Online - 2455-3891
Print - 0974-2441
Vol 10, Issue 12, 2017
Research Article
STAPHYLOCOCCUS AUREUS INFECTIONS AND THEIR ANTIBIOTIC SUSCEPTIBILITY
PROFILE AT A TERTIARY CARE HOSPITAL
ANTHONY N OFULAH, SHASHIDHAR VISHWANATH*, BARNINI BANERJEE, KIRAN CHAWLA
Department of Microbiology, Kasturba Medical College, Manipal University, Manipal, Karnataka. India. Email: drshashidharv@gmail.com
Received: 09 August 2017, Revised and Accepted: 29 September 2017
ABSTRACT
Objective: Staphylococcus aureus remains an important bacterial pathogen causing diverse infections which are both nosocomial and community
acquired. Increasing resistance among S. aureus to various antibiotics is a cause of concern.
Methods: A prospective observational study of 4 months duration was conducted to analyze the spectrum of infections caused by S. aureus and
to study its antimicrobial resistance to commonly used antibiotics. Specimens from various clinical sites received in the laboratory for culture and
sensitivity were processed as per standard techniques. Identification and susceptibility testing of S. aureus isolates were done using automated
systems.
Results: A total of 234 S. aureus isolates were obtained during the study period. Males accounted for 70.1% (n=164) of patients with S. aureus
infections. These patients were uniformly distributed across all age groups. S. aureus was most commonly isolated from pus and exudates (64.5%)
followed by respiratory specimens (20.5%) and mainly cultured from the skin and soft tissue infections (56%). Methicillin-resistant S. aureus (MRSA)
accounted for 47% (n=110) of isolates. Higher rates of susceptibility were noted for tetracycline (95.3%), gentamicin (85.4%), and trimethoprim/
sulfamethoxazole (88%). Low susceptibility rate was seen for ciprofloxacin (11.2%). Inducible clindamycin resistance was seen in 22.4% (n=50)
isolates. Methicillin-sensitive S. aureus isolates were found to be more susceptible to non-beta lactam antibiotics than the methicillin-resistant isolates.
Conclusion: A high frequency of MRSA was found in our study. Regular surveillance of antimicrobial resistance profile of this most frequent pathogen
is necessary to aid in providing appropriate empirical antibiotic therapy.
Keywords: Methicillin-resistant Staphylococcus aureus, Resistance, Skin and soft tissue infections, Staphylococcus aureus.
© 2017 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open access article under the CC BY license (http://creativecommons.
org/licenses/by/4. 0/) DOI: http://dx.doi.org/10.22159/ajpcr.2017.v10i12.21851
INTRODUCTION
METHODS
Staphylococcus aureus is an important bacterial pathogen responsible
for a wide spectrum of clinical infections causing both communityacquired and healthcare-associated infections [1]. They cause skin
and soft tissue infections (SSTIs) including impetigo, folliculitis,
furunculosis, cutaneous abscesses, cellulitis, necrotizing fasciitis, and
surgical site infections; pleuropulmonary infections; bone and joint
infections and device-related infections. S. aureus is also one of the most
frequent causes of infective endocarditis and bacteremia [1,2]. Toxinmediated illnesses, scalded skin syndrome, toxic shock syndrome, and
food poisoning are also caused by S. aureus [1].
Following Institutional Ethics Committee approval, a prospective
observational study was conducted of 4 months duration from January
to April 2017, to study S. aureus isolates from various clinical specimens
and to analyze their susceptibility pattern to various antibiotics.
Duplicate isolates of S. aureus isolated from the same patient during the
study period were excluded.
S. aureus frequently colonizes skin and mucosa and about 30%
individuals being persistent nasal carriers. The extra nasal carriage sites
include skin, perineum, and pharynx. S. aureus anterior nasal carriage is
also associated with subsequent staphylococcal disease [1,3].
Increasing resistance to different antibiotics including the glycopeptides
among S. aureus isolates is a cause for concern. Methicillin-resistant
S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA), and
vancomycin-resistant S. aureus (VRSA) are being increasingly
encountered [4]. Significantly high rates of MRSA have been reported
from India and various parts of the globe along with increasing reports
of community-acquired MRSA infections [4-6]. Increasing resistance
rates limit therapeutic options for S. aureus infections.
As S. aureus is one of the most frequent pathogens in a clinical setting
and in view of its increasing resistance to common antibiotics, a
prospective, observational study was conducted to analyze the spectrum
of infections caused by S. aureus and its antibiotic susceptibility profile
in a tertiary care teaching hospital setting.
Specimens from various clinical sites received in the laboratory for
culture and sensitivity were processed as per standard techniques [7].
The specimens were subjected to Gram stain and culture on 5% sheep
blood agar and MacConkey agar. Pus cells and bacteria were studied
in the Gram stain. The inoculated culture plates were incubated at
37°C for 18-24 hrs. S. aureus isolates were identified based on, colony
morphology, Gram stain, catalase, slide coagulase test and by automated
identification system - matrix-assisted laser desorption/ionization timeof-flight mass spectrometry (Vitek MS, bioMerieux Inc.). Antimicrobial
susceptibility testing was done using the automated system (Vitek,
bioMerieux Inc.). MRSA was identified with cefoxitin (6 µg/ml). Data
were analyzed using standard statistical software - Statistical package
for the social sciences (SPSS), version 17.0 (SPSS Inc., Chicago, Ill., USA).
Quantitative variables were expressed as percentages.
RESULTS
A total of 234 S. aureus isolates were obtained during the study period
from various infection sites. Males accounted for 70.1% (n=164) of
patients with S. aureus infections. Patients with S. aureus infections were
uniformly distributed across all age groups. Majority of these patients
were from surgical departments (65.6%) in the hospital. S. aureus
was most commonly (64.5%) isolated from pus and exudates (swabs,
Ofulah et al.
Asian J Pharm Clin Res, Vol 10, Issue 12, 2017, 396-399
aspirated pus, and tissue) followed by respiratory specimens including
sputum, endotracheal aspirates, bronchoalveolar lavage, throat swab,
and nasal swab (20.5%). S. aureus was mainly cultured from the SSTIs
including surgical site infections (56%) (Table 1).
Analyzing the resistance profile to various antimicrobials, we found
110 (47%) of isolates to be MRSA. Among non-beta lactam antibiotics,
higher rates of susceptibility were noted for tetracycline (95.3%),
gentamicin (85.4%), and trimethoprim/sulfamethoxazole (88%). Low
susceptibility rates were seen for ciprofloxacin (11.2%). Inducible
clindamycin resistance was seen in 22.4% (n=50) of S. aureus
isolates (n=223). All S. aureus isolates (100%) were found to be
sensitive to linezolid, vancomycin, and teicoplanin (Table 2). Lower
rates of susceptibility were noted for ciprofloxacin (4.6% vs. 16.9%),
clindamycin (62.6% vs. 89.5%), erythromycin (33.6% vs. 64.5%), and
gentamicin (73.4% vs. 96%) among MRSA isolates in comparison to
methicillin-sensitive S. aureus (MSSA) isolates (Table 2). There was no
significant difference in the infection profile between MSSA and MRSA
isolates (Table 3).
Table 1: Clinical and demographic profile of patients with
S. aureus infections (n=234)
Characteristic
n (%)
Gender
Male
164 (70.1)
Female
70 (29.9)
Males:Females
<1-20
48 (20.5)
21-40
63 (26.9)
41-60
73 (31.2)
>60
50 (21.4)
Mean age (year)
41±21.3
Median age (year)
43
Range (year)
<1-90
Patients admitted to hospital wards
137 (58.5)
Patients managed as outpatients
97 (41.5)
Patients distribution in clinical departments (n=215)
Surgical
141 (65.6)
Medical
74 (34.4)
Specimen types
Pus and exudates
151 (64.5)
Respiratory specimens
48 (20.5)
Blood and catheter tip
26 (11.1)
Urine
09 (3.8)
Infection site
131 (56)
Lower respiratory tract
26 (11.1)
Bloodstream
26 (11.1)
Upper respiratory tract
22 (9.4)
Otogenic
14 (6)
Urinary tract
09 (3.8)
Bone and joint
06 (2.6)
S. aureus: Staphylococcus aureus
S. aureus continues to be a significant human pathogen commonly
isolated from various clinical specimens. A high number of S. aureus
isolates were obtained from males (70.1%). Male gender and extreme
of ages are found to be at increased risk for infections caused by
S. aureus by population-based studies [2]. However, S. aureus infections
were evenly distributed across various age groups in our analysis.
In our study, S. aureus was most commonly isolated from SSTIs
(56%). Ray et al., in their retrospective analysis found S. aureus as the
etiological agent in 81% of positive cultures from SSTI specimens [8].
Globally, S. aureus is recognized as the most frequent pathogen isolated
from SSTIs [9]. Apart from S. aureus, Pseudomonas aeruginosa,
Enterococcus spp., Escherichia coli, and beta-hemolytic Streptococci are
other important causes of SSTIs [8]. Most SSTIs occur when the innate
immune barrier, the skin is breached by trauma or surgery. Infections
may also spread from a distant site [10].
Analyzing the antimicrobial susceptibility data of S. aureus isolates, high
rate of resistance to ciprofloxacin was seen (88.8%). Bouchiat et al., in
their analysis of 92 S. aureus clinical isolates, found 70.6% (n=65) of
them to be resistant to ciprofloxacin [11]. Gade and Qazi have reported
57.6% (n=144) isolates of S. aureus to be ciprofloxacin resistant [12].
High rates of quinolone resistance have also been noted earlier by
Metri et al. among S. aureus isolates (n=137) [13]. Use of quinolones for
various infections leads to the selection of resistant mutants among the
S. aureus colonizing flora which acts as a reservoir for future infections,
and quinolone resistance are more predominantly noted in MRSA
isolates [14].
2.3:1
Age group (year)
Skin and soft tissue
DISCUSSION
Lower rate of resistance to trimethoprim/sulfamethoxazole was
noted (12%) in our study. Trimethoprim-sulfamethoxazole can be
used for the treatment of S. aureus infections such as uncomplicated
SSTI [15-17]. Majority of our S. aureus isolates (77.1%) were sensitive
to clindamycin, an important alternative to a beta-lactam antibiotic
for S. aureus SSTIs [18,19]. Inducible clindamycin resistance (iMLSB)
was seen in 22.4% of our S. aureus isolates. Prabhu et al. and Deotale
et al. have reported lower rates of 10.5% (n=20) and 14.5% (n=36),
respectively, for iMLSB [18,19].
In our study, 97.8% of S. aureus isolates were resistant to
benzylpenicillin. This is because the majority of the clinical isolates
of S. aureus produce beta-lactamase enzyme which inactivates the
penicillin antibiotic [7]. The rate of MRSA was high in our study
(47%). Varying rates of MRSA prevalence have been reported across
different centers [11]. A multi-centric study by the Indian Network
for Surveillance of Antimicrobial Resistance group involving 15
tertiary care centers found a MRSA prevalence rate of 41% (n=10769)
[5]. Bouchiat et al. found 52.2% (n=48) isolates of S. aureus to be
methicillin-resistant [11]. Thati et al. recorded 79.6% (n=285) S. aureus
isolates to be methicillin-resistant [20]. Other studies have found lower
rates of MRSA prevalence [21,22]. Dilnessa and Bitew have reported
MRSA rates of 17.5% (n=34) in their analysis of 194 S. aureus clinical
isolates [21]. In an evaluation of antibiotic resistance profile of S.
aureus isolates over several years by Ragbetli et al., 21% of them were
methicillin-resistant [22]. S. aureus is commonly transmitted by skinto-skin contact with either a colonized or infected individual. Indirect
contact through fomites also plays a role in the transmission of MRSA.
The 5 Cs for MRSA spread proposed by Centers for Disease Control
and Prevention, USA includes crowding, frequent skin-to-skin contact,
compromised skin integrity, contaminated items and surfaces, and lack
of cleanliness [6]. We did not find a significant difference in infection
profile between MRSA and MSSA isolates, mirroring the finding of
Dilnessa and Bitew [21]. MRSA strains were found to be more resistant
to non-beta lactam antibiotics compared to MSSA (Table 2), similar
to findings of earlier studies [5,11,12]. Infection control practices
need to be further strengthened and complemented with judicious
antimicrobial prescribing to reduce the burden of MRSA infections.
397
Ofulah et al.
Asian J Pharm Clin Res, Vol 10, Issue 12, 2017, 396-399
Table 2: Susceptibility pattern of S. aureus isolates to various antibiotics
Antibiotic (No. of isolates tested)
Susceptible isolates
among MSSA n (%)
Susceptible isolates
among MRSA n (%)
Total susceptible isolates
of S. aureus n (%)
Benzylpenicillin (225)
Oxacillin (234)
Ciprofloxacin (232)
Gentamicin (233)
Erythromycin (231)
Clindamycin (231)
Tetracycline (232)
Trimethoprim/Sulfamethoxazole (233)
Rifampicin (229)
Daptomycin (225)
Linezolid (230)
Vancomycin (230)
Teicoplanin (229)
5 (4.1)
124 (100)
21 (16.9)
119 (96.0)
80 (64.5)
111 (89.5)
121 (97.6)
113 (91.1)
122 (100)
121 (100)
122 (100)
122 (100)
122 (100)
0
0
5 (4.6)
80 (73.4)
36 (33.6)
67 (62.6)
100 (92.6)
92 (82.4)
104 (97.2)
103 (99.0)
108 (100)
108 (100)
107 (100)
5 (2.2)
124 (53)
26 (11.2)
199 (85.4)
116 (50.2)
178 (77.1)
221 (95.3)
205 (88)
226 (98.7)
224 (99.6)
230 (100)
230 (100)
229 (100)
*MSSA: Methicillin-sensitive Staphylococcus aureus, MRSA: Methicillin-resistant Staphylococcus aureus, S. aureus: Staphylococcus aureus
Table 3: Distribution of MSSA and MRSA isolates in various infections
Infection type (Number of isolates)
Isolates of MSSA n=124 (%)
Isolates of MRSA n=110 (%)
Skin and soft tissue infections (131)
Lower respiratory tract infections (26)
Bloodstream infections (26)
Upper respiratory tract infections (22)
Otogenic infections (14)
Urinary tract infections (09)
Bone and joint infections (06)
Total
71 (54.2)
11 (42.3)
10 (38.5)
12 (54.5)
09 (64.3)
06 (66.7)
05 (83.3)
124 (100)
60 (45.8)
15 (57.7)
16 (61.5)
10 (45.4)
05 (35.7)
03 (33.3)
01 (16.7)
110 (100)
*MSSA: Methicillin-sensitive Staphylococcus aureus, MRSA: Methicillin-resistant Staphylococcus aureus, S. aureus: Staphylococcus aureus
All S. aureus isolates including MRSA were found to be
sensitive to vancomycin, linezolid, and teicoplanin. There were
no cases of VISA or VRSA in our study. All isolates of MSSA
and MRSA were sensitive to vancomycin with a median MIC of
0.5 µg/ml. A clinical isolate of VISA was initially reported
from Japan in 1997, and the first report of VRSA was from
the United States in 2002 [23]. Since then, even though less
frequent, studies from India and globally are increasingly
reporting
the
occurrence
of both
VISA
and
VRSA
among clinical isolates
of S. aureus
[20,24,25]. Large multi-centric studies are needed to
analyze the prevalence and implications of VISA and VRSA in the
clinical setting. It is estimated that <1% of S. aureus isolates
are linezolid-resistant [26].
4.
We did not analyze the antimicrobial prescription data and prognosis
of patients with S. aureus infections. Analysis of risk factors for MRSA
infections and colonization status was not done.
9.
5.
6.
7.
8.
10.
CONCLUSION
S. aureus was more frequently associated with SSTIs. A high frequency
of MRSA was found in our study. Generating local data on antimicrobial
resistance among the S. aureus isolates will help in choosing appropriate
empirical antibiotic therapy based on the clinical presentation.
11.
12.
REFERENCES
Tong SY, Davis JS, Eichenberger E, Holland TL, Fowler VG Jr.
Staphylococcus aureus infections: Epidemiology, pathophysiology,
clinical manifestations, and management. Clin Microbiol Rev
2015;28(3):603-61.
2. Que YA, Moreillon P. Staphylococcus aureus (Including Staphylococcal
Toxic Shock Syndrome). In: Bennett JE, Dolin R, Blaser MJ, editors.
Mandell, Douglas, and Bennett’s Principles and Practice of Infectious
Diseases. 8th ed. Philadelphia: Elsevier, Saunders; 2015. p. 2237-71.
3. Wertheim HF, 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(12):751-62.
13.
1.
14.
15.
16.
Chen CJ, Huang YC. New epidemiology of Staphylococcus aureus
infection in Asia. Clin Microbiol Infect 2014;20(7):605-23.
Indian Network for Surveillance of Antimicrobial Resistance (INSAR)
group, India. Methicillin resistant Staphylococcus aureus (MRSA)
in India: Prevalence & susceptibility pattern. Indian J Med Res
2013;137(2):363-9.
Kale P, Dhawan B. The changing face of community-acquired
methicillin-resistant Staphylococcus aureus. Indian J Med Microbiol
2016;34(3):275-85.
Baird D. Staphylococcus: Cluster forming gram positive cocci. In:
Collee JG, Fraser AG, Marmion BP, Simmons A, editors. Mackie and
McCartney Practical Medical Microbiology. 14th ed. London: Churchill
Livingstone; 2012. p. 245-61.
Ray GT, Suaya JA, Baxter R. Incidence, microbiology, and patient
characteristics of skin and soft-tissue infections in a U.S. population: A
retrospective population-based study. BMC Infect Dis 2013;13:252.
McCaig LF, McDonald LC, Mandal S, Jernigan DB. Staphylococcus
aureus-associated skin and soft tissue infections in ambulatory care.
Emerg Infect Dis 2006;12(11):1715-23.
Ramakrishnan K, Salinas RC, Agudelo Higuita NI. Skin and soft tissue
infections. Am Fam Physician 2015;92(6):474-83.
Bouchiat C, El-Zeenni N, Chakrakodi B, Nagaraj S, Arakere G,
Etienne J. Epidemiology of Staphylococcus aureus in Bangalore,
India: Emergence of the ST217 clone and high rate of resistance to
erythromycin and ciprofloxacin in the community. New Microbes New
Infect 2015;7:15-20.
Gade ND, Qazi MS. Fluoroquinolone therapy in Staphylococcus aureus
infections: Where Do We Stand? J Lab Physicians 2013;5(2):109-12.
Metri BC, Peerapur BV, Jyothi P. Drug resistance patterns of clinical
isolates of Staphylococcus aureus in tertiary care center of south India.
Int J Pharm Pharm Sci 2015;7(7):70-2.
Lowy FD. Antimicrobial resistance: The example of Staphylococcus
aureus. J Clin Invest 2003;111(9):1265-73.
Paul M, Bishara J, Yahav D, Goldberg E, Neuberger A, GhanemZoubi N, et al. Trimethoprim-sulfamethoxazole versus vancomycin
for severe infections caused by methicillin resistant Staphylococcus
aureus: Randomised controlled trial. BMJ 2015;350:h2219.
Cadena J, Nair S, Henao-Martinez AF, Jorgensen JH, Patterson JE,
Sreeramoju PV. Dose of trimethoprim-sulfamethoxazole to treat skin and
skin structure infections caused by methicillin-resistant Staphylococcus
398
Ofulah et al.
Asian J Pharm Clin Res, Vol 10, Issue 12, 2017, 396-399
aureus. Antimicrob Agents Chemother 2011;55(12):5430-2.
17. Liu C, Bayer A, Cosgrove SE, Daum RS, Fridkin SK, Gorwitz RJ,
et al. Clinical practice guidelines by the infectious diseases society of
America for the treatment of methicillin-resistant Staphylococcus aureus
infections in adults and children. Clin Infect Dis 2011;52(3):e18-55.
18. Prabhu K, Rao S, Rao V. Inducible Clindamycin Resistance in
Staphylococcus aureus isolated from clinical samples. J Lab Physicians
2011;3(1):25-7.
19. Deotale V, Mendiratta DK, Raut U, Narang P. Inducible clindamycin
resistance in Staphylococcus aureus isolated from clinical samples. Ind
J Med Microbiol 2010;28(2):124-6.
20. Thati V, Shivannavar CT, Gaddad SM. Vancomycin resistance among
methicillin resistant Staphylococcus aureus isolates from intensive
care units of tertiary care hospitals in Hyderabad. Indian J Med Res
2011;134(5):704-8.
21. Dilnessa T, Bitew A. Prevalence and antimicrobial susceptibility
pattern of methicillin resistant Staphylococcus aureus isolated from
22.
23.
24.
25.
26.
clinical samples at Yekatit 12 Hospital Medical College, Addis Ababa,
Ethiopia. BMC Infect Dis 2016;16:398.
Ragbetli C, Parlak M, Bayram Y, Guducuoglu H, Ceylan N. Evaluation
of antimicrobial resistance in Staphylococcus aureus isolates by years.
Interdiscip Perspect Infect Dis 2016;2016:9171395.
Sangappa M, Thiagarajan P. Methicillin resistant Staphylococcus
aureus: Resistance genes and their regulation. Int J Pharm Pharm Sci
2012;4 Suppl 1:658-67.
Holmes NE, Johnson PD, Howden BP. Relationship between
vancomycin-resistant
Staphylococcus
aureus,
vancomycinintermediate S. aureus, high vancomycin MIC, and outcome in serious
S. aureus infections. J Clin Microbiol 2012;50(8):2548-52.
Loomba PS, Taneja J, Mishra B. Methicillin and vancomycin Resistant S.
aureus in Hospitalized Patients. J Glob Infect Dis 2010;2(3):275-83.
Gu B, Kelesidis T, Tsiodras S, Hindler J, Humphries RM. The emerging
problem of linezolid-resistant Staphylococcus. J Antimicrob Chemother
2013;68(1):4-11.
399