**7. Vancomycin-resistant** *S. aureus* **(VRSA)**

Detection of oxacillin resistant staphylococci is important to guide therapies and also to avoid use of vancomycin, which is an antimicrobial agent with therapeutic complications, and can lead to selection of resistant strains. Acquired microbial resistance to vancomycin is a growing problem, in particular, within healthcare facilities such as hospitals. The widespread use of vancomycin makes resistance to the drug a significant worry, especially

Previous studies have used MLST for comparison between samples and the prevalence between different pandemic clones. Campanille et al. (2009) analyzed 301 MRSA samples isolated from 19 Italian hospitals from 1990 to 2001. An increase of clone ST228, known as Italian clone, was observed from 2000 to 2007, conjointly with the decrease of clone ST247

Clone ST228 is also associated with patients with cystic fibrosis. A study conducted on 93 MRSA samples isolated from patients with that disease at a treatment center in Madrid, Spain, identified 15 different PFGE patterns. A sample of each of these patterns was typed by MLST, with clone ST228 showing higher prevalence, with eight pulsetypes, followed by ST5, with two pulsetypes, and ST247, ST72 and ST255 with one pulsetype each (Molina et

In addition to epidemiological studies in hospitals and the detection of these pandemic clones from MRSA samples, the MLST method has been used to detect the transmission of oxacillin-resistant samples from animal reservoirs to humans, including its detection in hospitals. Some studied have detected the presence of MRSA clones in swines, thus emphasizing the importance of such animals as reservoirs. Smith et al. (2009) reported the presence of ST398 samples in swines and farmers in the mid-western region of the United States, which suggests transmission between animals and their breeders. In Germany, 1,600 swabs from swines from 40 farms were analyzed in a study where samples typed as ST398

MLST is usually used for detecting pandemic clones with good results. But this method can

Peacock et al. (2002) compared the MLST and PFGE methods in a study conducted on 104 *S. aureus* samples isolated from nasal swabs from patients under renal therapy. The isolated samples were typed by the MLST and PFGE methods with a similar discriminatory power

Vindel et al. (2009) analyzed 463 *S.aureus* samples isolated from 145 Spanish hospitals in 2006. In addition to MLST, several methodologies such as PFGE, spa typing, *SCCmec*  characterization and *agr* typing were used. MLST showed good correlation with the methodologies used for detecting circulating samples, with applicability in localized

The combination of the two molecular epidemiology techniques can increase discriminatory power for analysis of different clones. Cookson et al. (2007) reported that the combination of the MLST and *SCCmec* methods are more appropriate for multi-center studies. The authors analyzed MRSA samples from various European countries by means of PFGE, MLST,

Detection of oxacillin resistant staphylococci is important to guide therapies and also to avoid use of vancomycin, which is an antimicrobial agent with therapeutic complications, and can lead to selection of resistant strains. Acquired microbial resistance to vancomycin is a growing problem, in particular, within healthcare facilities such as hospitals. The widespread use of vancomycin makes resistance to the drug a significant worry, especially

also be utilized for characterizing samples involved in hospital outbreaks.

between the two techniques for identification of circulating samples in hospitals.

(Iberian clone) when compared to the 1990-1999 period.

were also identified (Köck et al., 2009).

nosocomial studies.

*SCCmec* analysis and *spa* typing.

**7. Vancomycin-resistant** *S. aureus* **(VRSA)** 

al., 2008).

for individual patients if resistant infections are not quickly identified and the patient continues the ineffective treatment. Vancomycin-resistant Enterococcus (VRE) emerged in 1987 and the transfer potential of such resistance to other bacteria, vancomycin resistance surveillance has been an object of great scientific interest worldwide. Vancomycin resistance emerged in more common pathogenic organisms during the 1990s and 2000s, including vancomycin-intermediate *Staphylococcus aureus* (VISA) and vancomycin-resistant *Staphylococcus aureus* (VRSA).

In 1996, the first clinical *S. aureus* isolate with reduced vancomycin sensitivity, with MIC value in the intermediate range (MIC = 8 g/ml) and referred to as VISA was reported in Japan (Hiramatsu et al. 1997). Additionally, in June 2002 [44], eight patients with infections caused by *S. aureus* with reduced vancomycin sensitivity were confirmed in the United States. One month later, the Centers for Disease Control and Prevention (CDC) published the first reported on vancomycin-resistant *S. aureus* (VRSA, with MIC = or 32 g/ml) in a patient in Michigan, United States. The sample isolated from the patient contained the *vanA* gene as well as the *mecA* gene for oxacillin resistance. The presence of the *vanA* gene in this VRSA suggests that resistance may have been acquired through the passage of genetic material from vancomycin-resistant enterococci to *S. aureus.* In October of the same year [44], the second clinical isolate of VRSA was reported in a patient in Pennsylvania. The VRSA isolate also contained the *vanA* and the *mecA* genes. The presence of the *vanA*  gene suggests that the resistance determinant was acquired from vancomycin-resistant *Enterococcus* isolated from the same patient. April 2004, the third VRSA isolated from a patient in New York was reported. The isolate also contained the oxacillin- and vancomycinresistance *mecA* and *vanA* genes, respectively. According to CDC, the three VRSA isolated did not seem to be epidemiologically related (CDC 2002; CDC 2004). The CDC (2010) has recently confirmed the 11th case of vancomycin resistant *Staphylococcus aureus* (VRSA) infection since 2002 in the United States (Table 2). This serves as a reminder about the


Source: CDC (2010)

Table 2. Vancomycin resistant *Staphylococcus aureus* (VRSA) infection in the United States

Epidemiological Aspects of Oxacillin-Resistant

567. ISSN 0892-3787

Available at:

0255-0857

660X

0857

ISSN:1198-743X

Accessed June 18, 2011.

Vol. 53, pp. 322-323. ISSN 0892-3787

Vol.26, pp.269-77. ISSN 1578-1852

*Diseases*. 2009; 13: 90-8. ISSN 1413-8670

*Staphylococcus* spp.: The Use of Molecular Tools with Emphasis on MLST 105

CDC. Centers for Disease Control and Prevention. (2002) *Staphylococcus aureus* resistant to

CDC. Centers for Disease Control and Prevention. (2004) Brief Report: Vancomycin-

CDC. Centers for Disease Control and Prevention. CDC Reminds Clinical Laboratories

Chaudhury, A.; Kumar, A.G. (2007) In vitro activity of antimicrobial agents against

Cuevas, O.; Cercenado, E.; Goyanes, M.J.; Vindel, A.; Trincado, P.; Boquete, T.; Marín, M.;

Cookson, B.D.; Robinson, D.A.; Monk, A.B.; Murchan, S.; Deplano, A.; de Ryck,

De Lencastre, H.; Severina, E.P.; Milch, H.; Thege, M.K.; Tomasz, A. (1997) Wide geographic

Ercis, S.; Sancak, B.; Hasçelik, G. (2008) A comparison of PCR detection of mecA

Gales, A.C.; Sader, H.S.; Ribeiro, J.; Zoccoli, C.; Barth, A.; Pignatari, A.C. (2009)

distribution of a unique methicillin-resistant *Staphylococcus aureus* clone in Hungarian hospitals. *Clinical Microbiology and Infection*. Vol. 3, pp. 289-296.

with oxacillin disk susceptibility testing in different media and sceptor automated system for both *Staphylococcus aureus* and coagulase-negative staphylococci isolates. *Indian Journal of Medical Microbiology.* Vol. 26, pp. 21-4. ISSN 0255-

Antimicrobial susceptibility of gram-positive bacteria isolated in Brazilian hospitals participating in the SENTRY Program (2005-2008). *Brazilian Journal Infectious* 

http://www.cdc.gov/HAI/settings/lab/vrsa\_lab\_search\_containment.html.

vancomycin-United States. *Morbity and Mortality Weekly Reports*.Vol. 51, pp. 565-

Resistant *Staphylococcus aureus*- New York. *Morbity and Mortality Weekly Reports.*

and Healthcare Infection Preventionists of their Role in the Search and Containment of Vancomycin-Resistant *Staphylococcus aureus* (VRSA), May 2010.

oxacillin resistant staphylococci with special reference to *Staphylococcus haemolyticus. Indian Journal of Medical Microbiology*.Vol.25, No.1, pp.50-52. ISSN

Bouza, E. (2008) *Staphylococcus spp*. in Spain: present situation and evolution of antimicrobial resistance (1986-2006). *Enfermidades Infecciosas y Microbiología Clínica.*

R.; Struelens, M.J.; Scheel, C.; Fussing, V.; Salmenlinna, S.; Vuopio-Varkila, J.; Cuny, C.; Witte, W.; Tassios, P.T.; Legakis, N.J.; van Leeuwen, W.; van Belkum, A.; Vindel, A.; Garaizar, J.; Haeggman, S.; Olsson-Liljequist, B.; Ransjo, U.; Muller-Premru, M.; Hryniewicz, W.; Rossney, A.; O'Connell, B.; Short, B.D.; Thomas, J.; O'Hanlon, S.; Enright, M.C. (2007) Evaluation of molecular typing methods in characterizing a European collection of epidemic methicillin-resistant *Staphylococcus aureus* strains: the HARMONY collection. *Journal of Clinical Microbiology.* Vol. 45, pp.1830-1837. ISSN 1098-

important role of clinical laboratories in the diagnosis of VRSA cases to ensure prompt recognition, isolation, and management by infection control personnel. Appropriate antimicrobial prescribing by healthcare providers, adherence to recommended infection control guidelines, and, ultimately, the control of both MRSA and VRE are necessary to prevent further emergence of VRSA strains.
