Genomic characterization of cocirculating Corynebacterium diphtheriae and non-diphtheritic Corynebacterium species among forcibly displaced Myanmar nationals, 2017-2019

Respiratory diphtheria is a serious infection caused by toxigenic Corynebacterium diphtheriae, and disease transmission mainly occurs through respiratory droplets. Between 2017 and 2019, a large diphtheria outbreak among forcibly displaced Myanmar nationals densely settled in Bangladesh was investigated. Here we utilized whole-genome sequencing (WGS) to characterize recovered isolates of C. diphtheriae and two co-circulating non-diphtheritic Corynebacterium (NDC) species - C. pseudodiphtheriticum and C. propinquum. C. diphtheriae isolates recovered from all 53 positive cases in this study were identified as toxigenic biovar mitis, exhibiting intermediate resistance to penicillin, and formed four phylogenetic clusters circulating among multiple refugee camps. Additional sequenced isolates collected from two patients showed co-colonization with non-toxigenic C. diphtheriae biovar gravis, one of which exhibited decreased susceptibility to the first-line antibiotics and harboured a novel 23-kb multidrug resistance plasmid. Results of phylogenetic reconstruction and virulence-related gene contents of the recovered NDC isolates indicated they were likely commensal organisms, though 80.4 %(45/56) were not susceptible to erythromycin, and most showed high minimum inhibition concentrations against azithromycin. These results demonstrate the high resolution with which WGS can aid molecular investigation of diphtheria outbreaks, through the quantification of bacterial genetic relatedness, as well as the detection of virulence factors and antibiotic resistance markers among case isolates.

Investigation of a Large Diphtheria Outbreak and Cocirculation of Corynebacterium pseudodiphtheriticum Among Forcibly Displaced Myanmar Nationals, 2017-2019

BACKGROUND

Diphtheria, a life-threatening respiratory disease, is caused mainly by toxin-producing strains of Corynebacterium diphtheriae, while nontoxigenic corynebacteria (eg, Corynebacterium pseudodiphtheriticum) rarely causes diphtheria-like illness. Recently, global diphtheria outbreaks have resulted from breakdown of health care infrastructures, particularly in countries experiencing political conflict. This report summarizes a laboratory and epidemiological investigation of a diphtheria outbreak among forcibly displaced Myanmar nationals in Bangladesh.

METHODS

Specimens and clinical information were collected from patients presenting at diphtheria treatment centers. Swabs were tested for toxin gene (tox)-bearing C. diphtheriae by real-time polymerase chain reaction (RT-PCR) and culture. The isolation of another Corynebacterium species prompted further laboratory investigation.

RESULTS

Among 382 patients, 153 (40%) tested tox positive for C. diphtheriae by RT-PCR; 31 (20%) PCR-positive swabs were culture confirmed. RT-PCR revealed 78% (298/382) of patients tested positive for C. pseudodiphtheriticum. Of patients positive for only C. diphtheriae, 63% (17/27) had severe disease compared to 55% (69/126) positive for both Corynebacterium species, and 38% (66/172) for only C. pseudodiphtheriticum.

CONCLUSIONS

We report confirmation of a diphtheria outbreak and identification of a cocirculating Corynebacterium species. The high proportion of C. pseudodiphtheriticum codetection may explain why many suspected patients testing negative for C. diphtheriae presented with diphtheria-like symptoms.

Genomic epidemiology of nontoxigenic Corynebacterium diphtheriae from King County, Washington State, USA between July 2018 and May 2019

Between July 2018 and May 2019, Corynebacterium diphtheriae was isolated from eight patients with non-respiratory infections, seven of whom experienced homelessness and had stayed at shelters in King County, WA, USA. All isolates were microbiologically identified as nontoxigenic C. diphtheriae biovar mitis. Whole-genome sequencing confirmed that all case isolates were genetically related, associated with sequence type 445 and differing by fewer than 24 single-nucleotide polymorphisms (SNPs). Compared to publicly available C. diphtheriae genomic data, these WA isolates formed a discrete cluster with SNP variation consistent with previously reported outbreaks. Virulence-related gene content variation within the highly related WA cluster isolates was also observed. These results indicated that genome characterization can readily support epidemiology of nontoxigenic C. diphtheriae.

Respiratory illness caused by Corynebacterium diphtheriae and C. ulcerans, and use of diphtheria anti-toxin in the United States, 1996-2018

Respiratory illness caused by Corynebacterium diphtheriae and C. ulcerans, and use of diphtheria anti-toxin in the United States, 1996-2018.

BACKGROUND

Respiratory diphtheria is a toxin-mediated disease caused by Corynebacterium diphtheriae. Diphtheria-like illness, clinically indistinguishable from diphtheria, is caused by C. ulcerans, a zoonotic bacterium that can also produce diphtheria toxin. In the United States, respiratory diphtheria is nationally notifiable: specimens from suspected cases are submitted to the Centers for Disease Control (CDC) for species and toxin confirmation, and diphtheria antitoxin (DAT) is obtained from CDC for treatment. We summarize the epidemiology of respiratory diphtheria and diphtheria-like illness and describe DAT use during 1996-2018 in the United States.

METHODS

We described respiratory diphtheria cases reported to the National Notifiable Diseases Surveillance System (NNDSS) and C. ulcerans-related diphtheria-like illness identified through specimen submissions to CDC during 1996-2018. We reviewed DAT requests from 1997-2018.

RESULTS

From 1996-2018, 14 respiratory diphtheria cases were reported to NNDSS. Among these 14 cases, 1 was toxigenic and 3 were non-toxigenic C. diphtheriae by culture and Elek, 6 were culture-negative but PCR-positive for diphtheria toxin gene, 1 was culture-positive without further testing, and the remaining 3 were either not tested or tested negative. Five cases of respiratory diphtheria-like illness caused by toxigenic C. ulcerans were identified. DAT was requested by healthcare providers for 151 suspected diphtheria cases between 1997-2018, with an average of 11 requests per year from 1997-2007, and 3 per year from 2008-2018.

CONCLUSIONS

Respiratory diphtheria remains rare in the United States, and requests for DAT have declined. Incidental identification of C. ulcerans-related diphtheria-like illness suggests surveillance of this condition might be warranted.

Clinical evaluation and validation of laboratory methods for the diagnosis of Bordetella pertussis infection: Culture, polymerase chain reaction (PCR) and anti-pertussis toxin IgG serology (IgG-PT)

Introduction

The appropriate use of clinically accurate diagnostic tests is essential for the detection of pertussis, a poorly controlled vaccine-preventable disease. The purpose of this study was to estimate the sensitivity and specificity of different diagnostic criteria including culture, multi-target polymerase chain reaction (PCR), anti-pertussis toxin IgG (IgG-PT) serology, and the use of a clinical case definition. An additional objective was to describe the optimal timing of specimen collection for the various tests.

Methods

Clinical specimens were collected from patients with cough illness at seven locations across the United States between 2007 and 2011. Nasopharyngeal and blood specimens were collected from each patient during the enrollment visit. Patients who had been coughing for ≤ 2 weeks were asked to return in 2–4 weeks for collection of a second, convalescent blood specimen. Sensitivity and specificity of each diagnostic test were estimated using three methods—pertussis culture as the “gold standard,” composite reference standard analysis (CRS), and latent class analysis (LCA).

Results

Overall, 868 patients were enrolled and 13.6% were B. pertussis positive by at least one diagnostic test. In a sample of 545 participants with non-missing data on all four diagnostic criteria, culture was 64.0% sensitive, PCR was 90.6% sensitive, and both were 100% specific by LCA. CRS and LCA methods increased the sensitivity estimates for convalescent serology and the clinical case definition over the culture-based estimates. Culture and PCR were most sensitive when performed during the first two weeks of cough; serology was optimally sensitive after the second week of cough.

Conclusions

Timing of specimen collection in relation to onset of illness should be considered when ordering diagnostic tests for pertussis. Consideration should be given to including IgG-PT serology as a confirmatory test in the Council of State and Territorial Epidemiologists (CSTE) case definition for pertussis.

Changes in Predominance of Pulsed-Field Gel Electrophoresis Profiles of Bordetella pertussis Isolates, United States, 2000-2012

These changes are concurrrent with other recent molecular changes and may be contributing to US pertussis reemergence.

To clarify the characteristics of circulating Bordetella pertussis isolates, we used pulsed-field gel electrophoresis (PFGE) to analyze 5,262 isolates collected in the United States during 2000–2012. We found 199 PFGE profiles; 5 profiles accounted for 72% of isolates. The most common profile, CDC013, accounted for 35%–46% of isolates tested from 2000–2009; however, the proportion of isolates of this profile rapidly decreased in 2010. Profile CDC237, first seen in 2009, increased rapidly and accounted for 29% of 2012 isolates. No location bias was observed among profiles during 2000–2010, but differences were observed among isolates from different states during 2012. Predominant profiles match those observed in recent European PFGE studies. PFGE profile changes are concurrent with other recent molecular changes in B. pertussis and may be contributing to the reemergence of pertussis in the United States. Continued PFGE monitoring is critical for understanding the changing epidemiology of pertussis.

Genome Structural Diversity among 31 Bordetella pertussis Isolates from Two Recent U.S. Whooping Cough Statewide Epidemics

During 2010 and 2012, California and Vermont, respectively, experienced statewide epidemics of pertussis with differences seen in the demographic affected, case clinical presentation, and molecular epidemiology of the circulating strains. To overcome limitations of the current molecular typing methods for pertussis, we utilized whole-genome sequencing to gain a broader understanding of how current circulating strains are causing large epidemics. Through the use of combined next-generation sequencing technologies, this study compared de novo, single-contig genome assemblies from 31 out of 33 Bordetella pertussis isolates collected during two separate pertussis statewide epidemics and 2 resequenced vaccine strains. Final genome architecture assemblies were verified with whole-genome optical mapping. Sixteen distinct genome rearrangement profiles were observed in epidemic isolate genomes, all of which were distinct from the genome structures of the two resequenced vaccine strains. These rearrangements appear to be mediated by repetitive sequence elements, such as high-copy-number mobile genetic elements and rRNA operons. Additionally, novel and previously identified single nucleotide polymorphisms were detected in 10 virulence-related genes in the epidemic isolates. Whole-genome variation analysis identified state-specific variants, and coding regions bearing nonsynonymous mutations were classified into functional annotated orthologous groups. Comprehensive studies on whole genomes are needed to understand the resurgence of pertussis and develop novel tools to better characterize the molecular epidemiology of evolving B. pertussis populations. IMPORTANCE Pertussis, or whooping cough, is the most poorly controlled vaccine-preventable bacterial disease in the United States, which has experienced a resurgence for more than a decade. Once viewed as a monomorphic pathogen, B. pertussis strains circulating during epidemics exhibit diversity visible on a genome structural level, previously undetectable by traditional sequence analysis using short-read technologies. For the first time, we combine short- and long-read sequencing platforms with restriction optical mapping for single-contig, de novo assembly of 31 isolates to investigate two geographically and temporally independent U.S. pertussis epidemics. These complete genomes reshape our understanding of B. pertussis evolution and strengthen molecular epidemiology toward one day understanding the resurgence of pertussis.

Pertactin-negative Bordetella pertussis strains: evidence for a possible selective advantage

BACKGROUND

A recent increase in Bordetella pertussis without the pertactin protein, an acellular vaccine immunogen, has been reported in the United States. Determining whether pertactin-deficient (PRN(-)) B. pertussis is evading vaccine-induced immunity or altering the severity of illness is needed.

METHODS

We retrospectively assessed for associations between pertactin production and both clinical presentation and vaccine history. Cases with isolates collected between May 2011 and February 2013 from 8 states were included. We calculated unadjusted and adjusted odds ratios (ORs) using multivariable logistic regression analysis.

RESULTS

Among 753 isolates, 640 (85%) were PRN(-). The age distribution differed between cases caused by PRN(-) B. pertussis and cases caused by B. pertussis producing pertactin (PRN(+)) (P = .01). The proportion reporting individual pertussis symptoms was similar between the 2 groups, except a higher proportion of PRN(+) case-patients reported apnea (P = .005). Twenty-two case-patients were hospitalized; 6% in the PRN(+) group compared to 3% in the PRN(-) group (P = .11). Case-patients having received at least 1 pertussis vaccine dose had a higher odds of having PRN(-) B. pertussis compared with unvaccinated case-patients (adjusted OR = 2.2; 95% confidence interval [CI], 1.3-4.0). When restricted to case-patients at least 1 year of age and those age-appropriately vaccinated, the adjusted OR increased to 2.7 (95% CI, 1.2-6.1).

CONCLUSIONS

The significant association between vaccination and isolate pertactin production suggests that the likelihood of having reported disease caused by PRN(-) compared with PRN(+) strains is greater in vaccinated persons. Additional studies are needed to assess whether vaccine effectiveness is diminished against PRN(-) strains.

Global population structure and evolution of Bordetella pertussis and their relationship with vaccination

Bordetella pertussis causes pertussis, a respiratory disease that is most severe for infants. Vaccination was introduced in the 1950s, and in recent years, a resurgence of disease was observed worldwide, with significant mortality in infants. Possible causes for this include the switch from whole-cell vaccines (WCVs) to less effective acellular vaccines (ACVs), waning immunity, and pathogen adaptation. Pathogen adaptation is suggested by antigenic divergence between vaccine strains and circulating strains and by the emergence of strains with increased pertussis toxin production. We applied comparative genomics to a worldwide collection of 343 B. pertussis strains isolated between 1920 and 2010. The global phylogeny showed two deep branches; the largest of these contained 98% of all strains, and its expansion correlated temporally with the first descriptions of pertussis outbreaks in Europe in the 16th century. We found little evidence of recent geographical clustering of the strains within this lineage, suggesting rapid strain flow between countries. We observed that changes in genes encoding proteins implicated in protective immunity that are included in ACVs occurred after the introduction of WCVs but before the switch to ACVs. Furthermore, our analyses consistently suggested that virulence-associated genes and genes coding for surface-exposed proteins were involved in adaptation. However, many of the putative adaptive loci identified have a physiological role, and further studies of these loci may reveal less obvious ways in which B. pertussis and the host interact. This work provides insight into ways in which pathogens may adapt to vaccination and suggests ways to improve pertussis vaccines. IMPORTANCE Whooping cough is mainly caused by Bordetella pertussis, and current vaccines are targeted against this organism. Recently, there have been increasing outbreaks of whooping cough, even where vaccine coverage is high. Analysis of the genomes of 343 B. pertussis isolates from around the world over the last 100 years suggests that the organism has emerged within the last 500 years, consistent with historical records. We show that global transmission of new strains is very rapid and that the worldwide population of B. pertussis is evolving in response to vaccine introduction, potentially enabling vaccine escape.

Bordetella holmesii bacteremia cases in the United States, April 2010-January 2011

We describe the first report of temporally related cases of Bordetella holmesii bacteremia. Demographic and clinical data were collected through chart abstraction and case-patient interviews. Twenty-two cases were identified from 6 states. Symptom onset dates ranged from April 2010 to January 2011. Median age of patients was 17.1 years and 64% had functional or anatomic asplenia. Pulsed-field gel electrophoresis profiles of a sample of isolates were identical. These cases occurred during a peak in pertussis outbreaks with documented cases of B. holmesii/Bordetella pertussis respiratory coinfection; whether there is a link between B. holmesii respiratory and bloodstream infection is unknown.

Serotypes and genetic profiles of Bordetella pertussis strains isolated in the city of São Paulo, 2006-2008

OBJECTIVE

Knowledge of Bordetella pertussis circulating in Latin America is limited. Therefore, the goal of this study was to use pulsed-field gel electrophoresis and serotyping to characterize B. pertussis strains isolated in the city of São Paulo, Brazil.

METHODS

This study, conducted between 2006 and 2008, analyzed 652 nasopharyngeal swabs from suspected pertussis cases and contacts, collected from 37 sentinel hospitals in São Paulo. Randomized samples of 91 (70%) strains of B. pertussis were subtyped by pulsed-field gel electrophoresis and serotyping.

RESULTS

Ninety-seven percent of strains from São Paulo were serotyped as Fim3. Fourteen pulsed-field gel electrophoresis profiles were identified; the most prevalent (57%) is also the most prevalent in the USA.

CONCLUSIONS

These data, in conjunction with surveillance activities, may impact strategies regarding prevention and control of pertussis in the region, providing useful information for introduction of new vaccination strategies and reduction of risk of transmission to infants less than 6 months of age.

Characterization of Corynebacterium species in macaques

Bacteria of the genus Corynebacterium are important primary and opportunistic pathogens. Many are zoonotic agents. In this report, phenotypic (API Coryne analysis), genetic (rpoB and 16S rRNA gene sequencing), and physical methods (MS) were used to distinguish the closely related diphtheroid species Corynebacterium ulcerans and Corynebacterium pseudotuberculosis, and to definitively diagnose Corynebacterium renale from cephalic implants of rhesus (Macaca mulatta) and cynomolgus (Macaca fascicularis) macaques used in cognitive neuroscience research. Throat and cephalic implant cultures yielded 85 isolates from 43 macaques. Identification by API Coryne yielded C. ulcerans (n = 74), Corynebacterium pseudotuberculosis (n = 2), C. renale or most closely related to C. renale (n = 3), and commensals and opportunists (n = 6). The two isolates identified as C. pseudotuberculosis by API Coryne required genetic and MS analysis for accurate characterization as C. ulcerans. Of three isolates identified as C. renale by 16S rRNA gene sequencing, only one could be confirmed as such by API Coryne, rpoB gene sequencing and MS. This study emphasizes the importance of adjunct methods in identification of coryneforms and is the first isolation of C. renale from cephalic implants in macaques.

Pertussis Pseudo-outbreak linked to specimens contaminated by Bordetella pertussis DNA From clinic surfaces

BACKGROUND AND OBJECTIVES

We investigated a pertussis outbreak characterized by atypical cases, confirmed by polymerase chain reaction (PCR) alone at a single laboratory, which persisted despite high vaccine coverage and routine control measures. We aimed to determine whether Bordetella pertussis was the causative agent and advise on control interventions.

METHODS

We conducted case ascertainment, confirmatory testing for pertussis and other pathogens, and an assessment for possible sources of specimen contamination, including a survey of clinic practices, sampling clinics for B pertussis DNA, and review of laboratory quality indicators.

RESULTS

Between November 28, 2008, and September 4, 2009, 125 cases were reported, of which 92 (74%) were PCR positive. Cases occurring after April 2009 (n = 79; 63%) had fewer classic pertussis symptoms (63% vs 98%; P < .01), smaller amounts of B pertussis DNA (mean PCR cycle threshold value: 40.9 vs 33.1; P < .01), and a greater proportion of PCR-positive results (34% vs 6%; P < .01). Cultures and serology for B pertussis were negative. Other common respiratory pathogens were detected. We identified factors that likely resulted in specimen contamination at the point of collection: environmentally present B pertussis DNA in clinics from vaccine, clinic standard specimen collection practices, use of liquid transport medium, and lack of clinically relevant PCR cutoffs.

CONCLUSIONS

A summer pertussis pseudo-outbreak, multifactorial in cause, likely occurred. Recommendations beyond standard practice were made to providers on specimen collection and environmental cleaning, and to laboratories on standardizing PCR protocols and reporting results, to minimize false-positive results from contaminated clinical specimens.

Novel Corynebacterium diphtheriae in domestic cats

Novel nontoxigenic Corynebacterium diphtheriae was isolated from a domestic cat with severe otitis. Contact investigation and carrier study of human and animal contacts yielded 3 additional, identical isolates from cats, although no evidence of zoonotic transmission was identified. Molecular methods distinguished the feline isolates from known C. diphtheriae.

Investigations of 2 cases of diphtheria-like illness due to toxigenic Corynebacterium ulcerans

BACKGROUND

We present 2 case reports in the United States and investigations of diphtheria-like illness caused by toxigenic Corynebacterium ulcerans. A fatal case occurred in a 75-year-old male Washington resident who was treated with clindamycin but did not receive equine diphtheria antitoxin. A second, nonfatal case occurred in a 66-year-old female Tennessee resident who received erythromycin and diphtheria antitoxin.

METHODS

Both case patients and close human and animal contacts were investigated by their respective state health departments.

RESULTS

C. ulcerans isolated from the patient who died was resistant to erythromycin and clindamycin. For both isolates, conventional polymerase chain reaction results were positive for A and B subunits of diphtheria toxin gene tox, and modified Elek tests confirmed toxin production. The source of infection remained undetermined for both cases. Neither patient was up-to-date with diphtheria toxoid vaccination.

CONCLUSION

These case reports highlight the importance of early treatment with diphtheria antitoxin, the selection of effective antimicrobial agents, and prevention through up-to-date vaccination.

Co-infection with two different strains of Bordetella pertussis in an infant

We report co-infection with two phenotypically and genotypically distinct strains of Bordetella pertussis in an infant male hospitalized with a 2-week history of cough, paroxysms and vomiting. Colonies from the two B. pertussis phenotypes were isolated and evaluated by PFGE profile analysis, gene sequence typing and PCR-RFLP of a portion of the 23S rRNA gene. These results demonstrated simultaneous infection with two different strains of B. pertussis.

Identification of a mutation associated with erythromycin resistance in Bordetella pertussis: implications for surveillance of antimicrobial resistance

Erythromycin treatment failures and in vitro resistance of Bordetella pertussis have been reported on several occasions in the past few years, but the mechanism of resistance has not been described. One potential mechanism, genetic modification of the erythromycin-binding site on the 23S rRNA of the 50S ribosomal subunit, has been observed in other bacteria. To explore this possibility, we amplified the portion of the 23S rRNA gene encoding the central loop of domain V. DNA sequencing and restriction fragment length polymorphism of the PCR products showed that each of the four erythromycin-resistant B. pertussis strains tested contained an A-to-G transition mutation at position 2058 (Escherichia coli numbering) of the 23S rRNA gene. The mutation was not found in seven erythromycin-susceptible isolates tested. Two of the resistant isolates were heterozygous, containing at least one mutant copy and one wild-type copy of the 23S rRNA gene. These results indicate that erythromycin resistance in these strains is likely due to a mutation of the erythromycin-binding site in the 23S rRNA gene. Identification of the resistance mechanism will facilitate development of molecular susceptibility testing methods that can be used directly on clinical specimens in the absence of an isolate.

Development of a real-time fluorescence PCR assay for rapid detection of the diphtheria toxin gene

We developed and evaluated a real-time fluorescence PCR assay for detecting the A and B subunits of diphtheria toxin (tox) gene. When 23 toxigenic Corynebacterium diphtheriae strains, 9 nontoxigenic C. diphtheriae strains, and 44 strains representing the diversity of pathogens and normal respiratory flora were tested, this real-time PCR assay exhibited 100% sensitivity and specificity. It allowed for the detection of both subunits of the tox gene at 750 times greater sensitivity (2 CFU) than the standard PCR (1,500 CFU). When used directly on specimens collected from patients with clinical diphtheria, one or both subunits of the tox gene were detected in 34 of 36 specimens by using the real-time PCR assay; only 9 specimens were found to be positive by standard PCR. Reamplification by standard PCR and DNA sequencing of the amplification product confirmed all real-time PCR tox-positive reactions. This real-time PCR format is a more sensitive and rapid alternative to standard PCR for detection of the tox gene in clinical material.

Bordetella pertussis isolates with a heterogeneous phenotype for erythromycin resistance

Erythromycin is currently being used for both prophylaxis and treatment of pertussis infections. Erythromycin resistance was first recognized in Bordetella pertussis in Arizona in 1994, and since then, three additional resistant isolates have been identified in the United States. To better assess the potential public health impact of erythromycin-resistant B. pertussis, we used the disk diffusion assay to evaluate the frequency of erythromycin resistance among 1,030 recently circulating U.S. isolates and found the rate of occurrence to be <1%. We also describe a novel heterogeneous phenotype, with erythromycin-resistant colonies appearing only after a 7-day incubation period. To optimize patient management, we recommend that clinicians be alert to potential treatment failures and that laboratorians use a 7-day incubation period when screening for resistance. Our ongoing national surveillance will continue to monitor for resistant B. pertussis isolates and their potential association with changing pertussis epidemiology.

Reproducibility of Bordetella pertussis genomic DNA fragments generated by XbaI restriction and resolved by pulsed-field gel electrophoresis

The intra- and interlaboratory variabilities of the molecular size measurements of each DNA fragment contributing to three pulsed-field gel electrophoresis (PFGE) profiles were assessed, as were the reproducibilities of the entire PFGE profiles for three Bordetella pertussis strains. The major source of variability within a laboratory occurred between subcultures rather than within gels or between gels. Each PFGE profile was generated reproducibly and was objectively defined by the molecular sizes of its composite fragments. A strain or profile most suitable for use as an internal reference standard was identified.

Molecular epidemiology of Bordetella pertussis by pulsed-field gel electrophoresis profile: Cincinnati, 1989-1996

Reported cases of pertussis have increased in the United States, with peaks occurring every few years. Bordetella pertussis isolates collected in Cincinnati from 1989 to 1996 were analyzed with pulsed-field gel electrophoresis (PFGE), to evaluate trends. Among 496 isolates, 30 PFGE profiles were identified; 32% were CYXXI-010, the profile that predominated each year. Eighteen profiles (198 strains) were identified in 1989-1992, 20 profiles (197 strains) were identified during the 1993 epidemic, and 11 profiles (101 strains) were identified in 1994-1996. From 1989 to 1996, among 42 patients, isolates from household members in 17 (89%) of 19 households had concordant PFGE profiles. There was no association between PFGE profile and seasonality, age, and hospitalization or pneumonia in infants <1 year old. The 1993 epidemic was associated primarily with an increased prevalence of PFGE profiles that circulated before and after 1993, which suggests that the epidemic was due to factors other than the emergence of a novel B. pertussis strain.

Analysis of Bordetella pertussis isolates from an epidemic by pulsed-field gel electrophoresis

We examined genetic variation among 78 clinical isolates of Bordetella pertussis, including 54 strains recovered during a 1986 pertussis epidemic. A total of 16 pulsed-field gel electrophoresis (PFGE) profiles, generated with each of three different enzymes (XbaI, SpeI, and DraI), were obtained from the epidemic and sporadic isolates included in the study. Indistinguishable profiles were seen among strains unrelated temporally or geographically, as well as among strains isolated sporadically from the same geographic areas. All isolates from the epidemic had indistinguishable PFGE profiles. The PFGE pattern of the epidemic strains was shared with only 1 of 25 strains isolated independently of the outbreak. This isolate was cultured from a specimen from a laboratory scientist who had been working with the epidemic strains, further implicating the usefulness of PFGE for the epidemiologic study of clinical strains of B. pertussis. Differences in PFGE profiles for single epidemic strains occurred occasionally upon repeated passage on agar medium, suggesting that subculturing of initial isolates should be minimized before pulsed-field analysis.

Comparison of Legionella pneumophila isolates by arbitrarily primed PCR and pulsed-field gel electrophoresis: analysis from seven epidemic investigations

Arbitrarily primed PCR (AP-PCR) and pulsed-field gel electrophoresis (PFGE) subtyping were applied to clinical and environmental isolates from seven unrelated outbreaks of Legionnaires' disease. The patterns observed with each method matched patient isolates and the epidemiologically linked source of disease for each of the seven outbreaks. PFGE allowed more discrimination among various isolates, although AP-PCR usually gave comparable results. With both methods, certain patterns appeared to predominate in the comparison of the seven outbreaks. Of five clinical isolates not associated with the outbreaks, three gave profiles distinct from those observed in the outbreaks by both methods. This suggests that there are at least two predominant subtypes of Legionella pneumophila serogroup 1 associated with outbreaks. Investigations of outbreaks of legionellosis should employ either PFGE or AP-PCR in addition to monoclonal antibody analysis.

Viability of Bordetella pertussis in four suspending solutions at three temperatures

We studied the survival of Bordetella pertussis in four suspending solutions (Casamino Acids broth, deionized water, phosphate-buffered saline, and serum inositol), subjected to three storage temperatures (4, -20, and -70 degrees C) and two freezing methods (direct freezing and fast-freezing in an ethanol-dry-ice bath). Recovery rates were higher for longer periods for suspensions stored at -70 degrees C than those stored at -20 or 4 degrees C. Serum inositol showed the highest recovery rates for all experimental conditions, followed by Casamino Acids, deionized water, and phosphate-buffered saline. Cell viability was significantly reduced in phosphate-buffered saline suspensions fast-frozen before storage. These results identify optimal conditions for storing B. pertussis cells and are applicable to the collection, transport, and storage of aspirated nasopharyngeal samples for use in the laboratory diagnosis of pertussis.

Rapid immunodot technique for identifying Bordetella pertussis

We developed and evaluated a rapid test with monoclonal antibodies to identify cultures of Bordetella pertussis. Samples of 5 microliters of cells suspended in formalin-saline were dried onto a nitrocellulose disk. The disk was placed in a filtration device, and 5-microliters volumes of murine monoclonal antibody directed against B. pertussis lipooligosaccharide and peroxidase conjugate were added consecutively, with washing after each addition. The disk was removed and immersed in peroxidase substrate solution. All of 66 B. pertussis isolates confirmed by direct fluorescent-antibody assay were correctly identified by using four different monoclonal antibodies. One of the monoclonal antibodies did not react with over 20 bacterial species tested, including other Bordetella, Acinetobacter, Haemophilus, Moraxella, Mycobacterium, Neisseria, and Staphylococcus spp. This technique detected > or = 2 micrograms of lipooligosaccharide per ml or > or = 5 x 10(8) B. pertussis cells per ml. This rapid procedure used small amounts of reagents, needed less equipment, and was less subjective and more specific than the direct fluorescent-antibody assay.

Replica plating of colonies from Listeria-selective agars to blood agar to improve the isolation of Listeria monocytogenes from foods

Bacterial colonies from Listeria-selective agars were replica plated to sheep blood agar to screen for beta-hemolysis. By using the replica plating method to test for the beta-hemolytic characteristic of all the colonies growing on Listeria-selective agars instead of picking 3 to 10 suspected colonies for further testing, we recovered Listeria monocytogenes from 59 of 142 Listeria-selective agar plates which contained colonies of hemolytic and nonhemolytic Listeria species and were negative when tested by conventional colony picks.

Evaluation of three newly developed direct plating media to enumerate Listeria monocytogenes in foods

LiCl-phenylethanol-moxalactam Agar (LPMA), ARS Modified McBride Agar, and Modified Vogel Johnson Agar were compared with previously tested plating media in the enumeration of Listeria monocytogenes from pasteurized whole milk, chocolate ice cream mix, Brie cheese, and raw cabbage. LPMA was most suitable for analyzing Brie cheese and cabbage. Gum base-nalidixic acid-tryptone-soya medium (previously tested) was most suitable for analyzing milk and chocolate ice cream mix.

Methods and Media to Isolate and Enumerate Listeria monocytogenes : A Review

Although long known to be harmful to livestock, Listeria monocytogenes has only recently been recognized as a serious food-borne pathogen in humans. Isolation of this organism from contaminated foods is often difficult due to the presence of naturally occurring microflora. Methods used to isolate L. monocytogenes have included cold incubation of samples, use of oblique lighting to examine the color of colonies, use of selective enrichment and plating media, and techniques in molecular biology. All of these methods have inherent disadvantages. A brief review of the methods and media used by various workers is presented in this paper.