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Research Article

Incidence and Pattern of Antibiotic Resistance of Staphylococcus aureus Isolated from Clinical and Subclinical Mastitis in Cattle and Buffaloes

Lalita Sharma, Amit Kumar Verma, Amit Kumar, Anu Rahat, Neha and Rajesh Nigam
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The main objective of the present study was to report the prevalence of methicillin resistant Staphylococcus aureus (MRSA) among bovines used for milk production in Mathura, India. A total of 80 milk samples were collected from clinical and subclinical cases of mastitis from cows (40) and buffalos (40). Milk samples were processed for isolation and identification of S. aureus using standard bacteriological procedures. Staphylococcus aureus were isolated from only 27 samples showing the overall incidence of Staphylococcus aureus in clinical as well as sub clinical mastitis was 33.75%. The incidence of Staphylococcus aureus was higher (50.00%) in clinical mastitis in comparison to that of subclinical mastitis (17.50%). The results revealed that the incidence of Staphylococcus aureus in clinical as well as sub-clinical mastitis was higher in cattle in comparison to buffaloes. Drug sensitivity revealed the 100% resistance against penicillins followed by vancomycin (88.89%), nalidixic acid (77.78%), cefixime, methicillin, novobiocin (66.67% each), amoxiclav, colistin, pipemidic acid (55.56% each), ofloxacin, streptomycin, sulphamethizole (44.44% each), ampicillin/sulbactam, cefalexin, cefazolin, cefoperazone, enrofloxacin, floxidin, meropenem (33.33% each), cefuroxim, ciprofloxacin, clindamycin, gentamicin, levofloxacin, norfloxacin, tetracycline (22.22% each). Eighteen isolates were found to be methicillin-resistant, while the remaining (09) were methicillin-susceptible. Similarly, twenty four S. aureus isolates were intermediate to vancomycin while three were vancomycin susceptible and no isolate was resistant to vancomycin. Thus, the findings are useful for formulating specific control programs for bovine mastitis caused by S. aureus in this region.

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Lalita Sharma, Amit Kumar Verma, Amit Kumar, Anu Rahat, Neha and Rajesh Nigam, 2015. Incidence and Pattern of Antibiotic Resistance of Staphylococcus aureus Isolated from Clinical and Subclinical Mastitis in Cattle and Buffaloes. Asian Journal of Animal Sciences, 9: 100-109.

DOI: 10.3923/ajas.2015.100.109

Received: February 05, 2015; Accepted: April 24, 2015; Published: May 06, 2015


Mastitis (inflammation of mammary gland) is one of the most devastating disease conditions leading to significant economic losses globally (Kumar et al., 2010a; Abd Ellah, 2013) because of reduced milk production, treatment costs, increased labor, milk withholding following treatment, death and premature culling (Lightner et al., 1988; Kaneene and Hurd, 1990; Miller et al., 1993; Szweda et al., 2014). Due to multiple etiologies, it always remained a challenge to veterinarian worldwide. Approximately, 140 species of microorganisms have been identified as etiological agents of bovine mastitis. Of these various etiological agents, Staphylococcus aureus is a major pathogen associated with bovine clinical and subclinical mastitis (Wilson et al., 1997; Brito et al., 1999; Tenhagen et al., 2006; Piepers et al., 2007; Bhatt et al., 2011; Cervinkova et al., 2013).

At present, there is paucity of reports about occurrence of these virulence factors among S. aureus isolates from India and about the possible distribution of single S. aureus clones as causative agents of bovine mastitis. Since the introduction of β-lactamase-stable antimicrobial drugs in clinical use, Staphylococcus aureus strains have emerged worldwide as important nosocomial pathogens. Their prevalence in the community is increasing substantially. The indiscriminate use of antibiotics like ampicillin, penicillin, oxacillin and methicillin may contribute to the increasing occurrence of antibiotic resistant strains in cows with mastitis. These strains in intramammary dissemination often produce incurable severe intra herd infections (Moon et al., 2007). Resistance of S. aureus to antimicrobial agents can complicate treatment of its infections (Lowy, 2003). Among S. aureus, Methicillin-resistant strains (MRSA) has recently emerged as a serious life-threatening infective agent which does not respond to a lot of antimicrobial treatments (Kamal et al., 2013). The mastitis caused by S. aureus is characterized by significantly lower cure rates compared with infections caused by other microorganisms, which may be either as a result of unusually frequent acquisition of antibiotic resistance mechanisms among this group of bacteria or also their ability to form biofilm (slime) (Cramton et al., 1999). Considering the potential of the area and the economic significance of dairy production to the local community, the present study was carried out to detect the incidence of Staphylococcus aureus infection in mastitis cases and their antibiotic susceptibility pattern.


Sample collection: A total of 80 milk samples from healthy, subclinical and clinical mastitis cases of cattle and buffaloes 10, 20 and 20 each, respectively were collected either from Instructional Livestock Farm Complex (ILFC) or cases presented to Teaching Veterinary Clinical complex (TVCC), DUVASU, Mathura or during animal health camps etc. All samples were kept at 4°C in insulated ice box and transferred to the laboratory, College of Biotechnology, DUVASU, Mathura and analyzed within 4 h of collection.

Examination for mastitis: The cases of Clinical Mastitis (CM) were diagnosed on the basis of history, clinical signs, physical examination of udder (swelling and pain) and milk (colour-yellow or blood tinged and consistency-watery, etc), while subclinical mastitis (SCM) was diagnosed on the basis of California Mastitis Test (CMT) (Schalm et al., 1971).

Bacterial isolation and identification: Each of the thoroughly mixed milk sample (Mastitis/subclinical mastitis) was transferred to 10 mL of nutrient broth and incubated at 37°C for 15-18 h to resuscitate the organisms. Thereafter, a loopful of inoculum from the nutrient broth was streaked on to nutrient agar plates and incubated at 37°C for 24 h. Presumptive Staphylococcus colonies (golden/white, round, smooth, glistening, opaque) were picked up and characterized biochemically as per Barrow and Feltham (1993). The smear was prepared from the isolated culture on clean grease free microscopic glass slide and stained with Gram’s Method of staining. The stained smear was observed under microscope. Smear revealed Gram positive, spherical cells arranged in irregular clusters resembling to bunch of grapes were considered to be Staphylococci. A battery of biochemical tests viz., Catalase test, Oxidase test, Voges Proskauer (VP) test, Oxidation-Fermentation (OF) test etc were carried out as per Barrow and Feltham (1993).

Antibiotic resistance: All the confirmed S. aureus isolated under study were examined for their antibiotic resistance pattern by disc diffusion method (Bauer et al., 1966) using 38 antibiotic discs (Hi-Media, Mumbai) viz., amikacin (30 μg), amoxiclav (10 μg), ampicillin/sulbactam (10/10 μg), Azithromycin (15 μg), Cefalexin (30 μg), cefazolin (30 μg), cefixime (5 μg), cefoperazone (75 μg) cefotaxim (30 μg), ceftriaxome (10 μg), cefuroxim (30 μg), chloramphenicol (30 μg), ciprofloxacin (30 μg), clindamycin (2 μg), colistin (10 μg), erythromycin (10 μg), floxidin (30 μg), gentamicin (10 μg), imipenem/cilastin (10/10 μg), levofloxacin (5 μg), meropenem (10 μg), methicillin (10 μg), nalidixic acid (5 μg), nitrofurantoin (300 μg), novobiocin (5 μg), ofloxacin (5 μg), penicillin (10 U), pipemidic acid (30 μg), piperacillin/Tazobactam (100/10 μg), rifampicin (5 μg), streptomycin (10 μg), sulfamethizole (300 μg), tetracycline (10 μg), vancomycin (30 μg) etc following (NCCLS., 2004).


The species wise incidence of Staphylococcus aureus in clinical and subclinical mastitis were shown in Table 1. Overall incidence of Staphylococcus aureus in clinical as well as sub clinical mastitis, was 33.75%. The incidence of Staphylococcus aureus was higher (50.00%) in clinical mastitis in comparison to that of subclinical mastitis (17.50%) and the incidences of Staphylococcus aureus in clinical as well as sub-clinical mastitis were higher in cattle in comparison to buffaloes. These results are almost in the concurrence of previous study conducted in the region in 2010, which revealed S. aureus as a major pathogen in the cases of mastitis in Mathura and its surroundings. The incidence of S. aureus was 37.03 and 31.70% in cattle and buffaloes, respectively (Kumar et al., 2010a). It clearly indicated the presence of S. aureus as most prevailing pathogen in the cases of mastitis in dairy animals. Moreover, it is persisting in the similar pattern not only in clinical cases but also in subclinical cases. Various studies have been conducted in different parts of country to assess the prevalence status of bacterial pathogens in mastitis of dairy animals. Similar to the present findings, Purohit (1990) also reported the staphylococcal mastitis in cows to be 31.94% while Ranjan et al. (2011), Mengistie (2003) and Kivaria et al. (2005) reported the incidence to be comparatively as 27.37% in Jharkhand, 27.1% and 21.0%, respectively. However, higher incidence of staphylococcal mastitis was reported by Wani and Bhatt (2003), Patel (2007) and Thennarrasu et al. (2003), who reported the incidence of staphylococcal mastitis in cows to be 45%, 44% and 47.06% respectively. The high prevalence of staphylococci has been reported by several workers in India (Tuteja, 1999; Kaya et al., 2000; Sharma et al., 2007) and abroad (Hawari and Dabas, 2008; Tenhagen et al., 2009; Nickerson, 2009; Zutic et al., 2012).

Table 1: Species wise incidence of Staphylococcus aureus in mastitis among dairy animals

This difference in the prevalence/incidence of pathogens is influenced by parity, type of sample, season and place (Sharma et al., 2007). Distribution of pathogens in mastitis changes over time, therefore, bacteriological examination at herd level must be taken regularly to monitor udder health. Incidence of Staphylococcus aureus from clinical cases of mastitis was found to be 50.00% which was slightly higher than that previous studies conducted by Thennarrasu et al. (2003) and Patel (2007), who reported an incidence of Staphylococcus aureus from clinical cases of mastitis as 47.06 and 40.40%, respectively. While incidence of Staphylococcus aureus from subclinical cases of mastitis was found to be 17.50%, which differed from that reported earlier by Purohit (1990) and Goswami (1998), who found the incidence of staphylococcal subclinical mastitis to be 21.64 and 51.29%, respectively. These findings are suggestive of improper management and failure to maintain good managemental practices in Indian dairy animals particularly in Mathura region. Being commensal to skin S. aureus are supposed to be first and foremost bacteria to enter in teat canal. However, the incidences can be reduced by maintaining proper hygienic conditions and pre and post milking sanitation of udder and its surroundings.

All of the 27 Staphylococcus aureus isolates (Fig. 1 and 2) were found catalase positive, oxidase negative, fermentative by O-F test, urease positive, failed to grow on Mac conkey agar, Voges Proskauer (VP) positive and coagulase positive on being subjected to above mentioned biochemical tests. The presence of coagulase enzyme is considered as criteria for the pathogenicity of S. aureus which is assessed to differentiate between pathogenic and nonpathogenic S. aureus. In present study, all the Staphylococcus aureus isolates from clinical and subclinical mastitis cases 27 (100.00%) were found positive for coagulase production. Similarly, previous studies conducted by Pandya (1991) and Patel (2007) also reported high percentage positivity of S. aureus for coagulase production i.e. 100.00%, where as lower percent positivity of S. aureus for coagulase production were also reported earlier by Kato and Kume (1980) 34.50%, Boerlin et al. (2003) 50.00% and Wani and Bhatt (2003) 51.11%. The presence of 100% coagulase positive isolates in present study further suggests the increase in the number of pathogenic S. aureus in dairy animals. This is an alarming condition as in general S. aureus are supposed to be non pathogenic commensal organisms.

Fig. 1:Staphylococcus aureus on Nutrient agar

Fig. 2:Staphylococcus aureus after Gram’s staining

Fig. 3(a-b): Antibiotic sensitivity test of Staphylococcus aureus on Mueller Hilton agar showing resistance to antibiotics

The in vitro antimicrobial sensitivity (Fig. 3a and 3b) patterns of isolates recovered from mastitis and subclinical mastitis cases revealed 100 percent sensitivity to amikacin, azithromycin, imipenem and nitrofurantoin and high sensitivity (88.89%) towards cefotaxim, ceftriaxone, chloramphenicol, erythromycin, furidic acid, piperacillin/tazo, rifampicin and tylosin. As far as resistance is concerned, all the isolates were resistant to penicillin (100.00%), followed by vancomycin (88.89%), nalidixic acid (77.78%), cefixime, methicillin, novobiocin (66.67% each), amoxiclav, colistin, pipemidic acid (55.56% each), ofloxacin, streptomycin, sulphamethizole (44.44% each), ampicillin/sulbactam, cefalexin, cefazolin, cefoperazone, enrofloxacin, floxidin, meropenem (33.33% each), cefuroxim, ciprofloxacin, clindamycin, gentamicin, levofloxacin, norfloxacin and tetracycline (22.22% each). Eighteen isolates were found to be methicillin-resistant, while the remaining (09) were methicillin-susceptible. Similarly, twenty four S. aureus isolates were intermediate to vancomycin, while three were vancomycin susceptible. None of the isolate was resistant to vancomycin.

Studies conducted by several workers (Sharma et al., 2007; Chavan et al., 2007; Roychoudhury and Dutta, 2009) have showed increased resistance towards different traditional and newly introduced antibiotics. Appearance of resistance against a particular antibiotic in a specific region may be due to its frequent and long-term use (Sabour et al., 2004; Moon et al., 2007; Kumar et al., 2010a, b). The results of the present study revealed that a significant number of isolates showed resistance to antibiotics (penicillin-G, amoxiclav, cefalexin, cefazolin, cefuroxim, gentamicin, streptomycin, ampicillin, enrofloxacin, ciprofloxacin and many others) that are frequently used in mastitic animals. These resistance patterns are alarming as in comparison to the previous study (Kumar et al., 2010a) conducted in similar region in the cases of dairy animals suffering from mastitis revealed almost entirely reversed drug resistance pattern. As per Kumar et al. (2010a) majority of S. aureus isolates (18 out of 23) were sensitive to ciprofloxacin and only 9 out of 23 were sensitive to amikacin. Thus, the continuous use of specific antibacterials might be the cause of this change of drug resistance pattern. In late nineties and the first decade of 21st century, quinolones have been the drug of choice of clinicians and this is similarly followed by laymen in field condition. Thus, indiscriminate use might have changed this drug sensitivity pattern within few years. Similarly, for last few years amikacin has not been drug of choice for veterinarians in large animal due to higher dose and twice a day application.

Antimicrobial resistance represents a serious problem in the treatment of infectious diseases including mastitis. In recent times, an increasing antimicrobial resistance rate has been recognized in S. aureus from bovine mastitis (Saini et al., 2012; Wang et al., 2013). Due to antibacterial usage over many decades, multiple drug resistance among the mastitis causing agents is a major problem in controlling intra-mammary infections. This is generally attributed to indiscriminate and continuous use of antibacterial drugs without prior drug susceptibility testing or selection pressure of antimicrobials on pathogens or colonization of the mammary gland by resistant strains. Such antimicrobial resistant organisms can pose serious health related problems to animals as well as human beings.

Moreover, there is an increased incidence of Methicillin Resistant S. Aureus (MRSA) all over the world. MRSA is the term used for any strain of Staphylococcus aureus that has developed resistance to β-lactam antibiotics, which include the penicillins (methicillins, oxacillin, dicloxacillin etc.,) and cephalosporins. Synonyms are multi- drug resistant Staphylococcus aureus and oxacillin resistant Staphylococcus aureus. These strains act as reservoir for multiple drug resistant genes. Due to antibiotic resistance, sometimes it is called as “superbug” (Batabyal et al., 2012). This methicillin resistance seems to be widely spread among S. aureus isolates from bovine milk, which is in accordance with this study results as well (Zutic et al., 2012). MRSA first emerged as a serious pathogen in human medicine during late 1970s and has been reported in animals during the past 10 years (Leonard and Markey, 2008). In India, scanty of information is available, however prevalence of MRSA in cattle in India is reported to be 13.1% (Kumar et al., 2011). However, the present study revealed a higher incidence of MRSA (66.67%) as compared with those in similar reports in the literature from other countries (Lee, 2003; Moon et al., 2007; Van den Eede et al., 2009). The higher prevalence of MRSA in present study clearly indicates the increase in the MRSA.

With the emergence of MRSA, methicillin became ineffective against them and vancomycin became the drug of choice for MRSA (Ng et al., 2011). The excessive use of vancomycin against MRSA led to the emergence of two types of glycopeptides resistant Staph. aureus, vancomycin intermediate Staphylococcus aureus and vancomycin resistant Staphylococcus aureus (Courvalin, 2006). Almost after 40 years of methicillin resistance, the resistance of vancomycin evolved among the Staphylococcus aureus. In 1996, first Glycopeptides-Intermediate Staphylococcus Aureus (GISA) isolate was described from a pediatric patient in Japan (Hiramatsu et al., 1997) and another one with high resistance to vancomycin was first diagnosed in a patient in the USA, which contained both V and A gene from enterococci and methicillin resistance mecA gene. World’s sixth VRSA had been isolated in Kolkata (India) in 2005 (Chakraborty et al., 2011). Thus, it can be concluded that VRSA isolate is rare but still is an emerging pathogen and it has been appeared in India. There is no report available regarding the vancomycin resistant S. aureus in dairy animals in India. The present study also revealed the presence of vancomycin intermediate S. aureus. The presence of twenty four vancomycin intermediate S. aureus isolates out of 27 isolates clearly indicated the reduction in drug sensitivity and it might be an indication of future vancomycin resistance in existing S. aureus population.


The incidence of Staphylococcus aureus in clinical as well as sub clinical mastitis, was 33.75%. Overall, antimicrobial resistance to penicillin, cefixime, methicillin, amoxiclav, ofloxacin, streptomycin, ampicillin/sulbactam, cefalexin, cefazolin, cefoperazone, enrofloxacin and tetracycline was found in bovine mastitis cases. Systematic records regarding the epidemiology of mastitis in dairy animals including status of infection and antibiogram studies would provide useful information to the producer, farmer and veterinarian for management of farms. High incidence of Methicillin resistant S. aureus among bovine mastitic milk represents major threats for transmission of this multidrug resistant to human beings. Routine surveillance for antibiotics resistance patterns of MRSA isolated from clinical as well as subclinical cases of mastitis from dairy animals (cattle and buffaloes) could be an important measure for detection of the emergence and spread of such resistance. It further highlighted the necessity of enforcement of hygienic implementations and practices within dairy facilities.


Authors are highly thankful to Hon’ble Vice Chancellor, DUVASU, Mathura, India for providing all the necessary support and facilities. Authors are also thankful to technical staff of Department of Veterinary Epidemiology & Preventive Medicine; Veterinary Microbiology for their assistance.

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