal disease was investigated against 901 Neisseria meningitidis isolates, 112 of which were recovered from patients and 789 of which were recovered from asymptomatic carriers. The proportions of isolates with decreased susceptibility to penicillin were 55.3 and 39.0%, respectively. Penicillin- and ampicillin-intermediate strains were more common among serogroup C meningococci than among non-serogroup C meningococci from both patients and carriers.

Organization of the ribosomal operon 165-235 gene spacer region in representatives of Neisseria gonorrhoeae

Ribosomal rRNA gene fragments (rDNA) encompassing part of the 16S rDNA, the 16S-23S rDNA spacer region and part of the 23S rDNA of 229 Neisseria gonorrhoeae strains were enzymatically amplified using conserved primers. The fragments of approximately 1200 bp were subjected to restriction analysis with HinfI. This revealed 13 patterns (patterns I-XIII) of which patterns I (78 strains), II (32 strains), III (38 strains) and IV (56 strains) were the most abundant, comprising 89.1% of the strains. The obtained restriction patterns consisted of 3 to 8 bands, ranging in size from 32 to 854 bp. The sum of the obtained bands was about 1200 bp for patterns I, II, III, IV, V, IX, and XIII. However, for patterns VI, VII, VIII, X, XI and XII, the sum of the bands well exceeded the estimated size of approximately 1200 bp. We demonstrated that this results from sequence divergence in the 4 rRNA operons, present in the genome of N. gonorrhoeae, giving rise to patterns that are a combination of several other patterns.

Evaluation of the discriminatory power of typing methods for Neisseria gonorrhoeae

A panel of 18 strains of Neisseria gonorrhoeae, known to be temporally and geographically diverse, was used to evaluate a number of typing systems, including conventional auxotyping and serotyping and the molecular methods of arbitrarily primed PCR (AP-PCR), amplified ribosomal-DNA restriction analysis (ARDRA), opa typing, and pulsed-field gel electrophoresis (PFGE). The discriminatory power of the different typing methods were determined with a collection of 87 clinical isolates from commercial sex workers in Indonesia, and Simpson's index of diversity was calculated. Of the two traditional techniques, auxotyping and serotyping, the latter gives the highest discriminatory index (DI) (DI, 0.846). The combination of auxotyping and serotyping yields a high DI (DI, 0. 928). D11344- and D8635-primed PCR showed low DIs of 0.608 and 0.622, respectively, but a combination of the two primers had a DI of 0. 849. The combination of serotyping with D11344-primed or D8635-primed PCR resulted in DIs of 0.936 and 0.937, respectively. ARDRA revealed a low DI of 0.743 alone but a DI of 0.955 in combination with serotyping. PFGE using the restriction enzyme BglII and opa typing produced the highest discrimination (DIs, 0.997 and 0. 996, respectively) for isolates of N. gonorrhoeae.

Molecular analysis by pulsed-field gel electrophoresis and antibiogram of Streptococcus pneumoniae serotype 6B isolates from selected areas within the United States

Fifty-eight clinical isolates of Streptococcus pneumoniae serotype 6B, including 16 from Alaska, 14 from Arizona, 11 from Washington, and 17 from seven additional states, were analyzed. The antibiograms of these isolates were assigned to 10 antibiotic profiles based on their susceptibilities to penicillin, erythromycin, tetracycline, and trimethoprim-sulfamethoxazole. Thirty-two (55%) of these isolates were penicillin nonsusceptible, while 21 (36%) were intermediate or resistant to three or more antibiotics. The restriction endonucleases ApaI and SmaI were used to digest intact chromosomes, and the fragments were resolved by pulsed-field gel electrophoresis (PFGE). The ApaI and SmaI PFGE patterns were combined, and 13 of the 16 Alaskan isolates showed indistinguishable PFGE patterns. One other isolate exhibited highly related ApaI and SmaI PFGE patterns, differing by only one band after restriction with ApaI. Among the 14 isolates from Arizona, 1 was indistinguishable from the predominant ApaI and SmaI PFGE patterns seen in the Alaskan isolates; 5 others were highly related (+/-1 band after cutting with either enzyme) to the Alaskan isolates, suggesting a common ancestral origin. Of the remaining eight isolates, six additional ApaI plus SmaI PFGE patterns were observed. The 28 isolates from the various contiguous states had 22 ApaI plus SmaI PFGE patterns. No correlations were found between specific PFGE patterns, antibiograms, dates of isolation, or geography. The serotype 6B isolates across the contiguous United States were genetically diverse, while the 6B isolates from Alaska appeared to be much less diverse.

Genomic homogeneity of the AHU/IA-1,2 phenotype of Neisseria gonorrhoeae during its disappearance from an urban population

BACKGROUND

Isolates of Neisseria gonorrhoeae requiring arginine, hypoxanthine, and uracil (AHU) appeared in Denmark in 1946, were preponderant in Seattle during the 1970s, were associated with disseminated gonococcal infections (DGI), and were primarily of the IA-1,2 serovar.

GOALS

To investigate the disappearance of the AHU/IA-1,2 phenotype and to examine by pulsed-field gel electrophoresis (PFGE) the genomic homogeneity of this unique phenotype isolated from Seattle-King County during the past decade.

STUDY DESIGN

This retrospective study used data extracted from previous publications for the period 1971 through 1984, and from existing records at the Neisseria Reference Laboratory, University of Washington for the period 1985 through 1996. Samples (n = 68) of AHU/IA-1,2 isolates from 1984 to 1985 and 1988 to 1993 were analyzed using endonucleases NheI and XbaI. For comparison, 10 AHU/IB isolates were included in the study.

RESULTS

AHU isolates, predominantly IA-1,2 strains accounted for 52% of the gonococcal isolates for the period 1971 through 1974, 40% for 1974 through 1976, 16% for 1984, and then declined from 7% in 1986 to 0% for each of the last 3 years, 1994 through 1996. Isolates with < or = 1 band difference after digestion with either NheI or XbaI were considered to belong to a single closely related pattern. Pulsed-field gel electrophoresis (PFGE) type designation was made from the combination of NheI and XbaI patterns. These criteria yielded 5 NheI and 8 XbaI PFGE patterns, and 11 PFGE types based on the combination of NheI and XbaI pattern. The most frequently occurring NheI and XbaI patterns accounted for 74% and 57% of isolates, respectively. One type persisted throughout the decade and accounted for 54% of the 68 isolates. Analysis of the 10 AHU/IB isolates yielded 7 NheI and 8 XbaI patterns that gave 9 types that were distinct from the types found in the AHU/IA-1,2 strains.

CONCLUSION

The AHU/IA-1,2 phenotype first documented 50 years ago in Denmark still shows a high degree of genomic homogeneity during the past decade in Seattle. The implementation of screening, decreased rates of sexual exposure in the acquired immune deficiency syndrome era, or other factors may explain its apparent elimination in Seattle-King County.

Antimicrobial activity of trovafloxacin tested against ciprofloxacin-susceptible and -resistant Neisseria gonorrhoeae. Interpretive criteria and comparisons with Etest results

Trovafloxacin, a new fluorinated naphthyridine, has enhanced activity against Gram-positive cocci, while retaining an excellent spectrum against Gram-negative pathogens. It has been used successfully in clinical trials for therapy of gonorrhea, and this investigation proposes in vitro susceptibility testing criteria for trovafloxacin. A total of 150 Neisseria gonorrhoeae clinical isolates (50 resistant to ciprofloxacin; MICs > or = 0.12 microgram/mL) were tested by methods recommended by the National Committee for Clinical Laboratory Standards (NCCLS) and the Etest (AB BIODISK, Solna, Sweden). Trovafloxacin was very active against gonococci (MIC90, 0.008 to 0.015 microgram/mL), but was generally eightfold less potent versus ciprofloxacin-resistant strains. Etest results correlated well (r = 0.96; 98% of MICs +/- one log2 dilution) compared to the reference agar dilution test. Reference agar dilution and Etest MICs were compared to disk-diffusion test zones (10-micrograms trovafloxacin disk), and excellent categorical agreement (89.4 to 99.3%) was achieved without significant false-susceptible or -resistant error (< or = 1.3%). Tentative breakpoints were suggested initially to outline the ciprofloxacin-susceptible and trovafloxacin-susceptible as susceptible (MIC, < or = 0.015 microgram/mL; zones > or = 47 mm), and strains with various well-characterized mutations of the gyr A and par C genes as either intermediate or resistant to trovafloxacin. When the results of clinical studies treating ciprofloxacin-resistant N. gonorrhoeae with trovafloxacin become available, the alternative breakpoints could be utilized for resistant MIC breakpoints of > or = 0.06 microgram/mL or > or = 0.5 microgram/mL. Trovafloxacin was stable in supplemented GC agar for 21 days stored at refrigerated temperatures. These in vitro results indicate that trovafloxacin should be a very acceptable agent for therapy of gonorrhea and other common sexually transmitted pathogens.