The history, taxonomy, geographic distribution, clinical disease, and therapy of the pathogenic nonpigmented or late-pigmenting rapidly growing mycobacteria (RGM) are reviewed. Community-acquired disease and health care-associated disease are highlighted for each species. The latter grouping includes health care-associated outbreaks and pseudo-outbreaks as well as sporadic disease cases. Treatment recommendations for each species and type of disease are also described. Special emphasis is on the Mycobacterium fortuitum group, including M. fortuitum, M. peregrinum, and the unnamed third biovariant complex with its recent taxonomic changes and newly recognized species (including M. septicum, M. mageritense, and proposed species M. houstonense and M. bonickei). The clinical and taxonomic status of M. chelonae, M. abscessus, and M. mucogenicum is also detailed, along with that of the closely related new species, M. immunogenum. Additionally, newly recognized species, M. wolinskyi and M. goodii, as well as M. smegmatis sensu stricto, are included in a discussion of the M. smegmatis group. Laboratory diagnosis of RGM using phenotypic methods such as biochemical testing and high-performance liquid chromatography and molecular methods of diagnosis are also discussed. The latter includes PCR-restriction fragment length polymorphism analysis, hybridization, ribotyping, and sequence analysis. Susceptibility testing and antibiotic susceptibility patterns of the RGM are also annotated, along with the current recommendations from the National Committee for Clinical Laboratory Standards (NCCLS) for mycobacterial susceptibility testing.

Clinical and Taxonomic Status of Pathogenic Nonpigmented or Late-Pigmenting Rapidly Growing Mycobacteria

Organisms causing nosocomial infection are frequently resistant to antimicrobial agents. Studies of the reasons for this have been hindered by difficulties in defining terms, by selection biases, by artifacts produced by study methods, and by failure to control for confounding variables. Major factors leading to increased prevalence of resistant organisms in hospitals are changes in organisms causing nosocomial infection (due in part to changes in characteristics of hospital populations and in procedures and instruments used in patient care), increasing prevalence of resistance in bacteria causing community-acquired infection, and use of antimicrobial agents. A causal relationship between antibiotic usage and resistance of hospital organisms is supported by consistent association and concurrent variation in several populations, presence of a dose-response pattern, and existence of a reasonable biologic model to explain the relationship. Major influences on emergence of resistant hospital bacteria include antimicrobial effects in treated individuals, mechanisms for transfer of resistance between bacteria, and routes of transmission within the hospital for bacteria or their resistance factors. Barrier isolation techniques can help control resistant hospital bacteria. However, virtually all reports agree that careful, discriminating use of antimicrobial agents remains the keystone for minimizing this problem. This need must be communicated more effectively to prescribers.

Antimicrobial Resistance in Hospital Organisms and Its Relation to Antibiotic Use

Epidemiologic evaluation of enterococci has been limited by the lack of a simple and effective method for comparing strains. In this study, we have compared chromosomal restriction endonuclease digestion patterns of 27 isolates of Enterococcus faecalis from three different locations by using pulsed-field electrophoresis of large chromosomal fragments (14 to 1,000 kilobases). All but two isolates generated a clear, evaluable pattern with a single lysis and digestion, and the remaining two were visualized when a larger quantity of bacteria was used. All isolates from different locations generated different restriction patterns, as did most isolates within a single location; there was also evidence of spread of strains between individuals in each location. The ease with which this analysis can be performed, together with the clarity and polymorphism seen in the patterns, suggests that this technique will be very useful for epidemiological evaluations of nosocomial enterococcal infections.

Comparison of genomic DNAs of different enterococcal isolates using restriction endonucleases with infrequent recognition sites.

We investigated the use of ribosomal RNA (rRNA) as a probe for molecular epidemiology of bacterial pathogens. The chromosomal DNA of Escherichia coli, Pseudomonas cepacia, and nontypable Haemophilus influenzae was digested with EcoRI. Agarose gel electrophoresis, Southern blotting, and hybridization by 32P-labeled rRNA revealed eight to 13 bands. The P. cepacia and H. influenzae banding patterns, observed by using an E. coli rRNA probe, were identical to those produced with homologous rRNA probes. Polymorphism of several hybridization bands distinguished all E. coli isolates, nine of 10 H. influenzae isolates, and seven of eight P. cepacia isolates. Two to four bands were common to all P. cepacia and E. coli isolates. The banding patterns of H. influenzae isolates cultured from the trachea and blood of an infant and from the mother's cervix were identical. These data demonstrate that this method is a widely applicable system for determining the molecular epidemiology of genetically diverse gram-negative organisms.

A Broad-Spectrum Probe for Molecular Epidemiology of Bacteria: Ribosomal RNA

For comparison of the impacts of infections due to antimicrobial-resistant bacteria with those of infections due to antimicrobial-susceptible strains of the same bacteria, data were evaluated from 175 published and unpublished reports of investigations of nosocomial and community-acquired infections with selected bacteria. The evaluation of outcomes of hospital-acquired infections with resistant organisms was often confounded by risk factors also associated with poor outcomes. Nevertheless, for both nosocomial and community-acquired infections, the mortality, the likelihood of hospitalization, and the length of hospital stay were usually at least twice as great for patients infected with drug-resistant strains as for those infected with drug-susceptible strains of the same bacteria. Poor outcomes could be attributed both to the expected effects of ineffective antimicrobial therapy and to the unexpected occurrence of drug-resistant infections complicated by prior antimicrobial therapy for other medical problems. Although the adverse economic and health effects of drug-resistant bacterial infections can only be roughly quantified, it is concluded that antimicrobial resistance is an important health problem and an economic burden to society.

Health and Economic Impacts of Antimicrobial Resistance

Depuis 15 ans on observe des epidemies de maladies infectieuses dues a des souches bacteriennes resistantes dans le monde

Antibiotic Resistance in Developing Countries

The techniques themselves fall into two categories: indirect and direct techniques Indirect techniques include agarose gel electrophoresis and restriction endonuclease analysis Electrophoresis of plasmids in an agarose gel provides a fairly accurate estimate of the size of a plasmid molecule [3] Re- striction endonucleases are bacterial enzymes that cleave double-stranded DNA at specific recognition sites to generate a series of plasmid fragments [4] The number and sizes of these fragments depend upon the number and location of specific recognition sites present in the plasmid molecule If two plasmids are of the same size and yield identical patterns of fragments on restriction endonuclease analysis, especially if two or more restriction enzymes are used, they may be assumed to be identical or nearly so Conversely, two plasmids of the same size may have entirely different base sequences; this can be recognized by the different fragment patterns generated by a restriction endonuclease Finally, two plasmids may be quite different in size but possess one or more homologous regions of DNA; an intimation of this may be obtained by finding shared fragments on restriction endonuclease analysis Direct techniques involve hybridization of DNA

Molecular analysis of plasmids in epidemiologic investigation.

At the Vanderbilt University Medical Center, Nashville, Tennessee, resistance to gentamicin was encountered with increasing frequency among several species of gram-negative bacilli between 1973 and 1977. Representative strains were screened for plasmid DNA content using agarose gel electrophoresis. In strains of Pseudomonas aeruginosa and Serrati marcescens isolated early in the outbreak, gentamicin resistance was mediated by a common 9.8-megadalton nonconjugative plasmid. Either an 80- or a 100-megadalton transferable plasmid coexisted with the nonconjugative plasmid in the isolates of Serratia. Transposition between the 100- and 9.8-megadalton plasmids in this species resulted in the formation of a 105-megadalton conjugative plasmid that mediated gentamicin resistance; this was observed in strains of Serratia and Klebsiella isolated in 1976-1977. Thus, during this five-year investigation separate outbreaks of nosocomial infections that were caused by different bacterial species were shown to be related by the presence of plasmids that contained a common transposable DNA sequence.

Evolution of a Plasmid Mediating Resistance to Multiple Antimicrobial Agents During a Prolonged Epidemic of Nosocomial Infections

Haemophilus influenzae type B, strain W-2, is highly resistant to ampicillin (MIC, 12.5 mug/ml). The ampicillin resistance of strain W-2 was transferred to an antibiotic-sensitive strain TF-2 (RifR, SmR) during mixed incubation on membrane filters at 36 C(transfeer frequency, 4.6 times 10(-5) per donor). Resistance was also transferred from the primary recipient to a secondary one (TF-3, EryR, NovR). The transfer frequency between these derivative strains was 10(-4) after incubation for 30 min. Resistance in strain W-2 remained even after growth in the presence of ethidium bromide or at an elevated temperature, although ampicillin resistance was lost from 13%-25% of transcipient cells after growth in broth. Strain W-2 and transcipients of ampicillin resistance had equivalent levels of beta-lactamase activity, while sensitive segregants and recipient strains demonstrated little or no enzyme activity. Transfer of ampicillin resistance between strains of H. influenzae is probably mediated by conjugation since transfer (1) requires cell-to-cell contact, (2) remains unchanged in the presence of DNase I, and (3) occurs in the absence of demonstrable bacteriophage.

Transfer of Ampicillin Resistance between Strains of Haemophilus influenzaeType B

Four newer cephalosporins (cefazolin, cefamandole, SK&F 59962, and cefoxitin) were investigated for determination of their antistaphylococcal activity and relative stability to staphylococcal beta-lactamase (penicillinase). Crude preparations of beta-lactamase from recent clinical isolates of Staphylococcus aureus were used. Cefamandole and SK&F 59962 were highly active against both large and small inocula of staphylococci and were resistant to staphylococcal beta-lactamase. Cefoxitin, although resistant to beta-lactamase, possessed less antibacterial potency but was still approximately as active as methicillin. Cefazolin was somewhat more susceptible to staphylococcal beta-lactamase than the other three agents and resembled cephaloridine in this respect. With minor exceptions, a correlation was found between the susceptibility of different agents to beta-lactamase and the magnitude of the effect of inoculum size when the drugs were tested against large and small inocula of staphylococci.

Farrar We

Papers

Antibiotic Resistance in Developing Countries

Molecular analysis of plasmids in epidemiologic investigation.

Evolution of a Plasmid Mediating Resistance to Multiple Antimicrobial Agents During a Prolonged Epidemic of Nosocomial Infections

Transfer of Ampicillin Resistance between Strains of Haemophilus influenzaeType B

Antistaphylococcal Activity and β-Lactamase Resistance of Newer Cephalosporins