Bacterial and Antimicrobial Susceptibility Profile of Skin and Soft Tissue Infections among Patients Attending the Tertiary Health Care Set Up

Amit Kumar Singh¹, Loveleena Agarwal², Taso Beyong^1* and Chuing Lundup¹

^*Correspondence: Taso Beyong, Tomo Riba Institute of Health and Medical Sciences, India, Email:

Author info »

Introduction

Skin and soft tissue infections (SSTIs) have variable etiology and clinical presentation and is commonly seen in both in ambulatory and hospital settings [1]. It may range from mild superficial infections such as cellulitis, furuncles, folliculitis which is often uncomplicated to deeper complicated SSTIs (cSSTIs) such as necrotizing fasciitis, surgical site infections and diabetic ulcers [2]. Deep seated complicated infections usually involve the subcutaneous tissues, fascia or the muscles which may progress rapidly and leads to septicemia and may increase the duration of hospital stay and cost of treatment [3]. It may also lead to complications that include osteomyelitis, endocarditis, gangrene, bacteremia and septicemia. Especially in patients with comorbidities, such as diabetes, obesity, immune compromise, renal and hepatic diseases [4,5].

Although the etiology of SSTIs is uncertain, the infection is commonly caused by Gram-positive pathogens, mainly S. aureus and beta-hemolytic streptococci in uncomplicated superficial infections [2,6]. Whereas, Gram-negative organisms are more frequently seen in healthcare-associated complicated SSTIs than community acquired complicated SSTIs [1,7]. Polymicrobial infections, especially mixed infections of Gram-positive and Gram-negative infections ranges from 10-24% and there is high risk of inappropriate empirical therapy in such cases [1,8].

Inadvertent use of antibiotics lead to emergence of antibiotic resistance among both the Grampositive and Gram-negative organisms is posing a challenge to the treatment and outcome of SSTIs. Methicillin-resistant S. aureus (MRSA) is very commonly isolated agent of uncomplicated SSTIs and is seen more commonly in hospital settings especially in emergency departments as purulent SSTIs [9]. Risk factors associated with MRSA-SSTIs are previous history of MRSA infection, prolonged underlying disease, unhealed open wounds, elderly age group and long duration of hospital stay or frequent hospital visit [10]. Extended spectrum β- lactamases (ESBL) producing Gram-negative organisms have also been found to be commonly associated with cSSTIs [11].

Effective management of SSTIs by empirical therapy requires knowledge of potential pathogens and their antimicrobial susceptibility pattern. It is important to monitor the changing trends in bacterial infection and their antimicrobial susceptibility pattern to provide appropriate antimicrobial therapy for controlling infection, preventing morbidity and improve the quality of life. The present study was undertaken to determine the bacterial etiology and their antimicrobial susceptibility pattern of soft tissue infections among patients attending the tertiary care set up.

Materials and Methods

The study was prospective observational crosssectional study conducted in the department of microbiology. The pus samples received in the bacteriology laboratory from the patients attending the outpatient departments and admitted in inpatient departments with presentation of SSTIs were included in the study. Those patients with history of oral and/ or topical antibiotic usage in last 4 weeks were not included in the study. Demographic data (age, sex), clinical conditions data (history of antibiotic usage, fever and wound) and other relevant information about the participants was recorded from each participants a structured questionnaire.

The received samples were processed immediately as per the standard laboratory protocol. All samples were inoculated in nutrient agar, MacConkey agar and 5% blood agar and incubated overnight at 37oC aerobically. Identification of the isolates were done on the basis of colonial morphology, Gram-staining and various biochemical tests such as catalase, coagulase, oxidase, indole, methyl-red, vogesproskauer, citrate utilization, sugar fermentation and decarboxylation test.

Antibiotic susceptibility testing was performed for the isolates obtained by Kirby-Bauer disc diffusion method as per the Clinical and Laboratory Standards Institute (CLSI) 2018 guidelines. MRSA was detected by using cefoxitin (30μg) discs by Kirby-Bauer disc diffusion method as per CLSI 2018 guidelines. ESBL production in Escherichia coli and Klebsiella spp. was determined phenotypically by cephalosporin/clavulanate combination discs method using ceftazidime (30μg) disc alone and combination with clavulanate (10μg). Quality control was done by using non-ESBL producer Escherichia coli ATCC 25922 and ESBL producer Klebsiella pneumoniae ATCC 700603.

Observations and Results

Out of 1672 pus samples received, 1088 (65.1%) bacterial isolates were obtained. Of the positive culture, 736 (67.6%) were obtained from male patients and 352 (32.4%) were obtained from female patients. The growth was commonly isolated from the age group 25-35 years (31%) as shown in the Table 1.

Table 1: Distribution of bacterial isolates in various age groups.

Out of 1088 obtained bacterial isolates, 674 (65.3%) were Gram-negative bacteria, 398 (36.6%) were Gram-positive bacteria and 16 (1.6%) were gram positive bacilli. Escherichia coli (26.6%) was the commonest isolate followed by S. aureus (13.1%) and coagulase-negative staphylococcus (CoNS) (13%). The distribution of various bacterial isolates is depicted in Table 2.

Table 2: Distribution of isolates obtained from various pus samples.

Methicillin resistance was found in 52 (36.6%) S. aureus isolates, while none of the isolate showed inducible clindamycin resistance. High level aminoglycoside resistance was observed in 6 (15%) enterococci isolates. ESBL production was found in 162 (55.9%) Escherichia coli isolates and 22 (40.7%) Klebsiella spp.

Antibiotic susceptibility profile of Grampositive isolates is depicted in Table 3. S. aureus isolates showed a higher resistance to penicillin, ampicillin and cotrimoxazole, whereas most of the isolates were susceptible to vancomycin (89.4%) and linezolid (97.9%). Similar findings were observed with beta-hemolytic streptococcus and Enterococcus spp. for vancomycin and linezolid. However, beta-hemolytic streptococcus were more susceptible to commonly used antibiotics as compared to S. aureus and Enterococcus spp.

Table 3: Antibiotic susceptibility profile of Gram-positive isolates.

Antibiotic susceptibility profile of Gramnegative isolates is demonstrated in Table 4. Gram-negative bacilli especially members of Enterobacteriaceae were highly resistant to ampicillin, amoxicillin-clavulanate, and 2nd generation oral cephalosporins. Resistance to fluoroquinolones was about 62%. Approximately 21.1% of them were resistant to fourth generation cephalosporin. Pseudomonas spp. showed maximum susceptibility to carbapenems followed by piperacillin–tazobactam. It was highly resistant to aztreonam. Acinetobacter spp. also showed a similar susceptibility pattern. Piperacillin-tazobactam combination and carbapenems showed best activity for gramnegative bacilli.

Table 4: Antibiotic susceptibility profile of Gram-negative isolates.

Discussion

Skin and soft tissue infections (SSTIs) are among the common presentation in both outpatients and inpatients department. The major challenge to the treatment of SSTIs, especially cSSTIs, is the development of resistance to the commonly used oral and topical antibiotics. Methicillin resistance among S. aureus is very common and treatment of such cases relies mostly upon topical antibiotics such as mupirocin, which in turn increases the irrational use of these antibiotics leading to development of resistance to them. Although, Escherichia coli and Pseudomonas spp. are not as regularly found as Gram-positive organisms in SSTIs, still they constitute an important cause for HA-cSSTIs.

In this study the culture positivity rate was found to be 65.3% with most of cases were found to be mono-microbial which is consistent with the findings of studies conducted by Sah . et al (62%), Singh A (64.7%) and Gupta et al. (73.8%) [12-14]. The infections was more common in male compared to female (2.08:1) which is similar to the findings of Sharma et al. [15,16]. In this study, SSTIs is commonly seen in age group of 25-35 years of age group which comparable to various studies [16-18].

The commonest isolates found in this study is Escherichia coli (26.6%) followed by S. aureus (13.1%) and CoNS (13%) which is not consistent with the findings of various studies in which S. aureus was the commonest organisms in SSTIs [12-16]. This might be attributed to the late presentation of cases in the facility leading to complicated SSTIs.

Escherichia coli the commonest isolate in the study showed high susceptibility to carbapenems, aminoglycosides and piperacillin-tazobactam; moderate susceptibility to cephalosporins, nitrofurantoin and fluoroquinolones; and least susceptibility to ampicillin and cefazolin. Similar susceptibility pattern was found in the study conducted by Sharma et al., Soumya et al., and Afroz et al. [15,16,19]. ESBL production was found in 55.9% isolates of Escherichia coli which is consistent with the findings of the studies conducted by Rao et al., and Fouzia et al., whereas Sharma et al., showed a higher rate of ESBL production [15,20,21]. Other members of Enterobacteriaceae showed similar pattern of susceptibility as shown by Escherichia coli.

Antibiotic sensitivity pattern showed that S. aureus isolates were least susceptible to penicillin (11.3%), ampicillin (19.7%) and cotrimoxazole (38.1%) and most susceptible to vancomycin (89.4%) and linezolid (97.9%). However, it was moderately susceptible to ciprofloxacin (51.4%), clindamycin (60.6%), and erythromycin (63.4%). Similar findings were observed in Sah et al. who showed 89.47% and 69.23% S. aureus isolates were resistant to amoxicillin and cotrimoxazole respectively [12]. Resistance to erythromycin (26.92%) and ciprofloxacin (29.41%) found in the study was also similar to the findings of our study. High susceptibility to vancomycin was found in studies conducted by Singh , Sah and Kamat et al. [12,13,22]. Methicillin resistance in S. aureus was found in 36.6% isolates which is similar to study conducted by Ioannou et al. (43.8%), Sharma et al. (40.25%), Singh et al. (28.57%) Gupta et al. (23.08%) and Waheed et al. (21.7%) [6,13,14,15,18].

Pseudomonas spp. and Acinetobacter spp. showed similar high sensitivity to carbapenems and piperacillin-tazobactam. Similar findings is also shown in the studies conducted by Kamat et al. Afroz et al. and Singh et al. [13,19,22]. However, susceptibility to fluoroquinolones, aminoglycosides and cephalosporins was relative less and it is consistent with the findings of studies conducted by Gupta et al. and Afroz et al. [14,19].

Conclusion

Continuous monitoring of antimicrobial susceptibility pattern in individual settings together with their judicious use is emphasized to minimize emergence of drug resistant bacteria.

References

1. Kaye KS, Petty LA, Shorr AF, et al. Current epidemiology, etiology, and burden of acute skin infections in the United States. Clin Infect Dis 2019; 68:S193-S199.
2. Ki V, Rotstein C. Bacterial skin and soft tissue infections in adults: A review of their epidemiology, pathogenesis, diagnosis, treatment and site of care. Can J Infect Dis Med Microbiol 2008; 19:173-184.
3. Kujath P, Kujath C. Complicated skin, skin structure and soft tissue infections-are we threatened by multi-resistant pathogens?. Eur J Med Res 2010; 15:544-553.
4. Leong HN, Kurup A, Tan MY, et al. Management of complicated skin and soft tissue infections with a special focus on the role of newer antibiotics. Infect Drug Resist 2018; 11:1959-1974.
5. Suaya JA, Eisenberg DF, Fang C, et al. Skin and soft tissue infections and associated complications among commercially insured patients aged 0-64 years with and without diabetes in the U.S. PLoS One 2013; 8:e60057.
6. Ioannou P, Tsagkaraki E, Athanasaki A, et al. Gram-negative bacteria as emerging pathogens affecting mortality in skin and soft tissue infections. Hippokratia 2018; 22:23-28.
7. Dryden MS. Complicated skin and soft tissue infection, J Antimicrob Chemother 2010; 65:35–44.
8. Golan Y. Current treatment options for acute skin and skin-structure infections. Clin Infect Dis 2019; 68:S206-S212.
9. Loewen K, Schreiber Y, Kirlew M, et al. Community-associated methicillin-resistant Staphylococcus aureus infection: Literature review and clinical update. Can Fam Physician 2017; 63:512-520.
10. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis 2005; 41:1373–1406.
11. Fish DN. Meropenem in the treatment of complicated skin and soft tissue infections. Ther Clin Risk Manag 2006; 2:401-415.
12. Sah P, Khanal R, Upadhaya S. Skin and soft tissue infections: Bacteriological profile and antibiotic resistance pattern of the isolates. J Univers Coll Med Sci 2013; 18-21
13. Singh A. A prospective study on bacteriological profile of skin and soft tissue infections with its antimicrobial sensitivity pattern in a tertiary care hospital. Int Arch BioMed Clin Res 2019; 5:SD1-SD3.
14. Gupta V, Datta P, Singla N. Skin and soft tissue infection: Frequency of aerobic bacterial isolates and their antimicrobial susceptibility pattern. J Assoc Physicians India 2008; 56:389-390.
15. Sharma A, Gupta S. Aerobic bacteriological profile of skin and soft tissue infections (SSTIs) and its antimicrobial susceptibility pattern at M.B. Govt. Hospital in Udaipur, Rajasthan. Int J Med Sci Edu 2016; 3:141-151.
16. Sowmya N, Savitha S, Mallure S, et al. A two-year study of spectrum of bacterial isolates from wound infections by aerobic culture and their antibiotic pattern in a tertiary care center. Int J Curr Microbiol App Sci 2014; 3:292-295.
17. Malhotra SK, Malhotra S, Dhaliwal GS, et al. Bacteriological study of pyodermas in a tertiary care dermatological center. Indian J Dermatol 2012; 57:358-361.
18. Waheed A, Amar A, Afridi I, et al. Bacteriological profile and antibiotics susceptibility patterns of complicated skin and skin structure infections in tertiary care hospitals, Peshawar. J Pak Asso Dermat 2020; 30:580-586.
19. Afroz Z, Metri B, Jyothi P. Bacteriological profile and antimicrobial susceptibility pattern of skin and soft tissue infections among gram negative bacilli in a tertiary care hospital of South India. J Pharm Sci and Res 2015; 7:397-400.
20. Rajeshwar RS, Jaya Lakshmi L, Pavani S, et al. Bacteriological profile, antibiogram of burn wound isolates and detection of MRSA and ESBL production at tertiary care hospital, Hyderabad. World J Pharma Pharma Sci 2014; 3:1691-1698.
21. Fouzia B, Damle AS, Maher G. Changing patterns of burn infections. J Den Med Sci 2013; 5:11-14.
22. Kamat U, Ghodge R. A retrospective study of common bacterial isolates and their antimicrobial susceptibility pattern from skin infections in a tertiary care hospital in Goa. J Evolution Med Dent Sci 2017; 6:114-117.