Epidemiological and biological characteristics of methicillin-resistant staphylococcal infections in a Mexican hospital

Antibiotic Resistance and Biofilm Production in Staphylococcus epidermidis Strains, Isolated from a Tertiary Care Hospital in Mexico City

Staphylococcus epidermidis strains isolated from nosocomial infections represent a serious problem worldwide. In various Mexican states several reports have shown isolates from hospitals with antibiotic resistance to methicillin. In Mexico City, there is scarce information on staphylococcal infections in hospitals. Here, our research findings are shown in a four-year period study (2006–2010) for Staphylococcus epidermidis strains. Susceptibility and/or resistance to antibiotics in SE strains were assessed by phenotypic and molecular methods as mecA gene by PCR, as well as the correlation with biofilm production for these isolates and the relationship to the infection site. Out of a total of 161 (66%) negative biofilm SE strains, just 103 (64%) SE strains were confirmed as MRSE by PCR to mecA gene. From 84 (34%) positive biofilm SE strains, 76 (91%) were confirmed as MRSE by PCR to mecA gene. Higher percentages of resistance to antibiotics and higher number of resistance markers were found in biofilm-forming clinical strains (9 to 14) than non-biofilm-forming SE strains (3 to 8). These research findings represent a guide to establish infection control programs for this hospital.

Slime production and antibiotic susceptibility in staphylococci isolated from clinical samples

A total of 187 isolates from several clinical specimens were identified to species level as 129 Staphylococcus aureus strains and 58 coagulase-negative staphylococci (CNS) strains by the API Staph System (Biomerieux). Slime production was detected both by the conventional Christensen's method as well as by the Congo red agar method. Seventy-two strains of staphylococci isolates (38.5%) were found to be slime producers by Christensen's test tube method whereas 58 strains (31%) were slime positive with Congo red agar method. There was no statistically significant difference between the two methods for the detection of slime production (P > 0.05). Susceptibility of isolates against antimicrobial agents was tested by the disk diffusion method. Staphylococcal species had resistance to one or more antibiotics. Among the various antimicrobial agents, oxacillin (71.1%) and erythromycin (47.1%) showed higher resistance than most of the agents used against all isolates. Oxacillin resistant S. aureus (ORSA) and oxacillin resistant coagulase-negative staphylococci (ORCNS), 97 (75.2%) and 36 (62.1%) respectively were frequently observed in strains isolated from clinical materials. Among the ORSA strains, two strains were resistant to vancomycin. Moreover, 96 (74.4%) of 129 S. aureus strains were positive for beta-lactamase enzyme. However, 78 (81.25%) of 96 beta-lactamase positive S. aureus strains were beta-lactamase positive ORSA isolates, but none of them had vancomycin resistance.

In vitro activity effects of combinations of cephalothin, dicloxacillin, imipenem, vancomycin and amikacin against methicillin-resistant Staphylococcus spp. strains

Background

combinations of drugs has been proposed as an alternative for oxacillin-resistant staphylococci infections, however, limited information about in vitro combinations are available for multi-resistant strains. The objective of this study was to describe the interaction of beta-lactams in combination with vancomycin or amikacin against 26 oxacillin and amikacin-resistant nosocomial Staphylococcus spp. isolates.

Methods

activity of dicloxacillin plus amikacin, cephalothin plus amikacin, cephalothin plus vancomycin, imipenem plus vancomycin and vancomycin plus amikacin was evaluated by checkerboard synergy tests and the fractional inhibitory concentration index (FIC) was calculated. Results: dicloxacillin plus amikacin, and cephalothin plus amikacin were synergistic or partially synergistic in 84.6% and 100% respectively. For nearly half of the isolates the mean concentrations of dicloxacillin, cephalothin and amikacin at which FIC indexes were calculated were achievable therapeutically. Vancomycin plus amikacin had synergistic effect only against two isolates, and partially synergistic in 38.6%. For the combinations vancomycin plus cephalothin and vancomycin plus imipenem the effect was additive in 76.9% and 80.7% respectively.

Conclusion

in this study the checkerboard analysis showed that amikacin in combination with cephalothin or dicloxacillin was synergistic against most of the resistant strains of S. aureus and coagulase-negative Staphylococcus. Vancomycin in combination with a beta-lactam (cephalothin or imipenem) showed additivity. An indifferent effect predominated for the combination vancomycin plus amikacin. Even though a synergistic effect is expected when using a beta-lactam plus amikacin combination, it is possible that the effect cannot be clinically achievable. Careful selection of antimicrobial combinations and initial MICs are mandatory for future evaluations.

Staphylococcal skin infections in children: rational drug therapy recommendations

Staphylococcus aureus remains one of the most common and troublesome of bacteria causing disease in humans, despite the development of effective antibacterials and improvement in hygiene. The organism is responsible for over 70% of all skin and soft tissue infections in children and accounts for up to one-fifth of all visits to pediatric clinics. Skin and soft tissue infections that are predominantly caused by S. aureus include bullous and non-bullous impetigo, folliculitis, furunculosis, carbunculosis, cellulitis, surgical and traumatic wound infections, mastitis, and neonatal omphalitis. Other skin and soft tissue infections may also be caused by S. aureus but are often polymicrobial in origin and require special consideration. These include burns, decubitus ulcers (particularly in the perianal region), puncture wounds of the foot, as well as human and mammalian bites. Treatment of staphylococcal skin infections varies from topical antiseptics to prolonged intravenous antibacterials, depending on severity of the lesions and the health of the child. The treatment of choice for oral antibacterials remains the penicillinase-resistant penicillins such as flucloxacillin. Cefalexin and erythromycin are suitable cost-effective alternatives with broader cover, although care must be taken with the use of macrolides because of development of resistance to multiple families of antibacterials, particularly the lincosamides. Other cephalosporins such as cefadroxil and cefprozil are also effective, can be given once daily and have a better tolerability profile -- while azithromycin has a further advantage of a 3-day course. However, all of these agents are more expensive. Although the antibacterials have been given for 10 days in most clinical trials, there is no evidence that this duration is more effective than a 7-day course. In children requiring intravenous therapy, ceftriaxone has a major advantage over other antibacterials such as sulbactam/ampicillin and cefuroxime in that it can be given once daily and may, therefore, be suitable for outpatient treatment of moderate-to-severe skin infections. Newer-generation cephalosporins and loracarbef are also effective and have a broader spectrum of activity, but do not offer any added benefit and are significantly more expensive. Skin and soft tissue infections due to methicillin-resistant S. aureus (MRSA) are still relatively uncommon in children. Well children with community-acquired MRSA infections can be treated with clindamycin or trimethoprim-sulfamethoxazole (cotrimoxazole), but must be observed closely for potentially severe adverse effects. In severe infections, vancomycin remains the treatment of choice, while intravenous teicoplanin and clindamycin are suitable alternatives. Linezolid and quinupristin/dalfopristin are currently showing great promise for the treatment of multi-resistant Gram-positive infections. While the choice of antibacterial is important, supportive management, including removal of any infected foreign bodies, surgical drainage of walled-off lesions, and regular wound cleaning, play a vital role in ensuring cure.

Molecular characterisation of a dominant methicillin-resistant Staphylococcus aureus (MRSA) clone in a Mexican hospital (1999–2003)

Methicillin-resistant Staphylococcus aureus (MRSA) isolates (n = 216), collected between January 1999 and May 2003 in a tertiary-care university hospital in Guadalajara, Mexico, were characterised by antibiotype, pulsed-field gel electrophoresis (PFGE) of SmaI macrorestriction fragments, and hybridisation of ClaI digests with mecA- and Tn554-specific DNA probes. Representatives of the single clonal type found were analysed by spa typing, multilocus sequence typing and staphylococcal chromosomal cassette mec (SCCmec) typing, and were tested for the presence of 22 virulence determinants and agr type. A single PFGE pattern was identified, with minor variations over time, with spa type 2, sequence type 5, SCCmec type II, agr type 2 and the presence of the enterotoxin genes seg and sei, the gamma-haemolysin variant gene hlg-v and the leukocidin lukE-lukD genes. In addition, the isolates showed antimicrobial resistance to beta-lactams, macrolides, chloramphenicol and imipenem, and susceptibility to gentamicin, rifampicin, trimethoprim-sulphamethoxazole and vancomycin. Following its appearance in 1997, this clone spread within the hospital, and is now present in most of the hospital units and wards.

Epidemiological comparison of true methicillin-resistant and methicillin-susceptible coagulase-negative staphylococcal bacteremia at hospital admission

We performed 2 case-control studies among 108 patients with true coagulase-negative staphylococcal (CoNS) bacteremia diagnosed within 48 h of hospital admission. Seventy-nine patients (73%) with methicillin-resistant (MR) CoNS bacteremia and 29 patients (27%) with methicillin-susceptible (MS) CoNS bacteremia were compared with 79 randomly selected control patients without CoNS bacteremia. The presence of a central venous catheter was an independent risk factor for both MR- and MS-CoNS bacteremia (P<.001). Patients with MR-CoNS bacteremia were more frequently admitted from health care facilities (P=.02), more likely to have had previous MR Staphylococcus aureus infection or colonization (P=.02), and more likely to have received antibiotics in the previous 30 days (P=.02). The probability that bacteremia was caused by an MR strain, rather than an MS strain, was 62% among patients admitted from the community and 84% among patients admitted from health care facilities. This study identified epidemiological characteristics that can be used to distinguish between MR- and MS-CoNS bacteremia and found high rates of methicillin resistance among CoNS isolates recovered from patients admitted from the community, as well as from health care facilities.

Community-acquired methicillin-resistant Staphylococcus aureus colonization in healthy children attending an outpatient pediatric clinic

BACKGROUND

We previously showed that children attending an inner city pediatric emergency department were sometimes asymptomatically colonized with clindamycin-susceptible community-acquired methicillin-resistant Staphylococcus aureus (MRSA) and borderline methicillin-resistant S. aureus (BRSA) as well. We wished to ascertain whether healthy children attending an outpatient clinic were colonized with these organisms. Therefore to estimate the prevalence of community-acquired MRSA and BRSA nasal colonization in a well child population, we cultured children attending an inner city pediatric outpatient clinic.

STUDY DESIGN

This was a prospective cross-sectional study conducted from January to August, 1999, at a primary care outpatient facility at the University of Chicago. The target population was 500 healthy children < or = 16 years of age who attended this facility to receive well child care.

RESULTS

One hundred twenty-two (24.4%) children were colonized with S. aureus. Three of the 122 (2.5%) S. aureus isolates were MRSA; they came from children who lacked predisposing risk factors and were susceptible to clindamycin, gentamicin, trimethoprim-sulfamethoxazole, rifampin and ciprofloxacin. Two (1.6%) additional S. aureus isolates were BRSA; both children had predisposing risk factors for MRSA colonization. The mecA gene was present in the 3 MRSA isolates and absent in both BRSA isolates.

CONCLUSIONS

These data document that a reservoir of asymptomatic MRSA colonization exists among healthy children who lack traditional risk factors for MRSA infections.

Current trends in community-acquired methicillin-resistant Staphylococcus aureus at a tertiary care pediatric facility

BACKGROUND

The prevalence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections increased at the University of Chicago Children's Hospital (UCCH) from 10 per 100,000 admissions from 1988 to 1990 to 259 per 100,000 admissions from 1993 to 1995. Because this increase may have represented a one time occurrence or a limited disease outbreak, we updated our previous observations at UCCH in 1998 and 1999 to see whether this trend had continued.

DESIGN

Prospective observational study.

RESULTS

Twenty-three hospitalized children had an MRSA isolate during the 1-year study period. Ten were community-acquired, equally distributed between children with predisposing risk factors and those without. The overall prevalence of community-acquired MRSA was 208 per 100,000 admissions. Seven of the 10 community-acquired MRSA isolates were susceptible to clindamycin. Skin and soft tissue infections predominated among the children with a community-acquired MRSA isolate. Pulsed field gel electrophoresis of the 10 community-acquired MRSA isolates revealed 8 distinct patterns; these data suggest that multiple clones were circulating at UCCH.

CONCLUSION

MRSA are no longer confined to children with established risk factors. The prevalence of community-acquired MRSA among children without identified risk factors is high in our institution.