Carmen Ardanuy

Changes in antimicrobial resistance, serotypes and genotypes in Streptococcus pneumoniae over a 30-year period

Over the past three decades, antimicrobial resistance in Streptococcus pneumoniae has dramatically increased worldwide. Non-susceptibility to penicillin in S. pneumoniae was first described in Australia in 1967, and later in New Guinea (1974), South Africa (1977), and Spain (1979). Most of these strains showed resistance to multiple antibiotics and belonged to serotypes 6A, 6B, 19A, 19F, and 23F. By the late 1980s and 1990s, the emergence and rapid dissemination of antibiotic-resistant pneumococci was observed in southern and eastern Europe, North America, South America, Africa, and Asia. Great geographical variability, both in serotype distribution and in the prevalence of resistant pneumococci, has been reported. However, the highest rates of resistance to penicillin and erythromycin worldwide were found in serotypes 6B, 6A, 9V, 14, 15A, 19F, 19A, and 23F. The introduction of the seven-valent pneumococcal conjugate vaccine (PCV7) in the 2000s and a reduction in antimicrobial use were associated with a significant decline in the incidence of invasive pneumococcal infections and in rates of antibiotic resistance in the USA. However, an increase in the incidence of infections caused by non-PCV7 serotypes, especially multiresistant serotype 19A pneumococci, has been observed in many countries over the last 5 years. The dynamic character of serotypes and antibiotic resistance in S. pneumoniae should be controlled by a policy of prudent antibiotic use and by implementation of the new generation of conjugate vaccines.

Molecular characterization of two high-level ceftriaxone-resistant Neisseria gonorrhoeae isolates detected in Catalonia, Spain

OBJECTIVES The aim of this study was to characterize the first two extended-spectrum cephalosporin-resistant and multidrug-resistant (MDR) Neisseria gonorrhoeae isolates collected from two sexually related patients (men who have sex with men) in Spain. METHODS Antimicrobial susceptibility was studied by Etest. Genes involved in quinolone, ceftriaxone and multidrug resistance were amplified by PCR and sequenced in both directions. The isolates were typed by N. gonorrhoeae multi-antigen sequence typing (NG-MAST). RESULTS The two isolates had the same MDR profile, showing resistance to penicillin (MIC 0.094 mg/L; β-lactamase negative), ceftriaxone (MIC 1.5 mg/L), cefixime (MIC 1.5 mg/L), cefotaxime (MIC 1 mg/L), ciprofloxacin (MIC >32 mg/L) and tetracycline (MIC 1.5 mg/L). NG-MAST showed that both isolates belonged to sequence type (ST) 1407 (porB-908 and tbpB-110). Ciprofloxacin resistance was due to amino acid substitutions in GyrA (S91F and D95G) and ParC (S87R). An A deletion in the promoter of the MtrCDE efflux pump (mtrR) was detected. No changes were detected in the pilQ gene. The outer membrane protein PorB showed two substitutions at G120K and A121N. An L421P substitution was observed in the PBP1A (ponA) sequence. The sequence of PBP2 (penA) showed a mosaic structure related to genotype XXXIV with a single additional amino acid substitution (A501P). This genotype was identical to a recently described French isolate (F89). CONCLUSIONS This is the first reported case of high-level extended-spectrum cephalosporin-resistant N. gonorrhoeae transmission. The molecular typing and MDR genotype suggest possible European spread of this strain, highlighting the need for surveillance and the importance of testing the susceptibility of N. gonorrhoeae to extended-spectrum cephalosporins.

Efficacy of Colistin versus β-Lactams, Aminoglycosides, and Rifampin as Monotherapy in a Mouse Model of Pneumonia Caused by Multiresistant Acinetobacter baumannii

ABSTRACT The treatment of life-threatening infections due to carbapenem-resistant Acinetobacter baumannii has become a serious challenge for physicians worldwide. Often, only colistin shows in general good in vitro activity against these carbapenem-resistant strains, but its antibacterial efficacy in comparison with the antibiotics most used in clinical practice is not well known. We studied the efficacy of colistin versus those of imipenem, sulbactam, tobramycin, and rifampin in an experimental pneumonia model with immunocompetent mice. We used three strains of A. baumannii corresponding to the main clones (A, D, and E) involved in the outbreaks of our hospital, with different grades of resistance to imipenem (imipenem MICs of 1, 8, and 512 μg/ml, respectively) and to the other antibiotics. The MIC of colistin was 0.5 μg/ml for the three strains. Reduction of log10 CFU/g in lung bacterial counts, clearance of bacteremia, and survival versus results with controls were used as parameters of efficacy. Imipenem and sulbactam (Δlung counts: −5.38 and −4.64 log10 CFU/ml) showed the highest level of bactericidal efficacy in infections by susceptible and even intermediate strains. Tobramycin and rifampin (−4.16 and −5.15 log10 CFU/ml) provided good results against intermediate or moderately resistant strains, in agreement with killing curves and pharmacodynamics. On the contrary, colistin showed the weakest antibacterial effect among the antibiotics tested, both in killing curves and in the in vivo model (−2.39 log10 CFU/ml; P < 0.05). We conclude that colistin did not appear as a good option for treatment of patients with pneumonia due to carbapenem-resistant A. baumannii strains. Other alternatives, including combinations with rifampin, may offer better therapeutic profiles and thus should be studied.

Risk factors for faecal carriage of Klebsiella pneumoniae producing extended spectrum β-lactamase (ESBL-KP) in the intensive care unit

In the course of an outbreak of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) in an intensive care unit (ICU), we conducted active surveillance to determine the risk factors for ESBL-KP faecal colonization of patients. We used weekly rectal samples during a four-month period. ESBL-KP was found in the faeces of 72 of 188 (38%) patients, and 42 (58%) of them were colonized within the first week of admission to the ICU. The probability of remaining free of faecal colonization was less than 20% at 30 days of ICU admission. The risk factors associated with ESBL-KP faecal colonization were clinical severity score at admission (P = 0.004), arterial catheterization (P = 0.002), total parenteral nutrition (P = 0.04), urinary catheterization (P = 0.01), mechanical ventilation (P < 0.001), and previous antibiotic therapy (P = 0.04). A logistic regression analysis identified duration of urinary catheterization (OR:3.5; 95% CI 1.2-10.3) and mechanical ventilation (OR:4.6; 95% CI 1.1-19.3) as independent risk factors for ESBL-KP faecal colonization. Our results suggest that in an ESBL-KP prevalent environment, manipulations that facilitate cross-infection are the most relevant in the acquisition of the micro-organism and risk increases throughout hospitalization.

Pneumococcal pneumonia presenting with septic shock: Host- and pathogen-related factors and outcomes

Background: Host- and pathogen-related factors associated with septic shock in pneumococcal pneumonia are not well defined. The aim of this study was to identify risk factors for septic shock and to ascertain patient outcomes. Serotypes, genotypes and antibiotic resistance of isolated strains were also analysed. Methods: Observational analysis of a prospective cohort of non-severely immunosuppressed hospitalised adults with pneumococcal pneumonia. Septic shock was defined as a systolic blood pressure of <90 mm Hg and peripheral hypoperfusion with the need for vasopressors for >4 h after fluid replacement. Results: 1041 patients with pneumococcal pneumonia diagnosed by Gram stain and culture of appropriate samples and/or urine antigen test were documented, of whom 114 (10.9%) had septic shock at admission. After adjustment, independent risk factors for shock were current tobacco smoking (OR, 2.11; 95% CI, 1.02 to 4.34; p = 0.044), chronic corticosteroid treatment (OR, 4.45; 95% CI, 1.75 to 11.32; p = 0.002) and serotype 3 (OR, 2.24; 95% CI, 1.12 to 4.475; p = 0.022). No significant differences were found in genotypes and rates of antibiotic resistance. Compared with the remaining patients, patients with septic shock required mechanical ventilation more frequently (37% vs 4%; p<0.001) and had longer length of stay (11 vs 8 days; p<0.001). The early (10% vs 1%; p<0.001) and overall case fatality rates (25% vs 5%; p<0.001) were higher in patients with shock. Conclusions: Septic shock is a frequent complication of pneumococcal pneumonia and causes high morbidity and mortality. Current tobacco smoking, chronic corticosteroid treatment and infection caused by serotype 3 are independent risk factors for this complication.

Epidemiological significance of cutaneous, pharyngeal, and digestive tract colonization by multiresistant Acinetobacter baumannii in ICU patients

The aim of this prospective study was to assess the relative epidemiological role of digestive tract colonization by Acinetobacter baumannii, in comparison with other body site colonizations, in patients admitted to intensive care units (ICUs). From January to May 1995, axillary, pharyngeal and rectal swabs were taken together within the first 48 h of admission, and then weekly during ICU stay. Seventy-three patients were included, 48 of them (66%) had axillary, pharyngeal, or rectal colonization with A. baumannii, nine (19%) of these 48 during the first 48 h and the remaining 28 (77%) during the first week. Twenty-one (29%) had clinical samples positive for A. baumannii and axillary, pharyngeal, or rectal colonization. In 15 of these 21 (71%), colonization on body sites occurred prior to isolation from clinical samples (mean seven days, range 1-20). Throughout admission, rates of detection of A. baumannii were 75% (36/48) for axillary or pharyngeal swabs and 77% (37/48) for rectal swabs. Combination of two body site swabs yielded culture positive rates of 90% (43/48) for axillary-pharyngeal or axillary-rectal sites, and 96% (46/48) for pharyngeal-rectal. Two epidemic clones were defined by antibiotype and pulsed-field gel electrophoresis (PFGE) of SmaI DNA digests in 48 isolates from 11 patients. We conclude that body sites of patients were a major reservoir for A. baumannii infections in the outbreak. This finding cases doubt on the value of selective decontamination of the digestive tract as an additional infection control measure in this kind of outbreak. The weekly performance of pharyngeal and rectal swabs appears to detect A. baumannii colonization early among ICU patients and enables barrier methods to be applied rapidly.

Emergence of a multidrug-resistant clone (ST320) among invasive serotype 19A pneumococci in Spain

OBJECTIVES Multidrug-resistant Streptococcus pneumoniae isolates of serotype 19A have emerged all over the world in recent years. The aim of this study was to characterize highly penicillin-resistant pneumococcal strains of the 19A serotype, collected in Spain from 1997 to 2007 from patients with invasive disease. METHODS Antibiotic susceptibility was studied by microdilution. All penicillin-resistant pneumococci were typed by PFGE and selected strains were studied by multilocus sequence typing (MLST). The presence of genes related to the Tn916 family of transposons was investigated by PCR. RESULTS From a total of 1197 invasive pneumococcal isolates of serotype 19A received at the Spanish Reference Laboratory between 1997 and 2007, 51 (4.3%) strains showed high-level resistance to penicillin (MICs of 2-4 mg/L). These 51 isolates belonged to three multiresistant clones related to sequence type (ST)81 (n = 21), ST320 (n = 19) and ST276 (n = 11). All 51 serotype 19A pneumococci were tetracycline-resistant and had the tet(M) gene, and 41 strains were macrolide-resistant, harbouring the erm(B) gene. The presence of int and xis genes was detected in all strains associated with other genes of the Tn916 family. CONCLUSIONS The rise in penicillin-resistant serotype 19A invasive pneumococci in Spain was associated with the emergence and clonal spread of two worldwide-disseminated multiresistant clones (ST276 and ST320). The Spain(23F)-1-19A (ST81) clone remained stable throughout the study period. Multidrug resistance was associated with transposons of the Tn916 family.

Fluoroquinolone Resistance in Penicillin-resistant Streptococcus pneumoniae Clones, Spain

Of 75 clones isolated, 1 had ciprofloxacin efflux, and 74 had mutations at the DNA topoisomerase gene.

Full-Genome Dissection of an Epidemic of Severe Invasive Disease Caused by a Hypervirulent, Recently Emerged Clone of Group A Streptococcus

Group A Streptococcus (GAS) causes an exceptionally broad range of infections in humans, from relatively mild pharyngitis and skin infections to life-threatening necrotizing fasciitis and toxic shock syndrome. An epidemic of severe invasive human infections caused by type emm59 GAS, heretofore an exceedingly rare cause of disease, spread west to east across Canada over a 3-year period (2006 to 2008). By sequencing the genomes of 601 epidemic, historic, and other emm59 organisms, we discovered that a recently emerged, genetically distinct emm59 clone is responsible for the Canadian epidemic. Using near-real-time genome sequencing, we were able to show spread of the Canadian epidemic clone into the United States. The extensive genome data permitted us to identify patterns of geographic dissemination as well as links between emm59 subclonal lineages that cause infections. Mouse and nonhuman primate models of infection demonstrated that the emerged clone is unusually virulent. Transmission of epidemic emm59 strains may have occurred primarily by skin contact, as suggested by an experimental model of skin transmission. In addition, the emm59 strains had a significantly impaired ability to persist in human saliva and to colonize the oropharynx of mice, and seldom caused human pharyngitis. Our study contributes new information to the rapidly emerging field of molecular pathogenomics of bacterial epidemics and illustrates how full-genome data can be used to precisely illuminate the landscape of strain dissemination during a bacterial epidemic.

Molecular characterization of macrolide- and multidrug-resistant Streptococcus pyogenes isolated from adult patients in Barcelona, Spain (1993–2008)

OBJECTIVES The increase in erythromycin resistance among Streptococcus pyogenes isolates is a cause for concern. We analysed trends in macrolide resistance, phenotypes, genotypes, resistance determinants and transposons among erythromycin-resistant S. pyogenes isolates collected from adults in a Barcelona hospital (1993-2008). METHODS Antibiotic susceptibility was studied by microdilution. Molecular typing was performed by PFGE, emm typing and multilocus sequence typing (MLST). Macrolide resistance genes and those related to the Tn916 family of transposons were detected by PCR. RESULTS Ninety-nine (18.3%) of 541 isolates were erythromycin resistant. Erythromycin resistance rates progressively increased from 0% (0/24) in 1993-1994 to 34.2% (50/146, P < 0.001) in 2001-2004, then falling to 7.4% (8/108, P = 0.02) in 2007-2008. Sixty-six erythromycin-resistant isolates were available for molecular studies. Of these, 26 had an M phenotype [mef(A)] and 40 had an MLS(B) phenotype [erm(B), n = 33; and erm(TR), n = 7]. Among M-phenotype isolates, the most frequent genotypes (88.5%) were emm4-ST39, emm6-ST382 and emm75-ST49, whereas genotypes emm11-ST403, emm28-ST52 and emm25-ST350 accounted for 72.5% of MLS(B)-phenotype isolates. Twenty-five isolates harboured both erm(B) and tet(M) genes related to the Tn916 family of transposons, Tn6002 being the most frequent. Ten isolates (10.1%) were ciprofloxacin non-susceptible, related to the emm6-ST382 clone with a ParC S79A change. CONCLUSIONS The peak of macrolide resistance rates among S. pyogenes observed in the 2001-2004 period was associated with an increase in the MLS(B) phenotype caused by the spread of emm11-ST403 and emm28-ST52 clones harbouring transposons of the Tn916 family. However, erythromycin resistance rates decreased significantly in the 2007-2008 period.