Marcelo Jenné Mimica
Disciplina de Microbiologia, Departamento de Ciências Patológicas, Faculdade de Ciências Médicas, Santa Casa de São Paulo, São Paulo, SP. Setor de Infectologia Pediátrica, Departamento de Pediatria, Faculdade de Ciências Médicas, Santa Casa de São Paulo, São Paulo, SP
Goud et al.1, in their very interesting article regarding the prevalence of Staphylococcus aureus in their community, have stated that “the anterior nares are the most common site for colonization”. Recent data suggest that the oropharynx could be more frequently colonized than the anterior nares by S. aureus2-4. Furthermore, even in some populations where nasal colonization is more common than oropharyngeal colonization, the use of a throat swab would significantly increase the rate of detection of carriers5.
In addition, another matter of discussion would be the chosen screening method for vancomycin resistance. The authors used disk diffusion, which is not considered to be accurate or reliable enough for the detection of the decreased susceptibility of S. aureus to this antimicrobial agent. It is of paramount importance to remember that, according to the current guidelines issued by the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards), minimum inhibitory concentration tests should be performed to determine the susceptibility of all staphylococcal isolates to vancomycin. Although the disk diffusion test can accurately detect S. aureus containing vanA (vancomycinresistant isolates), it cannot differentiate vancomycin-susceptible isolates from vancomycin-intermediate isolates6.
1. Goud R, Gupta S, Neogi U, Agarwal D, Naidu K, Chalannavar R, et al. Community prevalence of methicillin and vancomycin resistant Staphylococcus aureus in and around Bangalore, southern India. Rev Soc Bras Med Trop 2011;44:309-312. [ Links ]
2. Nilsson P, Ripa T. Staphylococcus aureus throat colonization is more frequent than colonization in the anterior nares. J Clin Microbiol 2006;44:3334-3349. [ Links ]
3. Hamdan-Partida A, Sainz-Espuñes T, Bustos-Martínez J. Characterization and persistence of Staphylococcus aureus strains isolated from the anterior nares and throats of healthy carriers in a Mexican community. J Clin Microbiol 2010;48:1701-1705. [ Links ]
4. Nakamura MM, McAdam AJ, Sandora TJ, Moreira KR, Lee GM. Higher prevalence of pharyngeal than nasal Staphylococcus aureus carriage in pediatric intensive care units. J Clin Microbiol 2010;48:2957-2959. [ Links ]
5. Mertz D, Frei R, Jaussi B, Tietz A, Stebler C, Flückiger U, et al. Throat swabs are necessary to reliably detect carriers of Staphylococcus aureus. Clin Infect Dis 2007;45:475-477. [ Links ]
6. Clinical and Laboratory Standards Institute (CLSI). Performance standards for antimicrobial susceptibility testing: 21st informational supplement M100-S21. Wayne, PA: CLSI; 2011. [ Links ]
Dr. Marcelo Jenné Mimica
Discip. Microbiologia/Depto de Ciências Patológicas/FCMSCSP
Rua Cesário Mota Jr 122, 01221-020 São Paulo, SP, Brasil.
Phone: 55 11 6393-8496
Received in 16/09/2011
Accepted in 09/12/2011
Resposta dos autores: colonização por Staphylococcus aureus resistentes à oxacilina e à vancomicina
Rajendra GoudI,II; Soham GuptaIII; Ujjwal NeogiII,III; Deepali AgarwalIV; Kesava NaiduI; Raju ChalannavarV; Gaddad SubhaschandraI
IDepartment in Studies in Microbiology, Gulbarga University, Gulbarga, Karnataka, India
IIDepartment of Microbiology, Administrative Managment College, Bangalore, India
IIIDepartment of Microbiology, St. John’s Medical College, Bangalore, India
IVDepartment of Pathology and Microbiology, Seema Dental College & Hospital, Rishikesh, Uttarakhand, India
VDepartment of Biotechnology and Food Technology, Durban, South Africa
We are thankful to Mimica MJ for his letter1 and showing interest in our study2. It is very truely pointed out by Mimica MJ that recent studies suggest oropharynx to be a more frequently colonised site by Staphylococcus aureus than anterior nares1. However our study was conducted in the period of 2003-2007, and during the initiation of the study anterior nares was considered to be the most common site for Staphylococcus aureus colonisation. Previous studies have also shown strong association between nasal carriage of Staphylococcus aureus with systemic infections3,4.
Mimica MJ has also raised concern regarding the screening method for vancomycin chosen. We agree that the disc diffusion method used may not reliably detect vancomycin resistance and often mis-interprets intermediately susceptible Staphylococcus as fully susceptible5,6. Current CLSI guidelines suggest determination of Minimum Inhibitory Concentration (MIC) by broth or agar dilution methods as the gold standard7. However in resource-constrained settings and in a routine diagnostic laboratory performing MIC may not be feasible. Similarly we also could not perform MIC for vancomycin and agreeably could not differentiate between vancomycin intermediate with vancomycin resistant Staphylococcus aureus strains. Moreover the study was conducted without any external funding source. However we detected the presence of vanA gene in the Staphylococcus aureus showing vancomycin resistance by disc diffusion, which is characterized by high-level vancomycin resistance8.
1. Mimica MJ. Methicillin-and vancomycin-resistant Staphylococcus aureus colonization. Rev Soc Bras Med Trop. Forthcoming 2012. [ Links ]
2. Goud R, Gupta S, Neogi U, Agarwal D, Naidu K, Chalannavar R, et al. Community prevaence of methicillin and vancomycin resistant Staphylococcus aureus in and around Bangalore, southern India. Rev Soc Bras Med Trop 2011; 44:309-312. [ Links ]
3. Von Eiff C, Becker K, Machka K, Stammer H, Peters G. Nasal carriage as a source of Staphylococcus bacteremia. N Eng J Med 2001;344:11-16. [ Links ]
4. Wertheim HFL, Melles DC, Vos MC, Van Leeuwen W, Van Belkum A, Verbrugh HA, et al. The role of nasal carriage in Staphylococcus aureus infections. Lancet Infect Dis 2005;5:751-762. [ Links ]
5. Srinivasan A, Dick JD, Perl TM. Vancomycin resistance in Staphylococci. Clin Microbiol Rev 2002;15:430-438. [ Links ]
6. Behera B, Mathur P. Erroneous reporting of vancomycin susceptibility for Staphylococcus spp. By Vitek software version 2.01. Jpn J Infect Dis 2009;62:298-299. [ Links ]
7. Clinical and Laboratory Standards Institute (CLSI). Performance standards for antimicrobial susceptibility testing: 21st informational supplement M100-S21. Wayne, PA: CLSI; 2011. [ Links ]
8. Perichon B, Courvalin P. Van-A type vancomycin-resistant Staphylococcus aureus. Antimicrob Agents Chemother 2009;53:4580-4587. [ Links ]
Dr. Rajendra Goud
Deptº Microbiologia/Faculdade de Gestão Administrativa
560083 Bangalore, India
Phone: 91 80 2782-8657
Received in 14/11/2011
Accepted in 09/12/2011