Outbreak of infection by extended-spectrum beta-lactamase SHV-5-producing Serratia marcescens in a Mexican hospital.

Previous outbreaks caused by Serratia marcescens have been associated with contaminated medical equipment, intravenous fluids and inadequate hygiene. We carried out the molecular characterization of an outbreak produced by a cephalosporin-resistant S. marscescens that occurred in a Mexican hospital in August 1999. The lethality of this outbreak was 26%. Positive isolates were collected from 20 patients, one medical staff and three chlorhexidine disinfectant solutions. Results of PFGE, beta-lactamase patterns, sequencing of PCR amplifications, plasmid profiles, and mating experiments showed that the outbreak occurred by the dissemination of a S. marcescens SHV-5 producing strain. The adequate enforcement of procedures under the supervision of an infection control resulted in the abrupt end of the outbreak.

Outbreak of scarlet fever caused by an erythromycin-resistant Streptococcus pyogenes emm22 genotype strain in a day-care center.

We report an outbreak of scarlet fever and pharyngeal colonization with Streptococcus pyogenes in a day-care center in Mexico City. The outbreak strain was resistant to erythromycin but susceptible to clindamycin. T-type 11,12 serotype was found in eight isolates, from two patients and six carriers, which had the emm22 gene. The recognition of streptococci resistant to macrolides causing outbreaks has implications for infection control and for improving antibiotic prescribing patterns in the day-care setting.

[Antimicrobial resistance characteristics of clinical isolates of Streptococcus pyogenes]. / Características de la resistencia antimicrobiana de una colección clínica de Streptococcus pyogenes.

OBJECTIVE: To determine the antibiotic susceptibility of recent isolates of Streptococcus pyogenes and to evaluate the prevalence of macrolide-resistant phenotypes. MATERIAL AND METHODS: In 1999, we conducted a cross-sectional study at Mexico Children's Hospital "Federico Gomez", to analyze one hundred strains of S. pyogenes isolated from 1992 to 1998, in children with uncomplicated pharyngotonsillitis. Strains were frozen at the bacteriology lab until they were analyzed. Strains were tested for susceptibility against some beta-lactams, macrolides and clindamycin. Double-disk testing was carried out to evaluate erythromycin-resistant phenotypes. Data are presented using central tendency measures. RESULTS: All tested strains were not resistant to beta-lactams and clindamycin; 16% of the strains were resistant to macrolides and all of them belonged to phenotype M. CONCLUSIONS: Susceptibility testing is recommended to identify possible changes in antibiotic resistance to streptococci.

[Clinico-microbiological characteristics of meningitis caused by penicillin-resistant Streptococcus pneumoniae]]. / Características clínico-microbiológicas de la meningitis por Streptococcus pneumoniae resistente a la penicilina.

OBJECTIVE: To evaluate the susceptibility to antibiotics of Streptococcus pneumoniae isolated from cerebrospinal fluid of children with meningitis. To describe and compare the clinical and microbiological characteristics, treatment and outcome among children infected with strains either susceptible or resistant to penicillin and cephalosporin. MATERIAL AND METHODS: A total of 38 children with pneumococcal meningitis were prospectively enrolled in the Institutional Surveillance Program for Pneumococcal Infections during 1994-1998. Clinical and laboratory data were collected by chart review. RESULTS: Of the 38 children, 24 (63%) were less than 2 years of age, 11 (28.9%) had drug-resistant S. pneumoniae, 18.4% had intermediate resistance, 10.5% high level resistance and 2.6% also showed high level resistance to cefotaxime. The only associated factors (by Fisher's exact test) associated to resistance were: previous use of antibiotics (p = 0.2), underlying disease (p < 0.001). Course of illness and clinical course were similar for children infected with penicillin or cefotaxime susceptible, vs. non-susceptible strains. CONCLUSIONS: Current levels of S. pneumoniae resistance to penicillin and cephalosporin are not associated to an increase in mortality in children with meningitis.

Allele-specific PCR method based on pncA and oxyR sequences for distinguishing Mycobacterium bovis from Mycobacterium tuberculosis: intraspecific M. bovis pncA sequence polymorphism.

An allele-specific amplification method based on two genetic polymorphisms to differentiate Mycobacterium tuberculosis from Mycobacterium bovis was tested. Based on the differences found at position 169 in the pncA genes from M. tuberculosis and M. bovis, a PCR system which was able to differentiate most of the 237 M. tuberculosis complex isolates tested in one of the two species was developed. All 121 M. tuberculosis strains showed the expected base (cytosine) at position 169. Most of the M. bovis isolates had a guanine at the cited position. Nevertheless, 18 of the 116 M. bovis isolates, all of them goat isolates, showed the pncA polymorphism specific to M. tuberculosis. These results suggest that goat M. bovis may be the nicotinamidase-missing link at the origin of the M. tuberculosis species. Based on the polymorphism found at position 285 in the oxyR gene, the same system was used to differentiate M. tuberculosis from M. bovis. In this case, DNAs from all 121 M. tuberculosis isolates had the expected base (guanine) at this position. In addition, all 116 M. bovis isolates, including those from goats, showed the identical polymorphism (adenine). The oxyR allele-specific amplification method can differentiate M. bovis from M. tuberculosis, is rapid (results can be obtained in less than 3 h), and is easy to perform.

In vitro plasmid-encoded resistance to quinolones.

The possibility of plasmid-encoded quinolone resistance is explored in two model systems. In the first, increasing amounts of wild-type gyrA allele moderately increased minimum inhibitory concentrations to quinolone antibiotics. In the second model, a mutant gyrA allele encoded by a multicopy plasmid produced a quinolone resistance phenotype upon its expression in a quinolone-susceptible Escherichia coli strain.

Genetic characterization of multidrug-resistant Mycobacterium bovis strains from a hospital outbreak involving human immunodeficiency virus-positive patients.

Nineteen multidrug-resistant (MDR) Mycobacterium complex strains isolated in a nosocomial outbreak were characterized at the molecular level. The strains were microbiologically characterized as Mycobacterium bovis. The mpt40 sequence was not present in chromosomal DNA from these strains, supporting the fact that they were M. bovis. All of the isolates were resistant to isoniazid, rifampin, pyrazinamide, ethambutol, streptomycin, para-aminosalicylic acid, clarithromycin, cycloserine, ethionamide, ofloxacin, capreomycin, and amikacin. By performing the standardized IS6110 fingerprinting by restriction fragment length polymorphism (RFLP) analysis, we were able to differentiate two groups (groups A and B) containing two (16 isolates) and three (3 isolates) IS6110 copies, respectively. These strains were typed by spoligotyping, developed to distinguish M. bovis strains and also to distinguish them from M. tuberculosis strains (J. Kamerbeek et al., J. Clin. Microbiol. 35:907-914, 1997). All the strains were confirmed to be M. bovis. In addition, spoligotyping showed a difference in only 1 of 43 spacers between RFLP groups A and B. The rpo beta region of several strains representative of each identified group was cloned and sequenced, and identical mutations (Ser-531 to Leu) responsible for the rifampin resistance phenotype were found. To our knowledge, this is the first characterization at the molecular level of an MDR M. bovis strain responsible for a nosocomial outbreak.

Comparative analysis of plasmids from nosocomial Klebsiella pneumoniae strains isolated from two hospitals.

A total of 46 clinical isolates of Klebsiella pneumoniae were studied. Of these, 33 were from "Hospital Infantil de México" (HIM) and 13 from "Hospital General de México" (HGM). The susceptibility of these strains to five antibiotics, as well as the plasmid DNA profiles, were determined for each group. Antibiotic susceptibility profiles were very similar in strains from both hospitals; however, most of the strains analyzed exhibited heterogeneous plasmid DNA profiles. Results showed that strains isolated in the two hospitals did not differ regarding morphology, biochemical profiles, antibiotic susceptibility or plasmid populations, and these characteristics may not be used as markers to differentiate Klebsiella pneumoniae strains from different hospitals.

[Polymerase chain reaction (PCR) in clinical diagnosis. Review of the use of the technique]. / Reacción de polimerasa en cadena (PCR) en el diagnóstico clínico. Revisión del uso de la técnica.

The use in clinical diagnosis of the polymerase chain reaction (PCR) technique is reviewed. This method consists of the amplification of a single molecule of DNA (50 to 2000 base pairs in length) to more than a million copies of DNA in a few hours. Relevant advantages of this technique are its specificity, sensitivity and ability to amplify impure DNA. Diagnostic methods for diagnosis of infectious diseases and genetic disorders in humans have been developed recently.

[Detection of TEM-beta-lactamase in strains of Haemophilus influenzae resistant to ampicillin using the polymerase chain reaction (PCR)]. / Detección de betalactamasa tipo TEM en cepas de Haemophilus influenzae resistentes a ampicilina utilizando la reacción de polimerasa en cadena (PCR).

With the purpose of determining the type of beta-lactamases that mediate ampicillin resistance to in Haemophilus influenzae strains in the Hospital Infantil de México "Federico Gómez", we determined the minimum inhibitory concentration of 180 strains, isolated from different sources, to ampicillin, amoxicillin-clavulanic acid and ampicillin-sulbactam. All ampicillin resistant strains (29) were beta-lactamase positive as determined by nitrocephin hydrolysis. Using PCR with the primers from pBR322, we detected the presence of the gene for the TEM-beta-lactamase in 100% of the ampicillin resistant strains.